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Contract No. W-7405-eng-26

Instrumentation and Controls Division

MSRF: DESIGN AND OPERATIONS W O R T

Part IIA.

Nuclear and Process Instrumentation

J. R. Tallackson

FEBRUARY 1968

OAK RIDGE NATIONAL LABORATORY Oak Ridge, Tennessee operated by UNION CARBIDE CORPORATION for the U.S. ATOMIC ENERGY COMMISSION

CONTENTS

..................................................... 1. MSRE INSTRUME~ATIONAND CONTROL SYSTEM- GFJERAL.............. 1.1 Introductory Remarks..................................... 1.2 Design Considerations.................................... 1.2.1 Introduction..................................... 1.2.2 Operational Requirements......................... 1.2.2.1 Compatibility with Centralized Control Philosophy............................. 1.2.2.2 Ease of Operation...................... 1.2.2.3 Flexibility............................ 1.2.2.4 Experimental Data...................... 1.2.2.5 Remote Main-benance..................... 1.2.2.6 Maintainability........................ 1.2.3 Safety Requirements.............................. 1.2.3.1 Containment............................ Redundancy. Separation. and Identifi1.2.3.2 cation................................. 1.2.3.3 Hazards to Operating Personnel......... 1.2.4 Performance Characteristics...................... 1.2.4.1 Overall Accuracy ....................... 1.2.4.2 Reliability............................ 1.2.4.3 Failure Modes .......................... 1.2.5 Effects of Process Conditions.................... Operating Temperature.................. 1.2.5.1 1.2.5.2 Operating Pressure..................... 1.2.5.3 Corrosion.............................. Salt Plugging and Vapor Deposition..... 1.2.5.4 1.2.5.5 Electrical Resistivity of Molten Salts.

P . D . . C A

1.2.6

1 1

17 17 17 17 19 20 20 20 21

21 21 27 27 27 27 27 28 29 29 29 30 30 31

Enviromentd Effects Ambient Temperature 1.2.6.1' Ambient Pressure 1.2.6.2 1.2.6.3 Radiation Damage

32 32 32 33

Physical 1.2.7.1 1.2.7.2 1.2.7.3 1.2.7.4 1.2.7.5

35 35 35 35 35 36

............................ ............... ............................. ................................... .............. ............................ 1.2.8 CQSt............................................. Plant Instrumentation Layout............................. 1.3.1 General Description.............................. 1.3.2 Main Control Area ................................ 1.2.7

1.3

............................ .................... ....................... .......................

Requirements Weld-Sealed Construction Ruggedness Size Materials of Construction Cleanliness

iii

36 37 37 37

\ iv

........................... 1.3.4 Transmitter Room.................................. 1.3.5 Field Panels ..................................... 1.3.6 Interconnections ................................. 1.3.7 Data Room ........................................ Plant Control System..................................... Safety System............................................ 1.5.1 Reactor F i l l and Drain System.................... 1.5.2 Helium Pressure Measurements i n the Fuel S a l t Loop............................................. 1.5.3 Afterheat Removal System......................... 1.5.4 Containment System Instrumentation ............... 1.5.4.1 H e l i u m Supply Block Valves ............. 1.5.4.2 O f f - G a s System Monitoring.............. 1.5.4.3 In-Cell Liquid Waste and Instrument A i r Block V a l v e s ....................... 1.5.4.4 In-Cell Cooling Water Block ..... 1.3.3

1.4 1.5

Auxiliary Control Area

Valves

1.5.5

38 38 39 39

44 55 67 69 70

71 72 72 76 76

Underpressure Protection f o r the Secondary Containment Cells

................................... 77 1.5.6 Fuel S a l t Sampler-Enricher Containment Instru. mentation ........................................ 77 2 . SAFETY INSTRUMENTATION AND REACTOR O LC O . ..................... 97 2.1 Nuclear Instrumentation: I n s t a l l a t i o n and Location ...... 97 2.2 BF3 Instrumentation ...................................... 106 106 2.2.1 General .......................................... 2.2.2 BF3 Counter ...................................... 106 2.2.3 High-Voltage Power Supply ........................ 107 2.2.4 P r e q p l i f i e r . ORNL Model Q.1857 .................. 107 2.2.5 Pulse Amplifier. ORNL Model Q-1875............... 107 2.2.6 Scaler. ORNL Model Q-1743........................ 108 2.2.7 Logarithmic Count R a t e Meter. ORNL Model Q.751 ... 108 2.2.8 Confidence Trips ................................. 108 Ill 2.3 Wide-Range Counting Channels ............................. 2.3.1 Principle of Operation ........................... 111 2.3.2 Fission Chamber and Preamplifier Assembly........ 115 2.3.2.1 Introduction ........................... 116 116 2.3.2.2 Preamplifier ........................... 2.3.2.3 Flexible Cables ........................ 118

............ ............................... Preamplifier Power Supply........................ 2.3.3.1 General................................ Construction........................... 2.3.3.2 2.3.3.3 Application............................ Specifications......................... 2.3.3.4 2.3.3.5 Circuit Description of the -22-v Supply................................. 2.3.3.6 Circuit Description of the +300-v and 2.3.2.4 2.3.2.5

2.3.3

2.3.4

2.3.5

2.3.6

2.3.7

119 119 120 120 120 120 120 121

.......................... 122 .................................. 123 ................................ 123 ........................... 123 ............................ 123 ......................... 124 .................... 125 ........ 135 ................................ 135

+11o-v supply Pulse Amplifier 2.3.4.1 General 2.3.4.2 Construction Application 2.3.4.3 2.3.4.4 Specifications 2.3.4.5 Theory of Operation 0.1-hp Servo Amplifier. ORNL Model Q-2615 2.3.5.1 General 2.3.5.2 Construction Application 2.3.5.3 2.3.5.4 Specifications 2.3.5.5 Theory of Operation Vernistat 2.3.6.1 Gener. 2.3.6.2 Construction Application 2.3.6.3 2.3.6.4 Specifications 2.3.6.5 Applicable Drawings 2.3.6.6 Theory of Operation

........................... ............................ ......................... .................... ........................................ ................................ ........................... ............................ ......................... .................... .................... Dual DC Amplifier................................ 2.3.7.1 General................................ 2.3.7.2 Specifications.........................

.................... .................... Fission Chamber Drive............................ 2.3.8.1 Description............................ 2.3.8.2 Drive Motor............................ 2.3.8.3 Lead Screw............................. 2.3.8.4 Position-Sensing Potentiometer......... 2.3.7.3 2.3.7.4

2.3.8

Electrical Shielding Layout Low Pickup-Noise Performance of the Assembly

2.3.8.5 2.3.8.6

2.3.8.7 2.3.8.8

2.3.8.9 2.3.8.10

Amplifier Balancing Theory of Operation

................................ ................................. .. .......................... ............................ .........................

Synchro Auxiliary Position-Sensing Potentiometer Vernistat Interpolating Potentiometer Gear Reducers Slip Clutch Limit Switches

135 135 135 136

138 138 138 139 139 139 139 140 140 141

141 141

146 146

147 147 147 147

148 148

148 148 148

2.4

2.5

Linear Power Channels 2.4.1 Description Visual Readout Device. Series 360 2.4.2 Keithley Model 418-20Picoammeter: Specifica2.4.3 tions and Description 2.4.4 Procedure for Field Testing and Compensating Compensated Chamber Q-1045 2.4.4.1 Description 2.4.4.2 Testing The Use of a Colloidal Dispersion of Boron in 2.4.5 Oil to Obtain a Uniform and Easily Applied Coating of Boron 2.4.6 High Current Saturation Characteristics of the ORNL Compensated Ionization Chamber (Q.1045)

164

165 165 165

............... 190 2.5.6 &RE Test Module, ORNL Model Q.2634 .............. 191 2.5.6.1 Description............................ 191 2.5.6.2 Theory of Operation.................... 192 2.5.6.3 Operating Instructions................. 195 Fast-Trip Comparator, ORNI, Model Q.2609 .......... 196 2.5.7 2.5.7.1 Description............................ 196 2.5.7.2 Theory of Operation.................... 199 2.5.7.3 Operating Instructions................. 201 Coincidence Matrix Monitor, ORNL Model Q-26% .... 203 2.5.8 203 2.5.8.1 Description............................ 2.5.8.2 Theory of Operation.................... 204 2.5.8.3 Operating Instructions................. 205 Shim and Regulating Rod Control System................... 221 Maintenance Instructions

6.i

163 164

................................. 168 ..... 168 177 Rod Scram Safety System.................................. 2.5.1 Rod Scram Safety Channel- Input Instrumentation........................................... 177 2.5.2 Rod Scram Safety Channel - Output Instrumentation........................................... 178 180 Safety Chambers.................................. 2.5.3 Period Safety Module, ORNL Model Q.2635 .......... 181 2.5.4 181 2.5.4.1 Description............................ 183 2.5.4.2 Theory of Operation.................... 2.5.4.3 Operating Instructions................. 184 Flux Amplifier and Ion Chamber High-Voltage 2.5.5 185 Supply, ORNL Model Q-2602........................ 2.5.5.1 Description............................ 185 187 2.5.5.2 Theory of Operation.................... 2.5.5.3 Operating Instructions................. 189 2.5.5.4

2.6

163

vii

2.6.1 2.6.2 2.6.3

2.6.4

2.8

221 221 228 228 229 230 231 234 235

.......................... 236 236 ........................... 236 ............................. 237 .......................... ................... 237 ............... 237 ........... ............ 237 238 Operational Situations Involving the Regulating 2.6.6 Rod Limit Switch and the Regulating Rod Servo... 238 263 Control Rods and Rod Drives............................. 263 General Arrangement............................. 2.7.1 264 Position Indication............................. 2.7.2 265 Shock Absorber .................................. 2.7.3 Cooling Air Flow and Temperature Monitoring ..... 265 2.7.4 Limit Switches.................................. 266 2.7.5 267 Control Rods.................................... 2.7.6 268 Rod Drop Timer.................................. 2.7.7 268 Performance Characteristics..................... 2.7.8 Component Descriptions and Specifications....... 269 2.7.9 2.7.9.1 Rod Drive Motor Assembly .............. 269 2.7.9.2 Electramechanical Clutch.............. 269 270 2.7.9.3 Overrunning Clutch.................... 2.7.9.4 Position-Indicating Synchros.......... 270 2.7.9.5 Position-Indicating Potentiometer..... 271 271 2.7.9.6 Limit Switches........................ 2.7.9.7 Electrical Wiring..................... 271 2.7.9.8 Lubrication........................... 271 2.7.9.9 Thermostatic Switches................. 272 2.7.9.10 Gears................................. 272 .Load Control System..................................... 301 2.8.1 Blower Operation ................................ 302 302 2.8.2 Door Operation.................................. 2.6.5

2.7

.................................... ............................ .................... ............. ................... .................. Regulating Rod Limit Switch Assembly. Q-2586 .... 2.6.4.1 Range Switching....................... 2.6.4.2 Range Seal............................ Introduction Rod Control Circuits The Automatic Rod Controller 2.6.3.1 Basic Rod Control Circuit 2.6.3.2 Temperature Control 2.6.3.3 Flux Demand Limiting

Component Descriptions 2.6.5.1 Servo Motor 2.6.5.2 Amplifier 2.6.5.3 Clutch-Br.e 2.6.5.4 Shim-Locating Motor 2.6.5.5 Mechanical Differential 2.6.5.6 Size 1 5 Control Transformer 2.6.5.7 Size 31 Torque Transmitter

viii

...................... 2.8.4 Manual Control.................................. Interlocks...................................... 2.8.5 2.8.6 Load Scram...................................... Health physics Monitoring............................... 2.8.3

2.9

2.9.1 2.9.2

2.9.3

Automatic Load Programing

2.12

2.13

Hand-and-Foot Beta-Gamma Monitor. Q.1939-B Beta and Alpha Sample Counters

.............................. ........ Process Radiation Monitors.............................. 2.10.1 Introduction.................................... 2.10.2 System Description.............................. Stack Monitoring System................................. 2.11.1 Introduction....................................

308 331

340 341 351 351 351 367 367

367 .............................. 368 .................... 368 ...................... .................. 368 ................ 368

System Description 2.11.2.1 Flow Channel m.S1 2.ll.2.2 In-Stack Sampler 2.11.2.3 Particulate Monitors 2.11.2.4 Iodine Monitor. KE.SlC 2.ll.3 ORNL Drawing List for the MSKF, Stack Monitoring System Data Logger.Computer 2.12.1 Introduction 2.12.2 Basic System Equipment Description 2.12.3 Peripheral Equipment Description 2.11.2

308 308

.................................... 331 ..... 331 .......................... 331 332 .................... 334 ............................ 339 General System.................................. 339 2.9.3.1 Introduction.......................... 2.9.3.2 Beta-Gamma Monitors. Q.2091 ........... 339

2.9.3.4

2.U

Introduction Facility Radiation and Contamination System 2.9.2.1 Introduction 2.9.2 . 2 System Description 2.9.2.3 Components

2.9.3.3

2.10

304

.......................................... .................................... .................................... .............. ................ 2.12.4 System Operation................................ Collection and Processing of Analog 2.12.4.1 and Digital Input Signals............. 2.12.4.2 Logging Functions..................... 2.12.4.3 Calculations.......................... 2.12.4.4 Miscellaneous Functions............... 2.12.5 References and ORNL Drawings.................... MSRE Beryllium Monitoring System........................

372 379 379 379 381 382 382 384 384 385 386 393

ACKNWDGMENT

This report represents the collective e f f o r t s of many more persons than t h e authors of record, who, i n some areas, served as editors, not writers. We g r a t e f u l l y acknowledge the contributions of the following. H. R. Brashear f o r checking and f i n a l e d i t i n g of the section on Process Radiation Monitoring. G. H. Burger2 f o r preparing the sections on Process Radiation Moni t o r i n g , Health physics Monitoring, Stack Monitoring, and the Data Logger-Computer S. J. Ditto and E. N. Fray3 f o r assistance i n writing and checking l a r g e portions of the sections on the nuclear and electronic instrument a t ion. P. G. Herndon, C. E. Mathews, J. L. Redford, and R. W. Tucker f o r continuous and invaluable assistance i n gathering information and i n reviewing t h e drawings and t e x t material. D. J. Khowles and J. A. Russell f o r help with reviews of the HekLth physics and Stack Monitoring sections. R. H. Guymon, Chief of E R E Operations, and h i s staff f o r giving generously of t h e i r time t o review the sections on control and safety. M. Richardson f o r help with the section discussing the control rod and the drive unit.

lExcept as noted, those l i s t e d below are members of the ORNL Instrumentation and Controls Division. 2Formerly with the Instrumentation and Controls Division, ORNL, now with Union Carbide Corporation, Mining and Metals Division, Niagara F a l l s , N.Y.

3Formerly with the Instrumentation and Controls Division, O m , now with General E l e c t r i c Co., San Jose, C a l i f . ix

M S R E INSTRUMENTATION AND CONTROL SYSTEM

- GENERAL

1.1 INTRODUCTORY FEMAFKS

Instrumentation is required by the MSRE to provide information and control for routine operations, to obtain experimental data, and to protect against hazard or damage to personnel or equipment resulting from abnormal conditions. Both nuclear and nonnuclear instrumentation are used for measurement, for control, and for protection; however, because of the nature of the system, nonnuclear instrumentation predominates. Vital operational instrumentation on the MSRE is that which measures and controls levels, flows, and temperatures of molten salts, helium gas, cooling air, and water and which is required for operation and control of the auxiliary systems. Two grades of instrumentation, control grade and safety grade, are found in the MSRE. Control-grade instrumentation is used where a failure of control o r a loss of information or protective action (though undesirable) can be tolerated. Safety-grade instrumentation is used where such failures o r losses cannot be accepted. The choice between the two systems is based on considerations of cost vs consequences. Safety-grade systems involve the use of redundant, reliable instruments and interconnections and tend to be much more expensive than controlgrade systems. Hence safety-grade instruments are used only where neces s a r y ; control-grade instrumentation predominates The experimental nature of the reactor has increased the instmentation requirements if compared to a power reactor. In some cases experimental data are obtained from instrumentation required for operation; however, in many cases, additional instrumentation was installed primarily for data. A second-generation, nonexperimental version of the MSRE w i l l require less instrumentation. The MSRE system,' the components comprising the system, and its nuclear and operating characteristics have been fully described pre~i0usl.y.~'~ It is not inappropriate to introduce a description of the

'The MSRE has been operating since June 1, 1965, and as of May 9, 1967, had developed a total of 32,654 M.whr. 2S. E. Beall et al., MSRE Design and Operations Report, Part V, Reactor Safety Analysis, ORNLTM-732 (August 1964). 3R. E. Wintenberg and J. L. Anderson, Trans. Am. Nucl. SOC. 2, 454-55 (1960). 4J. L. Anderson and R. E. Wintenberg, Instrumentation and Controls Div. Ann. Progr. Rept. July 1, 1959, ORNL2787, p. 145.

5P. N. Haubenreich, "Safety Aspects of the Molten-Salt Reactor Experiment," Nucl. Safety 8 ( 3 ) , 226-33 (Spring, 1967). 1

MSRE instrumentation and control system by repeating some of the essential features of the MSRE.

Figure 1.1.1is a pictorial drawing of the reactor installation, and Fig. 1.1.2 is a schematic drawing of the primary and secondary molten-salt loops in which nuclear power is generated and transferred. The primary (fuel) salt is a mixture of fluorides of lithium, beryllium, and zirconium with sufficient uranium fluoride to achieve criticality at the desired temperature. Several compositions of salt are under consideration for the MSRE,2 differing principally in the concentration of UF as a consequence of the degree of enrichment in 235U. The use of 234U is also being studied. These variations or changes in composition are not expected to affect the design of the instrumentation and controls. The coolant salt, containing no uranium, is similar to the fuel salt in its nonnuclear characteristics. The use of sodium fluoroborate coolant salt6, is under consideration, but this experiment is expected to have little or no effect on the instrumentation. Table 1.1.1 gives the composition and characteristics of the fuel and coolant salts currently (March 1966) being used in the MSRE.

-.'

6P. N. Haubenreich et a1 Consideration of Substituting Uranium-233 in the MSRE Fuel, ORNLCF-66-2-28. 7R. E. Brooksbank, P. N. Haubenreich, and J. H. Shaffer, "Study of the Use of U233 in MSRE," MSR-66-21 (internal memorandum).

Table 1.1.1.

Fuel Salt

LiF

BeF2 =F4

U F ~ (33 235~), approx

Coolant salt

65 29-2 5 .O 0.8

66 34

I34 20 0.47

120 24 0.53

840

850

Physical properties (at 200OF) Density, lb/ft3 Viscosity, lb ft"

hr-' Heat capacity, Btu''bl Liquidus.temperature, OF

( " F ) ' l

Since these s a l t s a r e frozen below 840째F, it i s necessary t o apply heaters t o t h e tanks and the piping throughout the s a l t systems. Figure 1.1.3 shows the reactor core vessel a f t e r assembly. The reactor i s graphite-moderated, with the graphite i n the form of long v e r t i c a l b a r s , o r stringers. These s t r i n g e r s a r e e s s e n t i a l l y square i n cross section with grooves cut i n t o the four faces t o channel the flow. Figure 1.1.4 i s a horizontal cross section through t h e a x i a l center l i n e of t h e core, showing the shape of t h e graphite moderator bars and the location of the control rods. Whereas the f u e l i s a homogeneous salt, the core i t s e l f has many of the nuclear c h a r a c t e r i s t i c s of a heterogeneous reactor. Table 1.1.2 l i s t s some of t h e nuclear parameters of i n t e r e s t t o the control and safety system designer. 2 * Table 1.1.2. Core s i z e

141 cm dim x 200 cm long

Neutron lifetime, k?*

240 psec

Temperature coefficient of r e a c t i v i t y I n fuel salt I n graphite Total

4.0 3.3 7.3

X X

(Gk/k)/'F (Gk/k)/'F

lom5 (Gk/k)/'F

Effective delayed neutron f r a c t i o n Stationary f u e l Circulating f u e l

0.0067 0.0045

Power density ( f u e l ) a t 7.5 Mw Maximum Average i n core Maximum allowable rod drop time

29.0 w/cm3 .3 w/cm3 1.35 sec

Control rods a r e employed for both s a f e t y and routine operational control. Nuclear excursions are not incredible, but none have been postulated t h a t cannot be averted by well-established techniques using a reliable protective system. Both t h e f u e l and coolant s a l t loops are blanketed and purged with flowing helium a t a s l i g h t positive pressure, nominally 5 psig. This i s accomplished i n t h e salt pumps, which are designed t o provide a gas space f o r the helium; see Fig. 1.1.5. The volute around t h e pump imp e l l e r i s enclosed i n a l a r g e r tank, t h e pump bowl. The pump bowl i s

8G. W. Allin and H. J. Stripling, Jr., Instrumentation and Controls Div. Ann. F'rogr. R e p t . Sept. 1, 1963, ORNL3578, pp. 114-15.

kept about half f i l l e d with f r e s h c i r c u l a t i n g s a l t by means of a bypass flow of 50 t o 65 gpm (-5.Oqd) around the pump. The salt, a t pump o u t l e t pressure, i s delivered t o the r e l a t i v e l y quiescent volume i n the pump bowl through a t o r o i d a l spray r i n g which allows t h e escape of gaseous materials from t h e salt. These released gases, composed mainly of f i s s i o n products and, perhaps, hydrocarbons, a r e carried t o the off-gas system by a continuous flow of helium which sweeps across the f r e e s a l t surface i n t h e pump bowl. Hydrocarbons, i f present, w i l l originate with s m a l l leaks i n the lubricating o i l seals i n t h e pumps. ~ ~ a vapor pressure of only 4.47 x f i e 1 a t 1 2 0 0 has while mm Hg, the 5-psig overpressure substantially reduces the amount of longterm s a l t carry-over i n t o the off-gas system; it a l s o helps t o prevent large-scale contamination of t h e pump i t s e l f by s a l t deposition. The gas spaces i n t h e pump bowl and the overflow tank provide extra volume f o r f u e l expansion from excessive temperature should the need a r i s e . A second helium flow i s used t o purge the lubricating and cooling o i l passages i n the pump t o prevent the entry of contaminants from the pump bowl. Helium i s used as a cover gas i n the f u e l and coolant s a l t drain and storage tanks and, by increasing the pressure, becomes the driving force used t o f i l l the circulating loops. The off-gas system conveys the helium from the tanks and the pump bowls t o p a r t i c l e traps, f i l t e r s , charcoal beds, etc., and thence t o discharge via t h e off-gas stack. I n addition t o the main nuclear heat r e j e c t i o n system, described i n Sect. 2.8, auxiliary cooling i s required i n the reactor and drain tank c e l l s . The ambient a i r temperature i n these c e l l s i s maintained a t 150째F o r l e s s by two air-to-water space coolers. Direct forced a i r cooling i s used on the freeze valves and on the control rods and t h e i r drives. This forced a i r pumping system i s a l s o used t o evacuate the reactor and drain tank c e l l s t o t h e i r operating pressure of -2.0 psig. The i n - c e l l cooling water system i s used t o cool such i n - c e l l components as t h e thermal shield, salt pump motors, and space coolers. Fuel additions and the removal of samples f o r analyses are made w i t h the sampler-enricher. This i s a device connected with a pipe t o the f u e l s a l t pump bowl and which, of necessity, penetrates a l l containment b a r r i e r s . Freeze valves are used i n the interconnecting s a l t pipelines between t h e various tanks and t h e reactor vessel. A length of f l a t t e n e d pipe t h a t can be cooled and heated i s a conceptual and perhaps oversimplified description of a freeze valve. Valve closure i s obtained by freezing a s a l t plug i n the f l a t t e n e d portion of t h e pipe. The complex of r e l i a b l e instrumented subsystems used solely f o r prot e c t i o n forms t h e WRE safety system. I n t h e MSRE t h e protection may be categorized as (1)protection against nuclear excursions, (2) protection against loss of containment, and ( 3 ) protection of v i t a l equipment. From the standpoint of extent and quantity, a majority of t h e safety system instrumentation i s i n category 2. These a r e process-type instruments based on measurements of pressure and radiation level. Their output actions are t o close valves, shut down pumps, etc., i n l i n e s which are possible escape routes f o r contamination. The preceding paragraphs highlight those features of t h e E R E t h a t a r e of particular i n t e r e s t t o the instrumentation and controls designer.

Two of the major problem areas created by the reactor system's design

are containment and temperature (its measurement, control, display, and recording). The first containment barrier, cladding, always present in a heterogeneous reactor, is missing. This placed more stringent requirements on the instruments used to measure pressures and levels inside the reactor loop. The problems were magnified by the higher than usual temperatures encountered in this service. Obtaining high-grade satisfactory measurements of important flows, pressures, levels, and temperatures is complicated by the general requirement that the number of primary containment penetrations be minimum and, even more so, by the environments of molten salt, fission products, and radiation inside the primary containment o r in the coolant salt loop, where measurements involve either molten fuel o r coolant salt. It is impossible to operate the MSRE and not breach the primary and secondary containment volumes with process lines for helium, air, and water (Fig. 1.1.6). In many cases these containment penetrations violate design criteria unless they are capable of being reliably blocked with instrumented systems when potential hazards are detected; hence the extent of the process-type instruments in the safety systems and the extensive use of sensors and transducers designed to meet containment requirements. In addition, wide variations of reactor and drain tank cell temperatures and pressures complicated the containment aspects of pressure-measuring instruments since this large and convenient contained volume could not serve as a stable reference. To a degree the apparent emphasis on problems of containment is EL result of the inherent characteristics of unclad, fluid-fueled reactor systems. However, the design of the MSRE was complicated by having to shoehorn it into an existing facility with size and general configuration less than ideal. This housing situation generated additional design problems with both the reactor system and the instrumentation and controls. Auxiliary systems for air, oil, water, helium, and emergency power are of necessity spread out and remotely located, cable and piping runs tend to be long and tortuous, power and signal cables could not be properly separated, and it was not feasible to put all the controls in one central area. Instead, some of the auxiliaries are provided with local control panels that are periodically supervised by the operators. These problems of interconnecting and integrating the various subsystems into an operating entity would have been substantially reduced in a facility engineered specifically for the MSRE. In particular, problenis of containment and the amount of instrumentation for containment could have been substantially reduced. Temperatures throughout the two salt systems are the most numerous and possibly the most vital single type of measurement in the MSRE. Both salt systems (freeze valves excepted) must be maintained above the freezing temperature (850째F) and should not exceed 1300째F. This upper temperature limitg is based on stress and metallurgical considerations and, depending on location, a reasonable and safe allowance for fuel expansion caused by

9R. B. Briggs, Effects of Irradiation on Service Life of MSRE, ORNLCF-66-5-16

any unscheduled temperature excursion. Stress producing temperature gradients a r e t o be avoided. If s a l t freezes, it may rupture the cont a i n i n g pipe or vessel on remelting. The coolant salt radiator i s part i c u l a r l y vulnerable i n this respect. Accurate, reliable temperature information i s e s s e n t i a l t o successful operation of the afterheat removal system, t o freeze valve operation, t o heat balance calculations, t o rea c t i v i t y balance calculations, t o a l l operations involving c r i t i c a l i t y , t o routine operational controls, and as input information t o the safety system. There a r e over 1050 thermocouples i n s t a l l e d on the MSRE. A preponderance of these a r e on the salt loops, on the storage and drain tanks, and on associated piping. These salt systems are equipped with many manually controlled heaters; safe and e f f e c t i v e control i s only possible if the operators have a clear, r e l i a b l e picture o r p r o f i l e of temperatures i n t h e system and i f they are a s s i s t e d by suitable off-limit interlocks and alarms. For these reasons, high-speed temperature scanning and display and continuous data logging are extensively used. These logging and display systems a l s o provide off-limit alarms. It i s worth w h i l e t o note t h a t these temperature instrumentation systems a r e most intensively used when the salt loops a r e being heated p r i o r t o f i l l i n g or before taking t h e reactor t o power. When t h e reactor i s on l i n e and generating power, the loop temperatures become more uniform and certain; hence the control and monitoring problem i s sharply reduced. Other areas which called f o r more than usual care i n design or f o r nonroutine solutions are: 1. measuring and controlling low flows of helium and off-gas t o and from the cover-gas system,

measuring helium cover-gas pressure i n t h e f u e l salt pump bowl,

measuring s a l t l e v e l i n t h e pump bowls,

measuring coolant salt flow rate,

measuring and controlling s a l t levels i n the drain tanks,

designing containment penetrations f o r instrument lines,

designing i n - c e l l instrumentation and r e l a t e d disconnects, piping, and wiring t o accommodate remote maintenance requirements.

It was recognized a t the onset of t h e MSRE design t h a t suitable and eminently s a t i s f a c t o r y instrumentation f o r some of these measurements w a s nonexistent. Therefore, i n some cases t h e methods and components now i n use have developmental s t a t u s . Sections 1.2 t o 1.5 are concerned with broad and quite general descriptions which are intended t o convey design philosophy and c r i t e r i a . Detailed descriptions of MSRE instrumentation and control a r e contained i n Sects. 2 t o 8. The outline which follows w i l l give t h e reader an idea as t o the scope and the arrangement of this report.

ORNL-DWG 634209R

Fig. 1.1.1.

MSm

Layout.

ORNL-LR-DWG

59158AR

COOLANT PUMP

It II

REACTOR CELL

TEMPERATURES A N D FLOWS ARE TYPICAL FOR REACTOR AT

COOLANT DRAIN TANK AND DRAIN TANK ( 73ft3)

DRAIN TANK (73 f t 3 )

Fig. 1J . 2 .

(73 ft3)

(44ft3)

MSRE Primary and Secondary Molten-Salt Loops.

ORNL-LR-DWG

6!097 R 2

ACCESS PORT COOLING JACKETS

FUEL O U T L E T

EACTOR ACCESS PORT

CONTROL ROD THIMBLES

CENTERING GRI

FLOW DISTRIBUTOR

GRAPHITESTRl

W FUEL INLET REACTOR CORE CA REACTOR VESSEL

ANTI-SWIRL VANES V E S S E L DRAIN L I N E

Fig. 1.1.3.

UPPORT GRID

MSRE Reactor Core Vessel After Assembly.

k2+

T Y P I C A L FUEL PASSAGE

Nom

STRINGERS NOS. 7.60 AND 6 1 (FIVE) ARE REMOVABLE.

ORNL-LR-DWG-56043-811

SHAFT COUPLING

3 I

2 -

r--=

WATER COOLED MOTOR

SHAFT SEAL

LUBE OIL IN B A L L BEARINGS (Face to Face)

BEARING HOUSING GAS PURGE I N

BALL BEARINGS (Back to Back LUBE OIL OUT

SHIELD COOLANT PASSAGES ( I n Parallel With Lube O i l

SHIELD PLUG LEAK DETECTOR GAS FILLED EXPANSION SPACE

SAMPLER ENRICHER (Out of Section)

XENON STRIPPER (Spray Ring)

HELIUM BUBBLER

HELIUM BUBBLER CONFIGURATION

To Overflow Tank

Fig. 1.1.5.

- I t #

\PUMP

MSRE Fuel Pump.

BOWL

mEW5QANt S t A L

I I

COmPONEN?' COOL1NG -LD

Fig. 1.1.6.

Schematic of MSRE Secondary Containment, Sharing Typical Penetration Seals and Closures.

OUTLINE OF CONTENTS OF TM-729

1. MSRE Instrumentation and Control System

1.2

- General

Design Considerations Discusses the considerations which influenced the design, p a r t i c u l a r l y those which a r e unique o r a r e peculiar t o the E R E .

1.3

Plant Instrumentation Layout Describes the physical layout of t h e instrumentation system. Gives a general description of the overall layout (Sect. 1.3.1) and then describes each area separately. The instrument systems a r e located by area, and the routing and ins t a l l a t i o n of t h e i r interconnections are included.

1.4 Plant Cpntrol System Gives a broad, all-inclusive picture of the e n t i r e MSRE instrumentation and control system, including control of auxiliary equipment and the instrument power system. The "mode control" used t o guide reactor operation i s discussed with diagrams which define (or give) t h e conditions f o r the The various modes ( P r e f i l l , Operate-Start, Operate-Run) i n t e n t of this section i s t o outline the main subsystems and not t o dig i n t o f i n e structure. The reader i s referred t o Sects. 2 t o 7 f o r d e t a i l s .

44 1.5

Safety S y s t e m Discusses the safety-grade instrumentation and controls associated with the MSRE safety system. The discussion includes general design c r i t e r i a (designer' s guidelines) i l l u s t r a t e d by a t y p i c a l system. The e n t i r e safety system, what it does, and why are tabulated and diagrammed. This section replaces similar but obsolete material i n r e f . 2.

Safety Instrumentation and Reactor Control 2.1

Nuclear Instrumentation Describes t h e instrumentation i n t h e neutron channel up to, but not including, t h e panel electronics. The neutron penetration, including t h e guide tube assembly, i s described, and t h e interconnecting cabling, junction boxes, etc., associated with transmission of signals t o the control rooms a r e diagrammed.

2.2

BF3 Instrumentation Describes briefly t h e instrumentation associated with the sensitive BF3 channels used f o r low-level f l u x measurement and control. The interlocks associated with the BF3 channels a r e discussed i n Sect. 2.6.

2.3

Wide-Range Counting Channels The, wide-range counting channels are described with block diagrams and an explanation of t h e i r operation. This i s followed by descriptions of t h e chamber assembly, of the chamber and t h e associated electronic c i r c u i t s , and of the electromechanical drive. "he interlock and control functions associated with the wide-range counting channels a r e covered i n Sect. 2.6.

2.4

Linear Power Channels Describes briefly t h e l i n e a r power channels and includes block diagrams and descriptions of the compensated ion chamber and of the picoammeter.

2.5

Rod Scram Safety System Contains a thorough description of the rod scram safety syst e m . Block diagrams and c i r c u i t diagrams i l l u s t r a t e the discussion. The associated electronics a r e discussed i n detail.

2.6

Shim and Regulating Rod Control System Gives a thorough description of t h e shim and regulating rod control system. Block diagrams and composite elementary c i r c u i t diagrams f o r both the servo rod and the s h i m rods are included. The "Confidence" interlocks originating i n the wide-range counting channels (see Sect. 2.3) are a l s o described

2.7

Control Rods and Drives Describes the control rods and the rod drive units. A description of the pneumatic f i d u c i a l zero position indicator i s included.

2.8

Load Control

Describes i n considerable d e t a i l the control of the equipment which determines the reactor load, namely: radiator, radia t o r doors, blowers, and bypass damper. 2.9

Health physics Monitoring

Describes t h e health physics instrumentation and includes a general description of the individual types of instruments used plus a description of t h e i r interconnections t o form an integrated alarm system.

2.10

Process Radiation Monitors The components and electronics used t o monitor process l i n e s carrying helium, water, off-gas, etc., are described. The operation of interlocks and alarms i s covered i n Sect. 4.

2.11

Stack Monitoring Describes t h e radiation monitoring i n s t a l l e d i n the off-gas stack. The components, how they function, and t h e i r purpose a r e included i n the discussion.

Process Instrumentation Provides a general description of the instrumentation i n the various systems. Included are descriptions of major control loops w i t h drawings of individual control loops and t h e i r instrumentation. The principles of operation of the various components as well as control c i r c u i t operations are discussed i n other sections. I n general, s u f f i c i e n t descriptive material, augmented by flowsheets and diagrams, i s included so t h a t a reader with a reasonable knowledge of instrumentation systems can determine the arrangement; and composition of t h e process instrumentation system.

4. E l e c t r i c a l Control and A l a r m Circuits 4.1

General Description Introduces i n very general terms the types of c i r c u i t s t o This t e x t material provides t h e background for succeeding sections (4.2 t o 4.U).

be found i n the MSRF: system and how they a r e related.

4.2 t o 4.10 Master Control Circuits, e t c . Describes t h e e l e c t r i c a l control c i r c u i t s with engineering elementary schematic c i r c u i t s diagrams and, where instructive, includes the nonobvious interlock functions and explains why they a r e required. The material presented enables a person with a reasonable knowledge of instrumentation and control systems t o understand t h e operation of the control c i r c u i t s .

4.11

Jumper Board Explains purpose and describes t h e physical construction of t h e jumper board. Layout and wiring of a t y p i c a l section of t h e board a r e included.

4.12 Annunciators The annunciator system i s described. Considerations involved i n the location of annunciators are outlined. Schematics of the annunciators used and t h e i r sequence of operation a r e included. Their operational use i s a l s o discussed.

4.D

Instrument Power Distribution Outlines t h e system which provides t h e E R E instrumentation, control c i r c u i t s , and annunciators with t h e necessary power. R e l i a b i l i t y considerations a r e included.

Standard Process Instrumentation Provides a general description of t h e various types of standard instruments used i n the MSRE and includes basic principles of t h e i r operation.

Special FYocess Instrument a t ion Contains descriptions of t h e nonstandard instruments required by t h e E R E . Their unique or s p e c i a l features are outlined.

Data Logging and Computation

Gives a general, broad description of the data system. Describes basic c a p a b i l i t i e s , operations, and purpose of t h e logger-computer. Note: The reader i s r e f e r r e d t o manufacturers' l i t e r a t u r e and t h e operations manual for detailed information.

Mscellaneous

8.1

Instrument Numbering System and Instrument Application Diagram Coding System Explains t h e system of flow plan symbols and numbering used i n preparation of instrument applications diagrams and tabulations with t y p i c a l examples.

8.2

Wiring Practices and Coding Describes the system used i n designing and identifying MSRE instrumentation and c o n t r o l wiring with t y p i c a l examples of panel and interconnection wiring.

8.3

Pneumatic Tubing I n s t a l l a t i o n Practices and Coding Describes t h e system used i n designing and identifying MSRE instrument tubing i n s t a l l a t i o n s and includes a t y p i c a l pneumatic schematic c i r c u i t and a t y p i c a l panel and i n t e r connection tubing i n s t a l l a t i o n .

1.2

DESIGN CONSIDERATIONS 1.2.1

Introduction

The design of the MSRF: instrumentation and controls system and the selection, procurement, and/or development of components involved consideration of a number of operational, safety, and physical requirements. Table 1.2.1 l i s t s the more important considerations, together with an indication of the design areas i n which these considerations apply. I n many cases, these considerations a r e similar t o those encountered i n the design of i n d u s t r i a l plants and research f a c i l i t i e s , such a s high-temperature liquid-metals systems, chemical processing plants, petroleum r e f i n e r i e s , and other types of nuclear reactors. Wherever possible, the design w a s based on existing technology, and components were procured from commercial sources of supply; however, i n some cases, individual considerations (or combinations of considerations ) presented problems which required special design o r the development of s p e c i a l components. A discussion of the considerations l i s t e d i n Table 1.2.1 i s presented i n the following paragraphs. 1.2.2

1.2.2.1

b-,

Operational Requirements

Compatibility with Centralized Control Philosophy

A s discussed i n Sect. 1.3.1, the MSRE instrumentation i s centralized i n t h e main control area so t h a t the information and controls needed f o r routine operation of the reactor a r e immediately available t o the operator. This philosophy of operation dictates t h a t modular-type systems with s i g n a l transmission from primary element t o receivers and from cont r o l l e r s t o f i n a l control elements be used r a t h e r than i n t e g r a l f i e l d mounted systems. For example, i n the MSRE pressure transmitters and receiver indicators a r e sometimes used when a simple pressure gage would have sufficed f o r a noncentralized system. This example, however, should not imply t h a t a l l the measured variables a r e transmitted t o the main control area. There are, i n f a c t , many direct-reading f i e l d instruments, such as pressure gages, rotameters, thermometers, etc., i n use i n t h e MSRE. This type of instrumentation i s used mainly where t h e instrument i s located i n an accessible area, usage i s low, and quick access t o information i s not required. Where frequent o r fast access t o information i s required; where containment, personnel safety, or basic instrument i n s t a l l a t i o n requirements d i c t a t e t h a t the primary sensing elements be located i n inaccessible areas; or where transmitted signals are required f o r operation of controls or interlocks o r f o r logging of data, transmitters a r e used and t h e receiving equipment i s located i n t h e c e n t r a l control area or i n other centralized locations such as the transmitter room and various f i e l d panels (see Sect. 1.3.1). Similar considerations apply t o the selection of f i n a l control elements. Where t h e f i n a l control elements a r e located i n inaccessible areas o r where control i s e i t h e r automatic o r r e s t r i c t e d by control

Table 1.2.1.

MSRF, Instrumentation and Control Design Considerations

mwsrui,b.rat*. ? ? ~ n l t t k. ~Wlvl . Ccntml mmt.

interlocks, remotely controlled pneumatic or e l e c t r i c actuators a r e used. Where frequent control adjustments are required,where the operator must have quick access t o the control, o r where it i s desirable t o prevent operation of the control element by persons other than the reactor operator, the control signal originates i n control devices (automatic controllers, control interlocks, manually operated switches, e t c ) located i n t h e main control area. Where centralized control i s not required, the f i n a l control elements are operated e i t h e r d i r e c t l y by hand o r i n d i r e c t l y by means of control devices mounted individually on l o c a l control s t a t i o n s or grouped on f i e l d panels.

1.2.2.2

Ease of Operation

The layout of control areas, the placement of instruments and cont r o l s within control areas, and the selection of receiving instruments, control switches, etc., were strongly affected by considerations of operator convenience and ease of operation. Insofar as possible, cont r o l s and adjustments needed f o r routine operations of the reactor were placed on the c e n t r a l control console, and the receiving instruments which provide the information required f o r routine operation were located on e i t h e r the console o r the main control board. To reduce the need f o r frequent reference t o flowsheets and t o reduce the chances of operational error, a graphic presentation w a s used i n the layout of the main control board and of the jumper board. This graphic presentation i s a l s o a valuable a i d i n t r a i n i n g of operators. A s nearly as possible and consistent with other considerations, the prime space i n the center of the main control board and console w a s reserved f o r the most important instrumentation and controls components. Components of l e s s e r importance were located i n auxiliary control areas or i n t h e f i e l d . Instrument components and control devices on the graphic panel were placed so t h a t they a r e visually associated with specific components o r portions of the reactor system.

Attention was

a l s o given t o the v e r t i c a l placement of components so t h a t receiving instruments could be e a s i l y read from various positions i n t h e control room and so t h a t control switches would be within reach of an operator of average height. Where a given operation requires frequent simultaneous observations of a receiving instrument and operation of control switches o r adjustments, the controls and adjustments were located near the receiving instrument and were placed s o t h a t t h e receiving instrument would not be obscured by the operator's arms. To implement the above design objectives and t o minimize space requirements i n t h e control areas, a t t e n t i o n w a s given t o the physical s i z e of instrument components mounted i n the controlboards. I n general, preference was given t o small-sized instrument components where the use of such components w a s consistent with other considerations. Attention was a l s o given t o readability i n the selection of receiving devices such as recorders and indicators.

Where possible and consistent with other considerations, systems were automated t o r e l i e v e t h e operator of the necessity of performing numerous manual operations and thus free him t o devote more time t o t h e more important aspects of reactor operation. For example, t h e freeze valve c i r c u i t s were designed t o perform "freeze" and "thaw" operations automatically. Also a number of other variables, such a s helium i n l e t purge flow, which might have been amenable t o manual control a r e automatically controlled. Further simplification of operations was obtained by use of t h e Computer-Data Logger described i n Sect. 2.12. 1.2.2.3

Flexibility

The experimental nature of t h e MSRE dictated that the design of the instrumentation and control systems be f l e x i b l e , t h a t i s , that it be amenable t o change. To accomplish this objective t h e use of point-topoint wiring was avoided, and control c i r c u i t interconnections were made a t centralized locations i n the r e l a y cabinets. Similarly, most thermocouples were routed t o a patch panel i n t h e main control area, where they were connected t o readout instrumentation by patch cords. k r r t h e r f l e x i b i l i t y w a s provided by the use of ORNL standard modular hardware f o r f a b r i c a t i o n of control panels and by s e l e c t i o n of instrument components which permits ranges t o be changed and c o n t r o l switches t o be r e s e t e a s i l y i n the f i e l d . I n addition t o gaining t h e capability t o change the system design a f t e r s t a r t u p of t h e reactor, t h e f l e x i b i l i t y designed i n t o the system was of great value during t h e i n i t i a l design since it permitted portions of the system t o be designed, fabricated, and ins t a l l e d before t h e f i n a l design c r i t e r i a were established. 1.2.2.4

Experimental Data

The requirements f o r experimental data from t h e E R E r e s u l t e d i n more instrumentation than would be required f o r a nonexperimental (second-generation) reactor of the same type. Also, i n many cases, t h e accuracy requirements imposed by the need f o r experimental data were greater than would have been required by process c o n t r o l considerations alone. Since t h e data inputs t o t h e Computer-Data Logger are e l e c t r i c a l (dc) voltages, f i r s t preference was given t o t h e use of e l e c t r i c a l transmission systems i n these applications. However, i n some applications, such as weigh c e l l s , it was found t h a t t h e use of pneumatic transmitters offered s i g n i f i c a n t advantages. I n these cases strain-gage pressure transducers were used t o i n t e r f a c e the pneumatic systems with t h e Computer-Data Logger.

1.2.2.5

Remote Maintenance

The requirement t h a t a l l major components located within b i o l o g i c a l shielding o r containment be amenable t o remote servicing or removal and replacement w a s a primary consideration i n t h e design of instrumentation

systems and the selection of instruments in these areas. In general, the design philosophy was to locate instrument components outside biological shielding so that they could be maintained directly. Where this was not possible, provisions were made for remote removal and replacement, or adequate operating and installed spares were provided. The major problem encountered in providing remote maintenance capabilities for in-cell instruments was the development of disconnect devices and methods of mounting instrument components. Disconnects were required for pneumatic tubing, electrical power wiring, and for low-level electrical signals. Because of the quantity involved, providing thermocouple disconnect capability required the greatest effort. With the exception of the weigh cell mountings, the design of in-cell instrument mountings did not present any special problems. The design of the weigh cell mountings required special attention because side loads must not be impressed on the cell and because the cells must be aligned so that the direction of force is parallel to the center line of the cell (see Sect. 6.6). Remote maintenance requirements also imposed severe restrictions on the design of in-cell instrumentation and control systems. To permit unrestricted vertical access for tools and f o r component removal, instrument components were located and associated wiring and tubing were routed in a manner that would not interfere with these operations. 1.2.2.6

Maintainability

Consideration was given to the maintainability of all instruments whether located in-cell or not. Whenever a choice between instrument component types existed and other considerations were equal, preference was given to the type that was easiest to maintain. Plug-in instruments were used extensively. The use of this type of instrument permits quick replacement of faulty components with minimun disturbance of operations and subsequent repair of the faulty components in field or central shops. Attention was also given to the location of instrument components to ensure that they would be physically accessible for maintenance. Wherever possible, provisions were made so that components could be tested, adjusted, or replaced without excessive disturbance of operations.

1.2.3 1.2.3.1

Safety Requirements

Containment

Since many of the primary instrument elements associated with measurement of variables in the reactor system are attached to, or require penetrations of, the reactor primary o r secondary containment, these instruments and/or associated lines are, in themselves, a part of containment. To avoid compromising the reactor containment, special precautions were required in the selection of these components and in the design of associated systems. The MSRE containment criteria require the presence of two independent barriers against the release of activity. Preferably these

barriers would consist of fixed b a r r i e r s such as a pipe o r a vessel w a l l ; however, the need f o r piping connections t o a u x i l i a r y systems and f o r transmission of instrumentation and control information t o and from t h e i n - c e l l reactor system d i c t a t e d t h a t containment b a r r i e r s be penetrated. I n general, the measurement of variables within t h e secondary containment involves t h e penetration of a t l e a s t one containment b a r r i e r . However, i n cases such as measurement of nuclear f l u x and process radiation, t h e desired information i s obtained without penetrating either primary barrier. I n other cases, such as measurement of primary system temperatures, drain tank weight, and pump speed, only secondary containment penetrations a r e required. Penetrations' may take the form of e l e c t r i c a l penetrations, piping penetrations, o r s p e c i a l penetrations t h a t are physically a p a r t of t h e containment vessel, with t h e type of penetration being determined by t h e type of s i g n a l transmitted. Such penetrations were made i n a manner t h a t d i d not seriously degrade t h e i n t e g r i t y of t h e containment b a r r i e r or were provided with instrumented closures t h a t will r e s t o r e t h e int e g r i t y of t h e b a r r i e r i f unsafe conditions occur (see Sect. 1.5). The most d i f f i c u l t penetrations t o close or protect were those associated w i t h piping penetrations of primary containment. Weld-sealed (helium l e a k - t i g h t ) construction i s used on a l l instrument components associated with such penetrations; connections a r e made by means of b u t t welds, leak-detected ring- j o i n t flanges, o r "autoclave" (or equivalent) connectors; and valves are provided with welded bellows stem seals. I n a l l cases where weld-sealed construction was required, t h e components were designed and tested t o ensure t h a t leakage through the body w a s less than l(r8cm3 of helium per second under conditions of 50 psig i n t e r n a l pressurization. Also, those valves which form a p a r t of t h e primary blocking system were designed and tested t o have very t i g h t shutoff c h a r a c t e r i s t i c s (see Sects. 6.5 and 6.20). Wherever possible, t h e instrument systems having primary system penetrations are designed t o dead-end t h e penetration i n a sealed component located inside the secondary containment. However, i n some MSRE instrument systems, the penetration extends through both primary and secondary containment barriers. Examples of such penetrations are the helium purge l i n e s associated with measurement of l e v e l and pressure i n the f u e l s a l t system and with the leak detection system used t o determine whether sampler-enricher valves and ports are closed and sealed (see Sects. 3.12 and 6.8). A similar type of penetration i s found i n t h e l i n e s connecting t h e drain-tank pressure transmitters t o drain tanks. This l a t t e r example differs from t h e preceding one i n that t h e

'In some cases, such as the helium flow elements, t h e coolant salt flow venturi, valves, and t h e helium flow r e s t r i c t o r s , t h e instrument components a r e an i n t e g r a l part of the system piping, and the required penetrations may be made on t h e instrument component r a t h e r than on t h e system piping. For the purpose of this discussion it w i l l be considered t h a t t h e component i t s e l f i s t h e penetration and t h e connections t o t h e component are extensions of t h e penetration.

l i n e s a l s o serve as process l i n e s which a r e used t o pressurize the drain tanks during f i l l i n g and t r a n s f e r operations. Similarly, the purge l i n e s t h a t supply helium purge flow t o the reactor as well as the flow elements and d i f f e r e n t i a l pressure c e l l s associated w i t h measurement of flow i n these l i n e s a r e p a r t of the primary containment. I n a l l the above cases, reliance i s placed on the flow of helium purge gas t o prevent the back diff'usion of a c t i v i t y , with check valves and instrumented closures being provided t o prevent the escape of a c t i v i t y . I n general, the r u l e was used that two block valves or one block valve and one check valve were equal t o one b a r r i e r . I n some cases, two s e r i e s check valves were ins t a l l e d , but i n the primary system the use of redundant check valves alone was not considered t o be adequate protection. Weld-sealed solenoid and pneumatically operated valves of the type discussed i n Sects. 6.5 and 6.20 were used t o provide the instrumented closures of these l i n e s . Blocking action i s i n i t i a t e d v i a the e l e c t r i c a l control c i r c u i t r y i n t h e event of occurrence of unsafe conditions such as high a c t i v i t y i n process lines, low helium supply pressure, high reactor c e l l pressure, etc. Operation of these protective systems i s discussed i n more d e t a i l i n Sect. 1.5. Other examples of instrument components t h a t form a part of primary containment are the pneumatic and hand-operated valves located i n primary system piping, the charcoal bed d i f f e r e n t i a l pressure c e l l , and the conductivity-type drain-tank l e v e l probe (discussed i n Sect. 6 .lo). The drain-tank l e v e l probes a r e an example of an instrument penetration where the instrument component i s physically a p a r t of the containment vessel. The most numerous (and fortunately the e a s i e s t t o s e a l ) penetrations of M'3RE containment a r e those required f o r t h e 495 thermocouples attached t o pipes and vessels within the secondary containment. These penetrations a r e closed by using ceramic (or g l a s s ) t o metal feed-through seals inside and epow s e a l s outside of the reactor containment vessel and biological shield (see Sect. 6.7). Similar techniques a r e used f o r sealing elect r i c a l penetrations required f o r i n - c e l l heater, motor, signal, and cont r o l wiring. Examples of devices requiring e l e c t r i c a l s i g n a l penetration of secondary containment a r e given below: Primary system pressure and d i f f e r e n t i a l pressure transmitters Primary system solenoid valves Fuel s a l t pump speed pickups Fuel s a l t pump microphones I n - c e l l valve position switches Conductivity l e v e l probes Primary system thermocouples Rod Drives A t this point it should be noted t h a t , with the possible exception of the conductivity l e v e l probes, there are no e l e c t r i c a l penetrations of primary containment i n t h e MSRX heated salt systems. T h i s lack of e l e c t r i c a l penetration of s a l t system primary containment i s due p a r t l y t o the lack of a suitable feed-through penetration s e a l and p a r t l y t o

the f a c t t h a t the high temperatures, high radiation, and low salt conductivity associated with t h e primary system tended t o discourage t h e

use of e l e c t r i c a l techniques f o r measurement inside t h e primary system. The next most numerous penetrations a r e the instrument piping penetrations of t h e secondary contaiment required f o r operation of valves, weigh systems, etc., within the secondary containment. With a f e w exceptions, these l i n e s connect t o closed systems o r instrument components and are e s s e n t i a l l y inward extensions of secondary containment. To protect against possible rupture of these l i n e s i n the event of t h e maximum credible accident, a blocking system i s provided which w i l l close these l i n e s i f t h e reactor c e l l pressure rises above atmospheric (see Sect. 1.5). Some instrument penetrations of secondary containment vent d i r e c t l y t o t h e space inside secondary containment and connect t o components outside containment. These form an outward extension of secondary containment. Where t h e l i n e s are short and t h e construction of t h e components satisfies t h e requirements f o r containment, as i s t h e case f o r the pressure switches used i n t h e blocking system, no blocking protection i s provided. However, where t h e connecting l i n e s a r e long o r where the components do not meet t h e containment requirement, block valves operated by t h e systems discussed i n Sect. 1.5 a r e provided. Instrument components t h a t form a part of secondary containment are, f o r t h e most part, standard commercially available i t e m s ; however, consideration w a s given i n t h e i r selection t o maintenance of minimum o v e r a l l leakage of t h e secondary containment. While Containment requirements f o r these components were much less stringent than f o r components that formed a part of t h e primary containment system, more a t t e n t i o n w a s given t o t h e leak-tightness of these components than was given t o similar components not associated with containment. Gasketed construction and standard tubing and pipe f i t t i n g s were considered acceptable i n most applications; however, t h e components w e r e tested before i n s t a l l a t i o n , and systems were t e s t e d after i n s t a l l a t i o n t o ensure that leakage was acceptably low. Although weld-sealed construction was not required f o r secondary containment, mamy components of t h e helium, lube o i l , samplerenricher, coolant s a l t , and chemical processing systems were weld-sealed and t e s t e d f o r helium leak-tightness t o conserve helium; t o prevent release of a c t i v i t y from p o t e n t i a l l y d i r t y systems (such a s t h e lube o i l , chemical processing, and coolant s a l t systems); t o minimize t h e possib i l i t y of inleakage of o q g e n t o t h e heated s a l t systems during periods of abnormal operation; and t o maintain t h e performance c h a r a c t e r i s t i c s of t h e instrument system. I n some cases, weld-sealed components were used because they were commercially available a t c o s t s comparable with similar components using standard construction. Examples of instrument components of secondary containment using standard construction are: 1. block valves i n t h e c e l l penetration blocking system,

(ei

2Wherever possible, valves were i n s t a l l e d s o t h a t t h e pressure (or r e a c t o r ) side of t h e valve was under t h e s e a t . Also, "fail-closed" (air-to-open) operator action was used s o t h a t l o s s of supply a i r pressure would cause valves t o close.

'6)

a l l components i n the cooling water systems,

pressure regulators i n the helium supply system,

pneumatically operated off-gas system valves downstream of the charcoal beds2 (these valves were, however, ordered with weld nipple connections and were welded i n t o the system),

solenoid block valves i n the chemical process system sampler, 2

drain tank weigh c e l l s and associated piping (special attention, beyond t h a t required f o r containment, was given t o the leaktightness of t h i s system t o obtain maximum accuracy),

7. some components connecting t o penetrations of the outer barrier of the f u e l sampler-enricher and chemical processing system sampler.

Examples of instrument components of secondary containment using weld-sealed, helium leak-tight construction are:

1. A l l components of the helium supply system and associated purge and supply lines, except regulators. Included i n t h i s category are pressure switches; flow elements; d i f f e r e n t i a l pressure and pressure transmitters; control valves; hand control valves i n the bubbler purge lines; and capillary flow r e s t r i c t o r s i n the sampler-enricher purge lines, i n t h e f u e l and coolant system bubbler purge lines, and i n the main helium supply t o the f u e l s a l t system drain tanks. 2.

Flow elements, capillary flow r e s t r i c t o r s , and d i f f e r e n t i a l pressure transmitters i n upper gas letdown l i n e s from the f u e l and coolant s a l t c i r c u l a t i n g pumps.

All f u e l and coolant lube o i l system instrument components except the o i l tank l e v e l transmitters. Included i n this catenom - - a r e flow

elements, pressure and d i f f e r e n t i a l pressure transmitters, control valves, &d pressure switches. The l e v e l transmitters u t i l i z e gasketed construction but were shop t e s t e d f o r leak-tightness before installation.

Components of the chemical processing system associated with reactor secondary containment and with containment of radioactive salts and gases during chemical processing operations. I n addition t o thosecomponents covered i n item 1 above, this category includes the u l t r a sonic l e v e l probe, described i n Sect. 6.11, and pressure and differe n t i a l pressure transmitters, f l o w elements, and pressure switches i n t h e associated HF, F2, N2, H2, and SO2 gas supply systems. I n general, a quality l e v e l intermediate between t h e weld-sealed cons t r u c t i o n required f o r reactor primary containment and the gasketed construction allowed i n secondary containment was used i n the chemical process system. For example, s i l v e r solder was accepted i n l i e u of welding, and Hoke type S-26 f i t t i n g s were accepted i n l i e u of autoclave-type connections. Gasketed construction and standard tubing and piping f i t t i n g s were not acceptable i n this service because of t h e r e l a t i v e l y high a c t i v i t y that w i l l be present i n the system during f u e l processing operations.

Components of t h e chemical process sampler connecting t o inner containmf of cc chemical processing system, m a n y compcments i n this category have a higher quality of construction than required because of sampler operational requirements and because t h e chemical process sampler was o r i g i n a l l y t h e prototype f o r t h e f u e l sampler-enricher. Instrumentation f o r this system i s discussed i n more d e t a i l i n Sect. 3 . 1 2 .

Components of t h e coolant s a l t system associated with reactor secondary containment. In addition t o those components covered by items 1 t o 3 above, this category includes t h e b a l l f l o a t l e v e l transmitter described i n Sect. 6.9, t h e coolant salt venturi described i n Sect. 6.13, t h e NaK-filled d i f f e r e n t i a l transmitter described i n Sect. 6.12, t h e coolant-salt drain-tank supply vent and bypass valves, t h e coolant pump-bowl pressure transmitter, the coolant-salt drain-tank pressure transmitter, and t h e coolant-salt pump bubbler-level system. Weldsealed construction w a s used i n these applications because of t h e consideration of conservation of helium and exclusion of oxygen noted previously and because of the high operating temperature of t h e venturi, NaK-filled d i f f e r e n t i a l pressure transmitter, and t h e b a l l - f l o a t l e v e l transmitter. Because t h e coolant salt system i s considered secondary containment, l e s s protection was provided on t h e coolant-salt helium-supply purge and vent l i n e s than w a s provided on similar l i n e s i n t h e f u e l system.

From t h e above discussion, it should be noted t h a t operational considerations, i n many cases, dictated a quality of construction greater than t h a t dictated by t h e containment considerations. Also, it should be noted t h a t no mention has been made of sealing or closure of penetrat i o n s associated with s i g n a l and control wires or tubing f o r those instrument components t h a t form a part of secondary containment. I n almost a l l such cases t h e components a r e i n s t a l l e d so t h a t the bodies of t h e components form outward extensions of secondary containment and no penetrations were required. I n t h e case of t h e f e w exceptions (notably t h e c e l l radiation monitors, c e l l ambient temperature thermocouples, and some components of t h e sampler-enricher and chemical process sampler), t h e signals a r e e l e c t r i c a l , and t h e required seals a r e made by means of feed-through penetration seals. With t h e exception of t h e c e l l ambient temperature thermocouples noted above, t h e measurement of temperature i n t h e secondary containment systems posed no containment problems since a l l such measurements were made by means of thermocouples located on t h e outside of pipes and vessels (or i n wells), and no penetrations were required. Other possible exceptions t o t h e above are t h e thermocouples i n s t a l l e d on t h e charcoal beds and t h e off-gas sampler (see Sects. 3.5 and 6.7). Penetration s e a l s are provided where these thermocouples penetrate enclosures; however, since t h e enclosures a r e vented t o t h e stack, these s e a l s should probably be considered part of building containment r a t h e r than secondary containment.

1.2.3.2

Redundancy, Separation, and Identification

As discussed i n subsequent sections of this report, the instrunentat i o n and control systems associated with reactor safety are required t o be redundant. I n the MSRE, t h i s redundancy i s i n t h e form of one-out-oftwo or two-out-of-three logic. ORNL practices require t h a t a l l components, wiring, and tubing be i n s t a l l e d so t h a t redundant safety channels a r e physically separated from each other and from control-grade components, wiring, and tubing and t h a t safety channels be i d e n t i f i e d as such. Where possible, separation w a s accomplished by means of separate conduits, wireways, junction boxes, cabinets, and metallic barriers. I n some cases, complete separation w a s not possible, and physical separat i o n with appropriate i d e n t i f i c a t i o n (painted signs, labeling, and col-or coding) w a s used. 1.2.3.3

Hazards t o Operating Personnel

Attention w a s given t o providing protection against hazards t o opera t i n g personnel beyond that provided by the reactor safety system. Wiring was i n s t a l l e d i n accordance with the National Electric Code and with ORNL recommended practices. Instrument l i n e s t h a t presented possible pressure o r radiation hazards were e i t h e r protected o r confined t o areas not normally accessible t o operating personnel. 1.2.4 1.2.4.1

Performance Characteristics

Overall Accuracy

Accuracy was a prime consideration i n the selection of instrumentat i o n associated with the acquisition of experimental data and with some process and nuclear control systems. However, i n reactor safety systems, accuracy was considered t o be secondary t o r e l i a b i l i t y . Also, i n many process instrumentation applications, high accuracy w a s not required, and accuracy was considered t o be secondary t o other considerations, particularly cost. Since accuracy i s a poorly understood and often misused term, the performance requirements f o r those instruments associated with the acquisition of high-accuracy data or information were specified i n terms of individual performance c h a r a c t e r i s t i c s such as l i n e a r i t y , zero drift, span shift, hysteresis, ambient temperature and pressure e f f e c t s , process temperature and pressure effects, etc. I n general, an e f f o r t w a s made t o match accuracy specifications t o the application; however, i n some applications, considerations of minimization of t h e number of instrument types used and reduction i n requirements f o r operating spares resulted i n t h e use of instruments having a higher accuracy than required. 1.2.4.2

Reliability

R e l i a b i l i t y was a prime consideration i n the selection of a l l instrument components and w a s of particular importance i n the selection of reactor safety system components. However, since obtaining high r e l i a b i l i t y

can be very expensive, t h e degree of r e l i a b i l i t y needed f o r a p a r t i c u l a r component was based, i n general, on considerations of "cost vs consequences .I1 Where high r e l i a b i l i t y was needed, r e l i a b i l i t y requirements were incorporated i n the specifications, and components were t e s t e d before and after i n s t a l l a t i o n . Where moderate r e l i a b i l i t y was s u f f i c i e n t , selection of component w a s based on experience and engineering judgment, and performance was proved during system shakedown t e s t i n g and subsequent operations. A t this point t h e d i s t i n c t i o n between component r e l i a b i l i t y and system r e l i a b i l i t y should be noted. A s discussed i n the following section, o v e r a l l r e l i a b i l i t y can be enhanced by t h e use of redundancy i n system design. Conversely, improper use of redundancy can reduce t h e o v e r a l l system r e l i a b i l i t y below t h a t of the individual components.

1.2.4.3

Failure Modes

Insofar as possible, components of the s a f e t y system (and of most control systems) were selected and i n s t a l l e d i n such a manner as t o " f a i l safe." That i s , t h e components were selected and systems were designed t o produce t h e desired corrective or control action i n t h e event of component failure or loss of supply power. A f a i l - s a f e action i s sometimes referred t o as a "failure toward danger,'' since such an action appears t o t h e controlled system as a dangerous condition and i s therefore i n t h e safe direction. A single " f a i l u r e toward danger" i n a system using two-of-three logic converts it t o one-of-two logic. The f a i l - s a f e mode of failure i s t h e d i r e c t opposite of t h e "unsafe f a i l u r e " mode, which r e s u l t s either i n an unsafe or undesired action or i n no action a t a l l . Examples of the l a t t e r would be an upscale f a i l u r e of an instrument channel having a downscale t r i p , an open-circuited c o i l i n a r e l a y which must be energized t o produce t h e desired action, a welded contact which must open t o produce t h e desired action, and an "in-place" f a i l u r e of an instrument r e s u l t i n g i n the controlled system remaining i n t h e s t a t e t h a t it w a s i n when t h e failure occurred. In-place failures are c h a r a c t e r i s t i c of motorized equipment and occur mainly i n servocontrolled equipment such as potentiometric recorder-controllers. This type of failure can be caused by l o s s of supply power, by desensitization of amplifiers by excessive noise on t h e signal, by d i r t y slide-wires, or by component failures. It should be recognized a t this point t h a t an "unsafe f a i l u r e " of one channel i n a safety system u t i l i z i n g redundancy can be very serious. In t h e case of systems using one-of-two logic, an "unsafe failure" of one channel w i l l convert the system t o a "single-tracked" system w i t h full dependence f o r s a f e t y being placed on each and every component of t h e remaining channel. The s i t u a t i o n i s even more c r i t i c a l i n t h e case of systems using two-of-three coincidence logic, since an "unsafe f a i l u r e " of one channel w i l l convert t h e system t o a two-of-two coincidence logic system, with full dependence f o r safety being placed on each and every component of both remaining channels. Routine t e s t i n g i s required t o detect such conditions. While f a i l - s a f e action i s desirable, it i s usually d i f f i c u l t or impossible t o obtain i n practice. Few ( i f any) devices have only one failure mode. For example, &n otherwise fail-safe device or system incorporating a feedback loop w i l l usually f a i l "unsafe" i f t h e feedback

loop is opened. Most devices have two possible modes, and some have more (such as upscale, downscale, and in place). However, the devices will usually have a "preferred" or "most probable" failure mode. Where one mode is predominant the device is said to fail in this mode, and circuits are designed accordingly. In some cases ambiguity of modes can be reduced or eliminated by the use of "confidence" circuitry and monitoring devices (such as "power-failure" relays), which produce a corrective action in the safe direction in the event of the occurrence of a condition that could result in an unsafe or unwarranted action. Although it is possible to design around some undesirable failure modes, components and system are, in general, too complex and too unpredictable to use this crutch extensively. In the final analysis the use of fail-safe design techniques must be recognized for what it is - a means for reducing the probability of unsafe or unwarranted actions and reliance must be placed on the use of the principles of redundancy and diversity together with surveillance, testing, and monitoring to obtain a level of reliability commensurate with the requirements for reactor safety and continuity of operations.

1.2.5

1.2.5.1

Effects of Process Conditions

Operating Temperature

Temperature effects were an important consideration in the selection of all primary sensing elements and were a primary consideration for those components which were attached to the heated salt systems. In these systems the 1200째F operating temperature presented problems which necessitated the development of special instrumentation. In other MSRE systems the temperatures were within the range where satisfactory performance was obtainable with commercially available instrument components. The effects of variations of temperature on accuracy and other performance characteristics are of interest at low temperatures (below 150째F) and become increasingly important as the temperature increases. At higher temperatures (above 300째F), damage to materials such as plastics and elastomers becomes important; at elevated temperatures (above 600째F) the general operability becomes a matter of concern. Also, since corrosion is accelerated and structural strength of material is degraded as the temperature is increased, the choice of materials becomes a prime consideration at elevated temperatures. The philosophy adopted in the design of MSRE salt system instrumentation was to avoid operation of instruments at high system temperatures wherever possible and to obtain readings indirectly with instruments operated under more favorable conditions. Where this was not possible or desirable, development of special instrumentation was initiated (see Sect. 6).

1.2.5.2

Operating Pressure

As in the case of temperature the effects of process operating pressure and of pressure variations on performance characteristics and structural strength become increasingly important as the pressure increases. These pressure effects are most important in applications

where t h e operating temperature i s high. Fortunately, M Sm pressures a r e low (below 50 psig) i n those portions of t h e system where temperatures are above 150째F; so t h e required s t r u c t u r a l strength w a s , i n most cases, obtainable with a minimum of e f f o r t . Close a t t e n t i o n t o e f f e c t s of pressure was required i n t h e selection or developent of components which operate a t temperatures above 600OF, and i n cases such as t h e molten-salt l e v e l probes, t h e requirements f o r s t r u c t u r a l strength and containment imposed severe r e s t r i c t i o n s on the design. I n other cases, such as t h e NaK-filled d i f f e r e n t i a l pressure transmitters, t h e e f f e c t s of pressure variations were t h e boundary conditions which limited t h e accuracy of t h e instrument.

1.2.5.3

Corrosion

Corrosion was a prime consideration i n t h e selection or development of a l l instrument components which were exposed t o process f l u i d . However, i n a l l reactor systems except the f i e 1 processing system, t h e requirements f o r corrosion resistance w e r e e a s i l y s a t i s f i e d by use of standard materials available f o r commercial components or by use of INOR-8 (Hastelloy N ) materials f o r developmental instruments I n the f u e l processing system t h e high corrosion r a t e s expected during fluorination precluded the use of t h e thin-walled conductivity l e v e l probes f o r l e v e l detection i n the f u e l storage tank and forced a redesign of the ultrasonic l e v e l probe t o obtain adequate corrosion allowance. In some cases materials were used which gave corrosion resistance beyond t h a t dictated by the process conditions. Thb w a s done t o permit decontamination of components with acid r i n s e s . Exposure of components t o corrosive conditions w a s avoided where possible by obtaining readings i n d i r e c t l y with components operated under more favorable conditions. For example, pressure i n t h e f u e l storage tank w a s obtained by measurement of pressure i n a purge l i n e connecting t o t h e tank. This technique i s similar t o t h a t used t o avoid temperat u r e problems (see Sect. 1.2.5.1). Since corrosive conditions d i d not e x i s t i n t h e MSRE operating areas, no s p e c i a l precautions w e r e required f o r t h e s e l e c t i o n of components and design of systems located i n these areas.

1.2.5.4

6.'

S a l t Plugging and Vapor Deposition

Consideration was given t o t h e p o s s i b i l i t y of plugging of instrument l i n e s with s a l t wherever these l i n e s penetrated l i n e s or vessels containing salt. Such plugs can occur as a r e s u l t of expulsion of s a l t i n t o cold instrument l i n e s o r as a r e s u l t of vapor deposition of s a l t i n t h e l i n e s . Lines can a l s o be plugged by formation of oxides where gas i s purged i n t o t h e system below s a l t level. The consequences of plugging range from minor t o very serious, since t h e r e s u l t a n t loss of information could f u r t h e r r e s u l t i n loss of experimental data, l o s s of control, or l o s s of one or more channels of safety protection. During i n i t i a l stages of MSRE design, it was believed t h a t vapor deposition and oxide formation might be very serious problems and might preclude measurement of pressures, d i f f e r e n t i a l pressures, etc., with

6.'

instruments attached t o purged gas l i n e s . This b e l i e f was based on experience i n e a r l i e r molten-salt systems i n which considerable d i f f i c u l t y with plugging w a s experienced. Further investigation revealed t h a t the vapor pressure of the MSRE s a l t s and the expected oxygen content of the MSRE cover gas would be much lower than those of previous systems. On the basis of this information the indirect measurement approach was adopted. To minimize the p o s s i b i l i t y of plugging, a l l instrument l i n e s which penetrated salt-containing l i n e s and vessels were made as large as w a s consistent with other considerations, and instrument taps were located as far above s a l t l e v e l as possible. In almost a l l cases MSRE instrument components a r e located on i n l e t gas lines, and a small purge flow i s maintained i n the lines. This purge flow a l s o serves t o minimize back diffusion of radioactive gases. Some components, such as t h e f u e l offgas letdown valve, the charcoal-bed differential-pressure transmitter, and the fuel-pump gas-letdown flow transmitters, were located on l i n e s downstream of t h e reactor. I n these cases the components were placed as far downstream as possible and were protected by f i l t e r s . I n cases such as t h e bubbler l e v e l indicator, where instrument l i n e s are required t o extend below s a l t level, provisions were made t o ensure that pressure t r a n s i e n t s w i l l not expel s a l t i n t o cold l i n e s (see Sect. 6.8). Experience t o date on the MSRE and on r e l a t e d engineering t e s t f a c i l i t i e s indicates t h a t the philosophy adopted was sound and t h a t the provisions made i n the design t o prevent plugging were adequate. Some plugging has occurred i n off-gas lines; however, t h i s plugging was due t o hydrocarbon plugging and was not expected during t h e i n i t i a l design. While the MSRE instrumentation and controls system has been essent i a l l y f r e e of s a l t plugging problems, the need f o r purge flow, together with other considerations (such as operating temperature and radiation damage), resulted i n a complexity of instrumentation beyond that required f o r the basic measurement. This increased complexity resulted from t h e additional instrumentation needed t o prevent the escape of a c t i v i t y through instrument l i n e s which penetrated both containment barriers. If radiation-resistant transmitters capable of operating i n d i r e c t contact with t h e s a l t had been available, this complexity of

instrumentation (and the probability of salt plugging) would have been reduced. NaK-filled transmitters o f f e r promise f o r use i n future reactor systems, provided t h e p o s s i b i l i t y of release of NaK i n t o the system can be tolerated. Also the b a l l f l o a t l e v e l transmitter described i n Sect. 6.9 may be a s a t i s f a c t o r y replacement f o r the bubbler-type l e v e l system i n some applications.

1.2.5.5

E l e c t r i c a l R e s i s t i v i t y of Molten Salts

The e l e c t r i c a l r e s i s t i v i t y of the MSRE fuel and coolant s a l t s was determined t o be approximately 1 ohm-cm a t 1200'F and 1kilohertz (1000 cps). While this r e s i s t i v i t y indicates t h a t the MSRE salt i s a f a i r conductor, it i s high i n Comparison w i t h the 120-microhm-cm r e s i s t i v i t y of Hastelloy N and Inconel and even higher i n comparison with the 35-microhm-cm r e s i s t i v i t y of sodium and 80-microhm-cm res i s t i v i t y of NaK a t l200'F. Conversely, t h e r e s i s t i v i t i e s of NaK and

sodium are low in comparison with Hastelloy N and Inconel. Therefore, while Inconel can be considered as a poor insulator in comparison with NaK and sodium, Hastelloy N is a good conductor in comparison with the MSRE salt. For this reason, devices such as magnetic flowmeters and "J" probe type level indicators, which are used extensively in liquidmetal systems, are not suitable for use in the MSRE molten-salt systems. However, the conductivity properties of the MSRE salt were utilized to obtain single-point indications of level in the MSRE drain tanks (see Sect. 6.10). 1.2.6 1.2.6.1

Ehvironmental Effects

Ambient Temperature

Ambient temperature effects did not impose severe restrictions on the selection or development of any MSRE instrument components, since the in-cell ambient temperatures are kept below UO째F by the use of space coolers and the temperatures in operating areas do not exceed loO째F. (The main control areas are air-conditioned, and temperatures are kept relatively constant at about 75OF). However, the effects of variations of ambient temperature on the accuracy of measurements were important, and they were considered during procurement of components and design of the system. Also, in some areas where natural circulation was restricted or density of heat-generating equipment was high, forced-draft air cooling was required to maintain the ambient temperature of the components and that inside the cabinets within acceptable limits. 1.2.6.2

Ambient Pressure

The effects of ambient pressure were important in the selection or development of all components that were referenced, directly or indirect, to atmospheric pressure or to in-cell pressures. I n some cases, such as determination of cell leak rate and monitoring of building containment, the pressures themselves were of direct concern. In all other cases, the interest lay in the effects of pressure on the accuracy of the measurement. Instrument components which are (or may be) sensitive to ambient pressure generally fall into one of the following three categories: 1. those which sense the difference between an internal pressure and the pressure of the surrounding medium and which generate a mechanical or electrical signal or indication (pressure gages, manometers, pressure switches, and pneumatic receivers);

2. those which convert a force, motion, or electrical signal into a pneumatic pressure (current-to-pneumatic converters and pneumatic valve positioners); 3 . combination of 1 and 2 (pneumatic pressure transmitters and pneumatic weigh cells).

Such instruments usually incorporate a bellows or a Bourdon tube i n the mechanism. Pressure i n t h e drain-tank c e l l can vary over a wide range (+5 t o -4 psig) during t h e course of normal operations. The pressure can vary l e s s i n areas ventilated by the containment a i r system since pressures i n these areas a r e maintained s l i g h t l y negative with respect t o the atmosphere (approximately -0.2 t o -2 i n . H2O gage). Also, variations of atmospheric pressure a r e of i n t e r e s t i n many instances. Variations over the range from 28.7 t o 29.5 i n . Hg were observed a t the MSRE s i t e over a six-month period, and larger variations a r e possible during extreme weather conditions. The observed variations correspond t o approximately 0.5 psi. Although this value i s small, it amounts t o I$ of the 50-psig measurement span of most MSRE pressure transmitters and 4$ of the =-psi output signal span of 3- t o 3 - p s i g pneumatic transmitters. The philosophy adopted i n t h e design of the MEW3 instrumentation and controls system w a s t o avoid t h e use of pressure-sensitive components i n areas where pressure variations occurred. Where this was not possible, or where t h e use of pressure-sensitive components offered significant advantages, t h e e f f e c t s of pressure variations were eliminated by i n t e r n a l compensation of t h e device o r by correcting the data. The drain-tank weigh c e l l s are an example of the use of i n t e r n a l compensation. Data correction was used t o correct gage pressure data such as obtained from the reactor c e l l pressure transmitter. Another form of compensation, which i s not usually recognized as such, i s the location of associated pneumatic transmitters and receivers i n the same pressure environment. Although t h i s technique i s common practice, significant e r r o r s can occur when this e f f e c t i s overlooked and transmitters and receivers are ins t a l l e d i n areas having different ambient pressures.

1.2.6.3

Radiation Damage

A l l instrument components located within t h e reactor and drain c e l l s a r e subject t o damage from nuclear radiation. However, some components of t h e sampler-enricher, t h e chemical process system, t h e chemical process system sampler, t h e off-gas system, and the off-gas sampler a r e less subject t o radiation damage. The radiation l e v e l i n t h e coolant salt and waste c e l l s i s r e l a t i v e l y low, and radiation damage i n these areas was not considered serious. The maximum radiation l e v e l s i n various areas of t h e MSRE are l i s t e d i n Table 1.2.2. The values l i s t e d are f o r peak conditions and assume that a c t i v i t y i n the system has b u i l t up t o saturation levels after sustained full-power operation. In general, the selection of materials f o r use i n high-radiation areas w a s governed by considerations of t o t a l integrated dose r a t h e r than dose r a t e , and the use of p l a s t i c s and elastomers was l i m i t e d t o those areas where t h e t o t a l gamma dose expected during the lifetime of the reactor w a s less than lo7 r and t h e expected neutron dose was less than nvt. Where higher dosage was expected, component materials were r e s t r i c t e d t o metals and inorganics. Exceptions t o t h i s r u l e a r e the rod drive motors and a l l semiconductor devices. The rod drive motors have organic insulation and lubricants and are designed t o be replaceable.

Table 1.2.2. Radiation Dose Rates i n Various Areas of t h e MERE During o r Following Sustained 7-Mw Power Operation Gamma. (r/hr)

Location

Reactor c e l l

7 x 104

Neutron (neutrons sec-l)

lo7 thermal,

Remarks

A t 7 Mw

108 fast

5.4 x 103 2.4 x 103 2 x

Drain c e l l

Negligible

Zero power, reactor drained and f lushedd

io3 io3

A t 7 Mw

A t 10 kwb Zero power, reactor draine dc

2.6 x 104 Fuel processing 5 x cell

A t 10 kwb

Zero power, reactor draine de

io3

4.2 x 4.2 x

io3

After 11 days cooling

Coolant c e l l

100

-0

Fuel samplerenricher

1000

Negligible

Fuel processing sampler

During sample w i t h drawal

Off-gas sampler

500

During sampling

High-bay area

< 20 x

A t 7 Mw

Main c o n t r o l area

<1x

Transmitter room

< 75 x

North e l e c t r i c service area

<3 x

Service room

< < < <

Water room Vent house

Diesel house

A t 7 Mw

During sample withdrawal

1x 10 x 10-3 10 x 10-3

x 1.0'~

aWith respect t o gamma dose rate.

bAf%er 5 h r 10-kw operation following sustained 7-Mw operation. C

Immediately following above 5-hr operation a t 10 kw.

days after drain following 7 Mw sustained operation.

Semiconductors are known t o be extremely s e n s i t i v e t o both dose rate and t o t a l dosage. The use of instrument components u t i l i z i n g semiconductors was r e s t r i c t e d t o areas outside b i o l o g i c a l shielding, where radiation l e v e l s were expected t o be r e l a t i v e l y low. For example, t h e t r a n s i s t o r i z e d amplifiers used with t h e Foxboro ECI pressure and d i f f e r e n t i a l pressure transmitters were placed remote from t h e transmitter body when t h e transm i t t e r was located i n a high-radiation area. I n areas such as t h e fuel sampler-enricher and t h e off-gas sampler, t h e maximum (peak) radiation l e v e l s a r e very high but t h e duration of t h e peak i s r e l a t i v e l y short. I n these areas, radiation-resistant components and materials were preferred, but p l a s t i c s and elastomers were permitted.

1.2.7 1.2.7.1

Physical Requirements

Weld- Sealed Construction

All instrument components which a r e an i n t e g r a l p a r t of primary containment were weld sealed, inspected, and t e s t e d t o ensure t h a t helium leakage through t h e body t o t h e surrounding area would be l e s s than low8 cm3/sec a t maximum expected i n t e r n a l pressures. To conserve helium, most instrument components of t h e cover-gas system were a l s o weld sealed.

1.2.7.2

Ruggedness

The a b i l i t y t o withstand shock and vibration without permanent damage or temporary l o s s of performance was a consideration i n t h e selection of a l l instrument components and was a prime consideration i n t h e selection of field-mounted instrumentation. O f p a r t i c u l a r importance was t h e ruggedness of those components which are located within t h e react o r and drain c e l l s and which may be subject t o abuse during remote maintenance operations.

1.2.7.3

Size

S m a l l physical s i z e i s generally desirable since reduction of the s i z e of individual components r e s u l t s i n an o v e r a l l reduction i n t h e s i z e of control panels and minimizes interferences i n t h e f i e l d . I n areas such as t h e sampler-enricher t h e a v a i l a b i l i t y of space dictated t h a t small-sized components be used; however, i n most applications, other considerations predominated. For example, r e a d a b i l i t y of receivers and general performance c h a r a c t e r i s t i c s were considered t o be more important than s m a l l size.

1.2.7.4

Materials of Construction

I n addition t o t h e requirements for physical strength and resistance t o the e f f e c t s of corrosion and radiation, discussed i n Sects. 1.2.5.1, 1.2.5.2, 1.2.5.3, and 1.2.6.3, consideration w a s given t o compatibility

of materials used i n instrument components with t h e general metallurgical requirements of t h e MSE. For example, t h e use of metals (such as lead, t i n , and aluminum) with melting points below 1600'F w a s not permitted i n areas where they could conceivably come i n contact with heated pipes and vessels. Also, t h e use of dissimilar-metal welds f o r attachment or connection of instrument components t o heated pipes and vessels was not permitted. The use of dissimilar-metal welds f o r thermocouple attachments was avoided by the use of a Hastelloy N tab which was welded t o t h e Inconel thermocouple sheath i n the shop and subsequently welded t o t h e pipe or vessel when t h e thermocouple was i n s t a l l e d .

1.2.7.5

Cleanliness

Since accumulation of dirt and other foreign materials w i l l cause degradation of performance of most instrument components and systems, cleanliness was an important consideration i n t h e procurement and i n s t a l l a t i o n of a l l MSRE instrument components. However, t h e degree of cleanliness required i s dependent on t h e application and varies over a wide range. I n most applications moderate cleanliness was adequate, and reliance was placed on t h e manufacturers' i n t e g r i t y and on preoperational checks and inspection f o r cleanliness control. A much higher degree of cleanliness was required f o r components which were an i n t e g r a l part of t h e heated s a l t systems or of pipes and vessels connected t o these syst e m s . To preclude t h e p o s s i b i l i t y of foreign matter being transported from these components t o the molten s a l t o r t o heated surfaces i n pipes and vessels, stringent cleanliness control w a s maintained during fabrication, transportation, and i n s t a l l a t i o n . Components fabricated outside ORNL were inspected by Company representatives during assembly. The degree of cleanliness was determined by wiping with dry s u r g i c a l gauze. Discoloration of the gauze was cause f o r rejection. After assembly and t e s t i n g , openings were capped, and t h e components were sealed i n p l a s t i c bags and cartons and remained sealed u n t i l they were i n s t a l l e d i n t h e MSRE system.

1.2.8

Cost

A continuing e f f o r t was made during t h e design of t h e M Sm i n s t r u mentation and controls system and during specification and procurement of components, t o minimize the o v e r a l l cost of t h e system. In n o n c r i t i c a l applications, cost w a s a primary consideration; however, i n applications where safety, operability, and continuity of plant operations were involved, other considerations predominated. Also, where c o n f l i c t s of objectives arose, decisions were based on consideration of "cost vs consequences. ''

1.3

PLANT 1NSTRUMEEC"TTIONLAYOUT General Description

1.3.1

Instrumentation i s centralized i n the main control area, where a graphic control panel and operating console are located. Only informat i o n needed t o operate the reactor i s displayed on these panels. Auxili a r y instrument and e l e c t r i c a l panels, relay and thermocouple cabinets, and a data-logging system a r e adjacent t o the main control room. A second area, the transmitter room, i s adjacent t o the reactor c e l l . The available space and the d e s i r a b i l i t y of mounting c e r t a i n components close t o t h e point of measurement dictated t h a t this be a control are&. With the exception of control-rod drives, thermocouples, pump speed pickups, microphones, high-level gamma ionization chambers, weigh c e l l s , and some control valves, a l l instrumentation components a r e located i n areas external t o t h e reactor containmest vessels. Other instrument panels f o r auxiliary systems a r e located a t convenient operating points throughout the building. Sixty-one 2 - f t modular instrument panel sections, one operating console, two r e l a y cabinets, one thermocouple patch panel, and two equipment racks a r e required f o r the MSm. 1.3.2

Main Control Area

The main control area, shown i n Figs. 1 . 3 . 1 and 1.3.2, contains 12 control panels and the control console. The 12 panels comprise the main control board, which i s i n the form of an a r c centered on the console. The main control board, Fig. 1.3.3, provides a f u l l graphic display of t h e reactor system and i t s associated instrumentation. These panels contain t h e instrumentation f o r the f u e l salt system, the coolant salt system, the f u e l and coolant pump o i l systems, the off-gas system, t h e jumper board, and a push-button s t a t i o n f o r t h e various pumps and blowers. The primary recorders f o r nuclear control are also on t h e main board. The instrumentation on the console consists of position indicators, control switches, and l i m i t indicators f o r t h e control rods, radiator doors, and f i s s i o n chambers, and other switches required f o r normal and emergency operation of t h e reactor. Routine control of t h e reactor i s accomplished from t h e main control area. Some of t h e auxiliary systems are a l s o cont r o l l e d here, with remaining portions controlled from the l o c a l panels shown i n Figs. 1 . 3 . 1 and 1.3.4. 1.3.3

Auxiliary Control Area

The auxiliary control area, Fig. 1.3.2, consists of eight auxiliary controlboards, f i v e nuclear controlboards, one relay cabinet, one thermocouple cabinet, four d i e s e l and switching panels, and a safety relay cabinet. The eight auxiliary panels contain the signal amplifiers, power computer, switches and thermocouple alarm switches, auxiliary indicators not required f o r immediate reactor operation, the f u e l and

coolant pump microphone amplifier and noise l e v e l indicator, and the subs t a t i o n alarm monitors. A l l t h e safety c i r c u i t control relays are located i n the safety cabinet, and most of the operating c i r c u i t relays are i n the control relay cabinet. The relay cabinet contains only the relays f o r the main control c i r c u i t r y . The thermocouple cabinet contains a patch panel with pyrometer jacks. A l l thermocouples i n the system except those on the radiator tubes a r e terminated i n this cabinet. The thermocouples on t h e radiator tubes are routed t o t h e temperature scanner and then t o the patch panel. The f i v e nuclear panels contain some of the instrumentation f o r the process radiation system, the o i l system, and the sampling and enriching system. "he health physics monitoring alarm system, the high-level gamma chamber electrometers and switching panel, and the reactor control nuclear amplifiers, servo amplifiers, and other equipment f o r the nuclear control system a r e a l s o located here. Four panels contain the instrumentation f o r the operation of t h e emergency d i e s e l generators. The distribution panels f o r the control c i r c u i t and instrument power a r e located on the south w a l l of the auxiliary control room.

1.3.4

Transmitter Room

The transmitter room, Fig. 1.3.5, consists of nine control panels, one solenoid power supply rack, and a transmitter rack. Panels 1 and 2 a r e f o r the leak detector system, and panels 3 and 4 a r e f o r f u e l drain tanks 1 and 2, t h e coolant drain tank, the f u e l f l u s h tank, and the f u e l storage tank w e i g h instrumentation. Panels 5 and 6 a r e f o r the f u e l and coolant pump bubbler-type l e v e l control, panel 7 i s f o r the freeze valve a i r control, panel 8 contains t h e power supply and alarm switches f o r the drain tank l e v e l probes and a transducer f o r the float-type coolant-saltpump l e v e l transmitter, and panel 9 i s f o r the sump bubbler system. The solenoid power supply rack contains most of t h e solenoids f o r the f u e l salt system and t h e power supplies and d i s t r i b u t i o n panels f o r the elect r i c transmitters and d i f f e r e n t i a l transmitters. The transmitter rack contains the remote amplifiers f o r the e l e c t r i c s i g n a l transmission syst e m and a l s o the current-to-air transducers. All e l e c t r i c a l and pneumatic l i n e s that connect transmitter room equipment t o input signals from t h e reactor, drain tank, water room, and a l l other areas outside the building enter through sleeves i n the floor. Output signals from the transmitter room equipment a r e conducted via feeder cable t r a y s t o the main cable t r a y system, which runs north and south i n the building on the 840-ft level.

1.3.5

Field Panels

Additional panels are required f o r t h e auxiliary systems. These (see Figs. 1.3.1 and 1.3.4) a r e located near the subsystems which they serve. Four panels f o r the cooling o i l systems are located i n the service room and service tunnel; one cooling- and treated-water system panel i s located i n the fan house; three panels a r e located on elevation 852 f t

a t column l i n e C-7 f o r the sampling and enriching system. Two cover-gas system panels a r e located i n the d i e s e l house. Two containment-air system panels a r e provided: one a t the f i l t e r p i t and the other i n the high-bay area. The reactor c e l l a i r pressure monitoring instrumentation and t e s t i n g f a c i l i t i e s a r e mounted on a single panel located i n the north e l e c t r i c service area, which i s d i r e c t l y below the transmitter room. Five panels f o r the f u e l processing system a r e located i n t h e high-bay area above the f u e l processing c e l l . Two of these control the process, and the other three a r e f o r the sampler. One panel located i n the high-bay area on top of the coolant c e l l serves the coolant s a l t sampler. Three panels f o r the f u e l off-gas analyzer and one panel f o r the reactor-cell-air oxygen analyzer a r e located i n the vent house. Two panels f o r t h e thermocouple scanning system are located on the 840-ft l e v e l near the heater control panels.

1.3.6

Interconnections

The control areas and the controlled systems are interconnected by cable t r a y s and conduit. This system includes the main cable t r a y system running north and south i n the building, with branch t r a y s and cond u i t s joining the main t r a y . These main t r a y s carry a l l tubing f o r the pneumatic system, thermocouple lead wire, and the ac and dc control wiring. Each category of s i s a l runs i n a different t r a y t o avoid mixing of the signals. Risers connect the panels and cabinets i n the control area on elevation 852 f t w i t h the main trays. No exposed t r a y s a r e i n the main or auxiliary control rooms. Safety system wiring i s completely enclosed i n conduit and junction boxes and i s separated from control and instrumentation wiring. 1.3.7

Data Room

The data room i s designed t o house the data logger-computer; see Sect. 2.12. It contains all t h e data system equipment except one logging typewriter, which i s located i n the main control room. The layout of t h e equipment i n the room i s shown i n Fig. 2.12.4 (Sect. 2.12). This room i s located i n the north end of t h e reactor building, next t o the main control room. There a r e e n t r i e s from t h e hallway and the main control room. A large glass window i s located so t h a t t h e main control panel can be seen from t h e data room. The data system cabinets are i n s t a l l e d i n two rows, back t o back, running e a s t t o w e s t about the center of the room. The f r o n t row of f i v e cabinets facing the control room contain the computer proper, and t h e s i x rows facing the north end of the room contain the analog input s i g n a l terminals and the control c i r c u i t s f o r the typewriters, magnetic tapes, and other input equipment. The data system operator's console i s located so t h a t the reactor control panel can be seen by an operator a t the console. Two desks and several t a b l e s a r e located i n the room f o r

use of reactor operating and analysis personnel and the computer maintenance engineer. A storage cabinet f o r magnetic tapes i s located a t the west wall of the room, and a spare parts storage cabinet i s located a t the north wall. The e l e c t r i c a l power panel f o r the system i s located i n t h e northwest corner of the room. The i n s t a l l e d equipment i s shown i n Figs. 2.12.1 and 2.12.3 (Sect. 2.12). The input s i g n a l cables f o r t h e data system a r e brought up t o t h e bottom of the room i n cable trays. Holes a r e cut i n the f l o o r beneath the cabinets f o r routing the input signal and control cables t o t h e cabinets. The data room i s a i r conditioned by two 7.5-ton a i r conditioners. These same units can be used t o supply a i r t o t h e main control room i n an emergency, and the control room a i r conditioner can supply a i r t o the data room when necessary.

ORNL-DWG 64-808R

BUILDING 7509

INSTRUMENT

MAIN CHANGE ROOM

PROCESSING

Fig. 1.3.1.

Main Floor Layout of Building 7503 a t 852-f't Elevation.

ORNL-OWG 64-630

N c (

IARY CONTROL AREA

Fig. 1.3.2.

Main and A u x i l i a r y Control Areas.

. .. d

m m

bD Fr

.ri

43 ORNL-DWG 63-8399

YBUILDING 7503-ELEVATION 840ft Oin. LEVEL

Fig. 1.3.4.

Layout of Building 7503 a t 840-ft Elevation. ORNL-OWG 64-629

Fig. 1.3.5.

Transmitter Room.

1.4 PLANT CONTROL SYSTEM The MSRE and i t s control and instrumentation complex may be viewed as a primary reactor system which generates nuclear power and r e j e c t s heat t o t h e atmosphere plus t h e collection of a u x i l i a r i e s o r subsystems required t o run t h i s primary system. This discussion of MSRE plant control i s concerned with how t h e control system interconnects these various systems and how they are coupled t o t h e reactor; it i s l i t t l e concerned with t h e reactor s a f e t y system. It i s s u f f i c i e n t t o point out t h a t t h e safety-grade instruments are not used as operational cont r o l s and that every e f f o r t is made t o keep the s a f e t y system instruments completely decoupled from t h e operational control equipment. The MSRE safety system, w h a t it does, and why are discussed i n Sect. 1.5. It i s appropriate t o separate t h e various systems and equipment and t h e i r associated instruments and controls i n t o categories, thus: 1. Those operator-controlled items which exert a d i r e c t and immediate influence on t h e state of t h e reactor; c o l l e c t i v e l y these are t h e operator's "handle" which runs the MSRE. 2. Redundant, e s s e n t i a l a u x i l i a r i e s not i n (1)which, should one u n i t malfunction, require immediate t r a n s f e r switching by t h e operator i f t h e redundance i s t o be effective. Examples are t h e instrument a i r compressors and the component cooling pumps. 3 . V i t a l monitoring and control instrumentation not subject t o adjustment o r control by t h e operator. These instruments produce offlimit alarms and control actions and provide continuous information as t o t h e conditions i n t h e monitored systems. Examples are t h e process radiation monitors, health-physics alarm instrumentation, s a f e t y system instruments, e t c . 4. Nonredundant but e s s e n t i a l a u x i l i a r i e s which operate as s e l f contained devices. These instruments e i t h e r require no control o r are controlled l o c a l l y and automatically. They a r e expected t o operate continuously and unattended. An example i s t h e 60-kva battery-powered s o l i d - s t a t e ac power supply. 5. The remaining instruments whose e f f e c t on t h e reactor system i s e i t h e r peripheral and i n d i r e c t o r i s f u r t h e r modified by t h e instrumentation in (1). Instruments used f o r chemical and physical a n a l yses, f o r gathering experimental data, and f o r monitoring slow trends i n n o n c r i t i c a l areas of t h e system are in t h i s group. This grouping, o r categorization, has been strongly implied by Sect. 1.3, which discusses plant instrumentation layout as it i s r e l a t e d t o the reactor operator's use of t h e instruments and controls. Figure 1.4.1 i s a functional diagram of t h e instrumentation i n and d i r e c t l y adjacent t o t h e main control room. Generally, t h e diagram shows that t h e main control room instruments are composed p r i n c i p a l l y of those i n t h e f i r s t three groups, and t h e instrumentation on t h e operator's console i s almost e n t i r e l y i n t h e first category. There i s a strong incentive t o maintain continuous operation a t t h e ERE; therefore t h e p l a n t and t h e instrumentation and control system are designed t o minimize unscheduled t o t a l shutdowns caused by equipment f a i l u r e s and e l e c t r i c a l power (TVA) interruptions. C r i t i c a l operating a u x i l i a r i e s such as instrument a i r compressors, water pumps, cooling blowers, etc., are redundant, and switchover t o t h e spare u n i t

i s accomplished a t the main control board. Each lube o i l package serving t h e salt loop pumps contains a spare o i l pump. Transfer switching t o t h e spare o i l pump i s automatic on l o s s of flow (pressure). E l e c t r i c a l power interruptions are a leading cause of shutdown conditions. Design of t h e MSKE assumes that TVA-supplied e l e c t r i c a l power w i l l be interrupted s e v e r d times a year by thunderstorms. Local emergency power from d i e s e l generators i s provided.1 The d i e s e l s are s t a r t e d and stopped i n t h e auxiliary control room j u s t a few steps from t h e operator's console. Short-term power interruptions t o the operating equipment w i l l not produce a t o t a l system shutdown. This allows s u f f i c i e n t time f o r manually controlled d i e s e l generator s t a r t u p and necessary t r a n s f e r switching. T o t a l shutdown i s defined t o include a reactor drain, which produces a completely quiescent system incapable of achieving c r i t i c a l i t y . The design and operation of t h e reactor and i t s controls do not assume unperturbed operation with a l o s s of TVA power. I n f a c t , i f t h e reactor i s a t power, t h e rods and the l o a d w i l l scram, and it w i l l not be possible t o resume high-power operation u n t i l TVA power i s restored. The procedure following a l o s s of TVA power i s t o restore c r i t i c d i t y and operate a t heat l o s s power u n t i l TVA power i s again available. The on-line r e l i a b i l i t y required by t h e instrument and control power system must meet more stringent requirements w i t h respect t o continuity. The operator's need f o r good information i s never more acute than during abnormal conditions such as those produced by an interruption of TVA power. Safety systems and high-grade interlocks normally a c t toward shutdown when t h e i r power i s l o s t , even momentarily. Therefore, the operation of e s s e n t i a l p l a n t controls and instruments does not depend on t h e normal TVA supply. The two-out-of-three redundancy extensively emplayed i n t h e plant safety system i s intended t o eliminate such a dependency. The p l a n t s a f e t y system and a t y p i c a l example of three-channel redundant design are discussed i n Sect. 2.5. Figure 1.4.2 i s a simplified one-line diagram of t h e power system used f o r t h e instrumentation and controls. This power d i s t r i b u t i o n system w i l l be thorodescribed i n Sect. 4.13, but it i s worth while t o point out t h a t : 1. The three-channel s a f e t y systems receive t h e i r power from t h r e e p r a c t i c a l l y independent sources within t h e d i s t r i b u t i o n system. Two of these a r e battery-powered and w i l l not be affected by shortterm interruptions of TVA power.

The controls and information channels e s s e n t i d t o continuous opera t i o n are battery-powered.

The control requirements of t h e MSKE d i f f e r , depending on whether or not t h e reactor loop i s f i l l e d o r empty and, i f f i l l e d , on t h e amount of power being generated. These d i f f e r e n t requirements must be accommodated within t h e control system; t h a t is, t h e interlocks which proh i b i t o r permit i n one operating regime must not prevent routine and

IS. E. Beall e t al., MSRE Design and Operations Report, Part V, F:ea c t o r Safety Analysis, ORNLTM-732 (August 1964).

proper operation i n another. Mode control, superimposed on t h e individual subsystem control channels, resolves t h i s problem of accommodation. It does so by making all t h e subsystem a l t e r a t i o n s required f o r accommodation t o operating regimes responsive t o a single, manually operated control. Figure 1.4.3 i s a diagram of the f u e l and coolant salt systems, showing the location of t h e instrumentation and controls which provide mode control. It can be seen from t h i s figure t h a t mode control i n t h e MSRE i s concerned with: 1. The location of t h e f u e l salt and the f l u s h salt, that is, whether i n t h e drain tanks o r t h e reactor loop. Note that the control system makes no d i s t i n c t i o n between f u e l salt and f l u s h salt. This i s because r e l i a b l e and c e r t a i n sensors which d i f f e r e n t i a t e between t h e two are not available.

The a b i l i t y t o t r a n s f e r s a t among t h e drain tanks or t o and from t h e reactor loop.

The power (flux) being developed and t h e r a t e of change of power, both a c t u a l and potential.

The operating i n t e g r i t y of important flux instruments used t o monitor and control reactor power.

The scope of the mode control system i s not extended t o t h e auxi l i a r i e s , t o the helium supply system, or t o the off-gas system. Equipment o r control system deficiencies and operating e r r o r s which a f f e c t these areas w i l l be reflected, indirectly, t o t h e mode control system or will become immediately apparent because of alarms and/or interlocks o r by t h e action of t h e s a f e t y system. Furthermore, t h e operating res t r i c t i o n s imposed by t h e mode controls are more numerous during trans i t i o n s from one operating mode t o another as power is being increased. This limits the rate of change of power t o reasonable values. After t h e new reactor mode has been established, many of these r e s t r i c t i o n s required t o e n t e r t h e mode are bypassed by relay seals. Figures 1.4.4 and 1.4.5 are condensed block diagrams which indicate t h e function and purpose of t h e mode controls. The manually selected operating regimes have been designated as O f f , P r e f i l l , Operate, Operatea discussion of these follows: S t a r t , and Operate--; 1. O f f . The "Off" mode could be designated "Not i n P r e f i l l o r i n O p e r a t F ( s e e 2 and 3 below) without s a c r i f i c i n g accuracy. I n " O f f " t h e e n t i r e MSRE system is not inoperative but t h e reactor i s shut down. When t h e reactor i s " O f f " t h e following conditions obtain: a) rod withdrawal i s prohibited,

not i n automatic load control,

rod control servo i s "Off,"

prohibits opening of t h e helium valves used t o f i l l t h e reactor vessel,

prohibits r a i s i n g t h e radiator doors by manual control, above t h e intermediate l i m i t i f reactor power i s above 1 Mw,

provides a control rod "Reverse" i f the power (flux) exceeds 1.5 Mw o r i f t h e reactor period i s less than 5 sec,

prevents s t a r t i n g the f u e l and coolant salt pumps; i f t h e pumps a r e running and t h e control system i s switched t o " O f f " these pumps w i l l continue t o run because of s e a l contacts i n t h e pump control c i r c u i t s ,

- t r a n s f e r freeze valves, thaw" - f i l l and drain freeze valves. P r e f i l l . - Intended t o e s t a b l i s h the necessary 'ho thaw"

2. and s u f f i c i e n t conditions required t o precede a reactor start. During t h i s period t h e reactor loop i s empty so t h a t helium may be circulated t o e s t a b l i s h uniform temperature conditions i n t h e loop. Safety system checkouts are being conducted, and other routine and nonroutine operations involving maintenance and equipment v e r i f i c a t i o n may be under way. S a l t t r a n s f e r s among t h e drain tanks, t o the chemical processing plant, or t o o r fron t h e f u e l storage tank are permitted during P r e f i l l . The primary requirement during P r e f i l l operation i s t h a t t h e reactor loop be maintained empty. P r e f i l l allows complete freedom i n t h e use of t h e jumper board f o r t e s t i n g and maintenance checks and, excepting the reactor f i l l r e s t r i c t i o n s , does not superimpose additional interlocked prohib i t i o n s on operating MSRE equipment. This mode establishes c e r t a i n conditions required 3. Operate. t o f i l l t h e reactor loop. Entering "Operate" requires t h a t t h e t r a n s f e r freeze valves between t h e f u e l storage tank and t h e drain tanks be frozen and t h a t a t l e a s t one freeze valve between t h e reactor drain l i n e and one of t h e f u e l drain tanks be open. The Operate mode automatically becomes Operate4 . Operate-Start. S t a r t when t h e reactor loop i s f i l l e d t o the correct l e v e l and t h e reactor drain valve (W-103) i s frozen. This mode permits reactor start; with power generation not exceeding 1.5 Mw provided t h e conditions f o r control-rod withdrawal, described i n Sect. 2.6, have been established. This mode i s obtained by manual selection when 5. Operate-Run. conditions r e q u i s i t e t o high-power operation have been met. OperateRun and Operate-Start are, by d i r e c t switching, mutually exclusive. Depending on whether or not t h e operator chooses t o control t h e reactor automatically o r manually, the requirements f o r going i n t o the OperateRun mode d i f f e r somewhat (see Fig. 1.4.5). If t h e operator chooses t o use t h e automatic rod c o n t r o l l e r o r programmed load control, o r both (see Sects. 2.6 and 2.8), c e r t a i n i n i t i a l conditions must be met which provide a smooth t r a n s i t i o n i n reactor power generation as it becomes responsive t o i t s load-following charact e r i s t i c s and as t h e rod servo assumes control. These i n i t i a l conditions are as follows:

Using t h e Automatic Rod Controller 1. The demand s i g n a l computed by the automatic rod c o n t r o l l e r i s asking f o r less than 1 Mw.

The regulating rod i s not being r e s t r i c t e d i n motion by i t s limit switches (see Sect. 2.6).

Using Programmed Load Control

1. The radiator doors are positioned so t h a t power extraction is limited.

The set-point s i g n a l which controls t h e r a d i a t o r bypass damper, described i n Sect. 2.8, is zero.

Entering t h e Operate-Run mode i s subject t o additional r e s t r i c t i o n s which a r e not contingent on t h e use of t h e automatic rod controller: 1. A t l e a s t one main r a d i a t o r blower must be on.

2. 3.

The f u e l salt pump must be operating (rpm

> 1100).

The range s e l e c t o r s i n t h e linear power channels (Sect. 2.4) must be i n t h e 1.5-Mw position.

4. A t least one wide-range counting channel must provide

confidence" and indicate t h a t reactor power is above 0.5 Mw and that t h e reactor period i s over 30 sec.

Once Operate-Run has been established, most of t h e requirements l i s t e d i n t h e preceding paragraphs are bypassed by a seal, as shown i n Fig. 1.4.5. When reactor power reaches 1Mw t h e "confidence" interlock (Sect. 2.6) is bypassed and, insofar as the mode control c i r c u i t r y i s involved, t h e o n l y requirement f o r continuing reactor operation i n t h i s mode i s t h a t t h e f u e l salt pump be running, one main blower be on, the t r a n s f e r freeze valves be frozen, a t least one drain l i n e freeze valve be thawed, and no safety system jumpers be used. The data logger-computer, adjacent t o t h e main control area, occupies a singular position in t h e h i e r a r c m of MSRE instrument and control systems. It i s added t o t h e MSRF: as an experiment intended t o evaluate t h e merit of such devices i n reactor systems. Therefore, the MSRE control system continues t o operate whether or not t h e data logger i s i n service. Although no d i r e c t reactor system control functions are vested i n t h e logger-computer, it i s capable of exerting considerable influence on reactor system operations. This i s because it provides t h e reactor operator with a l a r g e amount of current information on system s t a t u s and gives alarms f o r off-limit conditions. The available space in t h e m a i n and auxiliary control areas res t r i c t e d t h e i r use t o instrumenting t h e functions shown i n Fig. 1.4.1. It was necessary, and f o r no other reason, t o obtain t h e additional space required f o r t h e remaining instrumentation by decentralization with l o c a l control systems. I n many cases, and regardless of available space considerations, l o c a l control w a s a preferred choice f o r one o r more of t h e following reasons:

1. it r e s u l t s i n control loops which are less c o s t l y t o b u i l d and are more r e l i a b l e , 2.

it eliminates problems of data transmission o r retransmission over long l i n e s with consequent improvement i n accuracy,

it improves operation by locating t h e control system d i r e c t l y adjacent t o t h e controlled equipment.

These decentralized controls, whose location has been discussed i n Sect. 1.3, are i n categories 4 and 5 ( l i s t e d previously i n t h i s section) and are not needed continuously by the reactor operator. Monitoring by annunciation i s augmented by scheduled, routine inspection (the "walking log") as required.

ORNL-DWG 67-8147

OPERATORS CONSOLE

MAIN CONTROL BOARD

COrnOL ~0~

COrnOL~O!S

Operatillg w e Selection leactivity: (a) Mermal S h h i n g , all rods (a) Stack Pans on oft (a) SControl of Flux (a) mock Valves I (e) Servo control of (kltlct High Bsy Ventilation and Fressure T e m p rnturC I I r m m 4 ATIOX: H C l l t m supply: (a) l4mual Rod Scram (1) A s required for operrtor m l l l l l l l C e (a) Avge Flow to Salt 3. Reactor Iaad: to DuppOrt c o n b l f W h 2 a O M . (a) ~ ( a m u r iIndividual control of Radiator b r : and srpa~s am per (b) Autcmatieally Pr0p-d Control O f DIRECT (e) Flows and pressures to I DcOrs, Ismper, and 1 mover Lube O i l lkaks SURVEILLANCE (c) road scram salt Tmnsrars: AND IMMEbIATE 4. Fmergency bin, Manual CONTROL ACTION (a) See (4b) above \ 5. Fi~aionChamber Fosition by Manual (a) Freeze valves T h w and Rmc DiRECT Operation of Wide-Range Counting Channels SURVEILLANCE Reactor Fill and k i n : 6. m a i n Tank Selection f o r Routine F i l l ALARMS ANDand Tlgn8fer. (a) See also (4b) and ( 5 ) a b v c INFORMATION f[ IlWmlATrnN (b) k i n tank pressure rating to o f f e s s p t m As required for operator surveillance NEARLY REACTOR ( c ) ~ r m pmi Drain Tanh p r e s w e differewe to support above contm1 tunctions. Imd Contml ACTION (a) Win bl-s: QI 011 (a) dnqer l4mual positioning ALARMS Inbe O i l Systems AND (a) see (k) e.tove ,INFORMATION (b) O i l Rrmps: on-oft

1. 2.

Jumper B a r d

omw system:

3. 4.

----

Auxiliaries:

(a) Treated FIS3 Rnrps:

(b) Coo-

Tower FIS3

QI-oft Pnupn:

on-011

(e)

on-om

(d)

on-om

(g)

on on on -

CooTower Pans: Cmpnent Cooling Pnupn (e) cell Cooling Blnrcls (f) A i r Compressors Radiator h l u s B l o w a s

(h) Anti-BaeWlov IhmpW on &ln snd h m l l u a B l m s

off

3. 4.

5. 6. 7.

ALARMS INFORMATION AND

on-oft

AUXILIARY CONTROL BOARDS 1. 2.

INST+CTIONS

IN FORMATION

DATA LOGGER- COMPUTER Information frm a l l

areas of the

system.

- INFORMATION

AIUNlWiatom

safety Sy8tem mtrumentatlon m e s s Radistion Mcmitoring I n s h e n t a t i o n Health-Mies Radiation A l a r m Instrumentstion Rccze V a l v e Temperature Contml am3 Monitorhtrmentation S a l t I m p Temperature I n s h c n t e Flux Instruments: (a) E , charme1 (a) Wide-Range Counting ChanneM ( c ) Rod Control S m

MANUAL OPERATIONS AND CONTROL ADJUSTMENTS .ALARMS, DIRECT AND INDIRECT

SLIGHTLY DELAYED CONTROL ACTION

a e c t r i c a l pwer S Y S h Inshalts and

Controls voltage, Current, md pwer Indication (a) TVA E m Transfer Contml (e) meeel Stsrt -Stop me1 and Coolant salt Rrmp wonitoring )(.

Inshenta

(a) &lee Level (b) PWcr snd Cumnt 10.

Thamocouplc Patch panel

Fig. 1.4.1. Diagram of Instrumentation i n and Directly Adjacent t o t h e Main Control Room.

c ORNL-DWG 67-5890

---

Fig. 1.4.2.

MSF3 Instrument Pawer Distribution.

ORNL-DWG 67-4549

Fig. 1.4.3.

MSRE Instruments and Instrument Signals for Mode Control.

1 '

ORNL-DWG 67-6435

OPERATE

PREFILL

1. PROHIBITS FUEL TRANSFERS AMONG D R A I N T A N K S

I . REACTOR IS E M P T Y

2. ALLOWS REACTOR F I L L

2. REACTOR F I L L AND D R A I N V A L V E S FROZEN

3. NO J U M P E R E D S A F E T Y SYSTEM CONTACTS

3. P E R M I T S SALT T R A N S F E R S AMONG DRAIN TANKS

4. PERMITS H E L I U M C I R C U L A T I O N I N F U E L AND C O O L A N T LOOPS 5. PERMITS BYPASSING T H E S A F E T Y S Y S T E M WITH T H E J U M P E R B O A R D FOR S Y S T E M TESTING

RUN

4 . D R A I N VALVE FROZEN

4. DRAIN VALVE FROZEN

2. REACTOR F U L L

3. LOW P O W E R . c l . 5 MW

3. POWER ABOVE 1 MW OR A B O V E 200 kW W I T H GOOD COUNT

4. ONE M A I N RADIATOR BLOWER MAY B E "ON"

5. SERVO CONTROLS FLUX ONLY

REACTOR F U L L

RATE INFORMATION ("CONFIDENCE")

4. F U E L S A L T PUMP " O N " 5. ONE OR BOTH ,MAIN RADIATOR BLOW E RS "ON

6. SERVO CONTROLS REACTOR O U T L E T SALT T E M P E R A T U R E

Fig. 1.4.4.

MSRE Control System Modes.

ORNL-DWG 67-4609

F lFl NOT IN OPERATE

I INTERTANK TRANSFER VALVES FROZEN

AT LEAST ONE F I L L AND DRAIN VALVE THAWED I

I REQUEST

NO SAFETY SYSTEM JUMPERS I N USE

OPERATE MODE

O D E ( JOPERATE

LINEAR NUCLEAR POWER INSTRUMENTATION IN POWER RANGE

DRAIN VALVE FROZEN

"CON FIDE NCE 'I ESTAB L ISH ED I N AT L E A S T ONE CHANNEL OF WIDE RANGE NUCLEAR INSTRUMENTATION

REACTOR F U L L

NOT IN RUN MODE

REACTOR POWER GREATER THAN 0.5 MW PER WIDE RANGE CHANNEL WITH "CONFIDENCE "

I REACTOR PERIOD GREATER THAN 30 sec PER WIDE RANGE CHANNEL WITH "CON F IDENCE "

~= RUN MODE REQUEST

Y P, ct

b %?

EA+ - 7

NO L I M I T SWITCHES ACTUATED BY REGULATING tiOD

REGULATING ROD UNDER M A N U A L LUfJTKUL { K m K V U

BY TEMPERATURE SERVO NOT MORE THAN ONE (1.0)MW

MOMENTARY SWITCH ACTUATION WITH SPRING RETURN I N DIRECTION OF ARROW

NO DEMAND FOR LOAD INCREASE

I LOAD O K FOR "RUN" MODE OPERATION OF SYSTEM I

OR BOTH WIDE RANGE NUCLEAR INSTRUMENT CHA N NE L S I

SAME INSTRUMENTS

REACTOR POWER GREATER THAN 0.2 MW

I I EITHER OR BOTH MAIN

1.5 The

MSm

W E T Y SYSTEM

s a f e t y system is composed of instrumentation which must

be highly r e l i a b l e because it augments t h e containment o r protects v i t a l and expensive equipment, o r both. T h i s section i s confined t o a broad, o v e r a l l description of t h e r e l i a b l e protective subsystems i n the

MSm

and t h e basic principles which guided t h e i r design. Reliable protective systems f o r reactor i n s t a l l a t i o n s have, i n t h e past, been focused principally on t h e reactor core, and t h e i r operation has been centered on t h e behavior of t h e flux. I n designing t h e MSRE t h e use of r e l i a b l e protective instrumentation w a s not limited t o prot e c t i n g t h e reactor core f r o m t h e immediate e f f e c t s of excessive flux. It w i l l be seen, as we review and describe t h e protective subsystems, that safety-grade instrumentation is extensively employed t o enhance t h e primary and secondary containment and t o ensure a reactor drain. It i s worth while t o describe, b r i e f l y , some of t h e c h a r a c t e r i s t i c s of the MSm that a r e responsible f o r t h e safety-grade protective i n s t r u mentation w i t h which it i s provided. 1. The MSRE, being liquid-fueled, does not have f u e l cladding as t h e first, unpenetrated containment b a r r i e r . The core vessel, heat exchanger, f u e l salt storage tanks, and a l l interconnecting piping become t h e primary containment barrier t o t h e molten salt. I n addition, t h i s primary containment is pierced by inlet and o u t l e t l i n e s carrying helium used f o r sweep gas across t h e pump bawl, f o r bubbler l e v e l instruments, and f o r drain tank pressurization. These l i n e s v i o l a t e t h e primary containment b a r r i e r unless they a r e r e l i a b l y blocked. 2. I n common with solid-fueled reactors the MSRF: uses conventional poison r o b f o r control and safety. Anauses,1-3 tests, and operating experience have shown t h a t t h i s reactor i s a very docile and s t a b l e machine having a r e l a t i v e l y long neutron lifetime, a l a r g e heat capacity, and an e f f e c t i v e negative temperature c o e f f i c i e n t of r e a c t i v i t y . All hypothetical nuclear excursions i n the MSRE proceed slowly and do not develop high t r a n s i e n t vapor pressures; undesirably high temperatures a r e t h e consequence. The control rods are not capable of providing absolute reactor shutdown under a l l conditions. The shutdown worth i n t h e rods, a t r e a c t o r operating temperature, is l o s t became of t h e negative temperature coefficient i f t h e f u e l salt i n t h e core vessel is cooled s u f f i c i e n t l y . Transference of f u e l t o t h e drain tanks i s t h e c e r t a i n method of obtaining absolute shutdown, and t h e a b i l i t y t o e f f e c t such a t r a n s f e r (reactor drain) must be assured.

'S. E. Beall e t al., MSRE Design and Operations Report, P a r t V, Reactor Safety Analysis, ORNL-TM-732 (August 1964,).

2P. N. Haubenreich e t al., MSRE Design and Operations Report, Part 111, Nuclear Analysis, Om-TM-730 @eb. 3, 1964.).

3J. R. Engel, P. N. Haubenreich, and S. J. .Ball, Analysis of F i l l ing Accidents i n MSRE, ORNL-TM-497 bug. 16, 1966).

3. The chemistry of t h e f u e l salt does not disallow segregation4e5 of the d i f f e r e n t fluorides w i t h a consequent increased concentration of uranium i n one of t h e segregated phases. Segregated salt has been produced i n t h e laboratory under very carefully controlled conditions. The accidental and undetected segregation of s a l t i n a drain tank i s highly improbable but has not been demonstrated t o be incredible. F i l l i n g the reactor w i t h segregated salt may produce a nuclear excursion during the f i l l i n g operation which, ultimately, exceeds t h e limiting capacity of the coatrol rods. Rigid, r e l i a b l e control of t h e reactor f i l l i n g operation i s a necessity. 4. A temperature excursion w i l l cause the f u e l s a l t t o expand f a s t e r than its coDtainment. The volume available f o r such expansion is limited; therefore, it is e s s e n t i a l t o have rigid, r e l i a b l e control of temperature and Fuel salt l e v e l . See a l s o No. 3 above. 5. Fuel and coolant salts freeze a t temperatures i n t h e region of 84.0 t o 850'F. Freezing t h e s a l t i s not harmful, but remelting i s accompanied by expansion, which i s capable of rupturing the piping. The coolant salt r a d i a t o r i s p a r t i c u l a r l y vulnerable. Loss of the radiator would be costly and would be an intolerable setback t o the MSR program. Reliable protective measures (see Sect. 2.8) a r e included i n t h e MSRE. Principles employed i n achieving r e l i a b i l i t y i n reactor s a f e t y systems6-18 have been applied extensively t o the MBE. These principles a r e summarized as follows: 1. Redundancy is employed s o t h a t no single f a i l u r e of an instrument, coqonent, o r wiring having a reasonable probability of f a i l u r e could cause system failure. A single f a i l u r e could involve a l l coaductors i n a single conduit, all contacts of a switch, or, unless special barriers a r e provided, t h e e n t i r e contents of an enclosure. 2. Testing is employed, preferably on l i n e and without disconnecting equipment o r otherwise impairing t h e a b i l i t y t o protect during the test. Each channel is t e s t e d separately s o as t o disclose a f a i l e d coaponent which would prevent protective action o r a f a i l u r e which could interconnect two otherwise independent channels and thereby destroy channel independence and redundancy. 3. Diversity i s employed wherever feasible; t h a t is, unlike channels are paired t o accomplish a desired r e s u l t . For example, a flow l o s s caused by stopping t h e coolant salt pump is detected by both t h e pump speed moni t o r s and the flowmeters i n t h e coolant salt piping. 4 . Safety and control a r e separated so t h a t l o s s of control resulting i n an excursion w i l l not occur simultaneously with l o s s of protection. Separatioa is a l s o employed s o t h a t improvements intended t o enhance cont r o l o r other functions unrelated t o s a f e t y w i l l not be made, unwittingly, t o t h e detriment of safety. These precepts c o n s t i t u t e recommended design practices f o r w h a t a r e now thought t o be t h e best s a f e t y systems we knm haw t o build. Figure

4R. E. Thoma and H. A. Friedman, "Se regation of t h e MSRE Fuel Salt in Drain Tanks," m-65-15 (Mar. 17, 1965 (internal memorandum). 5E. A. Friedman, "Segregation of LiF-BeF2-UF'r; Fuel S a l t on Freezing in Drain Tanks, MSR-66-19 (July 12, 1966) (internal memorandum).

1.5.1 shows an example of a three-channel, h i g h - r e l i a b i l i t y subsystem i n t h e MSRE. This i s a simplified diagram of t h e instrumentation which closes t h e block valves i n t h e instrument air l i n e s t o t h e secondary containment c e l l i f t h e pressure i n t h e c e l l rises above 2 psig. It is a representative example of a s a f e t y subsystem i n the MSRE. The following description of i t s design and operation i s included here t o i l l u s t r a t e how these general precepts have been r e d u c e d t o practice. The instrumentation is simple; t h r e e high-grade pressure switches provide the switching contacts which operate t h e solenoid valves i n t h e valve matrix. This matrix is arranged s o that, i f any two of t h e t h r e e pressure switches a r e actuated, t h e pneumatic actuators (diaphragms ) of t h e block valves a r e vented t o t h e atmosphere, the a i r supply t o t h e valves i s shut o f f , and t h e spring-loaded valves close and block t h e i n strument a i r l i n e s .

%. H. Hanauer, "Design Precepts f o r Engineered Safeguards," Nucl. Safety 6 (41, 408-11 (Summer 1965) 7E. P. Epler, "Dangers i n Safety Systems," IRE Trans. Nucl. Sci NS-8(4), 51-55 (October 1961).

8S. H. Hanauer, "Instrumentation f o r Containment," Nucl. Safety

41-46

2(1),

(Septeniber 1961) '1. M. Jacobs, "Safety Systems f o r Nuclear Power Reactors," T r a n s . Am. Inst. Elec. Engrs., P t . I, 76, 6 7 W 3 (November 1957).

'OS. J. Ditto, "Redundancy and Coincidence i n Reactor Safety Systems," Nucl. SaSety 2(4), 16-17 (June 1961); M. A. Schultz, "Reactor Safety I n s t m e n t a t i ~ n , "Nucl. Safety 4(2), 1-13 (December 1962) 'IC. G. Lennox, A. Pearson, and P. R. Tunnicliffe, Protective System Design f o r Nuclear Reactors, AECL-U95

121. M. Jacobs, "Safety System Technology," N u c l . Safety &(3), 23145 (Spring 1965) 13S. J. Ditto, "Effect of Operating Experience on Safety System Design," Nucl. Safety 5(2), 183-84 (Winter 19644965).

14E. P. Epler, "Reliability of Reactor Systems," Nucl. Safety &(4), (June 1963). T e s t i n g f o r &-Pile Loops," Nucl. 15K. W. West, "Instrument S Safety 5(4), 3744'6 (Summer 16K. W. West, "Relative Functions of Loop Containment and Instrument a t i o n , " N u c l . Safety 4 ( 4 ) , 180-81 (June 1963). 17S. J. Ditto, "Failures of Systems Designed f o r High R e l i a b i l i t y , " Nucl, Safety 8(1), 35-37 (Fall 1966) 72-76

18E. P. Epler, "Safety System R e l i a b i l i t y Safety 6(4), 4ll-14 (Summer 1965)

VS.

Performance," Nucl.

The two-out-of-three redundancy permits on-line t e s t i n g without system perturbation. The completeness of the t e s t procedure employed is an operational decision and i s not limited by the design of the instrumentation. Testing i s done by simulating an increase i n c e l l pressure by using t h e nitrogen cylinder (Fig. 1.5.1) as t h e source of pressure and noting t h e response of the pressure gages i n the valve matrix or, if desired, by actually closing the block valves. A t y p i c a l t e s t i n channel A proceeds thus: 1. The hand valve in t h e l i n e which connects t h e nitrogen cylinder t o the l i n e from PSS-RC-B t o the reactor c e l l i s opened, and the pressure i s adjusted t o the 2-psig s e t point. The sintered disk snubbers provide s u f f i c i e n t flow r e s t r i c t i o a t o maintain t h i s pressure without mdue losslg of nitrogen t o the reactor c e l l . 2. The increase i n pressure actuates pressure switch PSS-RC-B and t h i s , i n turn, deenergizes solenoid valves E S V - 1 A 1 and E S V - l A 2 . 3 . These valves, E S V - U U and ESV-1A2, i n the valve matrix change t h e i r aspect, but not s o as t o a f f e c t t h e pressure i n t h e 80-psig air header; valve E S V - U . 2 vents pressure gage PI-LAS. During normal operat i o n pressure gages PI-lAl, PI-U.4, and PI-U.5 indicate header pressure, 80 psig. Pressure gage PI-lA5 w i l l now go t o zero. The block valves w i l l be unaffected since there i s s t i l l no open l i n e or l i n e s between t h e block valve operators and t h e vent l i n e and because the connection between t h e 80-psig header and the valve operators i s s t i l l maintained through E S V - I B 2 , E S V - U U , E S V - l B 1 , and ESV-1C. This t e s t , steps 1 t o 3 above, can be conducted w i t h any channel and without disturbing reactor operation. It does not t e s t t h e actual closure of t h e block valves. Now, suppose any two channels a r e t e s t e d coincidentally. For example, i f channels 1 and 2 a r e t e s t e d simultaneously, solenoids ESV-1A1, ESV-lA2, E S V - l B 1 , and ESV-U32 w i l l be deenergized, and, referring t o the valve matrix i n Fig. 1.5.1, the block valve operators w i l l be opened t o atmospheric pressure through E S V - 1 C 1 t o E S V - U 3 1 t o ESV-1C2 t o E S V - l A l t o S S V - l B 2 t o vent. Valves ESV-LA1 and E S V - l B 2 now prevent transmission of pressure from the 80-psig a i r supply t o the block valve diaphragms, and t h e spring-loaded valves w i l l close. Such a two-channel t e s t checks operation of the e n t i r e system. Failure of any block valve t o close can be detected by observing the response, or lack of response, of the i n - c e l l instruments supplied v i a t h e block valve. T h i s same basic scheme is used f o r protection elsewhere i n t h e MSRE. The protective instruments which close block valves i n t h e i n l e t helium l i n e s operate when t h e pressure i n l i n e 500 f a l l s belaw 28 psig (see Figs. 1.5.7 and 1.5.2). In t h i s situation, where protective action i s i n i t i a t e d by an undue reduction in pressure, t e s t i n g i s accomplished lgThe containment is normally held at -2.0 psig, and t h e t e s t pressure needs only t o produce a d i f f e r e n t i a l across the s n d b e r s of 4 psig. The nitrogen cylinder has a volume of appraximately 2 ft3 a t 2000 p s i . Should t h i s e n t i r e volme be introduced i n t o the secondary containment, with a volume of 18,000 ft3, t h e pressure r i s e i n the containment would be negligible. Also, t h e c e l l atmosphere is s p e c i f i e d t o be more than 95$ nitrogen and would not be degraded.

by venting t h e pressure switches t o atmospheric pressure by opening an individual hand valve and, as above, by observing t h e response of the pressure gages i n a valve matrix o r t h e block valves themselves. This same design i s used f o r protecting against t o o great a reduction i n reactor c e l l pressure below atmospheric (see input No. X I I , Fig. 1.5.2). In t h i s p a r t i c u l a r system the pressure switches a r e enclosed i n boxes which a r e vented t o atmospheric pressure through snubbers. Testing is accomplished by pressurizing t h e baxes. This increases the d i f f e r e n t i a l pressure across t h e pressure switches and thereby simulates a reduction of pressure within the c e l l . It is worth while t o examine t h i s p a r t i c u l a r s a f e t y subsystem from t h e standpoint of t h e "recommended practices" previously cited. Up t o but not including t h e output elements (block valves 1, redundancy and t e s t i n g requirements a r e completely s a t i s f i e d by t h e design. It should be pcdnted out, t h a t an on-line t e s t of t h i s particular subsystem which includes closing t h e instrument a i r l i n e block valves is operationally intolerable. The addition of a second valve i n each l i n e would improve the r e l i a b i l i t y of the instrumented blocking system but, of course, would not improve the on-line t e s t i n g situation. It w a s established while t h e MSRE w a s being designed t h a t the closed system of instrument a i r l i n e s , tanks, and compressors, w i t h associated valves, etc., cons t i t u t e d t h e second effective containment b a r r i e r (see Sect. 1.5.4). This p a r t i c u l a r system does not employ diverse channels i n obtaining redundant input channels. In t h i s p a r t i c u l a r case there i s no suitable and r e l i a b l e s u b s t i t u t e f o r the simple, d i r e c t measurement of c e l l pressure as it is done. The use of diverse sources of control power substantially reduces t h e likelihood of spurious action caused by f a i l e d o r f a u l t y parer sources. The pressure switches are i n s t a l l e d i n t h e north e l e c t r i c service area and a r e within 10 f't of t h e c e l l w a l l . The piping t o and from the switches is of autoclave tubing with autoclave fittings. The e l e c t r i c a l interconnections a r e run i n separate conduits, channel by channel, and contain no other w i r i n g . The solenoid valve matrix is located i n t h e north e l e c t r i c service area i n a s a f e t y instrumentation cabinet. A s t h e NSRE design proceeded, a few situations and conditions developed which resulted i n departures f r o m t h e i d e a l recommended practices outlined previously i n t h i s section. Two examples, with reasons, follow: 1. All three of our s a f e t y system neutron sensors are located i n a single penetration because both t h e amount of space and i t s configurat i o n absolutely prohibit three separate penetrations a t different 1oca.t i o n s (see Sect. 2.1). 2, I n some cases the r e l i a b l e instrumentation which automatically closes block valves closes only one valve i n each l i n e r a t h e r than two separate, independent valves i n s e r i e s . MSRE system design established a c r i t e r i o n t h a t a single block valve i n s e r i e s w i t h a p a i r of check valves was a necessary and s u f f i c i e n t alternate f o r two block valves i n s e r i e s (see, f o r instance, Sect. 4 . 8 ) . On-line t e s t i n g of t h e "load scram" system (refer t o Sect. 2.8) conf l i c t s , seriously, with reactor operating schedules and w i l l produce highly undesirable thermal t r a n s i e n t s . These, i n turn, produce therma.1 s t r e s s cycles which reduce t h e l i f e of t h e system. In order t o t e s t t h e door drive mechanism and the a b i l i t y of t h e doors t o scram when t h e reactor is dmn and t h e coolant system drained, it is necessary t o bypass

the safety instruments that scram the doors since these same instruments prevent r a i s i n g the doors t o perform the t e s t . This dilemma i s solved by using the j m p e r board t o bypass safety system board c i r c u i t r y ( r e f e r t o Sect. 4.11) i bypassing is permitted only when the reactor is e Safety system and, where emjumpering is resorted t o only when abso ployed on the MSRE, w a s adopted only s t was retained by t h i s found. In t h i s p a r t i c u l a r case t h e a b i l i t y compromise. It is usual and obvious practice t r a t e relays, solenoids, temperature switches, etc., so that power s cause them t o change s t a t e safety system toward safety; O e .g and t h e i r contacts break c i r c u i t s t o produce the s a f e t y action. The r e l a y contacts which stop the component cooling pump motors (see Sect. 1.5.5) must be closed t o energize t h e battery-powered "Stop" t r i p c o i l i n the motor s t s r t e r . Motor s t a r t e r s , typically, operate t h i s way, and it i s not i n the best i n t e r e s t s of r e l i a b i l i t y t o attempt t o redesign or modify well-engineered, time-tested equipment of t h i s type f o r reversemode operation. Furthermore, t h i s p a r t i c u l a r sgfety action i s diverse i n that protection is a l s o obtained by closing a valve (see outputs X I and XII, Fig. 1.5.2). Because of t h e very strong incentive t o keep t h e primary containment simple and s t r u c t u r a l l y uncomplicated, the MSRE does not have a m u l t i p l i c i t y of f u e l s a l t drain l i n e s , each with an individual drain valve, controlled by t h e safety system. The foregoing is intended t o provide a broad, overall view of the application of r e l i a b l e , safety-grade instrumentation t o the MSRE. Det a i l e d descriptions of the design and operation of these r e l i a b l e subsystems are contsined e i t h e r in the remainder of t h i s section o r e l s e where i n t h i s report and may be located by referring t o the "Supplement a r y Informatioal' column i n Table 1.5.1, or the last column i n Fig. 1.5.2. Much of t h e text which immediately follows i s an updated version of similar material, now p a r t i a l l y obsolete, o r i g i n a l l y presented i n ORNL-TM-732 ( r e f . 1). Figure 1.5.2 shows input-output diagram of the MSRE protective instrument system. Figure 1.5.3 i s an expanded signal flow diagram of the reactor drain instrumentation (described in Sect. 1.5.11, and Table 1.5.1 elaborates and augments the information i n t h e figures. The more detailed descriptions which follow a r e referenced t o t h e p a r t i c u l a r regions i n t h e reactor system which a r e principally involved.

z o n e reader is referred t o sect. 1.2, "Design Considerations, f o r a discussion of instrument f a i l u r e modes.

loblo 1.5.1 (continued)

lnput Ref. No. Vll.

Or Which Indicates a Real or Potential Hazard

Helium pressure in the pump bowl greater than 25 PSig

Causes of the Hazard, the Consequences, and the Corrective Action

1. Causes a. Rapid unchecked expansion of fuel salt by excess temperature, see I and ll above and Supplementary Information

b. Plugging of off-gas system 2. Consequences a. If unchecked, damage to pump seals, which are rated a t 100 psig, and possible overstressing of pnmary loop b. Exceed capacity of off-gassystem, with resulting threat to containment c. Possible l o s s of primary containment 3. Corrective actions a. Drain reactor vessel b. Vent pump bowl to the auxihary charcoal bed VIll.

Helium pressure in the fuel pump bowl gmater than "fill permit" valve

1. Causea a. Excess filling rate or overfill. b. Temperature excursion during fill (see ll and

m,this table)

c. Closing of HCV-533A1 normally maintamed open by administrative control. during the filling operation. 2. Consequences Not of itself a h a z d , a release of positive pressure may produce a sudden rise in fuel level durinl fill and, possibly, a nuclear excursion if the fuel salt is segregated. See VI. this table. 3. Conectiva action Drain reactor vessel

1x.

Excess radioactivity in reactor cell atmosphere

1. Causes Rupture o r leak in the primary containment 2. Consequences Contamination of secondary containment and increased possibility of contamination of area in the event that secondary containment fails. 3. Corrective action a. Drain reactor vessel b. Close cell evacuation valve which vents cooling air loop to the off-gas stack (valve No. HCV-565A1) c. Close HCV-915Al which blocks cooling air line to md drives and control md thimbles d. Close block valves in t h e lines to and from in-cell 0 , analyzer e. Close block valves in steam dome condensate drain lines

Supplementary Information

1. System design provides 5.0 ft' of overflow capacity, and power level scram and fuel overflow tank level systems (see 1 and lV, this table) protect against fuel salt expansion caused by power excursion; safety system holds bypass valves (Fig. 1.5.4)open during operation, in which case the pressure rise will be moderate until all the overflow volume is filled. 2. Redundancy: Two pressure channels. one in the pump bowl and one in the overflow tank. 3. Testing: Test procedure checks entire channel, with exception of transmitter bellows (see Fig. 1.5.5). 4. Monitoring: Loss of helium flow to bubblers caused by either low inlet pressure or line blockage is alarmed. 5. Safety only?: Yes 6 . Coincidence: Either of the two inputs will produce corrective action. 7. Draining (see Figs. 1.5.2 and 1.5.4) ensures immediate opening of the bypass valves to back up administrative control. Venting to the auxillary charcoal bed is less effective but useful backup.

This uses same instrumentation as VI1 (this table). 1. Redundancy: Two channels are used; one in the pump bowl and the other in the overflow tank. 2. Testing: See VII, this table. 3. Monitoring: See VU. this table. 4. Safety only?: Yes. 5. Coincidence: Either of the two inputs will produce corrective action.

m w

1. Redundancy: Two independent channels. Testing: Complete testing of each channel is possible. Monitoring: Certain system failores produce alarms. Safety only?: Yes. Coincidence: Either of the two inputs will produce corrective action.

2. 3. 4. 5.

Table 1.5.1 (contlnumd) ~

Input Ref.

No. X.

Condition Or Situation Which indicates a Real or Potential Hazard Supply pressure less than 28 psig in helium line 500 which supplies helium to all reactor cell components, drain tank cell, and fuel processing system

Causes of the Hazard, the Consequences, and the Corrective Action

Supplementary Information

1. Causes Loss of supply helium caused by: a. Empty tank b. Previous overpressure which operates relief valve and breaks rupture disk c. Malfunction of pressurcregulating valve PCV-SOOC (or alternately, PCV 605) which maintains supply at design-point value of 35 psig 2. Consequences Posaible loss of secondary containment (see I b above) 3. Comrctive action Block all helium lines to reactor and fuel salt drain tank cells

1. Redundancy: Three independent channels. 2. Testing: Complete testing possible. 3. Monitoring: Testing meets requirements. 4. Safely only?: Yes. 5. Coincidence: Any two-out-of-three. 6. Block helium lines to coolant salt system (pump bowl and drain tank)

XI.

High radiation activity in helium lines supplying fuel salt level bubblen or in deadended helium lines to zero psi, reference chambers connected to pressure transmittera

1. Causes Revenal of flow in these lines (or back diffusion) from pump bowl, drain tanks. overflow tanks 2. Consequences Radioactivity inside the helium piping in normally safe arcas. This activity r i l l be contained a s long a s piping i s not breached. 3. Consctive action Close block valves in helium lines to fuel salt pump bowl and overtlow tank.

1. Redundancy: T h m independent channels. 2. Testing: Complete testing of each channel i s possible. 3. Monitoring: Indicated, logged and alarmed. 4. Safetyonly?: Yes. 5. Coincidence: Any two-out-of-thm. 6. Flow rate, i n either direction. is limited by capillaries; check valvca, two in series, are used to back up block valves. TLe capillaries provide a long flow path ai high velocity and hence reduce back diffusion.

xn.

Preasure in secondary containment l e s s than 10.7 psia.

1. Causes

1. Redundancy: Three independent channels. 2. Tearing: Complete testing of each channel is possible. 3. Monitoring: Not applicable. 4. Safety only?: Yes. 5. Coincidence: Either of two will initiate safety action. 6. Pressure in the secondary containment is normally maintained appmximately 2 psi below ahnospheric (12.7 psia). 7. The blowers are of the positive displacement type and are. therefore. capable of reducing the pressure well below the value which endangers the containment vessel.

a. Malfunction of the secondary containment pressure contml system

which results in execssive pumpdown of the secondary containment b. Misoperation ofpumps and coolen during non-routine tests and equipment checkouts. 2. Cmaequencea Possible collapse of the secondary containment because of excessive external pressure 3. Corrsclive a d i o n a. Close cell evacuation valve. HCV-565A1, in the line which i s used to evacuate secondary containment to maintain p m s u r e a t 12.7 psia b. Shut off both component pumps. x111.

Pressure in the secondary containm e n t greater than two (2) psig.

1. Causea

1. Redundancy: T h m independent channels. Testing: Complete t e s t i n g i s possible. Monitoring: Indicated, logged and alarmed Safetyonly?: Yes Coincidence: Any two-out-of-three.

2. a. A rupture or leak in the primary Containment which allows hot fuel salt 3. to mix with water in the secondary containmenl; in the worst version this is the meximum credible accident. 4. 2 b. A mdfunction in or misoperation of the pressure control system 5. 2. Consequences Not, of itself, a dirrct hazard; during normal operation the reactor cell in maintained at a negative pressure of -2 p i g (12.7 psia) to ensure inflow in the event of a leak; the existence of positive pressure is evidence that a malfunction or misoperation exists; s loss of sewndary containment is a possible result. 3. Corrective action a. Close instrument air block valves b. Close liquid waste system block valves from reactor cell sump and drain tank cell sump to waste tank. c. Close block valves to and from in-cell oxygen analyzer d. Close block valves to and from off-gas sampler e. Close block vnlves in lines to the hook gage used for cell tank ratechecks f. Close steam dome condensate drain valves

Table 1.5.1 (continued) Input Ref,

No.

Condition or Situation Which Indicates a Real or Potential Hazard

Supplementary Information

Causes of the Hazard, the Consequences. and the Corrective Action

XlV.

High radioactivity in the ventilation line from off-gas sampler enclosure

1. Causes Leak in the off-gas sampler 2. Consequences This is a loss of primary Containment 3. Corrective a c t i m Close block valves in lines to and fmm the off-gas sampler

1. Redundancy: Two independent channels. 2. Testing: Complete testing is possible. 3. Mmitocng: Indicated, logged and alarmed. 4. Salety only?: Yes. 5. Coincidence: Either of two inputs will initiate safety action.

XV.

Helium pressure in fuel salt pump bowl greater than ten (10) psig.

1. Causes a. Same a s W,this table. b. Clogging of off-gas system du"ng normal operahon requiring operation at higher than usual pump bowl pressure c. Blowback a s an operational pmcedurn to open clogged off-gas system (see b above) 2. Consequences This value of presrmrr, 10 psig. will mt endanger reactor system. This interlock to pmtect the off-gas sampler and guard against a loss of containment 3. C m e c t i v e e c t i c a a. Close block valves in off-gns lines to and from the off-gas sampler b. Prevents opening operational end maintenance valves in fuel salt samplet-enricher (maintains containment)

1. 2. 3. 4.

XVI.

High radiation activity in line No.557 carrying off-gas from all charcoal beds and from the coolant pump, and from the lube oil systems

1. Causes

High radiation activity in in-cell treated water system

1. Causes a. Maximum credible accident with coincident ~puptureof in-cell water system piping b. Induced activity in treated water. 2. Consepuenma a. Local contamination by radioactive water leak b. Loss of secondary containment, with saompanying contamination If radioactive materid is discharged fmm the treated water system 3. Corrective actian a Closes block valves in water lines which are extensions of the secondary containment and which o ~ outside r the containment cell h. Closes valve in degassing tank vent which is located outside of secondary containment cell

XVII.

a. charcoal beds not operating c o d y (overloaded, see III above) or pump seal failurn allowing discharge of activity to lube-oil system b. Activity in tbe Coorant salt loop; see also V. this table 2. Conaepuencea Radioactive gases discharged up s t s c k 3. Correctipsactica a. Close off-gas block d m b. CIOSC hbo9il systems vent valves

Redundancy: Two independent channels. Testing: Complete testing of each channel is possible. Monitoring: Certain system failures pmduce alarms. Pressure is indicated and logged. Safety only?: Yes. 5. Coincidence: Either of two channels will initiate safety action. 6. The maximum pressure rating (rupture) of some components in the sampler is less than the 150% of maximum pressure (75 psig) normally required for primary containment components.

1. Redundancy: Two independent channels. Testing: Complete testing possible. Monitoring: Certain system failures are alarmed, radiation level is indicated and logged. Safety only?: Yes. coincidence: Either of two channels will initiate safety action

2. 3. 4. 5.

1. Redundancy: Three independent channels. Testing: Complete testing of each channel is possible. Monitoring: Certain system failures initiate alarms. Radiation level i s indicated and logged. Safety only?: Yes. Coincidence: Either of two channels will initiate safety action. The water lines and vent tank are extensions of the secondary containment..

2. 3. 4. 5. 6.

. -

Tobh 1.5.1 (continued) Input Ref.

No. XVm.

Condition or Situation Which Indicates a Real or Potential Hazard

Low temperature of coolant salt in outlet from radiator (line 202)

Loss of coolant salt flow

XIX.

XX.

Either or both doors at final upper limit

XXI.

Door drive motor current at overload value

Supplementary Information

Causes of the Hazard, the Consequences, and the Corrective Action

1. Causes a. Malfunction of load control system (complex of doors, blowers, and bypass damper) b. Cessation of power generation in core from any cause (scram, drain, rupture in primary containment, etc.) c. Loss of coolant flow (see XIX, this table) 2. Consequences No hazard; warns that potential radiator freezeup may be developing (see XIX, this table) 3. Corrective action a. Close radiator doors b. Shut down main blowers, MB-1 and M E 3 c. Drain coolant salt system 1. Cauaes a. Coolant pump stoppage b. Line break c. Unscheduled coolant salt drain d. Plug in line or radiator 2. Conaequences Unless accompanied by undctected contamination of the coolant salt, see V, this table, no hazard exists. Unless action i s taken a costly radiator freezeup will ensue. 3. Corrective action a. CIose radiator doors b. Shut down maln b I o r e n . ME1 and M E 3

1. Redundancy: Three independent channels. 2. Testing: A complete test of each input channel is possible; complete testing requires dropping doors, which disturbs operation.

3. Monitoring: Thermocouple break or detachment from pipe will produce safety action in that channel. Temperature i s indicated and logged. 4. Safety only?: Input channels used solely for safety. 5. Coincidence: Any two-out-of-three. 6. The corrective actions constitute a “load scram.”

1. Redundancy: Two direct flow channels which receive informstion fmm s common primary element, a venturi, plus two independent pump speed charnels.

2. Testing: Partial testing possible; a test which includes dropping radiator doors will perturb operation; input elements not tested.

3. Monitoring: By aurveillmce and comparison; flow and pump speed are indicated and logged. 4. Satety only2: Yes. 5. Coincidence: Refer to Section 2.0. 6 . These corrective actionr constitute a “load scram”; refer to Section 2.0.

1. Cacmes Failure of fimt u p p r limit switches and/or any circuit or circuit element sssocisted with these switches 2. Consequences a. Damage to the doors b Damage to the drive mechanism e. Loss of ability to scram the doors because of cable snarling or other damage per 2 s and 2b above. 3. Conective actions a. Stops door drive motor b. Disengages clutches in drive train between motor and cable sheave c. Applies brakes

1. Redundancy: Two independent limit switch channels which are c m a s connected so that if either door is at the final upper limit both doors are stopped. See also XIX. this table. Only one motor starter; i t must work. 2. Testing: Complete testing i s possible at some inconvenience. 3. Monitoring: Not applicable.

1. Causes a. Anything which jams the doors or the drive mechanism b. A failure of both first and final upper l i m i t switches and/or any circuit or any circuit element associated with these switches 2. Consequences Same a s for XX, this table 3. Corrective action Same a s for XX, this table

1. Redundmcy: Only one primary element, the overcurrent relay. Otherwise this interlock is composed of two (2) separate channels. See XX. this table, and (5) below. 2. Testing: During shutdown only. 3. Monitm‘ng: Not applicable. 4. Safety only?: Yes. 5. a. Insofar as preventing damage caused by forcing the door and d i v e mechanism against the hard. fixed upper limit, this interlock provides diverse redundancy with the final upper limit interlock, XX, this table. . b. Prevention of damage at other door pasitions than the final upper limits depends on the reliability of a single overcurrent relay and the reliability of a single motor starter-relay.

4. Safety only?: Yes. 5. Coincidence: See (1) above.

1.5.1 Reactor F i l l and Drain System

A simplified diagram i s shown i n Fig. 1.5.4 of the reactor vessel, t h e drain tanks, t h e interconnecting piping, and the control elements r e q u i r e d t o f i l l and drain the reactor system w i t h f u e l salt i n a safe, orderly way. The control rods a r e e s s e n t i a l t o a safe f i l l i n g procedure but a r e omitted from t h i s diagram i n t h e i n t e r e s t of simplification. The reactor is f i l l e d by applying helium pressure t o t h e gas space i n t h e selected drain tank and forcing t h e molten f u e l s a l t up and i n t o t h s core vessel. A s a t y p i c a l example, i f t h e reactor is t o be f i l l e d from f u e l drain tank 1 (FDT-l), pressurizing helium is admitted v i a l i n e s 517 and 572 (see Fig. 1.5.4). The f i l l i n g pressure i s controlled by pressure-regulating valve PCV-517-Al. The pressure s e t t i n g of t h i s valve i s controlled by the operator. The upstream c a p i l l a r y flow res t r i c t o r i n l i n e 517 limits the maximum i n l e t f l o w r a t e of pressurizing helium. Valves HCV-544-Al and HZV-573-Al i n t h e pipes which connect t h e gas space i n FDT-1 t o t h e pump bowl and t o t h e charcoal beds a r e closed. Since t h e net pressure head available t o produce f l o w decreases as the f u e l l e v e l r i s e s i n the core vessel, the f i l l rate becomes progressively slower as the f i l l proceeds i f constant i n l e t helium pressure i s maintained and i f t h e pump bowl pressure remains constznt. Helium pressure i n t h e pump bowl i s t h e second component of t h e d i f f e r e n t i a l pressure t h a t drives f u e l salt i n t o the core vessel. A sudden reduction i n pmp bowl pressure during t h e reactor f i l l i n g operation would cause an unscheduled r i s e i n salt l e v e l i n t h e core. I f , a t t h i s time, t h e reactor is on the verge of becoming c r i t i c a l , an unexpected nuclear excursion cannot be ruled out. The safeguard provided i s t o allow f i l l i n g o n l y when the positive pressure i n the pump bowl is equal t o o r less than +2 psig and thus keep the maximum possible increase i n net f i l l i n g pressure within safe l i m i t s . Two causes f o r a sudden decrease i n pump bowl pressure a r e considered. F i r s t , opening valve HCV533-Al after reactor f i l l i n g has s t a r t e d would vent t h e pump bowl t o the auxiliary charcoal beds, which normally operate a t close t o atmospheric pressure. The resultant pressure change i n t h e pump bowl would be -2 p s i . Administrative control is used t o maintain HCV-533-A1 open just before and during f i l l i n g . Second, a rupture or leak would allow t h e escape of pump bowl helium t o the reactor c e l l atmosphere, which is held a t -2 psig (12.7 psi&). This condition would cause a maximum pressure decrease i n the pump bowl of 4 psi. If t h e f u e l pump bowl pressure exceeds 2 psig, t h e s a f e t y eqdpment (1) initiates a drain by opening bypass valves HCV-544-Al, ECV-545-U, and HCV-546-Al, thereby equalizing helium pressure i n t h e drain tanks and pump bowl, and (2) shuts off t h e supply of pressurizing helium by closing valves FCV-517-Al, HCV-572-A2, HCV-574-A1, and HCV-576-Al. This i s t h e helium valve condition s h a m i n Fig. 1.5.4 and is required by normal operation w i t h the pump bowl a t 5 psig; therefore, t h e 2-psig channel need not be disabled during normal operation. Additional s a f e t y considerations involving pressure i n the f u e l s a l t system and the instrumentstion used f o r measuring helium precs u e s a r e discussed i n the following section. Excessive pressure, 25 psig, i n the pump bowl is relieved by opening HCV-533-Al. During reactor operation, with the bypass l i n e s open, one o r more of t h e drain tanks would be subjected t o t h i s pressure. The input signal used t o open HCV-533-Al originates i n e i t h e r of a redundant p a i r

of pressure transmitters, PT-592B and PT-589B, on i n l e t l i n e s t o the pump bowl and overflaw tank respectively. These same input channels provide the +2-psig safety signal discussed above. As a further safeguard during f i l l i n g , the s a f e t y system requires that a l l three control rods be p a r t i a l l y withdrawn i n order t o pressurize the drain tanks. The weigh c e l l s on t h e drain tanks provide information used t o monitor t h e t o t a l amount of f u e l s a l t noved i n t o t h e core vessel. The possible f i l l i n g accidents are discussed i n r e f . 1. Briefly, these accidents a r e (1)premature c r i t i c a l i t y during f i l l i n g caused by an overly high concentration of uranium brought about by selective freezi n the drain tank; (2) premature c r i t i c a l i t y during f i l l i n g of law-temperature (903'F f u e l s a l t of normal concentration, whose normal c r i t i c a l temperature w i t h the rods withdrawn appraximately half stroke i s 1200'F; and (3) premature c r i t i c a l i t y during f i l l i n g of normal f u e l salt a t normal temperature with all control rods fully withdrawn. Prot e c t i v e action is the same f o r a l l three cases: the control rods a r e scrammed, and the reactor vessel is drained t o ensure permanent shutd m . Rod scram is produced and vent valves HCV-573-Al, HCV-575-&, and HCV-577-A1 a r e opened by the excess f l u x signal. Since a premature c r i t i c a l i t y occurs before loop circulation is attained, the o u t l e t temperature sensors a r e ineffective. The safety system a l s o invokes a r e cator emergency drain t o enhance containment i f there is evidence t h a t radioactivity is escaping f r o m t h e primary f u e l loop. These subsystems a r e covered subsequently in t h i s section. Rnergency drainage is effected by the following actions (see Fig. 1.5.4) : 1. The freeze valve i n l i n e 103, which connects t h e reactor drain tanks, is thawed. Thawing is accomplished by closing valves HCV-919A and 919B, a redundant pair, t o stop t h e f l o w of cooling a i r . The system is designed with a heat capacity s u f f i c i e n t t o thaw t h e plug i n l e s s than 15 inin. 2. The helium pressures in the f u e l drain tank and the u n f i l l e d portion of t h e f u e l s a l t loop are equalized by opening bypass valves HCV-5U-Al, HCV-545-&, and HCV-546-Al. 3. Vent valves HCV-573-Al, HCV-575-Al, and HCV-577-Al, which r e lease pressurizing helium in the drain tank t o the off-gas system, a r e opened. 4. Pressure regulating valve PCV-517-KL i n l i n e 517, t h e i n l e t header t h a t supplies pressurizing helium t o all t h e drain tanks, i s closed and shuts off t h e supply of pressurizing helium. 5. The drain tank pressurizing vaLves, HCV-572-Al, HCV-574-Al, and HCV-576-Al, i n the helium supply l i n e s a r e also closed t o h a l t f u r t h e r additioa of f u e l salt. Actions 2 or 3 a r e immediately and independently effective i n reversing a f i l l , and hence the valves are redundant. Similarly, PCV-517-

21R. E. Thoma and H. A. Friedman, "Segregation of the MSRE Fuel Salt i n D r a i n Tanks, I t MSR-65-15 (Mar. 17, 1965) (internal memorandum). 22H. A. Friedman, "Segregation of LIF-BeF2-UF4 Fuel S a l t on Freezing i n Drain Tanks, MSR-66-19 (July 12, 1966) ( i n t e r n a l memorandum).

Al and the individual pressurizing valves, referred t o i n 4 and 5 above, form s e r i e s p a i r s and provide redundancy. For example, it can be seen from Fig. 1.5.4 that, taking fuel drain tank No. 1 as typical, pressure equalization and venting a r e accomplished by opening HCV-5U-Al and HCV573-Al respectively. Administrative control is used t o ensure t h a t when the reactor is f i l l e d w i t h f u e l salt, both drain tanks, FXC-1 and FXC-2, a r e empty and both of the freeze valves, FV-106 and FV-105, a r e thawed. The tmk condition is monitored by reference t o the weigh c e l l and l e v e l instrumentation on each tank. 1.5.2

H e l i u m Pressure Measurements i n the Fuel S a l t Loop

One channel of t h e instrumentation which measures helium pressure i n the f u e l pmp bowl and t h e overflar tank is s h u n in Fig. 1.5.5. The components and t h e i r i n s t a l l a t i o n are designed t o meet containment requirements. The pressure transmitters a r e i n s t a l l e d j u s t outside t h e main secondary containment s h e l l . From t h e standpoint of containment, t h e transm i t t e r housings a r e "blisters" on t h e main containment c e l l s . Containment c r i t e r i a would be s a t i s f i e d by 1. venting t h e reference pressure side of t h e transmitter diaphragms t o t h e inside of t h e containment c e l l ,

sealing t h e vent port a t the transmitter,

connecting the transmitter's vent port t o a colltainment-grade volwne which is maintained a t a known and c o n s t a t pressure.

If the transmitter's reference pressure port i s vented t o the coatainment c e l l , t h e pressure measurement includes c e l l pressure. This pressure i s controlled nominally a t -2.0 psig during operation, is a t atmospheric pressure during i n - c e l l maintenance, and i s well above atmospheric pressure during periodic checks t o v e r i f y the containment capability of t h e c e l l . The normal and acceptable fluctuations around t h e nominal -2.0psig value would reduce t h e accuracy of t h e transmitted measurement by an unacceptable amount. If the reference port of the transmitter is merely sealed shut, the reference pressure and hence t h e transmitted pressure would fluctuate with temperature changes i n t h e sealed r e f e r ence volume i n the transmitter. Evacuating t h e reference side of t h e transmitter was deemed unacceptable because these v i t a l measurements would then rely e n t i r e l y on the long-term r e l i a b i l i t y of t h e vacuum. The variable-volume reference chamber (see action 3 above) resolves these conflicting demands of containment and measurement accuracy. Coaceptually, it a c t s as a strong but extremely compliant bag which automatically adjusts i t s volume t o maintain an i n t e r n a l pressure very nearly equal t o the externally applied pressure. By connecting the reference ports of the transmitters t o these reference chambers which are located outside t h e containment c e l l s , t h e dual requirements of t h e containment and measurement accuracy are satisfied. A t the MSRE t h e reference volume is housed, and the housing is v e n t e d t o the off-gzs duct near the blawer inlet. During operation the ambient pressure i n the off-gas duct i s approximately -2.0 in. H20, t h e blawer i n l e t pressure. This -2.0-in. H2O o f f s e t i s not significant. The reference

chamber i s s h a m in diagram in Fig. 1.5.5 and i s described in d e t a i l i n Sect. 6.2. Two channels are used, one i n the pump bowl and t h e other in the overflo-d tank. These normally operate a t the same pressure. Any s a f e t y signal from e i t h e r channel i n i t h t e s the appropriate s a f e t y action. The system may be t e s t e d periodically aurin@;reactor operation by: (1) observing system response t o small operator-induced pressure changes and (2) shunting the torque motor in t h e pressure transmitter. These t e s t s w i l l e s t a b l i s h that, in t h e channel undergoing t e s t , the l i n e s from the pump bowl (or overflow tank) a r e c l e a r and the electronic equipment and associated w i r i n g a r e capable of operating the output relays. Since it takes from 10 t o 15 m i n t o thaw drain valve FV-103, t h i s time can be used t o observe t h e response of the thermocouples on the freeze valve as it heats ug but before actual s a l t flow begins. The valve can then be refrozen before an actual drain i s i n i t i a t e d . In such a t e s t , valve HCV-533 (Fig. 1.5.4) w i l l be opened, and the cont r o l l e d pressure (5 psig) in the pump bowl w i l l be l o s t f o r the durat i o n of t h e t e s t . The response of HCV-533 can be noted by observing the actuation of t h e position switch on the valve stem. This t e s t procedure checks the e n t i r e s a f e t y channel, except the a b i l i t y of the transmitter measuring bellows and the associated linkage t o transmit the pressure.

Monitoring of these channels is accomplished by indicating and alarming the pressure downstream f r o m t h e hand t h r o t t l i n g valves i n each helium l i n e serving the primary elements (the bubbler tubes) i n the pump bowl and i n the overflow tank. A downstream f l o w stoppage by a blocked l i n e i s indicated b a high-pressure alarm; l o w f l o w caused by a loss of upstream (supply pressure, an upstream blockage by foreign matter, or a hand valve closure i s indicated by a low-pressure alarm. The f u e l l e v e l in the overflow tank i s measured by t h e d i f f e r e n t i a l pressure across the helium bubbler probe which dips i n t o the f u e l salt i n the tank. The design c r i t e r i a f o r t e s t i n g andmonitoring these d i f f e r e n t i a l pressure measuring channels a r e the same as those which guided the design of the pressure channels described i n t h e preceding paragraphs. The reference chamber i s not required. Two channels a r e employed f o r safety, and e i t h e r w i l l i n i t i a t e a reactor drain i f t h e f u e l salt l e v e l i n the overflow tank exceeds 2oq& of full-scale l e v e l indication.

1.5.3 Afterheat Removal System The drain tank afterheat removal system, t y p i c a l l y the same f o r both drain tsnks, i s shown i n Fig. 1.5.6. Once placed in operation the evapor a t i v e cooling system is designed t o be self-regulating and t o operate without external control. Reliable operation of the afterheat removal system r e u i r e s (1) that the feedwater tanks contain a supply of cooling water, (2k t h a t an ample supply of cooling water is available t o the coadensers, (3) t h a t t h e system includes r e l i a b l e valves t o admit feedwater t o the steam drums, and ( 4 ) that r e l i a b l e block valves be provided

i n t h e drain l i n e s 2 3 from t h e steam drums. Administrative control i s r e l i e d 02 t o ensure that t h e feedwater tanks contain water. Valve ESV806 opens t o admit water automatically t o t h e steam drum when t h e salt temperature i n t h e drain tank exceeds 1300'F and recloses a t approximately 1 2 0 0 9 . This valve is i n p a r a l l e l with manual valve LCV-806A, and t h e p a i r are a redundant means of admitting water t o t h e steam drum. Normally the condensers are cooled by tower cooling water, but diversion valve HCV-882-C1 provides an a l t e r n a t e supply of water. Loss of tower water pressure caused by a l o s s of water o r pump shutdown is det e c t e d by pressure switch PS-851-B1, which operates diversion valve HCV-882-C1. When t h i s valve operates, t h e cooling water supply i s s h i f t e d from t h e tower t o t h e process water main. Since it takes over 12 hr f o r excessively high a f t e r h e a t temperat u r e s t o develop after a drain, there is s u f f i c i e n t time t o e f f e c t a transfer t o t h e other drain tank i n t h e event of a f a i l u r e o r malfunct i o n . This i s a l s o ample time t o make connections from t h e cooling water system t o a tank truck i n t h e event that t h e normal water supply is inoperative. The drain l i n e s , 806-2 and 807-2, a r e used t o keep t h e tanks dry during normal operation. They are extensions of the secondary containment and are provided with block valves. Reliable, safety-grade cont r o l instrumentation closes valves ESV-8064% and 806-2E3,a redundant p a i r , when the reactor c e l l pressure exceeds +2.O psig o r when the radiation monitors, RM-565A and B, i n t h e c e l l evacuation l i n e indicate excessive r a d i o a c t i v i t y i n t h e c e l l atmosphere.

1.5.4

Containment System Instrumentation

Contsinment requirements are met by providing a t l e a s t two independent, reliable b a r r i e r s , i n s e r i e s , between t h e i n t e r i o r of t h e p r i mary system and t h e atlnosphere. For example, t h e tvo-barrier concept is f u l f i l l e d by : 1. two independent, reliable, controlled block valves with independent instrumentation,

oae controlled block valve plus a r e s t r i c t i o n such as a charcoal bed which w i l l l i m i t t h e escape of a c t i v i t y t o t h e stack t o less than t h e maximum permissible concentration,

one controlled block valve plus two check valves,

4 . two s o l i d b a r r i e r s (vessel or pipe walls), 5 . one s o l i d b a r r i e r and one coatrolled block valve, 6.

one s o l i d b a r r i e r and one check valve.

23These drain l i n e s , 806-2 and 807-2, shown i n Fig. 1.5.6, were added a f t e r t h e MSRE was in operation. Development tests disclosed t h a t partially f i l l e d steam drums tended t o corrode a t t h e water l i n e .

The recommended design practices outlined previously i n t h i s section apply t o the r e l i a b l e instrumentation and control equipment u s e d t o ope r a t e t h e block valves. Block valves, generally, a r e not located a t such a distance from the containment penetration that the l i n e s become tenuous extensions of the containment vessel. Valves and other devices used i n l i e u of s o l i d b a r r i e r s w i l l be routinely t e s t e d and demonstrated t o be capable of m i n t a i n i n g leakage below the specified tolerance when closed.

1.5.4.1 Helium Supply Block Valves Figure 1.5.7 shows the helium supply l i n e s t o the primary containment vessel and t h e associated valves used f o r control and blocking these supply l i n e s against the escape of radioactivity from the primary system as a r e s u l t of reverse flow o r back diffusion. This sketch does not show the f u e l storage tank (FST) and l i n e 530, which supplies pressurizing helium t o t h i s tank. This l i n e is blocked by HCV-530-Al. Two types of input signals a r e u s e d t o i n i t i a t e helium supply block valve closure. The f i r s t , a reduction i n the supply pressure from i t s normal value of 40 psig t o 28 psig, actuates pressure switches and closes a l l the i n l e t helium block valves. The second, excess radiation measured by RM-596A, B, and C i n any of the helium l i n e s supplying the l e v e l probes (bubblers) and pressure measuring instruments i n the pump bowl and overflow tank, closes the block valves i n these l i n e s . A reduction i n heliua supply pressure i n l i n e 500 from i t s regulated value of 40 psig indicates a lealqy rupture disk o r leaky piping and, possibly, a loss of primary containment. In-service t e s t i n g of the loss-of-pressure channels i s accomplished by opening the hand valves on the l i n e s t o the pressure switches on the main supply pipe ( l i n e 5001, one a t a time, and observing the action of the relays i n the two-out-of-three coincidence matrix i n the control room. Actual block valve closure is not t e s t e d with t h i s procedure. Low- and high-pressure alarms a r e provided on l i n e 530; these w i l l actuate before the safety system pressure switches close the block valves. Additional t e s t i n g of the solenoid block valves i n the helium bubbler l i n e s is provided by closing each valve individually and observing the pressure change downstream of the hand t h r o t t l i n g valve. The three radiation monitoring s a f e t y input channels, RM-5964 B, and C, a r e t e s t e d by exposing each individual radiation element t o a source and noting t h e response of t h e output relays which produce valve closure. Since two-out-of-three coincidence is used, t h i s t e s t w i l l not perturb the system; neither does it pruvide a valve closure t e s t .

1.5.4.2

Off-Gas System Monitoring

The off-gas system (Fig. 1.5.8)

is monitored f o r excess radiation

in four places :

1. Une 557. -This l i n e receives off-gas from the main and auxiliary charcoal beds, helium from the coolant salt pump, and helium from t 3 e s a l t pump lube o i l systems and the sampler-enricher.

Line 528. - T h i s l i n e c a r r i e s helium f r o m t h e coolant salt circulating pump. Its primary purpose i s t o detect an i n t e r n a l leak i n t h e fuel-to-coolant-salt heat exchanger. Should such a leak occur,

bi'

f i s s i o n product a c t i v i t y w i l l be c a r r i e d i n t o l i n e 560 by the purgegas f l o w across the coolant salt pmp bowl. This l i n e is monitored by RM-528B and C. Note tbat RM-557A and B provide a redundant indication of t h i s a c t i v i t y level.

L, 3.

Line 565. - This l i n e is used t o pump the reactor and drain tank c e l l s dawn t o t h e operating pressure of 12.7 psia. A portion of t h i s l i n e continuously c a r r i e s a small f l o w of c e l l air, v i a bypass l i n e 566, across t h e component cooling pumps which circulate c e l l air (see Fig. 1.5.8). This continuous f l o w is monitored by RM565A and B.

O f f - G a s Stack. -Stack gas mollitoring is not a part of t h e MSRE s a f e t y system but is noted here f o r completeness. Refer t o Sect. 2.11 f o r a description of t h i s monitor. Its only output function is t o provide alarms. The stack gas monitor, located on t h e off-gas stack, provides a f i n a l check on the off-gas just before it i s discharged t o the atmosphere and a f t e r it has been f i l t e r e d . Excess radioa c t i v i t y in t h e stack gas is alarmed i n t h e MSRE control room, and an alarm signal is a l s o transmitted t o the OFUVL Central Monitoring Facility

It can be seen from Figs. 1.5.8 and 1.5.2 that an excess radioa c t i v i t y signal from e i t h e r RM-557A o r B produces three output actions, a l l intended t o preserve containment; these a r e as follows: 1. Closes HCV-557-Cl in l i n e 557. This l i n e is, in e f f e c t , t h e main helium off-gas exhaust header leading t o the off-gas stack f i l t e r s and c a r r i e s off-gas from several sources, namely: a ) t h e fuel salt circulating pump, b ) t h e f u e l salt drain tanks, c ) t h e coolant salt pump, d) t h e coolant salt drain tanks, e ) t h e fuel salt sampler-enricher, f ) tbe f u e l and coolant salt pmp lube o i l systems (Fig. 1.5.9).

Closes valve PCV-51O-A2.

Closes valve PCV-513-A2.

Actions 2 and 3 block t h e helium off-gas l i n e s from t h e lube o i l systems (Fig. 1.5.9). Radiation monitors RM-528B and C in l i n e 528, carrying helium from t h e coolant pump, a r e necessary because they w i l l provide an indication i f a leak e x i s t s i n t h e s a l t - t o - s a l t heat exchanger (frm t h e fuel salt loop t o t h e coolant salt loop). Such a leak could put f i s s i o n products i n t h e coolant salt; however, when t h e coolant salt c i r c u l a t i n g pump i s running, t h e coolant salt pressure i n t h e heat exchanger tubes is greater than the f u e l salt pressure i n the shell.. The f i s s i o n product gases would be c a r r i e d from the free surface i n t h e coolant salt pump bowl i n t o l i n e 528. This a c t i v i t y w i l l be read f i r s t by RM-528B and C and then by RY557A and B. The output actions produced by RM-528B o r C (see a l s o Fig. 1.5.2 and Table 1.5.1) a r e t h e following: (1) drain t h e reactor vessel,

and (2) stop t h e f u e l salt pump.24 T h i s a l s o produces a rod scram i f the reactor i s operating above heat l o s s power, 15 kw. The sequence of control actions which scram the rods is described i n Sect. 2.6. &cess radioactivity in e i t h e r the reactor o r the drain tank c e l l s is detected by RM-565A o r B. Either monitor w i l l produce protective a c t i o m thus:

1. Closes HCV-565-Al i n l i n e 565. This l i n e , the c e l l evacuation l i n e (Fig. 1.5.8), i s used t o exhaust the reactor and drain tank c e l l s when they are being pumped down t o t h e i r operating pressure of 12.7 psia

Closes the steam dome condensate drain valves ESV-806-2A and ESV806-2B (see Fig. 1.5.6).

Closes block valves HCV-566-Al, A2, A3, and A4 t o and f r o m t h e analyzer which moaitors t h e oxygen content of t h e i n - c e l l atmosphere. This aaalyzer (Fig. 1.5.121, is located i n the vent house.

4 . Closes block valve HCV-915-Al, which c a r r i e s exhaust cooling air t o the rod drives and the control rod thimbles (see Fig. 2.7.12 i n Sect. 2.7).

5. Drains the reactor vessel. i n Sect. 4.7.

The reactor drain system is described

These systems may be t e s t e d by inserting a radiation source i n t h e radiatioa monitor shields and observing (1) the radiation-monitor indicator, (2) t h e control c i r c u i t relays, and (3) the output actions of the control valves and other controlled elements which provide protection. The three pairs of radiation monitors, RM-528B and C, RM-557A and B, and RM-565A and B, a l l operate so that sn excess radiation signal from e i t h e r channel in a p a i r w i l l produce safety action. Since these a r e all one-out-of-two systems, on-line t e s t i n g of any channel w i l l produce protective control actions and, t o an extent, perturb the operating system. The system disturbances caused by on-line t e s t i n g of RW-557A and B and RV-565A and B can be t o l e r a t e d i f t h e t e s t i s of short duration. It w a s necessary t o provide j m p e r s f o r on-line t e s t i n g of RM-52813 and 2 . Without jumpering, a t e s t of e i t h e r channel w i l l stop the f u e l s a l t pump and, i f t h e reactor i s at power, scram the rods. This is unacceptable operationally. Jumpering is t h e preferred a l t e r n a t i v e t o omitting in-service t e s t i n g . Testing these s a f e t y channels is, therefore, subject t o very s t r i c t administrative control. The jumpers bypass contacts K-26C and K-27C in c i r c u i t 147, which starts and stops the f u e l salt pump. As has been pointed out in footnote 24, these contacts do not produce a safety-grade protective action. The MSEE off-gas sarrpler w i l l (1) u t i l i z e on-line instruments t o provide a semicontinuous indication of contaminant l e v e l and (2) i s o l a t e samples which may be transferred t o a hot c e l l f o r analysis. The off-gas sampler (Fig. 1.5.10) w a s designed and i n s t a l l e d a f t e r the re-

24Stopping the pump is not required t o ensure safety. t o reduce the r a t e but w i l l not eliminate leakage.

It may tend

6.1

actor was placed i n operation. Reference 25 contains a b r i e f , conceptual description of t h e sampler as originally proposed. In t h e current version the chromatograph c e l l has been omitted pending f u r t h e r development work. Figure 1.5.8 shows the location of the sampler with respect t o the main off-gas system. The samples %re obtained from l i n e 522, which c a r r i e s f u e l p a p bowl sweep gas t o t h e off-gas system. Bypass l i n e s w i t h valves across t h e piping t o and from the analyzer permit taking t h e sample e i t h e r before or a f t e r t h e gas has passed through the charcoal f i l t e r and the p a r t i c l e t r a p . The sampler is located i n the trench immediately south of the vent home. The r e a c t o r o f f - g a s i s highly radioactive, and since t h i s equipnent i s an extension of the primary containment i n t o an area frequented by operating persoanel, t h e use of block valves i n the supply and return piping t o t h e sampler is mandatory. The sampler is w e l l shielded and, except perhaps f o r the thermal conductivity c e l l s (these c e l l s a r e tested a t 20 psig), meets the general MSRE containment requirements with respect t o pressure rating and leak-tightness. The sampler is housed i n a v e n t i l a t e d enclosure which is exhausted t o t h e off-gas stack. Continuous circulation within the enclosure is maintained by two (for redundancy) blowers. This flow loop is monitored by two f l a w switches, FS-54-D and FS-54-C, connected t o a single alarm. Excess radioactivity i n t h i s circulating air i s detected by two separate, independent channels of radiation detection equipment, RM-54 a d RM-543. A high-radiation signal from e i t h e r monitor w i l l close block valves ESV-537A and B and ESV-53a and B, redundant p a i r s i n the inlet and o u t l e t l i n e s t o and from t h e sampler. The c i r c u i t s which control these valves are shown i n Fig. 1.5.ll. These valves a r e also closed (see output XVI, Fig. 1.5.2) i f t h e pressure i n t h e reactor and drain tank secondary containment c e l l s r i s e s above t2.0 psig or i f t h e fuel pump bowl pressure exceeds 10 psig. Tke c e l l pressure s a f e t y channels and the protective instrumentation u s e d t o measure pump bowl pressures were described e a r l i e r i n t h i s section. The atrnosphere i n t h e MSRE containment is kept a t no more than 5$ oxygen, with the remainder being nitrogen. Oxygen content i s continuously monitored by an on-line analyzer which measures t h e magnetic s u s c e p t i b i l i t y of the cell- atmosphere. The analyzer and i t s operation are described i n d e t a i l i n Sect. 6.4. Figure 1.5.12 sham t h e analyzer flawsheet and the f i n a l control c i r c u i t r y which closes t h e block valves t o and from the analyzer. The i n l e t gas t o t h e analyzer is taken from the c e l l evacuation l i n e , 565, and is d i s c h a r g e d t o l i n e 566. These two l i n e s form a low-flow bypass loop across the component cooling pmps which continuously c i r c u l a t e the air within t h e containment c e l l s . The piping t o and from t h e analyzer meets containment requirements; t h e analyzer, rated a t 30 psig, does not. Block valves are required f o r containment and because the instrument is located in an accessible, frequently used area and i s not e n t i r e l y protected from mechanical damage. The block valves a l s o permit naintenance and routine operations such as changing the cylinders of reference gas and purge nitrogen.

25MSFE Project Staff, Molten-Salt Reactor Program Semiann. Progr Rept. Feb. 28, 1966, ORNL-3936.

Block valve operation is apparent from Fig. 1.5.12. The valves a r e a u t o m t i c a l l y closed i f e i t h e r channel, RM-565B or C, i n the twochannel radiatioa moDitor, signals excess radioactivity in t h e c e l l ataosphere or i f the pressure in t h e secondary containment c e l l exceeds +2.0 psig. Tktese input channels have been described previously i n t h i s section. Complete on-line t e s t i n g i s possible, since block valve closure can be checked by observing the rotameters in the analyzer. A complete t e s t involving any two channels of the c e l l pressure input instrumentation i s not conducted during reactor operation, since t h i s same t e s t , described e a r l i e r i n t h i s section, causes unacceptable system changes elsewhere. The radiation channels a r e t e s t e d with a source, on-line, and the block valves and the control c i r c u i t s a r e redundant.

1.5.4.3 In-Cell Liquid Waste and instrument A i r Block Valves The i n - c e l l (secondary containment) l i q u i d waste l i n e s a r e blocked i f t h e reactor c e l l pressure exceeds 2 psig (see Fig. 1.5.13 and input

X I I I , Fig. 1.5.2). ' k e normal operating pressure i n t h e containment c e l l s i s 12.7 psia. Excess c e l l pressure is a symptom of system malThe protective function or, a t worst, the maximum credible accident.' instrumentation and control hardware and blockage of instrument a i r l i n e s have been described earlier i n t h i s section.

1.5.4.4

In-Cell Cooling Water Block Valves

A simplified f l o w diagram of t h e i n - c e l l cooling water system, with instrumented block valves, i s sham in Fig. 1.5.14. Tne signal t o close the block valves i s provided by an excess radiation l e v e l i n the pump return header. Three independent sensors, RE-827A, B, and C, i n i t i a t e block valve operation when any two of the input channels indicate excess radiation i n l i n e 827. Operatiolz of the system i s apparent from Fig. 1.5.14. Testing is accmplished during operation by manually inserting a radiation source i n the monitor s h i e l d ( r e f e r a l s o t o Sect. 2.10) and observing that the indicated radiation l e v e l increases and t h a t the proper relays operate. The construction of t h e sensor shield is such that each radiation monitoring channel can be t e s t e d individually. Since the moaitor contacts a r e arranged i n two-out-of-three coincidence, t e s t ing of individual channels does not close t h e valves. The valves may be t e s t e d individually by operating a hand switch and observing t h a t f l o w stops i n the l i n e u d e r t e s t . The complete system i s t e s t e d during shutdam. Valve ESV-DGT serves as a backup t o FSV-837-Al, FSV-84l-Al, FSV%6-A1, FSV-8474- and pravides redundant blocking i n the system. The thermal shield i s protected from excess hydraulic pressure by the rupture disk in l i n e 844. Pressure control valve PCV-844C and block valve FSV844-A1, actuated by e i t h e r pressure switch PSS-844-Bl or valve position switch ZS-847-Az on valve FSV-84l-A1, prevent breaking the rupture disk with the t r a n s i e n t pressure surge produced by closing FSV-847-Al. Valve FSV-844-Al is a l s o c l o s e d b y the action of pressure switch PSS-855-A.l when the pressure damstream f r o m t h e rupture d i s k exceeds 5 psig. This action serves two purposes: (1)maintains some protection of t h e thermal s h i e l d if downstream pressure develops on t h e rupture disk,and (2) minimizes the loss of cooling water when t h e rupture disk does burst.

19,

Any water discharged through a burst rupture disk passes i n t o t h e vapor condensing system and i s contained.

1.5.5

Underpressure Protection f o r t h e Secondary Containment Cells

Failure or malfunction of t h e pressure control system f o r the component cooling pumps, i f undetected, could lead t o a dangerous subatmospheric pressure reduction, causing a buckling type of f a i l u r e of the secondary containment structure. Protection against such an event i s provided by a three-channel, r e l i a b l e system, schematically i d e n t i c a l t o t h a t used f o r c e l l overpressure protection described above and e a r l i e r i n t h i s section. If c e l l pressure falls t o less t%an 12.2 psia, a control-grade alarm sounds. The safety-grade instruments (pressure switches actuate a t 10.7 p s i a (input X I I , Fig. 1.5.2) and produce two protective actions: (1) shut off both component cooling pumps, and (2) close HCV-565-A1 in the c e l l evacuation line (Fig. 1.5.81, thereby preventing f u r t h e r outflow of c e l l a i r t o the stack. 1.5.6

Fuel Salt Sampler-Enricher Containment Instrumentation

The sampler-enricher i s f u l l y described in Sect. 3.12 and i n refs. When in use it m u s t penetrate t h e primary containment and, there26-29. fore, is p o t e n t i a l l y capable of contaminating the area and exposing i t s operators t o a l l t h e various types of radioactivity associatedwith nuc l e a r fuel. The material i n t h i s section i s limited t o a functional des c r i p t i o n of t h e more important instrumentation and controls whose sole purpose i s t o prevent a loss of containment. Figure 1.5.15 is a simplified l i n e drawing which illustrates the operation of t h e sampler-enricher. It can be seen that sampling or enriching is accomplished by lowering and r a i s i n g the cable-suspended capsule i n t o and out of t h e f u e l pump bowl. Throughout most of i t s t r a v e l t h e capsule is guided by and contained i n t h e t r a n s f e r tube, which provides d i r e c t access t o the molten salt i n t h e pump Wwl. The samplingenriching operation may be likened t o withdrawing or adding w a t e r t o or from a well w i t h t h e "old o&en bucket" powered by a motor-driven winch. Contsinment is effected during these operations by subdividing the region through which t h e capsule t r a v e l s i n t o compartments which are opened and

26R. C. Robertson, MSRE Design and Operations Report, Part I, Des c r i p t i o n of Reactor Design, Om-TM-728 ( t o be published).

27Molten-Salt Reactor Program Semiann. Progr. Rept. July 31, 1963, ORNL-3529, p. 35. 28Molten-Salt Reactor Program Semiann. Progr. Rept. Feb. 28, 1965, ORNL-3812, pa 24, 29Molten-Salt Reactor Program Semiann. Progr. Rept. Aug. 31, 1965, ORNL-3872, p. 56.

closed i n sequence so that two containment b a r r i e r s are maintained. regions which a r e considered t o be primary coatainment are:

The

1. area IA, t h e t r a n s f e r t d e between the maintenance valve and tkte pump bowl; 2.

area lB, the t r a n s f e r tube between the maintenance valve and the operational valve;

area 1 C and the short length of t r a n s f e r tube which comects area 1C t o t h e operational valve. Note t h a t area 1C houses the motordriven winch which r a i s e s and lawers t h e capsule.

Compartmentalizatioa and closure of these primary containment regions is obtained by the maintenance and operational valves and by t h e port which closes the access t o area 1C. Since a c m p l e t e sampling or enriching procedure requires t h a t the material, e i t h e r f r e s h salt o r hot sample, pass through both the primary and the secondary containment b a r r i e r , the l a t t e r is a l s o compartmented. These compartments are maintained by

1. The access port, which separates the primary and secondary containment regions, 1 C and 3 C respectively. 2.

The removal valve, which when closed, i s t h e secondary containment b a r r i e r across the path traversed by the capsule. Note that area X contains the output side of the manually operated manipulator which the operator uses t o unlatch the capsule from the cable, move it i n t o area 3C, and thence t o the t r a n s f e r cask v i a the removal valve.

Figure 1.5.16 is an a u s t e r i t y version of the sampler-enricher instrument flawsheet and shows only the high-quality instrumentation whose sole purpose is t o e f f e c t containment. Figure 1.5.17 diagrams the funct i o n s of these instruments and controls. Table 1.5.2 shows the normal aspects or s t a t u s of the valves and the access door during use and when not i n service. It is proper t o point out that the sampler-enricher is used intermittently and by personnel well t r a i n e d in i t s operation. Intermittent usage and functional requirements resulted i n the arrangement of containment instruments i n accordance with Figs. 1.5.16 and 1.5.17. Where redundancy is not obtained by duplicating individual i n s t r u ment channels which produce the same specific output action, it is because the desired protection is obtained by d i v e r s i t y (explained e a r l i e r i n t h i s sectioa). There a r e additional instruments and alarms required by the device. These lend support t o tbe high-grade interlocks discussed herein; the reader is referred t o Sect. 3.12 f o r more information.

Table 1.5.2. Component Condition Operating Situation

Maintenance Valve

Operational Valve

Access Port

Removal Valve

Capsule entering sampler-enricher (above removal valve

Closed

Open

Capsule i n area 3A and being manipulated onto the l a t c h

Closed

Open

Closed

Capsule l a t c h e d t o drive u n i t cable i n area 1 C

Closed

Capsule i n t r a n s f e r tube and entering maintenance valve

open

men

Closed

Capsule in t r a n s f e r tube between maintenance valve and pump bowl

Open

Closed

ORNL-DWG 64-6477AR

EMERGENCY

ESV IC2

AC NEUTRAL

ALL VALVES SHOWN IN NORMAL

NORMAL OPERATING PRESSURE

INSTRUMENTATION VALVE SOLENOID (TYPICAL)

COMMON FORT’

Fig. 1.5.1.

MSRE-Redundant Instrumentation for Block Valves.

CUNL-OW 67-4580

OUTPUT REFERENCE NO.

ADDITIONAL INFORMATION

SECTIONS 1-5 AND 11-8

SECTION 1-5

VI SECTIONS

111

1-5 AND 11-8

VI1

SECTION 1-5

VI1

SECTIONS 1-5 AND 11-7

VI11

SECTION 1-5

VI11

f 3 M - 5 9 6 i)__(RsS-5963

60.61.62

6 3 TO 68

XI1

SECTION 1-5

30.31.32-

XI11

P F S ~ V R E ~ ~ C ~ ~ U R ~ N " T G R B A T W

marno

36.37-298

30.31.32--36,37 30.31.32-33.34

-38.39

30.31.32-36.37

XIV

_ .-

C U X S BWCS VALWd

111 I J N E a s I I P p L m B B l n N To mt SALT PUUP B(IyL AND O V B E r n

SECTION 1-5

XI1

SECTION 1-5

XI11

SECTION 1-5

XIV

SECTION 1-5

XVI

SECTION 1-5

XVII

SECTION 1-5

XVIII

SECTION 1-5

XIX

SECTION 1-5

SECTIONJ-8

XXI

SECTION 11-8

TANK

u -

M mad 61 AND Y BK"wXEII O R w I l SAUPLEII AND STACE

m a R*Duna-A

-11

C U R E BWCK VALVES NOB. PCY JJI-Al. PCY 331-AI, FCV 3 4 3 4 1 AND

fLIl 1 1 - A I . BI, ANDC1

7 TO IO INC'L-

XXI

II FROM OUTPUT I

I I '

C m BWCK VALVE8 NOB. FSV 831-Al, PJYMI-AI, M I - A l . AND W Y 8Psv-Ixil U A 1 , F sMy uTHB I-Al. RIV l'5ATKD WATER COoImG SYSTEU

255.256-568.13.15 255.256-568.I3,l5

82 ORNL DWG 67-4644

INITlATlNG CONDITION

INPUT REFERENCE NO.

t - 3

CORRECTIVE ACTION

EFFECT

OPEN VENT VALVES

-L,

HCV-573, HCV-575

FUEL PUMP OVERFLOW TANK LEVEL GREATER THAN 20%

HIGH RADIOACTIVITY IN COOLANT PUMP OFFGAS

SALT PUMP BOWL GREATER

OPEN (THAW) FREEZE VALVE NO. 105

L L Z Z L T ~ ~ ’

REACTOR DRAIN

DRAIN LINES

VALVE NO. 106

VALVE NO. 103

3 -b

HIGH RADIOACTIVITY IN EITHER REACTOR CELL OR DRAIN TANK CELL ATMOSPHERE

r.--\

OPEN BY-PASS VALVES HCV-544-Al. HCV-545-A1, HCV-546-A1

CLOSE MAIN HELIUM SUPPLY VALVE, PCV-517-Al AND BRANCH LINE SUPPLY VALVES, HCV-572-A1, HCV-574-Alv AND HCV-57641 -t TO FUEL SALT DRAIN TANKS

STOP FILL

-).

116 SALT PUMP BOWL GREATER

BLOCK INLET HELIUM LINES USED TO PRESSURIZE FUEL SALT DRAIN TANKS. DOES NOT INCLUDE HELIUM PURGE LINE VALVES ESV 519A AND ESV-519B

LEC ND

CIRCUIT NUMBERS COINCIDENCE OF A AND B REQUIRED TO GET C

Fig. 1.5.3.

Input-Output Diagram of the MSRE FI 1 Salt Fill and Drain Safety System.

. . . .

.. .

. _ ___ ~

,_l._

~.._ .~.

.-.

I-->

( X ON

l n d N l W31SAS A 1 3 j W S ) '6lsd 8Z N W H l S S 3 1 SI

YS6EB-E9 3MO -1NYO

-1

NOTE : OPERATIC OF PRES! COMPONi CONVERE BELLOW!

OF T H E TEST SWITCH S I M U L A T E S T H E APPLICATION ZE TO T H E T R A N S M I T T E R A N D CHECKS A L L

ORNL-DWG 64-627R TOSAFETY

IN THE SAFETY CHANNEL EXCEPT THE V OF P R E S S U R E TO FORCE BY T H E T R A N S M I T T E R SINGLE ALARM SWITCH

VENT T O STACK NTAINED, ZERO g REFERENCE A M B E R . RATED D T E S T E D AT 100 psig

SLACK DIAPHRAGM'

! N

5c -

I iig

NO. 2

2 psig

DUAL A L A R M SWITCH S W I T C H C A P A B L E OF P R O D U C I N G TWO D I F F E R ENT SAFETY INPUT SIGNALS TO DATA LOGGER

F R O M F U E L SALT OVERFLOW TANK P R E S S U R E TRANSMITTER

TEST SWITCH

I=1OTO 50mo

I= 10 TO 50 mo ISOLATION A M P L l FlER

I3 INLET HELIUM

1 TO PRESS T R A N S M I TTER U S E D FOR CONTROL

T O - C U R R E N T TRANSDUCER-AMPLIFIER. R A T E D A N D TESTED AT 250psip

REFERENCE L I N E TO 7 F U E L P U M P BOWL INLET HELIUM

Fig. 1.5.5.

TO OVERFLOW T A N K , INSTRUMENTATION S A M E AS ABOVE

Typic 1 Channel of Safety-Grade Pressure Instrumentation for Use in Primary Containment.

ORNL-DWF 63-8398R2

TO COOLANT SALT W M P BOWL BUBBLERS

FCV *T516BI

I .

w w

TO FUEL

PRESSURE GAE AND PRESSURE SWITCHES WITH HIGH AND LOW PRESSURI ALARM IS TYPICAL OF ALL BUBBLER LINES

-PUMP

5l6AI

T O L E V E L PROBES, (BUBBLERS)INFUEL SALT OVERFLOW TANK.

?: I

BE OIL MS FOR FUEL A N 0 COOLANT SALT PUMPS PCV

HCV

c . 1

L a

h l

TOCOOLANT DRAIN TANK

TO COOLANT PUMP

1 -

TO LEVEL PROBES (BUBBLERS) I N FUEL SALT PUMP BOWL.

i I

- 1 I

BLOCK VALVES SEE NOTE !

I-----

-- --.

TO FUEL STORAGE TANK AND CHEMICAL PROCESSING SYSTEM

Yyq PRESS

PRESS

THREE CHANNELS

FOR INPUT SIGNAL. PRESSURE SWITCHES ACTUATE AT 28 psig INDIVIDUAL TESTING OF EACH CHANNEL BY OPENING HAND VALVES

CAPILLARY FLOW TAINMENT BARRIERS

PURGE FLOW TO REACTOR DRAIN L I N E NO. 103

VENTED TO FILTERS AND THENCE TO OFF-GAS STACK OFF-GAS STACK

2. A LOW HELIUM SUPPLY Pf HELIUM PURGE LINE ASTERISK, THUS

Fig. 1.5.6.

MSRE Drain Tank A f t e r h e h t

i . -

Removal System.

,SURE ILIUM I

3. L I N E

AND ASSOCIATED PXM'S ARE A ZERO psig REFERENCE SYSTEM WHICH M A I N T A I N S CONTAINMENT AND PRESERVES ACCURACY OF T H E PRESSURE TRANSMITTERS DURING FLUCTUATIONS OF CELL PRESSURE

.-,

ORNL-DWG 63-8388R

TO OFF-GAS

TO COMPONENT

STACK

OPERATED BUTTERFLY VALVES (SEE NOTE 4 )

FROM RUPTURE

SUPPLY L I N E

._STEAM

CWM

REACTOR CELL EXHAUST L I N E 30-111.DlAM

__I_

3 DRAIN LINE + FROM STEAM DRUM ON FTD-2

NOTES:

I. THESE VALVES ARE CLOSED DURING NORMAL REACTOR OPERATION. VALVES ARE OPENED ONLY DURING MAINTENANCE OPERATIONS WHEN THE REACTOR CELL I S OPEN.

2. VALVES MARKED BY AN ASTERISK THUS

SIGNAL TO CLOSE FOR EXCESS RADIOACTIVITY I N REACTOR CELL OR I N REACTOR

FUEL

TANK (TYPICAL)

ARE SAFETY SYSTEM BLOCK VALVES,

ESV x

STEAM DRUM PUMP,CAPACITY-40 gpm ESV x

8 0 6 - 2 A 806-28 CONDENSATE DRAIN TANK

TO FLOOR DRAIN

Fig. 1.5.7. D i a g r a m of System Supplying H e l i u m t o Primary and Secondary Containment Regions.

87 f

i,i

VENT L I N E FROM FUEL DRAIN TANKS AND FLUSH SALT TANK

SAFETY SYSTEM INPUT NO. I X x

SAMPLER ENRICHER

OFF-GAS H E L I U M FROM F U E L S A L T PUMP BOWL, LOWER L I N E Y

/ I

TO IN-CELL COMPONENT

OXYGEN

ORNL-DWG 638397R2

ANALYZER

T--------7

----- -- - _ _ _ _

OFF-GAS SAMPLER

[

0. b.

r-+

-1

DRAINS BLOCKS REACTOR STEAM DC

BLOCKS L I N E S TO 0 2 ANALYZER d. BLOCKS COOLING

)NDENSATE ROM DRAIN

ROD DRIVES

REACTOR CELL EVACUATION LINE

v PRESSURE BLOWERS

ALARM

1 AUXILIARY CHARCOAQ BEDS MONITOR

OFF-GAS H E L I U M FROM F U E L SALT PUMP, UPPER L I N E TRAP

CHARCOAL FILTER

CAP1L L A R Y

OFF-GAS STACK 1

-MOTOR OPERATI BUTTERFLY VAL

4. HOT STORAGE CELL

5. FUEL STORAGE TANK I N - C E L L COMPONENTS RODS AND ROD DRIVES FREEZE VALVES, P U M P

4CTOR 5 TAIN IN FLOW TO CEI

VENTILATION AIR FROM

IS:

6. SPARE CELL

'x,

MPONENTS MARKED WITH ASTERISK, PERFORM INSTRUMENTED S A F E T Y FUNCTIONS

'ES AND DUCTS L A R G E R T H A N 2-117.D l A M R E Q U I V ) ARE DENOTED THUS DRAIN

TANK CELL

'REACTOR

CELL

PROCESS WATER

CONDENSING

FROM RUPTURE DISK ON THERMAL SHIELD COOLING WATER L I N E

c. f

Fig. 1.5.8.

MSRE Off-Gas \System. )1

ORNL-DWG 63-8393

SIGNAL TO CLOSE FROM RADIATION MONITORS R M - 5 5 7 A ORB, SAFETY SYSTEM INPUT XVI

PRESS CONTROL

r-G

ALARM

BREATHER, CONNECTS TO FUEL SALT PUMP

SIGNAL TO CLOSE WHEN INLET HELIUM

IS LESS T H A N 28psig (SAFETY SYSTtM INI'UI X I J HELIUM SUPPLY, 35 psig

TO OFF-GAS FILTERS AND STACK

"I"

- l i

INTERCONNECTING OIL RETURN LINE FROM COOLANT SALT PUMP

-Fix, 1

O I L RETURN FROM SALT PUMP FUEL

(50

- A T ? LOG

OIL SUPPLY TANK FOR

EXCESS FLOW RETURN FROM PUMP OUTLET

ALARM

TO OIL PUMPS FOP-I AND FOP-2

C C

NOTES: 1. BOTH LUBE OIL SYSTEMS ARE SIMILAR. NUMBERS ENCLOSED THUS ARE EOUIVALENTS%-COOLANT SALT PUMP LUBE OIL SYSTEM 2.VALVES MARKED WITH

WATER

DISCONNECT

ASTERISK, T

ARE SAFETY SYSTEM BLOCK VALVES.

F i g . 1.5.9.

Lube-Oil System Off-Gas Monitors.

Y3ONllA3 WnmH

U VP9-Ad I

3AlWA 331138

h K"'~"""~"""""

Y30Y033Y SS3Yd 01

W31SAS SW-330 3 H l 30 33NVWLIOlY3d Y33H3 A i i w a i a o w d 01 03sn IY3ONllA3) AlddnS Wnll3H

"""""""'

"""""""""""

--E-

02-A Y Y

r---

311 311108 Y3dSNVYl 3ldWVS

:-----%

:NOIlVlN3WnYlSNI 3WllVY3dW31

AX AIX lllX SON l n d N l W31SAS A L ~ ~ won3 W S 3~0x1

8))

O1 SlVNOIS

32lA

821A

vi1

133NN03S10/

'F2-l-e

'''' '' "

t w

r=--=T= I

Y3110YlN03 ONllW310NI 13A31

\ I

W V l W Mold--

S3H311MS M o l 3

1 l n d N l WIISAS

8 O N V V BEE AS3

8 ONV V LPE AS3 S 3 A l V A WW18

S3AlVA Y W 1 8 3S013 O l l V N 9 l S + - - J

L------+3S0901

1VNPS

ORNL-DWG 67-i296

379 30

25 kVA

7 'SS 589A3

48 V DC

319

48 V DC TVA DIESEL

318

48VI

S161A

25 kVA

PSS 592 83

J- KB379F

7 OPEN WHEN FUEL K A 379F PUMP BOWL

>ENS WHEN 'UEL PUMP 3OWL PRESS.

rXCEED> 0 psig

'SS- RC-B

4\(c7 OPEN

+ 41 hB318c

?ESS. >2psig

S163A (RESET)

KA348C

I KA348B

KA 318

IN6 319

KB 379

3433 39,298 81, 81, 318

38,37 ' 39,298 84, 81, 318

BLOCK DEMAND FOR: 1. 2. 3. 4.

LIQUID WASTE SYSTEM STEAM DOME DRAINS OXYGEN ANALYZER OFF-GAS SAMPLER

Fig. 1.5.U..

Block Vrtlve Circui

I-319B

KB 318 B

1 J

MPLER BLOCK VALVES CLOSED WHEN DE-ENERGIZED

1 319,318 348, Y

SAFETY SYSTEM INPUT XI11

R I-319A

KB 318

311 OFF-GAS

r T

3 +

KB348A

OPEN ON HIGH ACTIVITY IN OFF-GAS

SAFETY SYSTEM INPUT X V

.KA318A

PSS-RC-G

S162A (RESET)'-

KA 379

51658 (TEST)

EXCEEDS 2.0 psig PSS-RC-F !

CELL

S1648 (TEST)

for Off-Gas Sampler.

OFF-GAS SAMPLER BLOCK VALVES

c‘:

ORNL-DWG 67-764

20 psig RELIEF VALVES VENTED TO ATMOSPHERE

I -

NOTE: VALVES MARKED WITH ASTERISK,

3 I REFERENCE GAS 5% 0 2 95% Np

‘

. 1 I5-V AC

ARE SAFETY SYSTEM BLOCK VALVES

IANUAL SWITCHES N INSTRUMENT PANEL

, ,

MEASURING

N2 CYL

:TS OPEN WHEN -565-8 OR RM-565-C YCESS RADIOACTIVITY I N CELL

I Il

REFER TO INPUT IX FOR OTHER + SAFETY ACTIONS PRODUCEDBY RM 565 B O R C

CONTZ S U R CONTAIN!

OPEN WHEN I N SECONDARY NT CELLS EXCEEDS

-I

SAFETY SYSTEM INPUT NO. XI11 CELL PRESSURE>P.O psig HS-5(

-A3

HS-566-A2

VENT HOUSE/’

30,3!, 32

CKTS 36,37

II I

_ -

C 298

\BLOWDOWN

VALVE

I w

CKT 2 9 8 1

HCV-566-A2

HCV 566 A4

HCV 566-A4

{2z}w

- -- - I

--- -

565 C

CELL .___

EVACUATION LINE: FROM OUTLETOF CO M PONE NT COOLING PUMPS

+ 4 psig

REFER TO SAFETY

I I

HCV- 5 6 5 -A! TO INLET OF COMPONENT COOLING PUMPS

- 2 psig 4

+ I#

TO FILTERS AND OFF-GAS STACK

BLOCK VALVES ARE CLOSED

CELL AIR FINAL OXYGEN CONTROL ANALYZ CIRCUIT

-Fig. 1.5.12.

HEN SOLENOIDS

Block Valves to and from Cell Oxygen Analyzer. I

ARE DE-ENERGIZED

HS-566-84

“3

ORNL-DWG 63-839611

VALVES PRESSURE INDICATOR SINTERED fDlSK SNUBBER PRESSURE SWITCHES ((ACTUATE AT t2 psig)

CONTAINMENT

MATRIX OF LEVEL TRANS.

100 psig

332 B

LlOUlD WASTE TANK 11,OoOgol

NOTE: VALVES MARKED WITH ASTERISK, T H U X

LCLL

i CLOSE BLOCK VALVES IN VENTILATION LINES TO AND FROM OFF-GAS SAMPLER

ARE SAFETY SYSTEM BLOCK VALVES.

In-Cell Liquid Waste and Instrument Air Block VaLving.

pig. 1.5.13.

- .....

............

~~~

...

. ~ . ..

.....

. . . . .

._*. ... . .

ORNL-DWG 64-638A

DIESEL HOUSE 1

FILTER

ni,

M A I N SUPPLY

TO VAFOR CONDENSING SYSTEM

7 - - - - - - - - - -

[

49 psig

IN SPECIAL EQUIPMENT ROOM

VENT TO SURGE TANK FOR COOLING COMPONENT PUMPS

CENTRIFUGAL GAS

TREATED WATER PUMPS

------

PURGE AIR SEE NOTE N 0 . 2 S A L T PUMP

c I 1

SAFETY SYSTEM OUTPUT NO. XIX TO BLOCK VALVES, SEE NOTE NO.(

NOTES. 1. ON EXCESS RADIATION SIGNAL FROM ANY 2 OF 3 RADIATION MONITORS A L L VALVES

2. RUPTURE DISK A N D PRESSURE SWITCH PROTECT

CONTAINMENT

THERMAL S H I E L D FROM RUPTURE I N THE EVENT OF EXCESS WATER PRESSURE WASTE TANK

Fig. 1.5.14.

MSRE Safety System Block Valves in the In-Cell. Treated Cooling Water System.

94 ORNL-DWG63-58481

REMOVAL VALVE AND SHAFT SEAL CAPSULE DRIVE UN CASTLE JOINT (SHIELDED WITH DEPLETED URANIUM)

( F 'RIMARY CONTAINMENT SAMPLE CAPSULE

OPERATIONAL AND MAINTENANCE VALVES SPRING CLAM

AREA 2 8 (SECONDARY

RlTlCAL CLOSURES EQUlRlNG A BUFFERED

FEET

EXPANSION SECTION

SAMPLER-ENRICHER SCHEMATIC TRANSFER TUBE (PRIMARY CONTAINMENT

Fig. 1.5.15.

Sampler-Enricher Schematic.

_...I

_.I._...

I..I...I

lll___....

I__..._..__._..I ....

.. .. ..

95 I

ORNL-DW 67-6695

XCESS FLOW

Fig. 1.5.16.

Sampler-Enricher Simplified Flow Diagram.

96 ORNL-DWQ 67-6S96 PRIMARY INPUT INSTRUMENTS

CORRECTIVE ACTIONS

INITIATING CONDITIONS

\ , PREVENT OPENING REMOVAL VALVE

I (362 ) @--@---(-I-~ REMOVAL VALVE OPEN

(365)

(368)

@-@--'3s)-

MAINTENANCE VALVE OPEN BUFFER PRESSURE e40 psi0

1363)----

Ill

(359)

(LIMIT SWITCH)

> > ~ ~

PREVENT OPENING OPERATIONAL VALVE

PREVENTS OPENING CAPSULE ACCESS FORT

(368)

----1 L

PREVENTS OPENING MAINTENANCE VALVE

! CLOSE VALVE HSV-678-61 IN LINE BETWEEN

- --

@--(A394)-

MANIPULATOR COVER REMOVED p ( 3 6 2 ) -

(A3791 - - - d

@---

L(362)FUEL PUMP BOWL PRESSUREXOpalp

(6379)-

(365)-

--*,

CLOSE VALVE HSV-678A IN LINE BETWEEN VACUUM PUMP NO.( AND CAPSULE CHAMBER. AREA fC

MAINTAINS CONTAINMENT: INSTRUMENTED CLOSURES TOGETHER WITH INTERLOCKED

OPERATIONAL VALVE,

CLOSE VALVE HSV-6774 IN LINE 677 BETWEEN AREA 3A AND VACUUM PUMP N0.I

@ -A ,-377

HIGH RADIATION LEVEL IN ANY HIGH RADIATION LEVEL IN EITHER HELIUM OFF-GAS LINE NO.6750R N0.684

(A3781 (8378)

CLOSE BLOCK VALVE AS FOLLOWS: A. HSV-657D IN HELIUM PURGE LINE TO AREA 1C B. HSV-66BB IN HELIUM BUFFER SUPPLY TO OPERATIONAL VALVE C. HSV-6558 IN HELIUM BUFFER SUPPLY TO MAINTENANCE VALVE D. HSV-6808 IN SUCTION LINE FROM MANIPULATOR COVER AND MANIPULATOR BOOT TO VACUUM PUMP NO. 2

PRESSURE IN OFF-GAS LINE N0.542 GREATER THAN 7 palp

I CLOSE BLOCK VALVE HSV-675-AI CLOSE BLOCK VALVE HSV-659 IN LINE FROM AREA 2 8 TO VENT IN AREA 4 A

Fig. 1.5.17.

~ACCESS

PORTAND

REMOVAL VALVE MAINTAINS A MINIMUM OF TWO CONTAINMENT BARRIERS AND PREVENTS DIRECT ESCAPE OF ACTIVITY TO BUILDING OPERATIONAL AREAS OR TO SURROUNDING AREAS OR INDIRECT ESCAPE VIA THE HELIUM SUPPLY AMD BUILDING CONTAINMENT AIR SYSTEM.

1368) 1~5)1380

Sampler lnricher, Input-Output Diagram of Safety-Grade Control Actions.

SAFETY INSTRUMENTATION AND REACTOR CONTROL 2.1

â&#x20AC;&#x153;3INSTRUMEXCATION:

INSTALIATTON AND LOCATION

A l l permanent neutron sensors are located i n a single penetration. The penetration i s a 3-ft-dim pipe i n s t a l l e d a t an angle of 42â&#x20AC;&#x2122; t o the horizontal so t h a t i t s lower end i s opposite the midplane of the reactor core and i t s upper end terminates on the main f l o o r i n the high-bay area. Figures 2.1.1 and 2.1.2 a r e plan and elevation views, respectively, of the i n s t a l l e d penetration. The lower end of t h e penetration passes through the thermal shield, and the end closure p l a t e i s e s s e n t i a l l y f l u s h with the inner periphery of t h e thermal shield. The penetration i s , from a containment standpoint, an extension of the secondary containment s h e l l . The lower end of the tube i s welded t o t h e containment s h e l l , and the upper end i s embedded i n the e a r t h f i l l and the concrete floor. A bellows-type expansion j o i n t accommodates thermal expansion between these points. Since penetration was i n s t a l l e d during modifications t o the containment s h e l l , it was stress-relieved and pressure-tested a t the same t i m e . The penetration i s f i l l e d with water t o within approximately 1 f t from i t s upper end. A float-type instrument monitors the water l e v e l and gives an alarm when t h e l e v e l changes more than 4 i n . Water i s added with a hand valve adjacent t o the upper end of the penetration i n t h e high-bay area. A 5-gpm pump circulates the water i n the penetration t o reduce temperature gradients and maintain a uniform concentration of corrosion i n h i b i t o r . The inhibitor, containing lithium n i t r i t e ( L i N 0 2 ) arid lithium borate (LiH*B03), has 810 ppm of NO2 and 57 ppm of boron. The solution i s sampled periodically and t e s t e d t o maintain the pH a t 9.0 t: 0.2. The penetration i s designed t o accommodate t e n ion chambers. Each chamber i s located i n an individual guide tube; four tubes a r e 5 i n . I D and s i x a r e 4 i n . I D . The configuration of these tubes within the penetration and the types of chambers assigned t o them are shown i n Fie;. 2.1.3. The guide tubes a r e not made of single lengths of 30-ft-long tubes; instead subassemblies, each approximately 10 f t long, were made by welding the tubes i n t o end plates, o r bulkheads, and t h e subassemblies were bolted together when i n s t a l l e d i n the penetration. The tubes were constructed t h i s way (Fig. 2.1.4) because there w a s not enough headroom behind the upper end of the penetration t o ease the handling problem a t assembly. The tubes are open t o t h e water i n the penetration, and the upper, o r last, bulkhead p l a t e serves as the cover p l a t e over the end of t h e penetration. Individual, smaller cover p l a t e s a r e used over the upper end of each tube. These contain the necessary gland-type f i t t i n g s f o r signal leads and push rods f o r chamber positioning. Figure 2.1.5 shows the upper end of the penetration with the guide tubes and individual cover p l a t e s i n s t a l l e d . One of two ORNL model Q-2545 wide-range counting channel drive u n i t s (see Sect. 2.3) i s shown i n s t a l l e d i n the penetration. 97

The mounting flanges on these drive u n i t s f i t the d r i l l i n g f o r t h e cover plates, so that a complete drive u n i t i s handled as a module which i s inserted i n a tube and bolted i n place. E a r l y c r i t i c a l t e s t s disclosed t h a t the curve of neutron flux i n the penetration vs distance deviated grossly from the desired exponential type of curve. The deviation was beyond the c a p a b i l i t i e s of the compensating function generator (see Sect. 2.3) i n t h e wide-range counting channel. Cadmium sleeves' were placed around guide tubes 6 and 9 t o shield the f i s s i o n counters from neutrons which entered from the side and distorted t h e curve of count r a t e vs distance. The design of the shields, t h e i r location, and t h e i r e f f e c t on t h e count r a t e as a function of distance i n guide tube 6 are depicted i n Fig. 2.1.6. Figure 2.1.7 i s a diagram of the interconnection wiring layout. A s much a s possible the safety system wiring w a s separated from control and power wiring. It w a s not feasible t o separate the first runs of cabling from the drive u n i t s t o the junction boxes on t h e reactor c e l l w a l l . These jumper cables (described i n more d e t a i l i n Sect. 2.7) contain a l l the e l e c t r i c a l leads i n a single well-protected bundle. The safety system interconnections, consisting of t h e wiring t o the clutch c o i l s and the potentiometers i n the rod drive unit and the signal and chamber voltage leads t o t h e safety chambers i n the instrument penet r a t i o n , are i n individual and separate conduits t o t h e control room. Except where absolutely necessary, these safety interconnections are unbroken by terminal blocks, connectors, e t c . A l l the i n - c e l l wiring (excluding jumper cables ) i s e n t i r e l y w i t h mineral-insulated, coppersheathed cables. Control-grade wiring, not subject t o the r e s t r i c t i o n s imposed by separation, protection, and independence, i s r u n i n t r a y s and conduits as dictated by cost and convenience.

Project Staff, Molten-Salt Reactor Program Semiann. Progr. Part 1, p. 4 4 . Rept. Feb. 28, 1966, 0-3936,

Fig. 2.1.1.

MSFB Plan V i e w of Nuclear Instrument Penetration.

100

ORNL-DWG 64-62SR 24ff 2in.

I I Q FLANGE FACE

,REACTOR THERMAL SHIELD CONCRETE SHIELDING-

MIDPLANE OF CORE 830 ft 8 in;

Fig. 2.1.2.

MSRF, Elevation View of Nuclear Instrument Penetration.

101

ORNL-DWG 66-10143

LINEAR CHANNEL

WIDE RANGE COUNTING CHANNEL NQ 2

SAFETY

\ CHANNEL NQ

- 4i'DIA

HOLES NO 3,4,5,6,9

8 10

HOLES NQ I , 2 , 7 8 8

-5;DlA

COVER PLATE DIA.'

Fig. 2.1.3. trat ion.

SAFETY CHANNEL NQ2

HOLES HOLES

39[=

Location of Neutron Sensors Within Instrument Pene-

102

Fig. 2.1.4. i n Penetration.

Chamber Guide Tube on Shop Floor Prior t o Installa;tion

103

m 4 cd rl

ORNL-DWG 66-2744

MSRE COUNT RATES I N GUIDE TUBE N 0 . 6 BEFORE AND AFTER ADDING C A D M I U M S H I E L D I N G

MIDPLANE OF CORE 0

RE :TOR VE

40 x, DISTANCE WITHDRAWN (in.)

;EL

CADMIUM SHIELDING SUBASSEMBLY - T Y P I C A L IN GUIDE 6 AND 9 SECTION A-A LOCATION O F GUIDE TUBES

OUTER SHELL REMOVED FOR CLARITY- SHADED WEDGES ARE CADMIUM - U N S H A D E D WEDGES ARE A L U M I N U M

Fig. 2.1.6.

Cadmium Shielding of t h e Fission Chamber Guide Tubes.

105

ORNL- OWG 66-4101

JB-119 CELL PENETRATION NO. X I MAIN CONTROL BOARDS INCLUDIVG CONSOLE

JB-112 ( S P A R E )

JUMPER CABLES

AUXILIARY CONTROL BOARDS

ROD DRIVES

W INSTRUMENT PENETRATION TO SAFETY CHAMBERS TO LINEAR POWER CHAMBERS, FISSION CHAMBERS AND BF3 CHAMBERS

CONTROL

JB-JUNCTION BOX

SAFETY SYSTEM WIRING

Fig. 2.1.7.

MSRE Interconnection Wiring for Nuclear Instrumentation.

106

2.2

BF3 INSTRUMENTATION

2.2.1

General

The MSRE i s equipped with one channel of sensitive BF3 counting equipment. The counting chamber i s located i n guide tube 2 (Figs. 2.1.4 and 2.1.5). The electronic instruments used with these chambers follow t y p i c a l practice (Fig. 2.2.1). This sensitive BF3 channel i s required t o get counting-rate "confidence" a t the neutron source l e v e l when the reactor i s l e s s than half f i l l e d o r when it i s being f i l l e d with f l u s h salt. Except f o r the preamplifier, the electronic instruments shown i n Fig. 2.2.1 a r e mounted i n the nuclear instrument cabinet i n the auxiliary control room. As soon as confidence i s established by one or both wide-range counting channels, t h e BF3 chamber i s withdrawn manually t o prevent i t s being damaged.

2.2.2

BF3 Counter

The neutron counter i s a BF3 counter from Reuters-Stokes Company, No. RSN-28A, procured on UCNC purchase order No. 56s-1724, May 11, 1964. The specifications and c h a r a c t e r i s t i c s are as follows: Shell ( s h e l l i s cathode) Outside diameter Wall thickness ( w a l l i s the

2 in. 0.55 i n .

cathode ) Overall length

I 2 in.

Active length

8.13 i n .

Material

Aluminum

Anode

0.002-in.-diam wire insulated from the s h e l l with ceramic insulation

Filling

Enriched BF3 (96$ 'OB) t o a pressure of 40 cm Hg ab s

Performance Thermal-neutron s e n s i t i v i t y

15 counts sec-l (nv)-' -

Saturation curve

See Fig. 2.2.2

107

For use i n the MSRE, the counter i s encased i n a weighted waterproof can, described by Instrumentation and Controls Division drawings Q-2719-3 and - 4 . A jointed push rod i s used as a handle t o position the counter within the guide tube i n t h e penetration. 2.2.3

High-Voltage Power Supply

The high-voltage power supply i s manufactured by Electronic Research Associates, model 25/10UC. The output from the power supply i s continuously adjustable from 500 t o 2500 v dc, positive o r negative, by s i x step-switch positions and a f i n e control. Maximum load current i s 10 ma f o r any voltage. The t o t a l amount of ripple, hum, and noise i s l e s s than 5 mv ms. Line regulation i s +0.005$ f o r a +lo$ change of l i n e voltage. Load regulation i s a 60-mv change from no load t o f u l l load; recovery time i s l e s s than 10 msec. Front panel meters indicate from 0 t o 10 ma and from 0 t o 2500 v dc. The input i s 115 f 10 v ac, 60-hertz, single-phase, 1-amp. 2.2.4

Preamplifier, ORNL Model Q-1857

The preamplifier consists of a three-stage feedback loop, followed by a resistance-capacitance differentiator, and a second three-stage feedback loop. The t h i r d stage of the second loop i s a power stage t o drive a long, low-impedance transmission l i n e . The gain of each loop i s about 20. A 2.5:l voltage l o s s occurs i n t h e differentiator, so t h a t the o v e r a l l gain i s about 150. Variable compensation i s provided across the feedback r e s i s t o r i n each loop t o produce s a t i s f a c t o r y t r a n s i e n t response. The preamplifier power supply i s self-contained. 2.2.5

Pulse Amplifier, ORNL Model Q-1875

The output of the ORNL m o d e l Q-1857 preamplifier is developed across a 100-ohm r e s i s t o r i n the amplifier chassis. This r e s i s t o r serves a s

t h e c h a r a c t e r i s t i c impedance termination f o r the transmission l i n e from t h e preamplifier. The signal i s coupled t o a gain control whose output supplies the s i g n a l t o the pulse amplifier. The pulse amplifier has two separate three-stage amplifiers with feedback loops. The compensation on each feedback loop i s adjustable: compensation i s used i n t h e f i r s t amplifier t o adjust the r i s e time of the amplifier and i n t h e second amplifier t o make the t r a n s i e n t response satisfactory. The gain of each loop i s approximately 100, but, due t o losses i n t h e output cathode followers, the overall gain i s about 5000. The output of the main amplifier i s available a t "low" and "high" output jacks. The low output i s intended f o r driving long cables and has a maximum value of 5 v. The high output w i l l deliver approximately 100 v. A pulse-height selector (PKS) i s included on the amplifier chassis f o r measuring pulses between 0 and 100 v. The â&#x201A;Ź"S i s direct reading with

108

an accuracy of approximately 0.5 v. Two PHS outputs a r e provided: the first, a positive pulse with an amplitude of 3 v and a width of 0.4 psec, intended f o r driving a count rate meter, appears a t CN6; the second, with an amplitude of about 20 v negative and of s l i g h t l y longer duration, appears a t CN5. The second i s intended f o r driving a scaler. The amplifier contains i t s own power supply and i s designed t o operate with 115-v, 60-Hz power. 2.2.6

Scaler, ORNL Model Q-1743

The scaler has a fast input decade consisting of a type 6700 beam switching tube, a Schmitt trigger, and slow decades which a r e Ericsson GC-1OB glow t r a n s f e r tubes. Each glow t r a n s f e r tube i s driven by a dccoupled lAG4 tube. The glow tube stages a r e followed by a pulse shaper, r e g i s t e r driver, and a six-digit mechanical r e g i s t e r . The instrument contains a regulated power supply. The input resolving time i s 1 psec, with a counting l o s s of l e s s than 0.2% a t 20,000 random counts per second. 2.2.7

Logarithmic Count Rate Meter, ORNL Model Q-751

This instrument measures the average r a t e of a series of e l e c t r i c a l pulses. The input pulses are the output from the pulse-height selector (Sect. 2.2.5). The pulses a r e randomly spaced, positive 3 v amplitude and 0.4 psec long. The output of the instrument i s logarithmic and spans four decades. The average counting r a t e , i n counts per second, i s displayed on a meter. I n addition, provision i s made f o r remote readout on either a remote meter o r a 10-mv recorder, or both. The indicating meter i s graduated from 1 t o 10,000 counts/sec.

2.2.8

Confidence Trips

This instrument i s composed of two Control Data Corporation, Magsense l e v e l comparators. Each u n i t i s designed t o accept an input of 0 t o 100 pa dc. The t r i p i s continuously adjustable i n t h i s range. The t r i p l e v e l and hysteresis are adjustable by potentiometers mounted on the rear panel. The output consists of two SPDT relay contacts.

109

ORNL-OWG 66-2446

ELECTRONIC RESEARCH ASSOCIATES 2.5/IOUC

SUPPLY

PULSE AMPLIFIER

BF3 COUNTER REUTERS-STOKES RSN -28A

Q-1743-CI

L -

LOG COUNT RATE METER. RC13-10-58

TO BF3 CONFIDENCE CIF?CUIT 4

Fig. 2.2.1.

Diagram of BF3 Counting Channel.

110

ORNL- DWG 66 -io019

0.9

F i g . 2.2.2. Type RSN-28A.

4 .O

4.4

4.2 4.3 ANODE (kilovolts)

4 .4

4.5

Typical Plateau Curve for Reuters-Stokes l3F3 Counter

111

2.3

WIDE-RANGE COUNTING CHANNELS

2.3.1

Principle of Operation

The wide-range counting channel employs a 2-in. -dim, 6-1/2-in. long f i s s i o n chamber a s ' t h e neutron sensor and i s useful from s t a r t u p (with a f u l l y fueled core vessel) t o full-power operation a t 10 Mw. The principle of i t s operation, described elsewhere,l# i s repeated here as a convenience t o the reader. The design of t h i s wide-range counting system i s explained by examining the behavior of a movable neutron sensor submerged in, o r surrounded by, a neutron r e f l e c t i n g and absorbing medium i n which the neut r o n attenuation with distance i s approximately exponential. For purposes of explanation it i s s u f f i c i e n t t o consider the idealized case i n which neutron attenuation as a function of distance from the neutron source i s exactly exponential. For t h i s idealized s i t u a t i o n CR =

where CR (assumed p i s the chamber.

i s the count r a t e i n counts per second, P i s the reactor power proportional t o flux), x i s the distance from the reactor, and attenuation coefficient of the medium surrounding the f i s s i o n Rearrangement gives

log P = l o g CR

(1)

(2)

It i s apparent from Eq. ( 2 ) t h a t l o g P i s the sum of two e a s i l y obtained numbers: t h e logarithm of the counting r a t e (log CR) and the distance, x, of the sensor f r o m t h e neutron source multiplied by a constant, p. Inverse reactor period i s obtained i n the usual way by d i f f e r e n t i a t i n g Eq. ( 2 ) w i t h respect t o time. Figure 2.3.1 i s a simplified diagram of the arrangement of the instruments that perform the operations of measuring the neutron f l u x arid distance, obtaining a logarithm adding, and differentiating. I n the E R E ( o r any other i n s t a l l a t i o n j , neutron attenuation is not i d e a l l y exp ~ n e n t i a l ,as ~ assumed i n the preceding paragraph; instead, p varies w i t h x, and t h e form of t h i s variation can only be established by experiments with the equipment i n s t a l l e d for use a t the reactor. An adjustable position-sensing device, the O m model Q-2616 function generator, produces a signal proportional t o px. The adjustment feature provides a means t o compensate f o r variations i n p w i t h x and, further, permits; these adjustments i n s i t u .

lR. E. Wintenberg and J. L. Anderson, Trans. Am. Nucl. SOC.

454-55

(1960). 2J. L. Anderson and R. E. Wintenberg, Instrumentation and Controls Div. Ann. Progr. Rept. July 1, 1959, Om-2787, p. 145. 3MSRE Project S t a f f , Molten-Salt Reactor Program Semiann. Progr. Rept. Feb. 28,. 1966, ORNL-3936.

112

The f i s s i o n chamber i s moved toward o r away from the reactor by a servomechanism which attempts t o maintain a constant output from the count r a t e meters. The value of t h i s constant output (the count r a t e s e t point) is, within limits, arbitrary. It should be high enough t o ensure a good signa-to-noise r a t i o i n the input t o t h e count rate meters, but it should not be s o high t h a t f i s s i o n counter l i f e i s s e r i ously reduced. A t y p i c a l value f o r the count r a t e s e t point i s 10,000 counts/sec. These wide-range channels can provide useful operating and control information as long as the counting rate i s i n the range from 1 t o ~OO,OOO counts/sec. Limiting values of count r a t e are used t o provide control system interlocks, discussed i n d e t a i l i n Sect. 2.6. The operation of a wide-range counting channel is explained i n the discussion by tracing i t s response as the reactor goes from s u b c r i t i c a l t o full-power operation. Figure 2.3.2 shows curves of count r a t e and chamber position during a traverse of the reactor through i t s power range. The curves are based on the assmption that the count r a t e s e t point has been established a t 10,000 counts/sec. I n the source and very low power region, where the count r a t e i s l e s s than the set-point value of 10,000 counts/sec, the e r r o r signal, which i s the algebraic difference between the actual count r a t e and the s e t point, i s negative. This causes the servomechanism t o drive the chamber toward t h e reactor u n t i l i t s lower l i m i t i s reached. The chamber w i l l remain inserted at the lower l i m i t u n t i l the reactor power i s s u f f i c i e n t l y large t o produce a count r a t e of 10,000 counts/sec. While t h e chamber i s a t the lower l i m i t , px i s constant, and (see Fig. 2.3.1) the r i s e i n reactor power i s followed by the output of the logarithmic count rate meter. When the reactor power i s high enough t o produce 10,000 counts/sec w i t h the chamber a t the lower l i m i t , the e r r o r signal becomes positive and the servomechanism withdraws the f i s s i o n chamber t o maintain the count r a t e constant a t 10,000 counts/sec. Changes i n reactor power are now indicated by changes i n the "compensated position, I1 px, the output of the ORNL model Q-2616 function generator. If, f o r example, the count rate s e t point i s changed a r b i t r a r i l y from 10,000 t o 12,000 counts/sec while the chamber i s p a r t i a l l y w i t h drawn and the reactor i s i n steady state, the servomechanism w i l l i n s e r t the chamber a s u f f i c i e n t distance t o satisfy t h e increased count r a t e request. The decreased value of px w i l l exactly equal the increase i n log CR, and the s m of the two, log P, w i l l remain constant, as it should. Again, suppose that, with the reactor i n steady s t a t e , the operator switches from servo control of position t o manual control and a r b i t r a r i l y withdraws the chauiber a short distance. The decrease i n l o g CR w i l l be balanced by t h e increase i n px, and t h e i r sum, log P, w i l l remain constant. Now, suppose the operator continues t o withdraw t h e chamber manually so t h a t the counting r a t e approaches 2 counts/sec, which has been established as the useful threshold operating value f o r t h e system. The count r a t e signal w i l l contain a higher percentage of I1 spurious electrical. input "noise, and, also, the random variations i n the neutron f l u x w i l l become more apparent as the count rate is decreased. I n common with a l l counting instruments of t h i s general type, t h e response of the count rate meter becomes progressively slower as t h e count r a t e decreases. The loss in response i s such t h a t when the count rate is reduced t o about 500 counts/sec, the logarithmic count r a t e

(lii

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'6,

meter i s unable t o follow the change i n count r a t e produced by manual chamber withdrawal. Therefore, i n such a case, the indicated power would l a g and would be higher than actual power. This response l a g would continue t o produce an error, and the indicated power reading would be higher than actual power u n t i l the chamber had stopped moving and enough time had elapsed t o a t t a i n steady s t a t e i n the new position. This s i t u a t i o n obtains regardless of whether the chamber i s being inserted or withdrawn manually. I n manual insertion a t count r a t e s below 500 counts/sec, the indicated power w i l l l a g and appear lower than actual power. A s the count r a t e is lowered, the output of the counting system, log P, may become e r r a t i c and fluctuate about the average value. A t very low counting r a t e s the r a t i o of useful signal t o noise decreases and accuracy suffers. If chamber withdrawal continues u n t i l the count r a t e becomes l e s s than 2 counts/sec, the confidence c i r c u i t s w i l l be actuated and the "no-conf idence " interlocks governed by that channel w i l l be established. If the reverse process takes place, the chamber m a y be inserted u n t i l the counting r a t e becomes 50,000 counts/sec, a t which point the confidence c i r c u i t s w i l l also be actuated. This upper bound of system operation w a s established a t t h i s value t o keep the instruments within t h e i r operating range. The confidence c i r c u i t s and t h e i r functions are discussed i n Sect. 2.6.6. From t h e foregoing it i s evident t h a t , i f t h e count r a t e i s 500 counts/sec or more, the servo need be fast enough t o follow only norm& maneuvers; any t r a n s i e n t s too fast f o r the servo t o follow w i l l change t h e count r a t e so t h a t the channel w i l l read correctly. This technique has several advantages: the operator need not switch range o r take any other action, the system covers a very wide range of reactor power, manual w i t h d r a w a l of the chamber and the dead time induced when the chamber i s withdrawn are eliminated, and the constant, optimum count r a t e of the amplifier i s maintained when s u f f i c i e n t flux i s available. Figure 2.3.3 i s a detailed block diagram of a wide-range counting channel as used i n the ERE and includes the ORNL model Q-2609 f a s t - t r i p comparators (described i n Sect. 2.5) which produce the t r i p signals required by the reactor control system. The increased number of operational amplifiers shown i n Fig. 2.3.2 are required t o obtain signal gain f o r impedance matching t o output devices and f o r signal inversion (sign change ) The detector, preamplifier, and radiation-resistant interconnecting cable a r e contained i n an i n t e g r a l assembly, ORI%L model Q-2617. This assembly, approximately 2 in. OD, i s f l e x i b l e so that a guide tube or thimble, curved i f required, can be i n s t a l l e d i n t h e reactor shielding leading t o t h e core. The assembly i s waterproof and can operate continuously i n an ambient temperature of 1 0 0 째 C while surrounded by e i t h e r a i r or water. The detector i s a f i s s i o n chamber w i t h concentric cylindrical electrodes coated with 1mg/cm2 of 235U over a t o t a l area of 860 cm2. The chamber i s well saturated w i t h 200 v applied; t h e operating polarizing potential is 270 V. The collection time i s approximately 80 nsec. The pulse-height c h a r a c t e r i s t i c s of the chamber, obtained by using the preIt i s evident that amplifier described below, a r e shown i n Fig. 2.3.4. gamma pileup presents no problem, even i n f i e l d s as high as 2 x lo6 r. The chamber has ceramic insulation entirely, and the special cable con-

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necting the chamber t o t h e preamplifier i s designed t o withstand a g m a - r a y dose of 101O r. The output stage of the preamplifier drives one side of a balanced l i n e , the other s i d e of which i s terminated symmetrically. This symmetry and c a r e f u l a t t e n t i o n t o shielding and grounding make t h e assembly, as demonstrated in many f i e l d t e s t s , very insensitive t o e l e c t r i c a l noise pickup. The receiving end of the balanced l i n e feeds a pulse transformer f o r common-mode r e j e c t i o n and clipping t o give an approximately symmetrical waveform. This avoids base-line s h i f t s due t o changes i n counting r a t e and aids i n keeping the discrimination l e v e l constant. Pulses from the pulse transformer are sent t o t h e pulse amplifier and count r a t e meter, ORNL model Q-2614. Following a calibrated attenuator t h e pulses are amplified i n two feedback stages, each with a gain of 10, and e n t e r a biased amplifier whose variable bias l e v e l determines t h e discrimination level. Only pulses t h a t exceed t h e d i s crimination l e v e l are counted. The output pulses from t h e biased-amplif i e r discriminator are shaped and applied t o a conventional logarithmic count r a t e c i r c u i t of the Cooke-Yarborough type. The time constants are a compromise between t h e desire t o have rapid response and t h e necessity t o prevent excessive fluctuation i n the period signal. The output of the l o g count rate c i r c u i t i s applied t o an O m model Q-2605 operational amplifier (IA i n Fig. 2.3.3) whose gain i s adjusted t o give an output of 2 v/decade, o r 10v f ~ l lscale. The function generator output i s applied t o amplifier 2B through the normclosed contacts of ~ 1 .The gain gives an output of 2 v/decade. Amplifier 2B i s a l s o used i n a t e s t mode and w i l l be described l a t e r . The outputs of amplifiers IA and 2B are summed, with a gain of 1/2, in amplifier 2 A , yielding an output signal proportional t o reactor power. The span of t h e summing amplifier 2 A i s 10 v, or 1 v/decade. The outputs of t h e l o g count r a t e amplifier (IA), t h e summing amplifier (a), and t h e gain amplifier (3B) are indicated on panel meters i n drawer W-1. The generation of a period s i g n a l from t h e reactor f l u x s i g n a l i s accomplished with operational amplifiers 3A and 3B. The output from amplifier 3A i s t h e approximate derivative of t h e log P input with a dc gain of 4 (product of C 308 and R 331). To prevent excessive noise i n t h e period s i g n a l a 250-kilohm input r e s i s t o r and a 1-pf feedback cap a c i t o r are provided t o l i m i t t h e low- and high-frequency noise gain respectively. The output of amplifier 3A i s amplified by amplifier 3B and i s o f f s e t s o that 0 t o +10 v corresponds t o a period of -30 t o +5 sec. An i n f i n i t e period i s +1.428 v provided by t h e o f f s e t network a t t h e input of t h e amplifier. The amplifier gain i s 24.6. The pulse amplifier and count r a t e meter module, ORNL model Q-2614, has, i n add i t i o n t o t h e log count r a t e output, a simple diode pump c i r c u i t ( l i n e a r count r a t e c i r c u i t ) whose output is used as t h e s i g n a l f o r t h e chamber position servo. This c i r c u i t has an output of approximately 1.75 v a t lo4 counts/sec. This signal i s compared with t h e demand potentiometer (servo l e v e l ) in amplifier 1B. Amplifier 1B has a voltage gain of 50; f u r t h e r voltage and power gain are provided by a servo amplifier, ORNL model Q-2615, which has an approximate voltage gain of 3 and whose output drives t h e servo motor d i r e c t l y . I n addition t o t h e chamber, t h e motor drives a tachometer whose output i s applied t o t h e servo preamplifier

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1B and with a p o l a r i t y opposite that of the input signal; t h i s negative feedback loop provides servo s t a b i l i t y . To provide control interlocks, eight f a s t - t r i p comparators, ORM, model Q-2609, are used. Two f a s t - t r i p comparators receive t h e i r input from the log count r a t e amplifier ( U ) . Comparator 1 t r i p s i f the counting r a t e i s l e s s than 2 counts/sec, whereas comparator 2 t r i p s i f the counting r a t e i s greater than 50,000 counts/sec. Their output ( r e l a y contacts), i n s e r i e s w i t h t h e "calibrate-operate" relay contacts, provides counting channel confidence i f all eight comparators are prope r l y plugged i n t o the instrument cabinet drawer (see Sect. 2.5 f o r add i t i o n a l discussion of confidence). Summing amplifier 2A provides the input t o three f a s t - t r i p comparators. The f i r s t comparator operates i f the power "sags" below 200 kw while i n the "Run" mode; the second opera t e s when the power i s above 500 kw, thus giving permission t o enter the "Run" mode; and the t h i r d i n i t i a t e s a control rod "reverse" i f the power exceeds 1.5 Mw i n the "Start" mode. Several t e s t s are provided t o ensure t h a t the system i s operating properly. There i s contained i n the pulse amplifier module (Q-2614) a lo4- and 10-cps o s c i l l a t o r which may be applied t o the input of the pulse amplifier by proper positioning of the gain switch on the front panel. I n addition, w i t h t h e gain switch on period t e s t , the period t e s t relay ( K l ) must be actuated by a push button i n drawer W-1. This switches out the normal inputs and feedback r e s i s t o r s of the function generator amplifier and switches i n a 10-pf feedback capacitor and a selectable input r e s i s t o r . With an input of 25 v applied through the gain switch, t h i s amplifier thus generates a voltage ramp which produces a 5-, 25-, o r 30-sec period indication as selected. An additional push button i n drawer W-1 causes an adjustable voltage source t o be app l i e d t o amplifier 2A t o t e s t i t s f a s t - t r i p comparator. "In" and lloutl' push buttons on t h e same drawer provide normal override of the norma servo signal from the output of the Q-2615 module. The chamber drive mechanism i s a ball-bearing lead screw w i t h a l i n e a r speed of approximately 72 in./min and a t o t a l stroke of 90 in. The direct-current, variable-speed drive motor has an i n t e g r a l tachome t e r and i s protected from overload by a s l i p clutch. The positionsensing components are connected d i r e c t l y t o the lead screw s h a f t ahead of the s l i p clutch. The position-sensing t r a i n contains a ten-turn potentiometer whose output is connected t o a meter i n drawer W-1. I n addition, a one-turn data-logger potentiometer and synchro transmitter f o r driving a position indicator on t h e console i s provided. Upper and lower l i m i t switches r e s t r i c t the overall t r a v e l of the unit. 2.3.2 4).

Fission Chamber and Preamplifier Assembly

The following description has been excerpted from ORNL-3699 ( r e f . The 3/4-in. f i s s i o n chamber described i n ORNL-3699 has been re-

4D. P. Roux e t al., A Miniaturized Fission Chamber and Preamplifier Assembly (Q-2617) f o r H i g h Flux Reactors, ORNL-3699 (October 1964)

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placed w i t h one of more typically standard dimensions ( 2 in. d i m ) with greater s e n s i t i v i t y . The excerpted t e x t has been a l t e r e d accordingly. 2.3.2.1

Introduction

To meet the space and environmental requirements f o r high-performance reactors, an a r t i c u l a t e d assembly (Fig. 2.3.5) consisting of a f i s s i o n chamber, a preamplifier, and f l e x i b l e cables has been developed. Because high-flux reactor cores are usually inaccessible, it becomes necessary t o use a detector t h a t i s s m a l l and movable i n a tube which can be bent t o resolve the access problems a t each reactor. The r e l a t i v e l y low s e n s i t i v i t y of a s m a l l chamber i s compatible with t h e large neutron source l e v e l encountered i n such reactors. Locating the preamplifier close t o the f i s s i o n chamber d r a s t i c a l l y reduces the suscept i b i l i t y of the counting channel t o e l e c t r i c a l noise pickup, s o t h a t the system responds predominantly t o neutrons; consequently, the reactor operator i s assured of an adequate source. The assembly i s p a r t i c u l a r l y s u i t a b l e as p a r t of a wide-range counting channe1,l but also can be used as p a r t of a conventional counting channel. The e n t i r e assembly i s waterproof and can operate continuously a t a temperature of 100째C ambient. The maximm outside diameter of t h e assembly i s 2 in. (chamber diameter). The f i s s i o n chamber and the cable connecting it t o the {reamplifier can withstand a total integrated gamma radiation dose of lo1 rads; the preamplifier can withstand at l e a s t lo8 rads. 2.3.2.2

Preamplifier

Circuit The preamplifier c i r c u i t (Fig. 2.3.6) consists of two cascaded feedback amplifiers: a charge-sensitive input configuration (V and 1 v2A ), followed by a voltage-sensitive amplifier (V V3, and V4) with symmetric output. The signal pulses are d i f f e r e n t i a t e d both a t the input and a t the output of t h e preamplifier, giving the pulse shape shown i n Fig. 2.3.7. The gain of the preamplifier is 0.75 x 1 0 l 2 v/coulomb. This corresponds t o a system output pulse height of 150 mv f o r a nominal. 50-Mev f i s s i o n fragment. The counting l o s s f o r randomly spaced pulses i s IO$ a t a counting r a t e of 105 counts/sec. The advantages of a charge-sensitive configuration are t h a t , over a wide range of detector capacitance, (1)the output signal height depends only on the charge generated within t h e detector and i s insensitive t o t h e capacitance of the detector and connecting cable (variation of input capacitance from 0 t o 200 pf produces a gain change of only lo$), and (2) t h e decay time of the detector pulse i s a l s o insensitive t o the capacitance of t h e detector and cable (variation of input capacitance from 0 t o 200 pf produces a decay time change of only 1O$). The preamplifier output i s connected t o a balanced and shielded cable which i s terminated a t i t s receiving end by a pulse transformer. The common-mode e l e c t r i c a l fluctuation signals picked up by the two signal leads a r e canceled i n t h e pulse transformer. I n one application a t a reactor t h e common-mode rejection w a s greater than 95%.

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The double d i f f e r e n t i a t i o n reduces t h e e f f e c t s of pulse pileup. With t h e f i r s t d i f f e r e n t i a t o r a t t h e input t o t h e preamplifier, t h e maxi m u m counting r a t e i s limited by coincidence l o s s rather than by bias s h i f t s . The pulse transformer serves as the second d i f f e r e n t i a t o r . The second d i f f e r e n t i a t i o n time constant i s determined by the r a t i o of the primary inductance of the transformer t o i t s terminating resistance. The combined e f f e c t of both d i f f e r e n t i a t o r s eliminates any duty-cycle s h i f t i n the main-amplifier discriminator threshold. Figure 2.3.7 i s a photograph of t h e f i s s i o n pulses a t t h e main amplifier input. The int e g r a l s of t h e individual pulse areas on e i t h e r s i d e of the reference are equal. Component Selection The operating temperature, t h e radiation requirements, and t h e permissible o v e r a l l diameter of t h e assembly demanded prudent selection of t h e components used i n the preamplifier. Tubes. - Temperature and radiation conditions precluded t h e use of t r a n s i s t o r s ; consequently, flying-lead subminiature tubes were selected. Nuvistors were considered but were rejected because t h e i r diameter i s too l a r g e t o mount components side by side with the tubes i n t h e a l l o t t e d space. Resistors. - Resistors were limited t o those of wire-wound and deposited-carbon types. The wire-wound r e s i s t o r s (miniature power r a t i n g s ) were used i n all c r i t i c a l . c i r c u i t locations s e n s i t i v e t o the value of a r e s i s t o r ; deposited-carbon r e s i s t o r s were used i n n o n c r i t i c a l c i r c u i t s . Capacitors. - Capacitors were limited t o those of porcelain and s o l i d tantalum e l e c t r o l y t i c d i e l e c t r i c s . The p a r t i c u l a r ceramic capaci t o r s used (Vitramon type VK20) have maximal operating conditions of 15OoC and 200 v. A 108-rad gamma dose r e s u l t s i n a capacitance v a r i a t i o n of l e s s than 1%. The tantalum capacitors (Texas Instrument type SCM) are used only f o r bypassing in c i r c u i t s which can t o l e r a t e high leakage currents and considerable capacitance variations. The operating temperature of the tantalum capacitors i s limited t o 125OC. A s a r e s u l t , they are located i n t h e preamplifier layout, where negligible heat power is dissipated (see the following section).

Irradiation tests made at

ORNL on four type SCM tantalum capacitors t o an accumulated dose of rads showed an increase of l e s s than 5$ f o r the dissipation factor.

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Provisions f o r Operation a t 100째C Ambient For continuous operation of t h e preamplifier i n a i r o r water a t

100째C ambient, the following provisions were made: 1. The preamplifier w a s potted i n a mixture of 70 w t $ epoxy Helix P-430 and 30 w t $I epoxy Dow Chemical DER 732 t o which was added 6% of Helix hardener B. This p a r t i c u l a r potting compound improves the heat t r a n s f e r and increases t h e mechanical r i g i d i t y of t h e preamplifier. The advantages of using t h i s compound are t h a t it i s only slightly b r i t t l e a t room temperature, it shrinks minimally during curing ( t h e shrinkage of some epoxies during curing has caused tube and tantalum capacitor breakdowns), and i t s thermal expansion c o e f f i c i e n t i s compatible w i t h that of the preamplifier components. 2. The tube filaments are heated w i t h a voltage of only 5.5 v (6.3 v r a t i n g ) t o minimize the heat-power generation.

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3 . The tantalum capacitors (125OC max) are located a t t h e ends of t h e preamplifier, whereas the subminiature tubes are positioned i n the center of t h e preamplifier. The ceramic capacitors (15OoC max) are a l s o located a t t h e ends, except f o r a group which i s placed i n a gap between t h e first and t h e second tubes as shown i n Fig. 2.3.8. Two d i f f e r e n t t e s t s were performed t o e s t a b l i s h t h a t t h e capacitors operate below t h e manufacturers' specified maximum temperatures when the preamplifier i s i n a region with an ambient temperature of 100째C. I n t h e first t e s t t h e preamplifier was placed i n s t i l l a i r a t 100째C i n an oven. I n t h e second t e s t t h e preamplifier w a s immersed i n water a t 98OC. I n both t e s t s f i v e thermocouples were located inside t h e preamplifier close t o t h e components of i n t e r e s t , and the time p r o f i l e s of t h e temperatures were recorded. The r e s u l t s indicated t h a t t h e equilibrium temperatures of all capacitors were a t l e a s t 6OC below t h e manufacturers' maximum specified temperatures i n t h e first t e s t and 1 4 O C i n t h e second t e s t . The f i r s t t e s t l a s t e d t e n days; during t h i s time no change i n t h e preamplifier gain or output pulse shape w a s observed. Separation Distance of Preamplifier t o Chamber The separation distance between t h e preamplifier and t h e f i s s i o n chamber should be short t o satisf'y t h e e l e c t r i c a l noise pickup consideration, but must be long enough t o l i m i t t h e radiation damage t o t h e preamplifier. (The preamplifier was designed t o withstand an accumul a t e d dose of 108 rads over one year of continuous operation.) The evaluation of t h e e f f e c t s of t h e accumulated dose should be separated i n t o two parts: the dose accumulated during operation of t h e reactor a t power and t h e dose accumulated during reactor shutdown. I n l i g h t water-shielded reactors, t h e dose accumulated during reactor shutdown i s considerably a l l e v i a t e d i f t h e neutron counting r a t e i s r e s t r i c t e d t o ldr counts/sec or l e s s . The reason f o r t h i s i s that photoneutrons generated i n t h e water by t h e residual f i s s i o n product gamma rays will give a neutron counting r a t e that makes t h e i n s e r t i o n of t h e f i s s i o n chamber and preamplifier assembly i n t o a higher gamma flux unnecessary (see Sect. 2.3). For application i n light-water-moderated reactors, a separation length of 4-1/2 f% between t h e f i s s i o n chamber and t h e preamplifier i s adequate. This distance is also s u f f i c i e n t t o maintain t h e preamplifier i n a gamma f l u x less than lo4 r/hr (or lo8 ./year) when t h e reactor i s a t f u l l power. 2.3.2.3

Flexible Cables

Cable Between Fission Chamber and P r e m l i f i e r The cable between t h e f i s s i o n chamber and t h e preamplifier i s a BIW 50-ohm coaxial cable enclosed i n an externaJ inorganic insulation sheath (spaghetti). The sheathed cable i s i n s e r t e d i n t o a l/&in.-ID corrugated f l e x i b l e metal tubing f i t t e d with s t a i n l e s s s t e e l b r a i d and casing. The BIW cable i s a f l e x i b l e , high-temperature (5OO0C max), radiation-resistant coaxial cable. It consists of a %-gage stranded nickel-clad copper center conductor, an inorganic insulation, and a nickel-clad copper outer braid 0.200 in. i n OD. I t s capacitance i s 35 pf/f%. The corrugated tubing provides watertightness and f l e x i b i l i t y

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The measured linear-expansion coefficients of the cable assembly are approximately 2 x lo4 per l b and 1x 10per OC. w i t h negligible elongation.

Cable Between Preamplifier and Main Amplifier This cable i s a Raychem No. 10023 cable. It has preirradiated polyethylene d i e l e c t r i c s and jackets, i s radiation r e s i s t a n t , and i s a multilead coaxial cable. The center member of t h i s composite cable i s a shielded and jacketed two-conductor coaxial cable f o r the signals; around the center member are wound three 26-gage and two 20-gage hookup wires f o r preamplifier supplies, and over all of these are a nickel-clad copper shield and a preirradiated polyethylene jacket. The maximum overall OD i s 0.324 in. The cable w i l l withstand a maximum temperature of 125OC and an accumulated dose of 5 X lo8 rads. Following t h i s exposure the cable can s t i l l be coiled on a form whose diameter i s t e n times the overall cable diameter. The Raychem cable i s a l s o enclosed within a watertight metallic envelope which may be varied f o r different reactor applications. The metallic envelope a l s o serves as an e l e c t r i c a l shield. For example, a s t a i n l e s s s t e e l hose covered with polyvinyl chloride i s used a t t h e O a k Ridge Research Reactor (ORR)

2.3.2.4

E l e c t r i c a l Shielding Layout

Multiple e l e c t r i c a l shields are provided t o prevent excessive elect r i c a l noise pickup i n the f i s s i o n chamber and preamplifier assembly. Figure 2.3.9 shows, schematically, the general shielding and grounding layout. A f i r s t ( o r inner) shield covers the e n t i r e path of the signal. from the f i s s i o n chamber t o the main amplifier input. This shield includes the cathode of the f i s s i o n chamber, the outer braid of the BIW coaxial cable, a s o l i d brass f o i l surrounding the preamplifier, and the two braids of the Raychem multilead coaxial cable. The preamplifier common mode, o r ground, i s e l e c t r i c a l l y connected t o the inner shield, which i s e l e c t r i c a l l y insulated from an outer shield, o r s h e l l , of the assembly. This outer shield includes the f i s s i o n chamber casing, the corrugated f l e x i b l e metal. tubing between the chamber and the preamplifier, the preamplifier casing (insulated fromthe brass f o i l shield), the met a l l i c envelope surrounding the Raychem cable (described previously), and a shielding which forms an extension of the metallic envelope t o the main amplifier i n the reactor control room. The grounding of t h e inner and outer shields i s discussed i n Sect. 2.3.2.5. 2.3.2.5

Low Pickup-Noise Performance of the Assembly

Extensive experimentation with d i f f e r e n t counting channels using t h i s assembly w a s required t o reduce i t s s u s c e p t i b i l i t y t o e l e c t r i c a l noise pickup. The principal source of e l e c t r i c a l noise pickup i s electromagnetic radiation from ac power l i n e s which are shock excited where some piece of equipment i s turned on o r off. The s e n s i t i v i t y t o noise pickup has been minimized by the short separation distance between t h e preamplifier and the chamber, the large output signal from the preamp l i f i e r , the balanced configuration w i t h common-mode noise rejection, and the multiple e l e c t r i c a l shielding.

120

The lowest noise pickup is achieved w i t h t h i s assembly when the inner and outer shields are connected together i n several places, f o r example, a t the junction box and a t the main amplifier, as shown i n Fig. 2.3.9. This i s contrary t o the generally accepted precept of avoiding ground loops. Apparently, t h e capacitive coupling between shields def e a t s any attempt a t i s o l a t i o n of the system from the building ground. With the connections described herein and shown i n the Fig. 2.3.9, the pulses from pickup are no l a r g e r a t the main amplifier input than the pulses of t h e alpha p a r t i c l e s produced i n the f i s s i o n chamber, even when the assembly i s located i n t h e n o i s i e s t reactor i n s t a l l a t i o n s available a t ORNL. 2.3.3 2.3.3.1

Preamplifier Power Supply

General

The f i s s i o n chamber and preamplifier dc power supply provides three regulated output voltages from an unregulated input supply of -32 f 4 v f o r use w i t h the f i s s i o n chamber and preamplifier assembly ORNL model Q-2617-1. The three outputs are: +300 v f o r polarization of the f i s s i o n chamber, +110 v f o r the preamplifier anode supply, and -22 v f o r the preamplifier vacuum tube heaters and for biasing. The -22 v i s derived d i r e c t l y from the -32-v b a t t e r y supply through a s e r i e s regulator and a current-limiting c i r c u i t . The other two voltages, +300 v and +llO v, are developed by a dc-to-dc converter with a s e r i e s pre re gulator. 2.3.3.2

Construction

The f i s s i o n chamber and preamplifier dc power supply i s contained i n amodule 4.25 i n . wide, 4.72 in. high, and ll.90 in. deep. It i s a standard "three-unit" plug-in module of the ORNL modular reactor instrumentation s e r i e s depicted on drawings &-2600-1 through &-2600-5. The c i r c u i t s are on two printed c i r c u i t boards mounted p a r a l l e l t o each other and enclosed i n a perforated metal shield t o reduce e l e c t r i c a l radiation and coupling t o other modules. Adjustments and t e s t points are accessible through t h e shield from t h e top of the module. 2.3.3.3

Application

The module i s intended t o supply alJ. required voltages t o t h e fission chamber and preamplifier assembly. Because the assembly i s potted and unrepairable, t h e power supply is designed t o l i m i t currents and voltages t o protect both t h e assembly and the power supply against damage from ahnost any conceivable combination of crossed connections o r short c i r c u i t s . 2.3.3.4

Specifications

Overall specifications f o r the preamplifier power supply are given i n the following table. General Power required Ambient temperature range

-32 5 4 v dc, 0.5 amp m a x 0 t o 55OC

121

-22-v

supply

Output voltage range

Output current range Voltage regulation Current limiting

-20 t o -24 v dc 200 t o 400 m a + 1 $ l

Adjustable t o l i m i t the output current t o no more than llO$ of norm a l operating current from normal t o short c i r c u i t

+300-v supply Output voltage Output current Current l i m i t i n g Noise and ripple

+300 f. 15 v dc 0 t o 100 pa 3 m a max, any load 100 mv max

+llo-v supply Output voltage Output current Current l i m i t i n g Noise and ripple 2.3.3.5

+llo +

10 v dc 0 t o 15 ma 100 ma max, any load 10 mv max

Circuit Description of the -22-v Supply

The -22-v supply consists of a voltage regulator (Q8, Q9, QJO) and a current-limiting c i r c u i t (Q7, D12, D 1 3 ) . The l i m i t i n g c i r c u i t prot e c t s the s e r i e s heater s t r i n g of the preamplifier from damage when any of several possible fault conditions occur. The action of the limiting c i r c u i t i s similar t o t h a t of a constant-current c i r c u i t . The base voltage of Q7 i s held constant a t +2 v with respect t o the -32-v supply by the two Zener diodes D12 and D13. The breakdown voltages of the diodes are 12 and 10 v, respectively, but they are connected i n opposition so t h a t the reference voltage i s the difference i n the two voltages. This arrangement yields a sharper knee and a s t i f f e r reference voltage than a single low-voltage diode. The emitter voltage i s d i f f e r e n t from the base voltage only by Vbe, t h e baseemitter voltage drop of the t r a n s i s t o r , which i s fairly constant. Thus, t h e emitter voltage i s constant across a fixed resistance R22 and R26, yielding a constant current i n the emitter of Q7, provided t h a t the collector-emitter voltage i s large enough t o keep the t r a n s i s t o r out of saturation. When "normal" output current i s flowing (less than the l i m i t current), the voltage a t the collector of Q7 i s l e s s than 2 v more posi t i v e than t h e -32-v supply, and Q7 i s saturated. I n this conditian Q7 simply a c t s l i k e a s e r i e s r e s i s t o r and does not control the output current. It i s only when the output current tends t o increase above normal that Q7 comes out of saturation and limits t h e output current t o

122

where V 'be

i s t h e difference i n the breakdown voltages of D12 and D 1 3 and

i s t h e forward base-emitter voltage drop of Q7.

The voltage regulator consists of Q8, Q9, and QlO. The output voltage i s sensed by the base of Q9 and i s compared w i t h t h e voltage of reference diode D l 4 i n the emitter of Q9. The amplified difference on t h e c o l l e c t o r of Q9 i s applied t o t h e base of Q8; Q8 provides current gain only t o drive t h e base of t h e output t r a n s i s t o r Q l O . The regulated output voltage appears between the emitter of QlO and ground. Diode D15 i s used t o protect Q8 from turnon t r a n s i e n t s . The output voltage i s adjusted with trimpot R30. The current a t which the c i r c u i t limits i s s e t w i t h t h e "current l i m i t " potentiometer R22. 2.3.3.6

Circuit Description of t h e +300-v and +llO-v Supply

The supply is designed t o operate from a nominal 32-v s t a t i o n b a t t e r y with a terminal voltage variation from 28 t o 36 v dc. This wide v a r i a t i o n makes necessary a voltage preregulation, which consists of t r a n s i s t o r s Ql, Q2, Q3, and Q4. The preregulator output voltage i s sensed by r e s i s t o r s R7, R8, and R9 and applied t o t h e base of amplifier stage Q3. A reference voltage (16.8 v) generated by Zener diode s t r i n g D2, D3, and D 4 i s applied t o t h e emitter of Q3. The amplified difference appears a t t h e c o l l e c t o r of Q3 and is applied t o driver Q2 and pass t r a n s i s t o r Q4. A constant Zener l , diode D1, c o l l e c t o r current i s provided f o r Q3 by t r a n s i s t o r Q and t h e associated network. The preregulator output ( t e s t point TP1) i s f i l t e r e d by C1, C2, and R27 and is applied t o t h e dc-to-dc converter. Q5, Q6, T1, and t h e associated c i r c u i t r y comprise a free-running square-wave o s c i l l a t o r inverter. Networks C15-R32 and C16-R33 round t h e edges of t h e square wave somewhat t o avoid t h e generation of sharp, high-frequency spikes, which may be coupled t o other c i r c u i t s . The 110-v output i s obtained from a full-wave r e c t i f i e r and f i l t e r , and t h e 300-v output from a voltage t r i p l e r . The supply can be short c i r c u i t e d without damage. Most t r a n s i s t o r inverters w i l l stop o s c i l l a t i n g when overloaded. The o s c i l l a t o r t r a n s i s t o r s can be damaged unless t h e i r nono s c i l l a t i n g current i s limited t o a safe value. Current l i m i t i n g by s e r i e s resistance in a primary l e a d i s undesirable because power will be wasted and t h e i n v e r t e r w i l l have poor load regulation. On t h e other hand, biasing so t h a t t h e t r a n s i s t o r current goes t o zero i n t h e nono s c i l l a t i n g condition w i l l not allow o s c i l l a t i o n s t o start when the short i s removed. The current-limiting scheme used here consists of a combination of clamping and series-emitter resistance t o s e t t h e current t o a predetermined value. Rll and FU.2 b i a s the bases of Q5 and Q6 i n t o conduction. FU.3 and FU.4 l i m i t t h e t r a n s i s t o r currents i n t h e nonoscill a t i n g condition t o a l i t t l e l e s s than t h e o s c i l l a t i n g currents. The voltage drop across these r e s i s t o r s i s l e s s than t h e value t h a t causes appreciable current flow through D5, 06, and D7 u n t i l o s c i l l a t i o n begins. I n t h e o s c i l l a t i n g condition, t h e drops across R13 and FU.4, respectively, are limited by t h e diodes t o 1.4 v. The low dynamic resistance of t h e diodes assures a stable, nonoscillating current value.

123

2.3.4 2.3.4.1

Pulse Amplifier

General

The pulse amplifier and count r a t e meter m l i f i e s and counts pulses from a f i s s i o n chamber. The input s e n s i t i v i t y i s such t h a t some preamplification i s required. The module consists of a pulse amplifier, a pulse-height discriminator (PHD), a logarithmic count r a t e meter of t h e Cooke-Yarborough type, a l i n e a r count r a t e meter, and two calibrat5on o s c i l l a t o r s (10and 1 0 4 counts/sec)

2.3.4.2

Construction

The pulse amplifier and count r a t e meter i s constructed i n a module 5.6 i n . wide, 4.72 in. high, and 11.9 in. deep. It i s a standard "fouru n i t " plug-in module of t h e modular reactor instrumentation s e r i e s depicted on drawings &-2600-1 through &-2600-5. The pulse-height discriminator and the l i n e a r and log count r a t e c i r c u i t s are constructed on one printed c i r c u i t board. The pulse amp l i f i e r and t h e two o s c i l l a t o r s a r e constructed on separate boards. The pulse amplifier and discriminator count r a t e boards are housed i n a cadmium-plated s t e e l compartment which covers the e n t i r e top of the module. The two boards within t h i s compartment are shielded from each other by a cadmium-plated p a r t i t i o n . The o s c i l l a t o r printed c i r c u i t board i s mounted horizontally a t t h e back end of t h e module beneath t h e compartment. The f r o n t panel controls include a ten-turn potentiometer f o r t h e pulse-height discriminator and an 18-position switch f o r amplifier gain control (13 positions) and module c a l i b r a t i o n control. A BNC connector i s mounted on t h e f r o n t panel t o provide a signal f o r a scaler. 2.3.4.3

Application

The pulse amplifier and count r a t e meter i s one element of a widerange counting channel1 f o r monitoring neutron f l u x over a ten-decade span. It amplifies pulses from a f i s s i o n chamber and preamplifier assembly4 and provides logarithmic and l i n e a r count r a t e output signals.

An output pulse i s a l s o provided t o operate a scaler. The pulses from t h e p r e q l i f i e r assembly are bipolar i n shape, which eliminates t h e problem of duty-cycle s h i f t s i n t h e pulse amplifier. The pulse amplifier, however, can be used with positive unipolar pulses. Count r a t e s up t o lo4 counts/sec of unipolar pulses 1 psec wide can be accommodated, with a r e s u l t i n g shif't i n e f f e c t i v e pulse amplitude of less than 1%. The logarithmic output s i g n a l i s a current which drives an external, conventional operational amplifier. The output of t h e operational amp l i f i e r i s used t o operate indicators and other c i r c u i t s . The l i n e a r output signal i s a l s o a current which drives an external, conventional operational amplifier. The output of t h e operational amp l i f i e r i s used t o operate other c i r c u i t s . I n the wide-range counting channel, t h i s l i n e a r signal i s used as t h e control signal f o r a servo system.

124

2.3.4.4

Specifications

Overall specifications f o r t h e pulse amplifier are as follows: Pulse amplifier

Gain Rise time (10 t o 9096) Linear pulse output (1OO-ohm load o r greater) Saturated output Attenuator control

90 5 5 Less than 0.07 psec 0 t o +5 v Less than 7.5 v f o r pulse widths l e s s than 0.5 psec 13-position, 100-ohm ladder tyye a t amplifier input i n 1, 1.5, 2, 3, 5, and 7 sequence

Pulse-height discriminator Range I n t e g r a l nonlinearity (including pulse amplifier)

0.25 t o +5 v with ten-turn Helipot (500 divisions) Less than k0.2$ of 5 v from 0.25 t o 5 v a t 30째C and v a r i e s l e s s than O.O3$/"C of i t s 30째C value between 0 and 50째C

Output pulse f o r s c a l e r Amplitude

+3.5 k 0.25 v i n t o load of 100 ohms

Rise time (10 t o 90$) F a l l time (10 t o 90$) Pulse width

or greater 0.05 psec 0.05 psec (no output cable) Varies with pulse amplitude i n excess of PRD b i a s

Log count r a t e output Range Amplitude Accuracy ( a t 3OoC) Terqperature e f f e c t s

1t o lo5 counts/sec i n f i v e decades o a t 1 count/sec and up t o approx 40 pamp a t lo5 counts/sec Output deviates l e s s than +3$ from the t r u e log reading a t any point with regularly spaced input pulses Output deviates l e s s than 21% from t h e 3OoC value for any temperature from 0 t o 3OoC; from 30 t o 5OoC, output deviates less than +3$ from t h e 3OoC value a t each point

Linear count r a t e output Range Amplitude

0 to 2.5 x ldt counts/sec Approximately 170 pamp a t lCf+ count s/sec

125

Accuracy (at 3OOC)

Temperature e f f e c t s

Output deviates l e s s than the equivalent of rt25 counts/sec from the t r u e counting r a t e from o t o 104 counts/sec with regularly spaced input pulses The deviation of the lo4 count/sec point from i t s 3OoC value i s l e s s than 0.3$/"C from 0 t o 3OoC and l e s s than 0.155/째C from 30 t o 5OoC

Power requirements Voltage Current drain Regulation Ripple

+25 rt 0.01 V; -25 5 0.01 v 75 ma from +25 v supply; 25 m a from -25 v supply +0.04$ o r b e t t e r against r t l % l i n e changes and with load changes from no load t o full load Peak-to-peak ripple l e s s than 0.01 v

10count/sec o s c i l l a t o r

Stability

Thermal e r r o r Output pulse Output pulse load Power supply 104

30 ppm a t 2OoC with v e r t i c a l orientation of spring balance wheel axis; 300 ppm a t 2OoC i n any other orient a t ion ll ppm/OC from 0 t o 3OoC -11.7 v, 6 msec width, l e s s than 20-psec r i s e time (10 t o 9%) 50 kilohms minimun lo$ a t 0.15 ma average; 3-ma -12 v peak per pulse

count/sec o s c i l l a t o r

Calibration accuracy a t

Positive 0.00%;

negative 0.0045

7OoC

Thermal e r r o r Output pulse Output pulse impedance Power swly Ambient temperature range ( a units) ~ 2.3.4.5

4 ppm/OC a t 7OoC 8-v peak-to-peak square wave; l e s s than l-psec r i s e time (10 t o 9 9 ) 800 ohms -12 v f lo$ a t 7 ma 0 t o 55OC

Theory of Operation

General The following description of the module (Fig. 2.3.10) i s divided i n t o f i v e main groups: (1)pulse amplifier and control switch; (2) pulse-height discriminator, which includes the shaper stage and emitterfollower; (3) pump driver, which includes the flip-flop, Q-25 as a

limiter-amplifier, and Q16 and Q17 as t h e complementary emitter-follower drive; (4)pump c i r c u i t s , which include both the l o g and l i n e a r pumps; and (5) t e s t o s c i l l a t o r s .

Pulse Amplifier and Control Switch The pulse amplifier consists of two fed-back groups which are cascaded t o achieve an o v e r a l l gain of 100. Each group has a voltage gain of about 10. These two stages of amplification a r e preceded by a laddertype attenuator, where t h e input impedance i s a constant100 ohms a t all s e t t i n g s and t h e impedance, looking back from t h e amplifier input i s 50 ohms. The attenuator i s p a r t of an 18-position switch t h a t (1)provides attenuation of t h e input s i g n a l i n 13 positions, (2) disconnects t h e amplifier input from t h e attenuator and grounds it through 100 ohms i n two "off" positions, (3) disconnects t h e amplifier from t h e attenuator and applies ldr counts/sec t o i t s input, ( 4 ) disconnects t h e amplifier from t h e attenuator and applies 10 counts/sec t o i t s input, and (5) disconnects t h e amplifier from t h e attenuator and supplies a dc voltage f o r application t o a 5-sec period generator c i r c u i t t h a t i s external t o t h e module. Also, i n a l l positions other than attenuator positions, the control switch provides a dc voltage which actuates a f r o n t panel l i g h t and can be used t o actuate an external alarm. The pulse amplifier design i s t a i l o r e d t o amplify pulses of t h e shape shown i n Fig. 2.3.ll-A. This pulse shape i s produced by a preamplifier which double d i f f e r e n t i a t e s t h e pulses from a f i s s i o n chamber with a 0.125-psec time constant. (The second d i f f e r e n t i a t i o n i s made a t a pulse transformer which terminates t h e balanced transmission l i n e driven by the preamplifier.) The preamplifier has a 0.1-psec integrating time constant. The amplifier may a l s o be used t o a m p l i q unipolar pulses clipped t o 1 psec width or l e s s , with t h e p o s s i b i l i t y t h a t appreciable base-line s h i f t may occur a t counting r a t e s greater than 5 X lo4 counts/sec. Both fed-back groups are of i d e n t i c a l design. Each fed-back group i s a t h r e e - t r a n s i s t o r configuration, w i t h t h e f i r s t two t r a n s i s t o r s Q3 and Q2 constituting a d i f f e r e n t i a l p a i r . The output from t h e second c o l l e c t o r Q2 drives t h e t h i r d t r a n s i s t o r Q3, which i s an emitter-follower. Feedback i s made from t h e emitter of Q3 t o t h e base of Q2. The output s i g n a l is taken f r m t h e emitter-follower, and t h e input s i g n a l drives t h e first base Q of t hl e d i f f e r e n t i a l p a i r . This results i n a group with an output pulse of t h e same p o l a r i t y as that of t h e input signal. The pulse gain of the stage i s very nearly (R6 + R7)/R6, neglecting t h e shunting e f f e c t of R 8 and R6. The measured5 high-frequency feedback f a c t o r f o r t h e stage was 10. The fed-back group i s dc-coupled and has excellent dc s t a b i l i t y by nature of t h e d i f f e r e n t i a l input and a dc feedback f a c t o r i n excess of 100. The b i a s i n t h e amplifier has been selected s o t h a t both positive and negative portions of the bipolar input signal w i l l be clipped proportionakely under overload, thereby retaining i t s b i p o l a r nature.

'The procedure f o r measurement i s given by E. Fairstein, Pulse Amplifier Manual, Om-3348, p. 20 (Oct. 26, 1962).

127

A closed-loop analysis, u t i l i z i n g the hybrid-.sc equivalent c i r c u i t , shows that the predominant time constant i s nearly C ob 6 [(% + R1_5)/R15], where Cob and are t h e c o l l e c t o r t r a n s i t i o n capacitance a i d

base resistance of Q2 respectively. The output impedance of the stage w a s computed t o be 12.6 ohms.6 The ac input impedance of the stage i s very nearly equal t o that of t h e base r e s i s t o r R l of t h e input t r a n s i s t o r Q because l , t h e emitter impedance of Q1 i s R2 (5.1 kilohms) i n p a r a l l e l with t h e looking-in impedance of Q2, which i s nearly 300 ohms because of the feedback t o t h e base of Q2. Thus, w i t h an effective emitter impedance of about 300 ohms, t h e impedance looking i n t o the base of Q i s about l 30 kilohms f o r an hfe of 100. Capacity coupling i s used between t h e two fed-back stages and on t h e output t o t h e pulse-height discriminator. These coupling time cons t a n t s are i n excess of 300 psec, which i s adequate t o eliminate t h e e f f e c t s of any f u r t h e r d i f f e r e n t i a t i o n . The bipolar nature of t h e input s i g n a l eliminates any possible duty-cycle s h i f t s across these capacitors. Pulse-Height Discriminator

The pulse-height discriminator (PHD) i s based on a biased amplifier scheme which i s very similar t o that used i n t h e pulse amplifier. The PHD control potentiometer R26 has t e n turns, and t h e d i a l has 500 divisions. The position of R26 determines the d i f f e r e n t i a l bias t h a t exislx between t h e bases of Q7 and Q8. Since Q8 is conducting a t any p o s i t i o n of t h i s potentiometer, any positive input signal applied t o t h e base of Q7 must exceed t h i s d i f f e r e n t i a l before Q7 i s brought i n t o conduction, a d any portion i n excess of t h i s d i f f e r e n t i a l i s amplified by a f a c t o r of 10. The voltage drop across the PHD potentiometer R26 m u s t be 5 v t o achieve t h e full-range control of 5 v f o r pulse-height discrimination. The voltage can be trimmed t o t h i s value by adjusting R32. The "zero" of t h e PHD can be trimmed by adjusting the values of R24 and R27.

6The output impedance :R

(open c i r c u i t ) (short; circuit)

where A = open-loop gain, 100,

A' = closed-loop gain, 10, RO

= open-loop output impedance.

base impedance of Q3 I n t h i s case, Ro = re + hfe of Q3 = 26

104 += 100

126

ei(A) 7 e A Ro =

128

An ac-coupled Schmitt t r i g g e r i s used t o shape t h e pulse from t h e biased amplifier. The t r i g g e r s e n s i t i v i t y i s 2.5 V. A more s e n s i t i v e t r i g g e r w i l l create s t a b i l i t y problems even though any s e n s i t i v i t y changes are reduced by a f a c t o r of 1 0 when referred t o t h e pulse amplitude. The s e n s i t i v i t y cannot be less than 0.5 v, because t h i s i s about t h e amplitude of "feed-through" pulses of the biased amplifier. Another consideration f o r keeping t h e Schmitt t r i g g e r s e n s i t i v i t y large i s t o r e l a x t h e bandwidth requirements of t h e biased-off amplifier. The triangular-shaped character of t h e positive portion of t h e amplifier pulse places a bandwidth burden on t h e biased-off amplifier f o r t h e pulses which barely exceed t h e threshold level. The l a r g e r t h e pulse required t o actuate t h e Schmitt t r i g g e r , t h e greater t h e output required f r o m t h e biased amplifier. These l a r g e r pulses, because of t h e i r triangular shape, w i l l be wider a t the base l i n e and w i l l require l e s s bandwidth from t h e amplifier. The 2.5-v s e n s i t i v i t y of t h e Schmitt t r i g g e r r e s u l t s i n PHD potentiometer control t h a t is ineffective below a pulse amplitude of 0.25 V. This i s only 5% of t h e 5-v full range and is considered t o be only a minor limitation. Trigger s e n s i t i v i t i e s i n excess of 2.5 v would r e s u l t i n even l e s s usable portions of t h e PHD potentiometer and would not be desirable. Transistor Q7 of the biased amplifier must have a base-to-emitter breakdown voltage greater than 5 V. The 2N2432 t r a n s i s t o r designed f o r rating. inverted chopper applications has a 15-v BV

EBO

The pulse out of t h e Schmitt t r i g g e r is applied t o emitter-follower QJ.2. The magnitude of t h i s pulse i s +3.5 v, and i t s width depends on t h e amount t h a t the pulse amplifier pulse exceeds t h e b i a s s e t t i n g (of t h e PHD). The emitter-follower output drives t h e succeeding binary stage and an external scaler. The recovery of t h e pulse a t t h e emitterfollower w i l l be slow a t the termination of each pulse i f an unterminated cable i s used t o make connection t o a scaler, because t h e charged cable w i l l hold Q12 off and m u s t be discharged through R47, a 6.2kilohm r e s i s t o r . hrmp Driver

The pulse f r o m t h e Schmitt t r i g g e r and i t s emitter-follower does not have t h e proper amplitude o r t h e width t o drive t h e l o g and l i n e a r pumps. A binary stage (also c a l l e d a f l i p - f l o p ) i s used t o f u r t h e r shape the pulse. The output pulse of t h e f l i p - f l o p i s rectangular, having a width equal t o t h e time elapsed between two successive pulses. This method of shaping automatically provides t h e pump c i r c u i t s with wide pulses without any increase in dead-time losses. The consequent division of t h e pulse rate by a f a c t o r of 2 must, of course, be considered i n t h e pump design. The f l i p - f l o p design composed of Q13 and Q14 i s a saturated type (i.e., t h e "on" t r a n s i s t o r i s driven i n t o saturation) with resolution c a p a b i l i t i e s of lo7 counts/sec. When e i t h e r Ql3 o r QJ.4i s "on, t h e other i s "off." The p o s i t i v e pulse from t h e emitter-follower a c t s t o turn t h e "on" t r a n s i s t o r off, and t h e regenerative nature of t h e c i r c u i t then switches t h e s t a t e of t h e flip-flop. Diodes D2 and D6 serve t o s t e e r o r apply t h e pulse t o t h e base of t h e "on" t r a n s i s t o r . To understand how t h e s t e e r i n g i s achieved, assume Q13 t o be "on" and QJ.4t o be

129 If

off." The c o l l e c t o r of Q13 w i l l be near +8.5 v, and t h e c o l l e c t o r of &I4 w i l l be near ground. Diodes D6 and D5 a r e i n s e r i e s and are back biased by t h e difference i n p o t e n t i a l between t h e c o l l e c t o r and base of &I4 (about 8.5 v). The base of QJ4 i s clamped t o a p o t e n t i a l slightly more p o s i t i v e than +8.5 v by D4. (The only purpose f o r D 3 and D4 i s t o l i m i t t h e back b i a s applied t o Q13 and Ql4 when they are turned off. With these diodes t h e back b i a s can never exceed about 0.5 v.) I n contrast, diodes D 1 and D2, which are a l s o i n s e r i e s , are only back biased by a few t e n t h s of a volt. Thus, a positive input pulse w i l l take t h e route through D2 (and t o t h e base of t h e "on" t r a n s i s t o r ) i n preference t o that through D6 because of t h e greater b i a s on D6. Diodes D1 and D5 a i d i n another manner. They help discharge cap a c i t o r s C19 and C20, respectively, by providing a low-impedance path t o C21 ( a 2.2-pf capacitor) through t h e c o l l e c t o r of t h e "on" t r a n s i s t o r between input pulses. These capacitors w i l l acquire some charge as t h e input s i g n a l proceeds t o t u r n off t h e "on" t r a n s i s t o r and, i f permitted t o accumulate o r t o not s u f f i c i e n t l y recover, can cause a malfunction of t h e f l i p - f l o p . The c o l l e c t o r swing of Ql3 and QJ4 i s approximately 8 V. This value i s marginal t o provide r e l i a b l e operation of a pump c i r c u i t . Also, t h e pump c i r c u i t input impedance i s quite low and would d r a s t i c a l l y load t h e f l i p - f l o p and impair i t s speed. Thus, some f u r t h e r amplification i s s t i l l required, and some impedance i s o l a t i o n i s needed. It should be recognized t h a t any amplification process must a l s o achieve high amplitude s t a b i l i t y t o achieve good pump performance. Transistors Ql5, Ql7, and Ql6, along with diodes D13, D14, D15, D16, and D17, a r e used t o perform t h i s task. Diodes D 1 3 and D14 are fast-recovery conventional diodes, and diodes D15, D16, and D 1 7 are 5.2-v Zener diodes. The r o l e of D 7 w i l l be explained below. Amplification w i t h controlled amplitude is accomplished by Ql5, t h e two fast diodes, and t h e three Zener diodes. The c o l l e c t o r current; of QJ4 forward-biases diode D7 and t u r n s QJ5 off "hard." The collectolof Q15 i s caught a t approximately -17 v by the s e r i e s s t r i n g of t h e two fast diodes and t h e three 5.2-v Zener diodes. When Q14 i s turned o f f , D 7 i s released and Q15 i s turned on "hard" by t h e base drive through R53. Thus, t h e c o l l e c t o r swing o f 615 is from -17 v t o e s s e n t i a l l y 0 v. The two diodes i n s e r i e s with t h e Zener diodes i s o l a t e the l a r g e capacitance of t h e Zener diodes from t h e c o l l e c t o r of Ql5, permitting fast r i s e and f a l l times. One diode is adequate f o r t h i s i s o l a t i o n , but two diodes give b e t t e r temperature compensation f o r diode e f f e c t s on t h e diode pumps. The Zener diodes have a specified r a t i n g of 0.005$ per O C change, and the v a r i a t i o n of t h e saturation voltage of QJ5 i s l e s s than a few tenths of a m i l l i v o l t per O C . It should be apparent t h a t t h e scheme just described i s one where t h e c o l l e c t o r current of Q14 i s sampled, r a t h e r than i t s c o l l e c t o r voltage, s o t h a t amplification is not achieved i n t h e usual sense. How ever, t h e method employed i s one where no loading i s placed on t h e f l i p flop, permitting it t o operate a t maximum speed. 7 comprise a complementary emitter-follower Transistors Q16 and a driving stage which applies t h e 17-v pulses t o t h e pump c i r c u i t s . The necessity of a complementary design over t h a t of a single emitter-follower can be explained i f we momentarily include t h e pump c i r c u i t s i n

130

t h e discussion. The following section w i l l discuss these i n greater d e t a i l . The negative-going s t e p of t h e 17-v pulse proceeds t o charge t h e feed capacitors of t h e pump c i r c u i t s (C26 through C30 f o r the l o g pumps and C39 f o r t h e l i n e a r pump) through t h e i r respective diodes (D18, D20, D22, D26, D28, and D32) t o t h e f u l l 17 v. On t h e positivegoing edge of t h e pulse (or t h e r e t u r n t o ground), these capacitors must now be discharged quickly t o 0 v t o be prepared f o r t h e next pulse. This discharge path must proceed through t h e second diode of each pump i n t o t h e smoothing capacitor o r output capacitor of each pump f o r proper action of t h e pump. A t t h i s time Ql7 i s biased off and cannot provide t h i s discharge. Q 7l i s off, since i t s base i s a t o r near ground, and i t s emitter i s a t -17 v because t h e feed capacitor i s behaving as a 17-v battery. With Ql6 i n the c i r c u i t as t h e NPN complement, it w i l l be biased "on" and w i l l permit the feed capacitor t o discharge.

Pum Circuits

The l o g pump design i s composed of s i x pumps Logarithmic P m p s . and i s based on the e a r l i e r work of Cooke-Yarb~rough.~The dc currents from each pump are summed a t t h e common junction of R88, R90, R92, R94, R96, and R98 and are delivered t o t h e summing junction of an external ope r a t i o n a l amplifier. The composite response of s i x pumps i s shown i n Since the output voltage of each putq i s positive, the Fig. 2.3.12. conventional current flow w i l l be out of these r e s i s t o r s . An additional current of opposite p o l a r i t y i s supplied through Rll3 and i s adjustable by t h e "calibrate" control potentiometer RIJ-2. The gain of t h e external amplifier and hence t h e "span" of t h e log count r a t e meter are cont r o l l e d by t h e p a r a l l e l combination of Rll5 and FUl.6. For trimming purposes the value of Rll6 i s adjusted. A 250-kilohm feedback r e s i s t o r f o r t h e operational amplifier, in addition t o a 1-kilohm r e s i s t o r which forms a voltage divider network with R115 and Rll6, i s located a t t h e operational amplifier. I f these r e s i s t o r s were located i n t h e pulse amplifier and count r a t e meter module and the module were unplugged, it would open-circuit t h e feedback loop on t h e operational amplifier and cause t h e operational amplifier t o saturate. It i s not advisable t o leave these amplifiers i n t h i s s t a t e f o r extended periods of time. The operation of the pump c i r c u i t , discussed b r i e f l y i n t h e preceding section, w i l l be described i n more d e t a i l here. A s charge from the feed capacitor i s t r a n s f e r r e d t o t h e smoothing capacitors C32 through C37, a voltage i s developed across these capacitors which causes t h e current flow through any shunt resistance such as R88 and R87 of t h e f i r s t pump. R88 i s essentially returned t o ground since it i s t i e d t o t h e summing junction (a v i r t u a l ground) of t h e external operational amplifier. A t a steady count r a t e , t h e r e i s an equilibrium condition established where t h e r a t e of charge, or current inflow, is equal t o the current outflow, and a steady dc voltage (with superimposed statist i c a v a r i a t i o n ) i s established across each smoothing capacitor.

7E. H. Cooke-Yarborough and E. W. Pulsford, "An Accurate Logarithmic Counting Rate Meter Covering a Wide Range," R o c . IEEE, P a r t 11, 98, 1 9 6 2 0 3 (April 1951).

131

The voltage on each smoothing capacitor w i l l bear the relationship'

vinRc v0 =

1 + nRc

where vi

= input pulse amplitude,

n = detector count r a t e divided by 2, C = capacity of feed capacitor, R = t o t a l shunt resistance across smoothing capacitor.

This response i s shown graphically by any of t h e s i x curves i n For s m a l l values of n, where nRC i s smcompared w i t h Fig. 2.3.12. unity, t h e response i s nearly l i n e a r as a function of n, t h e count r a t e . A s n becomes l a r g e r , t h e response becomes nonlinear (appearing t o be l i n e a r on a semilog p l o t ) and ultimately reaches a saturation value of V. when nRC i s much greater than unity, A s t h e count r a t e increases, 1

each pump becomes successively saturated (pumps with t h e l a r g e s t RC product s a t u r a t e f i r s t ) , r e s a t i n g i n a constant output current from each pump. The Cooke-Yarborough principle w i l l show end e f f e c t s when a limited number of pumps are used t o approximate t h e logarithmic response. To compensate f o r t h i s , t h e two end pumps deliver about lo$ more current than t h e four middle pumps. This i s accomplished by making t h e value of t h e feed r e s i s t o r s R 8 8 and R98 smaller than that of t h e other four feed r e s i s t o r s R90, R92, R94, and R96. The values of t h e shunt res i s t o r s R87, R89, R91, R93, R95, and R97 are adjusted t o keep t h e pump time constant RC a t values which d i f f e r by a f a c t o r of 10.

'The derivation i s as follows:

v = ioR 0

where

Thus v

= (Vi

- vo)nCR

vim

-1+nRc*

132

The value of the t o t a l shunt resistance R across each smoothing capacitor w a s made as s m a l l as possible, but s t i l l permitting reasonable values of smoothing capacitors (i.e., values l e s s than 100 pf). The product of the resistance and t h e smoothing capacitor values determines the s t a t i s t i c a l noise superimposed on t h e dc current. The values shown were determined by experiment on t h e complete wide-range counting channel. The f i r s t three time constants involving C32, R33, and C34 were selected t o keep t h e period noise a t reasonable values while the widerange counting channel w a s behaving as a straight counting instrument. The remaining three time constants were selected t o optimize the speed of response of t h e counting channel. The leakage of t h e smoothing capacitors and diodes D19, D21, D23, D25, D27, and D29 behaves as an additional shunt resistance across t h e various pump outputs. The lN914A i s specified t o have a maximum leakage of 0.025 pa at a reverse bias of 20 v a t 2OoC. This w i l l have negligible e f f e c t on t h e performance of t h e pumps. The e l e c t r o l y t i c capacitors C32, C33, and C34 were purchased with a specified leakage not t o exceed 0.2 pa a t 25OC a t a working voltage of 20 v, which i s equivalent t o a dc leakage resistance of 100 megohms. A reduction i n leakage resistance t o 50 megohms would represent an e r r o r of 2.5% of reading over only a s m a l l range of the scale. Also, e r r o r s caused by leakage of t h e capaci t o r s w i l l not accumulate, because as each pump goes i n t o saturation, i t s output current i s a function of only t h e pulse amplitude and t h e junction of t h e operamagnitude of t h e r e s i s t o r feeding t h e s-ng t i o n a l amplifier. I n addition, any e r r o r s caused by t h e three electrol y t i c capacitors, since they apply t o t h e pumps a t t h e l o w end of t h e scale, are negligible a t the high end. The other c r i t i c a l components of t h e various pumps, such as the feed capacitor and output r e s i s t o r s , are high-quality, h i g h - s t a b i l i t y 'I$ components, o r b e t t e r . The e f f e c t of t h e v a r i a t i o n of diode p o t e n t i a l s i n t h e pump i s equivalent t o a v a r i a t i o n of t h e amplitude of t h e input pulse. The e f f e c t i s such t h a t , a t higher temperatures, t h e input pulse appears bigger and there i s greater output from t h e pump. More clearly, as the forward drop of D 1 8 reduces with a temperature increase, t h e feed cap a c i t o r w i l l charge t o a l a r g e r voltage. Also, t h e forward drop across D 1 8 i s l e s s , and more charge i s transferred. The two diodes D 1 3 and D 1 4 i n s e r i e s with t h e three 5.2-v Zener diodes have a tendency t o compensate f o r t h i s . A s t h e temperature r i s e s , t h e forward drop of these two diodes w i l l be l e s s and w i l l result i n a reduced pulse amplitude. Linear S. The l i n e a r pump c i r c u i t i s designed t o give a l i n e a r output c u r r e z i g n a l up t o a value of about 170 pa f o r lo4 counts/sec. This current i s fed through R99, a 10-kilohm r e s i s t o r , i n t o the summing junction of an e x t e r n d operationaJ. amplifier. This amounts t o a voltage of +1.7 v a t t h e output of the pump. Without my attempt (such as bootstrapping) t o improve l i n e a r i t y , t h e output s i g n a l would depart from l i n e a r i t y by nearly 9%. This can be computed from t h e general count rate expression given i n t h e preceding

133

section with RC = (R99)(C39) = (104)â&#x20AC;&#x2122;(0.002Z)(104) and n = 5 x lo3 counts/sec. The bootstrapping c i r c u i t consisting of a 8 and a 9 serves t o e f f e c t i v e l y increase t h e magnitude of t h e input pulse by an mount equal t o t h e output dc voltage. D i s c o k t i n g t h e s m a l l drop i n Rl.17, any change i n t h e output voltage appears a t t h e anode of D32 and i s i n a d i r e c t i o n t o increase the voltage t o which the feed capacitor i s charged with each input pulse. Thus, t h e output current without bootstrapping i s

This becomes

which i s independent of vo. Here all terms have t h e same meaning as i n t h e preceding section. The cascaded emitter-follower arrangement (Darlington p a i r ) i s used t o r a i s e t h e looking-in impedance of t h e bootstrapping c i r c u i t , thereby reducing i t s loading e f f e c t on t h e output voltage. The voltage drop of t h e base-to-emitter voltages of QJ8 and QJ9 plus t h e drop across Rll7 i s of s u f f i c i e n t magnitude t o ensure t h a t D 3 1 i s s u f f i c i e n t l y back biased during t h e charging time of the feed capacitor t o avoid a leakcage of charge from the smoothing capacitor. Temperature e f f e c t s i n t h e l i n e a r diode pump are due primarily t o changes i n the two diodes D 3 1 and D32. Variation i n t h e forward voltages of these two diodes i s compensated f o r by changes i n input pulse amplitude i n a manner described i n t h e preceding section. Diode leakage currents and leakage i n t h e e l e c t r o l y t i c smoothing capacitors are negligible, p a r t i c u l a r l y since the value of t h e output r e s i s t o r i s only 1 0 kilohms Temperature e f f e c t s caused by t h e bootstrapping scheme are small, but are not negligible. Vbe changes of QJ.8 and QJ9 w i l l have a signif-

i c a n t e f f e c t on t h e output. These changes w i l l predominantly show up as a change i n emitter p o t e n t i a l of QJ9 of about 4 mv/OC. Only slight changes of Vbe due t o temperature are seen a t t h e base of QJ8, because t h e 10-kilohm base impedance of QJ.8 i s so much smaller than t h e lookingi n impedance of Ql8. The variations a t t h e emitter of Q 9J w i l l change t h e magnitude of t h e bootstrapping voltage with temperature. A t 5OoC (assuming 4 mv/OC) t h e change i n bootstrapping signal from t h e 3OoC value i s 120 mv, which i s a change i n output signal of [0.120/(17 X 20)]100, o r O.O3$/OC, where 17 v i s t h e amplitude of t h e input pulse. This change i s i n a d i r e c t i o n t o increase t h e output signal. I f t h e output s i g n a l from t h e bootstrapped configuration had been taken from value w i l l be increased by an addithe emitter of Q19, the 0 . 0 3 f ~ / ~ C

134

t i o n a l [0.120/(1.7 x 20)]100, o r 0.3$/"C, a t lol. counts/sec. This occurs because t h e pump output voltage (1.7 v a t 10" counts/sec) receives the f u l l e f f e c t of t h e Vbe changes. The a c t u a l temperature d r i f t observed on t h e pump operating at lo4 counts/sec i s t h r e e times worse than 0.03$/"C. A t 5000 counts/sec t h e The cause of the increased measured d r i f t i s more nearly O.O3$/'C. d r i f t a t the 104-count/sec rate, which nearly amounts t o an additional 2 mv/'c, i s not d e f i n i t e l y known. and t h e base current of Q18 w i l l flow through R99 i n t o the IC0

summing junction of t h e external amplifier and appear as s i g n a l currents. e f f e c t s w i l l be negligible, because 0.001 pa i s t y p i c a l f o r &18 and

IC0

Q l 9 ("N s i l i c o n ) .

Temperature e f f e c t s on

% are

a l s o s m a l l , since the

base current of Ql8 i s about 0.5 pa o r about 0.3% of t h e f u l l - s c a l e output (i.e., 170 pa a t lo4 counts/sec). The value varies about 0.4%/OC i n t h e range 0 t o 50'C.

Test Oscillators

10-count/sec Oscillator. This i s a Swiss-made (Zenith model E59GJ) electromechanical o s c i l l a t o r w i t h a spring balance wheel mounted i n ruby bearings. The spring balance wheel i s driven by an electronic c i r c u i t containing two t r a n s i s t o r s and two c o i l s . The t w o c o i l s a r e fixed and a r e located c o a x i a l l y above and below a permanent magnet s e t i n the rim of t h e balance wheel. The a x i s of t h e magnet i s p a r a l l e l t o the a x i s of r o t a t i o n of t h e spring balance wheel. A s t h e magnet passes through t h e region between t h e c o i l s , a voltage induced i n one c o i l (the pickup c o i l ) t u r n s on a t r a n s i s t o r amplifier which has t h e second c o i l (the drive c o i l ) as a c o l l e c t o r load. The current i n t h e drive c o i l imparts a force t o t h e balance wheel i n a d i r e c t i o n t o s u s t a i n i t s movement. The output pulse is taken from t h e c o l l e c t o r of t h e amplifier t r a n s i s t o r . The other t r a n s i s t o r i s connected as an emitter-follower and provides t h e necessary power amplification f o r the s i g n a l from t h e pickup c o i l . The o s c i l l a t o r produces an output pulse of t h e same p o l a r i t y each time t h e magnet passes under t h e c o i l s . This r e s u l t s i n two pulses f o r each complete cycle. The time duration between successive pulses can d i f f e r by as much as 3 msec; however, t h e sum of t h e two i n t e r v a l s remains precisely a t 0.1sec (i.e., a lo-count/sec r a t e ) . m e v a r i a t i o n i n time duration a r i s e s because t h e spring on t h e balance wheel i s wound i n one d i r e c t i o n and i s unwound i n t h e other direction. l@-count/sec Oscillator. The 104-count/sec o s c i l l a t o r i s crystalcontrolled by a 104-count/sec quartz c r y s t a l . The o s c i l l a t o r consists of an Engineered Electronics Campany. (EECO) plug-in u n i t T-107, requiring a standard nine-pin miniature tube socket. The quartz c r y s t a l (EECO tyye Hl45-31) i s mounted separately. The T-107 unit contains three t r a n s i s t o r s , two of which are used as a two-stage common emitter amplifier with feedback f r o m t h e second c o l l e c t o r t o t h e first base through t h e inrpedance of t h e crystal. There i s a f u l l 360' phase s h i f t , and t h e c i r c u i t w i l l o s c i l l a t e a t a frequency which experiences n e i t h e r phase s h i f t nor appreciable attenuation through t h e c r y s t a l . The t h i r d t r a n s i s t o r serves as an emitter-follower output stage.

135

Oscillator Shaper. Since t h e output waveforms of t h e 10- and t h e 104-count/sec o s c i l l a t o r s are widely d i f f e r e n t , preshaping i s required i f a uniform pulse i s t o be applied t o the pulse amplifier. Q20 and Q2l form a conventional Schmitt t r i g g e r f o r t h i s purpose. Q U i s normally on and Q20 i s off. The s e n s i t i v i t y i s such t h a t about 4 v i s needed f o r triggering. The output pulse from t h e c o l l e c t o r of Q21 i s EL positive pulse which i s sharply d i f f e r e n t i a t e d by C 3 8 and R86. The r e s u l t a n t pulse i s about 0.1 v i n amplitude. A negative pulse of about t h e same amplitude i s obtained, but it i s of the wrong p o l a r i t y t o t r i g g e r the pulse-height discriminator.

2.3.5 2.3.5.1

0.1-hp Servo Amplifier, OIWL Model Q-2615

General

The 0.1-hp dc servo amplifier i s a dc power amplifier t h a t can supply a maximum of 75 w power a t voltage and current limits of 25 v and 5 amp respectively.

2.3.5.2

Construction

The servo amplifier i s constructed i n a module 4.22 in. wide, 4.72 in. high, and l l . 9 in. deep. It i s a standard "three-unit" plug-in module of t h e modular reactor instrumentation s e r i e s depicted on drawings Q-2600-1 through Q-2600-5. The four output t r a n s i s t o r s are mounted on separate heat sinks; these are supported by four rods that connect t h e f r o n t and back p l a t e s of the module. The four intermediate t r a n s i s t o r s of t h e amplifier are mounted on smaller separate heat sinks; these are clustered on a metal p l a t e supported by t h e four t i e rods. The input t r a n s i s t o r and most of the other components of t h e amp l i f i e r are mounted on a printed c i r c u i t board near the f r o n t panel of t h e module. The s e r i e s l i m i t i n g r e s i s t o r s f o r t h e output t r a n s i s t o r s are mounted on t h e r e a r plate. A l l decoupling r e s i s t o r s and capacitors are mounted on a metal p l a t e supported by the four t i e rods and located neaz t h e r e a r of t h e module. This metal p l a t e also shields t h e amplifier from the heat t h a t i s dissipated i n t h e l i m i t i n g r e s i s t o r s .

2.3.5.3

Application

The servo amplifier drives a Globe Industries, Inc., type BD dc motor with a 27-v armature. It can drive t h i s motor under a U cond i t i o n s from no load t o blocked rotor. The motor i s used as the servo motor t o position a f i s s i o n chamber i n a wide-range counting channel.

2.3.5.4

Specifications

Specifications f o r the 0.1-hp dc servo amplifier are as follows:

* 1%

Voltage gain

3 v/v

M a x i m u m l i n e a r output (supply voltage 2 32 v)

k28 v a t no load; +25 v w i t h 12-ohm r e s i s t i v e load; and +15 v w i t h 3-ohm r e s i s t i v e load

noninverting

136

Nonlinearity (with 12-ohm r e s i s t i v e load)

Less than 0.1 v deviation from straight l i n e drawn between maximum positive and negative outputs

Maximum power output Output impedance Input impedance

75 w

Input dc o f f s e t (input voltage f o r zero output)

30 milliohms 4700 ohms f o r signals not exceeding +lo v Negative 0.8 v

Transient response

Rise time (10 t o 90$) l e s s than 2 m e c f o r input s t e p

Zero d r i f t with temperature

Less than 9 mv/'C from 0 t o 50'C; the output decreases as t h e temperature r i s e s

Power supply requirements Voltage Current drain

Positive and negative 32 v 5 4 v 58mpmaximum

Ambient temperature range

0 t o 55OC

2.3.5.5

Theory of Operation

General The 0.1-hp dc servo amplifier i s a dc-coupled amplifier with feedback around two voltage-gain stages and two cascaded emitter-followers. The emitter-follower stages are complementary NPN and PNP p a i r s t o perm i t t h e output t o swing negative and positive with respect t o ground. The l a s t emitter-follower stage i s a parallel combination of two t r a n s i s t o r s t o increase i t s power handling c a p a b i l i t i e s . Circuit Description Reference i s made t o Instrumentation and Controls drawing Q-2615-1. The input s i g n a l is applied t o t h e base of Ql, a PNP s i l i c o n t r a n s i s t o r . A 1-kiloha r e s i s t o r R2 i n series with t h e base limits t h e maximun load placed on t h e input s i g n d in t h e event of any f a i l u r e i n t h e servo smplifier. Diode D2 limits t h e base-to-emitter voltage on Ql when l a r g e negative input signals are applied under blocked r o t o r conditions. Negative feedback is applied t o t h e emitter of Ql through t h e res i s t i v e network R3 and R8. The feedback r a t i o i s R3/(R3 f R8), which gives a closed-loop voltage gain of approximately 3. The c i r c u i t shown produces a dc o f f s e t between input and output. With no input, t h e voltages w i l l be as shown (f2.4 v on t h e output and 0 v on t h e input). For t h e output t o be a t a zero potential, t h e base in a l of t h e input t r a n s i s t o r m u s t be a t a negative 0.8 v t o keep Q conducting s t a t e .

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Voltage gain i n the loop i s obtained from Ql and Q2. Q3 i s a curr e n t source which functions as a high-impedance c o l l e c t o r load f o r Q2 while s t i l l providing adequate current t o drive t h e emitter-follower stages under all d e s i a conditions. When t h e servo amplifier i s driving positive w i t h respect t o ground, p a r t of the c o l l e c t o r current of Q3 i s diverted i n t o t h e base of Q5. When the servo amplifier i s driving nega t i v e w i t h respect t o ground, all the Q3 c o l l e c t o r current flows through Q2, and Q2 must be capable of handling t h i s current plus the required drive current i n t o t h e base of Q4. Transistor Q4 and t r a n s i s t o r s Q6 and Q8 i n p a r a l l e l function as an emitter-follower chain; they operate when t h e servo amplifier i s driving negative with respect t o ground. Transistor Q5 and t r a n s i s t o r s Q7 and Q9 i n p a r a l l e l operate when t h e servo amplifier i s driving positive with respect t o ground. The t r a n s i s t o r not operating i s held in a backbiased s t a t e by the base-to-emitter voltage of i t s complement. Diode D 1 i n t h e emitter of Q2 permits Q2 t o be turned off "hard" when t h e amplifier i s delivering i t s f u l l positive output. Any s m a l l c o l l e c t o r current could create a large dissipation i n Q2, since Q2 w i l l have i n excess of 60 v from c o l l e c t o r t o emitter. Capacitor C1, connected from t h e base t o t h e c o l l e c t o r of Q2, along with t h e c o l l e c t o r m e d a n c e of Ql, shapes the open-loop response t o improve t h e high-frequency s t a b i l i t y . The t o t a l capacitance a t t h e coll e c t o r of Ql i s increased i n magnitude by t h e Miller e f f e c t . This results i n a smaller value of capacitance f o r the same shaping of the open-loop response. This i n t e r n a l time constant, coupled w i t h t h e compensating e f f e c t of C 2 across R8, s t a b i l i z e s the amplifier over i t s e n t i r e range of operation with as much as 0.22 pf capacitance i n shunt w i t h t h e output. The behavior of the amplifier with a s t e p input s i g n a l i s d i f f e r e n t w i t h positive and negative input signals. With a negative input step, QJ and Q2 are immediately driven i n t o a higher conducting s t a t e , and the output r i s e time i s exponential i n character and i s controlled primarily by the value of C2. With a positive step, QJ and Q2 are both immediately turned o f f i n the absence of a return s i g n a l f r o m t h e feedback network. Thus, t h e current from Q,3 flows i n t o C1, generating a ramp u n t i l there i s s u f f i c i e n t signal from t h e feedback network t o return Q t o a conl ducting s t a t e and thereby restore t h e closed loop. Under these cond i t i o n s the output wave shape w i l l have a ramp-type leading edge. Resistors R9 and FU2 i n t h e emitter of Q6 and Q8 tend t o balance the current contribution of each t r a n s i s t o r , even with l a r g e differences i n t r a n s i s t o r parameters, such as current gain and transconductance. Resistors FUO and a 3 are used f o r t h e same purpose with t r a n s i s t o r s Q? and Q9. Resistor R11, which i s a s e r i e s combination of three 1-ohm r e s i s t o r s , p r o t e c t s t r a n s i s t o r s Q6 and Q8 under severe load conditions. With a blocked r o t o r condition t h e Globe Industries type BD motor w i l l behave as a >ohm load, and t h e maximum dissipation possible i n e i t h e r p a r a l l e l t r a n s i s t o r is about 27 W. This i s assuming supply voltages of +36 v. These p o t e n t i a l s are possible when t h e b a t t e r i e s t h a t normally power t h i s module are full3r charged. Resistor RI.4 provides similar protection f o r t r a n s i s t o r s Q7 and Q9.

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The c o l l e c t o r s of Q4 and Q5!, are connected t o r e s i s t o r s FUl and Rl4 respectively. This prevents damage t o these t r a n s i s t o r s under overload conditions. 2.3.6 2.3.6.1

Vernistat

General

The Vernistat adjustable function generator i s composed of two separate, but integral, units: a function adjusting assembly and an interpolating Vernistat potentiometer. A function i s s e t up simply by manually adjusting t h e positions of s l i d e r s on t h e function adjusting assembly panel. The panel i s marked off i n rectangular coordinates, w i t h percent output as t h e ordinate and s h a f t position as t h e abscissa. The s l i d e r s provide a v i s u a l p l o t of the f'unction t h a t is s e t i n t o the function generator. By r o t a t i o n of t h e s h a f t of t h e interpolating Vernistat with an e x c i t a t i o n voltage applied, t h e output voltage curve conforms t o a s e r i e s of s t r a i g h t - l i n e interpolations between voltages s e t up by t h e s l i d e r . Clockwise r o t a t i o n scans t h e function from l e f t t o right (i.e., from s l i d e r 1 t o s l i d e r 34). 2.3.6.2

Construction

Vernistat Function Adjusting Assembly The function adjusting assembly i s approximately 1 b y 7 by 8 in. and contains (1) a l o l - t a p voltage divider; (2) a %-pole, 101-position printed-circuit switch; and (3) a function adjusting panel. The voltage divider has a t o t a l of 101 equally spaced taps. These taps divide t h e input voltage i n t o 100 equal voltage increments. The 34-pole, 101-position switch i s a rectangular coordinate array. A printed-circuit g r i d consists of 101 p a r a l l e l l i n e s connected sequent i a l l y t o t h e voltage-divider taps. Each of t h e 34 s l i d i n g contacts can be moved independently across t h e grid l i n e s s o t h a t each s l i d e r may contact any of the 101 voltage divider taps. The voltage divider taps are spaced a t 1% increments, and therefore any voltage may be selected t o within +0.5$1. A panel, marked off in r e c t a n w a r coordinates, mounts d i r e c t l y over the printed c i r c u i t switch so t h a t t h e 34 sliders protrude through s l o t s i n t h e panel and can be manually adjusted. The Y axis i s proportional t o voltage, and t h e X a x i s i s proportional t o t h e position of t h e interpolating Vernistat shaft. The X a x i s represents a range of approximately 11 shaft turns. Interpolating Ve r n i st a t Potentiometer The interpolating Vernistat consists of (1) a s e r i e s of commutator bars which correspond t o t h e s l i d e r s of t h e function adjusting assembly, (2) a switching mechanism, and (3) a 360째 t o r o i d a l resistance element precisely tapped a t 120' intervals. Connection of the function adjusting assembly t o t h e commutator bars of the interpolating Vernistat is made through a multiconductor cable. This cable i s an i n t e g r a l p a r t of the

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interpolating Vernistat and plugs i n t o t h e function adjusting assembly. This i s t h e only connection made t o the function adjusting assembly. Rotation of t h e s h a f t of t h e interpolating Vernistat switches t h e t a p s of t h e interpolating resistance element one a t a time along t h e commutator and simultaneously controls t h e potentiometer output wiper. There a r e approximately three interpolations per s h a f t t u r n of t h e interpolating Vernistat

2.3.6.3

Application

The Vernistat adjustable function generator provides a convenient means of generating mathematical and empirical. nonlinear functions. The function generator i s used i n t h e wide-range counting instrument t o modify a l i n e a r position s i g n a l so t h a t it i s equal t o t h e logarithm of t h e neutron attenuation. 2.3.6.4

Specifications

Overall specifications for the Vernistat function assembly are given below: Vernistat Function Adjusting Assembly

Adjustable points on r o t a t i o n axis

Resolution of s l i d e r adjustment

Maximum input voltage

50 v

Ambient temperature range

0 t o 55OC

Interpolating Vernistat Potentiometers ( s i z e 18, U - t u r n continuous rotation units) Linearity Maximum output impedance

-t-0.02$

Minimum output-voltage increment

O.Ol$

Ambient temperature range

0 t o 55OC

2.3.6.5

540 ohms

Applicable Drawings

The Instrumentation and Controls Division drawing number and subt i t l e for t h e Vernistat adjustable function generator i s &-2616-1, Circuit. 2.3.6.6

Theory of Operation

Figure 2.3.13 shows t h e electrical. r e l a t i o n of t h e Vernistat int e r p o l a t o r commutator bars, interpolating resistance element, and output wiper. By synchronization of the switching of the interpolating resistance element taps along t h e commutator bars with the movement of t h e potentiometer wiper arm, the voltage output becomes a s e r i e s of

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l i n e a r voltage interpolations between adjacent commutator bars. The interpolating resistance element, used r e p e t i t i v e l y f o r each s h a f t turn, i s a 360' t o r o i d a l potentiometer precisely tapped a t 120' i n t e r v a l s . Switching of resistance element t a p s from one commutator bar t o t h e next only requires about 30' of shaft rotation, whereas a complete interpolation requires approximately 120'. Theref ore, t h e switching process of t h e interpolating resistance element i s a n o n c r i t i c a l operation. No discontinuities of output occur, since i n each instance as t h e output wiper approaches a new commutator bar, t h e next interpolating resistance element section i s already i n position. Switching of t h e taps of t h e interpolating resistance element along t h e commutator bars i s accomplished with a planetary gear reduction. The output wiper i s s o synchronized with the switching operation t h a t it i s always on an energized section of the resistance element. This r e s u l t s i n continuous, smooth interpolation throughout t h e output voltage range. The heart of t h e switching mechanism is a planetary gear reduction t h a t consists of three elements: an i n t e r n a l tooth gear with as many t e e t h as there are commutator bars, a planetary gear with one tooth l e s s , and an eccentric on the shaft which keeps t h e two gears i n mesh. These gears are shown schematically by t h e eccentric c i r c l e s i n Fig. 2.3.13. Because of the one-tooth difference, one shaft r o t a t i o n results i n a counterrotation of t h e planetary gear, which i s equivalent t o t h e angular spacing between commutator bars. The resistance element i s mounted on t h e planetary gear and r o t a t e s with it a t a reduced speed. The commutator wipers, connected t o t h e resistance element taps, are a l s o mounted on t h e planetary gear. The output wiper i s attached t o t h e Vernistat shaft. Because t h e resistance element rotates, t h e output wiper moves from one t a p t o t h e next i n less than 120' of t h e shaft rotation. The 34 s l i d e r s of the function adjusting assembly equal t h e number of commutator bars i n t h e interpolating Vernistat. Eleven s h a f t t u r n s (3960') are required t o generate an e n t i r e 34-chord function. Each chord represents 116.47' (3960'/34) of shaft rotation. S l i d e r s 34 and 1 are adjacent e l e c t r i c a l l y ; therefore, a r e p e t i t i v e function may be generated by continuous r o t a t i o n of t h e input s h a f t . 2.3.7 2.3.7.1

Dual DC Amplifier

General

The ORNL m o d e l Q-2605-1 dual dc amplifier i s designed and manufactured by Electronic Associates, Inc., as t h e EAI model 6.720. The u n i t consists of two independent high-gain amplifier c i r c u i t s packaged on an etched-circuit board. The amplifiers are t r a n s i s t o r i z e d and designed f o r optimum s t a b i l i t y and frequency response. Each amplifier can be used i n conjunction with appropriate networks t o perform l i n e a r camputations such as summation, integration, and multiplication by a constant.

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2.3.7.2

Specifications

Specifications f o r t h e dual dc amplifier are given below: Output voltage range

k1.2 v min (no load); +IO v m i n (20 ma load)

Offset ( a t t h e swmning junction) unity-gain i n v e r t e r with 10-kilohm r e s i s t ors

+20 pv, max

Output current a t +lo v

20 m a min

Frequency response (-3 db) f o r a unity-gain i n v e r t e r with 10-kilohm r e s i s t o r s (20 pv p-p input)

200 kc m i n

Noise (p-p) from dc t o 300 kc

400 pv rms max

2.3.7.3

Amplifier Balancing

The amplifiers should be periodically balanced t o assure accuracy. Under normal circumstances, t h e amplifier w i l l remain balanced f o r periods of weeks. However, a t i n t e r v a l s it i s desirable t o check this condition, and i f an amplifier i s found t o be unbalanced, then an adjustment should be made. The period between balance checks depends t o a l a r g e extent on t h e application of the amplifier. For uses which m i g h t be unusually s e n s i t i v e t o amplifier unbalance o r i n t e g r a t o r d r i f t , t h e amplifier should be balanced a t more frequent i n t e r v a l s . I n any case, maintenance personnel should recognize t h e f a c t t h a t many amplifier and network malfunctions can be detected by checking amplifier balance. Consequently, it i s recommended t h a t a check of amplifier balance be made biweekly. If t h e check indicates t h a t t h e amplifier balance i s within tolerance, no adjustment need be made. 2.3.7.4

Theory of Operation

Basic Block Diagram The dual dc amplifier consists of an EAI model 6.715 dual dc amplif i e r card housed i n a s p e c i a l package. The components f o r one channel The major components consist of t h e stabiare shown i n Fig. 2.3.14. l i z e r amplifier, t h e chopper, and t h e dc amplifier. The c i r c u i t i s arranged s o t h a t t h e d r i f t - f r e e c h a r a c t e r i s t i c s of an ac amplifier are used t o maintain constant dc amplifier balance by providing a voltage t o t h e input of the dc amplifier which tends t o maintain t h e summing junction a t virtual ground. The r e s u l t i n g c i r c u i t has excellent longterm s t a b i l i t y and allows t h e use of a wide-bandwidth dc amplifier without the necessity of frequent manual balancing. Inputs t o t h e amplifier a r e applied through an external input imThe dc and low-frequency components of the signal voltage pedance Zin.

a t t h e summing junction (SJ) cannot pass d i r e c t l y t o t h e input of t h e dc amplifier section because of C1. Instead, they are connected through R3 t o contact 9 of chopper D1. A chopper, o r synchronous vibrator, con-

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sists of a coil-driven vibrating reed 8 (Fig. 2.3*14) t h a t a l t e r n a t e s between contacts 9 and 7 on each half cycle of t h e c o i l excitation voltage. The chopper a l t e r n a t e l y grounds contact 9, producing a 60-cps square-wave input t o t h e s t a b i l i z e r amplifier. After amplification, t h e r e s u l t i n g s i g n a l i s demodulated ( o r synchronously r e c t i f i e d ) a t t h e second contact 7 of t h e chopper. The r e s u l t i n g s i g n a l a t contact 7 i s a pulsating dc signal whose p o l a r i t y i s the same as t h e p o l a r i t y of t h e s i g n a l a t t h e summing junction. The dc s i g n a l i s f i l t e r e d by R 8 and C2 and applied through R7 t o t h e input of t h e dc a q p l i f i e r section. Thus dc and very low-frequency signals are amplified by the s t a b i l i z e r amp l i f i e r and by t h e dc amplifier. The c i r c u i t from contact 9 of D 1 t o contact 7 i s a modulated carrier-type amplifier t h a t provides high-gain dc amplification w i t h no d r i f t . The s t a b i l i z e r i s phase-sensitive; i f t h e p o l a r i t y of t h e summing junction s i g n a l changes, t h e phase of t h e modulated s i g n a l changes and t h e p o l a r i t y of the pulsating dc output voltage changes. High-frequency components of t h e input s i g n a l a r e passed through C 1 t o t h e dc amplifier and are amplified by the gain of t h e dc amplifier only. The open-loop gain of the amplifier thus depends on t h e frequency of t h e input signal. A t very low frequencies t h e gain i s extremely high because the s t a b i l i z e r amplifier i s placed i n s e r i e s with t h e dc amp l i f i e r . At higher frequencies t h e gain i s decreased but remains high enough t o satisfâ&#x20AC;&#x2122;y a31 expected operations when t h e feedback loop i s closed. Any component of t h e amplifier output voltage due t o d r i f t i n t h e dc amplifier section i s fed back through t h e feedback impedance Zf t o

t h e swming junction of t h e amplifier. Since my drift-produced voltage has a very low frequency, it w i l l be amplified by t h e s t a b i l i z e r section, f i l t e r e d , and then applied as a drift-correction s i g n a l t o t h e input of t h e dc amplifier section. The drift-produced component i n t h e output i s reduced by a f a c t o r equal t o t h e e f f e c t i v e gain of t h e s t a b i l i z e r section. The amplifier would require balancing every few minutes without s t a b i l i z a t i o n . The d r i f t compensation produced by chopper s t a b i l i z a t i o n allows the amplifier t o be used f o r weeks without attention. The amplifier i n t h e s t a b i l i z e r section has a very high gain. Since it i s connected t o t h e summing junction, it serves as a monitor of the summing junction voltage. Under normal circumstances t h e input current of t h e operational amplifier i s equal t o t h e feedback current, and t h e summing junction i s a t v i r t u a l ground. If t h e currents are not equal, t h e amplifier i s not performing properly, and the summing junction dep a r t s from v i r t u a l ground. This r i s e i n voltage is amplified by t h e s t a b i l i z e r and r e s u l t s i n an output s i g n a l which may be connected through t h e appropriate push-button switch t o t h e balance monitoring meter c i r cuit. DC Aurplifier Section

Refer t o Fig. 2.3.15 f o r the following description. The summing junction of t h e operational amplifier i s connected t o t h e input t e r minal. The ac components of t h e input s i g n a l are applied t o t h e base of t r a n s i s t o r Q through lR 2 and C1. The input s i g n a l i s a l s o connected through R3 t o t h e input of t h e s t a b i l i z e r section. Two reverse-connected

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diodes CRl and CR2 are connected from t h e input t o ground so that C 1 cannot be charged t o a high voltage should an overload occur. This feature allows the amplifier t o recover rapidly following an overload condition. The voltage a t t h i s point i s normally l e s s than the diode conduction point. Transistors QJ and Q2 comprise the anrplifier input stage. Trans i s t o r Q2 i s connected i n a common-emitter configuration, with R 7 ( i n etched-circuit r e s i s t o r network NW1) and thermistor R15 providing s e l f b i a s . Transistor Ql i s used i n t h e emitter-follower configuration and uses t h e voltage drop (approximately 0.3 v) across the base-emitter diode of Q2 as i t s operating voltage. The emitter-base resistance of . Q2 provides a load f o r Q Thisl configuration gives t h e amplifier a r e l a t i v e l y high input impedance. The base c i r c u i t of QJ i s completed through R 8 ( i n NWl), Rl, and the balance potentiometer. These components form a voltage divider between -15, +15, and +25 v. The balance potentiometer s e t s t h e optimum operating point for Ql, as indicated by a zero output from the s t a b i l i z e r section. The high-frequency r o l l o f f of t h e input stage i s controlled by C 3 and R5. Temperature compensation i s provided by thermistor Rl5 and r e s i s t o r R6, which tend t o keep the c o l l e c t o r of Q2 a t a constant potentia3 regardless of temperature variations. The s t a b i l i z e r output i s connected through R 8 and R7 t o t h e input of Ql. The output of Q2 i s coupled t o the base of Q3 through NWl-RS. B i a s f o r Q 3 i s provided by NWl-R4 and NWl-RS. The feedback network consisting of R l O and C5 provides t h e proper high-frequency r o l l o f f f o r t h e Q3 stage. Capacitor C4 provides correct phasing f o r higher frequencies. The c o l l e c t o r load f o r Q3 consists of r e s i s t o r s NWl-R3 and NW1-Rl. Resistor NW1-R3 provides d i r e c t coupling from t h e output of Q3 t o t h e base of Q4, as well as forming a voltage divider with NW1-Rl t o s e t t h e operating point f o r Q4. The Q4 stage i s connected i n t h e commonemitter configuration. The emitter i s connected t o +15 r a t h e r than ground, t o e s t a b l i s h t h e correct operating points f o r Q4, Q5, Q6, and Q7. The c o l l e c t o r load f o r t h e stage consists of NWl-R2. Capacitor C 7 provides high-frequency degenerative feedback f o r this stage, and the network consisting of C6 and RIl controls t h e high-frequency r o l l o f f f o r Q4 and Q5. The c o l l e c t o r of Q4 i s connected t o t h e base of Q5 through an incandescent lanrp DS1. The filament of t h i s lamp has a high positive temperature c o e f f i c i e n t of resistance, providing an increase i n r e s i s t ance with an increase i n current flow. This s t a b i l i z e s t h e operation of Q5 by l i m i t i n g base drive. The Q5 stage i s connected as an emitterfollower, with r e s i s t o r lU.2 providing t h e emitter load r e s i s t o r . Diode CR3 provides a s m a l l forward b i a s f o r output t r a n s i s t o r Q7, eliminating crossover d i s t o r t i o n in t h e output stage. The output stage consists of t r a n s i s t o r s Q6 and Q7, connected i n a complementary-symmetry configuration. This c i r c u i t arrangement provides t h e advantages of push-pull operation with a single-ended input. Both transistors are connected as emitter-followers. Since t r a n s i s t o r Q6 (F'NP) conducts with a negative input and t r a n s i s t o r Q7 (NPN) conducts w i t h a positive input, one of t h e t r a n s i s t o r s delivers current t o t h e

144

load regardless of input p o l a r i t y . With a zero input, both t r a n s i s t o r s conduct equally, and t h e voltage drop across the load i s zero. Incandescent lamps DS2 and DS3 perform a function similar t o that of DS1; by providing an increase i n resistance w i t h an increase i n current, they protect t h e output t r a n s i s t o r s from excessive current flow. Res i s t o r Rl3 provides a dc feedback t o t h e base of Q4 which tends t o keep t h e output of t h e amplifier a t zero v o l t s with a zero input and compens a t e s f o r minor t r a n s i s t o r and temperature variations. S t a b i l i z e r Section The s t a b i l i z e r section consists of a four-stage direct-coupled amplifier (Q8, Q9, QlO, and Q input ll) and, output coupling capacitors ( C 8 and C12 respectively), and a 60-cps chopper ( D l ) . The s t a b i l i z e r preamplifies t h e dc and very low-frequency components of t h e s i g n a l appearing a t t h e amplifier summing junction and applies t h e r e s u l t i n g signal. as an input t o the dc amplifier section. S t a b i l i z e r Amplifier. The s t a b i l i z e r amplifier receives i t s input from t h e summing junction through r e s i s t o r s R3 and R9. The chopper grounds t h e junction of R 3 and R9 60 times each second, making t h e input appear as a s e r i e s of pulses between ground and t h e input l e v e l . These pulses are coupled through C 8 t o t h e base of t r a n s i s t o r Q8. The input stage of t h e s t a b i l i z e r consists of t r a n s i s t o r s Q8 and Q9. Transistor Q8 i s connected as an emitter-follower and uses the base-emitter voltage drop of Q9 t o provide operating voltage. The c i r and l c u i t arrangement of Q 8 and Q9 is similar t o t h e arrangement of Q Q2 i n t h e dc amplifier section and provides a r e l a t i v e l y high input impedance. Resistors NW2-Rl and NW2-Rll provide b i a s f o r Q8. Capacitor C9 f i l t e r s high-frequency t r a n s i e n t s from t h e input waveform. Resistor NW2-R2 provides t h e emitter load f o r Q 8 and, together w i t h NW2-Rl2, proare l connected l i n the vides bias f o r Q9. Transistors Q9, QlO, and Q common-emitter configuration and are d i r e c t l y coupled through r e s i s t o r s NW2-R4 and NW2-R6. Capacitor C10 provides high-frequency degeneration f o r the Qll stage, removing unwanted high-frequency components from t h e output waveform. Resistor NW2-R8 provides a feedback t o t h e junction of NW2-FU and NW2-Rl1, adjusting t h e bias on Q 8 t o maintain t h e stabil i z e r amplifier t r a n s i s t o r s a t the correct operating point. The network consisting of R14 and C l l provides phase correction f o r very low frequencies and f i l t e r s high frequencies f r o m t h e NW2-R8 feedback loop. The stabilizer amplifier consists of an emitter-follower input stage which i s noninverting and three common-emitter stages which provide an overdl phase s h i f t of 540". This c o n s t i t u t e s an apparent 180" phase shift, o r an inversion from input t o output. This cannot be t o l e r a t e d by t h e o v e r a l l amplifier, since t h e dc amplifier section provides a 180' phase s h i f t . Any feedback under these conditions would be regenerative, and t h e amplifier would not be usable. For t h i s reason contacts 7 and 8 of t h e chopper demodulate t h e output of t h e s t a b i l i z e r amplifier t o provide a pulsed output t o t h e f i l t e r network (R8 and C2) having t h e same p o l a r i t y as t h e input. This i s accomplished as described below. Chopper. - The chopper used i n t h e EAI model 6.720 amplifier i s a specially designed high-speed relay. It consists of a double-pole

145

armature assembly which is driven by a 60-cps ac source and which alt e r n a t e s i n position frcm one s e t of contacts t o t h e other a t t h i s rate. Figure 2.3.14 shows how one pole of t h e chopper (pin 8 ) a l t e r n a t e l y grounds t h e s t a b i l i z e r input (pin 9) and t h e s t a b i l i z e r output (pin 7 ) . The closing of contacts 8 and 9 a t a 60-cycle rate causes t h e s t a b i l i z e r input t o appear as a s e r i e s of pulses. This permits amplification of very low frequencies o r dc l e v e l s while i s o l a t i n g t h e amplifier operating l e v e l s through t h e use of a coupling capacitor. The closing of contacts 8 and 7 e f f e c t i v e l y s h i f t s the phase of t h e output by providing a short r-c charge o r discharge time f o r C12 when closed and a longer time (through R8) when open. This operation i s more e a s i l y understood with t h e use of examples. If t h e input t o the smming junction tends t o go positive, the input t o t h e s t a b i l i z e r amplifier consists of a s e r i e s of positive pulses. The output waveform a t the c o l l e c t o r of Q thenl consists l of a s e r i e s of negative-going pulses. However, during the time that t h e input pulse i s present (positive), the output (negative) a t t h e junction of C12 and R8 i s connected t o ground through contacts 7 and 8 of t h e chopper. This allows C12 t o charge rapidly t o t h e l e v e l a t the c o l l e c t o r of Qll. The chopper arm then closes t o contact 9, driving the s t a b i l i z e r input t o ground. The c o l l e c t o r of Qll goes from i t s negative l e v e l toward ground a t t h i s time, and t h e positive change i s coupled through C12 and R8 t o t h e input of t h e dc amplifier. The dc restoring action of contact 7 and t h e arm of t h e chopper thus makes t h e apparent output a s e r i e s of positive pulses which are f i l t e r e d by C2 and R8 and provide a dc input t o t h e dc amplifier through R7. If t h e input t o the summing junction tends t o go negative, t h e s t a b i l i z e r input i s a s e r i e s of negative pulses. The output a t t h e c o l l e c t o r of Qll i s a s e r i e s of pulses from a negative l e v e l toward ground. I n t h i s case, the chopper provides a short-time-constant discharge path f o r C12 when t h e c o l l e c t o r of Qll i s close t o ground. A s contacts 8 and 9 o f t h e chopper break and contacts 8 and 7 close, t h e c o l l e c t o r of Q goesl l negative and t h e change i s coupled through C12 and R8 t o f i l t e r capacitor C2. Stabilizer Filter. The s t a b i l i z e r output f i l t e r , consisting of capacitor C2 and r e s i s t o r R8, has a time constant of 3 sec. This i s extremely long with respect t o t h e s t a b i l i z e r output waveform, consequently reducing t h e r i p p l e a t t h e junction of R8 and R7 t o a negligible level. S t a b i l i z e r Functions. The s t a b i l i z e r performs t h e apparently dual functions of p r e q l i f ' y i n g dc and very low-frequency input signals and maintaining the amplifier summing junction a t a point very close t o ground p o t e n t i a l over wide variations i n amplifier balance. When t h e amplifier feedback loop i s closed (as it must be) and no input i s applied, t h e amplifier output should be zero v o l t s . Any departure of t h e amplifier output from this point i s coupled through t h e feedback r e s i s t o r t o t h e summing junction. This causes the s t a b i l i z e r t o generate a correction voltage which returns t h e amplifier output and, consequently, t h e s m n g junction t o zero. If an input signal i s applied t o t h e summing junction, t h e s t a b i l i z e r again generates a voltage. I n t h i s case, however, t h e output of t h e dc amplifier i s s h i f t e d from ground

146

p o t e n t i a l t o produce an output with a p o l a r i t y opposite t o that of the input and a magnitude equal t o t h e input voltage multiplied by t h e r a t i o of the feedback resistance t o t h e input resistance. This output produces a p o t e n t i a l at t h e summing junction equal i n magnitude and opposite i n p o l a r i t y t o the input signal, returning t h e absolute p o t e n t i a l at t h e summing Junction t o a point very close t o ground. It i s i n this way t h a t t h e s t a b i l i z e r attempts t o keep t h e summing junction a t ground regardl e s s of input voltage changes o r variations within t h e dc amplifier. 2.3.8 2.3.8.1

Fission Chamber Drive

Description

The f i s s i o n chamber drive, ORNL model Q-2545, i s shown i n Figs. This u n i t contains a direct-current motor and as2.3.16 and 2.3.17. sociated drive t r a i n f o r positioning t h e preamplifier and f i s s i o n chamber assembly. I n addition, t h e r e is a position-sensing t r a i n f o r providing position signals t o t h e servo power amplifier and t o the data logger. Performance specifications are: Stroke

90 in.

Chamber velocity

72 in./min

Environment

150'F i n water containing 2000 ppm sodium n i t r i t e corrosion i n h i b i t o r

A ball-bearing lead screw turning a t 288 rpm provides t h e rotational-to-linear motion conversion with an efficiency r a t i n g of approximately 9%. A water-resistant calcium-complex-base grease was selected as t h e lubricant f o r the lead screw. The ball-bearing nut i s attached t o a guide block which rides on nylon runners between two aluminum guide rails mounted within a 3-3/&in.-OD s t a i n l e s s s t e e l drive tube. A t h r u s t tube connected t o t h e guide block i s attached t o a cabling r i g which i s connected t o t h e preamplifier and f i s s i o n chamber assembly. The f i s s i o n chamber signal cable, sheathed i n Tygon tubing f o r water protection, and a piece of music wire a r e coiled i n t o a helix. These are held together with nylon s p i r a l wrapping t o form a spring-loaded coiled cord. This h e l i x provides t h e necessary cable takeup and i s coiled loosely around t h e t h r u s t tube between t h e cabling r i g and t h e lower end of t h e drive tube. This cabling r i g rides on nylon r o l l e r s inside t h e 4-in.-ID instrument penetration tube. (This tube i s not a p a r t of t h e positioner assembly.) The direct-current drive motor with i n t e g r a l gear reducer and tachometer is protected from any torque overloads by a disk-type s l i p clutch. The position s i g n a l system is d i r e c t l y connected t o t h e leadscrew s h a f t ahead of t h e s l i p clutch by a p a i r of precision gears. The position s i g n a l system consists of a ten-turn auxiliary position-sensing potentiometer driven by a 48:l r a t i o reducer, t o provide 7-1/2 revolutions f o r 90 in. of chamber t r a v e l . This, i n turn, drives

6.I

147

a 1O:l r a t i o reducer which i s connected t o a one-turn position-sensing, data-logger input potentiometer. On the same s h a f t there i s a synchro transmitter f o r driving a position indicator on the console. A ten-turn Vernistat interpolating potentiometer, previously described, i s gear-driven from the shaft of the ten-turn auxiliary positionsensing potentiometer t o provide t e n revolutions f o r 90 in. of chamber travel. This interpolating potentiometer provides t h e position feedback signal t o t h e function generator amplifier ( O m model &-2616). Upper and lower l i m i t switches are actuated by rods which are tripped by the guide block a t each end of i t s travel. These rods are held captive i n grooves between the guide r a i l s and t h e drive tube. This permits mounting of the l i m i t switches i n the motor drive assembly where they are readily accessible. 2.3.8.2

Drive Motor

The permanent magnet dc drive motor i s a Globe Industries, Inc., type BL-7, 27 v, with a 30.7:l r a t i o gear reduction and a 1-7/8-in.square flange mounting. It has an i n t e g r a l permanent magnet dc generator, type U-1, which produces a minimum of 1.8 v per 1000 r p m a t no load. The motor has a 350-to-450-rpm no-load speed range, rated a t 137 in.-oz torque, p a r t No. 102A276, purchase order No. 62X-20042 s p e c i d ; the output shaft is 5/16 in. i n diameter by 3/4 in. long with a 1/8-in.-square key seat. 2.3.8.3

Lead Screw

The actuator assembly i s a commercial-quality b&U-screw type, No. 1000-0250-C1, by Saginaw Steering Gear. The screw i s 8 f t 6 in. long. The screw threads have a 1-in. p i t c h diameter, a 0.250-in. lead, and a 0.820-in. root diameter, and are right-hand threads. The nut has a 11/2-in.-square body with a 1.583-18NS thread. The screw and nut are heat-treated 17-4 PH s t a i n l e s s s t e e l . The balls are heat-treated type 440C s t a i n l e s s s t e e l , with every other b a l l 0.002 in. undersize.

2.3.8.4

Position-Sensing Potentiometer

The position-sensing potentiometer, which provides the input t o the data logger, i s by Beckman Instruments, Inc., Helipot No. 5203R5KL.25RS. It i s a single turn with servo mount, ball bearings, and double-ended s h a f t extensions. The c h a r a c t e r i s t i c s are: 5000 ohms, +0.25$ l i n e a r i t y tolerance, and 3 W. 2.3.8.5

Synchro

The synchro is a Norden No. 1 2 U U torque transmitter, 115 v, single phase, 60 cps ac. I t s c h a r a c t e r i s t i c s are: three-phase s t a t o r , 0.38 in.-oz torque gradient, 0.50 in.-oz f r i c t i o n a l torque, and +8 min e l e c t r i c a l error. The shaft i s 0.2405 in. i n diameter with ASA spline and threads.

148

2.3.8.6 Auxiliary Position-Sensing Potentiometer The auxiliary position-sensing potentiometer is by Beckman Instruments, Inc., Helipot No. 7603lUXL.15RS. It is a ten-turn potentiometer with servo mount, b a l l bearings, and double-ended shaft extensions. The characteristics are: 1000 ohms, +0.15$ linearity tolerance, and 5 W.

2.3.8.7

Vernistat Interpolating Potentiometer The Vernistat interpolating potentiometer is a Perkin-Elmer Corporation Vernistat No. 2x5. Its characteristics are: interpolating, 3960째, electrical rotation (continuous), 34 chords, 470 ohms maximum output impedance, 0.004% approximate angular resolution, and size 18 servo mounting, part No. 124-Oll8.

2.3.8.8

Gear Reducers The two gear reducers are by Metron Instrument Co. One, Metron No. 9B48R, has a 48:l ratio with a 15-min maximum backlash, servo mount, and 3/16-in.-diam shafis. The other, Metron No. 9AlOR, has a 10:l ratio with a 15-min maximum backlash, servo mount, and 3/16-in.-diam shafts. 2.3.8.9

Slip Clutch

The Sentinel Manufacturing Corporation makes the type 40, size 2000 single-disk slip clutch. It is a coupling type with a 6 in.-lb setting, a 5.16-in. bore-through disk hub, no bore in the housing hub, and a 1/2-in.-diam housing hub.

2.3.8.10 Limit Switches The snap-action limit switches are Micro Switch units, No. BZ2RW82255-A2, with a short roller lever, 6 o z operating force, and a rating of 15 amp at 125 v ac.

Fig. 2.3.1.

MSFiE Wide-Range Fission Channel Block Diagram.

150

ORNL-DWG 66-7635

106

100

I I I-

lo2

0 V

COUNT RATE SET POINT ( 10 k

ACTUAL COUNT RAT

*ACTUAL CHAMBER

counts/ sec 1

POSITION

(SEE NOTE LAED ; / 1 ,) /

/J4 I

WITHDRAWAL

101

2-'1 -

100

cps

LOG REACTOR POWER-

*NOTE I: THIS SOLID LINE CURVE IS NOT NECESSARILY REPRESENTATIVE OF AN ACTUAL OR TYPICAL CURVE BUT ILLUSTRATES THAT THE ACTUAL CURVE WILL DEPART FROM THE IDEAL STRAIGHT LINE.

Fig. 2.3.2.

Actual and Ideal Curves of Count Rate vis Reactor Power.

ORNL-DWG 6%4102R

0-2614

LOO REACTOR WWER SIGNAL

LOO COUNT RATE SIGNAL FOR READOUT

1 FORREADOUT

r FLOG COUNT RATE SIGNAL L

LMPLlFlER SUMMING

LINEAR CWNT RATE METER

__________ J

I-

COUNT RATE SET POINT.

REACTOR SIGNAL m PERIOC R READOUT

LCGP

M 3A

Na3B GAIN

DIFFERENTIATING AMPLIFIER

AMPLIFIER

- POWER REACTOR SIGNAL LCG

S A G -* PRODUCES TRIP SIGNAL WHEN REACTOR POWER IS LESS THAN 200 kw

PRODUCES TRIP SIGNAL WHEN COUNT RATE EXCEEDS

PRODUCES TRIP SIGNAL WHEN REACTOR PERIOD IS LESS THAN 5 sec

SIGNALS

ro REACTOR

POSITION SIGNAL

READOUT

NOTE "0"NUMBERS REFER TO OAU RIDGE NATIONAL LABORATORY INSTRUMEN1 AN0 CONTROL DIVISION DRAWING NUMBERS

VERNISTAT INTERPOLATING POTENTIOMETER

PRODUCES TRIP SIGNAL WHEN REACTOR WWER EXCEEDS xK)kw

FISSION CHAMBER POSITION SIGNAL

IN START MODE

mR READOUT AT

CONSOLE

No2

* ------

TRANSMITTER

PRODUCES TRIP SIGNAL WHEN REACTOR POWER EXCEEDS 1.5Mw

ELECTRICAL SIGNAL MECHANICAL DRIVE

OPERATIONAL AMPLIFIER

Fig. 2.3.3.

MSRE Wide-Range Counting Channel.

*INHIBIT

CONTROL SYSTEM

PRODUCES TRIP SIGNAL WHEN REACTOR PERIOD IS LESS THAN 25

NI"*

CJl WITHDRAWAL" ROO

PERMIT"

152

lo3

ORNL-DWG I

67-11922

PULSE HEIGHT CHARACTERISTICS OF 2-in. FISSION CHAMBER FISSION CHAMBER WX- 31095 CONNECTED TO ORNL MODEL Q-2647 PREAMPLIFIER AND A l AMPLtFlER WITH GAIN OF 64

I \ a AND NOISE

PILEUP

Id) 5

IO-' 0

PULSE HEIGHT SELECTOR

Fig. 2.3.4.

MSRE Wide-Range Counting Channel.

153

Fig. 2.3.5.

"Snake" Asselribly.

154 ORNL-LR-WG 6973ZR

RECEIVINGEND PRENAPUFIER

PIC H-71'

I-Y2iq6T/i 250n 4.7

Fig. 2.3.6.

Preamplifier Circuit Diagram.

PHOTO P- 55826

b0.5psec TIME

Fig. 2.3.7.

Fission Pulses at t h e Main Amplifier Input.

L F

5 0

r i :

8k 0

. .

__ .. .

.. . . .

157

@ INPUT

@ OUTPUT

I-

@ OUTPUT-NO

OVERLOAD

@ OUTPUT-

X 2 OVERLOAD

@ OUTPUT-

X I 0 OVERLOAD

Fig. 2.3.11.

Pulse Amplifier Wavefo m .

158

ORNL-OWC

Fig. 2.3.12.

67-7040

Composite Response of Six Diode Pumps with Individual C1 X R l .

Pump Response Where Cn X Rn = 0.1â&#x20AC;?-

159

The output wiper has just passed commutator bar 2 and i s interpolating between bars 2 and 3. Resistance element tap A i s just about t o disengage from commutator bar 1.

As the output wiper moves i n a clockwise direction, the output voltage changes linearly from the voltage on commutator bar 2 t o t h a t on commutator bar 3. Resistance element tap A has disengaged from commutator bar 1 and i s switching t o commutator bar 4 .

The output wiper i s approaching commutator bar 3. Resistance element t a p A has completed switching and i s i n contact w i t h canmutator bar 4 , Continued clockwise rotation of the output wiper w i l l result i n smooth interpolation past commutator bar 3.

Fig. 2.3.13. E l e c t r i c a l Relation of Vernistat Interpolator Cornmutator Bars, Interpolating Resistance Element, and Output Wiper.

160

ORNL- OWG 67-7036

1 I

CRI

:-R3

*’

TO OUTPUT MONITORING CKTS

+ISV

Fig. 2.3.14. One Channel.

TO BALANCE MONITORING C I R C U I T S

Dual dc Amplifier Card Simplified Block Diagram,

ORNL-DWG 67-7038

NOTE: PIN CONNECTiONS SHOWN FOR CHANNEL 2.

Fig. 2.3.15.

6.715 Amplifier C a r d Sbnplified Schematic, One Channel.

161 1

Fig. 2.3.16.

Fission Chaniber Drive*otor

Drive Assembly.

ORNL-OWQ 66-429

THE VERNISTAT INTERPOLATING POTENTIOMETER IS PART OF MODEL 0-2616 FUNCTION GENERATOR, 10 TURNS EQUALS 90 In. OF CHAMBER TRAVEL.

7b2 TURNS EOUAL w i n . OF CHAMBER TRAVEL (OR 1 TURN EOUALS 12 In. CHAMBER TRAVEL)

POTENTIOMETER SAGINAW BALL BEARING LEAD SCREW, 4 threads/ln.

270' ROTATION EQUALS 90In. OF CHAMBER TRAVEL

PREAMPLIFIER

90 in. TRAVEL 7 2 in./min

(6in.- Ibr )

RETRACTABLE CORD

Fig. 2-3-17. MSRE Drive Unit f o r Wide-Range Counting Channel, Block Diagram.

FISSION CHAMBER

163

2.4

LINEAR POWER CHANlVELS

2.4.1

Description

These l i n e a r power channels (Fig. 2.4.1) comprise the instruments used f o r t h e most accurate determination of reactor power and f o r input t o the rod control servo system. These compensated ion chambers and associated power supplies, ORNL models Q-1045 and Q-995, respectively, were removed from the HRT and reconditioned f o r use i n the MSFU3. The design of t h e chamber, t e s t i n g and compensation procedures, and i t s high-current saturation characteristics have been described i n two ORNL documents,ln2 applicable portions of which are included l a t e r i n t h i s section. The MSRE chambers, unlike the i l l u s t r a t i o n i n ref. 1, are equipped with motor-driven remote compensation adjustment and do not use a continuous flow of nitrogen. The Q-995 power s w p l y i s a conventional regulated supply designed t o provide t h e requisite positive and negative voltages t o the two sect i o n s of t h e chamber. The negative voltage adjustment i s used t o assist compensation i n accordance with r e f . 1. For the c i r c u i t diagram see Fig. 2.4.2. The picoammeter i s a Keithley Instruments, Inc., model 418-20 It has an overall range from t o 10" amp, ac(Sect. 2.4.3). complished by range switching. Range switching i s described i n Sect. 2.6; it may be done l o c a l l y a t the instrument o r remotely a t the console. Detailed specifications and performance characteristics, abs t r a c t e d from the manufacturer's instruction manual, are given i n Sect. 2.4.3. Figure 2.4.1 shows only one channel of l i n e a r input instrumentation. For a more complete diagram the reader i s referred t o Sect. 2.6. Either of the two channels may be used t o supply input t o the l i n e a r recorder on the main control board and t o t h e regulating rod controller. The output channel not being recorded i s read out on a console-mounted meter. The strip-chart recorder i s a two-pen, s e l f balancing potentiometer type arranged i n a somewhat unorthodox fashion i n order t o record both t h e output voltage of t h e picoammeter and t h e

range switch s e t t i n g unambiguously. This simultaneous record of p i c o m e t e r output and range s e t t i n g i s unambiguous because the range s e t t i n g uses t h e left-hand 40$ of the chart width and the picoammeter output i s r e s t r i c t e d t o t h e remaining 60$. Therefore t h e chart t r a c e s do not overlap or cross over a t any time, and there can be no question as t o t r a c e i d e n t i f i c a t i o n a f t e r the paper r o l l i s removed. The above i s i l l u s t r a t e d by Fig. 2.4.3, t h e chart paper used f o r t h i s power recorder.

l H . E. Banta and S. H. Hmauer, Testing Procedures f o r Reactor Instrumentation, Section J, Compensated Chamber Field Testing, ORNLCF-56-5-30 (Feb. 8, 1954). 2J. L. Kaufman, H i g h Current Saturation Characteristics of the ORNL Compensated Ion Chamber (&-1045), ORNL-CF-60-5-10Lt (May 25, 1960).

164

2.4.2

Visual Readout Device, Series 360

A v i s u a l readout device, mounted above t h e l i n e a r power recorder and l e g i b l e t o personnel i n both t h e control room and t h e v i s i t o r s ' area, displays t h e range s e t t i n g multiplier s o t h a t t h e reactor power can be read a t a distance by simply noting t h e position of the indicating flag on t h e right-hand pen of t h e l i n e a r power recorder. This readout device (Fig. 2.4.4) consists of an assembly of o p t i c a l projection modules which display selected characters (numbers, l e t t e r s , symbols, e t c . ) on a translucent screen located f l u s h t o t h e main board. I n the MSRE t h e projection lamps i n t h e modules are selected by the range s e l e c t o r switches on t h e console.

2.4.3

Keithley Model 418-20 Picoammeter: Specifications and Description

10-12 t o 10-2 amp f ~ l lscale i n twenty-one IX and 3~ RANGFS: overlapping ranges. Any range may be selected at t h e main chassis location or from a remote location. ACCURACY: +2 of MU. scale from 10-2 t o 10-8amp; f3$ of f u l l scale from 3 x 10 t o 10-l2amp. ZERO DRIFT: With source voltages greater than 1v and a f t e r a 30-min warmup, t h e d r i f t i s l e s s than 1% per 8 h r on any range. RISE TIME, MAXIMUM (seconds, from 10 t o go$ of f i n a l current):

Range (amp) 10-12

No ExternaJ. Capacitance 0.03

With 5000 pf Across Input

With 50 pf Across Input 0.06

With 500 pf Across Input 0.4

4.0

10-11

0.005

0.01

0.035

0.4

10-10

0.004 0.004

0.006

0.04

10-9

0.004 0.004

0.004

0.006

10-8

0.004

4.001

<o .001

lo+

and

001

.001

TIME: 5 msec maximum. INPUT: Grid current is l e s s than 3 x amp. Change i n input voltage drop i s less than 1mv f o r f u l l - s c a l e deflection on any range. Input resistance increases from 0.1 ohm a t loC2-amp range t o 1000 megohms a t 10-12-amp range i n decade steps. OUTPUT: A 43-v output a t up t o 1 m a i s developed f o r f u l l - s c a l e meter deflection. Impedance is l e s s than 1 ohm. P o l a r i t y is opposite t o input polarity. Noise i s less than 246 rms of f u l l scale on 10-l2amp range. Provision i s made f o r lower voltage outputs. ZERO CHECK: Allows zeroing without disturbing t h e c i r c u i t . RENOTE CONTROL: Local o r remote control selected by front-panel switch. Remote range switching requires a f i v e - b i t binary input with Wc;E SWITCHING

165

binary "1" corresponding t o t h e 10째2-amp range i n numerical order t o binary "21" corresponding t o the 10-12-amp range. Zero check requires a separate input signal.. AU. inputs require closure t o ground. CONNECTORS: Input: Teflon-insulated uhf-type receptacle. Output: Amphenol 80 PC2F receptacle. Remote: Cannon DAl5S. Remote control: Winchester type XAC 34-S-F-2-A-016G. TTEE COMPMMNT: One 5886. POWER: 105-125 v o r 2l+250 v, 5Ck1000 cps, 22 W. 2.4.4 2.4.4.1

Procedure f o r Field Testing and Compensating Compensated Chamber Q-10453

Description

The compensated chamber (Fig. 2.4.5) r e a l l y consists of two chambers, one of them boron-coated. The output current i s t h e sum of t h e currents of t h e individual chambers; since the high-voltage electrodes of these individual chambers are a t p o t e n t i a l s opposite i n sign (one i s +600 v; t h e other, -300 v), t h e output current w i l l be t h e difference of t h e two chamber currents. The current from t h e boron-lined chamber i s proportional. t o t h e neutron f l u x and t o t h e gamma flux, while t h e uncoated chamber responds t o gammas only. By making the gamma responses equal., t h e output current i s proportional t o neutron f l u x alone, even i n the presence of a high gamma flux. It would not do t o make t h e coated and uncoated chambers identical; they would then have t o be placed i n t h e same location i n t h e reactor. What i s done i s t o build them very close together and then make one adjustable t o accommodate differences i n gamma f l u x a t the two chamber locations. The process of finding t h e b e s t adjustment i s known as compensating t h e chamber. It must be done i n t h e reactor a t the exact location where t h e chamber i s t o be used. The reactor i t s e l f i s used as a source of gamma radiation. 2.4.4.2

Testing

Insulation Tests The purpose of these t e s t s is t o determine whether t h e leakage current of t h e chamber i s negligible compared with t h e operating current. To do t h i s , one applies a high d i r e c t voltage t o t h e high-voltage electrodes and observes t h e leakage current with a s e n s i t i v e device. Two high-voltage supplies are needed: +lo00 v and +500 v. They need not be well regulated, but they must be well f i l t e r e d and have a low noise and hum output. It i s desirable t o operate them from a sine-wave Sola constant-voltage transformer. Connect t h e +lo00 v t o t h e positive high-voltage receptacle on t h e chamber; t h e i-500 t o t h e negative highvoltage. Connect t h e output t o a current-measuring device capable of

3This section (written by J. C. Gundlach and S. H. Hanauer) was excerpted from r e f . 1 (Specification 126)

166

indicating a current of amp. This may be an electrometer; often it i s convenient t o use t h e l o g N amplifier, calibrated as per Q-915-6. The ground (or low) side of the log N o r electrometer m u s t be connected t o t h e ground s i d e of t h e high-voltage supplies, since t h e receptacle s h e l l s are not connected t o t h e chamber. This may be done w i t h a c l i p lead, but i n view of the high voltage involved, a wire properly secured t o a screw i s safer. A leakage current greater than 1x 10l2 amp i s excessive, and t h e chamber must be disassembled and cleaned by someone experienced i n t h i s job. Do not attempt t h i s i n t h e f i e l d .

Compensation 1. The preferred method of compensation consists i n varying p i l e power l e v e l and comparing t h e output of t h e chamber t o be compensated w i t h t h e p i l e l e v e l as read on another instrument, usually t h e f i s s i o n chamber. The p i l e i s run a t a high l e v e l f o r half an hour o r more ( t o build up gammas); t h e f l u x i s then changed as quickly as possible t o a lower l e v e l . The procedure i s trial and error; increase the high-tolow f l u x r a t i o as t h e compensation gets nearer and nearer t h e correct value. The reference instrument w i l l give t h e r a t i o of t h e two f l u x levels; compare t h i s w i t h t h e r a t i o as measured on the t e s t chamber. If t h e r a t i o f r o m t h e t e s t chamber i s too low, the chamber i s undercompensated, and the compensation must be increased. If the r a t i o from the t e s t chamber i s too high, t h e chamber i s overcompensated, and the compensation must be decreased. 2. The compensation may be varied by screwing i n o r out t h e compensating adjustment on t h e chamber and by varying t h e negative p o t e n t i a on t h e compensating electrode. Changing t h e adjustment of t h e chamber varies t h e r e l a t i v e volume of t h e uncoated chamber; t h i s i s how t h e compensation i s usually changed. The adjusting screw i s turned clockwise t o decrease t h e compensation of an overcompensated chamber; turning it counterclockwise increases the compensation. When t h e adjustment i s nearly correct, turning t h e adjusting screw 30' w i l l change t h e (negat i v e ) gamma current by about 1%. The e f f e c t of t h i s change on t h e t o t a l current w i l l , of course, depend on how l a r g e t h e gamma current i s with respect t o t h e neutron current, and t h i s will i n t u r n depend on how large t h e gamma f l u x i s compared with the neutron flux. Changes i n negative p o t e n t i a l on t h e high-voltage electrode of t h e uncoated chamb e r may a l s o be used t o adjust t h e compensation. Decreasing t h e voltage decreases t h e compensation; increasing t h e voltage (more negative v o l t s ) increases the compensation. The magnitude of t h e change i n compensation depends on t h e gamma current and on t h e position of t h e negative highvoltage electrode, which is moved by turning t h e compensating adjustment. The e f f e c t of a 30-v change may be equivalent t o as l i t t l e as 1/20 t u r n change i n t h e compensating adjustment, o r t o as much as 1/2 turn. A t newer i n s t a l l a t i o n s , means are provided f o r turning t h e compens a t i n g adjustment remotely, s o t h a t it i s not necessary t o dismantle lead cables, shield plugs, and t h e l i k e . Compensation of chambers so i n s t a l l e d i s far b e t t e r c a r r i e d out using t h e compensating adjustment exclusively, with negative high voltage s e t a t i t s maximum value, since t h e uncoated chamber has b e t t e r saturation c h a r a c t e r i s t i c s a t higher voltages. Where chambers are i n s t a l l e d without means of remote adjustment, it will, i n some cases a t l e a s t , require considerable time

167

and e f f o r t t o make each change i n t h e compensating adjustment. One may, i f access i s d i f f i c u l t o r time short, a i m a t slight overcompensation with full negative high voltage and then decrease t h e voltage as a f i n d adjustment. It i s especially necessary i n t h i s case t o guard against leaving t h e chamber slightly overcompensated (see No. 6 below). A p r i n c i p a l reason f o r avoiding t h i s method l i e s i n t h e variable e f f e c t of the voltage adjustment - it i s quite possible t h a t compensation cannot be achieved a t any reasonable voltage and that the chamber adjustment w i l l have t o be turned again. DO NOT adjust a compensated chamber t o operate with t h e negative high voltage l e s s than -50 v. 3 . The choice of flux l e v e l a t which t o perform t h i s experiment i s not easy, i n some cases. Usually t h e only instrument one can believe as a reference i s t h e f i s s i o n chamber, because only t h a t device permits r e j e c t i n g all signals due t o gammas. One must use f l u x l e v e l s such that t h e low l e v e l gives a s u f f i c i e n t counting r a t e t o permit good s t a t i s t i c s i n a reasonable time and the high l e v e l gives a counting r a t e l e s s than 10,000 counts/sec, a t which r a t e t h e e r r o r due t o resolving time i n t h e A - 1 amplifier starts t o be important. 4 . One must take care that t h e control rod positions are as nearly a l i k e as possible f o r the two f l u x levels; variations may cause "shading" e f f e c t s which impair the v a l i d i t y of t h e experiment. 5. I n reactors where t h e y-n contribution t o the shutdown f l u x i s negligible, t h e compensation may be checked, a t l e a s t approximately, by leaving t h e l o g N recorder chart running during any shutdown of 6 h r o r more. The flux w i l l decrease on a period which approaches t h e 80-sec h a l f - l i f e of the longest-lived delayed neutrons. If, a t some point, t h e f l u x deviates from t h i s 80-sec-period straight l i n e , and t h i s i s not explained by l a t t i c e o r experiment changes or something similar, then one can usually assume t h e chamber compensation i s incorrect. Upward deviation (toward a constant l e v e l instead of a constant period) indicates undercompensation; downward deviation indicates overcompens a tion. 6. It i s b e s t i n t h e period channel t o err on t h e side of undercompensation. Overcompensating the chamber w i l l r e s u l t i n a negative output current; as the current passes through zero during s t a r t u p t h e period c i r c u i t s will scram t h e reactor. Prolonged negative current w i l l induce "sleeping sickness" i n t h e 9004 diode i n the l o g N. 7. It i s not a foregone conclusion t h a t every compensated chamber can be exactly compensated i n every reactor. I n cases where t h e chamber cannot be compensated with t h e adjustment available, t h e dimensions of t h e cups w i l l have t o be changed. This i s not a job f o r t h e f i e l d ; t h e ORNL Instrument Department Counter Laboratory should be consulted.

168

The Use of a Colloidal Dispersion of Boron i n O i l t o Obtain a Uniform and E a s i l y Applied Coating of Boron4

2.4.5

(This specification supersedes ORNL drawing Q-lC45-U.)

The process of applying a boron coating t o g r a ~ h i t e ,as ~ developed a t O m , i s t o quickly heat the boron-painted graphite electrode i n an i n e r t atmosphere t o a temperature s u f f i c i e n t t o drive off t h e o i l carrier. The following s p e c i f i c steps are used here t o obtain a known thickness of boron coating. 1. Heat to a d u l l red color by means of rn induction furnace, t h e graphite electrode which is t o be coated, t o drive out some of the collected gases and surface contamination. A flow of nitrogen6 over t h e piece during heating and cooling prevents oxidation.

2. Weigh graphite electrode. 3 . Apply the dispersion of boron i n o i l with brush t o t h e graphite electrode. A t h i c k coat, but not sloppy, on fine-grained graphite r e s u l t s i n a f i n a l coating thickness of approfimately 0.8 mg/cm2. 4.

Weigh t h e painted graphite electrode; 2oq& x weight of applied dispersion + cm2 of painted surface = desired coating thickness (2% by w e i g h t of t h e dispersion i s boron). The desired coating thickness f o r a single-plate chamber i s 0.8 mg/cm2 (k0.4 mg/cm2 Y 90$ current). The desired coating thickness f o r a 4-plate chamber i s 0.5 mg/cm2; t h e desired coating thickness f o r a 16-plate chamber i s 0.3 mg/cm2.

Under a strong flow of nitrogen, heat t h e painted graphite electrode t o a temperature a t which no more o i l i s being driven off ( d u l l red heat) and allow t o cool quickly. It i s important t h a t the nitrogen6 flow carry away t h e o i l vapors quickly and t h a t t h e flow i s continued u n t i l t h e coated graphite electrode has cooled t o near 100째C. Boron oxidizes quickly a t temperatures above 20OoC.

The coated electrode may be weighed again t o check t h e thickness of coating. It i s expected that some amount of t h e graphite w i l l be l o s t by oxidation. 2.4.6 High Current Saturation Characteristics of t h e ORNL Compensated Ionization Chamber (Q-1045)7

The saturation voltage and current c h a r a c t e r i s t i c s of the ORNL compensated ionization chamber (Q-1045) have been measured with s p e c i a l 4Excerpted from r e f . 1; t h i s portion was written by J. C. Gundlach. 5Magnesium, brass, aluminum, etc., may a l s o be s a t i s f a c t o r i l y coated

%trogen

with 1% hydrogen i s perhaps b e t t e r .

7Excerpted from ref. 2.

169

regard t o high voltage and current ranges. The chamber was sealed i n an enclosure containing dry nitrogen a t 15 t o 20 psia. The chamber was secured a t a position i n the g r i d p l a t e of the B u l k Shielding Reactor such t h a t the sensitive volume was approximately 15 in. f r o m t h e reactor core face on the horizontal center l i n e of the reactor. This position was chosen so t h a t the chamber current a t f u l l power would be of the order of 1 m a w i t h only a s m a l l gamma background e r r o r ( 5 % ) a t a reactor power three decades lower. The chamber w a s connected as shown i n Fig. 2.4.6. The output of the regulated high-voltage power supplies was measured w i t h a D'Arsonval microammeter ( 1 / 2 $ F.S. accuracy) w i t h 1% precision r e s i s t o r s i n s e r i e s . H i g h currents (loo5 amp and up) were measured with a D'Arsonval microm e t e r and lower currents with a Leeds and Northrup micromicroammeter (model 98368) The reactor was held a t power l e v e l s between 1 kw and 1 Mw, and the chamber voltage w a s varied i n 200-v increments. The data are shown i n Fig. 2.4.7. The actual reactor power w a s 4% lower than the indicated power a t 100 kw and lo$ low a t 1Mw due t o the decreased neutron a t tenuation i n the shielding caused by decreased water density a t higher temperatures. It can be seen from the curves i n Fig. 2.4.7 that the neutronsensitive volume i s well saturated f o r currents l e s s than 100 pa a t any voltage above 600 v. For high accuracy the chamber should therefore be operated only a t currents of 100 pa and below with the standard power supply Q-995. The saturation voltage f o r 800 pa i s approximately 2000 V. The inaccuracy a t 400 pa a t 600 v i s about 2076. Since the chamber can e a s i l y withstand high potentials, there i s no reason w h y it cannot be operated a t 1 m a w i t h a suitable power supply. Thanks are due K. M. Henry and the staff a t the B u l k Shielding F a c i l i t y f o r t h e i r help i n making the measurements.

170

ORNL-Dwg. 66-3912

RCACTOR CLUX,LINtAR 8IQNAL COR READOUT AND CONTCIOL.8LE CIOURL t . 2 0 , 099 TM-782. COMPENSATED ION CHAM8ER 0-1045

Fig. 2.4.1.

" Q " N U M 0 C R S R L F L R T O OAK R I D G E NATIONAL LABORATORY INSTR e C O N T R O L DIV. DWQ. N U M B E R S .

MSRE Linear Power Channel.

Two i n s t a l l e d .

T LT

0 Y

9 rD

- 8

! - !

CHART NO. SE04-N

WONLlWCLL

CWIUDCLCWIA. ?A.

! S !

PHOTO 88131

The IEE Series 360 readout meets human engineering requirements for distance viewing by displaying characters up to 2" in height. The unit operates on a reareprojection principle. When one or more of the 12 lamps at the rear of the unit is lighted, it illuminates the corresponding film message, focuses it through a lens system, and projects it onto the viewing screen at the front of the unit.

Fig. 2.4.4.

Visual Readout Device, Series 360.

174 O R N L - O W G 67-7039

NEGATIVE C POSITIVE V O L T A C E C A B L E S FROM H.V. POWER SUPPLY

W EXIT TO GAS -MONITOR mHRoucn RG-64(1 CABLE

OUTPUT CURRENT NITROGEN CAS I N L E T THROUGH R G - 6 N C A B =

NEUTRON ABSORBING MATERIAL FOR PROTECTION OF AND CONNECTORS

READED SCREW FOR VOLUME A D J U S T M E N T SCREW DRIVER ROUGH CAP

GATIVE VOLTAGE NNECTION C GAS A N N E L TO NEGATIVE LTAGE CONNECTOR

LECTRICAL C O N N E C T Y P ( ROM O U T P U T C U R R E N T SHIELD TO ITE CORE

Q QUARTZ

TUBING I N S U L A T I O N COVERING MAGNESIUM ROO

RTZ ERINC

TUBING I N S U L A T I O N Pb WIRE

GRAPHITE CORE INSULATE

FROM MAGNESIUM CASING

OUARTZ I I O U L A T O R SPACER A R T 2 I N S U L A T O R PINS NG L E A K A G E P A T H

NEGATIVE VOLTAGE E L E C T R O D E

7 VOLUME A D J U S T M E N T

COMPENSATING

BORON

COATED

Fig. 2.4.5.

Y VOLUME

U T CURRENT

SITIVC

VOLTAGE

ELECTRODE

SURFACES

Compensated Ionization Chamber, Neutron Sensitive.

175

ORNL-DWG 67-7037

io1

METER,:%

f 1%

NOTE: WGATIVE TERMINAL DIXONECTED THROUCHOUT TEST

o-'ooya

I '

WESTON

0-50, ~oo,m,~oooy a METER, I % F.S.

ORNL COMF! ION CHAMBER (4-1045) Fig. 2.4.6. Chamber.

Schematic Diagram of ORNL Compensated Ionization

176

5 x 10-~

ORNL-LR-DWG 48t62

407po

-,to4

I f

.. . .. . I

- 7

--w

I-

__ -..--

-. . . I I

. 1

(oo kw

- . _. . . - .

82 pa

42.5~0 I

8.5 p a A.

N z

iI t I-

4.4 pQ

I 1.7po 0.88p0

10-â&#x20AC;&#x2122;

10-8

400

800

4200

1600

2000

2400

COLLECTOR VOLTAGE

Fig. 2.4.7. Saturation Characteristics of ORNL Compensated Ionization Chamber (Q-1045).

177

2.5 2.5.1

ROD SCRAM SAFETY SYSTEM

Rod Scram Safety Channel- Input Instrumentation

The control rods are scrammed by excessively high flux, short react o r period, and excessively high reactor o u t l e t temperature. The safety system employs three independent channels f o r inputs t o the safety system logic and requires t h a t any two out of three indicate unsafe conditions i n terms of e i t h e r flux, period, o u t l e t temperature, or c i r c u i t i n t e g r i t y t o produce a scram. Table 2 . 6 . 1 i n Sect. 2.6 l i s t s control rod actions and t h e conditions which produce them. A t y p i c a l channel of neutron f l u x input instrumentation i s diagrammed It consists of a neutron-sensitive ion chamber, a period i n Fig. 2.5.1. safety module, a flux amplifier' and ion chamber high-voltage supply, EL t e s t module, and f a s t - t r i p comparators.2 The outputs from the period safety module and t h e flux amplifier a r e t h e reactor period and power l e v e l signals which become the inputs t o the f a s t - t r i p comparators. Flux amplifier s e n s i t i v i t y i s adjusted by changing the s i z e of a feedback r e s i s t o r . I n the E R E the f l u x l e v e l t r i p point has two settings, depending on whether o r not f u e l s a l t i s being pumped around t h e loop. Current relays i n the f u e l s a l t pump motor three-phase supply are used t o determine whether the pump i s c i r c u l a t i n g s a l t o r i d l i n g i n helium. These relays provide the signals used t o actuate switching relays which change the value of the f l u x amplifier feedback resistance by a factor of 1000 and thereby provide rod scram t r i p points of 15 kw o r 15 Mw. Figure 2.5.2 diagrams the c i r c u i t r y which s h i f t s f l u x l e v e l t r i p point, and Fig. 2.5.3 i s a block o r signal flow diagram of t h i s c i r c u i t r y . The f a s t - t r i p comparator i s a fast-acting electronic relay w i t h s u f f i c i e n t power-handling capacity t o operate small relays and similar logic and control devices external t o the instrument. It a l s o contains two s m a l l , fast-acting electromechanical p i l o t relays which have greater powerhandling capacity with somewhat reduced response time. The "on-off" outputs of the p i l o t relays i n the comparators a r e the primary input signals t o the safety system logic and t o the control system. Detailed descriptions of these instruments a r e given i n Sects. 2.5.3 t o 2.5.8. The temperature input s i g n a l instruments a r e block diagrammed i n Fig. 2.5.4. The measuring thermocouples ( r e f e r t o Sect. 6.7) a r e composed of two individual thermocouple wires, Chrome1 and Alumel, welded adjacently but separately t o t h e f u e l s a l t o u t l e t piping, thus forming a grounded junction. Each thermocouple wire i s contained i n an individual Inconel sheath and i s insulated from t h i s sheath by magnesium oxide. This construction, using individual, separated wires f o r each l e g of the thermocouple, i s used i n preference t o a dual thermocouple assembly (both wires i n a single sheath), so t h a t i f a thermocouple breaks o r becomes

'Ronald Nutt, Instrumentation and Controls Div. Ann. Progr. Rept. Sept. 1, 1963, ORNL-3578, pp. lo-.

2J. F. Pierce and D. C. Shattuck, Instrumentation and Controls Div. Ann. F'rogr. Rept. Sept. 1, 1963, ORNL3578, pp. 105-6.

178

detached from the pipe, an open c i r c u i t i s created. An open-circuited thermocouple causes the emf-to-current converter t o indicate a f a i l u r e toward safety, t h a t i s , upscale. Thermocouple emf ( i n the 25-mv region) i s amplified by a Foxboro Company type 693 emf-to-current converter which provides an output current, l i n e a r with input emf, of from 10 t o 50 ma i n t o an impedance of from 600 t o 150 ohms f o r the selected input range of t h e thermocouple, i n this case 0 t o 1500째F. The type 693 converter uses magnetic amplifiers t o obtain voltage and power amplification? contains no moving parts, and employs solid-state diodes where required i n t h e c i r c u i t r y . The 10- t o 50-ma output f r o m t h e type 693 converter i s t h e input signal t o t h e high-temperature t r i p switch. This switch, a Foxboro model 63 alarm, compares a set-point voltage with a voltage developed by the input current from the type 693 converter and actuates an alarm relay when t h e input signal voltage i s greater3 than t h e set-point voltage. A contact on t h e alarm relay, closed during normal reactor operation, provides the high-temperature input s i g n a l t o one channel of the rod scram safety system, as w i l l be pointed out subsequently. The emf-to-current converter a l s o supplies a signal, t h e voltage drop across the 400-ohm r e s i s t o r , t o an i s o l a t i o n amplifier. This amplif i e r provides a barrier between the safety system instruments and the remaining nonsafety instruments which make up an input channel. The i s o l a t i o n amplifier transmits t h e input signal i n the forward direction t o the remaining current-actuated switches but decouples the safety instruments i n t h e reverse direction. This v i r t u a l l y eliminates the p o s s i b i l i t y t h a t the e f f e c t s of malfunctions o r misoperation, calibrations, etc., of the nonsafety instruments w i l l be transmitted i n t h e reverse direction t o the safety system. The i s o l a t i o n amplifier i s a Foxboro Company NlllLE'magnetic amplif i e r designed s p e c i f i c a l l y t o amplify t h e output of Foxboro type 630 pressure transducers and t o be compatible with the other Foxboro compoThe amplifier has an input of 0.2 t o 4.0 m a i n t o nents i n Fig. 2.5.4. 10,000 ohms impedance and an output of 10 t o 50 ma i n t o 600 ohms load. The remaining two current-actuated switches i n Fig. 2.5.4, whose outputs a r e labeled "Alarm" and "Control Rod Reverse," a r e Foxboro dual type 63 alarms, both i n a single case. The meter i s a Foxboro modelM65PV-OHT. This i s a D'Arsonval curr e n t meter designed t o operate over an input from 10 t o 50 ma dc.

2.5.2

Rod Scram Safety Channel- Output Instrumentation

The output section of a t y p i c a l safety channel (channel A ) i s diagrammed i n Fig. 2.5.5. From t h e l e f t side of t h e figure, it can be seen t h a t the four t r i p relay contacts i n t h e input instruments a r e i n series and a r e maintained closed during normal reactor operation. These contacts a r e located as follows:

31n other applications an alarm may be produced when the input signal i s l e s s than set-point voltage. This mode of operation (low alarm) i s accomplished by a simple wiring change.

179

1. high- temperature t r i p ( Toutlet

greater than 1300'F) i n the Foxboro

model 63 alarm switch, Fig. 2.5.4;

channel i n t e g r i t y monitor t r i p i n the Q-2634 MSRE t e s t module, Fig. 2.5.1;

high neutron flux t r i p i n a Q-2609 f a s t - t r i p comparator, Fig. 2.5.1;

reactor period t r i p

+1.0 sec) i n a Q-2609 f a s t - t r i p comparator.

A f i f t h s e t of normally closed contacts formed by a manual "Test" button i s a l s o included, followed by a s e a l contact i n p a r a l l e l with a "Reset" push button. During normal reactor operation relays K 1 t o KA5 a r e A energized. These relays, push buttons, and associated indicating lamps make up t h e ORNL model Q-2623 relay safety element, which provides the contact multiplication needed t o produce the safety actions required. The contacts of relays K 1 t o K 3 are interconnected with similar conA A t a c t s from corresponding relays i n channels B and C t o produce three two-out-of-three coincidence matrices i n the power c i r c u i t s t o the rod drive clutches. A t y p i c a l matrix appears on the right-hand side of Fig. Relay K 4 provides one of the control rod "Reverse" signals and 2.5.5. A the "Seal" contact, and relay K 5 i s used t o open t h e drain tank vent A valves and close the radiator doors (load scram). Figure 2.5.6 shows it block diagram and t h e additional c i r c u i t s which operate the vent valves, radiator door, e t c . Each rod drive clutch (see Sect. 2.7) receives i t s power through i t s corresponding contact matrix, and it can be seen t h a t a l o s s of clutch current (rod scram) requires t h a t relays i n a t l e a s t two safety channels be deenergized. This permits t e s t i n g of individual channels during operation without disturbing the reactor and a l s o allows the disabling of any one channel f o r maintenance. Each l e g i n the two-out-of-three matrix shown i n Fig. 2.5.5 contains a 100-ohm r e s i s t o r and a current meter i n s e r i e s with a p a i r of relay contacts. These meters function as input channelmonitors, as can be seen from the following example. Assume t h a t channel A i s being t e s t e d during operation. This may be done with e i t h e r t h e t e s t routine b u i l t i n t o t h e Q-2634 t e s t module (see Sect. 2.5.6) i n channel A or, by using the thermocouple t e s t a s ~ e r n b l y . ~A l e s s complete t e s t i s i n i t i a t e d by pushing t h e "Test" button i n the Q-2623 relay safety element shown i n Fig. 2.5.5. I n any case, relays K A l t o KA5 w i l l be

deenergized and thereby produce open c i r c u i t s i n two of the three branc:h c i r c u i t s i n each of t h e Q-2623 coincidence matrix monitors. From Fig. 2.5.5, it can be seen t h a t the meters labeled "A and C" and "A and B" w i l l change t o show zero current. The t o t a l clutch current w i l l now be c a r r i e d by the t h i r d l e g i n t h e matrix, and meter "B and C" w i l l change upscale t o r e f l e c t t h i s change. The 100-ohm r e s i s t o r s are required t o

'Molten-Salt Reactor Program Semiann. Progr. Rept. Jan. 31, 1964, ORNL-3626, p. 44.

180

ensure equal current division among the three legs i n the matrix. Without these r e s i s t o r s very s m a l l differences i n relay contact resistance would produce large inequalities i n the currents normally carried by the three meters. This r e s i s t o r i s sized so t h a t i t s resistance must be a t l e a s t an order of magnitude larger than any anticipated value of t o t a l relay contact resistance i n s e r i e s with it. Also, it must not be so large t h a t it reduces clutch current t o the "Scram" point when it assumes t h e t o t a l current load of t h e clutch, as it must, when one channel i s i n "Scram" mode. Tests on t h e prototype rod drive show t h a t a t y p i c a l clutch w i l l transmit 39 in.-lb torque a t 22.6 v, whereas the scram torque produced by t h e weight of t h e rod and unbalanced drive mechanism components i s approximately I 2 in.-lb. Thus, it can be seen that there i s ample margin t o prevent undesirable scrams during t e s t i n g or i n t h e event t h a t a single channel be tripped as by removal for maintenance or m a l function. The 32-v Zener diode across t h e clutch c o i l prevents high peak reverse voltages t h a t would otherwise take place when the clutch c o i l curr e n t i s interrupted. Figure 2.5.7 i s a functional diagram of a l l three channels and consolidates the contents of Figs. 2 . 5 . 1 t o 2.5.6.

2.5.3

Safety Chambers

These a r e Reactor Control Inc.' ionization chambers type R.C. 16- (2-2.88k) (Fig. 2.5.8). Specifications a r e as follows: General I n t e g r a l cable construction with redundancy on both s i g n a l and high voltage Cable volume separate from chamber volume No organic materials used i n t h e chamber or cables

Construction:

a l l welded, guard on s i g n a l

Mechanical

Maximum diameter Chamber length Sensitive length I n t e g r a l cable length

%CNC

2.5 in. 7.25 in. 4.25 in. 45 f t

Purchase Order No. 56X-71207, Jan. 24, 1964.

18 1

Material Outer s h e l l

99.97% pure nickel

Inner electrodes

1100 aluminum

Cable sheath and conductor

Stainless s t e e l

Insulation Detector

Alumina ceramic

Cable end s e a l s

Alumina ceramic

Cable

A1203 Enriched 'OB

Electrode coating Resistance a t 25OC Electrode t o ground without cables Electrode t o ground with 45-ft cable Maximum ratings Applied p o t e n t i a l

1000 v dc

Temperature

200째C

Operating c h a r a c t e r i s t i c s Thermal neutron s e n s i t i v i t y

1.6 x

Gamma s e n s i t i v i t y

5 x

Saturation

See curve i n Fig. 2.5.9

2.5.4 2.5.4.1

amp/nv amp r-'

Period Safety Module,6 ORNL Model Q-2635

Description

General

The input, o r current- sensing element (logarithmic diode ) of the period safety module (see Fig. 2.5.10) i s connected i n s e r i e s with the f l u x amplifier input. The voltage across t h e logarithmic diode i s d i f f e r e n t i a l l y amplified with a very high input impedance amplifier so t h a t the chamber current passes undisturbed i n t o the f l u x amplifier module. This voltage i s further amplified and differentiated t o give outputs proportional t o the logarithm of t h e current and i t s period 6This description of t h e Q-2635 Module i s taken from the Instruction Manual, pp. 4-9, written by E. N. Fray, Instnunentation and Controls Division, Aug. 25, 1965.

182

(time required f o r the current t o increase by one E f a c t o r ) respectively. to amp. I n the usual appliThe input current range i s from cation t h e period output serves as an input t o a nuclear reactor safety system; hence the name "period safety

Construction The period safety module i s 1.40 i n . wide, 4.72 i n . high, and 11.90 i n . deep. It i s a standard "one-unit" plug-in module of the ORNL modular reactor instrumentation series depicted on ORNI, drawings Q-2600-1 t o Q- 2600- 5 The c i r c u i t s a r e on a printed c i r c u i t board which i s completely enclosed by a shield. The outputs are displayed on front-panel meters. Test points and access holes t o trimming potentiometers a r e located along t h e top of the shield enclosure. Application The period safety module i s primarily intended t o continuously monitor t h e neutron f l u x and period of a nuclear reactor. Since the module i s not intended t o measure reactor power accurately, the panel meter on t h e output of the logarithmic amplifier i s calibrated i n "log current" from 10-l' t o low4 amp. The output of the period amplifier i s displayed on a panel meter which i s calibrated i n seconds from -30 t o +l.

Specifications Overall specifications f o r t h e period safety module a r e as follows:

Period Output voltage range

-0.033 t o +10 v f o r -30- t o 4.1sec period

Output current

0.1 ma i n t o 100-kilohm load

Scale Zero d r i f t

-30 t o +1 sec

Power required

+15 v dc with regulation +O.l$ 0 t o 55OC

Ambient temperature range

Less than 20 mv/month

Log current Output voltage

Approximately 1.67 v/decade with zero voltage point determined by "Hi C a l l ' s e t t i n g

Output current

1ma i n t o lo-kilohm load

Scale Zero d r i f t

10-10 t o 10-4 amp

Less than 50 mv/month

Input leakage current Power required

Less than amp a t 25OC -+l5v dc with regulation +O.l$

Ambient temperature range

0 to 55OC

183

Applicable Drawings The following l i s t gives the &awing numbers (ORNL Instrument Department drawing numbers) and s u b t i t l e s f o r t h e period safety module:

Q-2635-1 Q-2635-2 Q-2635-3 Q-2635-4 Q-2635- 5 Q- 2602-6

Circuit Details Metalphoto Panel Printed Circuit Board Assembly Parts List

The following l i s t gives the drawing numbers and s u b t i t l e s f o r the plug-in chassis system:

Q- 2600- 1 Q-2600- 2 Q- 2600-3 Q- 2600-4 Q-2600-5 2.5.4.2

Assembly Detai Is Details Details Details

Theory of Operation

General The ionization chamber current passes through a thermionic diode i n the period s a f e t y module and then i n t o t h e flux amplifier (Q-2602) o r equivalent. The voltage drop across this "log" diode i s approximately proportional t o the logarithm of t h e current. The diode voltage i s applied t o a very low leakage d i f f e r e n t i a l amplifier, whose output i s f u r t h e r amplified with a second d i f f e r e n t i a l amplifier t o give the "log current" output. The "log current" output i s differentiated with an operational amplifier t o generate the "period" output. It i s required t h a t the leakage of t h e input difference amplifier be s m a l l compared with t h e f l u x amplifier input leakage.

This leakage

current must come from the ionization chamber current, and i f t h e leakage current i s excessive, t h e current amplified by the f l u x amplifier w i l l be i n error. Circuit DescriDtion

The input current flowing through the thermionic diode V1 develops a voltage across t h e diode t h a t i s e s s e n t i a l l y logarithmic over the curr e n t range of to amp. This voltage i s applied t o a difference amplifier which uses insulated-gate f i e l d - e f f e c t t r a n s i s t o r s (FET's) as active elements The gate leakage current of the FET's i s extremely s m a l l , so t h a t e s s e n t i a l l y a l l the s i g n a l current flows through t h e diode and then i n t o the f l u x amplifier. The gates a r e protected against overvoltage t r a n s i e n t s by neon tubes I1 and 12. (Ordinary Zener diodes are not adequate t o furnish this protection because of t h e i r high leakage current. ) A constant-current c i r c u i t , comprised of t r a n s i s t o r Q2 and r e s i s t o r s R7, R8, and R9, furnishes the b i a s current f o r the difference

(a).

184

amplifier and appears as a large source load impedance t o improve t h e common-mode r e j e c t i o n r a t i o . The gain of t h e difference amplifier i s approximately 2.5. Its output i s applied t o a Fairchild type ADO-3 d i f f e r e n t i a l amplifier whose gain i s adjustable from 2.67 t o 4 by t h e trimming potentiometer R l l (I'M C a l l ' ) . The p a r t i c u l a r gain required i s determined by the c h a r a c t e r i s t i c s of log diode Vl, and it i s adjusted t o give approximately 1.67 v/decade a t t h e output of t h e "log current" amplifier. Trimming potentiometer R18 ("Hi C a l " ) i s required f o r proper scale adjustment of meter M l . The "log current" output i s d i f f e r e n t i a t e d by an additional ADO-3 amplifier whose gain (product of C4 and R25) i s such t h a t a 1-v output corresponds t o a 1-sec period. Two s i g n i f i c a n t smoothing time constants a r e associated with t h e "period" amplifier. They a r e determined by t h e product of R20 and C 4 and R25 with C5, and each i s approximately 100 msec. 2.5.4.3

Operating Instructions

Installation The period safety module i s a module i n t h e ORNL modular reactor instrumentation s e r i e s . Like t h e other modules i n t h i s series, it has standard connectors and dimensions and has a pin-and-hole code on t h e r e a r p l a t e so t h a t the module w i l l not be i n s e r t e d i n a wrong location i n a drawer. The module i s i n s t a l l e d by placing it i n i t s proper location, i n s e r t i n g t h e module firmly, and tightening t h e thumbscrew. The module may be plugged i n with p o w e r on without damage.

Operating Controls Mg Current Panel Meter. - The log current panel meter i s c a l i b r a t e d t o indicate current from his represents a voltage t o 10-4 amp. swing of -10 v; however, t h e output voltage measured with respect t o ground a t a p a r t i c u l a r current w i l l vary from u n i t t o u n i t . This i s determined by t h e "Hi cal" s e t t i n g , which adjusts f o r variations of input diode c h a r a c t e r i s t i c s . Period Panel Meter. The period panel meter i s c a l i b r a t e d t o indicate reactor period from-30 t o +1 sec. This i s a voltage range from 4 . 0 3 3 t o + L O V. The meter i s mechanically zeroed t o give an f f ~ l lindication with no voltage applied. Zero Adjustment. " B a l l " i s f o r zeroing t h e output of t h e insulatedgate difference amplifier &1 with TPl and TP2 shorted together. " B a l 2" i s f o r zeroing t h e output of t h e "log current" amplifier with TP3 and TP4 shorted t o ground. "Bal 3" i s f o r zeroing t h e output of t h e "period" amplifier any time when t h e input i s not changing. Test Points. - The t e s t points a r e located a t t h e t o p of the f r o n t side of t h e shielding enclosure. These a r e used primarily when zeroing o r balancing t h e instrument, as described above.

Connections ~~

All connections a r e made through t h e rear connector P29 when t h e module i s inserted.

185

Operating Procedures The balance of t h e insulated-gate difference amplifier, log current amplifier, and the period amplifier should be checked periodically f o r d r i f t . If correction i s required, the following procedure should be followed:

1. Place a jumper between TP1 and TP2 and measure t h e voltage between TP3 and TP4 with a T r i p l e t t meter (or equal). Adjust "Bal 1" u n t i l t h e voltage i s zero.

Place the jumper across TP3 and TP4 and Tp6 (ground). Adjust " B a l 2" u n t i l the voltage between TP5 and TF6 i s zero.

The period amplifier may be zeroed a t any t i m e the input i s not changing by adjusting "Bal 3" u n t i l the front-panel meter indicates IlmI? o r u n t i l the output i s zero. 2.5.5

2.5.5.1

Flux Amplifier and Ion Chamber High-Voltage Supply, ORNL Model Q-26027

Description

General

The f l u x amplifier (Fig. 2.5.11) i s a low-level dc amplifier t h a t amp from an ionization amplifies current i n t h e range of 10-l' t o chamber. The current from t h e ionization chamber i s proportional t o reactor neutron f l u x i n the usual application; hence the name "flux amplifier. '' An ion chamber high-voltage supply, a dc-to-dc converter, i s contained i n the same module with t h e f l u x amplifier t o provide +250 v t o polarize the ion chamber. The two sections a r e e l e c t r i c a l l y independent. Construction The ion chamber high-voltage supply and the flux amplifier a r e i n a single module 2.83 i n . wide, 4.72 i n . high, and 11.90 i n . deep - a standard "two-unit" plug-in module of the modular reactor instrumentation series depicted on ORNL drawings Q-2600-1to Q-2600-5. The c i r c u i t s are on two printed c i r c u i t boards mounted side by side. The output i s displayed on a front-panel meter. A balance meter, mounted i n the t o p front of the module, i s v i s i b l e when the module i s plugged i n and the drawer i s withdrawn. Near t h e meter i s a "zero" push button arid a trimming potentiometer f o r balancing t h e f l u x amplifier.

Application The ion chamber high-voltage supply and flux amplifier a r e intended primarily t o continuously monitor neutron f l u x i n a nuclear reactor. To

Written by J. L. Anderson, Mar. 3, 1965.

186

this end the panel meter i s calibrated i n percent power from 0 t o 200%. However, the amplifier may be used, with o r without the ion chamber high-voltage supply, wherever it i s desired t o measure current i n the range 10-8 t o 10-4 amp ~ U U . scale. The amplifier has two i n t e r n a l feedback r e s i s t o r s and provisions f o r connecting an external feedback r e s i s t o r t o e s t a b l i s h any desired scale calibration vs current within t h e capability of the instrument. A f l u x reset mechanism Q-2603, a companion u n i t , can be used with the f l u x amplifier t o continuously adjust the feedback factor or gain over a 3 t o 1 range. The flux r e s e t mechanism i s a small instrument servo t h a t adjusts the feedback r a t i o of t h e f l u x amplifier so as t o force t h e flux amplifier output t o agree with another signal, t y p i c a l l y computed heat power.

Specifications Overall specifications f o r t h e flux amplifier and ion chamber highvoltage supply-are given below. Flux Amplifier Output voltage range

0 t o +I2 v l i n e a r f o r positive current (flowing into amplif i e r ) ; 0 t o -1.2 v f o r negat i v e current

Output current

30 ma i n t o 300-ohm load

Scale

O t o 200% power

Zero d r i f t

Less than 1mv/day a t cons t a n t temperature; l e s s than +lo mv f o r 0 t o 55째C

Input leakage current

Less than 10-l'

Response time

10 t o 90% r i s e time i n less than 100 psec with a 200kilohm feedback r e s i s t o r and 0.002-pf capacitor on input

Power required

+25 + 0.25 v dc with regulation +0.1$; -25 k 0.25 v d C with regulation +O .I$

Ambient temperature range

0 t o 55OC

amp a t 25OC

Ion Chamber High-Voltage Supply Output voItage

+250

Input power required

+32 rt 4 v dc and 200 ma maximum Rated 5 ma continuous; w i l l deliver -50 ma i n t o a 3kilohm load o r 1 ma minimum i n t o a short c i r c u i t

Output current

25 v dc

187

Overload protection

Undamaged by any overload, inc luding a short c i r c u i t

Load regulation

Less than S$, O t o 5 ma

Line regulation

Less than log, 28 t o 36 v dc

Output r i p p l e and frequency

Less than 50 mv a t 5 ma load;

-8 kc Adjustments

None

Starting

Self-starting, no load t o f u l l load

Ambient temperature range

0 t o 55OC

Applicable Drawings The following l i s t gives the drawing numbers (ORNL Instrument Department drawing numbers) and s u b t i t l e s f o r t h e ion chamber highvoltage supply and the f l u x amplifier:

Q-2602- 1 Q-2602-2 Q-2602-3 Q-2602-4 Q-2602-5 Q-2602-6 SF- 239

Circuit Details Metalphoto Panel Printed Circuit Board Assembly Parts List Fabric a tion Speci f ica tion

The following l i s t gives the drawing numbers and s u b t i t l e s for the plug-in chassis system:

Q-2600- 1 Q-2600-2 Q-2600-3 Q-2600-4 Q-2600- 5 2.5.5.2

Assembly Details Details Details Details

Theory of Operation

General The ion chamber high-voltage supply and f l u x amplifier consist of a stable, direct-coupled low-leakage amplifier and a self-contained highvoltage supply f o r ionization chamber polarization. The chamber voltage supply consists of a s e r i e s preregulator, t o regulate the b a t t e r y input voltage, and an unregulated dc-to-dc converter. Circuit Description of t h e Ion Chamber High-Voltage Supply The power supply i s designed t o operate from a nominal 32-v s t a t i o n b a t t e r y with a terminal voltage variation from 28 t o 36 v dc. This wide variation makes necessary a voltage preregulator consisting of t r a n s i s t o r s Q9, &lo, &11, and Q

188

The preregulator output voltage i s sensed by r e s i s t o r s R24 and R26 and applied t o t h e base of amplifier stage Q11. A reference voltage (16.8 v) generated by Zener diode s t r i n g D4, D5, and D6 i s applied t o the emitter of QJ1. The amplified difference appears a t t h e collector of Ql1 and i s applied t o driver QlO and pass t r a n s i s t o r Ql2. A constant coll e c t o r current i s provided f o r Q by tl r al n s i s t o r Q9, Zener diode D3, and t h e associated network. The preregulator output (test point TP1) i s f i l t e r e d by C3, C4, and R27 and i s applied t o the dc-to-dc converter. Ql3, Q4 l, T1, and the associated c i r c u i t r y comprise a free-running square-wave o s c i l l a t o r ; D7, I@, and D9 assure t h a t the c i r c u i t w i l l be both self-protecting and s e l f - s t a r t i n g . Capacitors C6 and C7 round t h e edges of the square wave somewhat t o avoid the generation of sharp, highfrequency spikes which may be coupled t o other c i r c u i t s . A square wave of approximately 250 v peak-to-peak amplitude and frequency of approximately 8 kc appears on winding 1-3 of transformer T1. This voltage i s r e c t i f i e d by diode bridge D10-Dl3 and i s f i l t e r e d by a pi-section RC f i l t e r composed of C8, C9, and R32. The output i s approximately 250 v dc with less than 50 mv of 8- or 16-kc ripple. When The output voltage vs load current i s shown i n Fig. 2.5.12. the output i s short-circuited, the c i r c u i t continues t o o s c i l l a t e a t a very low amplitude and supplies about 1 m a of current. The c i r c u i t w i l l recover undamaged upon removal of t h e short c i r c u i t or overload.

Circuit Description of the Flux Amplifier The f l u x amplifier converts a low-level current from an ionization chamber t o a usable voltage. The current range i s determined by feedback r e s i s t o r R33, which may be paralleled by R10 o r an external res i s t o r . The input current i s converted t o a f u l l - s c a l e voltage of 10 v a t t h e output of the amplifier. The amplifier i s an operational type with a high open-loop gain and Only a small leakage current a high open-loop impedance (Fig. 2.5.13). flows i n the input of the amplifier; therefore, a l l the s i g n a l current flows through feedback r e s i s t o r Rf. The voltage produced a t t h e output is

where Is i s the s i g n a l current i n amperes and Rf i s t h e resistance i n ohms. The s e n s i t i v i t y of the f l u x amplifier can be adjusted by f l u x reset mechanism Q-2603. Instead of feedback r e s i s t o r being connected dir e c t l y t o the output as shown i n Fig. 2.5.13, it i s connected through a Potenvoltage-dividing network t o t h e output as shown i n Fig. 2.5.14. tiometer R6 i s motor driven t o adjust the output voltage (with constant input current) u n t i l t h e flux amplifier output agrees with an independent signal as might be derived from a heat-power computer. The output voltage i s then R6 Eo = 'inRf (OX6 where

+ R7

+ R?

i s the potentiometer s e t t i n g as indicated i n Fig. 2.5.14.

189

The f l u x amplifier i s composed of eight s i l i c o n t r a n s i s t o r s and a s i l i c o n diode. Input device Q1 i s a f i e l d - e f f e c t t r a n s i s t o r which has low gate-leakage current. I n the specified range of input current, the f i e l d - e f f e c t t r a n s i s t o r i s a satisfactory e l e c t r i c a l replacement f o r an electrometer tube and i s f a r more rugged. Some unusual characteristics of the f i e l d - e f f e c t t r a n s i s t o r a r e used advantageously i n this particular amplifier. The field-effect t r a n s i s t o r drain-voltage d r i f t with temperature i s a function of t h e drain current. When t h e drain current i s larger than approximately 30 pa, the temperature coefficient i s positive. When the drain current i s l e s s than approximately 30 pa, t h e temperature coefficient i s negative. The f i e l d - e f f e c t t r a n s i s t o r i s biased a t approximately 45 pa so t h a t i t s net current d r i f t w i l l be i n a positive direction t o cancel out drifts of opposite direction due t o the remaining t r a n s i s t o r s and diodes. The voltage gain from gate t o drain of the field-effect stage i s about 20. The remaining t r a n s i s t o r s are operated i n standard configurations. Transistor Q2, an emitter follower with near unity voltage gain, impedance matches f i e l d - e f f e c t t r a n s i s t o r Q1 t o the following gain stage. Q3 and Q4 comprise a d i f f e r e n t i a l high-voltage-gain stage. The gain from the base of Q3 t o the collector of Q4 i s about 500. Transistors Q5, Q6, Q7, and Q8 are complementary emitter-follower power-gain stages with unity voltage gain. The function of these four t r a n s i s t o r s i s t o allow the output t o swing plus and minus 10 v and deliver up t o about 30 m a of current t o the load.

2.5.5.3

Operating Instructions

Installation The chamber high-voltage supply and f l u x amplifier i s a module i n the ORNL modular reactor instrumentation s e r i e s . U k e the other modules i n this s e r i e s , it has standard connectors and dimensions and has a pinand-hole code on the r e a r p l a t e so t h a t the module w i l l not be inserted i n a wrong location i n a drawer. The module i s i n s t a l l e d by placing it i n i t s proper location, i n s e r t i n g the module firmly, and tightening the thumbscrew. The module may be plugged i n with power on without damage. Operating Controls

The panel meter i s calibrated t o indicate power from Panel Meter. 0 t o 2009; this corresponds t o a voltage output of 0 t o -10 v. If t h e amplifier i s t o be used with a negative input current, t h e meter leads should be reversed. Balance Meter. - A zero-center balance meter on the t o p of t h e module i s v i s i b l e with the module inserted and the drawer pulled out. The meter i s used with t h e push button and zero adjustment located a t t h e edge of t h e printed c i r c u i t board nearby t o correct f o r d r i f t periodically. Zero Adjustment. The zero adjustment i s used t o balance the dc amplifier t o correct f o r d r i f t . Zero Push Button. - This push-button switch short-circuits the input of the amplifier so t h a t it may be balanced even when signal current i s present.

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Connections All connections a r e made through the rear connector F9 when the module i s inserted. A jumper between pins 2 and 3 of â&#x201A;Ź9 i s provided so t h a t i f the module i s removed from a drawer a warning s i g n a l i s given.

Operating Procedures The balance of t h e f l u x amplifier should be checked periodically by depressing zero push button S1 and observing balance meter M 2 . If t h e meter reads anywhere on scale less than plus or minus full scale when t h e push button i s depressed, the balance i s satisfactory. With the push button released the meter should read upscale t h e same amount as the front-panel meter reading. If adjustment i s necessary, t u r n zeroadjustment potentiometer R3 clockwise t o move the indicator i n a positive direction or counterclockwise t o move the indicator i n a negative direction. There a r e no adjustments on the chamber high-voltage supply. Precautions Since t h e output of the high-voltage supply can be l e t h a l , care should be taken not t o place fingers i n t h e rear portion of this module. W e r n a l connections t o t h e ionization chamber should be made with the power off or the module unplugged t o avoid possible damage t o f i e l d e f f e c t t r a n s i s t o r Q,l.

2.5.5.4

Maintenance Instructions

General

This module i s designed t o opera-e continuously with a minimum of maintenance and adjustment. Zero adjustment and voltage t e s t points a r e accessible from t h e top of the drawer with the module inserted and the c i r c u i t s energized. Periodic Maintenance The amplifier balance should be checked (see Operating Procedures, above) once every three or four weeks. The high-voltage output should be checked every three o r four months by measuring with a voltmeter a t t h e t e s t points. The w h i t e point on t h e module i s ground test point TP3; the red point i s t h e highvoltage output t e s t point TP2; and t h e gray point i s t h e preregulator output t e s t point TP1. The voltages a t t h e t e s t points should read (with respect t o TP3); TP1, +25 f 1 v; and TP2, +250 f 25 v. Calibration Procedures There are no calibration procedures.

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2.5.6

W 2.5.6.1

MSRE Test Module, ORNL Model Q-26348

Description

General The MSRE t e s t module (Fig. 2.5.15) i s a special-purpose u n i t desigped t o supply calibration signals f o r t e s t i n g the response of p a r t s of t h e safety system of t h e MSRE. The module provides two calibrated current ramps a t different r a t e s t o check t h e response and approximate calibration of t h e flux amplifier and associated f a s t - t r i p comparators. An adjustable steady-state current can be substituted f o r the ramps f o r more precise calibration. I n addition, the module provides two steady-state currents f o r calibration of the "log current" portion of the period safety module and two voltage ramps f o r calibration of t h e "period" portion of the period safety module and associated f a s t - t r i p comparator. An ion chamber undervoltage monitoring c i r c u i t i s provided i n this module. A l l these a r e i n i t i a t e d by push buttons from the module front panel. Construction The module i s 2.83 i n . wide, 4.72 i n . high, and 11.90 i n . deep. It i s a standard "two-unit" plug-in module of the ORNL modular reactor instrumentation s e r i e s depicted on drawings Q-2600-1 t o Q-2600-5. The c i r c u i t r y i s constructed on two large printed c i r c u i t boards mounted within t h e module. Amlication The module i s intended t o supply signals f o r both preoperational and on-line t e s t i n g of the nuclear safety system of the MSRE. Although. the signal types and c i r c u i t r y used a r e generally applicable t o any reactor safety system employing the ORNL modular reactor instrumentation series, the signal levels and rates f o r this module a r e t a i l o r e d especially f o r t h e MSRE. SDeci f i ca t ions Output Ramps. - The basic ramp generator supplies a voltage ramp of 0 t o +14 with a r a t e of +1 v/sec. "his ramp voltage i s applied t o suitable multiplier r e s i s t o r s t o obtain t h e required current-ramp. The output currents are: high rate (300 kilohms), 0 t o 46.? x amp; and low r a t e (300 megohms), 0 t o 46.7 x amp. Output Currents, Steady State. The output currents a r e adjustable with a ten-turn precision potentiometer on the f r o n t panel calibrated t o be d i r e c t reading from 0 t o 100. The output currents are: high current amp; and low current (200 megohms), 0 t o (200 kilohms), 0 t o 100 x 100 x 10-9 amp. Log Current, Steady State. Two c a l i b r a t i o n currents are derived from the ion chamber high-voltage supply by suitable multiplier r e s i s t o r s

8This material was taken from the Instruction Manual, pp. 5-14, written by E. N. Fray, July 28, 1965.

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f o r current c a l i b r a t i o n of t h e period safety module. They are: high (25 megohms), lom5 amp; and low (250,000 megohms), lo-' amp. Period Calibration. - The +1-v/sec ramp i s applied t o t h e log curr e n t amplifier i n t h e period safety module through a s u i t a b l e input res i s t o r . This produces a constant output a t t h e period amplifier f o r c a l i b r a t i o n purposes. Two approximate c a l i b r a t i o n points are provided: +1 sec period (500 kilohms) and +2 sec period (1megohm). Undervoltage Monitor. - The c i r c u i t continuously monitors the polarizing voltage of t h e ionization chamber on a r e t u r n lead from t h e chamber. When t h e chamber voltage i s greater than 200 ? 10 v, a green light labeled "Normal" on t h e f r o n t panel i s lit. When t h e chamber voltage f o r any reason drops below 200 ? 10 v, t h e c i r c u i t changes s t a t e and l i g h t s both a red "Low" indicator lamp and a yellow f'Lg;tchffindicator lamp. When t h e voltage i s restored, t h e "Low" indicator i s extinguished, and t h e "Normal" l i g h t again comes on. The "Latch" l i g h t remains on u n t i l t h e front-panel "Reset" push button i s depressed. The r e l a y t h a t actuates t h e indicator lamps has additional contacts (single pole, double throw) f o r use i n external c i r c u i t s . An additional front-panel push button labeled "Test" simulates a low-voltage condition t o t h e monitor c i r c u i t without a f f e c t i n g a c t u a l chamber voltage. Power Requirements. - The module requires +32 f 4 v unregulated and +25 v f 0.1% regulated. Ambient Temperature Range. - The ambient temperature range i s 10 t o

55OC. Applicable Drawings The following l i s t gives t h e drawing numbers (ORNL Instrument Department drawing numbers) and s u b t i t l e s f o r t h e MSRE t e s t module: Q-2634-1 Q- 2634- 2 Q- 2634-3 Q-2634-4 Q- 2634- 5 Q-2634-6

Circuit Details

Metalphoto Panel Printed C i r c u i t Board Assembly Parts List

The following l i s t gives t h e drawing numbers and s u b t i t l e s f o r t h e plug-in chassis system: Q- 2600- 1 Q- 2600-2 Q- 2600- 3 Q- 2600- 4 Q- 2600- 5 2.5.6.2

Assembly Details Details Details Details

Theory of Operation

General The M Sm t e s t module i s a special-purpose module designed t o provide signals t o t e s t parts of t h e nuclear s a f e t y system of t h e MSRE.

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Although it was originally intended t o have a general-purpose t e s t module which would be applicable t o several reactors, and such a module Q-2601 w a s designed, it soon developed t h a t a single t e s t module would not suffice because of the different instrument s e n s i t i v i t i e s and varied functions of t h e several reactor systems under design. Consequently, a separate t e s t module was designed f o r each reactor t h a t uses this type of instrumentation. I n s p i t e of t h e unique project application of t h e module and because of t h e general applicability of the c i r c u i t s used i n t h e module, a "Q" number was assigned t o t h e MSRE t e s t module f o r t h e convenience of designers of future systems. Circuit Description

Ramp Generator. - A l i n e a r voltage ramp i s generated by charging a capacitor with a constant current. I n c i r c u i t diagram Q-2634-1, it i s i s held a t a constant p o t e n t i a l with seen t h a t the base of t r a n s i s t o r Q1 respect t o t h e +25-v supply by Zener diode D1. T h i s i n t u r n causes t h e emitter voltage of Q t o bel constant across a fixed r e s i s t o r R2, establ i s h i n g constant emitter current. To a first approximation, t r a n s i s t o r collector current i s equal t o emitter current, regardless of collector voltage, u n t i l saturation i s reached, that is, u n t i l the collector voltage equals the emitter voltage. Thus, the collector current of Q is l constant and flows i n t o capacitor C1. I n the standby condition, the capacitor i s short-circuited by cont a c t s of relays K l and K2 and by contacts of push buttons S7 and S 8 . When any one of these contacts opens, t h e capacitor begins t o charge. The rate of change of voltage across t h e capacitor i s determined by t h e magnitude of the current and the s i z e of the capacitor. I n this case

The voltage across C 1 is sensed by a very high beta Darlington-pair emitter follower Q2 and Q3. The maximum amplitude of the ramp i s limited by saturation of Q1 and Zener diode D l t o about 15 v across C 1 o r 14 v

a t the emitter of &3.

'b,

The MSRE t e s t module i s designed t o provide Current Switching. t e s t currents f o r both the flux amplifier and t h e period safety module. Since t h e input of the f l u x amplifier i s i n s e r i e s with the l o g diode of t h e period safety module, any t e s t current w i l l be sensed and indicated by both instruments. Since t h e f l u x amplifier has 100% feedback t o t h e input terminal, there i s no input voltage o f f s e t . T h i s means t h a t a r e l a t i v e l y low-voltage current source i s adequate f o r generation of i t s t e s t currents. For application t o the period safety, a b e t t e r current source i s required, since t h e voltage across the log diode i s not cons t a n t but changes with input current. To this end t h e calibration curr e n t s for t h e period safety are produced by using t h e chamber high-voltage supply and s u i t a b l e multiplier r e s i s t o r s . The "Rate" t e s t currents and the "Adjustable" t e s t currents are intended f o r use with the flux amplif i e r only; further, application of e i t h e r of these currents causes t h e

194

period safety t o indicate an incorrect current, which should be ignored. Since a l l t e s t currents a r e applied by way of a second ionization chamber signal lead, which i s separate a l l the way t o t h e chamber plates, a t e s t s i g n a l must t r a v e l t o t h e chamber and back t o the safety channel input. I n this way a successful current t e s t v e r i f i e s t h a t t h e chamber i s connected. Flux Amplifier. - For steady-state calibration o r checks, a voltage adjustable from 0 t o 20 v by a front-panel Helipot may be applied through e i t h e r a 200-kilohm o r a 200-megohm r e s i s t o r t o t h e amplifier input by energizing relay K4 or K3 respectively. The corresponding currents a r e 0 t o 100 pa and 0 t o 100 na. The Helipot d i a l labeled "Current Adjust" i s read d i r e c t l y from 0 t o 100 units. The voltage ramp described above may be applied through a 3oo-kilohm or a 300-megohm r e s i s t o r by energizing relay K1 or K2, respectively, res u l t i n g i n current ramps ranging from 0 t o 46.7 pa and 0 t o 46.7 na. The ramp i s i n i t i a t e d by a second contact of K l o r K2, which removes t h e short c i r c u i t from capacitor C1. Period Safety. - Fixed calibration currents f o r t h e period safety module are generated by applying t h e chamber high voltage (approximately 250 v) through e i t h e r a 25- or a 250,000-megohm r e s i s t o r , r e s u l t i n g i n currents of or lo" amp. These currents a r e i n i t i a t e d by energizing relays K5 and K6 respectively. To check t h e calibration of t h e period amplifier, t h e voltage ramp i s applied t o t h e input (terminal 6 ) of t h e log current amplifier. Subsequent d i f f e r e n t i a t i o n i n the period amplifier r e s u l t s i n a constantvoltage output (constant indicated period) whose magnitude i s determined by t h e generated ramp r a t e and the gain of the log current amplifier. Two calibration points a r e provided by applying t h e voltage ramp through e i t h e r a 500-kilohm or a l-megohm r e s i s t o r ; the r e s u l t i s a period indication of about 1 and 2 sec respectively. Actually, the l-sec period t e s t should always generate a period slightly l e s s than 1 sec, so t h a t the l-sec f a s t - t r i p comparator will t r i p . These t e s t s a r e i n i t i a t e d by depressing push buttons S7 o r S8 t o generate the 1- o r 2-sec period. Chamber Voltage Monitor. I n a manner similar t o the signal lead, a separate high-voltage lead i s returned from t h e p l a t e s of t h e ionization-chamber. "his voltage i s continuously monitored by a c i r c u i t cons i s t i n g of t r a n s i s t o r s Q4 through Q8. If t h e voltage, normally 250 v, i s interrupted o r reduced below approximately 200 v, an undervoltage alarm occurs. The sensed voltage i s reduced from 250 t o 100 v a t R 5 by two Zener diodes, D2 and D3. The voltage i s f u r t h e r reduced t o 20 v a t the base of Q4 by the dividing action of R5 and R6. The emitter of Q4 i s biased a t 10 v, so t h a t t h e t r a n s i s t o r i s reverse biased and not conducting under normal conditions. Since t h e c o l l e c t o r of Q4 i s near ground pot e n t i a l , t h e Darlington emitter follower @ and Q6 and the relay drivers Q7 and Q8, driven by the emitter-follower output, a r e also not conducting. A normally closed contact of X7 energizes the green "Normal" lamp on the f r o n t panel. When the input voltage drops below 200 v, the Q4 base voltage i s reduced t o below 10 v, and &1: conducts. The collector voltage of @t increases t o 10 v, turning on @, Q6, Q7, and Q8 and energizing both K7 and K8. The contacts of K7 extinguish the "Normal" lamp and l i g h t the

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red "Low" chamber voltage lamp. A second s e t of K7 contacts controls external c i r c u i t s . K8 seals i t s e l f i n and w i l l remain energized, l i g h t ing t h e "Latch" lamp, u n t i l input voltage i s restored and "Reset" button S2 i s depressed. This enables the operators t o identify a momentary chamber voltage f a u l t . The voltage monitor c i r c u i t i s t e s t e d by pressing "Test" push button S1 on t h e f r o n t panel. This reduces the voltage a t the base of Q4, simul a t i n g a low input condition without causing significant reduction of the chamber voltage i t s e l f . 2.5.6.3

Operating Instructions

Installation The MRE t e s t module i s one of t h e ORNL modular reactor i n s t m e n t a t i o n s e r i e s . Like the other modules i n t h i s series, it has standard connections and dimensions and has a pin-and-hole code on t h e r e a r p l a t e s o t h a t the module will not be inserted i n a wrong location i n a drawer. The module i s i n s t a l l e d by placing it i n i t s proper location, i n s e r t i n g the module firmly, and tightening t h e thumbscrew. The module may be plugged i n with power on without damage. Operating Controls on Panel

Chamber Voltage Monitor. Three p i l o t lamps indicate the state of chamber voltage. The green "Normal" light i s on when the voltage i s greater than 200 v. The red "Low" l i g h t i s on when the voltage i s l e s s than 200 v. The amber "Latch" l i g h t comes on when t h e voltage drops below 200 v and remains on until the "Reset" button i s pressed. When the " T e s t " button i s depressed, it causes a simulated low voltage t o t e s t the monitor. High Rate. - When the "High Rate" button i s depressed, a current ramp of 3.33 pa/sec i s applied t o t h e safety channel input. Low Rate. - When the "Low Rate" button i s depressed, a current ramp of 3 . 3 3 i s ~ applied t o the safety channel input. High Current. - When the "ELgh Current" button is depressed, a current, adjustable from 0 t o 100 pa by t h e "Current Adjust" potentiometer, i s applied t o the safety channel input. Low Current. When t h e "Low Current" button i s depressed, a current, adjustable from 0 t o 100 na by t h e "Current Adjust'' potentiometer, i s applied t o the safety channel input. When the "High Log Current" button i s depressed, High Log Current.

a current of amp i s applied t o the safety channel input. Low Log Current. - When t h e "Low Log Current" button i s depressed,

a current of amp i s applied t o the safety channel input. 1-sec Period. - When t h e "1-sec Period" button i s depressed, a voltage ramp i s applied t o t h e period safety module, r e s u l t i n g i n an output indication of approximately a 1-sec period. 2-sec Period. When t h e "2-sec Period" button i s depressed, a voltage ramp i s applied t o the period safety module, r e s u l t i n g i n an output indication of approximately a 2-sec period.

Connections A l l connections a r e made through the r e a r connector P28 when t h e module i s inserted. A jumper between pins 4 and I 2 i s provided so t h a t i f the module i s removed from a drawer, a warning signal may be given.

Operating Procedures A l l tests a r e i n i t i a t e d simply by depressing t h e proper push button on the f r o n t panel.

2.5.7 2.5.7.1

Fast-Trip Comparator, ORNL Model Q-2609'

Description

General The f a s t - t r i p comparator" c i r c u i t (Fig. 2.5.16) compares the m a g n i tude of two input dc signals having opposite p o l a r i t i e s and produces an output voltage having e i t h e r of two possible values, depending upon which input voltage i s larger. Two electronic outputs drive logic c i r c u i t s ext e r n a l t o this u n i t , and there a r e a l s o two relay drivers within the u n i t . The change i n voltage from one l e v e l t o the other i s completed i n l e s s than 200 psec after t h e t r i p s i g n a l occurs. The relays can change states i n approximately 10 msec. Each relay has one set of contacts f o r external connections and one s e t t o perform an indicating function on the front panel. One relay can be connected t o hold a t r i p indication a f t e r the t r i p has cleared, and t h e other relay indicates the immediate s t a t e of t h e c i r c u i t . Several ex%ernal connections can be made t h a t allow the c i r c u i t t o t r i p f o r a variety of input conditions. With a reference serving as one signal, the c i r c u i t can t r i p on a positive o r a negative input s i g n a l and on an increasing or a decreasing signal. For t h e case of two ext e r n a l signals A and B, tripping action can take place when the magnitude of A i s greater than or less than t h a t of B, provided A and B have opposite p o l a r i t i e s .

Construction The f a s t - t r i p comparator i s constructed i n a single module 1.40 in. It i s a standard "one-unit" plug-in module of the modular reactor instrumentation s e r i e s depicted on drawings Q-2600-1 t o Q-2600-5. The c i r c u i t i s constructed on a printed c i r c u i t board mounted within a shielding enclosure with removable sides.

wide, 4.72 i n . high, and 11.90 i n . deep.

'Taken from Instruction Manual, written by J. I,. Anderson, Instrumentation and Controls Division, Apr. 13, 1965. 'OJ. F. Pierce and D. C. Shattuck, Instrumentation and Controls Div. Ann. Progr. Rept. Sept. 1, 1963, ORNL3578, pp. 10%.

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Application The f a s t - t r i p comparator i s intended primarily t o be used as a voltage l e v e l discriminator f o r safety and control functions i n a nuclear reactor. For maximum f l e x i b i l i t y t h e u n i t has two inputs, so t h a t it may be used e i t h e r t o compare two signals o r t o compare one signal with an external reference. The c i r c u i t i s b i s t a b l e i n nature; t h a t is, there i s no change i n output indication u n t i l the predetermined t r i p l e v e l i s exceeded, a t which time the output suddenly changes from one s t a t e t o t h e other. The t r i p l e v e l i s nominally zero volts; t h a t i s , the two inputs must be of opposite polarity, so t h a t when the magnitude of one input exceeds t h e magnitude of t h e other, t h e c i r c u i t changes s t a t e . By use of s u i t a b l e external jumpers t h e c i r c u i t can be arranged t o t r i p o:n e i t h e r net positive or net negative input. Two types of output are available. The logic output, intended f o r use i n fast safety systems, i s -10 v normally and 0 v when tripped. The switching time i s l e s s than 200 psec. Normally the logic l e v e l will revert t o normal as soon as t h e input s i g n a l drops below the t r i p level. However, by use of external jumpers, t h e c i r c u i t can be made t o latch, o r seal, t h e logic output i n the t r i p s t a t e u n t i l manually r e s e t , provided the t r i p s i g n a l p e r s i s t s f o r 10 msec o r more. The second type of output i s provided by two relays. Both relays a r e driven by t h e logic s i g n a l described previously and respond accordingly. Kl. may be arranged t o l a t c h i f the t r i p signal persists f o r more than 10 msec; the relay w i l l go t o the t r i p s t a t e and remain there u n t i l manually r e s e t , regardless of whether o r not the logic l e v e l signal i s arranged t o latch. This arrangement i s sometimes called a "scram catcher,'' i n t h a t it allows a momentary t r i p t o be located and i d e n t i f i e d a f t e r it has disappeared. K2 operates d i r e c t l y off the logic signal and w i l l be i n the same s t a t e . Contacts of both relays a r e available f o r actuating external c i r c u i t s . Speci f i c a t ions Specifications f o r t h e f a s t - t r i p comparator a r e as follows:

Trip range

The t r i p range shall be adjustable from +1 v t o +10 v o r from-1 v t o -10 v

Trip point accuracy

Once t h e t r i p point has been s e t , variations i n temperature from 10째C t o 55Oc and aging of components should not cause the t r i p point t o change more than 50 mv referred t o t h e t r i p c i r c u i t input signal

Trip point hysteresis

When the s i g n a l f a l l s 60 mv below the t r i p point, the c i r c u i t s h a l l r e s e t i t s e l f ; the c i r c u i t s h a l l not r e s e t l e s s than 4-0 mv below the t r i p point

198

Input impedance

150 kilohms, e i t h e r input

Logic output

In the normal s t a t e t h e logic l e v e l output s h a l l be -10 v f 1/2 v, 20 ma maximum drain; i n the t r i p s t a t e t h e logic l e v e l output s h a l l be 0 v k 1/2 v

Tripping time logic l e v e l

The change from normal t o abnormal cond i t i o n (-10 t o 0 v) shall require l e s s than 200 psec

Relay outputs

Type l i s a DPEC relay having contacts rated a t 2 amp a t 32 v dc and 2 amp a t U5 v ac; this relay must change s t a t e i n less than 100 msec Ty-pe 2 i s a fast-latching relay that w i l l operate i n less than 10 msec; t h e purpose of t h i s relay i s t o indicate t h e location of a momentary t r i p signal

Power required

+I5 v

0.25 v dc with regulation of

0.1%; -15 v k 0.1 v dc with regulat i o n of O.l$; +10 v 0 . 1 v dc with regulation of 0.1%; -32 v 4 v dc,

unregulated

Ambient temperature range

10 t o 55OC

Indication

Front-panel indicator lights shall show the immediate s t a t e of the t r i p , that is, "Trip" o r "Normal," and a l s o "Latch," which indicates t h a t a momentary t r i p of 10 msec or more has occurred

T e s t and r e s e t

Front-panel push buttons s h a l l cause t h e c i r c u i t t o t r i p regardless of the input s i g n a l ("Test") and t o reset t h e l a t c h indication ("Reset")

Applicable Drawings and Specifications

me following l i s t gives t h e drawing numbers (ORNL Instrument Department drawing numbers) and s u b t i t l e s and fabrication specification number f o r t h e f a s t - t r i p comparator:

199

Q-2609-1 Q-2609-2 Q-2609-3 Q- 2609 4 Q-2609-5 Q-2609-6 SF-253

Circuit Details Metalphoto Panel Printed Circuit Board Assembly Parts List Fabricat ion Speci f ication

The following l i s t gives the drawing numbers and s u b t i t l e s f o r the plug-in chassis systems :

Q-2600-1 Q-2600-2 Q-2600-3 Q-2600-4 Q-2600-5

2.5.7.2

Assembly Details Details Details Details

Theory of Operation

General

The f a s t - t r i p comparator i s composed of three functional parts: a, voltage comparator, logic switching c i r c u i t s , and r e l a y drivers. The input stage, consisting of Q and Q2, l i s a compound (Darlington) d i f f e r e n t i a l amplifier having a high degree of temperature s t a b i l i t y and a high input impedance. This stage drives a simple d i f f e r e n t i a l amplif i e r Q3, which, i n turn, drives a Schmitt t r i g g e r c i r c u i t Q4. These three stages make up t h e voltage comparator. A l l t r a n s i s t o r s a f t e r t h e Schmitt t r i g g e r c i r c u i t a c t as switches and a r e e i t h e r off (open) o r saturated (closed). Transistor Q5 a c t s as a buffer t o prevent t h e Schmitt t r i g g e r c i r c u i t from being affected by variations i n t h e load. Electronic output points a r e located a t the collectors of Q6 and Q7. Two double-pole, double-throw relays K l and K2 each provide one s e t of contacts f o r t h e operation of external c i r c u i t s and one s e t f o r t h e operation of indicator lamps on t h e f r o n t panel of the t r i p c i r c u i t . Rel a y K l may be connected t o hold t h e "Latch" indicator lamp I1 from t h e time a t r i p has occurred u n t i l t h e manual r e s e t switch S2 has been depressed, even i f the signal l e v e l decreases below t h e t r i p point. Relay K2 energizes indicator lamp I2 ("Trip") o r I3 ("Normal"), depending upon t h e existing state of the c i r c u i t . Either o r both of the relay drivers Q8 and Q9 may be driven from e i t h e r electronic output. For operational f l e x i b i l i t y the connections t o the electronic outputs and t h e relay drivers are made externally through plug P7. The following sections provide a detailed discussion of t h e design and operation of t h e various stages of t h e c i r c u i t . The Voltage Comparator

The input stage Q1 and Q2 i s a compound d i f f e r e n t i a l amplifier. The compounding Q1 provides high input impedance. The two inputs a r e applied t o a single base, rather than d i f f e r e n t i a l l y t o the two bases, so t h a t no shift i n output will occur when the two inputs a r e of equal magnitude

200

a t various l e v e l s from -10 t o +10 v. The 2-kilohm trimming adjustment R2 i s used t o balance the input r e s i s t o r s R 1 and R3. The output of t h e first stage appears a t t h e c o l l e c t o r of Q2A and i s coupled t o t h e second stage through R10 and RlOa. The second stage Q3 i s a simple d i f f e r e n t i a l amplifier t h a t provides additional voltage gain t o increase the s e n s i t i v i t y of the amplifier. Overall negative feedback i s employed from t h e c o l l e c t o r of Q3B t o t h e base of QlA (R36) t o adjust t h e s e n s i t i v i t y t o t h e desired l e v e l and t o improve t h e temperature-drift c h a r a c t e r i s t i c s . The dc l e v e l i s adjusted by trimpot R10 t o establish t h e correct t r i p point. The output of the second stage Q3 i s d i r e c t l y coupled t o the Schmitt t r i g g e r c i r c u i t Q4. The Schmitt t r i g g e r c i r c u i t i s a regenerative b i s t a b l e c i r c u i t t h a t provides t h e a c t u a l voltage l e v e l discrimination. The output of t h e Schmitt t r i g g e r c i r c u i t and a l l succeeding stages have only two stable s t a t e s , "Normal" and "Trip."

Logic Switching C i r c u i t s Loading e f f e c t s on t h e Schmitt t r i g g e r c i r c u i t a r e buffered by an i s o l a t i o n stage Q5. The b i s t a b l e s i g n a l i s then coupled t o Q6, where t h e logic l e v e l s a r e established. When t h e c o l l e c t o r of Q,5 (and t h e base of Q6) i s i n t h e "high," o r more positive, s t a t e , Q6 i s biased o f f , allowing Zener diode D1 t o be f i r e d through R25. The logic l e v e l output a t pin A of I7 i s then -10 v, as determined by the breakdown voltage of D1. In t h e "low" s t a t e , when t h e voltage a t the base of Q6 i s l e s s positive (actually slightly negative), Q6 i s saturated, shunting Zener diode D1, and t h e magnitude of the output a t pin A i s near zero (less than 0.2 v ) . The Q7 stage i s nearly i d e n t i c a l t o Q6 and provides an inverted logic l e v e l output f o r maximum f l e x i b i l i t y ; t h a t i s , when t h e l e v e l a t pin A i s -10 v, Q7 i s saturated, producing "zero" l e v e l a t pin J. Conversely, when t h e l e v e l a t pin A i s "zero," Q7 i s cut off and t h e output a t pin J i s -10 v. The inherent speed of response of t h e e n t i r e electronic c i r c u i t , from a s u f f i c i e n t l e v e l change a t t h e input pin T t o a logic l e v e l change a t e i t h e r pin A o r pin J, i s about 10 psec. However, this speed of response has been i n t e n t i o n a l l y lessened t o about I20 psec by capacitors C 1 t o C4 t o reduce t h e tendency t o respond t o sharp noise spikes.

6.'

R e l a y Drivers

Either logic output may be connected t o e i t h e r o r both of t h e two r e l a y drivers Q8 and Q9. Normally I U i s intended t o pick up when a t r i p (abnormal) condition e x i s t s . To accomplish t h i s , t h e base of Q8 i s connected through R30 and pin K of W t o a logic output t h a t i s a t -10 v i n t h e "Trip" s t a t e , namely, e i t h e r pin A o r pin J. Note that "Trip" and "Normal" are related t o t h e character of t h e input s i g n a l and r e f e r t o a s i g n a l which may be e i t h e r too large o r too s m a l l and e i t h e r positive or negative. The proper connections f o r a desired s i g n a l and function can be determined by r e f e r r i n g t o t h e connection table on c i r c u i t diagram Q-2609- 1 One s e t of contacts of K1 i s used t o l a t c h i n t h e c o i l of K l t o keep it energized after a t r i p has occurred and cleared. This optional funct i o n i s accomplished by connecting pin d of I7 t o b a t t e r y ground (pin W).

201

Relay K2, driven by Q9, i s normally connected so as t o drop out i n the t r i p s t a t e . This relay i s intended t o show the immediate s t a t e , and no provisions a r e made t o l a t c h it. One s e t of form C contacts i s available from each relay t o operate external c i r c u i t s . The logic l e v e l output may be latched i n the t r i p s t a t e by using t h e output contacts of relay K l . Pin b i s connected t o pin B, and eit;her positive o r negative 15 v i s connected t o pin F, depending upon t h e nature of t h e input signal. When t h i s connection i s used, K2 a l s o latches, because it i s driven by the logic signals. 2.5.7.3

Operating Instructions

Installation The fast t r i p comparator Q-2609 i s a module i n the ORNL modular reactor instrumentation s e r i e s . Like t h e other modules of the series, it has standard connectors and dimensions and has a pin-and-hole code on t h e r e a r p l a t e so t h a t the module w i l l not be inserted i n a wrong location i n a drawer. The module i s i n s t a l l e d by placing it i n i t s proper location, i n s e r t i n g t h e module firmly, and tightening t h e thumbscrew. The module may be plugged i n with power on without damage.

Operating Controls The only i n t e g r a l operating controls are t h e "Trip Test" and t h e "Reset" push buttons. The "Trip T e s t " push button causes the c i r c u i t t o t r i p by overriding the input signal. The c i r c u i t w i l l remain i n the t r i p position i f t h e screwdriver-actuated push button i s rotated clockwise a f t e r being depressed. "Reset" i s a momentary push button t h a t releases relay K l and the "Latch" indication. I n a good many applications of the f a s t - t r i p comparator, a single signal w i l l be compared against a reference. The reference can be fixed by a simple external voltage divider, o r it can be adjusted by means of a Helipot located i n the drawer i n t o which the t r i p c i r c u i t i s plugged. This adjustment i s shown on t h e c i r c u i t diagram as R 4 and i s , i n e f f e c t , an operating control of t h e t r i p c i r c u i t . Connections A l l connections t o the f a s t - t r i p comparator a r e made through the rear connector â&#x201A;Ź7 when the module i s inserted. After i n i t i a l calibration i s completed, there a r e no adjustments o r connections t o be made within the module i t s e l f . However, a high degree of f l e x i b i l i t y i s provided through external connections. The various possible modes of operation and t h e connections required t o achieve them a r e detailed i n t h e connection t a b l e on c i r c u i t diagram Q-2609-1 and i n the following section.

Operating Procedures

Input Signals. The input signals t o t h e t r i p c i r c u i t should be supplied from a low-impedance source (500 ohms or l e s s ) . A single signal may be e i t h e r positive or negative within t h e range of +lo V. The magni-

202

tude of two d i f f e r e n t signals may be compared, but they must be of oppos i t e polarity. The input terminal f o r a single s i g n a l i s pin T, and an external reference voltage of opposite p o l a r i t y i s required on pin M. I f two signals are compared, the reference voltage i s not required, and t h e second s i g n a l i s connected t o pin M. Reference Voltage. - The external reference voltage i s required on pin M when t h e input i s a single signal. This reference must be exactly equal i n magnitude t o the desired signal t r i p point and of opposite polarity. The source impedance shouldbe 500 ohms or l e s s . I n applicat i o n s where the t r i p point i s t o be changed occasionally, the reference may be derived from a 500-ohm precision potentiometer connected t o a 10-v supply. A potentiometer with 0.1% l i n e a r i t y w i l l be s u f f i c i e n t l y accurate t o allow d i r e c t reading of the potentiometer d i a l as the t r i p voltage. Such a potentiometer i s shown on the c i r c u i t diagram as R4. I n applications where infrequent or no changes i n t r i p point a r e anticipated, the reference should be derived from a 10-v supply and a fixed voltage divider with a t o t a l s e r i e s resistance of approximately 500 ohms. It should be noted t h a t , within t h e accuracy specifications of the t r i p comparator, the t r i p point i s d i r e c t l y equal i n magnitude t o the reference voltage, and any d r i f t or inaccuracy of the reference w i l l res u l t i n equal e r r o r of the t r i p point. The accuracy specifications do not apply i n the range - 1 t o 0 t o +1 v, and adjusting the reference t o a t r i p point i n t h i s range should be avoided. Signal Polarity and Direction. - Since t h e comparator i s designed f o r general-purpose use, it i s capable of providing a t r i p s i g n a l f o r any of t h e following conditions: 1. positive input signal increasing t o a value greater than a r b i t r a r y pdsitive reference value; 2.

positive input signal decreasing t o a value l e s s than a r b i t r a r y positive reference value;

negative input signal decreasing, becoming more negative than a r b i t r a r y negative reference value;

negative input signal increasing, becoming more positive than a r b i t r a r y negative reference value;

when input signal "A" i s greater (more positive) than input s i g n a l "B," both "A" and "B" positive;

when input s i g n a l "A" i s l e s s (more negative) than input signal "B," both "A" and "B" negative.

Different external connections a r e required f o r different types of input signals t o achieve proper output sense. These connections a r e shown i n t h e t a b l e on t h e c i r c u i t diagram (Fig. 2.5.16). The column headings r e f e r t o the nature of the signal; f o r example, the second column i s headed "Pos. Signal, High Trip." This means t h a t the input signal may range from 0 t o +10 v, and t r i p w i l l occur when the s i g n a l i s greater i n magnitude than t h e reference. The f i f t h column i s headed "Neg. Signal, Low Trip," which means t h a t t h e s i g n a l range i s 0 t o -10 v and t h a t t r i p occurs when t h e s i s a l i s smaller i n magnitude than t h e

203

reference. The column e n t r i e s under the selected heading show t h e voltage o r destination f o r the pin or terminal i n t h e same row of column 1 on the l e f t . The preceding discussion of t h e second column, labeled "Pos. Signal, High Trip," i s continued. The f i r s t row shows pin T a s the s i g n a l i n put. Pin M connects t o t e r m i n a l l , which i s the wiper of the reference potentiometer. Pin M could go instead t o t h e pickoff t a p of a fixed divider i f a fixed t r i p point i s desired. Pin L connects t o +10 v t o provide the proper t e s t voltage. Pin A i s jumpered t o pin K t o provide proper drive t o Q8. Pin J i s jumpered t o pin Z t o provide proper drive t o Q9 and i s a l s o t h e correct logic l e v e l output f o r driving external circuits. Latching. - Latching instructions are not shown i n the t a b l e i n Fig. 2.5.16, but they a r e shown a t t h e appropriate connector pins on the c i r c u i t diagram. With no latching, K1, K2, and the logic l e v e l outputs w i l l a l l indicate the immediate s t a t e of the comparator. Connecting pin d t o b a t t e r y ground causes only K1 t o latch, t h a t is, t o remain i n the t r i p s t a t e a f t e r a t r i p signal has cleared u n t i l t h e r e s e t button i s pressed If it i s desired t o a l s o l a t c h the logic l e v e l outputs i n t h e same manner, it i s necessary t o jumper pin b t o pin B and connect an appropriate voltage t o pin F, as shown i n t h e t a b l e . I n this condition a l l outputs, K1, K2, and both logic levels w i l l l a t c h and remain i n the t r i p s t a t e a f t e r a t r i p - l e v e l signal occurs.

Precautions Relay Contacts. - The contacts of the relays used i n t h e f a s t - t r i p comparator c i r c u i t are rated f o r r e s i s t i v e loads only. If inductive loads a r e necessary, appropriate contact-arc suppression techniques should be employed. Transistors. - Some of t h e t r a n s i s t o r s used i n the c i r c u i t unavoidably have small reverse base-emitter voltage ratings. Most ordinary laboratory-type ohmmeters, such as t h e T r i p l e t t 630 o r t h e Simpson 260, have s u f f i c i e n t l y high voltage on some resistance scales t o permanently damage these t r a n s i s t o r s . The common practice of using an ohmmeter t o check t r a n s i s t o r s when trouble-shooting should be avoided i n t h i s u n i t . Trip Point near Zero Volts. The trip-point accuracy specifications do not apply a t t r i p voltages near zero. Owing t o possible inaccuracy, t r i p points between -1 and +1 v should be avoided.

2.5.8 2.5.8.1

Coincidence Matrix Monitor, ORNL Model Q-262411

Description

General The coincidence matrix monitor i s designed t o monitor and indicate on front-panel meters t h e current through each l e g and t h e t o t a l current i n a two-out-of-three relay matrix. ~

"Taken from Instruction Manual, written by E. N. Fray, Instrumentation and Controls Division, July 23, 1965.

204

Construction The coincidence matrix monitor i s constructed i n a module 5.66 i n . It i s a standard "four-unit" plug-in module of t h e ORNL modular reactor instrumentation s e r i e s depicted on drawings Q-2600-1 t o Q-2600-5.

wide, 4.72 i n . high, and 11.9 i n . deep.

Application The coincidence matrix monitor i s intended t o monitor and t o regul a t e t h e current supplied t o a safety-rod scram clutch, o r magnet, i n a nuclear reactor. Figure 2.5.17 i s a diagram of a t y p i c a l application, where relay contacts A, B, and C come from separate s a f e t y channels. Applicable Drawings The following l i s t gives t h e drawing numbers (ORNL Instrument Department drawing numbers) and s u b t i t l e s f o r t h e coincidence matrix monitor. Circuit Details Metalphoto Panel Assembly Parts Iiist

Q-2625- 1 Q-26 24-2 Q-2624-3 Q-2624-5 Q-2624-6 2.5.8.2

Theory of Operation

A s indicated i n Fig. 2.5.17, t h e t o t a l current delivered t o t h e clutch i s adjusted by r e s i s t o r R1. If a l l the r e l a y contacts are closed, and since r e s i s t o r s R2, R 3 , and R4 are equal, t h e current w i l l divide equally i n the t h r e e legs of t h e matrix. The t o t a l current goes through the clutch and returns t o ground through t h e "clutch current" meter. The maximum voltage t h a t can be applied t o t h e clutch i s limited by Zener diode D1 t o +30 v. An external meter may be connected between pins 10 and 14. If a single c h a n n e l t r i p s , two legs of t h e matrix a r e opened and a l l the current flows through the remaining leg. Therefore, t h e tripping of e i t h e r of t h e two remaining channels causes t h e t h i r d l e g t o open, which i n t e r r u p t s t h e clutch current. With two legs open, t h e resistance of t h e matrix i s increased by a f a c t o r of 3; thus r e s i s t o r s R2, R3, and R4 must be small enough so t h a t t h e current delivered t o t h e clutch i s not decreased t o less than a r e l i a b l e holding current. To ensure t h a t t h e clutch c o i l can be deenergized, t h e monitor must be able t o detect leakage paths around t h e r e l a y contacts. If t h e leakage resistance i s small enough, s u f f i c i e n t current can be supplied t o keep t h e clutch energized with t h e contacts open. For example, suppose channel A has been tripped. However, one CoQtact, instead of completely opening, can now be represented by resistance R The minimum resistance value of X

i n t e r e s t can be found by t h e equation i

R4 + Rc + Rx

205

where = minimum clutch holding current, cm R = clutch resistance,

= maximum supply voltage.

The clutch current will divide between the branches B-C and A-B, where t h e current through A-B i s given by the equation

The requirement i s t h a t the current ixbe e a s i l y detected on the meter A-B

2.5.8.3

Operating Instructions

Installation The coincidence matrix monitor i s a module i n the ORNL modular reactor instrumentation s e r i e s . Like the other modules of t h i s series, it has standard connectors and dimensions and has a pin-and-hole code on t h e r e a r p l a t e so t h a t the module w i l l not be inserted i n a wrong location i n a drawer. The module i s i n s t a l l e d by placing it i n i t s proper location, i n s e r t i n g t h e module firmly, and tightening the thumbscrew. The module may be plugged i n with t h e power on without damage. Operating Controls Current Adjustment. - A recessed screwdriver adjustment, labeled "Clutch Current Adjust," i s located on t h e front panel. The proper operating clutch-coil current determines t h i s adjustment. Panel Meters. - The panel meters are calibrated t o indicate from 0 t o 250 ma. These meters a r e i n s e r i e s with t h e clutch and indicate c o i l current d i r e c t l y .

ORNL-DWG e e - 5 m ~

"B" CHANNELS AND "C"

SIGNAL FROM REACTOR OUTLET TEMPERATURE INSTRUMENTATION PRODUCES T R I P WHEN REACTOR OUTLET : ~ ~ ~ E ~ ~ ~ E " , " ~(MANUAL) "TEST" ~ ~ ~ G N A LTEMPERATURE s EXCEEDS 1300OF CURRENT SENSORS

{F~E] I

SWITCHING SIGNAL WHICH REDUCES FLUX AMP. GAIN

P'RODUCES WHEN:

TRIP SIGNAL

FOXBORO TYPE 6 3 ACTUATED CURRENT SWITCH

I I

, ,$

RELAY SAFETY

Rq 0-2623

CHAMBER HIGH VOLTAGE POWER SUPPLY

SAFETY CHANNEL"A". FLUX INPUT (TYPICAL. ONE OF THREE 1

FAST TRIP COMPARATOR

"8" AND "C"

0-2624

"8"AND"CX

,CHANNEL MONITORS (METERS) ZERO READINGS ON ANY 2

SCRAM TRIP SIGNAL IF:

METERS INDICATE THAT A SCRAM TRIP ORIGINATED I N T H E INPUT CHANNEL COMMON TO BOTH METERS

2. REACTOR FLUX EXCEEDS 11.3 MW A N 0 FUEL SALT PUMP CURRENT LESS THAN 3 5 amp PRODUCES SCRAM T R I P SIGNAL I F REACTOR PERIOD Q +LO see

+ COMPARATOR

1.0-NOS. REFER TO ORNL INSTRUMENT AND CONTROL DIVISION DWG NOS.

CONTROL ROD "REVERSE" INSERTION OF A L L RODS)

PRODUCES TRIP SIGNAL I F REACTOR FLUX EXCEEDS 9.0 MW

2. ROD SCRAM REQUIRES THAT T H E COINCIDENCE MATRIX MONITOR RECEIVE AT LEAST TWO ( 2 1 TRIP SIGNALS FROM A N Y TWO OF THE THREE SEPARATE I N P U T CHANNELS "A". "8" AND "C",

PRODUCES TRIP SIGNAL I F REACTOR FLUX EXCEEDS 4 MW

3.REFER TO DWG RC-13-9-53. O R N L INSTRUMENT AND CONTROL DIV. FOR DETAILS, A L L 3 CHANNELS FAST TRIP COMPARATOR

Fig. 2.5.1.

R m [O H oQ ;;;

1. REACTOR FLUX, EXCEEDS (1.3 MW AND FUEL SALT PUMP CURRENT EXCEEDS 35 amp OR I F

L - -- - - - --- ---

NOTES:

MONITOR RELAY SAFETY ELEMENTS I N CHANNELS

SEE NOTE 2

'PRODUCES

, I

FAST TRIP COMPARATOR 0-2609

2. CIRCUIT CONTINUITY LOST

NEUTRON SENSITIVE ION CHAMBER

1 I

CLUTCH CURRENT METER

1. CHAMBER LOSES VOLTAGE

3."TEST" (MANUAL) PROVIDES CURRENT TO FLUX AMPLIFIER TO SIMULATE HIGH FLUX

CONTROL ROD "REVERSE" ON SCRAM

"SAG* BYPASS

MSFE Safety System f o r Control Rods.

Block diagram of t y p i c a l channel.

292 f

PH4

URRENT TRANSFORMERS

294

K293B T I M E DELAY TO OPEN JKA

THESE RELAYS ARE T I M E

DELAYED

K293

292 A

PHASE CURRENTS:

1;; I

BUS

3+- 4 4 0 V

PUMP MOTOR

,TVA-DIESEL

295

K 2( S9E4ABL )

TIME DELAY

K294

DE-ENERGIZE

Fig. 2.5.2.

K 2 9 3 8 , T I M E DELAY TO OPEN K295A)

INPUT SIGNAL FROM PERIOD SAFETY MODULE CURRENT RELAYS SET TO TRIP AT 35 a m p KF 2 9 2 294

795 __ -

T (K294A.

FAST T R I P COMPARATORS RM-NSCI-AI

NOS. I N PARENTHESES DESIGNATE FLUX AMPLIFIERS I N CHANNELS 2 A N D 3

~ ~ ~ : ~TYPICAL ~ $FLUX~ AMPLIFIER l \

SWITCHING WHICH CHANGES TRIP L E V E L BY A FACTOR OF I O 0 0 (FROM 11.3 kW TO (4.3 MW

426

K295B

K292CZZ

T I M E DELAY

OPEN

yKB292A

WHEN THIS CONTACT IS CLOSED AMPLIFIER S E N S I T I V I T Y I S REDUCED BY A FACTOR OF 4000. ( R E F E R CKT 2 7 5

ZOO k

I.FULL L O A D - 5 0 o m p 2. NO L O A D - 2 0 o m p 3. ONE PHASE OPEN, NO W A D - 3 5 o m ~

PH 3

ORNL-DWG 66-9425R

K292D K293C

-_-

WHEN AT LEAST 2 OF THESE RELAYS ARE ENERGIZE0 THE FLUX LEVEL TRIP POINT IS AT !XI%F U L L POWER (I!3 M W )

MSRE Flux Level Scram Trip Point Switching.

__ __

K294C

K2930

OPEN

KC 2 9 2 A

K295

.K 2 9 4 0 -+ -

ORNL-DWG 66-9124R

CHANNEL N 0 . 2

C H A N N E L NO.(

CURRENT I N P H A S E NO.( TO F U E L SALT P U M P MOTOR

CHANNEL N0.3

CURRENT I N PHASE N0.2 TO F U E L SALT PUMP MOTOR

PRI lARY I N UTS

RELAY K D 292

RELAY K A 2 9 2

T H A N 35 a m p

T H A N 35 o m p

L-

RELAY KC 292 E N E R G I Z E D WHEN C U R R E N T GREATER THAN 3 5 o m p

RELAY K F 2 9 2 ENERGIZED WHEN CURRENT GREATER T H A N 35 a m p

- -----I

MATRIX

CONTACT MATRIX

I I

FROM CHANNEL NO. 2

CONTACT

*WHEN ANY TWO OF THESE THREE RELAYS A R E ENERGIZED, ROD SCRAM S E T P O I N T IS AT REACTOR P O W E R ( F L U X 1 = 1 1 . 2 M W

CONTAC MATRICES PROVlDll G INPUT C H A N N E L REDUNDANCY

CONTACT

GI* RELAY

DIRECT ELECTRICAL CONNECTION

----- INDIRECT

CONNECTION (SWITCH OR R E L A Y CONTACT)

Fig. 2.5.3.

-I

~ - c ~ ; E L

(CONTACT I N R E L A Y 2931

FROM

C H A N N E L N0.3 RELAY K 2 9 2

RELAY KE 292 CONTACT

SENSITIVITY CONTROL FLUX A M P NO. l

I I

CONTACT

CONTROL FLUX A M P N 0 . 2 (CONTACT I N

[+I*

RELAY

I I

I CONTROL FLUX A M P N 0 . 3 (CONTACT I N

OUTPUT

Flow D i a g r a m of Switching Signals t h a t Change Reactor Power S e t Point f o r Rod Scram.

209

ORNL-OWG64-6261

CURRENT ACTUATED SWITCHES

TE-100-82 CHANNEL N 0 . 2 SAME AS ABOVE CHANNEL N 0 . 3

SPARE

NOTE: 1. POLARITY SHOWN FOR TEST THERMOCOUPLE IS THAT USED TO TEST SYSTEM RESPONSE TO A TEMPERATURE INCREASE

Fig. 2.5.4. Diagram of Instruments Used to Measure Temperature in a Typical Safety System Input Channel.

ORNL-OW 66-10024 R ROD DRIVE UUTCH CONTROL CIRCUIT, ITYPICAL OF ALL THREE DRIVES I

OUTPUT CONTACTS AND RELAYS FROM ONE CHANNEL OF SAFETY SYSTEM (TYPICAL OF ALL THREE CHANNELS, CHANNEL"A" SHOWN) t32VDC

+32 V Dc------r

CONTACTS

, 4 f

RELAY CONTACT. PART OF 0-2609 FAST TRIP COMPARATOR

TEST UNIT

TEST

OPENS WHEN FLUX EXCEEDS ISMW(ORII.2kW IF FUEL SALT PUMP CURRENT IS LESS THAN 35 amp I

TO SIMILAR CIRCUITS, OTHER RODS RELAY SAFETY

SYSTEM CIRCUIT CONTINUITY IS LOST

I $

RELAY CONTACT. PART OF 0-2609 FAST TRIP COMPARATOR

MATRIX MONITOR (TYPICAL IOF 31

,+I

OPENS WHEN REACTOR OUTLET TEMPERATURE EXCEEDS 1300.F

TYPICAL ( 4 OF 3 1

OPENS I F REACTOR PERIOD IS 1.01.c OR LESS

A.BANDC

2 lKA4

CHANNEL MONITORING

COlNCl 0-2624 DENCE

MATRIX MONITOR (TYPICAL IOf

SCRAM

CLUTCH CURRENT METER

ZENER IIODE 32 V

"ON" WHEN CHANNEL HAS BEEN TRIPPED

VOLTAGE SIGNAL CURRENT TO OY

f0-V BATT

RELAYS K A I TO KA5 ( I N C L I ENERGIZED DURING NORMAL OPERATION

NOTES: 4.0-NUMBERS REFER TO ORNL INSTRUMENT AND CONTROL OIVISION DWG. NOS.

EXCEPT AS NOTED, CIRCUIT ELEMENTS SHOWN ABOVE COMPRISE A TYPICAL COINCIDENCE MATRIX MONITOR, 0-2624.

2. ALL RELAY CONTACTS AND SWITCHES SHOWN WITH SYSTEM ENERGIZED AND OPERATING NORMALLY. 3. THIS RELAY ( K ~ 4 1 PROVIDES ONE OF THE "REVERSE" ON SCRAM CONTACTS; TYPICALLY CONTACT NO. RSS-NSCI-A4 IN CIRCUIT NO. 2 4 8 ON DWG 0-HH-B 57327.

Fig. 2.5.5.

Diagram of Safety System Rod Scram Circuits.

211 ORNL-OWG 56-100tOR

t32VDC

CONTACTS IN RELAY SAFETY ELEMENTS CHANNELS A B

m SEAL CONTACT.

RELAY K4

ELEMENT," CHANNEL A I

K249

+ Ai-

TVA-DIESEL)

> K2

K3 COINCIDENCE MATRIX MONITOR

]

COINCGENCE Y MATRIX V EMONITOR N0.3

K4-4 THESE CONTACTS

-J

CKT N0.248

e-4 24V ZENEF DIODE

"HOLD"

KA125

RELAY SAFETY ELEMENT (TYPICAL) ORNL MODEL 0-2623

CHANNEL

TEMPERATURE

ELEMENTS

KB 125

KC125

TEMPERATURE

-CONTACTS RELAY K5-I INSAFETY 0-2623

CHANNEL 4BV DC

TEMPERATURE

m}n] YF] RELAY SAFETY ELEMENT

RELAY SAFETY ELEMENT

TO 0-2624 COINCIDENCE MATRIX MONITORS, ROD DRIVES NOS. 1.2. AND 3

117

119

118

CONTACT MATRIX (CIRCUIT 1241

tKA124A

6 pN;3 RELAY KAI24

RELAY KB 124

IT VE

bt 6t HCV 573A2

I L

t HCV 575 A2

CONTACTS

dHCV 577A2

DRAIN TANK VENT VALVES, HCV'S 573-AI 575-AI AN0 577-A1 OPEN WHEN THESE SOLENOIDSDE-ENERGIZED

MSRF: Nuclear Safety System Circuit Detail,

! . I , . . .

E R: :K A 1$

J LOAD SCRAM WHEN EITHER KAll OR KA12 DE-ENERGIZED

Fig. 2.5.6.

:KAf24C

i::)

VALVES

TWO-OUT-OF-THREE CONTACT MATRIX (CIRCUIT 124

4BV OC

212

UCIj -N 7A

I----

L-

dtV4-4Ar-J

M. s.R. E.

c/RCU/T D/AGRAM

Fig. 23.7.

%fety

ystem Circuit Diagram.

. ....

.._

213

ORNL-DWG 67-1404 THREADED RECEPTACLE FOR PUSH ROD ATTACHMENT, M A T ' L ; HIGH PURITY N i

M H V CONNECTORS SIGNAL-CABLE JACKS, 2 EACH HIGH VOLTAGE-CABLE PLUGS, 2 EACH

PURITY Ni OUTER

$e-in.-OD STAINLESS STEEL SHEATH A l p 0 3 INSULATED COAXIAL CABLES.4 E A C H - 2 SIGNAL, 2 HlGH VOLTAGE

Fig. 2.5.8.

I-,ENGTH

MSRE Safety Chamber.

300

SENSITIVE 41/44

ORNL-DWG 67-1103

i . 4 ~ 4 0 nV ' ~ +-,IO7

r/hr (GAMMA)

250

2 200 !-

z w

- 5 ~ 1 0nV ~

400

450

200

+*to6

250

r / h r (GAMMA)

300

350

400

450

500

POSITIVE VOLTS

Fig. 2.5.9.

Saturation Curves -MSRE Safety Chamber.

-"-.

c 4@a

------*--t

215

e -25V

Fig. 2.5.ll.

Chamber High-Voltage Supply and Flux Amplifier Circuit.

-i

-I

& 0

-J I

OUTPUT VOLTAGE

0” 0

Io t W I

P-

r--

I I

L--

1 I I

I I I I

I I I

I I

hi"

--- -- -tc--l----i---c

J-

/-609Z-Ol 1

, I

A2f-

(U)#

I UW AOT

t; h)

221

2.6

SHIM

AND

REGULClTING ROD CONTROL SYSTEM

2.6.1

Introduction

This section i s concerned with t h e c i r c u i t r y and c i r c u i t compoaents which a r e used routinely f o r operational control of t h e reactor. The rod control system should be considered as a separate system from t h e rod safety system described in Sect. 2.5. It is t r u e t h a t there is w e a k coupling between the systems, but only t o t h e extent that c e r t a i n i n t e r locks i n t h e control system depend on information received from s a f e t y syst e m channels. Reverse coupling is not designed i n t o t h e system; that is, t h e rod control system c i r c u i t s and components do not perform any s a f e t y functions, e i t h e r as input or output elements. The design of t h e control rods and t h e drive u n i t s i s described i n Sect. 2.7. "be location of t h e rods w i t h respect t o t h e core, t h e i r mounting and i n s t s l l a t i o n , rod wort%, etc., a r e discussed i n Sect. 2.7 and i n refs. 14.

2.6.2

Rod Control Circuits

Figures 2 . 6 . 1 t o 2.6.4 a r e block and elementary diagrams that provide t h e basic c r i t e r i a f o r t h e design of t h e rod control system. Table 2.6.1 l i s t s t h e interlocks, s a f e t y actions, prohibitions, and permitted actions governing control rod action.' The reactor system is designed s o that rod manipulation i s e i t h e r a lOogd man^ operation or, optionally, an automatic rod control servomecbmism is used t o maintain e i t h e r constant f l u x o r constant core outl e t temperature, depending on t h e power being generated in t h e core, The rod servo is used t o control one rod only; t h i s rod is a r b i t r a r i l y designated ucontrol rod 1"on MSRE design drawings and i n t h e text and f i g ures i n t h i s report. The rod drive u n i t s (see Sect. 2.7) are i n t e r changeable, and individual rod worths (ref. 3, p. 5 8 ) do not d i f f e r widely from thimble t o thimble. Therefore, t h e control system is designed s o t h a t any one of t h e three rods may be selected as t h e servocontrolled rod (rod 1). From t h i s it can be seen that, without supplementmy information, t h e rod numbers used i n design drawings, reports, etc., cannot be used as t h e only information required t o designate thimble

'S. E. Beall e t al., MSRE Design and Operations Report, P a r t V, Reactor Safety A n a l y 9 ORNL-TM-732 (August 1964). 2R. C . Robertson, MSRE Design and Operations Report, Part I, Des c r i p t i o n of Reactor Design, Om-TM-728 ( t o be pu3lished). 3P. N. Haubenreich e t al., MSRE Design and Operations Report, 111, Nuclear Analysis, ORNL-TM-730 (Feb. 3, 19%).

pa^-

CServomechanisrn Fundamentals Philco Corporation, Technical Center S t a f f , Library of Congress No. TJ2l4, p . 47. Rept

Project Staff Molten-Salt Reactor Program Semi-. 1966, ORNL-3936.

. Feb . 28,

Progr.

Table 2.6.1.

Conditions of Operation Interlocks, Permissive Actions, Prohibitions, Automatic Actions

Operational Mode 1. Manual scram 2.

Automatic scram

Individual i n s e r t (manual) 4 . Group i n s e r t (manual "Reverse") 5. Group i n s e r t

Control Rod Operation

1. No restrictions; a t discretion of operator a t control

console When any two of the three rod scram safety channels c a l l s f o r "Scram." Each channel requests "Scram" f o r inputs a s follows: a ) F ~ U X(reactor power) greater than ll.3MW; see b b e l m b ) Flux (reactor parer) greater than 11.25 kw when fuel salt pump motor three-phase currents are less than 35 amp c ) Positive reactor period is l e s s 5han 1.0 sec a) Reactor outlet temperature greater t h a n 1300'F e ) Channel integrity monitor shows a malfunction No r e s t r i c t i o n s other than l a r e r l i m i t

References and Notes The manual switch contacts are not sealed See r e f . 1, sect. 2.2.1, p. 5 8

Motor currents l e s s than 35 amp imply that no fuel salt is being circulated

4 . No r e s t r i c t i o n s other than lower l i m i t N

N N

Autamstically takes place when: a ) ~ n two y of three fuel salt outlet temperature measurement channels indicates greater than

1275'F b)

c) a) e) f)

Fuel salt l e v e l in the pmp bowl exceeds 75% Any two of three flux measurement channels indicate reactor parer greater than 9.0 Mu ~ n two y of three flux measurement channels indicate reactor parer greater than 9.0 kw, and t h e fuel pump motor is drawing l e s s than 35 amp When reactor power (flux) exceeds 1.50 Mw and control system is i n Operate-Start mode When positive reactor period is l e s s than 5 sec and control system is i n Operate-Start mode ROCI "Scram" takes place

See 2b, this t a b l e Power and period information used t o i n i t i a t e 5e and 5f comes from e i t h e r of the two widerange counting channels; see Sect. 2.3, r e f . 1, Sect. 2.8, and Sect. 1.4 Applies motor torque i n addition t o gravity t o i n i t i a t e s c m . If a rod w i l l not f a l l under action of gravity the motor w i l l drive rod in

c Table 2.6.1.

Individual rod withdrawal

Group withdrawal

Conditions of Operation Interlocks Permissive Actions, Prohibitions Automatic Actions

Operational M o d e 6.

(continued)

a ) Prohibited, with two exceptions, i f the control system calls f o r "Insert." A l l manual switches and relays a r e cross-interlocked s o that "Insert" mode (see preceding Nos. 3, 4, 5 , t h i s t a b l e ) takes precedence over 'kithdraw" mode. The exceptions are : 1. The servo can withdraw rod 1within the span of the regulating rod l i m i t switch, approximately 6 in., while rods 2 and 3 are being inserted 2. By manually actuating t w o switches simultaneously, t w o rods can be withdrawn while the third is being inserted b Prohibited during Operate-Start control system mode unless one of the following conditions i s met: 1) '%onfidence" i s established i n one or more wide-range counting channels and the reactor period i n the chamel(s) providing "Confidence" is greater than +Z sec 2) Confidence is established i n the BF3 counting channel and the reactor vessel i s l e s s than half f u l l of f u e l s a l t 3) Confidence is established i n BF3 counting channel and the drain ta& selector switch 56 ( F i l l ) i s i n the FFT position; i.e., when using flush s a l t i n the reactor vessel, the "half - f u l l " requirement (see preceding Par. 2) is bypassed c ) Pemttted i n Operate-Run mode without having "Confidence" (see b l above) providing no "Ins e r t " request exists. However, i f "Confidence" exists in one, or both channels, the reactor period in channelb) w i t h "Confidence" m u s t be greater than +25 sec d) Prohibited i n Pre-Fill unless conditions per b above are met a ) Prohibited i f , f o r any reason, the control system c a l l s f o r "Insert" as i n 6a above \ __._ _.._ si&V I r i u i u u L b e J . u l u e b b GUIII,LUL byb~,e:mis iii St=% mode ?

n.,-,-,-L2L-

__.__I___

L.--.l

L--.

References and Notes

Discussed i n Sect. 2.6.2 and i n r e f . 5, P. 4.4

hl hl

Table 2.6.1. operational Mode

(continued)

Conditions of Operation Interlocks, Permissive Actions, Prohibitions, Automatic Actions

References and Notes ~

1) Control system must be i n Operate-Start mode

"Start" is a submode of the "Operate" mode (Sect. 1.4);S t a r t and Run are mutually exclusive

Reactor drain valve bV-103) & m be frozen 3) Pump bowl be f i l l e d NOTE: Group w i t h d r a w a l is only intended for use during startup and a t puwers l e s s than 500 kw. Parer limitation i s by means of a c i r c u i t interlock i n the radiator door control c i r c u i t r y which requires t h a t t h e reactor control system be i n the "OperateRun" mode i n order t o raise t h e doors and thus demand parer levels above 500 kw. 2)

22s

locations i n t h e core. The selection of "control rod 1" as the servoo2erated regulating rod is administrative and i s accomplished by making t h e a p p o p r i a t e interconnections between the rod drive units and the control and servo system c i r c u i t s . These interconnections a r e made i n junction box 120, located i n the north e l e c t r i c a l service area. Control rods 2 and 3, designated as shim rods, a r e always manually controlled. Figures 2.6.5 t o 2.6.7 shuw the contacts and relays which d i r e c t l y govern control rod operation. Figures 2.6.5 and 2.6.6 a r e concerned o n l y w i t h t h e control of rod 1, the regulating rod. The dynamic brake (Fig. 2.6.6) is an addition t o the design (see r e f . 5, pp. 41-42], and while it does not appear on Fig. 2.6.5, it is always used i n the c i r c u i t controlling rod 1. Because it is the servo-controlled rod, the c i r c u i t r y i s more complex than t h a t required by the manually operated shim rods 2 and 3. The automatic rod c m t r o l servo and t h e principles governing i t s design and operation a r e described i n Sect. 2.6.3. Certain interlocks a r e common t o all control rod "iithdraw" c i r c u i t s . The contact arrangement of these interlocks is sham in the upper l e f t corner of Fig. 2.6.5. These interlocks a r e shown i n block The "Confidence, "No Confidence, I' and diagram form i n Fig 2.6.8. "Reactor Period" interlocks originate in the BF3 counting channel and the wide-range counting channels described in Sects. 2.2 and 2.3 of t h i s report. The "Automatic Reverse" (group insertion of all rods) has been outl i n e d i n d e t a i l i n Table 2.6.1, and t h e c i r c u i t r y is diagrammed i n Fig. 2.6.9. The reactor operating modes are discussed i n Sect. 1.4. The interlocks diagrammed in Figs. 2.6.5 and 2.6.8 meet the f o l l m ing c r i t e r i a :

1. Control rod withdrawal, during reactor s t a r t and at low p w e r s ("Start" mode), is prevented unless a t l e a s t one channel of t h e lcrrl e v e l flux instrumentation i s complete, i s operating correctly, ant3 is on scale This defines "Confidence. If "Confidence" is established by a wide-range channel when a l l t h e folluwing conditions a r e met: a ) the indicated count r a t e is not l e s s than 2 cps and not greater than 50,000 cps, b) the selector switch on the model Q-2614 pulse amplifier and logarithmic count r a t e meter module is i n t h e "Operate" position, see c ) a l l the Q-2609 f a s t - t r i p compara;tors (a total. of eight Fig. 2.3.3, Sect. 2.3) a r e plugged i n t o t h e i r cabinet drawers and t h e channel is selected by t h e operator. I! Confidence" i s established by the BF3 counting channel when these requirements a r e met: d ) the indicated count r a t e is not l e s s than 10 cps and not g r e s t e r than 10,000 cps, e ) t h e "Use-Calibrate" switch on t h e count r a t e meter is i n the "Use" p o s i t ion

Control rod withdrawal during the %tart" mode is prevented i f the reactor period, measured by e i t h e r or both of the wide-range count11 ing channels i n which there is Confidence," is l e s s than 25 sec.

226

Control rod withdrawal, e i t h e r by t h e operator or by the servo cont r o l l e r , i s prevented i f an automatic "Reverse" is i n force.

4. S i m u l t a n e c i withdrawal (group withdrawal) of all rods i s desirable only during reactor start and a t l o w powers and should be prohibited as a means of shimning when t h e reactor i s i n the pover range (the R U mode ~

5. Once t h e reactor is i n the power region (the Run mode) and developing more t?xm 1Mw, t h e wide-range counting channel "Confidence" interlocks in the Run mode c i r c u i t r y (see Sect. 1.4) a r e bypassed so that a loss of "Confidence" w i l l . not require a return t o the S t a r t mode and consequent reduction i n reactor parer. This bypassing requires t h a t two of the three s a f e t y channels be i n operation. This bypassing is a c c q l i s h e d by control signals from the model Q-2609 f a s t - t r i p ccunparators in the control rod s a f e t y system (see Fig. 2.5.1, Sect. 2.5) and a s e a l contact on the R u n mode relay. This i s done t o permit long, sustained runs a t power uninterrupted by m a l functions in, or maintenance of, the wide-range counting channels. The block diagram in Fig. 2.6.8 may be d i f f i c u l t t o i n t e r p r e t a t It may be Fnstructive t o l i s t and c m e n t on the different conditions which produce continuity t o point A in the diagram. The conibinations l i s t e d i n Table 2.6.2 a r e consistent w i t h the design c r i t e r i a and t h e c h a r a c t e r i s t i c s of the instruments involved. Note that i f e i t h e r one of t h e wide-range counting chaanel log count r a t e meters is functioning correctly as defined by "confidence," but i f the reactor period is l e s s than +25 sec, rod withdrawal. is prevented regardless of whether the reactor system is in S t a r t o r Bun mode. This may appear inconsistent with t h e c r i t e r i a in paragraph 5 above and cond i t i o n 4 in Table 2.6.2. This arrangement recognizes that it is higkly desirable t o have at l e a s t one wide-range channel in service a t Elll levels of reactor power a n d t b t when they a r e i n service t h e interlocks which they provide w i l l be i n force. For example, suppose that t h e MSRE was in the middle of a long, sustained power run at, say, 5 and that wide-range counting channel 2 was out of service f o r routine maintenance. This i s condition 2 in Table 2.6.2. Now, suppose t h a t a malfunction develops in the URM in the remaining wide-range counting channel l, r e s u l t i n g in a l o s s of "Confidence" i n t h i s remaining channel. This i s condition 4; reactor operation nay continue unaffected by t h e loss of t h e remaining wide-range channel as long as power i s above 1Mw. Again, suppose that a malfunction not in the URM develops which produces a spurious, short ( l e s s than 25 sec) reactor period signal. This i n h i b i t s rod withdmwal, and the indication that a t r i p has taken place appears on t h e panel of the Q-2609 f a s t - t r i p canparator (see Fig. 2.3.3, Sect. 2.3). If a thorough check shows conclusively that t h e period indication is spurious, operation can be restored by manual selection of the other cha.nnelwith the switch on the console or by putting the switch on the Q-2614 URM in t h e '%alibrate" position, thus going i n t o '%o Confidence" on t h e offending channel and establishing a s i g n a l path per condition 4. Similarly, i f it develops t h a t , in this remaining channel, one of t h e Q-2609 f a s t - t r i p comparators requires removal f o r servicing, the loss of "Confidence" so produced w i l l not i n h i b i t reactor operation i f power is above 1-I&.

first glance.

6.i

Situation or Condition No.

"No Confidence in mcc Fro. 1

'%O

Confidence"

inmcc no. 2

Reactor Period >+asec (mcc NO. 1)

Reactor Period >+aSSC (WRCC NO. 2)

Table 2.6.2 True; F = Fal8ei NA = Not AuDlicable

,tConfidence,t in wRcc

Control system

Reactor Vessel Less

In mcc No.

No. 2

in nR."

than

ttConfidence,,

"Confidence" in BF3 Channel

N l

Drain ~ank Selector i n FFT Position

Notes

T or F

This is normal situation with the reactor f i l l e d with fuel salt above "EF3 Confidence" level and with both wide-range counting channels i n operation

T or F

Reactor situation same as l b u t only one wide-range counting channel in operation

T or F

Reactor situation Same as 1 but only one wide-range counting channel i n operation

T or F

Reactor i s operating a t power (flux) h and neither widegreater than 1 P range counting channel is operating; note that getting into "Run" mode can only be accmplished v i a condition 1 or 2 lhis situation obtains during early part of a "Reactor F i l l " with fuel salt and before flux is sufficiently high to produce 2 cps i n the wide-range counting channels Reactor bei f i l l e d from the flush s a t t d y m ) ; selection of FFT e l i minates the requirements for "Confidence" i n either the BF3 or the widerange counting channels

T or F

228 11

Reverse" is t h e insertion, i n group, of all cantrol rods. It takes place when the instruments indicate that system conditions have exceeded operating limits t o the extent that rod i n s e r t i o n is the prudent action t o be taken. The conditions or s i t u a t i o n s producing '%everse'' a r e l i s t e d in Table 2.6.1, and the c i r c u i t r y which actuates t h e It Reverse" relay is depicted in Fig. 2.6.9.

2.6.3

The Autamatic Rod Controller

The l i n e a r puwer channels ( r e f e r t o Sect. 2.4) and automatic rod The controller of the MSF43 are shown in block diagram in Fig. 2.6.10. pinpose of this system i s t o provide automatic control of the reactor by the movement of oae of t h e three shim rods in e i t h e r of two controller modes ( r e f e r t o Sect. 1.4). There i s a l s o a provision f o r disabling, through t h e servo "on-off" switch, t h e automatic c o a t r o l l e r in e i t h e r mode t o permit manual operation of the rod by the operator. The other two shim rods a r e always operated manually, as pointed out above. One of the two autamatic modes is c a l l e d t h e flux mode and provides autamatic control of neutron f l u x a t a l e v e l selected by the operator when t h e reactor i s i n i t s "Start" mode of operation. The power range in which t h i s mode is used extends from about 10 w t o 1W . The second mode is used t o control the t-aperatme of t h e me1 salt leaving the core and is c a l l e d t h e temperature mode. This mode i s used when the reactor i s in -be "Run1'mode and is capable of adjusting the neutron f l u x t o maintain t h e reactor o u t l e t temperature at a s e t point established by the operator. In this mode the steady-state reactor pajrer is a function only of t h e thermal load, which may be varied from about 1 t o 10 Mw. The instantaneous puwer l e v e l s depend upon the thermal load and any changes in system temperatures required t o achieve t h e desired o u t l e t temperature. Switching between these two modes of controller operation is automatically a c c q l i s h e d when the reactor operating mode is changed. Reference 1, pages 104 t o 108, is suggested f o r additional reading t o augment t h i s paragraph. Significant features of t h e controller and i t s a u x i l i a r i e s w i l l be described belov by referring t o Yig. 2.6.10. The a c t u a l c i r c u i t diagram is sham in Fig. 2.6.ll.

2.6.3.1

Basic Rod Control Circuit

The output element of t h e rod controller (Fig. 2.6.10) is a p a i r of p i l o t relays which operate as simple "on-off" switches t o actuate t h e "Insert" and 'vithdraw" relays i n t h e rod drive motor c i r c u i t of control rod 1. Tbese "Insert" and 'vithdraw" relays must a l w a y s be actuated t o produce controlled rod movement regardless of whether the reactor is being operated manually or automatically. The p i l o t r e l a y contacts a r e i d e n t i f i e d in Fig. 2.6.5 as contacts %SS-NARC-Al and A2 f o r '~ithdrm"and "Insert" respectively. The puwer contactors which they coatrol a r e relays Kl83 and Kl76, whose contacts a r e in the puwer leads t o t b e servo motor Fn t h e control rod drive selected as "control rod 1." Amplifier 8 a c t s as a comparator w i t h three inputs: (1)measured neutron flux, (2) f l u x demand, and (3) a s i 1 proportional t o rod speed. The model Q-2627 synchronous d e m o d u l a t o r q s used t o convert

229

t h e ac s i g n a l from the t a c h m e t e r t o a dc voltage w i t h a.n amplitude proportional t o rod speed and a p o l a r i t y tlmt depends upon the direction of r o t a t i o n of the rod drive motor. This dc s i g n a l provides negative feedback t o optimize the response of the servo mechanism. When the controller is i n the "flux" mode of operation, the operator chooses t h e flux a t which the reactor is t o operate and a t which the cont r o l l e r output is zero by adjusting the demand potentiometer and t h e range of t h e picoasrmeter i n the channel selected as t h e control input channel. This demand signal is i d e n t i f i e d as 'I@demand" in Fig. 2.6.10 and originates w i t h the operator at the console. The "@ demand" s e t t i n g determines t b e voltage f r o m the picoatmeter that is required t o bring the output of the comparator t o zero (assuming no tachometer signal) and, w i t h the range selection, determines the value of neutron flux required t o produce that volt%e. As indicated i n Fig. 2.6.10, t h e range and t h e output voltage l e v e l of the picoamrneters are recorded by the data logger. In addition, the r w e s e t t i n g and l e v e l of the selected channel a r e recorded on a strip-chart; power recorder located on the main control board. Although not s h a m i n Fig. 2.6.10, there i s an illuminated indicator on the main board immediately abwe the recorder, which displays the range of the selected channel. In t h e "temperature control" mode the demand voltage is generated by the rod controller complex, and the range of the picoammeters is fixed. The way i n which t h i s is accomplished i s described i n the next section.

2.6.3.2

Temperature Control

The control of reactor o u t l e t temperature i s achieved by continuously computing a flux set point so t h a t the temperature r i s e of the f u e l salt through the core is j u s t equal t o the difference between t h e o u t l e t temperatme s e t point [T 1 and the measured reactor i n l e t tem0

Figure 2.6.12 is a Gagram of the array of Q-2605 aperaperature Ti. t i o n a l amplifiers that wxxnplish t h i s conputation. The system is best explained by neglecting, f o r the moment, amp l i f i e r 5 and its connection t o amplifier 6. Considering the other t w o inputs t o the summing amplifier 6, we note that, by proper choice of polarity, the algebraic sum of these two inputs i s equal t o the d i f f e r (selected by the ence between the desired o u t l e t temperature [T ] 0

operator through the model Q-2628 temperature servo demand drive unit) and the measured i n l e t tanperature Ti. The output of amplifier 6 i s ( s t i l l neglecting the t h i r d input) proportional t o t h e desired temperat u r e r i s e through t h e core and, at constant flow, is a measure of the nuclear power required t o achieve the desired o u t l e t temperature. This output, through a sign-changing amplifier 7 and limiting c i r c u i t s not included on Fig. 2.6.12, beccanes t h e f l u x demand or set-point signal t o amplifier 8. Because of t h e varying conditions, both i n the relationship of neutron f l u x t o t o t & heat generation and possible sensor errors, it is necesssry t o modify t h i s s e t point i f t h e measured o u t l e t temperat u r e is t o be t r u l y equal t o t h e desired set-point value. The modificat i o n of the s e t point i s accomplished by use of amplifier 5 , the r e s e t

230

a m p l i f i e r , t o generate a correction term. The r e s e t amplifier is an integrator which continuously compares the measured f l u x @, t h e measured core differential. temperatwe (To Ti), and a correction term whose value is a function of t h e sum of t h e other three inputs and s l a J l y a l t e r s the value of t h e correction term u n t i l t h e sum of the four inputs i s zero, w i t h the proper algebraic signs of t h e inputs considered. Since t h e correction term, the output of amplifier 5 , is f o r c e d b y this integration t o be numerically equal t o any discrepancy between measured flux and measured differential. temperature, applying t h i s same correct i o n term w i t h the proper p o l a r i t y a l t e r s t h e flux demand as required t o assure that t h e steady-state value of the measured o u t l e t temperature is exactly equal t o the s e t point. The response of t h e integrator is purposely adjusted t o be considerably sluwer than t h e response of t h e other amplifiers on this canputing system. merefore, i f e i t h e r the reactor flux o r i n l e t temperature, or both, experience a rapid change caused, f o r example, by a load t r a n s i e n t or high r a t e of manual shimming, the e r r o r signal c q u t a t i o n w i l l i n i t i a l l y proceed as i f t h e integrator were not present. The controller w i l l respond immediatelyto the transient, as explained in the first part of t h i s paragraph. Because of t h e rapid respoase of flux demand, and therefore flux, t o a change in inlet temperatnre or o u t l e t temperature s e t point, it is desirable that neither of these be permitted t o change rapidly under normal opemting conditions. I n l e t temperature changes, assuming cont r o l of o u t l e t temperature at a constant s e t point, a r e caused by load changes. These load changes a r e not aormally permitted a t a r a t e tht exceeds the capability of the rod controller t o hold the o u t l e t terqperat u r e constant. The rate of change of o u t l e t temperature s e t point is limited by using a motor-driven potentiometer t o determine t h e r e f e r ence voltage. This r a t e is necessarily very slow t o prevent undesirable thermal gradients i n the system when the controller is operating in t h e temperature mode, and, since it is desirable t o match t h e o u t l e t temperature s e t goint t o the a c t u a l o u t l e t temperature p r i o r t o changing from manual t o automatic control, a f a s t e r r a t e of a l t e r i n g the s e t point is available t o the operator when the temperature i s not being autcraatically controlled

2.6.3.3

Flux Demand Limiting

Because components and devices do occasionally f a i l o r malfunction and may thereby cause an unscheduled increase o r decrease i n f l u x demand in t h e temperature mo5e, a limiting c i r c u i t , block diagramed i n Figs. 2.6.10 and 2.6.U, has been providedwhich prevents t h e f l u x demand s i g n a l from departing appreciably outside i t s normal range. This feature i s also useful t o mitigate t h e consequences of an operator e r r o r such as turning on t h e controller when the o u t l e t temperature s e t point is grossly a f f e r e n t f r o m t h e measured value. In addition, a Q-2609 f a s t - t r i p comparator, sham i n Fig. 2.6.10, is used t o provide an interlock (see Sect. 2.5, Fig. 2.5.8) t o grevent i n i t i a t i o n of the Run mode of reactor operation while under automatic control unless the computed f l u x demand is less than about 1Mw. Since the t r a n s f e r from S t a r t t o Run m u s t be made (by c i r c u i t s not r e l a t e d t o the automatic rod c o n t r o l l e r ) a t a power l e v e l of about 1Mw, this comparator assures that no significant parer excursion w i l l occur.

(41

6.I

231

2.6.4

Regulating Bod L i m i t Switch Assembly, Q-2586

It is good practice t o limit t h e r e a c t i v i t y change t h a t can be produced by t h e automatic c o n t r o l l e r t o an amount equal t o o r s l i g h t l y less than t h e e f f e c t i v e delayed neutron f r a c t i o n Bef Since each rod i n t h e MSRE has a t o t d f u l l - s t r o k e worth of appraximagely 2.2$ i n &/k (ref. 3, Sect. 4.3, Table 4.1, p. 581, t h e regulating rod l i m i t switch assembly, hereinafter r e f e r r e d t o as RRLSA, i s provided t o l i m i t t h e stroke of No. 1 control rod t o 6 i n . when t h e automatic c o n t r o l l e r i s i n use. Figure 2.6.13 is a simplified functional diagram of t h e RRLnsA.. This diagram does r o t depict t h e actual configuration of t h e system. The rod drive u n i t does nut a c t u a l l y contain any intermediate movable limit switches as implied by the diagram. The a c t u a l short stroke l i m i t switching takes place i n t h e c o n t r o l room, and t h e mechanism which accomplishes t h i s is s h a m i n Figs. 2.6.14 t o 2.6.17. Figure 2.6.18 is a mechanical diagram of t h e drive train, and Fig. 2.6.19 is a detailed block diagram of t h e assembly. An ac servomechanism i s used t o position t h e limit switch cam when t h e autccnatic reactor c o n t r o l l e r is operating. This follows t y p i c a l pos i t i o n i n g servo practice4 when a synchro control transformer i s used as the position e r r o r sensor. The servo loop (Figs. 2.6.18 and 2.6.19) consists of a s i z e 15 control transformer whose outzut goes t o an ac amplifier (Fig. 2.6.201, which drives t h e positioning servo motor. The c o n t r o l transformer is mechanically coupled t o the positioning servo motor and is driven i n a d i r e c t i o n which reduces t h e e r r o r s i g n a l toward zero. When t h e rod c o n t r o l l e r is "on," t h e electromechanic clutch is engaged (the brake is o f f ) and t h e cam is a l s o connected, through speed changing gears and t h e d i f f e r e n t i a l gear s e t , t o t h e ac servo motor. 'The shim-locating motor is a l s o d i r e c t l y connected t o t h e l i m i t switch cam 3y gears and through t h e other input of t h e mechanical d i f f e r e n t i a l . Because t h e d i f f e r e n t i a l gear s e t is included in t h e drive train, both the ac servo motor and t h e shim-locating motor may be used independently and simultaneotlsly t o obtain cam motion. The n e t cam r o t a t i o n is proportional t o t h e algebraic sum of these two input rotations. The electramechanical clutch-brake in the output gear t r a i n between the shim-locating motor t5e d i f f e r e n t i a l (see Figs. 2.6.18 and 2.6.19) i s a design modification which does not appear in t h e photographs. It w a s added t o eliminate the undesirable e f f e c t s of coastdawn of t h e shim-locating motor and of baclrl a s h in t h e motor's built-in gear reducer. Table 2.6.3 gives t h e rotat i o n a l c h a r a c t e r i s t i c s of t h e various components i n t h e system when t h e reactor i s i n the automatically controlled mode and with t h e gear r a t i o s in accordance w i t h Fig. 2.6.18. When t h e reactor is i n t h e "mual Control" mode, t h e control c i r c u i t r y big. 2.6.5) causes tkte electromecl?asical clutch-brake t o become deenergized; t h e mechanical drive connection f r o m t h e ac servo motor t o t h e cam i s broken and t h e brake is applied. Control c i r c u i t interlocks a l s o prevent applying power t o t h e shim-locat motor. Because of t h e very high b u i l t - i n reduction gearing (2400 t o 1 i n t h i s motor, it i s not susceptible t o being driven by torque applied t o t h e output shaft. The brake prevents r o t a t i o n of t h e other input t o t h e d i f f e r e n t i a l . Therefore, both inputs t o the d i f f e r e n t i a l are locked, and the l i m i t switch cam i s not f r e e t o r o t a t e when torqued externally.

""3

Table 2.6.3 RF'M Outputs (Component Rotations i n Q-2586, Regulating Rod L i m i t Switch Assembly)

Input Conditions

Size 15 Control Transformer -~

1. Withdrawing a t 0.5 in./sec

L i m i t Switch AC Servo Motor

Cam and Size 3 1 Position

Shim-bcating Motor

Transmitter ~~~

~~~~

Stationary

+0.42

+5.0

+2.50

Zero

-5 .O

-2.50

Zero

-2.25

-1.5

Zero

+2.25

+1.5

Inserting a t 0.5 in./sec

Stationary

Sta t ionary

Withdrawing

Stationary

Inserting

-0.42 Zero Zero

Withdrawing a t 0.5 in. /sec

Withdrawing

+O .42

+5 .O

+O .25

-1.5

Withdrawing a t 0.5 in./sec

Inserting

+O .42

+5.0

+4.75

+1.5

Inserting a t 0.5 in./sec

Withdrawing

-0.42

-5 .O

4.75

-1.5

Inserting a t 0.5 in./sec

Inserting

-0.42

3 .O

-0.25

+1.5

233

From Table 2.6.3 it is seen that t h e cam speed resulting from relocating t h e span of t h e l i m i t switches with t h e shim-relocating motor is s l i g h t l y l e s s than t h e cam speed produced by control rod motion. With the gear r a t i o s shown i n Fig. 2.6.18, these speeds a r e 2.25 and 2.50 rpm respectively (see Table 2.6.3). The cam is cut f o r a maximum of 180" rotation between limits, which is equivalent t o 6 i n . rod motion. The position of the l i m i t switches is adjustable; hence, the effective span Ayl (Fig. 2.6.13) of t h e regulating rod may be adjusted within t h i s maximum of 6 i n . From Fig. 2.6.14, it can be seen that t h e gearing, clutch, motors, etc., a r e supported on movable mounts and bearing hangers. Therefore, it i s simple and inexpensive t o change t h e cam speeds and t h e span. A detailed description of the major coqonents used i n t h i s u n i t i s given i n Sect. 2.6.5. A s noted above (see a l s o Figs. 2.6.5 and 2.6.191, t h e net rotation of t h e l i m i t switch cam i s the resultant of two coInponents: (1) the r o t a t i o n produced by the balance motor and (2) t h e rotation of t h e shim-locating motor. When t h e reactor i s i n t h e servo control mode and if the operator i s not relocating the position of the regulating rod span, t h e balance motor, driving through the clutch (the brake i s disengaged) and the d i f f e r e n t i a l , r o t a t e s the l i m i t switch cam through an angle t h a t is d i r e c t l y proportional t o t h e l i n e a r motion of t h e servocontrolled rod. Assume, f o r t h e sake of discussion, t h a t t h e reactor is being operated i n steady s t a t e and t h a t no f u e l is being added. Burnup and poisoning w i l l cause slaw w i t h d r a w a l of rod 1, t h e servo-controlled rod, unless the reactor i s manually shimmed by t h e other two rods. If no shimmi takes place, t h e l i m i t switch cam w i l l continue t o r o t a t e clockwise7see Fig. 2.6.51, and, unless t h e shim-locating motor i s actuated t o produce counterclockwise cam rotation, t h e upper s h i m regulating rod l i m i t switch w i l l be opened, i t s associated r e l a y K240 w i l l drop out, and contact K 2 0 w i l l open. This w i l l prevent t h e servo system 'vithdraw" relay contact SSS-NARC-Al from transmitting power t o t h e rod w i t h d r a w r e l a y Kl76. Note that t h e servo system is not turned off and t h a t it continues t o exert control i n the "Rod I n s e r t " direction; t h a t is, if f o r any reason the servo c a l l s f o r t h e insertion of negative r e a c t i v i t y w i t h t h e servo rod a t t h e upper l i m i t of t h e regulating rod span, the rod i n s e r t requirement w i l l be transmitted t o r e l a y m83, which causes the rod drive motor t o i n s e r t the rod. T h i s rod 1 insert relay, Kl83, cross-interlocks t h e rod w i t h d r a w r e l a y K176 so that an llInsert" request from any source overrides a l l 'Vithdraw" requests. This cross interlock is included i n a l l rod drive c i r c u i t s . The operator must now shim t h e reactor. If he chooses t o shim by using rod 1, the servo-controlled rod, he does s o by means of the individual rod control switch, 2319, used f o r manual operation. This closes contact S19A and energizes Kl.75, t h e rel a y which causes t h e shim-locating motor t o t u r n t h e cam counterclockwise. The l i m i t switch closes, contact K24m closes, and t h e servo is i n command of rod 1. The servo now w i t h d r a w s rod 1u n t i l t h e upper l i m i t is again reached o r u n t i l shimming requirements are met. The s h i m relocating motor mmes t h e cam a t a s l i g h t l y lower speed than does t h e balance motor, and t h e a c t u a l w i t h d r a w a l of rod 1 i n these circumstances is a s e r i e s of start and stop movements u n t i l t h e span of t h e regulating rod i s relocated. The a l t e r n a t e method of shimming i s t o w i t h d r a w e i t h e r o r both of t h e manually controlled rods 2 and 3 u n t i l the servo automatic a l l y returns rod 1 t o a suitable place within t h e regulating rod span.

234

Should t h e servo c o n t r o l l e r malfunction and ask f o r a continuous out-of-control withdrawal of rod 1, t h e w i t h d r a w a l w i l l only p e r s i s t u n t i l the upper regulating rod limit is reached. The "on-off" pawer amplifier relays i n t h e servo c o n t r o l l e r do not exert d i r e c t control of t h e rod drive motors (see Fig. 2.6.5); instead they control t h e f'Withdraw" and lfInsert" relays Kl76 and Kl83, and a servo malfunction has t o be accompanied by f a i l u r e of other control-grade interlocks t o become of consequence. Should the regulating rod limit switch mechanism misoperate i n conjunction with a servo c o n t r o l l e r malfunction s o t h a t t h e cam fails t o r o t a t e as t h e rod is being withdrawn by the servo, the control system interlocks may c a l l f o r a "Reverse" (group i n s e r t i o n of a l l three rods) i f the failure produces any of t h e s i t u a t i o n s l i s t e d i n Table 2.6.1. "Reverse" by t h e control system is independent of t h e condition of the servo c o n t r o l l e r and may a l s o be invoked should t h e operator inadverte n t l y withdraw e i t h e r shim rod s o as t o produce any of t h e l i s t e d conditions. If one of t h e shim regulating rod l i m i t switches remains actuated o r i f t h e cam f a i l s t o move off t h e mechanical stop, rod 1 is inhibited from f u r t h e r motion in one direction only. The operator can provide cont r o l w i t h rods 2 and 3 and can switch over t o manual control u n t i l t h e trouble is cleared. A d e t a i l e d step-by-step breakdown of t h e c i r c u i t and RRLSA responses t o various s i t u a t i o n s i s included i n Sect. 2.6.6. 2.6.4.1

Range Switching

The range switching c i r c u i t s of t h e flux channels a r e extensive because of t h e large number of operating conditions possible. Figure 2.6.21 shaws these c i r c u i t s , as w e l l as those associated w i t h t h e various reactor and rod c o n t r o l l e r modes. The first two stages of t h e operator's range switches a r e u s e d t o connect t h e proper feedback r e s i s t o r s by energizing appropriate relays i n t h e picoammeters. Contacts K2W and K204.B (Fig. 2.6.21) are used t o disconnect t h e range s e l e c t o r switches and t o automatically connect a feedback r e s i s t o r corresponding t o a f u l l - s c a l e range of 15 Mw when a "range s e a l " condition exists. The "range seal" is described belaw. Stages 3 and 4 of t h e range switch a r e used f o r proper switching of t h e inputs t o t h e range indicator l i g h t assembly. This r m g e indic a t o r displays, i n exponential form, t h e nominal f u l l - s c a l e range of t h e selected channel i n w a t t s . The range switching is by a l t e r n a t e steps of f a c t o r s of 3 and 3-1/3. Stage 3 monitors t h e position of t h e range switches and t h e console channel s e l e c t o r switch and causes one of two multiplying f a c t o r s (1.5 and 0.5) t o be illuminated. In t h e event that K205 (another "range s e a l " r e l a y ) i s energized, t h e 1.5 l i g h t is operated regardless of t h e position of e i t h e r range switch. Stage 4 causes illumination of t h e proper exponent i n t h e range indicator, thereby completing t h e i d e n t i f i c a t i o n of t h e range. The range seal condition causes a 7 t o appear i n t h e exponent position, indicating a range of 1.5 X lo7, or 15 Mw, when t h e range s e a l condition exists.

235

Stage 5 is a voltage divider used t o provide range information t o t h e data logger and range recorder. K208B contacts a r e u s e d t o switch t h e range recorder input t o t h e selected channel range switch. Again K205 contacts disconnect t h e range selector switches and i n s e r t signals corresponding t o the 15-Mw condition when t h e range s e a l i s energized. Stage 6 i s a permissive switch used t o enforce t h e 1.5-Mw range r e q u i r e d t o switch t h e operating mode of t h e reactor from Start t o Run. Stage 7 is used f o r t h e range s e a l function, which w i l l now be described

2.6.4.2

Range Seal

The t r a n s f e r from S t a r t t o Run o r Run t o S t a r t i n reactor operation involves a number of d i s t i n c t , but related, operations. To assure that a l l these are performed and t h a t no severe t r a n s i e n t s a r e introduced as a r e s u l t of such transfer, t h e range s e a l c i r c u i t s have been developed. The range seal, as t h e name may imply, i s an e l e c t r i c a l latching c i r c u i t which is energizedwhenever t h e reactor operating mode i s switched by t h e operator from S t a r t t o Run. T h i s t r a n s f e r i s r e s t r i c t e d t o power l e v e l s i n t h e v i c i n i t y of 1Mw. Energizing t h e range seal, represented i n Fig. 2.6.21by relays K203, K204, and K205, disconnects the range s e l e c t o r switches and causes t h e range of each picoammeter t o become 15 M w , as described above. Inasmuch as the range s e l e c t o r switches a r e now t o t a l l y ineffective, it is reasonable t o assume t h a t they may be i n any position during subsequent operations i n t h e Run mode. It should be noted t h a t t h e Run mode may be terminated automatically under c e r t a i n conditions. Should t h i s OCCUT, t h e range s e a l c i r c u i t s are used t o automatically force t h e rod controller f l u x set point t o about 1 M w . The operator can then assume control of flux s e t point by putting both range s e l e c t o r switches i n t h e 1.5-Mw position, a t which time the flux s e t point becomes 1.5 Mw multiplied by t h e s e t t i n g of the f l u x demand potentiometer. The above features a r e shown i n Fig. 2.6.21 a t t h e bottom of t h e sheet. Relays K203 through K208 are operated i n t h e following manner: A contact from t h e R u n r e l a y i n t h e rod control system operates K206, c a l l e d a run auxiliary relay. "his relay i n t u r n energizes K203, K204, and 205. If e i t h e r of t h e range s e l e c t o r switches i s turned from i t s 1.5-Mw position, t h e relays a r e sealed i n t h e i r energized condition through S1 or S2 and K203A. Relay K207 is t h e r e l a y which defines, f o r t h e controller and f o r t h e reset of t h e control system, the temperature mode of operation. Although it i s c l e a r that K204 should always be energized when K206 is energized, the interposition of K2W between K206 and K207 has a purpose. Inasmuch as t h e temperature control system cannot function properly unless t h e picoammeter range i s 15 Mw, it w a s decided t o i n i t i a t e t h e temperature mode by the operation of t h e same relay, K204, t h a t switches range. K208 is the r e l a y which s e l e c t s either channel 1 o r channel 2 signals t o be t h e input t o t h e controller a t the request of t h e operator. A t t h e bottom of Fig. 2.6.21 is a l s o shown the switching c i r c u i t f o r t h e servo amplifier demand input. As described e a r l i e r , i n t h e temperature mode t h e computed flux demand serves as a reference t o be compared w i t h t h e measured flux l e v e l . K207A, normally open, serves

236 t h i s function. If K 2 0 7 i s deenergized, as it w i l l be whenever t h e rrrunrr relay is deenergized, the c o n t r o l l e r w i l l be i n the flux mode, and a

f l u x demand voltage is suppliedthrough a K203, or range seal, contact. If K203 is energized, t h e picoammeters a r e on t h e i r 15-Mw ranges, and t h e s e t t i n g of t h e operator's demand potentiometer is i n terms of percent of full s c a l e and could represent as much as 15 Mw i f used as a reference t o the c o n t r o l l e r . Therefore, K203 i s u s e d t o introduce a demand of 1Mw, based on a 15-Mw range, whenever t h e range s e a l i s energized and the run r e l a y deenergized, as described e a r l i e r . The temperature r e s e t amplifier, described e a r l i e r , compares f l u x and temperatures t o compute a correction term s o t h a t t h e reactor outl e t temperature i s equal t o i t s set point i n steady state. Since the f l u x s i g n a l i n t o the c o n t r o l l e r depends upon t h e range of t h e picoammeter and t h e temperature s i g n a l does not, t h e r e s e t mechanism would be saturated during most operations a t l o w power. To provide a means f o r minimizing t h e e r r o r i n t h e correction term a t t h e time of transfer from S t a r t t o Run, a f i c t i t i o u s s i g n a l representing a 1-Elw f l u x l e v e l has been introduced whenever t h e range seal is deenergized. Since 1Mw corresponds t o a d i f f e r e n t i a l temperature of 5 O , t h e correction term w i l l a t most be 5O, even i f t h e power l e v e l i s s o low as t o produce an unmeasurable d i f f e r e n t i a l temperature. As t h e reactor power approaches 1Mw, p r i o r t o i n i t i a t i n g the Run mode, t h e r e s e t amplifier begins t o operate properly. If t h e f l u x l e v e l i s held a c t u a l l y a t 1 M w f o r a few minutes p r i o r t o transfer t o t h e Run mode, there should be no appreciable change a f t e r transfer, since energizing K204 t r a n s f e r s t h e input t o t h e r e s e t amplifier from a f i c t i t i o u s 1-Mw s i g n a l t o a r e a l 1-Mw s i g n a l corning from the selected picoammeter. 2.6.5 2.6.5.1

Component Descriptions

Servo Motor

This i s a two-phase, 60-hertz ac motor primarily designed t o be t h e balancing pen drive motor i n Minneapolis-Honeywell Company s e l f balancing potentiometer-type s t r i p - c h a r t recorders. It contains i n t e g r a l gear reduction such t h a t it has a maximum no-load speed of 27 rpm. It is capable of operating a t stalled torque continuously without damage. Its e l e c t r i c a l c h a r a c t e r i s t i c s provide a good match t o t h e amplifier described beluw. The motor i s designated by Minneapolis-Honeywell as t h e i r p a r t No. 76750-3.

2.6.5.2

Amplifier

This is a general-purpose instrument servo amplifier designed t o accept 60-hertz input signals i n t h e m i l l i v o l t range and t o amplify them t o a puwer l e v e l capable of driving t h e servo motor described above. This amplifier (Fig. 2.6.20) i s manufactured by Minneapolis-Honeywell and modified i n accordance with ORNL Instrumentation and Controls D i v i s i o n Drawing No. RC-2-10-12.

237

IC(

2.6.5.3 Clutch-Brake The clutch-brake is manufactured by Autotronics, Inc Florissant [Refer t o UCNC (ORNL) Missouri, and i s i d e n t i f i e d as p a r t No. MB-34-2. Requisition No. R-7674, April 4, 1963, and Purchase O r d e r 63X47734.1 Its performance c h a r a c t e r i s t i c s a r e outlined below.

Operating voltage Coil resistance, +lo$ Clutch torque, min Brake torque, min Response time t o energize a t 28 v dc Maximum no-load torque (drag) When energized When deenergized Operating mode

2.6.5.4

24 t o 28 v dc

138 ohms 80.0 02-in. 100.0 oz-in. 0.020 sec

0.20 02-in. 0.50 oz-in. With c o i l energized t h e input gear flange i s f r e e t o rotate and t h e output i s braked t o t h e how ing

Shim-Locating Motor

The shim-locating motor i s a synchronous capacitor type w i t h int e g r a l gear reducer. It is manufactured by Bodine E l e c t r i c Company, 2504 West Bradley Place, Chicago, I l l i n o i s , and is i d e n t i f i e d by catalog No. B8122E-l200C, frame KYCC22RC w i t h K-45 capacitor. (Refer t o UCNC Its performance c h a r a c t e r i s t i c s Purchase Order 63X-50673, June 10, 1963. are outlined belaw. Input Output speed Output torque Capacit o r

ll5-v, 60-hertz, single-phase 1.5 r p m 105 oz-in.

0.85 pf

2.6.5.5 Mechanical D i f f e r e n t i a l The mechanical d i f f e r e n t i a l is a bevel gear type supplied by Reeves Instrument Corporation, Roosevelt Field, Garden City, New York. 2.6.5.6

Size 15 Control Transformer

T h i s transformer (U.S. Government type 15CT6b, Mil. Spec. S-20708) is manufactured by t h e Bendix Corporation, Montrose Division, South Montrose, Pennsylvania, and is i d e n t i f i e d by Ben& Catalog No. Ay1501Iill-B2, Dwg. 15OlB-0, o r equal. (Refer t o UCNC Purchase Order 63X-47764., April 29, 1963, Specifications are given below.

238

Voltage, primary/seconda.ry Current, max (typical) Power, primary (typical-) Total voltage a t n u l l Fundamental voltage a t n u l l E l e c t r i c a l accuracy Phase s h i f t 2.6.5.7

90/57.3,

60 h e r t z

0.oll amp 0.13 w 90 mv 60 mv 6 min 20' lead

Size 31 Torque Transmitter6

The s i z e 31 torque transmitter (U.S. Government type 31TX6b, Mil. Spec. S-20709) is manufactured by t h e Bendix Corporation, Montrose D i vision, Montrose, Pennsylvania, and is i d e n t i f i e d by Bendix catalog No. AY-310lB-l2-E2, B e n u Dwg. 301OB-0, or equal, (Refer t o UCNC Purchase Order 63X-47764, April 29, 1963.) Specifications a r e given below. Voltage, primary/seconda current, primary (typicalPower, primary (typical) E l e c t r i c a l accuracy Max t o t a l s i g n a l a t n u l l Max t o t a l signal, fundamental a t n u l l

115/90, 60 hertz 0.395 amp 4.75 w 10 min 125 mv 35 mv

Phase s h i f t

6.5" lead 0.40 oz-in./deg

Torque gradient 2.6.6

Operational Situations Involving the Regulating Rod L i m i t Switch and t h e Regulating Rod Servo (Refer t o Figs. 2.6.5, 2.6.7, and 2.6.9)

I. Servo w i t h d r a w s rod t o upper l i m i t of t h e RRLSA A.

This moves cam clockwise t o upper l i m i t switch; t h i s actuates (deenergizes K240. The a c t i v e contact chain during 'withdraw, " i n servo, i s : K24W KAl70D K228cI K229A 1. RXSS-NARC + A l K18X r e l a y Kl76. 2. K 2 m opens and prevents f u r t h e r withdrawal by t h e servo. +

---f

11. Regulating rod a t upper l i m i t of t h e RRLSA; operator a c t s t o l e t servo continue rod withdrawal A . This requires t h a t t h e c i r c u i t t o r e l a y Kl76 be restored t o energize r e l a y K240 (see A above). B. This i s permitted i f t h e RFWA i s withdrawn s o t h a t i t s upper l l m i t switch is not actuated. This i s accomplished by manual operation of S19A t o energize r e l a y Kl75. The contact chain i n c i r c u i t 175 is: S19A + S2UB + S2l.B + Kl70H + K24lA + r e l a y 175 energized.

synchro was a l s o designed f o r use as a control transmitter.

239

'c,

C. When r e l a y 175 i s energized, t h e RRLSA cam moves off the upper l i m i t and these actions follow: 1. K24OF' closes.

K176 is energized since, by hypothesis, the servo e r r o r signal requesting w i t h d r a w rod 1 s t i l l exists and servo r e l a y contact RxSS-NARC-Al i s s t i l l closed. The FBLSA cam is now receiving motion from two sources: a ) Clockwise r o t a t i o n produced by t h e a c t u a l withdrawal of rod 1, which r o t a t e s t h e position synchro i n t h e RRLSA. b ) Counterclockwise r o t a t i o n produced by t h e operator Is closure of t h e manual shim switch (S19), which operates t h e shim-locating motor i n t h e RRLSA. c ) Since the cam speed produced by withdrawing rod 1 is s l i g h t l y f a s t e r than t h e speed in t h e opposite direction produced by t h e shim-locating motor, t h e n e t r o t a t i o n of t h e cam tends t o be clockwise. Therefore, t h e motion of rod 1w i l l tend t o keep the cam a t i t s upper l i m i t , while a t t h e same time t h e operator is continuing t o reverse t h e cam. Rod 1w i l l move up i n steps as long as t h e servo requests w i t h d r a w a l . d) When the servo e r r o r signal becomes zero: 1) r;i,SS-NARC-Al opens and r e l a y K176 is deenergized. 2 ) If t h e operator continues t o request w i t h d r a w a l of rod 1by actuating S19A and energizing relay KL75, t h e cam continues t o move counterclockwise. Presumably t h e operator w i l l stop t h e cam s o t h a t it is miCtway between limits. If t h e cam reaches t h e lower l i m i t and energizes r e l a y K241, rod 1 i s prevented from responding t o a servo e r r o r signal c a l l i n g f o r rod insertion. 111. Servo i n s e r t s regulating rod t o lower l i m i t of t h e RRLSA Control system response i s same as i n I, but i n opposite directions. I V . Regulating rod a t lower l i m i t of t h e RRLSA; operator a c t s t o l e t servo continue rod insertion Control system response is same as i n 11, but i n opposite directions. V. ~ u a i nl s e r t of rod 1 ( r e m a t i n g rod) o r manual or automatic reverse of a l l rods is requested A . Any one of contacts S22B, S19D, o r Kl86F i s closed. B. Assume t h a t rod 1 i s between limits of t h e RRLSA; then the pertinent contact chain becomes: (S22B, S19D, o r KL86F) + I(lll70E + K24.OA + r e l a y IU82. C. The shim-locating motor r o t a t e s cam i n the "Insert" direction. Note: Rod 1 does not move during t h i s s t e p as t h e cam approaches t h e upper l i m i t switch i n t h e RRISA. D. The upper l i m i t switch is actuated by t h e cam and relay K240 is deenergized. 1. Contact K24.OA opens and stops t h e shim-locating motor. 2. Contact K24oC closes and t h e relevant contact chain becomes: (S22B, S19D, or K186F) 4 KAl70E + W 4 C E + K23OA 4 K23U relay Kl83. E. Relay contact KL83A closes, causing the drive motor f o r rod 1 t o i n s e r t t h e rod. The cam w i l l be rotated opposite i n direc2.

240

t i o n t o i t s o r i g i n a l r o t a t i o n per VC above, and t h i s action w i l l continue u n t i l it is backed away from the upper l i m i t switch i n the RRISA. Relay a 4 0 i s energized, and the cycle, s t a r t i n g w i t h VB above, is repeated. The action is similar t o that described above i n IIB. F. Once rod 1has reached e i t h e r of the l i m i t switches i n the RRLSA, its speed i s limited by t h e speed with which the posit i o n of the RRISA can be changed. T h i s is appraximately 1C$ less than that of rod 1. G. If, during a request f o r "insert" per VA above, the servo a l s o requests rod 1 i n s e r t , the resulting action is t o i m mediately i n s e r t rod 1u n t i l t h e lower cam l i m i t switch i n RRLSA i s reached. During t h i s time t h e r o t a t i o n a l speed of t h e cam w i l l be t h e absolute difference of two speeds; namely: 1. The speed, counterclockwise, of rod 1reproduced by the rod.position synchro which drives the cam. 2. The speed, clockwise, of the RRLSA produced by the shimlocating motor. The shim-locating motor moves t h e cam a t a s l i g h t l y lower r a t e (appraximately lo$ l e s s ) than the position-transmitting synchro. The net speed i s t h e algebraic sum (absolute difference) of t h e two, thus ( r e f e r a l s o t o Sect. 2.6.4 and Table 2.6.3): Cam speed =

(speed produced by shim-locating motor) (speed produced by rod 1motion)

0.9 (rod speed)

- 0.1

(rod speed)

rod speed.

Therefore, i n these circumstances, the cam w i l l be turning, slowly i n a counterclockwise direction u n t i l the lower l i m i t switch i n the RRLSA i s actuated. A s long as the servo is calling f o r rod 1 t o i n s e r t , the rod w i l l be nudging t h e lower l i m i t switch the same manner as described a t t h e upper l i m i t (see IIB)

If, during a reverse, the servo is requesting w i t h d r a w a l of rod 1, the reverse relay contact Kl86A (see Fig. 2.6.9) i s open and prevents energizing relays Kl.74, Kl75, and Kl76. This, i n turn, prevents group w i t h d r a w of a l l rods, withdraw RRLSA, and individual withdraw of rod 1. I f the operator requests "insert rod 1" while t h e servo is requesting "withdraw,," the r e s u l t is, i n terms of pertinent contacts : 1. P@S-NARC-Al + K24OF + m 7 0 D 4 D228A + K229A 4 Kl83C + energize relay Kl76 4 (withdraw, rod 1). Rod 1withdraws, and t h e position transmitter r o t a t e s t h e cam clockwise toward the upper l i m i t of t h e RRLSA. 2. S19D + KAl70E 4 K24OA + energize r e l a y Kl.82. The shimlocating motor r o t a t e s the cam clockwise toward the upper l i m i t RRLS. 3. The net r e s u l t of 1 and 2 above i s t o make t h e RRISA cam approach i t s upper l i m i t switch at a r a t e nearly twice as fast as normal; that is, net speed, the absolute sum of the

241

two speed components, instead of the difference as described i n VG. 4 . When the upper l i m i t switch of t h e RRLSA i s actuated, the closed c i r c u i t , per 2 above, i s broken because contacts K24U, K24QF, and KA24oC change t h e i r aspect. This energizes r e l a y Kl.83 and deenergizes Kl.76, thus: KA24GC -, K23U 4 K23lA + enera ) S19D 4 KALI'OE gize Kl.83. This c a l l s f o r "insert rod 1.'' Note t h a t Kl76 becomes deenergized for e i t h e r of two reasons: 1) Energizing K183 opens K18X (see Jl above) 2) ~ 2 4 0opens. ~ I n addition, contacts K183A and Kl.83D appear i n both " i n s e r t " and "withdraw" power leads t o t h e motor i n rod drive 1, s o t h a t "insert" overrides 'bithdraw." Note t h a t , when t h e servo is controlling, t h i s overriding interlock i s not i n e f f e c t u n t i l t h e q p e r l i m i t switch i n the RRLSA has been actuated. b ) Rod 1 is inserted, and the RRLSA cam i s rotated counterclockwise and away f r o m t h e upper l i m i t of the RRISA. c ) Insertion of rod 1 continues momentarily u n t i l t h e RFUSA cam leaves i t s upper l i m i t switch. 1) K A ~ O Copens. 2) Relay Kl.83 is deenergized. 3) ROC^ 1 stops inserting. 4 ) K24OA closes and t h e shim-locating motor drives the cam clockwise toward t h e RRLSA upper l i m i t . 5) K24OF closes, K183 closes, and r e l a y Kl76 i s energized, causing rod 1 t o withdraw. The RRLSA cam is a l s o now being driven toward i t s 6) upper l i m i t by the position transmitter. d) This condition (4, 5, and 6 above) is the same as t h a t o r i g i n a l l y postulated, assuming t h a t t h e servo i s s t i l l requesting rod 1withdraw and the operator is manually c a l l i n g for " i n s e r t . " .--)

r t

:-.

A,p

i( c

J D

c*,

246 ORNL-DWG 64-608214 SEE NOTE 2

(74 415-v AC-2H

175

I76

I82

I R,S-NCCI -A4 THESE CONTACTS LOCATED IN 0-2609

FAST TRIP COMPARATORS

IN WIDE RANGE COUNTING CHANNELS. CONTACTS OPEN IF REACTOR PERIOD IS LESS THAN 25 Sac, I INHIBIT ROD WITHDRAWAL )

THESE CONTACTS OPEN WHEN WIDE RANGE

COUNTING CHANNEL 'CONFIDENCE

b K B l 3 9 G

ESTABLISHED

OPEN WHEN DRAIN TANKS FDT-I AND/OR 2 SHOW LOSS OF 4 5 5 0 Ib OF FUEL SALT

Kl93H

S65-CLOSED IS SELECTEDWHEN FLUSH SALT TANK

kKI9.H

I(/ CLOSED WHEN "CONFIDENCE" ESTABLISHED IN BF,CHANNEL

CLOSED WHEN WIDE RANGE COUNTING

__ --

OPENS ON AUTOMATIC "REVERSE"

ESTABLISHED

MODE

'PREFILL"

IN "START" MODE

yky

T :

5208 SHIMS NO. 2 ]AND NO. 3 5218 ACTUATE

(A17OC )PEN WITH SERVO "ON"

KI70H CLOSED SERVO .ON' WITH

RELAY CONTACT IN a-2615

Sl9A SHIM NO. I ACTUATE WITHDRAW

1 1

?CTUATEM INSERT K24lE OPENS WHEN SHIM REG. ROD LIMIT SWITCH ASSEMBLY CAM AT LOWER LIMIT

KAIB3A INSERT ROD NO. I

KAI76A WITHDRAW ROD N0.t

UPPER LIMIT:

[

SWITCHES

LOWER LIMIT

INSERT" REG. ROD LIMIT SWITCHES

,K240

K24IA OPENS WHEN SHIM REG. ROD LIMIT SWITCH CAM AT LOWER LIMIT

THIS RELAY, WHEN ENERGIZED,

I NEUTRAL

GROUP ROD WITHDRAW

SWITCH. WITHDRAW DIRECTION CAM ROTATES

ROD NO. I WITHDRAW

AN0 VICE VERSA FOR COUNTERCLOCKWISE CAM ROTATION 2.

THIS DWG DOES NOT SHOW DYNAMIC BRAKE CIRCUITRY FOR ROD N0.I IN CIRCUIT N0.179

SWITCH AND RELAY CONTACT ASPECT (OPEN OR CLOSED) ON THIS SKETCH I S FOR FOLLOWING CONDITIONS: a. SERVO "ON". ZERO ERROR SIGNAL b. REACTOR SYSTEM IN "OPERATE-RUN" MODES c. REGULATING ROD BETWEEN LIMITS e. "CONFIDENCE" d. REACTOR I N STEADY-STATE ESTABLISHED IN BOTH WIDE

DIRECTION, CAM ROTATES

REG. ROD LIMIT SWITCH ASSEMBLY WITHDRAW

3 )RAW

DRIVE M O T O ~ ROD N0.4

KA47OD CLOSED WITH SERVO "ON"

K476 THIS RELAY, WHEN ENERGIZED, OPERATES ROD DRIVE MOTOR IN ROD WITHDRAW DIRECTION, CAM ROTATES WITH S T V O "ON"

SWITCHES T KW2C

K244'

K240A OPENS WHEN SHIM REG. ROD LIMIT SWITCH CAM AT UPPER LIMIT

K183C OPENS FOR ROD N0.I INSERT

Kl75

REG. Roo LIMIT

ROD N0.I

F175A WITHDRAW"

. !l82A '

WITHDRAW ROD N0.I

K240F WHEN SHIM OPENS REG. ROD LIMIT SWITCH CAM AT UPPER LIMIT

ASSEMBLY SHIM REG. LIMIT ROD

ROO N0.I

KBl7OE :LOSE0 WITH SERVO' ON

CLOSED WHEN SHIM-REG. KA240C ROD ASSEMBLY CAM AT UPPER LIMIT

+t-

:ERVO CONTROLLER INSERT" ROD NO.(

St9D

KA170E CLOSED WIIH SERVO "ON

MODE

1CLOSED K138A 1GROUP KI74A ONLY WITHDRAW

S22B MANUAL REVERSE"

TO "ROD WITHDRAW" CONTROL CONTACTS 7FOR RODS NO. 2 AND 3 SEE FIG. RCS-2

CLOSED I!

R X S - NCC2-A4

REG. ROD LIMIT SWITCH INSERT

Fig. 2.6.5.

RANGE COUNTING CHANNELS

m D NO. I INSERT

MSRE

Circuits.

ANY ONE : 0 THE THREE CONTROL RODS MAY BE DESIGNATED "ROD NO. I , THIS NUMBER HAS BEEN ASSIGNED To THE ROD WHICH IS INTERCONNECTED TO THE SERVO CONTROLLER

SHIM LOCATING MOTOR

247

ORNL-DWG 66-5716

145V A<

KA483A

6 KAI83D KAI76A

KB183C

300pf /250V

AI KA476C

500. NEUTRAL

5051

Fig. 2.6.6.

Circuit Diagram f o r Regulating Rod Dynamic Brake.

ORNL-DWG 66-9430 L I M I T SWITCH CIRCUIT, TYPICAL OF ALL L I M I T SWITCHING CIRCUITS NO. 232 TO 239 INCL

CIRCUITS NO. 174 (78 INCL

-----it

184

s22c

4R-l

MANUAL "REVERSE" 5 . 2 2 ~

I: K186C

I STR U M EN,? REVERSE

[

SWITCH CONTACTS, SEE BELOW

KI 7 7 A l WITHDRAW RELAY CONTACT

K 234 A

K 235A

A :

K238A

K236A

UPPER LIMIT SWITCH K 2 3 7 ~ ) RELAY CONTACTS

K 239A

LOWER L I M I T SWITCH RELAY PHASE SHIFTING CAPACITOR

PHASE SHIFTING CAPACITOR

'84 Kb8p5EkS FOR

,ENERGIZE RELAYS TD WITHDRAW

LIMIT SWITCH RELAY

"INSERT"

Kt7$

ENERGIZE RELAYS / T O INSERT

K (84 <

ROD NO. 2

ROD NO. 3

DRIVE MOTOR

K 185

ROO N0.2

ROD N0.3

INSERT NO, WITH DRAW

INSERT NO, WITHDRAW

L WITHDRAW SHIM RODS 2 AND 3

INDIVIDUAL SHIM ROD ACTUATDR SWITCHES NO. S19. S 2 0 AND 521. MANUAL. ON CONSOLE CONTACT

POSITION

INSERT SHIM RODS 2 AND 3

CONTROL ROD DRIVE UNITS

GROUP SHIM ROO ACTUATOR SWITCH 522 CONTACT NO.

DRIVE MOTOR

POSITION REVERSE(INSERTI HOLD( WITHDRAW

CIRCUIT NO.

S 1 9 8 . S 2 0 8 . S21B

Fig. 2.6.7.

MSRE Control Rods 2 and 3 . C i r c u i t s .

ORNL-DWG 66-9014

I '

I I

K193B

K194B

r""'

IlLmRUoB

ccim YIIB m J -8 CmmL#2

C m m l l Q CIUllwL #l

CONFIDENCE CIRCUITS

Fig. 2.6.8.

mB n PrI- r a O R, C ~ L

MSRE Control System Confidence Circuits.

THESE CONTbCTS LOCATE0 IN 0-2623 RELAY

--CONTACTS OPEN WHEN REACTOR OUTLET TEMPERATURE EXCEEDS I275.F

CONTKTS OPEN WHEN REACTOR POWER (FLUX1 EXCEEDS SEE NOTE 2

JK248 I

PUMP EOWL LEVEL INPUT CIRCUIT

DE-ENERGIZED WHEN ANY 2 OF 3 REACTOR OUTLET TEMPERATURE INSTRUMENTS INDICATE TEMPERATURES GREATER THAN I275.F

1 ~ 2 4 -K8NC ~

3249A 3 2 m A

3.5..

R,S-NCCI-AB

LEVEL INSTRUMENT

K203A. CLOSEO WHEN REACTOR WWER (FLUX1 EXCEEDS 12MW (OR XWI

CONTACTM A m x m PR)WCE 'REVERSE' IF ANY 2 OF 3 CONTROL RODS ARE SCRAMMED

vG R,S-NCCI-b3

KEKW K207C -6 CONTACT -4 CLOSEO REACTORWHEN OUTLET 4 9 ~ IF FUEL SALT LEVEL EXCEEDS TEMPERATURE 78U N L L SCALE ON EXCEEDS 1275.F

-4 7

2 RxS-NCC2-b3

RxSN -CC2A G -il

CLOSED WHEN AWIDE RANGE COUNTING CHANNEL "CONFIDENCE' EXISTS KB139C

'-L

THIS CONTACT CLOSED IN .START" MODE OF REACTOR OPERATION

KI86

CONTROL ROD "REVERSE' OUTPUT ClRCUll

Fig. 2.6.9.

JK2.0

ROO.REVERSE' ON SCRAM INPUT CIRCUIT

REVERSE 2 OUT OF 3 REACTOR FLUX AND TEMPERATURE INPUT CIRCUITS FOR CONTROL ROD 'REVERJE"

JK249

MSRE Control Rod "Reverse" Circuits.

"THESE IN 0-2609 RELAY FAST CONTACTS. TRIP COMPARATORS R,S-*lc.. IN WIDE RANGE COUNTING CHANNELS. SEE NOTE I

NOTES: I.(o1 CONTACTS RIS-NCCI-A8 AND RxS-NCC2-A8 CLOSE WHEN REACTOR WWERIFLUXI EXCEEDS I.5MW ( b l CONTACTS &S-NCCl-A3 AND RXS-NCC2-A3 CLOSE WHEN REACTOR F'ERIOO IS LESS THAN 5 *ec

2. WHEN FUEL SALT PUMP MOTOR CURRENT IS LESS THAN 55 AMPERES TRIP WlNT IS REDUCE0 TO 9kW

251

c ORNL-DWG 6.-635

CHANGER

COMPENSATED ION CHAMBER 0-1045

. \ /

RANGE CHANGER

SUPPLY

.--I

TO INLET TEMPERATURE SENSOR TWOPEN RECORDER

'I CONSOLE CHANNEL SELECTOR SWITCH

NOTE:

a-zw5 ISOPERATIONAL AMPLIFIER

k&n

I I 'IER

COMPENSATED ION CHAMBER 0-1045

- !

CONMLE

TEMPERATURE SERVO DEMAND DRIVE UNIT 0-2628

COMRJTED FLUX DEMAND

TACHOMETER NO RANGE SEAL MOTOR

DEMAND

Fig. 2.6.10.

Linear Power Channels and Automatic Rod Controller.

r--'

3 1I f

253

ORNL-DWG

66-93'34

SUMMING AMPLIFIERS: OUTPUTS A R E NEGATIVE S U M OF I N P U T S

+T,

FLUX DEMAND S I G N A L TO S E R d O PILOT RELAYS

[GIsp

FLUX DEMAND

ROD D R I V E MOTOR SIGNAL FROM TACHOMETER

-S P E E D ;=FUEL

S A L T T E M P E R A T U R E , CORE I N L E T

T,=FUEL

S A L T T E M P E R A T U R E , CORE O U T L E T

=NEUTRON FLUX SET POINT, FUEL SALT OUTLET TEMPERATURE

[GIsp=

Fig. 2.6.12.

Diagram of Regulating Rod Servo C o n t r o l l e r .

ORNL-DWG 64-6PZR2

REGULATING ROD L I M I T SWITCH ASSEMBLY I N INSTRUMENT C A B I N E T ROD DRIVE MOTOR, SERVO OR M A N U A L L Y CONTROLLED

SHIM LOCATING MOTOR, OPERATOR CONTROLLED

ROD POSITION

, TRANSMITTER

W I T H CONTROL ROD ACTUATOR SWITCH. USED DURING SERVO OPERATION ONLY,

NOTE A S REDUCE0 TO PRACTICE THE CONTROL ROD MOTION IS REPRODUCED I N THE CONTROL ROOM AND L I M I T SWITCHES ARE ACTUATED BY THE REGULATING ROD LIMIT SWITCH ASSEMBLY. SEE DIAGRAM.

TOTAL Roo STROKE

DRIVE MOTOR: OPERATED BY ROD CONTROLLER ONLY WHEN I N SERVO OPERATION AND BY ROD ACTUATOR SWITCH I N MANUAL OPERATION ROD DRIVE UNIT

LOWER

LIMIT SWITCH-

I I

I L-__

CONTROL ROD/

REGULATING ROO

REGULATING ROD

I I I

I I

I I I

I I I I

TRANSFORMER

’I

MOTOR

:LUTCH-BRAKE: a. I N SERVO OPERATION THE CLUTCH IS ENGAGED A N D THE CAM IS COUPLED TO THE B A L A N C E MOTOR b. I N M A N U A L OPERATION T H E D U T W T SHAFT IS LOCKED AND THE BALANCE MOTOR I;\ DECOUPLED UPPER REGULATING

I I

a b. WITHDRAW INSERT L I M IROD T SWITCH N0.4 SPAN [DECREASE y,)

FINE

SHIM ROD POSITION INDICATORS

REG. ROD POSITION INDICATOR (RELATIVE TO SPAN L I M I T SWITCHES)

CONTROL CONSOLE

Fig. 2.6.13.

Regulating Rod L i m i t Switching -Operational D i a g r a m .

GEAR BOX FOR SPAN CHANGE GEARS

REGULATING ROD POSITION TRANSMITTER (SYNCHRO)

:LOCK CAM ROTATION 3 2 J I V TO:

I -J COARSE

CLUTCH

‘SLIP

ROD LIMIT SWITCH’

DIFFERENTIAL

2 55

PHOTO 62304A

SLIP CLUTCH

Fig. 2.6.14.

REGULATING ROD POSITION TRANSMITTER (SYNCHRO TORQUE TRANSMITTER SIZE 31)

Regulating Rod L i m i t Switch Assembly -Top View.

257

258

2. THIS ILLUSTRATION SHOWS FOUR (4)L I M I T SWITCHES SO THAT INTERMEDIATE SWITCH POINTS BETWEEN EXTREME LIMITS CAN BE PROVIDED. I N THE MSRE ONLY TWO ( 2 ) ARE USED

Fig. 2.6.17.

Regulating Rod L i m i t Switch Assembly -Underside View.

2 59

ORNL-DWG 66-4l05R

Fig. 2.6.18. Train Diagram.

MSRE Regulating Rod L i m i t Switch Assembly, Drive

ORNL-DWG 66-4tO4R

TO M A N U A L CONTROL SW

SHIM ROD NO.1, ON CONSOL

SYNCHRONOUS MOTOR (DUMMY SHIM LOCATING MOTOR )

ELECTROMECHANICAL BRAKE, RELEASED MECHANICAL DIFFERENTIAL

M E C H A N I C A L D R I V E CONNECTION

E L E C T R I C A L CONNECTION

ELECTRO-MECHANICAL CLUTCH-BRAKE

S I Z E I5 C O N T R O L TRANSFORMER

WHEN ROD SERVO I S "ON"

STATOR W IN D ING S OF S I Z E 34 SYNCHRO I N ROD D R I V E

Fig. 2.6.19.

SYNCHRO RECEIVER ( R E G U L A T I N G ROD POSITION) ON C O N S O L E

MSRE Regulating Rod Lhit Switch Assembly, Block Diagram.

+ @I-

II .

$ k

262

+ 1

I /

t -t

FOR INFORWITION ONLY DO NOT USE FOR MAINTENANCE OR CONSTRUCTIOY

Fig. 2.6.21.

Automatic Rod Controll r Range Switching and Range S e a l Circuits.

263

2.7

CONTROL RODS AND ROD DRIVES 2.7.1

General Arrangement

The control rod drive u n i t and i t s housing are shown i n Figs. 2.7.1 t o 2.7.3. Figure 2.7.4 i s a simplified electromechanical diagram which shows t h e functional location of t h e e s s e n t i a elements which comprise t h e drive t r a i n . The gearing and t h e clutches are inside a cast-aluminum gear box. The drive motor, t h e two position-transmitting synchros, and t h e position-indicating potentiometer a r e mounted on and outside t h e gear box with t h e i r s h a f t s carrying t h e i r drive gears projecting inside t h e box so as t o mesh with t h e appropriate gears i n t h e drive t r a i n (Fig. 2.7.2). The gear box subassembly, which includes t h e position transmitters and t h e clutches, i s located at the upper end of t h e drive u n i t i n an e f f o r t t o keep t h e radiation-sensitive camponents ( e l e c t r i c a l insulation and l u b r i c a n t ) as far from t h e reactor as feasible. Figure 2.7.5 i s a diagram of t h e gear t r a i n and t h e clutches. The worm and gear s e t i s of somewhat unorthodox design, i f compared w i t h t y p i c a l standard pract i c e f o r t h i s type of gearing (see Sect. 2.7.9.10). The other gears are conventional. The rod i s scrammed by interrupting current t o t h e electromechanical clutch. During scram, t h e driven element of t h e overrunning clutch i s f r e e t o r o t a t e and, except f o r a s m a l l amount of f r i c t i o n and i n e r t i a , does not i n t e r f e r e with r o t a t i o n of the output sprocket i n t h e "rod i n s e r t d i r e c tion. The electromechanical clutch and the overrunning clutch provide p a r a l l e l power transmission paths between the motor and t h e output sprocket. The arrangement i s such that t h e overrunning clutch transmits motor torque i n t h e "rod i n s e r t " direction only and can be used t o apply motor torque t o the drive sprocket i n t h e event t h a t a rod s t i c k s o r binds following a scram. If external torque i s applied t o the output sprocket i n t h e "rod withdraw" d i r e c t i o n of rotation, t h e overrunning clutch provides a s o l i d mechanical coupling between t h e drive sprocket and the input s i d e of t h e drive t r a i n . The worm and gear s e t are inherently self-locking with respect t o torque i n e i t h e r d i r e c t i o n o r i g i nating a t t h e output sprocket. This combination of overrunning clutch and worm and gear s e t prevents rod w i t h d r a w a l s by upward forces applied t o t h e control rod o r by a torque applied t o t h e drive sprocket. The drive u n i t housing, with t h e drive u n i t secured thereto, i s attached t o t h e control rod thimble by means of a flange welded t o t h e bottom of t h e housing. Figure 2.7.6 i s a photograph of the rod thimble, which extends i n t o t h e core vessel, and shows the mating flange. The radial s l o t s i n t h e rim of t h e thimble flange mate with pins i n t h e housing flange and are required t o ease t h e problem of orientation during remote maintenance operations. The milled s l o t i n the face of t h e flange accepts t h e T-shaped. flange f i t t i n g , which i s cap-screwed t o t h e It prevents rod drive tow block (see Figs. 2.7.19, 2.7.20 and 2.7.14). t h e rod from twisting when it i s being detached from t h e tow block during remote maintenance. Figure 2.7.7 i s a photograph of the subassembly formed by t h e thimbles and the graphite sanpler taken before i n s t a l l a t i o n

264

on the reactor vessel. This i l l u s t r a t i o n a l s o affords a good view of t h e lower, stationary halves of t y p i c a l thermocouple disconnects designed f o r remote handling. Figure 2.7.8 shows t h i s subassembly mounted on t h e reactor vessel; Fig. 2.7.9 i s a l i n e drawing of t h e control rod drives and rod thimbles on t h e reactor vessel. The rod drives are offs e t radially t o make room f o r the graphite sampler tube (not shown on t h i s sketch), which occupies space on the v e r t i c a l center l i n e through the core vessel. Figure 2.7.10 shows t h e top of t h e control rod drives i n s t a l l e d on t h e reactor. This picture was taken looking down through t h e access hole i n t h e top of t h e secondary containment c e l l . The e l e c t r i c a l jumper cables and cooling a i r hoses w i t h t h e i r disconnects are v i s i b l e i n t h i s picture. E l e c t r i c a l interconnections between drive u n i t s and junction boxes on the w a l l of t h e reactor c e l l are made w i t h f l e x i b l e jumper cables. Each drive u n i t has i t s individual cable assembly, which i s designed f o r remote handling. The wires making up t h e cable are designed f o r high temperatures and use radiation-resistant insulation (see Sect. 2.7.9). The wires are t i g h t l y bundled by means of heat-shrinkable p l a s t i c tubing. This wire bundle i s sheathed i n a loose-fitting, s p i r a l l y wound stainless s t e e l hose t o give mechanical protection. The f i t t i n g s a t each end use ceramic p i n and socket i n s e r t s of standard p a t t e r n in s h e l l s and receptacles which have been designed t o meet remote handling requirements. The interconnection cabling and junction boxes are described i n Sect. 2.1. 2.7.2

Position Indication

Continuous indication of rod position i s provided by two synchro torque transmitter-receiver pairs, one "fine" and one "coarse. The location of t h e transmitters on t h e gear box i s shown i n Fig. 2.7.2. The "coarse" rod position transmitter r o t a t e s 5' per inch of rod t r a v e l . Since t h i s i s l e s s than one full t u r n f o r t h e maximum rod t r a v e l of 60 in., t h e indication i s unambiguous. The "coarse" position receivers, one f o r each rod, are located on t h e main control board. The "coarse" transmitter a l s o supplies the ac e r r o r s i g n a l t o t h e synchro control transformer i n t h e torque amplifying rod position follower. This u n i t (see Fig. 2.6.20) drives t h e potentiometer which provides the rod position input s i g n a l t o t h e logger. On rod 1, t h e same ac s i g n a l i s used as t h e input t o t h e Honeywell servo amplifier i n t h e Instrumentation and Controls drawing Q-2586 shim regulating rod l i m i t switch assembly. This device i s discussed i n Sect. 2.6. The "fine" transmitter r o t a t e s 60" per inch of rod t r a v e l and i s expected t o be capable of resolving incremental sprocket chain motions t o within k0.050 in. Since both t h e "coarse" and "fine" synchro transmitters are geared t o the sprocket shaft, they indicate sprocket s h a f t r o t a t i o n and do not take i n t o account changes i n rod length caused by thermal expansion, stretching, e t c . I n order t o l o c a t e t h e control rod as accurately as possible w i t h respect t o t h e reactor core, a single-point, pneumatically operated, position device i s employed. The position sensor consists of an a i r nozzle a t t h e bottom of t h e control rod which c a r r i e s the flow of rod cooling air f r o m t h e hollow inside of t h e rod t o t h e thimble. When t h e rod i s a t t h e bottom of i t s normal stroke t h e nozzle i s op-

265

posite a flow r e s t r i c t o r b u i l t i n t o the thimble. The increase i n pressure drop caused by the r e s t r i c t i o n i s t h e position indication. The nozzle and r e s t r i c t o r are shown i n Fig. 2.7.11, and t h e schematic diagram of t h e pressure measuring instrumentation i s shown i n Fig. 2.7.12. This device i s manually operated and i s used t o check t h e zero readings of the position-indicating synchros and, i n f e r e n t i a l l y , provides information on how temperatures and s t r e s s e s produce s m a l l changes i n t h e r e l a t i v e position of the rod with respect t o t h e thimble.

2.7.3

Shock Absorber

The shock absorber i s a development of the Vard Division of Royal Industries, who b u i l t t h e drive units. It uses the g e n e r a p r i n c i p l e of a t y p i c a l hydraulic shock absorber but d i f f e r s i n t h a t t h e working "fluid" consists of 3/32-in.-diam s t e e l balls. Figure 2.7.13 i s a v e r t i c a l cross-section view of t h e shock absorber i n s t a l l e d i n t h e drive unit. Referring t o t h i s figure, t h e piston i s the knob, which i s an i n t e g r a l p a r t of the plunger. The l a t t e r i s a tubular rod which i s threaded i n t o t h e carriage and which connects t h e control rod tow block t o t h e carriage. The closed cylinder, p a r t i a l l y f i l l e d with s t e e l balls, t r a v e l s w i t h t h e carriage and i s positioned r e l a t i v e t o the carriage (and t h e plunger) by t h e buffer return spring. A t the end of a scram t h e bottam face of t h e cylinder s t r i k e s the stationary s t e e l blocks which are bolted t o the housing flange. The plunger continues t o move downward and i s decelerated by t h e forces developed by the springs and by the flow of t h e s t e e l balls around t h e knob on t h e plunger. Shock-absorbing c h a r a c t e r i s t i c s are adjusted by changing e i t h e r t h e spring constants or t h e preloading of t h e buffer return and b a U r e s e t springs, or both, by changing the quantity and s i z e of t h e s t e e l balls, and by s i z i n g the knob on t h e plunger. A stroke of from 2.75 t o 4.00 in. i s considered satisfactory. During t e s t s 1 of the prototype, t h e shock absorber performed consistently and provided a stroke of 3.4 k 0.2 in. following rod scrams from a height of 51 in. This produced an average deceleration of 6.2 g.

2.7.4

Cooling A i r Flow and Temperature Monitoring

The drive i s provided with two separate flows of cooling air. The first i s conducted i n t o t h e thimble by means of a thin-walled tube thak p r o j e c t s i n t o t h e stainless s t e e l hose which supports t h e poison elements of t h e rod. This flow of air e x i t s through t h e nozzle a t t h e lower end of t h e rod (see Fig. 2.7.ll) and returns up through t h e annulus formed by t h e outside of t h e rod and t h e inside of t h e thimble. The second air stream is admitted at t h e top of t h e rod drive housing and flows downward within t h e housing. This a i r flow i s counter t o t h e f i r s t flow and prevents heated a i r from t h e thimble from r i s i n g i n t o the drive unit. Both streams are discharged i n t o t h e reactor c e l l a t t h e upper end of t h e thimble. Two bimetallic thermostatic switches are mounted on t h e support column of t h e drive u n i t approximately 8 in. above t h e lower sprocket.

1MSR-64-7,Feb. 10, 1964 ( i n t e r n a l memorandum).

266

Their contacts are i n s e r i e s f o r redundancy and are s e t t o open a t Switch actuation i s annunciated i n t h e control room; no control 200'F. action r e s u l t s . These switches (Fig. 2.7.14) were added t o t h e drive u n i t s a f t e r they had seen service during t h e initial c r i t i c a l t e s t s and low-power runs of the reactor; hence they do not appear i n t h e photographs of t h e drive u n i t assembly. Their purpose i s t o s i g n a l t h e control room that t h e drive u n i t is in danger of being subjected t o damaging temperatures, a condition which could r e s u l t from l o s s of air flow i n t o t h e housing, excessive thimble temperatures, stoppage of t h e exhaust l i n e , o r excessively high ambient c e l l atmosphere temperature. The switches are described i n Sect. 2.7.9.9. A second, o r backup, method of checking temperatures within the rod drive i s shown in Fig. 2.7.15. This method uses t h e temperature c o e f f i c i e n t of resistance of t h e cooling fan motor windings ( p a r t of t h e rod drive motor assembly) t o measure t h e temperature within t h e rod drive u n i t housings. The fan motor f i e l d windings t y p i c a l l y have roomtemperature resistances of 520 ohms. Copper has a temperature coeff i c i e n t of resistance of 2.18 X low3 ohm/ohm-OF over t h e temperature range of i n t e r e s t . The s l i g h t l y more than lo$ change i n resistance f o r a 50'F change i n winding temperature provides more than ample s e n s i t i v i t y . Periodic measurements made during reactor operation showed t h a t t h e dc resistance of these windings gave a good l i n e a r c o r r e l a t i o n i n following i n - c e l l air temperature. The duty cycle of t h e rod drive motors i s exceedingly light; f o r example, the servo motor was "on" f o r a t o t a l of 51 sec i n a 2-1/2-hr period with t h e reactor a t an intermediate power l e v e l and i n servo control of t h e o u t l e t temperatures. Manual. shimming i s an infrequent operation and requires only a few seconds t o accomplish. I n addition, t h e servo motors operate a t a f r a c t i o n of t h e i r rated capacity. The l i g h t load and duty cycle permit shutting off t h e fan long enough t o measure t h e dc resistance of one of t h e fan motor f i e l d windings. It i s l i k e l y t h a t t h e motor cooling fans a r e not needed i n t h e MSFB. A s can be seen from Fig. 2.7.15, t h e fan motor being checked f o r temperature i s turned off temporarily by energizing t h e selector-switched relays, and t h e temperature i s indicated on the meter i n t h e output c i r c u i t of t h e regulated voltage supply. The diodes across t h e motor windings prevent insulation damage by preventing high-voltage switching t r a n s i e n t s caused by opening t h e highly inductive f i e l d winding. 2.7.5

L i m i t Switches

Limit switches and t h e i r actuators are a frequent problem area i n devices of t h i s type. The MSKE rod drive u n i t was no exception; during t h e first c r i t i c a l t e s t s , t h e actuator became stuck a t t h e lower l i m i t . This was caused by excessive wear and g a l l i n g of s o f t s t e e l s l i d i n g bearing surfaces i n the switch actuator guide. The design was a l t e r e d by providing hardened-steel, spring-loaded, f l o a t i n g bearing pads t o replace t h e galled bearing surfaces. T.e revised desi@ is shown i n The slide assembly i s lubricated with Neolube (see Sect. Fig. 2.7.16. Figures 2.7.17 and 2.7.18 are photographs of t h e l i m i t 2.7.3.8). switches and actuators i n s t a l l e d on t h e drive u n i t .

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2.7.6

Control Rods

Figure 2.7.19 i s a photograph of the upper end of a display model of the E R E control rod with the poison elements2 removed. The poison There are three control rods, which elements2 are shown i n Fig. 2.7.11. are i d e n t i c a l i n construction, each weighing approximately 11.2 l b . The rod lengths are s l i g h t l y d i f f e r e n t because of the required o f f s e t of the control rod thimbles. The rod lengths are: rod 1, 11 f t 9-7/16 in.; rod 2, 11 f t 9 in.; and rod 3 , U f t 7-3/16 in. The control rod i s attached t o the control rod drive by means of a two-bolt (3/8 i n . X 16 thread) flange o r tow block made of 304 s t a i n l e s s s t e e l . The drive mechanism contains a matching flange containing the captive b o l t s . The assembly i s designed t o permit attachment of the control rod drive flange t o the control rod flange through an access hatch i n the drive u n i t case using a remote, manually operated extension wrench. The upper hose consists of a length (-6-1/2 f t ) of 0.850-in.-OD by 1/2 in.-ID annularly corrugated, 321 stainless s t e e l , f l e x i b l e metal hose with a single exterior l a y e r of wire braid, The corrugated hose provides a l e a k t i g h t passage f o r the low-pressure (-8 psig, -5 scf'm) rod cooling a i r t o reach the poison elements. The wire mesh serves the purpose of protecting the hose from abrasion, minimizes stretching of the hose, and a c t s as an emergency r e t a i n e r i n the event of hose f a i l u r e . The 1/2-in. inside diameter of the hose permits passage of the 7/16-in.OD stationary cooling a i r tube which i s attached t o the upper drive mechanism. When the rod i s i n motion, the corrugated hose and tow block move up and down over the a i r tube. The w e l d adapter serves t o align the two types of metal hose used i n t h e rod construction. It a l s o serves as the upper anchor point f o r a 1/8-in.-OD INOR-8 retaining rod, which i s located inside the lower hose. The lower hose i s 5 ft 2 in. long, Inconel 600, f u l l y interlocked, unpacked, strip-wound f l e x i b l e metal hose 47/64 in. OD and 5/8 i n . I D . The 38 Inconel-clad poison elements, detailed i n Fig. 2.7.ll, are beaded over the strip-wound hose, as shown i n Fig. 2.7.20. The lower end of the strip-wound hose i s welded t o the air exhaust nozzle, which a c t s as the element r e t a i n e r and lower anchor point f o r the 1/8-in. retaining rod. The rod supports a portion of the weight of the poison elements, contains the stretching of the strip-wound hose, and a c t s as safety r e t a i n e r i n the event of hose f a i l u r e . During the two years of rod testing, there have been three incidents of rod f a i l u r e . Two f a i l u r e s were due t o misoperation of the equipment, and one incident w a s due t o misalignment of 7/16-in.-OD a i r tube i n t h e corrugated upper hose. The upper hose was worn by the a i r tube rubbing the inside surface of the hose so t h a t when t h e rod was

2S. E. Beall e t al., MSFUI Design and Operations Report, Part V, Reactor Safety Analysis, ORNL-TM-732 (August 1964); G. M. Tolson and A. Taboada, MSKE Control Elements: Manufacture, Inspection, Drawings, and Specifications, ORNL-4123 (July 1967).

268

released i n scram, t h e hose broke away from the tow block when it h i t t h e mechanical stop i n t h e shock absorber mechanism. A bronze bushing w a s i n s t a l l e d i n t h e tow block t o assure alignment of t h e a i r tube and hose. Subsequent examination revealed only minor wear a t t h i s point.

2.7.7

Rod Drop Timer

Routine operation of t h e MSRE3 requires t h a t t h e drop time f o r each rod be checked each time before f i l l i n g t h e reactor with f u e l salt. Figure 2.7.21 diagrams t h e timing c i r c u i t r y used t o measure drop times. The timer consists of a continuously running synchronous motor connected, via gearing, t o a fast-acting electromechanical clutch-brake whose output shaft drives an indicating pointer. The elapsed time indicated by t h e pointer, therefore, i s t h e time during which t h e clutch i s engaged. The drop time i s easily measured. The rod i s scrammed using the manual scram switch on t h e console. This closes relay contact K29A, and t h e timer clutch i s engaged and remains engaged u n t i l a lower rod l i m i t switch is actuated by t h e rod a t the end of t h e drop. 2.7.8

Performance Characteristics

This l i s t of performance c h a r a c t e r i s t i c s i s derived from prototype t e s t data: 1. Rod speed with e i t h e r 25- o r 10-w motor running continuously a t rated voltage ( U 5 v ac, 60 cps), 0.53 in./sec. Note: The change i n speed i n going from "Up" t o 'lDown" i s approximately 1%.

2. Rod speed with the 25-w motor i n "inching" mode (1/2 sec "On," sec " O f f , " e t c . ) , motor a t rated voltage, 0.22 in./sec.

1/2

3. Motor speed as a function of applied voltage, see Fig. 2.7.22. Note: Rod speed (in./sec) = 1.53 X lo4 X r p m of motor. 4. Scram performance1 a ) Elapsed time t o drop 51 in., 0.80 sec (see Fig. 2.7.23). b ) Average acceleration during scram f o r a 51-in. drop, 13.2 ft/sec2 = 0.4lg. c ) Clutch release time, inferred from a curve of t h e square root of distance vs elapsed time (see Fig. 2.7.24), 0.012 see. d) Figure 2.7.25 compares a c t u a l and required r e a c t i v i t y insertions during scram. These curves are calculated from curves ''A'' and "Btr on Fig. 2.7.23 and t h e calculated percent of t o t a l rod worth vs distance curve, Fig. 1.19, p 59, ref. 2, and a t o t a l worth This value of t o t a l worth approximates t h e t o t a l of 4 . l $ &/k. r e a c t i v i t y inserted by scramming any two of t h e three rods. The i n i t i a l height p r i o r t o scram was taken as 51 in.

3S. E. Beall and R. H. Gqymon, MSRE Design and Operations Report, P a r t V I , Operating Safety L i m i t s f o r t h e Molten S a l t Reactor Experiment, ORNL-TM-733 (Rev. 2) (Sept. 19, 1966).

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2.7.9

2.7.9.1

Component Descriptions and Specifications

Rod Drive Motor Assembly

General Descrintion The drive motor i s a l l 5 - v ac, 60-hertz, two-pole, two-phase servo motor rated a t 25 w maximum output.4 A s used i n the MSRE, the input power i s single-phase l l 5 - v ac, and phase s p l i t t i n g i s obtained with a 10- t o 12-pf capacitor i n s e r i e s with one of the f i e l d windings. An ac tachometer is mounted i n t e g r a l l y on the motor shaft. The tachometer output i s used as a feedback signal t o s t a b i l i z e the servo controller. Tachometer output is 6 v per 1000 rpm. A s m a l l blower i s included as p a r t of the assembly. The blower i s powered by a separate, capacitortype two-phase motor and runs continuously whether the servo motor i s on o r off. These three u n i t s (motor, tachometer, and blower) a r e incorporated i n t o a single u n i t supplied by the Diehl E l e c t r i c a l Division of t h e Singer Manufacturing Company. The u n i t specified f o r the MSRE i s simi l a r i n shape, size, and performance t o a standard D i e h l 25-w motor No. FPF 49-91-1. They are special i n that they c a l l f o r c l a s s H radiationr e s i s t a n t electrical. insulation and use radiation-resistant grease. Performance data are given i n Figs. 2.7.26 and 2.7.27. Procurement Information Procurement specifications are contained i n Vard Specification No. ll4096, modified by ORNL, and dated April 12, 1964, and i n ORNL Purchase Order No. 63-76819. 2.7.9.2

Electromechanical Clutch

This clutch i s of the single-disk type w i t h a stationary f i e l d c o i l . It i s supplied by the Electroid Corporation, Union, New Jersey, Characteristics and specifications are as t h e i r Drawing ZC-6CC-8-8. follows :

Rated s t a t i c torque

75 in.-lb

Rated c o i l voltage

32 dc

Coil current a t 32 v dc

0.24 amp

Nominal s i z e (clutch disk d i m ) a Engagement t ime

2-5/8 in.

Release time

Not available

Electrical. insulation

Class H

F r i c t i o n torque ( m a )

0.5 in.-oz

0.0075 sec o r l e s s

%is nmber from Electroid catalog for this s i z e clutch with both 24- and 90-v dc coils. 4A 10-w motor, i d e n t i c a l i n all respects but power rating, may be substituted f o r the 25-w motor.

270

Detailed procurement information i s on Vard Corporation Drawing No.

ll4701. Overrunning Clutch 2.7.9.3 The overrunning clutch i s a standard, commerciaUy available device manufactured by t h e Formsprag Company, 23601 Hoover Road, Warren, Michigan. It i s a Formsprag model FS-05 i n which t h e O i l i t e sintered bronze bushing normally used has been replaced with a bronze bushing and which has been packed with California Research Corporation type NRRG-159 o r S h e l l type Am, grease. The manufacturer s t a t e s it meets performance requirements as follows: normal running torque, 3 l b - f t a t 8 rpm; and stall torque, 20 lb-ft a t 8 rpm. Additional specification-type information i s contained i n a l e t t e r dated February 1, 1963, from W. T. Cherry, Formsprag Campany, 609 West Lincoln Avenue, Anaheim, California, t o P. Butkys, V a r d Division of R o y a l Industries.

2.7.9.4 Position-Indicating Synchros The synchro torque transmitters, both "Fine" ( s i z e 18) and "Coarse" ( s i z e 31), meet m i l i t a r y standard (Mil. S-20708) design requirements with respect t o size, shape, mounting dimensions, and performance c h a r a c t e r i s t i c s . They are nonstandard i n that t h e e l e c t r i c a l insulation and lubricant a r e f o r a high-radiation environment. The torque transmitters i n t h e prototype rod drive unit were supplied by t h e Vernitron Corporation, 1742 Crenshaw Boulevard, Torrance, California. Additional specification data f o r these transmitters are as follows: Item -

Size 18b

Size 31a

Primary winding

Rotor

Primary voltage, nominal

ll5

Frequency

60 cps 462 m a 6.6 w 0.783 k 2% 6.5O lead 10 min 0.40 oz-in./deg.

60 cps 105 m a

Input current, m a x Input power, max Transformation r a t i o Phase s h i f t , max E l e c t r i c a l error, max Torque gradient N u l l voltage ( t o t a l ) , max

125 mv

N u l l voltage ( fundamental), max

35 mv

4.0 w 0.783

18.oo 6 min 0.05 oz-in./deg.

%ernitron Corp. No. VTX31-6R1, Vernitron Dwg. OD10581. %ernitron Corp. No. vTx18-6R1, Vernitron Dwg. OD10582.

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2.7.9.5

Position-Indicating Potentiometer

b, The specifications f o r the position-indicating potentiometer, a Beclunan Company type 6200 s e r i e s potentiometer with b a l l bearings lubr i c a t e d as described i n Sect. 2.7.9.8, are as follows: I n f i n i t e resolution, cermet resistance element, continuous rotation with no stops, metal housing, 1-1/16 in. d i m X 5/8 in. long with standard servo mounting dimensions, b a l l bearings Resistance

1000 ohms 5 5% a t 150'F

Linearity

0.5$

E l e c t r i c a l rotation

350 k 5'

Power r a t i n g

5 w a t 185'F derated t o zero a t 300'F

Refer t o UCNC Purchase Order 56S1446, Item 1 (Requisition L-8824.), January 29, 1965. 2.7.9.6

L i m i t Switches

L i m i t switches are Micro Switch type V3-1301, a higbtemperature nuclear-radiation-resistant design, manufactured by Micro Switch D i vision, Minneapolis-Honeywell Regulator Company, Freeport, I l l i n o i s . Catalog information describing t h i s switch i s slrpplemented by two l e t t e r s written by V. J. Brown, Los Angeles 22, California, t o Povilas Butlqys, Vard Corporation. The l e t t e r s are dated December 20, 1962, and January 9, 1963.

2.7.9.7

E l e c t r i c a l Wiring

I n t e r n a l wiring within the rod drive u n i t from the terminals on the disconnect t o the various components i s of high-temperature, radiationr e s i s t a n t hookup wire. The prototype used Supertemp type MGT, manufactured by American Super-Temperature Wires, Inc., 50 West Canal S t r e e t , Winooski, Vermont. Micatemp, a similar type of wire manufactured by Rockbestos Wire and Cable Company, Division of Aero Corporation, Nicoll and Comer Streets, New Haven, Connecticut, is equally acceptable.

2.7.9,8

Lubrication

The gears, overrunning clutch, and t h e bearings i n t h e gearbox, motor, synchros, etc., are lubricated w i t h a nuclear-radiation-resistant grease: S h e l l Corporation type APL or California Research Corporation type NRRG-159. This l a t t e r grease586 i s composed of ' ' ~ ~ 6 - ~ 8 - a ~ c y l b i -

5James G. Carroll e t al., "Field Tests on a Radiation Resistant Grease, " Lubrication Engineering (February 1962). 6WADC-TR-57-299, 3%.

11, p. 9 (report r e f e r s t o NRRG-159).

272

phenyl f l u i d inhibited with didodecyl selenide and gelled with a sodium terephthalamate." The sprocket chain and t h e l i m i t switch actuator are coated with Neolube, a film of c o l l o i d a l graphite deposited as a dispersion of graphite i n a v o l a t i l e c a r r i e r (isopropanol). Neolube i s manufactured by Huron Industries, Post Office Box 1W, Port Huron, Michigan. 2.7.9.9

Thermostatic Switches

The thermostats are sma31 bimetal-type u n i t s with t h e bimetal mounted i n a ceramic tube. Sample switches were t e s t e d well beyond destruction by heating t o over 1200'F, and no release of solder o r other low-temperature melting point material was observed. Technical data on these switches, based on t h e s e l l e r ' s catalog, are as follows: ElectricaJ rating

50 w a t 115 t o 230 v ac, noninductive load

Ope r a t i g g temperature

Adjustable, by means of a screw, t o 300'F.

raws Physical appearance

1/4 in. diam, 1-1/8 in. long; terminal a t each end with a 2-56 tapped hole f o r making e l e c t r i c a l connection

Contact operation

To open on r i s i n g temperature

h e range specified f o r t h e MSRE w a s 150 t o 200'F. The thermostats were purchased from the George Ulanet Company, 413-415 Market S t r e e t , Newark, New Jersey, t h e i r model No. 17-L3. Refer t o UCNC Purchase Order 5%-17341, Requisition No. L-9682 dated August 10, 1965. 2.7.9.10

Gears

A l l gears are of carbon s t e e l o r s t a i n l e s s s t e e l . The 24 diametralp i t c h gears i n t h e power t r a i n between t h e motor and t h e output sprocket are of s t e e l and designed p a r t i c u l a r l y f o r t h e drive u n i t . The 32 diametral-pitch gears which drive t h e synchros and t h e position potentiometer a r e commercially available components w i t h minor modifications where required f o r mounting, e t c . The worm and gear set i s t h e end product of t e s t stand experience with t h e prototype u n i t . The o r i g i n a l design specified an aluminum bronze worm wheel mating with a steel worm. The worm had a hardness of 38 t o 42 on t h e Rockwell C scale and a surface f i n i s h of 64 pin. maximum roughness. These gears f a i l e d a t a rapid r a t e by abrasive wear. The f i n a l desi@ of t h i s gear p a i r , based on additional t e s t stand experimentation and l i f e t e s t i n g with t h e prototype u n i t specified type 44,oC s t a i n l e s s s t e e l , hardened t o Rc 55 or b e t t e r , f o r both t h e worm

and gear.

The worm thread was ground and had a surface f i n i s h of ap-

273

:e, ~

proximately 20 pin. The gears were lapped t o form selectively f i t t e d pairs. Gear s e t s of other hardenable s t e e l s were t r i e d i n the prototype, and it was concluded t h a t the determining f a c t o r f o r the s t e e l s used i n t h i s service is probably surface hardness and finish, not any p a r t i c u l a r type or U o y .

274

Fig. 2.7.1.

W Control Rod D r i v e Unit and Housing.

, .

275

PHOTO 6 2 0 5 5

37- PIN DISCONNECT

POS ITION- INDlCATOR SYNCHROS

DRIVE SPROCKET

GEAR REDUCTION AND CI-UTCH U N I T CHAIN DRIVE

L I M I T SWITCHES

25-w

aIC LOW INEFtTIA SELRVO MOTOR I

SHOCK ABSORBER AND TOW BLOCK

bp,

MSRE Control Rod Drive Unit -Upper End Shuw,ag Fig. 2.7.2. Box and Servo Motor.

Gear

276

UPPER AND LOWER LIMIT SWITCHES

Fig. 2.7.3. MSRE Control Rod Drive Unit -Upper End Shuwing Location of Limit Switches.

277

ORNL-DWG 63-839tR I N P U T S I G N A L TO S I Z E 18 S Y N C H R O C O N T R O L T R A N S F O R M E R , P A R T OF TORQUE A M P L I F Y I N G ROD POSITION TRANSMITTER I N SHIM REGULATING ROO L I M I T S W I T C H A S S E M B L Y

INPUT SIGNAL TO Q-2560

TORQUE^

A M P L I F I E D ROD P O S I T I O N P O T E N TIOMETER DRIVES IN LOGGERC O M P U T E R ROOM

TO POSITION READOUTS IN CONTROL ROOM

I-1

(~~~~~

SYNCRO N0.2

OF€€loRODPER MOTION INCH OF ROD MOTION

0.5 in./sec

POISON E L E M E N T S

HORIZONTAL G R A P H I T E BARS

GRID PLATE

CORE V E S S E L

Fig. 2.7.4.

Electromechanical Diagram of Control Rod Drive Train.

278 ORNL-hrg. 66-3915

RATIOS..

Flu€ SYNCHRO EO?WiON I ROD TRAVEL /N COARSE SYNCHRO RQTAE'ON ROD TRAVEL

Fig. 2.7.5.

-- IN3

MSRE Control Rod Drive Unit Power Transmission Diagram.

279

280 PHOTO 7 t 1 1 l A

Fig. 2.7.7. Sample Tube.

MSRE Subassembly of Control Rod Thimbles and Graphite

Fig. 2.7.8.

281

Subassenibly (Fig. 2.7.7)

Mounted on Reactor Vessel.

282 ORNL-DWG 64-6083

CONTROL ROD DRIVE MOTOR HOUSING

CONTROL ROD THIMBLE NO. 3

CONTROL ROD NQ 2

I -----THIMBLE -CONTROL

-7

.ROD THIMBLE NO 4.

REACTOR ACCESS PLUG FLANGE

-THERMAL

-I

REACTOR ACCESS NOULE

SHIELD

SALT OUTLET TO CIRCULATING PUMP CONTROL ROD

REACTM VESSEL-

Fig. 2.7.9.

Diagram of Control Rods, as Installed.

283

Fig. 2.7.10. MSRE V i e w Looking Down Through Access Opening i n Secondary Containment C e l l Showing Control Rod Drives as I n s t a l l e d .

284

j I

ORNL-CWG

63-8394R3

+-ia DIAM HASTELLOY ( I N O R - 8 ) WIRE

END FITTING WITH INTEGRAL AIR NOZZLE ,OUTER

TUBE

Gd203- 812 0 3 BUSHINGS LOWER SEALING RING

POISON SLUG TWICE SIZE

Fig. 2.7.U.

MSBE Lower End of Control Rod.

ORNL-DWG 64-4004R2

RESTRICTOR. ADJUST 3 FLOW TO CONTROL ROD THIMBLE COMPONENT COOLING PUMP

pI - PRESSURE

IN MAIN SUPPLY HEADER, APPROX 20.7 psi0

P2 -PRESSURE I N SUPPLY L I N E N0.945 TO ROD DRIVES P3 - PRESSURE AT I N L E T TO ROD DRIVES p4 -ADJUST TO EQUAL P3 WHEN NOZZLE IN THROAT OF RESTRICTOR Ps -EXHAUST PRESSURE ( REACTOR CELL PRESSURE), APPROX (2.7psi0

S N I O T

NOTE: 4. THIS VALVE IS ALSO A SAFETY SYSTEM BLOCK VALVE. CLOSES I F R M 565 B OR C INDICATES EXCESS RADIOACTIVITY.

Fig. 2.7.12.

Diagram of I n s t m e n t a t i o n Used t o Locate Rods a t Fiducial Zero Position.

286 ORNL-DWG 64-983

CARRIAGE

AIR INLET TUBE-

DRIVE CHAN IBUFFER RETURN SPRING-

BALL RESET SPRING

----

CYLN I DERPLUNGER '&-in.-OlAM STEEL BALLS-

CARRIAGE TRACK-

ROD DRIVE HOUSING

Fig. 2.7.13.

Cross Section of MSRE Control Rod Drive Shock Absorber.

287

Fig. 2.7.14. Switches.

MSRE Saock Absorber and Thermostatic Temperature

.-.

.. .. . . . .. __..

. -..

. .

. . .

. .

~__.^_.._.I

ORYL-W&

AMMETER

66-117111

AMMETER

1970

IOTA

KBI

KC I 9 7 D L

197A

197D-

K A I97

NOTE:

REGULATED SUPFLY IS ZENER DIODE TYPE DESIGNED x)REPLACE STANDARD CELLS IN POTENTIOMETERS

Fig. 2.7.15.

MSRE Rod Drive Temperature Indicator.

1970

00 00

SMCERS, ADJUST TOTAL TO OBTAIN PROpb4 SPRING LOARINQ HARD ( R e SS-SO) STECL BEARING PAD* 2 REQ'D.

SPRING LOADED AD JUSZER

swrcn

LIMIT SWITCMS

.At€

ATENOS OF STROKC

A Fig. 2.7.16.

S4tCTION

A-A

MSRE Rod Drive Unit, Switch A c t u a t o d u i d e Bearing Assembly

290

Fig. 2.7.17. Upper End of Rod Drive U n i t , Showing Inlet Air W e f o r Control Rod Cooling Air and Side View of Upper and Lower Position L i m i t Switches.

291

Fig. 2.7.18. Switches.

Upper End of Rod Drive U n i t , Sharing Position Limit

Fig. 2.7.19.

MSRE Control Rod with Poison Elements S h a m Removed fâ&#x20AC;&#x2122;rm Supporting Structure.

293

294

ORNL-DWG 66-1+377

SUPPLY

4 8 V DC

THIS CONTACT IS CLOSED BY MANUAL ROD SCRAM SWITCH, S-1.

K29A

ROD DRIVE NO. f

s 120

ROD DRIVE

I 7 1 }

TOGGLE SWITCH ON CONSOLE

-L

K230B

K23'D

1 . GROUND

K235D

CLUTCH COIL

K238B

K2340

THESE CONTACTS OPEN WHEN CONTROL RODS AT LOWER L I M I T

K239D

JACKS MOUNTED ON CONSOLE

(--'

I 7. J

NEUTRAL

10 rps I

PORTABLE TIMER, STD ELECTRICAL T I M E CO, TYPE MS1100

INDICATING DIAL 0.001-sec GRAD.

________-__-______-

Fig. 2.7.21.

I I

ELECTROMECHANICAL CLUTCH

MSRE Rod Drop Timer Circuitry.

295

ORNL- DWG 66-iOiEIO

GEAR RED.

CONTROL ROD

DIEHL NO. 49-91-1 SERVO MOTOR,25 watts RATED OUTPUT

TOTAL SUSPENDED WEIGHT = 18.0 Ibs

4000

3500

E a L

3000

2 0

FROM TESTS OF MARCH 9,1964 SYSTEM CONTINUOUSLY CYCLING FOR FULL STROKE. NOT IN "INCHING" MODE. I I I I I

cn 2500 4

400

410

E, (AC volts) Fig. 2.7.22.

MSRE Control Rod Drive Motor Speed vs Voltage.

ORNL-DWG

64-1109R

-.-

W 0

Z 4

I-

0.25

0.50

0.75

1.00

ELAPSED T I M E ( s e d CURVE A-REFERENCE CURVE OF SATISFACTORY SCRAM PERFORMANCE; BASED ON ACCELERATION OF 5 f t / s e c 2 AND RELEASE T I M E O F 0.400 sec CURVE 6-SCRAM

PERFORMANCE FROM TESTS O f JAN.

Fig. 2.7.23.

27-28,1964

MSRE Control Rod Height vs Time During Scram.

4.50

297

ORNL-DWG 6 6 - i O t 81

9 4 .-c v

0.10

0.20

0.30

0.40

0.50

0.60

0.70

ELAPSED TIME (sec) Fig. 2.7.24.

MSRE Scrai Performance Tests (Jan. 27-28, 1964).

0.80

298

Fig. 2.7.25.

MSRF: Control Rod Performance D u r i n g Scram.

ORNL DWG. 67-2414 v O M E T E 3 ELECTRICAL DATA

60 CYC.+

5.0

Fs h

(0050

vommE

I VARIATION

h.)

*May vary m$. on tach. load of 0.1 megohms.

'Eased

60.30

4020

10Wp.EOZM

Fig. 2.7.26.

Performance Curves, 25-w Servo Motor.

300

W A T

1 S

50 A

M 40

P E R

Fig. 2.7.27.

Performance Curves, 10-w Servo Motor.

301

2.8

LOAD CONTROL SYSTEM

The reactor loading system i n the ERE has been described i n d e t a i l i n ORNL-TM-728.l Some design changes t o improve the effectiveness of the air s e a l s and the annulus cooling a i r flow have been made since the publication of TM-728, but the basic design remains unaltered. BriefLv, the nuclear power generated by the reactor i s f i n a l l y dissipated by a coolant-salt-to-air radiator and discharged t o the atmosphere v i a a stack 70 f t high and 10 f t i n diameter. A i r flow through the radiator i s supplied by two large, 250-hp (nominal), a x i a l flow fans. The rad i a t o r consists of a bundle of 120 thin-walled tubes (0.750 in. diam, 0.072-in. wall, 30 f t long) bent i n the shape of a zee (Fig. 2.8.1). The radiator i s enclosed by two v e r t i c a l l y s l i d i n g doors which act, t o a degree, as air flow control elements. Additional control of a i r f l o v i s obtained with a bypass damper and by selecting e i t h e r one o r both fans. When the doors are f u l l y lowered, cams on the guide r o l l e r t r a c k force the gasketed door against a f l a t sealing surface t o prevent t h e entry of a i r t o the radiator. Figure 2.8.2 shows the radiator, the doors and t h e i r drive mechanism, and the coolant salt pump as they are i n s t a l l e d i n the duct. Figure 2.8.3 i s a simplified drawing of the door drive mechanism. Note the flywheel which reduces the door acceleration during a load scram when the clutch and brake are released. The flywheel i s connected t o the s h a f t by an overrunning clutch so that; it continues t o coast a f t e r the door reaches the lower l i m i t . The coolant salt experiences a calculated temperature drop (subject t o s m a l l changes caused by slight variations i n flow) i n the radiator of 56'F a t full power of 7.5 Mw. When ambient i n l e t a i r temperature i s i n the 40OF region, t y p i c a l operating parameters a t the radiator are as follows : Coolant s a t i n l e t temperature 1015O F Coolant salt o u t l e t temperature 1073O F A i r i n l e t temperature 42 OF A i r o u t l e t temperature 151째F A i r flow 200,000 cfm Coolant salt freezes a t 850째F, and the operating margin above the freez,ing point i s therefore 165OF. This margin w i l l be l e s s on cold days, when t h e ambient temperature i s reduced. The remainder of t h i s section i s concerned with the instrumentaticn, control, and protection of the camplex of equipment that i s used t o rej e c t t h e reactor's energy output t o the atmosphere. It has been pointed out i n ref. 2 (pp. 107 and 140) t h a t t h e MSRE i s a load-following reactor and i s inherently self-regulating when developing any appreciable power. I n any r e a l i s t i c power reactor system,

l R . C. Robertson, MSRE Design and Operations Report, P a r t I, Des c r i p t i o n of Reactor Design, ORNL-TM-728 ( t o be published). 2M3RE Project Staff, Molten-Salt Reactor Program Semi-. Rept. July 31, 1964, OEWL-3708.

Progr.

302

t h e operators have l i t t l e o r no d i r e c t control over t h e public's demand f o r power. There was, therefore, no incentive t o control closely t h e load on t h e reactor. The only requirement i n t h e MSRE i s t h a t t h e ope r a t o r s be able t o e s t a b l i s h and adjust t h e load about a point i n any region within t h e operating range, up t o 7.5 Mw, of t h e reactor and t o do so i n an orderly fashion. It can be seen from Fig. 2.8.4 t h a t t h e reactor load (the heat r e j e c t i o n a t t h e r a d i a t o r ) i s determined by f i v e independently variable elements, namely: (1)i n l e t r a d i a t o r door, (2) o u t l e t radiator door, ( 3 ) main blower 1, (4) main blower 3, and ( 5 ) bypass damper. Over a considerable portion of t h e range, t h e same value of load can be obtained by two or more d i f f e r e n t operating configurations of t h e above equipment. It follows t h a t load changing and adjusting, i f done s t r i c t l y by manually manipulating these f i v e d i f f e r e n t components, may add considerably t o t h e duties of t h e operator a t a time when he l e a s t needs such additional responsibility and, i n addition, may produce unnecessarily high thermal shocks With accompanying high s t r e s s e s . I n view of t h e foregoing, t h e adjustment of t h e thermal load of t h e reactor has been designed f o r e i t h e r manual o r programmed control. With programmed control, load changes are accomplished by means of a single control a t t h e console (Fig. 2.8.5) when the s e l e c t o r switch (S-23) i s i n t h e "Auto" position. 2.8.1

Blower Operation

The m a i n blowers, 1 and 3 , are axial flow propeller-type fans. They are driven by direct-connected, 250-hp, 1750-rpm, three-phase, 440-v ac wound r o t o r induction motors. High r o t o r resistance s t a r t i n g i s incorporated i n t h e power c i r c u i t s t o l i m i t s t a r t i n g currents t o acceptable values. During start, t h e motor windings are connected i n s e r i e s t o external resistances. A s t h e motor accelerates, the externd. resistance i n each winding i s successively reduced by timer-controlled switching. This requires approximately 30 sec. After a t t a i n i n g full speed, when all external resistances have been disconnected, the motors operate as t y p i c a l squirrel-cage induction motors. This s t a r t u p c i r c u i t r y operates automatically when a motor c i r c u i t breaker i s closed t o s t a r t a blower and, i n t h e following discussion, i s not included as a p a r t of the reactor control system. The control system relays control t h e blowers by operating t h e "Close" and "Trip" c o i l s i n these c i r c u i t breakers. 2.8.2

Door Operation

Figure 2.8.6 i s a diagram of t h e door drives. A single gear-reduced motor provides power t o r a i s e both doors; individual door control i s obtained by means of clutches and brakes located on t h e separate sheave drive shafts. Operating conditions of t h e elements governing door movement i n d i f f e r e n t s i t u a t i o n s are shown i n Table 2.8.1.

303

Table 2.8.1

Situation

Motor

Clutch, I n l e t Door

Brake, Door Inlet

Clutch, Outlet Door

Brake, Outlet Door

1. Normal, r a i s e or lower both doors simultaneously

Engaged

Off

Engaged

Off

Normal, r a i s e o r lower inl e t door only

Engaged

Off

Disengaged

Normal, r a i s e or lower outl e t door only

Disengaged

Engaged

Off

Load scram

On or

Disengaged

Off

Disengaged

Off

Door position i s indicated on the control console (Fig. 2.8.5) by synchro position receivers driven by synchro transmitters. The transmitters are mechanically connected, through gear reducers, t o the sheave drive shafts. The intermediate limit switches (Fig. 2.8.7), used as control interlocks, are actuated by cams on the transmitting synchro drives. The position of these switches i s adjustable over a wide range. The upper and lower limit switches are i n redundant p a i r s and are actuated d i r e c t l y by t h e doors. These limit switches are an i n t e g r a l p a r t of the control system used during normal operation. Additional switches used solely t o protect the doors and the drive mechanism from overtravel and overload are provided. These are described i n Sect. 2.8.6. The bypass damper i s positioned by an a i r cylinder w i t h a built-i:n Cylinder position, d i r e c t l y positioner, as diagrammed i n Fig. 2.8.6. proportional t o cylinder pressure, is controlled e i t h e r d i r e c t l y and manuaXLy o r with a pneumatic servo. The servo positions the bypass damper t o maintain the d i f f e r e n t i a l pressure drop AP across the damper equal t o the set-point value AP SP Direct manual control of damper position may be obtained by manu a l l y adjusting the i n l e t pressure t o the a i r cylinder with a pressure regulator i n the manual control s t a t i o n mounted on t h e main control board. A three-way valve t r a n s f e r s cylinder a i r supply from the servo t o the pressure regulator. Assuming t h a t one o r both blowers are gn, servo control of AP across the damper is accomplished from the console by operator adjustw i t h the switch labeled DP Demand (see Figs. 2.8.5 and ment of AP SP This switch operates an electric-motor-driven pressure regu2.8.6). lator, P X-AD2-A1, whose o u t p u t m goes t o the pneumatic servo. If a SP the condition of other elements i n the system (doors and blowers) i s not

304

altered, a request f o r an increase (decrease) i n LIP

w i l l cause t h e SP bypass damper t o close (open). I f , however, t h e doors are moved o r blowers are turned on or off, t h e damper w i l l a l s o respond t o maintain LIP equal t o AP SP' When load control i s being automatically programmed, t h e adjustis included i n t h e program and i s not d i r e c t l y manipulated ment of LIP SP by t h e operator. I n e i t h e r control mode t h e values of LIP and LIP and SP t h e damper position are indicated on t h e console.

2.8.3

Automatic Load Programming

A s t h e reactor system i s brought from zero t o full power, t h e various elements (as s t a t e d previously) governing reactor load are proThis diagram i s based on t e s t s grammed i n accordance with Fig. 2.8.8. conducted on January 31, 1967. The dashed portion of t h e door position curve merely connects t h e end-point values of power obtained by moving t h e doors from t h e f u l l y closed t o fully open positions. The curves w i l l s h i f t slightly with changes i n ambient temperature. The programmed control system w a s designed with these f a i r l y obvious assumptions: 1. When t h e radiator i s presenting a constant f r o n t a l area t o t h e a i r stream, heat t r a n s f e r therefrom i s closely r e l a t e d t o s t a t i c pressure drop across t h e r a d i a t ~ r . ~

Heat t r a n s f e r from t h e r a d i a t o r increases as the doors are raised as long as the operating condition of t h e other flow elements (blowers and bypass damper) remains unaltered. The t e s t s referred t o above and i n Fig. 2.8.8 indicate t h a t t h e l a s t 2 o r 3 ft of door t r a v e l exerts l i t t l e influence on t h e load; t h a t is, t h e doors are most e f f e c t i v e during the e a r l y stages of t h e i r movement.

The s t a t i c pressure drop measured across t h e bypass damper (see Fig. 2.8.6) d i f f e r s only slightly from t h e s t a t i c pressure across t h e radiator; t h a t is, t h e pressure drop i n the branching ducts t o and f r o m t h e r a d i a t o r doors and t h e bypass damper, respectively, i s s m a l l compared with t h e pressure drop across t h e r a d i a t o r tubes.

The programming control system diagrammed i n Fig. 2.8.6 uses t h e a i r flow d i f f e r e n t i & pressure-LIP across t h e bypass damper and t h e limit switches (Fig. 2.8.7) t o program t h e sequence in which t h e doors are raised, t h e blowers are turned on, and t h e bypass damper i s opened o r closed. Control system pressure and l i m i t switches a l s o provide res t r i c t i v e and permissive interlock s i g n d s . Figures 2.8.9 t o 2.8.U are, respectively, t h e block diagram and t h e relay c i r c u i t s which implement t h e block diagram. The operation of t h e load control system when t h e programmed load control ("Auto" control) i s i n use i s b e s t explained by t r a c i n g t h e sequence of events and operations which take place as a p a r t i c u l a r power l e v e l i s established following a reactor start.

3W. M. Kays and A. L. London, Compact Heat Exchangers, McGraw-Hill, New York, 1958.

3 05

Suppose that operation a t 7.5 Mw i s required and the operator w i l l e s t a b l i s h t h i s value of reactor load using the programned o r automatic load control mode of operation. Procedure and system actions are outl i n e d below ( r e f e r t o Figs. 2.8.5 t o 2.8.11 i n following the discussion): Actuate the load control selector S23 t o the "Auto" position. This switch i s spring-returned t o the "Hold," o r center, position; but, i f the conditions required t o establish automatic operation have been met, automatic load control i s i n force. These conditions are (see c i r c u i t 150, Fig. 2.8.10):4 1. reactor system i n %perate" mode, contact KAl36F closed (see Sect. 1.4);

salt l e v e l i n the fuel-pump bowl above 43$ of f u l l - s c a l e level, contact K97C closed;

f u e l - s a l t pump speed greater than 1000 rpm, contact K96D closed;

coolant-salt pump speed greater than 1400 r p m , contact ICloE closed;

drain valve FV-103 frozen, contact K659D closed;

s t a t i c a i r pressure drop Dp across the radiator equal t o the operi n the bypass damper controller ator-established s e t point Dp SP (Fig. 2.8.6), contact K211A closed.

Alternate conditions t o 6 above are: 7.

system not i n Run, contact W39C closed;

bypass damper lOO$ "Open," contact K214A closed;

operator-established set-point signal controller s e t a t zero.

t o t h e bypass damper

With the automatic load control mode established and, i n the case under discussion, the conditions l i s t e d above obtaining, reactor power is increased from near zero t o approximately 1.0 Mw by the operator turning on main blower 1 or 3 and requesting the load increase with the load demand switch Sa. Assume t h a t it i s decided t o begin the ascent t o 100$ power (7.5 Mw) uslng main blower 1. The operator w i l l actuate the main blower 1 S t a r t switch 529, and, i f system conditions are not producing preventive interlocks, the following conditions prevail ( r e f e r t o the block diagram i n Fig. 2.8.9 and the c i r c u i t s i n Figs. 2.8.10 and 2.8.11) :

1. The bypass damper i s being held 1 0 9 open

both radiator doors are closed,

main blower 1 i s rrOn,r'

main blower 3 is " O f f , "

(Dp

= O),

4Conditions 1 t o 5 must be met a t all times t o maintain automatic load control; that is, they are not sealed. The remaining conditions are required only t o enter automatic load control but are not required t o s t a y i n t h i s mode.

306

main blower 3 has been selected t o t u r n on automatically when the load demand cannot be met by a single blower. Had the operator elected t o start with main blower 3, he would then have selected m a i n blower 1 t o t u r n on automatically when t h e load demand requires both blowers.

After main blower 1 i s turned "On," the operator starts t o load the reactor by actuating load demand switch s%. This causes the radiator doors t o s t a r t opening and, as long as S24 i s actuated, they w i l l continue t o do s o without r e s t r i c t i o n u n t i l t h e lower intermediate limit i s reached. The operator follows the course of reactor power by observing e i t h e r the l i n e a r power recorder on the main control board or the two indicators, RI-NLC1-A1 and RI-NLC2-A2, on t h e console. The doors w i l l continue t o rise u n t i l t h e lower intermediate l i m i t i s reached and the system power l e v e l i s approximately 1 Mw. The doors may be stopped a t aay point before t h i s i f it i s desired t o operate a t powers l e s s than 1 Mw. When t h e doors have been raised t o the lower intermediate limit, system conditions are: 1. main blower 1 i s "On,

2. 3.

bypass damper i s being held lo$ open (aP = O), SP reactor power is approximately 1 Mw.

The 1-Mw l e v e l i s the t r a n s i t i o n point from "Operate-Start" mode t o "Operate-Run," and f u r t h e r increases in power l e v e l require t h a t the R u n mode of system operation be established. This has been discussed i n Sects. 1.4 and 4.2. Once the system i s in "Run" mode the operator can again request additional load, using ,524 as before. This can be seen by r e f e r r i n g t o c i r c u i t s 162 and 164, in which "Run" relay contacts KAl39G and KB139D bypass the intermediate l i m i t relay contacts K219A and K223A respectively. Note t h a t i f the automatic rod controller has been used during the preceding operations it has been i n t h e "Flux" control mode during "Start." Going from %tart" t o "Run" automatically puts the automatic controller i n t o the "Outlet Temperature" mode (see Sects. 1.4 and 2.6). A s the operator continues t o request more load, the doors continue t o r i s e u n t i l fully open. As the doors are going from the p a r t i a l l y raised, intermediate l i m i t , position t o the upper limit position, the bypass damper remains fully open since t h e control system, by means of contact S%A i n c i r c u i t 151, Fig. 2.8.10, i s keeping LP = 0. The load is inSP creasing because of the increasing exposure of t h e radiator t o the flowing air stream. Once both doors reach t h e i r upper limits, t h e bypass damper must start closing t o d i v e r t more a i r through the radiator and thus increase heat rejection. This is accomplished i n c i r c u i t 153, Fig. 2.8.10, by switch contact S24C. Closure of t h i s contact turns on the motor which drives t h e AP device, P X-AD2-A1, i n Fig. 2.8.6; SP d i s increased, and the bypass damper controller PdC-AD2-A closes the apSP damper t o satisfy the requirement f o r increased AP; more a i r i s diverted

cel

3 07

through the fully exposed radiator and more heat i s extracted from the system. Reactor power r i s e s t o meet t h i s increased load. A s before, the operator continues t o request increased load w i t h S24 and t o follow the power by watching the l i n e a r channel instruments on the console and the main board. Any power l e v e l i n t h i s region can be established by the operator. This type of system response continues u n t i l the bypass damper i s f u l l y closed and the e n t i r e output of main blover 1 i s flowing throiigh the radiator. A s m a r y of system conditions i s : 1. main blower 1 "On,

main blower 3 " O f f

bypass damper 109 closed,

Al?

a t intermediate value, SP power l e v e l a t approximately 5 Mw.

The o n l y way now remaining t o increase heat rejection (load) by the radiator i s t o t u r n on the second blower, main blower 3 i n t h i s discussion. Note, i n Fig. 2.8.10, c i r c u i t s 153 and 154, that when the bypass damper i s f u l l y closed, the following c i r c u i t actions take place: (1)contact K215A i n c i r c u i t 153 opens, preventing further increases i n and ( 2 ) contact K215F i n c i r c u i t 154 closes and permits energizing %p' of relay 154, which w i l l turn on t h e second main blower. A t t h i s point, the value of Al? i s established and i s equal t o o r greater than the SP actual AP across the radiator. With the radiator presenting a constant f r o n t a l area t o the a i r stream, as it will when the doors are fixed a t t h e i r upper limits, the heat rejection i s related t o the AP across t h e radiator. Now, when the operator asks f o r more load v i a the Load Demand switch, S24, the c i r c u i t r y (see action 2 above) i s such t h a t relay K154 i s energized; t h i s i n i t i a t e s the s t a r t of main blower 3 . A s t h i s blower picks up speed, it delivers additional a i r through the radiator, thus r a i s i n g AP above Al? and the bypass dmper w i l l open an amount SP' sufficient to bypass some or all of the additional air flow produced by main blower 3 , depending on whether o r not LYl? and AP were o r were not SP exactly equal when main blower 3 was turned on. The load may change slightly when main blower 3 i s turned on. This i s a t t r i b u t e d t o the large duct and t h e nonuniform shape of the radiator, which permits slight changes i n a i r flow which are not measured by the single probe i n the center of the duct. After t h e second main blower ( 3 ) i s turned on, the bypass damper i s open, and the control c i r c u i t configuration ( c i r c u i t s 153 and 154) i s as it was just before the damper was completely closed w i t h only one blower running; that i s , (1)contact K215A i n c i r c u i t 153 (Fig. 2.8.10) i s closed, permitting changes i n AP by energizing relay 153, SP and (2) contact K215F i s open, and main blower 3, once "On," i s sealed and i s no longer controlled by relay 154. With both blowers "On" and with the bypass damper p a r t i a l l y open, the heat rejection (load) i s increased, as before, by actuating Load

308

Demand switch Sa.

This causes AP

t o increase, and t h e automatic SP damper c o n t r o l l e r (Fig. 2.8.6) closes t h e bypass damper t o d i v e r t more a i r through t h e radiator. This mode of operation continues u n t i l t h e bypass damper i s from 75 t o 100$ closed5 and t h e load, somewhat dependent on ambient temperature, i s in t h e 7- t o 8-Mw region. Reduction i n load under automatic load control proceeds i n t h e revers e direction.

2.8.4

Manual Control

When the reactor load i s i n t h e Manual Control mode, t h e separate components governing heat r e j e c t i o n (see e a r l i e r p a r t of t h i s section) are t r e a t e d as independent u n i t s and are controlled separately, Referr i n g t o Figs. 2.8.5, 2.8.10, and 2.8.ll, it can be noted t h a t each door, I n l e t and Outlet, has i t s own "Raise" and "Lower" switch and that bypass damper position i s controlled by a AP demand switch. The blowers are not cross-interlocked with each other or controlled by door position as they are during Automatic Load Control. The selection of a p a r t i c ular operating configuration of these components and t h e operational path required t o a r r i v e a t t h e desired configuration are e n t i r e l y a t the operator's discretion.

2.8.5

Interlocks

I n e i t h e r control mode the reactor loading system i s subject t o a number of interlocks and control actions whose primary purpose i s t o prevent o r reduce t h e p o s s i b i l i t y that t h e coolant salt w i l l freeze in t h e radiator. These interlocks and control actions and t h e i r purpose are l i s t e d and described i n Table 2.8.2 and, i n some cases, amplified i n subsequent paragraphs of t h i s section.

2.8.6

Load Scram

Load scram ( o r emergency closure of the r a d i a t o r doors) i s provided t o prevent freezing of coolant salt i n t h e r a d i a t o r tubes. A pessimistic, worst case, calculation6 showed t h a t salt freezing can take place i s l e s s than a minute. Operating experience tends t o confirm t h i s calculation. Figure 2.8.12 is a diagram of t h e instrument system used t o provide load scram, and Figs. 2.8.13 and 2.8.14 a r e elementary diagrams of t h e associated control c i r c u i t s . The primary input information i s coolant salt temperature a t t h e r a d i a t o r o u t l e t . Three independent temperature measuring channels are used so t h a t i f any two of t h e three indicate an abnormally low temperature, t h e clutches and brakes i n the door drive mechanism are automatically deenergized and t h e doors drop t o t h e closed position.

5Final damper position i s adjusted t o keep system temperatures a t reasonable values J. B a l l , '"Freezing Times f o r Stagnant S a l t i n MSRE Radiator Tubes, I' private comunication (Apr. 9, 1963).

Table 2.8.2.

I n i t i a t i n g Condition( s ) or Situation( s)

System Response

Interlock or Control Action

I. Load scram

Load Control System Protective Interlocks

1. Radiator doors are dropped 1. Abnormally low (980째F)& coolant salt temperature in radiator t o closed position o u t l e t pipe, l i n e 202 2.

Both main blowers, MB-1 and M&3, are shut down

Abnormally low (less than 700 ~JX )II f l o w r a t e of coolant salt

Abnormally low speed of coolant salt P W 4. Control rod scram 3.

Supplemental and Explanatory Notes

1. Low salt temperature i s the primary indi-

cation t h a t freezing i s imminent 2 and 3. A loss or substantial reduction of salt flow through t h e radiator i s the prelude t o a freeze; particularly t r u e when system is developing full power

4. Power generation ceases with a rod scram. Unless heat rejection by the radiator is reduced, a freeze is inevitable. Note ( r e f e r t o Sect. 2.5) t h a t when the reactor i s developing power, a rod scram w i l l be produced by an e l e c t r i c a l power system failure, a l o s s of f u e l salt l e v e l in the pump bowl, or any other condition which reduces input current t o the f u e l salt purmp motor These are safety-grade interlocks with addit i o n a l description in Sect. 2.8.6.

11. F i r s t upper l i m i t s

Prevents doors from being raised

Door(s) at normal, fully open, position actuate l i m i t switches, two each per door

1. These are typical limit-switching controls of the type usually associated with mechanisms having limited motion. They are not the f i n a l l i m i t s whose sole purpose is t o prevent damage t o t h e system (see interlock No. 111)

Redundancy: a) Two switches per door. Actuation of e i t h e r switch i s capable of releasing the door drive clutch and applying the brake b)

When doors are being raised one a t a time (manual control), l i m i t switch actuation opens the "Raise" c i r c u i t i n the door drive motor s t a r t e r

Table 2.8.2.

(continued) 3.

4. III.

~ind (maximm, upper

limits

Shuts off door drive motor Door(s) raised above n o d f u l l y open position by approximately 8 in.

Disengages door drive clutche s

Applies brakes in door drive mechanism

For d e t a i l s r e f e r to: a) Limit switch c i r c u i t s 2l6, 220, 224, and 225, Fig. 2.8.7 b)

"Raise" c i r c u i t s 162 and 164, Fig. 2.8.ll

Clutch and brake c i r c u i t s 13 t o 16, Fig. 2 . 8 . U

d) Motor s t a r t e r c i r c u i t 568, Fig. 2.8.16 These switches also used in t h e automatic load control c i r c u i t s

1. Actuation of these l i m i t switches indicates an abnomal situation which, i f continued, will damage the drive mechanism o r t h e doors. I f tk damage includes a jammed door or. snarled cable, it m a ~ rprevent lowering the doors, e i t h e r n0rmaXI.y or by a load scram, and hence cause a radiator freeze

Reliability: a ) Two switches per door b)

Two independent relay c i r c u i t s with

both r e l q s actuated i f e i t h e r door at the f i n a l l i m i t

c ) Either channel (relay c i r c u i t ) w i l l produce t h e actions tabulated i n the "System Response" column a)

Interconnection wiring carried i n separate, individual conduits t o control room

I n general safety system c r i t e r i a (Sect. 1.5) were used wherever possible i n design of t h i s interlock 3.

For d e t a i l s , r e f e r to: a) Limit switch c i r c u i t s 255 and 256, Fig. 2.8.7 b ) Clutch and brake c i r c u i t s 13 t o 16, Fig. 2.8.13 c)

Motor s t a r t e r c i r c u i t 568, Fig. 2.8.16

Table 2.8.2.

Iv. Motor overload

Manual emergency bypass of coolant pwq control c i r c u i t

(continued)

Same as I11 above

Motor current i n one phase indicates t h a t door drive motor i s overloaded

1. This augnents I11 above. Except t h a t only one excess current relay i s used, it has same degree of r e l i a b i l i t y and redundancy. The excess current relay has i t s contacts i n s e r i e s with the f i n a l upper l i m i t switches and hence the output actions are identical

Maintains forced circul a t i o n of coolant s a l t

Variable and a t discretion of reactor operator

1. This consists of a manually operated switch with contacts i n the control power c i r c u i t s of breaker K. This c i r c u i t breaker controls ac power t o the coolant salt pump

3. VI.

Lower l i m i t s

Drops door( 8 )

1. Door(s) being lowered and

A t "lower limit" position (see Fig. 2.8.7)

This switch bypasses all the interlocks i n c i r c u i t 142, which controls the coolant salt pump ( r e f e r t o Sects. 3.3 and 4.2.3). It is used only f o r short periods, when it i s absolutely mandatory, regardless of other considerations, t h a t the coolant pump be operated t o prevent a radiator freeze.' This switch does not bypass t h e overcurrent protection which i s b u i l t i n t o the c i r c u i t breaker. Coolant punp operat i o n by t h i s switch is annunciated

Refer t o Fig. 2.8.17 f o r c i r c u i t d e t a i l s

1. This i s not a t r u e lower l i m i t (Sect. n ~ t h i s table). These switches are actuated approximately 8 in. above the f u l l y closed, o r sealed, position. The doors then f a l l freely as i n load scram and acquire suff i c i e n t velocity t o ensure an effective s e a l against leakage air flow across t h e radiator (door sealing i s described i n ref. 1, p. 298)

2. Redundancy: Two switches f o r each door with contacts i n s e r i e s connected t o one relay 3. For d e t a i l s r e f e r to: a) Limit switch c i r c u i t s 217 and 221, Fig. 2.8.7 b)

"Lower" door(s) c i r c u i t s 163 and 165, Fig. 2.8.11

Door clutch and brake c i r c u i t s 13 t o 16, Fig. 2.8.13

Table 2.8.2.

VII. "secit." l i m i t s

1. Stops doors at fully s e d e d (fully closed) position

Disengages clutch(es) If not disengaged by

VI Applies brake( 6 ) providing door(sj are being lowered Shuts off door drive motor

(continued)

1. Door(s) a t f u l l y closed position actuate l i m i t switches

1. The s e a l l i m i t is the true lower l i m i t door position. A t t h i s location the door(s) has been self-cammed by i t s own weight against the sealing gaskets which prevent excessive air leakage across the radiator

Reliability: a) Two switches per door

b) Any one of following outputs based on switch actuation W i l l stop door(8): Clutch disengagement via e i t h e r of l i m i t switch contacts in each clutch c i r c u i t ; refer t o c i r c u i t s 13 and 15, Fig. 2.8.13 Clutch disengagement by e i t h e r of two l i m i t switch contacts which deenergize "lower door" relay( s). Refer t o c i r c u i t s 163 and 165, Fig. 2.8.11 Drive motor shutdown by e i t h e r of two l i m i t switch contacts which deenergize "lower" contactor in t h e motor starter. Refer t o c i r c u i t 568, Fig. 2.8.13 Drive motor shutdown by contact on "lower door" relay, which deenergizes t h e lower" contactor in the motor s t a r t e r . Refer t o c i r c u i t 568, Fig. 2.8.16 Brake actuation by e i t h e r of two l i m i t switch contacts in c i r c u i t s 14 and 16 ( r e f e r t o Fig. 2.8.13)

If, because of malfunction, drive motor is "on" when a door (or doors) is sealed and brake is engaged, the excess motor current re1a;y (see IV, t h i s table) w i l l shut motor off

313

Figure 2.8.15 depicts a t y p i c a l temperature input signal channel. Note that t h i s is v i r t u a l l y i d e n t i c a l t o t h e temperature instrumentation used t o provide rod scram (Sect. 2.5) except t h a t t h e p o l a r i t y of t h e thermocouple i n t h e t e s t assembly7 i s reversed; therefore, t h e application of heat and t h e r e s u l t i n g temperature increase of t h i s t e s t thermocouple appear as a reduction i n temperature t o t h e r e s t of t h e instruments. Each temperature input channel can be t e s t e d by turning on t h e heater i n t h e t e s t assembly and observing t h e response of t h e relays, which are controlled by t h e Foxboro temperature switches. The equivalent drop i n temperature produced during t h e t e s t procedure can be observed on a meter by t h e person conducting t h e t e s t . A l o s s of coolant salt flow w i l l inevitably produce freezing i f t h e doors are open and there is any appreciable a i r flow through t h e radiator. Therefore, t h e doors a r e a l s o closed automatically by combinations of signals f r m the flowmeters on t h e r a d i a t o r o u t l e t l i n e and from t h e coolant salt p ~ l pspeed monitors. These s i g n a l combinat i o n s are tabulated i n Fig. 2.8.12. The pump speed measuring instrumentation i s discussed i n Sect. 6. A "loss of speed" input s i g n a l t o one of the speed monitors i s simulated, f o r t e s t i n g purposes, by means of t h e c a l i b r a t i o n switch b u i l t i n t o thle speed monitor. Output relay action indicates whether o r not t h e system i s responding properly. The instrumentation used t o measure coolant salt flow r a t e i s described i n Sect. 6. For t e s t purposes, a simulated l o s s of flow s i g n a l may be produced i n each channel by shunting a l e g of t h e resistance bridge i n t h e d i f f e r e n t i a l pressure c e l l . Observation of t h e output relays gives an indication of input channel response. Redundant door travel l i m i t switches (Fig. 2.8.16) a r e employed t o p r o t e c t t h e a b i l i t y of t h e doors t o drop when t h e safety system c a l l s f o r a load scram. Door l i m i t switching has been described i n Table 2.8.2, but it i s worth while t o emphasize here that t h e primary purpose of t h i s redundancy is t o prevent jamming of t h e doors or t h e drive mechanism which, i n turn, i s l i k e l y t o compromise t h e i r a b i l i t y t o drop. An excess current relay in the motor c i r c u i t (Fig. 2.8.16) i s used t o detect an overload caused by a jammed door, snarled cable, o r similar malf'unction i f it occurs e i t h e r i n t h e normal motion span of t h e doors or a t t h e limits. The action of both of these l i m i t i n g c i r c u i t s i s t o stop t h e drive motor by deenergizing t h e relays i n t h e motor s t a r t e r . Manual r e s e t ( r e f e r t o c i r c u i t s 255 and 256, Fig. 2.8.16) i s required before r e s t a r t i n g t h e drive motor. Insofar as possible t h e l i m i t switch design and i n s t a l l a t i o n follow the recornended safety-system p r a c t i c e s outlined i n Sect. 1.5. The predominant requirement i n controlling and operating t h e load control system i s t o prevent a frozen radiator. To t h i s end t h e c i r c u i t r y diagrammed i n Fig. 2.8.17 was added. The time required t o freeze the salt i n t h e r a d i a t o r i s extended i f c i r c u l a t i o n i s maintained with

7Molten-Salt Reactor Program Semiann. Progr. Rept. Jan. 31, 1964, ORNL-3626, p. 44-.

314

t h e coolant pump. The coolant pump control c i r c u i t (see Sect. 4 ) cont a i n s interlocks which stop t h e purnp i f it experiences a loss of motorcooling water o r lube o i l . The salt pumps cannot run for any appreciable length of t i m e without oil o r cooling water, but no harm w i l l come t o e i t h e r pump o r motor during t h e first minute o r s o following a l o s s of e i t h e r . The manual switch, S127, located on t h e main control board, overrides these interlocks which are capable of stopping t h e coolant pump. It does not bypass t h e overload protection i n t h e coolant pump c i r c u i t breaker. Use of t h i s overriding switch i s controlled administ r a t i v e l y and i s only permitted i f t h e pump stops and a frozen r a d i a t o r i s imminent.

315

ORNL IWG 64-8826

2-7/16* I.D. MANIFOLDS (10)

420 S-SHAPED 314" O.D. TUBES

JTL

Fig. 2.8.1.

Radiator Coil Configuration.

316

ORNL-LR-DWG

Fig. 2.8.2.

Radiator Coil and Enclosure.

55841R2

317

ORNL-DWG 63-8390R

ELECTRO /MECHANICAL BRAKE

ELECTROMECHANICAL

J FLYWHEEL

DRIVE MOTOR WITH GEAR REDUCER. SIN MOTOR USED TO DR

SPRING SHOCK ABSORBERS NOTE: THIS ARRANGEMENT IS TYPICAL AND IS USED FOR BOTH DOORS

RADIATOR DOOR

Fig. 2.8.3.

Diagram of Radiator Door Drive. ORNL-OM. 66-10633

n BY PASS

DAMPCR

Fig. 2.8.4.

Diagram of Radiator Air Flow System.

318

Fig. 2.8.5.

Load Controls Located on Operator's Console.

ORNL-DWG 66-11719

Fig. 2.8.6.

Load Control System Bypass Damper Servo.

ORNL-DWG 67-950

i flDoea IN SEALED

t 4 0

POSITION

t 9 t h I 9

a 0 0

-MSRE-

2 4 6 HEAT BALANCE POWER-MW

ONE BLOWERON

RADIATOR SYSTEM PERFORMANCE I N L E T A I R T E M P 40' F

Nore DASH€D PART O f A P CURV€. "A' T0"BH To 'IC 11 IS ES TIMATED.

r’

- ;

e----

UTL

--------

E3 E3

324

ien

-I

I I

I I r -

fKbZl4A

T**22zA

.l I

I I I

Fig. 2.8.11.

d i a t o r Load Control System.

CUNL- O W 63-8389

INS S

MOTOR TO PUMP SHAFT COUPLING

_____

HEAT EXCHANGER

TRANSMITTERS

4 CLUTCH

BRAKE

UPSTREAM DOOR

L3 Ul

EMERGENCY CLOSURE PRODUCED BY INPUT SIGNAL COMBINATIONS AS FOLLOWS: (a) SI OR S2 t F, (b) S, OR S p t F2

LINE 202

THERMOCOUPLES -.--

(d) ANY TWO OF THE THREE TEMPERATURE

INPUT SIGNALS

CLUTCH TO READOUTS

LOGGER ETC.

Fig. 2.8.12.

Diagram of Load Scram System.

BRAKE

DOWNSTREAM DOOR

I .

OPEN IN~~RAISE" OTHER DOOR

CLOSED IN

MANUAL LOAD SCRAM -'OPEN N I

"RAISE OOOR'REOUEST

CLOSED AT OR FOR UPPER MAXIMUM LIMIT

OPEN IN "LOWER" OTHER DWR

K260A

TWO-OUT-OF THREE CONTACT MATRIX, CONTACTS OPEN WHEN COOLANT SALT TEMP LESS THAN 98D.F

:EA yT

& L

KA6G

CtOSEO IN

DOOR"LOWER REOUEST

c:l

EXCESSIVE MOTOR CURRENT

KA6D

)

LOSS OF FLOW AN0 W M P SPEED CONTACTS. K 7 AND K 8 CONTACTSOPEN WHEN COOLANT SALT FLOW I S LESS THAN 700gprn; K9 AND KIO CONTACTS OPEN WHEN PUMP SPEED IS LESS THAN 1400 rpm

L KA11B

KBltB

GND

14,tI.l3,14,45 16,155,458

082

-KAlIH

WEN IN "LOWER DOOR" REQUEST

-l

CLUTCH

K263A

K8C

BRAKE COI

TO REVERSING STARTER, CKT 568

480 V

DOOR DRIVE MOTOR

KAl28

11,12,13,14 45.16,155,158

fKBI2

12.12

499.4082

Fig. 2.8.13.

COILS DE-ENERGIZED

RELEASE BRAKE AND DISENGAGE CLUTCH

NOTE: INLET AND OUTLET DOOR CIRCUITS ARE IDENTICAL NOS. IN PARENTHESES REFER TO OUTLET DOOR CONTROL CIRCUITS

LOAD SCRAM WHEN DE-ENERGIZED

OPEN AT

SAFETY JUMPERS GRADE

OPEN AT MAXIMUM

T K7A

OPEN AT

A-

SAFETY GRADE JUMPERS

(K256G) -CLOSED WHEN WOR IS SEALED

K255B

!K26lA

EXCESSIVE METER

Load Scram Output Circuits.

w ul

s W . I

z 0

0 0

I-

z W

327

> m

n (I)

328

ORNL-DWG 66-11424 CURRENT ACTUATED SWITCH

'YD

EMF m CURRENT CONVERTER

MEASURING THERMOaXlPLE

E ' t<-

TYPE 63

ISOLATION AMPLIFIER

L ,

ALARM

loo

h Y

FOXBORO CO. MODEL 63 PV OR MODEL 65 PH METER

CHANNEL N 0 . 2

SAME AS A0OVE

CHANNEL N0.3

SPARE

RADIATOR OUTLET PIPE, LINE 202

Fig. 2.8.15. Scram.

Temperature Measuring Equipment Used t o Provide Load

c ORNL-OWG 67-911

RADIATOR DOOR DRIVE MOTOR

568 CURRENT TRANSFORMER

SEAL BREAK CONTACTS IN DOOR DRIVE MOTOR STARTER RELAYS

CLOSED IN

W rNi

N O (( THESE CONTACTS OUTLET

WOR IS SEALED

T2X

CLOSED IN "LOWER DOORS"

"RAISE" INLET

0 ~

4W E~N WHEN INLET DOOR IS

DooR<I (1 T f-r

SEAL I

KB162A

KB464A

K463A

RELAY, GE NO.4AC

K569B

1 255.256

RELAY ENERGIZED WHEN MOTOR IS OVERLOADED

( K 569 A I

MOTOR IS OVERLOADED

ZS-OD-B38

-OPEN

WHEN INLET DOOR AT FINAL UPPER LIMIT-

-OPEN

WHEN OUTLET DOOR AT FINAL UPPER LIMIT

RESET MANUAL

zs~0D~84B

MANUALS2l6,

sw'TcH~

K-255A

!i7ES:H 4 -

S 4 2 5 A v <K-255 255.13.44.15 1097.46.568

K-256A

K-256

256.43.44.15 4097.16.568

FINAL MAXIMUM TRAVEL LIMIT SWITCHES

Fig. 2.8.16.

Radiator Door Drive Motor Control Overtravel and Overload Interlocks.

K(65A

ORN L- DWG 67- 685

240 V AC MOTOR STOPS I N NORMAL CONTROL WHEN CLOSED.

S (270 L

TO START MOTOR I N NORMAL CONTROL

TRIP COIL IN CKT BK'R "K". STOPS MOTOR WHEN ENERGIZED CLOSING, (START), COIL I N CKT BK'R "K"

-L'la''

"X" RELAY I N CKT BK'R "

S127A

CONTACT DEVELOPMENT

St27F"

*AN NUNCI ATOR CONTACTS

2.8.17.

POSIT1ON

CONTACT

Fig

REFER TO I V - 9 . 7 FOR TYPICAL MOTOR CONTROL CIRCUITS

S 127, EMERGENCY START SWITCH,LOCATED ON M A I N CONTROL BOARD

THIS CONTACT CLOSED WHEN BREAKER IS CLOSED

I x

I oc---o SPRING RETURN

Normal and Emergency Control of Circuit Breaker ?KK"Which Operates Coolant Pump Motor.

33 1

2.9

HFALTH PHYSICS MONITORING

2.9.1

Introduction

The purpose of the Health Physics Monitoring System' i s t o provide personnel protection a t the reactor s i t e from radiation hazards due t o airborne and fixed source a c t i v i t y . The monitors composing t h i s system a r e placed a t s t r a t e g i c a l l y located points throughout the reactor building. Those monitors which measure area a c t i v i t y and airborne a c t i v i t y make up t h e F a c i l i t y Radiation and Contamination Sy~tern''~ and produce signals which a r e transmitted t o a c e n t r a l annunciator panel located i n t h e reactor auxiliary control room and t o the Laboratory Emergency Cont r o l Center i n Building 2500. The F a c i l i t y Radiation and Contamination System a l s o produces a building evacuation signal based upon finding a coincidence of a t l e a s t two monitors i n an alarmed s t a t e . The other monitors composing the general system a r e mainly f o r personal survey and include such items as beta-gamma survey meters, a hand-and-foot counter, and smear counters f o r use by Health Physics personnel. 2.9.2 2.9.2.1

F a c i l i t y Radiation and Contamination System

Introduction

A F a c i l i t y Radiation and Contamination System was i n s t a l l e d i n the Molten-Salt Reactor Experiment Building 7503 t o continuously and automatically monitor gamma radiation (by seven gamma monitrons) and a i r contamination (by seven beta-gamma a i r monitors) i n the e n t i r e f a c i l i t y . These instruments and other components i n the network provide health physics monitoring information, sound l o c a l alarms when abnormal conditions occur, and indicate the abnormal conditions on a c e n t r a l panelboard and a t t h e Laboratory Emergency Control Center i n Building 2500. Operating personnel a r e f i r s t given warning when a "caution level" of 7.5 m r / h r o r 1000 counts/min i s detected by a monitron o r beta-gamma a i r monitor respectively. A second warning i s given when a "high level" i s detected, t h a t i s , 23 mr/hr by a monitron o r 4000 counts/min by a beta-gamma a i r monitor. The building evacuation system operates automatically when two o r more monitrons or two or more air monitors from a specific group of instruments detect a "high level" of radiation o r a i r contamination. An

'The system i s further described i n ORNLTM-1127, Description of F a c i l i t y Radiation Contamination System I n s t a l l e d i n the Molten-Salt Reactor Experiment Building 7503, May 13, 1965, by J. A. Russell and D. J. Knowles. Parts of this report have been extracted verbatim from TM- 1127 2D. J. Knowles e t a l . , Instrumentation and Controls Div. Ann. Progr. Rept. Sept. 1, 1963, ORNL3578, pp. 37-40. 3L. F. Ueber, "Radiation-Monitoring and Warning System a t ORNL," Nucl. Safety 6(4), 414-20 (Summer 1965).

332

audible alarm i n the building w i l l be actuated, warning lights outside the building will flash, and an alarm signal w i l l be transmitted t o t h e Laboratory Eknergency Control Center, Building 2500. 2.9.2.2

System Description

The gamma radiation l e v e l i s monitored by seven monitrons located throughout t h e building (Table 2.9.1). Air i s monitored f o r b e t a - g m a emitting p a r t i c l e s by seven constant a i r monitors located throughout the building. See Figs. 2.9.1 and 2.9.2 f o r the location of a l l the instruments.

Table 2.9.1.

Radiation and Contamination Monitors I n s t a l l e d i n Building 7503 Locat ion

Monitor No.

1. F a c i l i t y radiation monitorsajb Control room High bay, south

High bay, west Basement, north Transmitter room Basement center 2.

3 4 5 6

RE-7002 RE-7003 RE-7004 RE-7005

Contamination monitors with control room alarm onlyc High bay, west High bay, south

7 RE-7017

F a c i l i t y contamination monitorsb" Offices Basement, north Transmitter room Service tunnel

RE-7012 RE-7013 RE-7014 RE-7015 RE-7016

Radiation monitors with control room alarm on&+ Service tunnel

1 RE-7011

2 3 4 5 6

Mobile a i r monitor

1 RE-7000

RE-7001

7 RE-7006

a Allmonitrons a r e Q-1154B-13.

bCoincidence of any two high-level alarms i n the group causes automatic evacuation. C

ORNL model Q-224OB-4 constant air monitor.

i d

333

Since none of the health physics functions originally designed i n t o t h e monitrons and a i r monitors were altered, each instrument i s an independent u n i t that r e t a i n s a l l i t s l o c a l alarm features. Each instrument, however, i s connected t o an individual indicator module on the monitoring panel located i n the Auxiliary Control Room, Nuclear Board 5 . By means of three colored lamps, which normally give a d i m l i g h t , an indicator module indicates the condition of t h e instrument t o which it i s connected; t h a t i s , a white lamp burns a t f u l l i n t e n s i t y i f the instrument i s inoperative, an amber lamp burns a t f u l l i n t e n s i t y i f t h e "caution alarm level" (7.5 mr/hr f o r a monitron and 1000 counts/min f o r a beta-gamma a i r monitor) i s reached, and a red lamp burns a t f u l l int e n s i t y i f the "high level" (23 mr/hr f o r a monitron and 4000 counts/min f o r a beta-gamma a i r monitor) i s reached (Table 2.9.2). Any change i n the i n t e n s i t y of any lamp, t h a t i s , from d i m t o bright, i s announced by the sounding of a buzzer a t t h e monitoring panel and by annunciation on the main board. The high-level alarm outputs of s i x selected monitron indicator modules a r e connected t o a coincidence module, and the high-level alarm outputs of four selected constant a i r monitors a r e connected t o a coincidence module. If a coincidence module receives a high-level alarm signal from any two or more constant a i r monitors o r monitrons i n a group, the See Fig. building evacuation system i s actuated (see Table 2.9.1). 2.9.3 f o r a block diagram of the system and Fig. 2.9.4 f o r the control schematic.

Table 2.9.2.

Central Control Panel Alarm Indications f o r Monitrons and A i r Monitors Lamp Intensity

Instrument Condition Red

Amber

White

Normal operation

Dim

Caution levela

Dim

Bright

Dim

Bright

Dim

Instrument inoperative

Dim

Bright

Instrument removedC

Bright

g levelb h

a Caution l e v e l f o r a beta-gamma a i r monitor i s 1000 counts/min arid f o r a monitron i s 7.5 mr/hr. No caution l e v e l alarms a r e available on constant alpha a i r monitors. bHigh l e v e l f o r a beta-gamma a i r monitor i s 4000 counts/min and f o r a monitron i s 23 m/hr. C

Lamp i n t e n s i t i e s remain bright u n t i l a maintenance connection i s made giving "inoperative" indication.

334

2.9.2.3

Components

Panel boar d The c e n t r a l panelboard f o r the e n t i r e system, located i n the Auxili a r y Control Room on Nuclear Panel 5 , consists of two 12-module racks, one c e n t r a l control chassis, and one dc power supply (Fig. 2.9.2). The 12-module racks contain one indicating module f o r each instrument, coincidence modules f o r t h e beta-gamma radiation alarm system and the contamination alarm system, a remote alarm module, a buzzer module, and a manual evacuation module. The remote alarm module transmits a signal t o a single annunciator on the main control panel. The racks and modules are made of anodized aluminum. The modules have anodized Metalphoto f r o n t panels. A Metalphoto t e x t s t r i p i s provided a t the top of each rack f o r instrument identification. The c e n t r a l control chassis contains manual switches, timers, relays, and monitoring equipment which a r e parts of the system but not located i n modules. For c i r c u i t d e t a i l s on the c e n t r a l control chassis, see Fig. 2.9.5. Monit r o n The remote monitron (ORNL model Q-1154B) i s an ac-powered, null-type radiation detection instrument f o r monitoring gamma radiation. The monitron consists of two basic units: (1)a control chassis, which cont a i n s t h e power supply, the main amplifier, a radiation-level indicating meter, and the controls; and (2) a preamplifier and ion-chamber detector assembly. The detector assembly can be located remotely 50 f t or more from the control chassis. A 0-to-10-mv recorder o r a 0-to-1-ma meter can be connected t o the monitron. The range of the meter i s 0 t o 25 mr/hr, and the calibrated accuracy of the meter i s within 3% f o r gamma radiation. The zero s e t t i n g may be checked by means of a push button. When the set point of an alarm c i r c u i t i n the main chassis i s exceeded, a b e l l i s rung and a red lamp on the instrument i s lighted. A connection on t h e instrument f o r an external alarm i s used t o operate the caution-level alarm f o r t h e system. I n addition t o these standard features, the monitrons i n s t a l l e d i n Building 7503 have two other features: (1)warmup time delay relays i n s t a l l e d on the main chassis and (2) a high-level alarm meter relay i n s t a l l e d on an accessory chassis. The instrument and alarms operate as follows:

1. A power f a i l u r e or a disconnected power cord will cause the white lamp on t h e c e n t r a l control panel t o burn brightly. After power i s restored and a 1-min delay f o r w m u p , the white lamp r e s e t s i t s e l f . During this 1-min delay, caution and high-level a l a r m s a t t h e instrument might sound, but the same alarms on the c e n t r a l panel a r e locked out and will not sound. 2.

I f the caution l e v e l of 7.5 mr/hr i s exceeded, an electronic alarm c i r c u i t causes the yellow lamp on t h e c e n t r a l panel t o burn b r i g h t l y and the b e l l a t t h e instrument t o ring. The alarms are automatically r e s e t a t t h e instrument when the radiation l e v e l decreases below 7.5 m r / h r , but they must be r e s e t manually a t the c e n t r a l panel.

The 0-to-1-ma meter output terminals a r e connected t o the accessory meter relay, which i s s e t t o operate when t h e 23 m r / h r (high-level)

335

alarm s e t point i s exceeded. A t 23 m/hr t h e b e l l a t t h e instrument w i l l be ringing, since it s t a r t e d a t 7.5 mr/hr, and the red lamp on t h e c e n t r a l panel w i l l burn brightly. When the radiation l e v e l decreases t o l e s s than 23 mr/hr, the high-level alarm a t the instrument i s automatically r e s e t by a signal interrupter (allows a r e s e t every 30 sec) from the c e n t r a l panel. The c e n t r a l panel alarm i s r e s e t manually. Beta-Gamma Constant Air Monitor

This monitor consists of an aspirating system, a paper-tape f i l t e r , a halogen-type Geiger-Mueller tube detector, a l i n e a r count-rate meter, a recorder, and v i s i b l e and audible alarms. Air i s drawn through the f i l t e r by a Roots blower. A sample containing beta-gamma-emitting p a r t i c l e s i s collected on the paper-tape f i l t e r (collected sample s i z e of 1 X 2-1/2 i n . ) . The sample tape i s advanced automatically every 24 hr. The tape may be advanced manually a t any time by the operator. The det e c t o r counts the sample as it i s being collected. The count-rate meter i s a l i n e a r duty-cycle type u t i l i z i n g a single range and having an int e r n a l high-voltage supply. The normal range i s 0 t o 5000 counts/min, and ranges of 0 t o 250, 0 t o 1000, 0 t o 10,000, and 0 t o 25,000 counts/min a t f u l l scale may be obtained by various interconnections of two jumper wires under the chassis. The input voltage s e n s i t i v i t y of the r a t e meter i s 200 mv. The o v e r a l l accuracy of the r a t e meter, including t h e e f f e c t of long-term d r i f t , i s within 5%. The corona-regulated high-voltage supply i s nominally 900 v with 5150 v adjustment. The maximum load curr e n t i s 20 pa. The r a t e meter has adjustable high-level and caution alarms and puts out a 1-ma f u l l - s c a l e signal t o drive an i n t e g r a l l y mounted Rustrack recorder. The caution alarm i s adjustable over t h e range of approximately 2 t o 58% of f u l l scale, and the high-level alarm i s adjustable from the caution-alarm s e t point t o f u l l scale. The caution alarm i s an electronic c i r c u i t which employs a dual t r i o d e and p l a t e relay with potentiometer adjustment. The relay i s energized below the t r i p point and i s deenergized by current t r a n s f e r from one t r i o d e t o the other by a diode t h a t couples t h e cathode c i r c u i t s . Hysteresis i s approximately 4% of f u l l scale. The high-level t r i p i s accomplished by t h e high contact on a contact-making meter which energizes the high-level t r i p relay. When the s e t point i s reached, the meter contacts and relay a r e locked in; these are released by depressing the r e s e t push button. A low-level pointer on the panel meter has no contacts and i s used only as a v i s u a l indicator. The pointer should be set a t t h e l e v e l corresponding t o t h e caution-alarm s e t point. The instrument has an alarm panel with four l i g h t s , a b e l l , and a buzzer. When the caution set point i s reached, an amber lamp i s lighted and t h e buzzer i s energized. There i s no switch t o silence the buzzer, and t h e operator i s expected .to advance t h e tape when this point i s reached. When t h e high-level t r i p point i s reached, a red lamp i s lighted and t h e b e l l rings. The b e l l can be silenced by a toggle switch, and when t h i s i s done, an amber neon indicator i s lighted. When t h e f i l t e r tape breaks, a red neon indicator i s energized and the caution c i r c u i t i s energized through a flasher. The amber neon bulb

336

burns continuously, and t h e caution l i g h t and the buzzer come on i n t e r mittently. If a tape breaks and, the caution alarm sounds a t this same time, t h e tape-break neon light, the caution l i g h t , and t h e buzzer w i l l be on continuously. A test push button permits checking the alarm panel by simultaneously simulating tape break and high-level alarm signals. I n addition t o these standard features, a l l a i r monitors a t Building 7503 have an accessory "instrument-inoperative" chassis containing a meter relay. The instrument and alarms operate as follows: 1. An accessory meter relay connected t o the 0-to-1-ma output of t h e count-rate meter w i l l cause t h e white "inoperative" l i g h t on the c e n t r a l panel t o burn brightly whenever t h e meter pointer drops t o zero, indicating no s i g n a l from the instrument. After power i s restored and a 60-sec delay, this alarm c l e a r s i t s e l f . During the 60-sec delay, l o c a l caution and high-level alarms do not sound since they are locked out. 2. A t the caution l e v e l of 1000 counts/min, an electronic alarm c i r c u i t w i l l cause the yellow lamp i n t h e control room t o burn brightly. With an ORNL model Q-2240 a i r monitor, a buzzer w i l l sound a t the instrument. The alarm i s automatically reset when the f i l t e r i s changed. 3 . A t the high l e v e l of 4000 counts/min, the panel meter relay on t h e instrument causes the red lamp i n t h e control room t o burn brightly. Also, the b e l l sounds. These alarms a r e r e s e t by advancing the f i l t e r and by pressing t h e manual reset button on t h e monitor. Indicator Module The indicator module (ORNL model Q-2563-1) consists of three independent t r a n s i s t o r i z e d channels, each operating an indicator lamp and pro.viding a dc voltage shift s i g n a l f o r alarm o r control purposes and a voltage pulse signal f o r operating the buzzer module. The three lamps and a push button a r e on the front panel. Each module i s 35.8 mm wide, 120 x n high, and 125.8 mm deep. All connections a r e made on printed s t r i p connections a t t h e rear edge of the plug-in module. When the instrument connected t o an indicator module i s operating normally, a l l lamps on t h a t module a r e dim (Table 2.9.2). When the module receives a signal that t h e primary instrument i s operating abnormally or t h a t t h e caution o r the high-level alarm values have been exceeded, the lamps burn a t f u l l intensity: white f o r inoperative instrument, yellow f o r caution level, and red f o r high level. A signal i s a l s o generated by the module which causes a buzzer t o sound. The white lamp indication w i l l remain u n t i l t h e condition causing the alarm i s cleared, a t which time t h e lamp will return t o t h e dim condition. The red and amber lights w i l l remain bright u n t i l they a r e manually r e s e t by a push button on the indicator module. If the indicator module i s r e s e t when the alarm or abnormal condition s t i l l e x i s t s , the lamps w i l l mmentarily become dim when the r e s e t button i s depressed and then w i l l become bright and the buzzer w i l l sound again when the r e s e t button i s released. All indicator modules are i d e n t i c a l and can be interchanged o r replaced without a l t e r a t i o n (see Fig. 2.9.6 f o r c i r c u i t d e t a i l s ) .

337

Coincidence Module The coincidence module (ORNL model Q-2563-2) consists of one trans i s t o r i z e d c i r c u i t which accepts a dc s h i f t voltage alarm signal from as many a s s i x indicator modules. The c i r c u i t can be adjusted by int e r n a l jumper connections t o operate a relay f o r alarm o r control purposes on any combination of one t o s i x input signals. A l l coincidence modules a t Building 7503 are arranged t o operate the relay when there i s a coincidence of any two alarms from a selected group of instruments. Each module i s 35.8 mm wide, 120 mm high, and 125.8 mm deep. A l l connections a r e made on printed s t r i p connections a t the r e a r edge of the plug- i n module. Four selected air-monitor indicator modules a r e connected t o a coincidence module. Six selected monitron indicator modules a r e connected t o a separate coincidence module. When two or more monitron indicator modules o r two or more air-monitor indicator modules receive high-level alarm signals, the associated coincidence module w i l l actuate the building warning and evacuation equipment and w i l l transmit a s i g n a l t o t h e Emergency Control Center, Building 2500. A red lamp on t h e affected coincidence module will indicate which s e t of instruments has detected an abnormal condition. When the indicator modules showing an abnormal condition are r e s e t manually, t h e coincidence module w i l l a l s o be r e s e t . A l l coincidence modules a r e i d e n t i c a l and can be interchanged o r replaced without a l t e r a t i o n , except f o r an i n t e r n a l jumper connection which determines t h e number of coincidental input signals required f o r an output s i g n a l (see Fig. 2.9.7 f o r the c i r c u i t schematic). Relay Module To a l e r t the reactor operator, a relay i n the relay module operates an annunciator a t the main control panel whenever the buzzer module operates; t h a t i s , any alarm a t the auxiliary panel a l s o annunciates a t the operating position. The annunciator a t t h e main control panel ope r a t e s i n the same manner as a l l other Tigerman annunciators a t t h a t point.

To reset the annunciator, t h e operator m u s t f i r s t s i l e n c e the

buzzer a t the auxiliary control panel. Buzzer Module The buzzer module (ORNL model Q-2563-4) consists of a transistorized t r i g g e r c i r c u i t t h a t operates a s i l i c o n controlled r e c t i f i e r t o actuate a buzzer when a voltage s h i f t pulse i s received from an indicator module. The buzzer module i s the same s i z e as a l l other modules and i s interchangeable with other buzzer modules (see Fig. 2.9.8 f o r t h e c i r c u i t schematic). The buzzer module gives audible notice that an indicator module has received any one of three input signals. The buzzer module, which serves a l l indicator modules, i s r e s e t by a push button a t t h e f r o n t of t h e module. After being r e s e t , the buzzer w i l l sound again whenever an input s i g n a l i s received by one of t h e indicator modules. For example, a change from a normal condition t o a "caution alarm level" a t some location will s t a r t the buzzer. After it i s reset, a change t o 'kigh alarm level" o r t o "inoperative instrument" will s t a r t the buzzer again.

338

Air Whistle and Beacon Lights When a coincidence module has been energized by two o r more monitrons o r a i r monitors, four a i r whistles are activated by nitrogen gas b o t t l e s (one f o r each whistle) t o notify the building occupants t o leave t h e building. The air w h i s t l e , a "Clarion whistle" by Westinghouse Air Brake Company, w i l l sound from 2 t o 4 min on one f i l l e d gas b o t t l e . A control box f o r each whistle contains a pressure valve, pressure switches which monitor tank and regulated pressures, and a solenoid valve t h a t i s opened by an e l e c t r i c a l s i g n a l from the coincidence module. A momentary signal w i l l open the solenoid valve, and t h e valve w i l l remain open u n t i l it i s closed manually by pressing t h e mushroom head of t h e valve stem inward. See Fig. 2.9.1 f o r t h e locatiop of t h e whistles and Fig. 2.9.9 f o r t h e control c i r c u i t schematic. The normal gas pressures f o r proper operation of the whistles a r e not less than 1000 psig tank pressure and 80 t o 120 psig l i n e pressure t o t h e solenoid valve. Abnormal pressures a r e indicated by red lamps (labeled "horn trouble") on t h e c e n t r a l control panelboard, one lamp f o r each w h i s t l e . A dim lamp indicates normal pressures, and a bright lamp indicates abnormal pressures. Inspection of the gages w i l l indicate whether the tank pressure o r the l i n e pressure i s abnormal. Federal Sign and Signal Corporation model 27s 110-v beacons with magenta-colored lenses a r e i n s t a l l e d a t 15 locations (Fig. 2.9.2) i n and around the reactor building complex and the o f f i c e building t o warn personnel t o evacuate the building. These beacons a r e actuated simultaneously with the a i r whistles by a s i g n a l from a coincidence module, and they a r e automatically stopped when the coincidence module has returned t o a normal condition. A key-operated switch, labeled "normal-disable, on the c e n t r a l control panelboard may be used t o disconnect the a i r whistles and beacons during maintenance o r abnormal operation periods. Since the Eknergency Control Center receives an alarm signal when the switch i s moved t o the "disable" position, the Control Center should be n o t i f i e d before the switch i s s e t a t t h i s position. A large red push button located on a module i n the c e n t r a l control panel, labeled "manual evacuate, actuates t h e a i r whistles and beacons and transmits an alarm signal t o the Ehergency Control Center ( i f the Center has not already received an alarm). Remote manual evacuation switches a r e provided on the reactor control console and i n t h e maintenance control room. If one of the manual evacuation push buttons has been used, the system may be restored t o the normal condition by pressing the "reset" push button on the "manual evacuate" module. Power Supplies The main power f o r the system i s I20 v, 60 hertz, supplied from instrument power panel 5 i n Building 7503 t o the 24-v dc power supply and t h e monitoring instruments. The 24-v dc t r a n s i s t o r i z e d power supply i s a regulated voltage and current u n i t . A green "power on" lamp on t h e control chassis and a neon lamp on the power supply panel w i l l be brightly lighted t o indicate that t h e power supplies are operating. Also a "dc f a i l u r e relay" i s used which t r i g g e r s an annunciator on t h e main control panel should the dc power supply f a i l .

339 ;I

Drawings The F a c i l i t y Radiation and Contamination System i s described i n the following ORNL Instrumentation and Controls and Reactor Division drawings. 1. Q-2354-1to -7, instrumentation location and wiring diagrams.

Q-2563-1 t o -4, and Q-2563-16B, -17, and -19B, plug-in modules.

Q-2358-7, horn control box.

Q-1l54B-1 t o -14, monitron.

Q-2359-12, monitron high-level alarm.

Q-2240-1to -23, constant a i r monitor.

Q-231lB, constant a i r monitor instrument f a i l u r e box.

D-HH-Z-Lx)641, instrument placement plot.

Operating Manual See ORNLTM-1127 (Revised)' f o r operating and checkout procedures. 2.9.3 2.9.3.1

General System

Introduction

This p a r t of the Health Physics Monitoring System consists of allthe instruments used f o r health physics purposes which are not included i n the F a c i l i t y Radiation and Contamination System. I n general, these instruments are f o r use by the area health physicists and f o r operating personnel i n conducting personal surveys of t h e i r bodies and clothes. Included i n this system are seven beta-gamma survey-type monitors, a beta-gamma sample counter, an alpha sample counter, and a hand-and-foot monitor. See Fig. 2.9.1 f o r location of these instruments.

2.9.3.2

Beta-Gamma Monitors, Q-2091

The beta-gamma monitors a r e mostly placed i n contamination-free areas t o provide a means of personal survey of clothing and body. However, when not used f o r this purpose, they a r e l e f t operating and s e n r e as backup monitors f o r t h e monitrons. I n four places (the cooling-water equipment room, t h e hallway between Buildings 7503 and 7509, t h e instrument shop, and t h e venthouse) t h e i r primary purpose i s area monitoring. They a r e used instead of the monitron because of the lower u n i t cost md low area background expected. They provide a l o c a l aural alarm only and a r e not t i e d t o any c e n t r a l alarm system. The Q-2091monitor consists of a G-M tube and a count-rate meter with i n t e g r a l power supply. The G-M tube has an adjustable beta shield and i s attached t o the r a t e meter by a 3-ft length of coax cable.

340

The count rate meter (Q-2091) i s of the duty-cycle, linear-scale type. It includes an amplifier designed t o accept t h e G M beta-gamma tube input. A high-voltage power supply, a high-level alarm c i r c u i t , an aural monitor with volume control, and a l-ma f u l l - s c a l e output f o r recorder o r telemeter are included features. The u n i t weighs 19 l b and i s enclosed i n a cabinet approximately 8 i n . wide, 9 i n . high, and I 2 i n . deep. It operates from 115 v, 60 hertz ac.

6.1

Performance SDecifications Performance specifications a r e given below. Input s e n s i t i v i t y

200 mv

Circuit l i n e a r i t y

2.5$;

Amplifier gain control

None

High voltage

900 k 150 v, corona-regulated,

o v e r a l l accuracy, including d r i f t , 5$

20 pa Range selector

250, 1000, 2500, 10,000, and 25,000 counts/min

Integrator time constants

1, 11, and 21 sec

Alarm

Adjustable, zero t o f u l l scale on any range f o r high l e v e l only, manual r e s e t

Recorder output

0 to 1 Output, 50,000-ohm impedance

Aural monitor

Gated relaxation o s c i l l a t o r and power amplifier with volume control

2.9.3.3

Hand-and-Foot Beta-Gamma Monitor, Q-1939-B

The hand-and-foot monitor i s located i n an area which serves as t h e main entrance and e x i t from the reactor building (7503). This instrument i s an ac-powered four-channel monitor f o r beta-gamma radiation with a channel f o r each hand, a channel f o r the shoes ( f e e t ) , and a channel with a movable probe. The probe i s mounted approximately w a i s t high i n order t o monitor t h e front of clothes when not used f o r special monitoring. Three channels a r e i d e n t i c a l modular-constructed units, actuated by a halogen-quenched stainless-wall G-M tube. The counting rate i s indicated by glow t r a n s f e r s c a l e r tubes and e l e c t r i c a l r e s e t r e g i s t e r s . The fourth channel, the survey probe, i s an aural channel. The count i n this channel i s not t o t a l i z e d . Maximum counting r a t e i n the probe channel i s approximately 5000 counts/sec. To s t a r t the instrument, a manual push button i s depressed which energizes a timer, a f t e r which the operation i s automatic. The instrument r e s e t s i t s e l f , and there i s a 5-sec waiting period before the counting cycle starts, t o give the user

341

time t o get both hands i n position f o r monitoring. The a c t u a l counting period i s 23 sec. The t o t a l cycle i s 30 sec. The maximum count r a t e per channel i s approximately 250 counts/sec, and t h e input resolving time per channel i s approximately 200 psec. The instrument i s contained i n a rack cabinet 68-3/8 i n . high, 21-1/16 i n . wide, and 220 i n . deep. A detachable base, 4 i n . high, 18 i n . long, and 2 1 i n . w i d e , contains t h e foot-monitoring assembly. The power requirements a r e 115 k 10 v, 60 hertz, 75 w, 0.7 amp. Operating temperature limits are 0 t o 135OF.

2.9.3.4

Beta and Alpha Sample Counters

The b e t a and alpha sample counters a r e located i n t h e h e a l t h physics counting room a t t h e north end of t h e reactor building.

Beta Sample Counting System, Q-2344-1 The Q-2344 b e t a counting system includes a Tracerlab end-window G M tube mounted i n a v e r t i c a l lead s h i e l d (ORNLQ-2089). The lead shield also contains a card sample holder. Attached t o t h e s h i e l d i s a preamplifier and cable. The preamplifier s i g n a l i s transmitted v i a t h i s cable t o a decade s c a l e r containing the high-voltage power supply (ORNL Q-2188-1) A timer i s a l s o included i n t h i s unit. The complete assenibly i s usually mounted on a t a b l e or a laboratory bench.

Alpha S c i n t i l l a t i o n Counting System, Q-2345-1 This system uses a s c i n t i l l a t i o n detector composed of a 2 x 2 N a I c r y s t a l and a 2-in. photomultiplier tube (ORNLQ-2287). The tube and c r y s t a l are mounted i n a housing which i s attached t o a smear o r s l i d e sample holder. The system uses a preamplifier and the combined power supply u n i t used f o r t h e b e t a sample counter (Q-2188). This system, l i k e t h e b e t a system, i s mounted on a t a b l e o r a laboratory bench.

343

I -I*

r .I*

-I* ul

20-

\ RM 70?3

CENTRAL A L A R M CUASSfS Q

- 9 3>.3-/0

RX 7024 POWER SUPPLY 0 50-36 A NJE K D.C. RVC-36-5

BLANU

NOlES: I. Centra/ contrd 8nd annunciafor pane/ +o be located in euxiliery control room fcanmon) 2. sthgte on Nudeor annuncietcr A m / f'o5r all atarms in m i n

' C

Fig. 2.9.2.

Instrument Panel and Health Physics Instruments Locations.

344

ORN L- DWG 67- 7830

W H .

Fig.

9.3.

M..

Functional Block Diagram of MSRE Health Physics Monitoring System.

e <

Qui

N 0

I I I

347

ORNL DWG. 67-7842

FOR NON-LATCHING OPERATION USE A CONDENSER INSTEAD OF A J U M P E R FROM A 2 TO 82

Fig. 2.9.6.

Nore-

?&4

Indicator Module.

348

ORNL-DWG 67-783t

T H I S JUMPER PROVIDES TWO-OUT-OF-SIX ACTUATION O F RELAY K - I P," 8 P,n 7 P,n

Pur 5

P,,. 4 Pl"

di P,"

Fig. 2.9.7.

Coincidence Module Circuit Diagram.

349

350 ORNL IIWG. 67-7836

92358-7

Fig. 2.9.9.

Air Whistle Schematic Diagram.

351

2.10

PROCESS RADIATION MONITORS

2.10.1

Introduction

The process radiation monitoring system monitors radioactivity levels i n process pipelines, vessels, and operating components. T h i s system i s d i s t i n c t from the Health Physics Monitoring System, Sect. 2.9, which i s designed t o warn personnel throughout the reactor area. Signals from t h e process monitoring system detectors located on or near pipes and components a r e used t o produce alarm control signals and safety system input signals when a c t i v i t y levels indicate abnormal conditions. These monitors a l s o provide information which indicates operating conditions of various p a r t s of t h e reactor system.

2.10.2

System Description

Two kinds of detectors are used i n the process monitors, ion chambers and Geiger-Mueller (G-M) tubes. The G-M tubes a r e used t o monitor levels up t o 100 mr/hr. Three types of ion chambers a r e used. One i s a standard, commercial Reuter-Stokes chamber (Fig. 2.10.1) used t o cover a range of 30 m r / h r t o 300 r/hr. The second (Fig. 2.10.2) i s an OWL model Q-2818 and i s used t o cover a range of 100 mr/hr t o 5 x lo4 r / h . The t h i r d (Fig. 2.10.3) i s a special high-level ion chamber used t o cover a range of lo3 t o lo7 r/hr. This chamber i s of special design t o withstand the high radiation i n t e n s i t y and temperature present i n the reactor and draintank c e l l s during reactor power operation. It a l s o has mineral-insulated cables sheathed with s t a i n l e s s s t e e l t o s a t i s f y the c e l l containment rlequirements A t y p i c a l E M tube monitoring channel' consists of an Anton 106C G-M tube supplying the input signal t o an OFUYL model Q-1916 logarithmic response g m a radiation monitor. This model Q-1916 instrument was developed t o meet the requirements of most gamma radiation monitoring of reactors and in-pile loop systems. It has been i n use a t ORNL since 1958. The G M tube (Fig. 2.10.4) i s enclosed i n a s t a i n l e s s s t e e l housing less than 1 in. i n diameter and 8 i n . long, and it can be located up t o 500 f t from the electronics. No preamplifier i s used. The scale indicat i o n on the monitor i s proportional t o t h e logarithm of the radiation l e v e l over a three-decade span. f i l l - s c a l e indication i s normally 100 mr/hr, but it can be increased t o 1 r/hr by use of a different G-M tube and by appropriate changes i n the electronics. While the u n i t has a normal range of 100 mr/hr, it can handle l e v e l s i n excess of 100 r/hr without impairing i t s alarm and control functions. The monitor provides an upscale electronic a l a r m . The alarm l e v e l may be s e t a t any point over the readout range, and t h e alarm point may be read on t h e meter w h i l e t h e s e t t i n g i s being made without tripping the alarm c i r c u i t . A relay which i s energized during normal in-limit operation provides the a l a r m and control signals.

'ORNL Instrumentation and Controls Div. Ann. Progr. Rept. July 1,

1958, ORNL2647.

352

Figure 2.10.5 i s a block diagram of a t y p i c a l Q-1916 monitor, with c i r c u i t d e t a i l s shown i n Fig. 2.10.6. The G-M tube detector i s operated a t 900 v, and t h e radiation l e v e l indicated i s determined from the average current through t h e tube r a t h e r than from t h e pulse r a t e . Radiation int e n s i t y causes t h e tube t o conduct. The voltage drop across a r e s i s t o r i n s e r i e s with t h e G-M tube provides the input s i g n a l t o the averaging f i l t e r . The f i l t e r ' s output, an analog signal, i s fed t o a dc amplifier having a logarithmic response. The amplifier i s used t o drive t h e alarm limit detector, panel meter, and recorder. The alarm limit detector drives a DPM' relay which i s used f o r alarm and control signals. The monitor i s fabricated using modular construction; t h e Q-1916 monitor assembly contains three plug-in modules (Fig. 2.10.7), each of which i s a complete monitor. A single power supply (Fig. 2.10.8) f o r a l l three modules i s located along the back of the chassis. A single-channel u n i t with i n t e g r a l power supply i s also available. The Q-1916 monitor was chosen because of i t s operating simplicity, a v a i l a b i l i t y , small det e c t o r size, ease of monitor replacement, fast response, and f a i l - s a f e features. An E-H Research Laboratories model 202 electrometer i s used t o measure and indicate t h e signal produced by the ion chambers. This electrometer incorporates a 5889 low-leakage input tube and double feedback. Negative feedback reduces t h e e f f e c t of cable and source capacitance, thereby improving t r a n s i e n t response; positive feedback reduces the input capacitance a t low frequencies and f u r t h e r extends electrometer response. The seven input r e s i s t o r s from 106 ohms t o 3 x OW, selectable i n seven steps, provide a wide operating range. The electrometer has an adjustable alarm set point on t h e front-panel meter. An alarm r e s e t button i s provided t o r e s e t the instrument a f t e r an alarmed condition has cleared. It contains a DPIYI relay t o provide alarm and control signals and it produces an output s i g n a l scaled t o drive a 0-to10-mv recorder. A BO-v power supply i s provided f o r chamber polarization. Figures 2.10.9 and 2.10.10 a r e a f r o n t panel view of t h e electrometer and the c i r c u i t schematic respectively. Excluding t h e Chemical Processing Plant a t o t a l of 16 G-M tube monitors and 12 ion chamber detectors a r e used f o r process monitoring a t t h e MSRE. A l i s t of these monitors, t h e i r function, and t h e i r location i s shown i n Table 2.10.1. The column i n Table 2.10.1 labeled "Number of Units and Type of Coincidence Circuit" describes the number of complete monitor channels a t one location and how they are used t o increase r e l i a b i l i t y . I n a one-of-two c i r c u i t , e i t h e r monitor reaching t h e alarm s e t point i n i t i a t e s the desired alarm o r control action. If e i t h e r monitor fails, the other u n i t i s s t i l l available t o monitor the system and produce t h e required action should it be required. With but one exception a f a i l u r e of the monitor power supply produces control and alarm s i p a l s as does any other f a i l u r e which causes the monitor response t o appear l i k e t h a t caused by a high radioactive l e v e l (see sect. 1.5). The one-of-two system i s used i n those applications where the output control action can be t o l e r a t e d during an on-line t e s t . I n t h e two-out-of-three coincidence systems, two monitors are required t o produce an alarm or control action. This arrangement allows

c Table 2.10.1. ~~

Radiation Level

Process or

InsZrument

Detector

No.

Component Monitored

RE-596A, B, C

Fuel pump bubbler inlet lines

G M tube

Detector ucationa

Bac~ound

Ala%any

East O f <7mr/hr transmitter room a t 840ft l e v e l

Zomrlhr

Vent house

mmr/hr

Number of U n i t s and !l'ype of Coincidence Circuit 3

Two of three

Control o r Alarm Functionb

Alarm; close bubbler i n l e t

valve5

Monitoring Function

To prevent f i s s i o n gas backup i n fuel pump and pump overflow tank bubbler helium supply lines and ensure containment v a l i d i t y

Coolant pump sweep gas

RE-528B, C

Helium supply l i n e

RE-5OOD

G M tube

Water room

<5m/hr

2omr/hr

Fuel sample box exhaust

RE-675A, B

G M tube

mgh bay

< 7 mr/hrc

lo mr/hr

Fuel pump o i l tank

RE-mIB

G M tube

Service tunnel

<7mr/hr

2omr/hr

1 One of one

coolant pump O i l tank

RE-oT;?B

E M tube

Service tunnel

<7mr/hr

20mr/hr

1 One of one

Reactor c e l l containment air

I1E-565B, C

GM tube

Vent house

< 7mr/hrc

20 m/hr

2 One of two

Alarm; emergency f u e l drain; close valve HCV-565Al

To Indicate f u e l leak i n t o containment area and prevent excessive amounts from discharging t o stack

Off-gas sampler

RE-52A, 52B

G M tube

Sampler box a t vent house

<7mr/hr

loomr/hr

2 One of two

Alarm Only

To indicate leaks i n the offgas sampler system

Charcoal bed discharge

RE-557A, B

G M tube

Vent house

<7mr/hrC

20mr/hr

2 One of two

Alarm; f u e l and close cool-

To check operation of charcoal f i l t e r s and prevent excess a c t i v i t y discharge t o stack and pump lube o i l systeme

G M tube

<7mr/hrC

2 One of two

1 One of one

2 One of two

Alarm; emergency To monitor coolant s a l t f o r f u e l drain; f u e l i n leakage through f u e l pump off break in heat exchanger

Alarm only

To monitor for f i s s i o n gas backup i n helium supply header

Alarm; close valves i n l i n e t o filter pit

To indicate and control amount of f i s s i o n gas going t o stack

Alarm only

To indicate a c t i v i t y buildup in o i l To indicate a c t i v i t y buildup In o i l

a n t system vent valves; close off-gas vent valve Fuel sampler vacuum l i n e

RC678C, D

Ion chamber

High bay

<7mr/hrc

25 r/hr

2 One of two

Alarm only

Reactor c e l l space coolers 1 and 2, drain-tank c e l l space cooler, and f u e l pump coolant water return l i n e header

RE-827A, B, C

Ion chamber

Blower house

< 5 mr/hrc

50 mrlhr

3 TWO of three

Alarm; close valves i n water supply lines

Reactor c e l l

RE-6ooO-1, 2, 3

Ion chamber

Reactor ce 11

3 No alarm c i r c u i t

Indication only

Drain-tank c e l l

RE-6000-4, 5, 6

Ion chamber

Drain-tank cell

3 No alarm c i r c u i t

rndlcation o ~ u y Indicate operating levels i n the c e l l

Radiator p i t

RE-6010

Ion chamber

Radiator p i t

1 No alarm c i r c u i t

Indication only

aSee Dwgs. E-EH-A-55588 and D-HE-B-41668. bSee instrument flow diagrams f o r controlled element 'After

shielding detector.

To indicate when sample exchange area i s f r e e of f i s s i o n gas To indicate break i n the water l l n e s in the c e l l s and prevent a c t i v l t y from escaping the containment area

Indicate operating levels i n t h e cell

Indicate operating levels i n the r a d i a t o r p i t

354

t h e monitors t o be tested, channel by channel, without actuating the f i n a l alarm and control o r safety c i r c u i t s . Each monitoring channel can be t e s t e d completely up t o and including t h e a l a r m l i g h t and the alarm and control relay i n t h e module. The two-out-of-three coincidence arrangement i s used where maintenance and on-line t e s t i n g of any single channel must be accomplished without producing control action and where f a l s e output control action caused by a f a i l u r e o r malfunction of a single channel i s highly undesirable. A l l the detectors, except the high-level ones i n the reactor and drain-tank c e l l s and the radiator p i t , a r e capable of being tested with a radiation source. A 6oCo source i s used t o t e s t each location. I n areas where substantial background radiation e x i s t s , the lowl e v e l detectors are provided with lead shields (Fig. 2.10.11). Shielding reduces t h e background and improves t h e signal-to-noise r a t i o , thus preventing spurious alarms from a rise i n a c t i v i t y l e v e l a t another location. These shields consist of lead sheet formed i n t o the required shape or of concentric l e a d - f i l l e d pipes. The shields are designed2 t o f a c i l i t a t e the replacement of detectors and are b u i l t with access holes t o accept a radiation source f o r calibrating and t e s t i n g the monitors. No shields o r t e s t sources are provided f o r t h e high-level ion chambers since t h e i r operating range i s i n the neighborhood of lo5 r/hr. The high-level chambers a r e mounted a t selected locations i n t h e reactor and drain-tank c e l l s . Three cha,uibers are located near the wall of the reactor c e l l , one a t elevation 844.5 f t , one a t elevation 838.5 f t , and one d i r e c t l y over t h e reactor t o measure control rod drive dose. Two of the three chambers i n the drain-tank c e l l s a r e mounted on the w a l l s , and a t h i r d i s mounted between the two f u e l tanks on the thermocouple tray. The chanbers a r e f i l l e d with nitrogen, employ alumina insulators, and a r e b u i l t with mineral-insulated signal and high-voltage cables. The chamber i s 7 - 7 / 8 i n . long and 1-1/16 i n . i n diameter. The chamber sensitivity i s 4 x amp r-â&#x20AC;&#x2122; hr; 98% saturation i s obtained i n a f i e l d of lo7 r/hr with 350 v applied. Only one chamber i s monitored a t a time. This i s done by using a single electrometer and a six-position selector switch. The selector switch connects the signal from any selected chamber t o the electrometer. Two high-voltage power supplies are used, each supplying 350 v t o three chambers. A l l the process monitoring electronic instruments except those used with t h e sampler-enricher system and t h e pump lube o i l tanks a r e mounted i n nuclear boards 4 and 5.3 The other detectors a r e mounted i n panels associated with t h e i r respective systems. To obtain t h e required r e l i a b i l i t y f o r the monitoring system, t h e ac input power t o the monitors i s obtained from the 25-kva emergency power system. I n addition, i n t h e

Process l i n e detector shields, ORNL Reactor Division Drawings D-HE-B-41527, 41528, 40551, and 40552 3

Nuclear control board panels 4 and 5 layout, ORNL Reactor Division Drawings D-HE-A-41532 and 4,1533.

cai

355

one-out-of-two monitor system, each channel has i t s own separate power bus, providing added dperating r e l i a b i l i t y . With t h e exception of the s i x high-level, in-cellmonitors, a l l monitor outputs a r e transmitted t o the data system f o r alarm detection and logging. Each monitor i s provided with an individual a l a r m indication. I n addition, the alarm s i g n a l from each monitor s t a t i o n i s transmitted t o annunciators i n t h e auxiliary control room. These annunciator signals a r e interconnected and transmitted t o a single annunciator i n t h e main control room, labeled "PTocess Radiation Monitors . I 1

356

357

. cv I-l

! I

358

359

360 !

ORN L- LR-OWG 3 I t 6 6 A R

I S T R I P CHART -C RECORDEROR

DATA LOGGER GAMMA RAD IAT10 N DETECTOR

AVERAGING FILTER

LOGARITHMIC AMPLIFIER UPPER LIMIT DETECTOR

MMIhLT-

ALARM INDICATOR

RELAY CONTACTS

I ‘UP

TO 500 f t OF 3- CONDUCTOR SHIELDED CABLE

Fig. 2.10.5.

PANEL METER

-CONTROL

ALARM SET POINT

Block Diagram of Q-1916 Radiation Monitor.

CIRCUITS

ANNUNCIATORS

P <

s i

I i

362

Fig. 2.10.7.

Three-Module Q-1916 Radiation Monitor.

_ _-

I I I

I I 1

I I

I i

I I

.. I

.; ,. ..

' _4'

:*w

t-I

$; h

lu 0 lu

% ! 0

___ c

T.*OT'Z '%A

n-r-n

c--

c I

99E

367

2.11

STACK MONITORING SYSTEM 2.11.1

Introduction

The MSRE stack monitoring system monitors t h e MSRE off-gas f o r abnormally high radiation l e v e l s i n the 100-ft-high off-gas stack. The l e v e l of a c t i v i t y of the gas emitted from the stack is recorded on i n struments located i n the reactor auxiliary control room and by t h e computer data logger. Abnormally high l e v e l s of a c t i v i t y generate an aural and visual alarm i n t h e reactor control room and i n t h e Laboratory Waste Monitoring Control Center located i n Building 3105. All hot-cell ventilation, some building ventilation, and a l l waste gas (off-gas from process vessels and experiments) a t ORNL are monitored and discharged through one of several stacks. This section describes the principal features of t h e MSRE stack monitoring system. This stack is the main disposal f a c i l i t y f o r gaseous waste a t t h e MSRl3.l Cell ventilat i o n air (high f l o w , low contamination) makes up the bulk of t h e a i r flow; reactor off-gas ( l o w flow, high contamination) i s also disposed through t h i s f a c i l i t y . F i l t e r i n g equipment consisting of multilayer f i b e r g l a s s roughing and absolute f i l t e r s (see Fig. 1.5.10) i s a l s o located near the stack. These f i l t e r s are, i n general, a second l i n e of defense, since a l l a i r and gas i s cleaned near i t s source by t h e use of p a r t i c l e t r a p s and charcoal beds before entering t h e roughing f i l t e r s All continuous waste effluent monitoring systems a t ORNL feed i n formation t o panelboards a t t h e Waste Monitoring Control Center located i n Building 3105.2 The information is displayed by signal lights indicating alarm conditions o r by records on single-point o r multipoint strip-chart recorders.

2.11.2

System Description

The basic concept of stack monitoring i n s t a l l a t i o n s divides t h e channels of information i n t o two functional p a r t s . One p a r t provides day-to-day information necessary t o a r r i v e a t monthly and quarterly i n ventories of radionuclides e m i t t e d from t h e stack. The other p a r t provides a continuous surveillance of the minute-to-minute condition of the stack inventory i n order t o sound an alarm i f an unusual burst of a c t i v i t y OCCUTS

The function of t h i s second p a r t of t h e system, i n addition t o providing an e a r l y warning of unusual conditions, i s t o provide gross information about t h e incident useful i n locating the source and i n a s s i s t i n g a l l emergency groups involved t o evaluate t h e extent of t h e incident. A t present t h e r e a r e f i v e channels of information available from t h e MSRE stack t o meet these requirements. All t h e primary instrumentation f o r

'R. C. Robertson, MSRE Design and Operations Report, Part I, Des c r i p t i o n of Reactor Design, ORNL-TM-728 ( t o be issued).

2L. F. Lieber, "Radiation-Monitoring and Warning System a t ORNL, Nucl. Safety 6 ( 4 ) , 414-20 (Summer 1965).

368

these channels i s located on a balcony 40 f t up the stack, w i t h t h e i n dicating instruments located i n t h e reactor building (Fig. 2.11.1). These information channels are given below. 2.11.2.1

Flow Channel FT-S1

A P i t o t t ~ i ne t h e stack a t the 40-ft l e v e l continuously measures the t o t a l flow of a i r i n t h e stack (appraximately 18,000 cfm). This measurement provides surveillance t o detect unusual changes i n a i r f l o w . The f l o w data a r e a l s o required, t o calculate t h e average concentrations of material passing through the stack. The stack flow r a t e i s recorded by the data-logger and printed on t h e hourly log.

2.ll.2.2

In-Stack Sampler

An in-stack sampler i s located a t the 40-ft l e v e l . This sampler coll e c t s a sample from the a i r stream by means of a cartridge w i t h an i n t e g r a l f i l t e r and a charcoal t r a p (Fig. 2.11.2). Isokinetic sampling i s attempted, and t h e cartridge i s removed once a day routinely f o r counting room analysis and would be removed and replaced as often as necessary during an incident o r any unusual s i t u a t i o n . 2.11.2.3

Particulate Monitors

Beta-Gamma Monitor, RE-SlA A sample i s continuously withdrawn fromthe stack stream a t t h e 40f t l e v e l and passed through a f i l t e r paper which i s monitored by a G-M

tube. The buildup of beta-gamma-emitting p a r t i c u l a t e s provides t h e first clue as t o t h e physical form and c h a r a c t e r i s t i c radiation of contamination. as from t h i s monitor i s sent t o the 1311 monitor ( r e f e r t o 2.11.2.4 Alpha Monitor, RE-SIB A similar device monitors t h e stack stream f o r alpha a c t i v i t y . gas from t h e alpha monitor i s returned t o t h e stack.

2.11.2.4

Exit

Iodine Monitor, RE-SlC (Fig. 2.11.3)

After passing through t h e paper f i l t e r of the beta-gamma monitor (Sect. 2.11.2.31, t h e gaseous sample passes through a charcoal t r a p a t ambient temperature; here it is monitored by G-Mtubes. The charcoal bed receives t h e sample f r e e of p a r t i c u l a t e s and detects iodine and other materials, such as tellurium, i n v o l a t i l e gaseous form. These gases a r e poorly trapped by the preceding f i l t e r ; 1311 i s t h e contaminant usually detected, thus explaining t h e name, iodine monitor. A second clue as t o the physical form and i d e n t i f i c a t i o n of stack gas material is, therefore, provided by t h i s channel. A sample of stack air i s constantly pumpedthrough t h e beta-gamma monitor RE-SlA a t 2 cfm by a Roots blower. A 2-1/2- by 1-in. section

369

of f i l t e r - p a p e r tape catches b e t t e r than 9 6 of the p a r t i c u l a t e matter of greater than 0.3 p s i z e which passes, and any radiation of s u f f i c i e n t energy i s detected by a G-M tube. The paper used i s Whatman No. 4 and i s i n rolls 3 i n . wide and 145 f t long. No regulation of a i r f l o w i s provided. Since t h e f i l t e r is changed a t l e a s t every 8 hr, the a i r flow remains reasonably constant a t the blower-rated flow of 2 cfm. A pressure switch i n t h e intake a i r l i n e is held closed during operation and sounds an alarm i n Building 3105 i f there is a blower f a i l u r e . The sample i s collected inside a s t a i n l e s s s t e e l shield that provides approximately 2 i n . of metal i n a l l directions except where an opening is necessary t o admit a i r and tape. A mica end-window G-M tube (Lionel Electronic Laboratories t e 21OT) i s used as t h e detector. Window thickness i s 1.4 t o 2 mg/cm nominal and w i l l pass beta p a r t i c l e s of energies down t o 35 kev. Since stack gas may contain p r a c t i c a l l y any isotope, good energy s e n s i t i v i t y is required. Details of t h e assembled f i l t e r , detector, and s h i e l d a r e on Instrumentation and Controls Division Dwg. &-2325-5. The design of t h i s assembly alluws the f i l t e r tape t o be advanced by a 24-v dc signal from the control center i n Building 3105 and a l s o includes broken tape detect i o n before and a f t e r the shield. If the filter-paper tape breaks or runs out, it cannot be advanced, and an alarm signal is sounded i n Building 3105. A method of calibration i s described i n ref. 3. The tape assembly i s based on t h e ORNL Q-2118 design used i n t h e standard Q-2240 constant a i r monitors except t h a t the intake portion has been a l t e r e d t o allow e a s i e r disassembly f o r decontamination (see Instrumentation and Controls Division Dwg. Q-2218-1 f o r d e t a i l s ) . Also, the a i r intake d i ameter has been a l t e r e d t o match t h e sample probe and t o reduce t h e num-ber of diameter changes i n t h e sampling l i n e . A t t h e time of i n s t a l l a t i o n , isokinetic sampling conditions were approximated by estimating the flow, assuming 2-cfm sample volume and sizing the sample pipe accordingly. In addition, the end of t h e pipe w a s shar.pened, placed close t o t h e center of t h e stack, and headed i n t o t h e a i r stream. The number of degrees of t u r n between t h e pipe entry and t h e f i l t e r were minimized, and all pipe bends were a t t h e maximum allowable radius. All piping is of s t a i n l e s s s t e e l except f o r a small section of p l a s t i c tubing where f l e x i b i l i t y i s needed. The sample i s taken approximately t e n diameters downstream from t h e input t o t h e stack. The G-M tube i s connected w i t h RG59/U coaxial d i r e c t l y t o t h e indicating instrument located i n Building 7503. The cable runs a r e i n conduit, and lengths a r e t y p i c a l l y 100 t o 250 ft. The indicating instrument (RI-SIA) i s a Q-2313 count r a t e meter w i t h a current-sensitive input and is located i n nuclear panel board 5 (NB5) i n t h e auxiliary control room. The current-sensitive input allaws t h e signal and high voltage f o r t h e G-M tube t o be put on the coaxial cable without using preamplifier a t the G-M tube. The count-rate meter chassis a l s o holds t h e +HV supply, an audio output, a R u s t r a k recorder, and a panel meter. Range and time constant switchings a r e manual. The count-rate meter ranges a r e 0-250,

3E. D. Gupton, W. L. Ohnesorge, and N . M. Butler, Calibration of ORNL Model Q-2240 Continuous A i r Monitor, ORNL-TM-864 (May 14, 1964).

370

M O O , &lO,OOO, and 0-25,000 counts/min. Damping t i m e constants a r e 1, 11, and 22 sec. I n addition t o display by t h e r a t e meter and recorder, the beta-gamma l e v e l i s a l s o checked f o r alarms recorded by t h e computerlogger and output once a s h i f t on t h e 8-hr log. The signal t o the logger is 0 t o 10 mv and i s obtained from the output of t h e ratemeter. The alpha monitor (RI-SlB) i s similar t o t h e beta-gamma p a r t i c u l a t e monitor. The stack-gas sample is withdrawn by means of a separate sample pipe a t t h e 40-ft l e v e l . The 2-cfm sample i s drawn through a f i l t e r tape deck, as w i t h the beta-gamma monitor, by a Roots blower. In t h i s monitor, however, t h e radiation detector i s . a thallium-actuated zinc s u l f i d e screen (see Instrumentation and Controls Division Dwg Q-2218-5 f o r d e t a i l s 1. The area viewed is 1-5/8-in. i n diameter (2 in.2), and the detector is on t h e top (intake) s i d e of t h e f i l t e r tape t o avoid absorption of alpha p a r t i c l e s by t h e f i l t e r paper. No shielding is necessary owing t o the l o w s e n s i t i v i t y of t h e screen t o beta-gamma radiation. The indicating instrument, a Q-2313 count rate meter labeled RE-SIB, i s located i n t h e same panel as t h e beta-gamma rate meter. The alpha l e v e l i s a l s o monitored f o r alarm condition, recorded by the logger-computer, and output on t h e 8-hr log. After leaving the beta-gamma p a r t i c u l a t e monitor, t h e gas is passed through the model Q-2725 iodine monitor detector RE-S1C (Fig. 2.11.3) and returned t o the stack. A charcoal trap, made of a disposable p l a s t i c b o t t l e and containing 6-14 mesh coconut charcoal about 3 i n . i n depth, is used t o t r a p 1311(and other materials such as tellurium t h a t adsorb on charcoal). The trap, placed within a standard 2-in. -thick l e a d s h i e l d (Q-1907-15), i s monitored by four Lionel 10% G-M tubes. The air flow i s 2 cfm, and t h e measured cross-sectional flow area of the charcoal bed is 5.41 in.2. From curves given i n OFUYL-2872, t h e pressure drop i s appraximated a t 2 i n . H2O or l e s s , and t h e a i r velocity i s 55 fpm. The decontamination f a c t o r is estimated from t h e above report t o be lo3 or b e t t e r . As a rough rule of thumb, 6 1 4 mesh charcoal w i l l c o l l e c t 905 of 1311per inch, s o t h a t t h e high concentration i s a t the upstream face of t h e charcoal. Data presented i n t h e report a r e f o r v e l o c i t i e s of 200 fpm and l e s s . Actually t h e charcoal i s e a s i l y recoverable and can be used f o r analysis since t h e t r a p i s e a s i l y replaced. When s e n s i t i v i t y i s too great, t h e number of G-M tubes can be reduced. About 75 g of charcoal i s used i n each t r a p . The output of the G-M tubes (operated i n p a r a l l e l ) i s connected by RG59/U coaxial cable t o the input of a Q-2313 count-rate meter (RI-S1C) located i n NB5 i n t h e auxiliary control room. The 10-mv output of t h e rate meter is transmitted t o t h e data-logger, which p r i n t s out t h e iodine l e v e l on t h e 8-hr l o g . The collected material is monitored by a halogen-filled G-M tube (Lionel 106C) which has a 30-mg/cm2 w a l l t h a t excludes a l l beta energies below about 300 kev. The G-Mtube a l s o sees i n e r t and v o l a t i l e gases which a r e not collected by t h e f i l t e r paper. These show as only a r i s e i n count r a t e on t h e recorder f o r the time of t h e i r passage through the monitor. Iodine-131 w i l l c o l l e c t on t h e f i l t e r paper but w i t h very l a w efficiency, depending on t h e stack conditions and t h e physical form of t h e iodine. I n e r t gas such as 85Kr w i l l be seen i n both t h e p a r t i c u l a t e and 1311channels f o r t h e duration of i t s presence i n the stack f l o w . It

371

L 4

w i l l not c o l l e c t t o any extent on the f i l t e r o r the charcoal. While some adsorption on the charcoal has been noted, collection and r e t e n t i c n a r e very poor at ambient temperatures. A s can be seen, p a r t i c u l a t e matter i s immediately i d e n t i f i a b l e since it is collected by t h e beta-gamma monitor f i l t e r before it reaches t h e iodine monitor. Iodine-131 w i l l cause a long-term (&day h a l f - l i f e ) buildup on the charcoal; i n e r t gas can be i d e n t i f i e d since it shows on both channels i n a t r a n s i e n t r a t h e r than an integrated manner. A s s t a t e d previously, t h e indicating instruments f o r the stack monitors a r e located i n NB5 i n t h e auxiliary control room (Fig. 2.11.1). The indicating instruments consist of t h e three r a t e meters with the i n t e g r a l recorders f o r t h e three monitor channels, beta-gamma, alpha, and iodine, plus t h e alarm detection and display c i r c u i t r y f o r t h e three channels. The alarm detection equipment provides a l o c a l annunciation of t h e alarm from any of t h e detection channels and transmits the alarm signal t o the Waste Monitoring Control Center i n Building 3105. Figure 2.11.4 i s t h e functional block diagram of the system. The alarm-detection equipment consists of three t r a n s i s t o r i z e d switches which operate two alarm relays, a buzzer, and a lamp, a l l powered by a 24-v dc power supply. The equipment, except f o r the power supply is mounted on modular cards located i n an i n t e g r a l panel (Fig. 2.11.5). The modular card panels a r e s l i g h t l y modified, but t h e c i r c u i t s a r e i d e n t i c a l with those used i n t h e Health Physics Monitoring System (Sect. 2.9). The three alarm switches a r e actuated from signals derived from the three r a t e meters. See Fig. 2.9.6, Sect. 2.9, f o r a schematic of t h e switch c i r c u i t . Any channel i n an alarmed condition w i l l cause t h e appropriate alarm switch t o t r i p , which turns t h e alarm lamp "On" on the switch, t u r n s on a l o c a l buzzer (Fig. 2.9.8, Sect. 2.91, actuates a l o c a l annunciator, turns on a l o c a l alarm lamp, and actuates a relay a l l through t h e action of t h e alarm module (Fig. 2.9.7, Sect. 2.91, which a l s o t r i p s the stack monitor alarm i n t h e Waste Monitoring Control Center also. The alarm f o r each channel i s s e t by the contact meter on each r a t e meter. Once a channel i s i n t h e alarmed s t a t e , the alarm w i l l continue u n t i l t h e signal has decreased below the alarm s e t point, the individual alarm switch i s r e s e t , and t h e common buzzer is r e s e t . There is an additional module, c a l l e d t h e remote alarm r e l a y module (Fig. 2.11.5), which t r i p s an annunciator i n t h e main control room should the 24-v dc power supply f a i l . See the ORNL Q-2563 s e r i e s of drawings l i s t e d i n Sect. 2 . l l . 3 f o r d e t a i l s on t h e t r a n s i s t o r i z e d alarm c i r c u i t r y . See Fig. 2.1.1.6 f o r the operational schematic and elementary diagram of t h e beta-gamma, alpha, and iodine monitors.

372 ORNL Drawing L i s t f o r t h e MSRE Stack Monitoring System

2.11.3

Icr

Q-2370-1 Stack Sampler Location and Control A l a r m Panel Assembly Q-2370-2 -Functional Block Diagram Q-2370-3 - Operational Block D i a g r a m Q-2370-4 -Power Wiring a t Stack Q-2370-5 Interconnection D i a g r a m Q-2370-6 -Alarm Panels R e a r View Wiring

- Beta-Gamma Monitor, Operational gram Q-2370-8 - In-Stack Sampler Assenibly Q-2370-7

Schematic and Elementary D i a -

Q-2370-9 - In-Stack Sampler Details Q-2370-10 - In-Stack Sampler Probe Details Q-2370-13 -Tape Deck Cabinet Assembly and Details Q-2370-14 - Sampling Cabinet Assembly and Details Q-2563-lA Hi-Level Module, Schematic Q-25634% -Alarm Module, Schematic Q-25634 -Reset Module, Schematic

Q-2563-1% Remote Alarm Relay, Schematic Q-2328-13 -Alpha Monitor

Q-2325-5 F i l t e r and Shield Q-2313-15 - Countrate Meter Schematic Q-2218-5 Iodine Detector Q-2118 - Tape Assembly

vi I

.E-.lc- - - -

---

374

ORNL-DWG 67-696

9 -CUT FROM WHATMAN NO. 4 i FILTER PAPER Y-12 STORES ITEM NO. i5-157-4450

INCH

LOA0 CARTRIDGE WITH 6-14 ACTIVATED COCOANUT CHARCOAL NO. 269 FISHER SCIENTIFIC CO. CATALOG NO. 61 OR EQUAL

AS SE M B LY

MAT'L. CUT TO PROPER WIDTH FROM 1-02 POLYETHYLENE BOTTLE, ORNL STORES ITEM NO. 15-Oi4-9602 2 REQ'D.

Fig. 2.11.2.

0 3

END PLUG

HOUSING

STACK GAS FLOW

MAT'L. CELLULOID MAKE FROM 32-mm O.D. CENTRIFUGE TUBE ORNL STORES ITEM NO

STR A IN ER MAT'L 40-mesh SST 2 REQ'D. SCREEN WIRE

15-242-2483 1 REQ'D

Charcoal Cartridge for In-Stack Sampler.

I -

375

SHIELD

GM TUBES PLASTIC CENTRIFUGE TUBE WITH PERFORATED END CHARCOALTRAP 8-02 PLASTIC WIDEMOUTH B O T ~ WITH E PERFORATED CAP

O-RINGS

Fig. 2.11.3.

Iodine Monitor Detector.

I r---1

-tI

I 1

I I

1 1

378

qrsm.5

Cenfr2 Abrm

3 79

2.12 DATA LOGGER-COMPUTER 2.12.1

Introduction

A d i g i t a l data collecting and computing system i s used on the NSRE t o augment the conventional instrumentation system (Figs. 2.12.1 and 2.12.2). It i s designed t o c o l l e c t and process 350 analog and 112 onoff contact signals ( a t present it processes only 291 analog signals). The remaining signals can be added by merely wiring i n the signal leads and a l t e r i n g the system program. Signal processing includes conversion of the analog signals t o d i g i t a l values i n engineering units; alarm monitoring by comparing the signals against preset upper and lower alarm limits; and calculations t o provide heat balances, t o t a l power, reactivity, and other operational and analytical information. These d i g i t a l values may be logged on typewriters, displayed by a d i g i t a l lamp unit, o r recorded on magnetic tape, a t the system operator's option.

2.12.2

Basic System Equipment Description

The system consists of a Bunker-Ramo model 340 d i g i t a l computer, operating console, analog and d i g i t a l input-ou%put cabinets, typewriters, x-y p l o t t e r , d i g i t a l display lamp bank, and two magnetic tape units1 (Fig. 2.12.3). The analog input-output equipment i s housed i n three 23- by 84-in. cabinets (Fig. 2.12.4). These cabinets contain four dc amplifiers, an input signal multiplexer composed of mercury wetted contact relays, an analog-to-digital converter, a thermocouple reference unit, power supplies, and t h e input-output terminals with associated f i l t e r s and signal conditioning c i r c u i t s . The dc amplifiers and the converter were manufactured by the Redcor Corporation, Canoga Park, California. The analog signals from the process instruments are transmitted by signal leads t o the f i r s t two cabinets, where they are scanned by the m u l t i plexer, then amplified, digitized, and transmitted t o the computer memory. The analog input system i s designed t o handle analog input signals ranging from m i l l i v o l t s dc t o 220 v de o r a c . l r 2 The lower-level sign a l s are amplified t o 10 v dc, while t h e higher-level dc signals are attenuated t o the 10-v range and ac signals are r e c t i f i e d before attenuation. The analog input signals are transmitted t o the input terminals and then through 60-cycle noise f i l t e r s before reaching the input

lJ. F. Pierce and D. C. Shattuck, Instrumentation and Controls Div. Ann. Progr. Rept. Sept. 1, 1963, Om-3578, pp. 10%.

2E. N. Fray and J. T. DeLorenzo, Instrumentation and Controls Div. Ann. Progr. Rept. Sept. 1, 1963, OIWL-3578, p. 107. Note: Figure 9.4.1, t h i s reference, contains an error. The lower block, labeled "Linear Count Rate Meter," should read 'kogarithimic Count Rate Meter."

380

multiplexer. These f i l t e r s have a manually s e t variable 60-cycle rejection of from 6 t o 50 db. They are mounted on plug-in cards i n the two analog input cabinets. I n addition, d i g i t a l f i l t e r i n g (integration) i s applied t o selected input signals, most of which are thermocouple signals used i n precise calculations. The analog-to-digital converter operates on a 0- t o 10-v dc range. A l l analog signals are converted t o d i g i t a l values on t h i s basis, w i t h t h e proper scaling done under program control. D i g i t a l signals are compared with preset alarm limits and can be s e l e c t i v e l y transmitted t o digital-to-analog converters t o produce up t o 36 analog signals f o r recorders, oscillographs, an x-y p l o t t e r , o r f o r control. Three cabinets, indicated as 1/0 Nos. 1 t o 3 i n Fig. 2.12.4, house the d i g i t a l input/output equipment. This equipment handles t h e contact input signals from relays, typewriters, and t h e input keyboard and contains t h e control units f o r all t h e output devices. The contact input signals are transmitted t o the arithmetic and control u n i t of t h e computer t o perform operations under computer program control. The d i g i t a l output signals from t h e arithmetic and control u n i t are transmitted through t h e d i g i t a l input-output u n i t t o operate relays, typewriters, and t h e d i g i t a l lamp display u n i t . The computer consists of t h e basic d i g i t a l computer, t h e master input/output control unit, and t h e memory units. The computer cont a i n i n g t h e basic electronics i s housed i n three labeled cabinets, Input/outcentral. processor, core memory, and drum memory (Fig. 2.12.4). put i s housed i n one cabinet labeled Master I/O. The basic 340 computer has a l l - s o l i d - s t a t e c i r c u i t r y w i t h t h e f o l lowing specifications. Core memory

12,288 words, expandable t o 16,384, i n blocks of 2048

Drum memory

28,672 words, expandable t o 49,152, i n blocks of 4096

Machine cycle time

6.0 msec

Data word length

28 b i t s including sign plus one p a r i t y b i t on all memory operations

I n s t r u c t i o n format

Two f i e l d s : a 14-bit operation f i e l d and a 14-bit operand f i e l d ,

Addre ssing

Direct addressing of up t o 16,384 words, single l e v e l indirect, and immediate operand addressing

Number system

2's complement binary

Operat ion

Arithmetic, control, and core memory c i r c u i t s : p a r a l l e l ; magnetic drum memory c i r c u i t s : s e r i a l

Clock frequency

Arithmetic, control, and core memory c i r c u i t s : 478 kc; magnetic drum memory c i r c u i t s : 239 kc

381

Registers

Three major arithmetic registers, three index r e g i s t e r s , and addit i o n a l r e g i s t e r s f o r peripheral equipment

Environmental conditions

Standard operation t o 85'F cabinet temperature. !The power consumpt i o n a t 115-v single-phase, 60hertz i s 2000 w. The t o t a l system power consumption i s approximately 7000 w, including the two tape drives which operate on 208 v, three phase

Software

An integrated package designed f o r process control; includes r e a l time executive, u t i l i t y package, assembler, and FORTRAN I1 comp i l e r , and l i b r a r y of subroutines

Input-output subsystems

350 analog inputs, expandable t o over 2000; 32 d i g i t a l outputs, expandable t o over 1000

Priority interrupt

Handles over 100 l e v e l s of program p r i o r i t y (program operating time schedule )

2.12.3

Peripheral Equipment Description

Aside from the computer i t s e l f and the analog input and output subsystems, there are a number of peripheral devices which provide communication between the operators and the machine. The devices are l i s t e d below and can be seen i n Fig. 2.12.1. Four typewriters:

two w i t h 30-in. carriage and two with 16-in. carriage

Two magnetic-tape u n i t s

Paper-tape punch, reader Input keyboard x-y p l o t t e r Console:

function matrix and d i g i t a l display

I n normal operation, four IBM typewriters are used t o provide hard-copy records of reactor data (see Fig. 2.12.4 for location of the typewriters). TWO 3O-in.Ocarriage typewriters are used t o record ess e n t i a l l y a l l logs and calculation results. The periodically appearing r e s u l t s are all typed on one device on preprinted forms; r e s u l t s of demanded operations are typed on the second typewriter. One of the two 16-in.-carriage typewriters i s i n s t a l l e d i n the reactor control room t o

382

record alarm conditions associated with analog signals and calculation r e s u l t s . The second 16-in. typewriter (console) records all operations performed at t h e computer console. The p r i n c i p a l depository f o r reactor data i s magnetic tape. The values of all t h e analog signals are stored on magnetic tape every 5 min. I n addition, all intermediate and f i n a l calculation r e s u l t s a r e stored on tape. (The typeout of calculation results i s generally l e s s frequent and more limited i n extent.) Two tape drives (IBM model 729-2) are available, with t h e second u n i t normally i n standby. However, t h e second u n i t can be used f o r off-line functions such as data processing or program development while t h e f i r s t u n i t i s on l i n e . The paper-tape punch and reader (Teletype model BFRE-2 and Digit r o n i c s model 2500 respectively) are used primarily i n connection with programming functions, f o r example, assembly and compiling. There i s normally no input or output of reactor information through these devices. The input keyboard (Invac model FX-164) operates i n conjunction with the on-line program development package ( O m ) i n t h e computer. From t h e standpoint of reactor operation, it i s t h e means of entering data f o r t h e trend logging and p l o t t i n g functions. The x-y p l o t t e r (Moseley ty-pe 2D2) i s capable of p l o t t i n g any input variable as a function of time o r of any other input variable. Parameters f o r both coordinate axes must be entered by t h e operator. The computer console i s t h e focal point f o r use of t h e computer by t h e reactor operators. It contains t h e function matrix as well as the d i g i t a l switches for the selection of t h e various request functions. The console a l s o houses the panel f o r d i g i t a l display of s i g n a l values (Fig. 2.12.5). 2.12.4 2.12.4.1

System Operation

Collection and Processing of Analog and D i g i t a l Input Signals

A t t h e present time there are 291 analog signals from t h e reactor system connected t o t h e computer. The types and numbers of signals are summarized i n Table 2.12.1.3#4 See Fig. 2.12.6 f o r a complete l i s t of all input signals. These signals are arranged i n a scan t a b l e t h a t contains 350 e n t r i e s . Under normal conditions t h e r a w a n a o g signals f o r all 350 points a r e scanned, compared with high and low alarm limits, and stored i n core once each 5 sec. I n order t o provide a more frequent look a t selected variables, some analog signals appear a t several points i n t h e table. For instance, t h e outputs of the three neutron s a f e t y channels a r e arranged so t h a t one of t h e signals i s read every 200 msec. Another reason f o r multiple entry i n t h e scan t a b l e i s t o permit integration ( d i g i t a l f i l t e r i n g

3Ronald Nutt, Instrumentation and Controls Div. Ann. Progr. Rept. Sept. 1, 1963, ORNL-3578, pp. 103-4. 4R. C. Robertson, MSKE Design and Operations Report, P a r t I, Descrintion of Reactor Desim, ORNL-TM-728 ( t o be published).

383

Table 2.12.1.

Analog Input Signals Number of Signals

Thermocouple Conventional Integrated

169 17

Pressure

Flow

Amplifier gain

Weight

Power and voltage

Liquid l e v e l

Pump speed and tachometer

Position

Nuclear

Process radiation

23 Total

292

over 1/60 sec) of t h e signal f o r greater accuracy and resolution. Ternperatures t h a t are used i n calculations are integrated and converted t o the nearest O.l째F i n t h e range from 900 t o 1300'F. Thus, t h e signal m u s t appear a second time, unintegrated, t o provide information over the e n t i r e operating range. A s a r e s u l t of these multiple appearing signals, t h e 350-entry scan t a b l e contains 346 actual analog signals with four spare locations. R e a l i s t i c high and/or low process limits are imposed on most of

the analog signals. I n t h e remaining cases the l i m i t s are s e t a t t h e instrument extremes. The normal computer response t o an out-of-limits condition i s t o actuate the logger annunciator i n the main control room and t o p r i n t a message on the control-room typewriter identifying the variable, i t s value, and the time. Such a message i s typed i n red when the variable f i r s t goes out of limits and i n black when it returns within limits. No other information (except f o r a 4-hr out-of-limits log) i s typed while the signal i s e i t h e r out of o r within limits. There i s one group of 65 analog signals (type 2) that i s recorded on magnetic tape, i n engineering units, each 5 sec w h i l e any one of the signals i s out of limits. The typed messages f o r t h i s group of variables a r e similar t o those f o r the other signals. The recording function can be inhibited by operator request on any o r all of t h e signals t h a t w i l l produce t h i s action. An out-of-limits condition on any one of another group of 22 analog signals ( f o r instance, neutron flux) switches the computer t o a "fast scan" mode of operation. I n t h i s mode the scan t a b l e i s reduced t o 64.

384

important variables and all 64 are scanned, converted t o engineering units, and stored on magnetic tape once each 1/4 sec. This mode of operation continues f o r 1 min, without l i m i t checking, a f t e r i t s i n i t i a t i o n . A t t h e end of t h a t minute t h e normal scan i s resumed u n t i l another s i g n a l t o s t a r t "fast scan" i s detected. The "fast scan" mode of operation can a l s o be inhibited by operator request on any o r all of t h e signals t h a t will produce it. Once each 5 min, regardless of t h e scanning mode, all 350 signals are read, converted t o engineering units, and stored on magnetic tape. 2.12.4.2

Logging Functions

The computer generates and types out a number of periodic logs, which are tabulated below: 1-hr l o g (54 analog signals)

8-hr l o g (175 analog signals) D a i l y report (21 parameters)

Out-of-limits log (once every 4 h r ) Calculation r e s u l t s The 1- and 8-hr logs simply present t h e values of selected analog sign a l s t o record t h e status of t h e system. I n both cases t h e values t h a t are printed are t h e same as those that were recorded on magnetic tape during t h e l a s t 5-min taping operation. The daily report summarizes a number of operating parameters such as integrated power, time a t temperature, and numbers of thermal cycles on important components. The out-of-limits log i s an hourly summary of all analog signals (up t o 40) that are out of limits a t t h a t time along with t h e i r current values. Selected r e s u l t s of some calculations, such as t h e average reactor inl e t and o u t l e t temperature, are a l s o typed on t h e l o g sheet periodically. 2.12.4.3

Calculations

Aside from t h e routine functions, such as u n i t s conversion, t h e computer performs a number of on-line calculations using current reactor data.44 M a n y of these calculations include alarm functions t o c a l l att e n t i o n t o abnormal conditions. The calculations are normally performed on a periodic b a s i s with t h e r e s u l t s being printed usually l e s s f r e quently. Many of t h e calculations can be performed a t nonscheduled times on operator demand; r e s u l t s of nonscheduled calculations are always printed. Table 2.12.2 summarizes the schedule f o r some of t h e major calculations.

5G. W. Allin and H. J. S t r i p l i n g , Jr., Instrumentation and Controls Div. Ann. Progr. Rept. Sept. 1, 1963, ORNL-3578, pp. 114-15.

6J. L. Anderson e t al., Instrumentation and Controls Div. Ann. Progr. Rept. Sept. 1, 1963, ORNL-3578, p. 100.

385

Table 2.12.2.

Calculation

Major Routine Calculations Normal Interval

P r i n t out Interval

Demandable ? ~~

Re a c t i v i t y balanc e

5 min

1h r

Yes

Average reactor i n l e t and o u t l e t temperature

1h r

Yes

Reactor-vessel temperature difference

10 min

1 hr

Cell- atmosphere average temperature

1h r

8 hr

Yes

Heat balance

4 hr 8 hr

4 hr

Yes

8 hr

Yes

S a l t inventory 2.12.4.4

Miscellaneous Functions

Some of t h e miscellaneous functions that are, o r can be, performed by the computer are l i s t e d below. Trend l o g (up t o 26 variables)

Trend p l o t D i g i t a l display Contact and analog outputs On-line program development ( OLP'D) Data r e t r i e v a l and processing General-purpose computing

'cs

The f i r s t three items, trend log, trend p l o t , and d i g i t a l display, a r e means of providing v i s u a l information f o r operator guidance. The variables t o which these functions are applied can be selected a t w i l l by t h e operators. The l a s t three items i n t h i s l i s t are all r e l a t e d i n t h a t they are nominally o f f - l i n e functions t h a t can be performed w i t h t h e computer on l i n e . The system program requires only about 30$ of t h e c a p a b i l i t y of t h e computer under normal circumstances; t h i s u t i l i z a t i o n increases t o about 40$ i n t h e " f a s t scan" mode of operation. I n addition, t h e system program requires only about two-thirds of t h e core memory. Thus, there i s ample c a p a b i l i t y f o r background processing of o f f - l i n e material. The purpose of t h e computer is t o provide close surveillance, rapid processing, and compact storage of l a r g e amounts of reactor data. Since it i s associated with a reactor experiment, it i s not possible t o define all t h e data and calculations t h a t are required f o r a complete analysis of t h e system. Therefore a great deal of data are being coll e c t e d which may be used much l a t e r o r which may never be used.

386

2.12.5

References and ORNL Drawings

For more d e t a i l s on aJ1 p a r t s of the system, r e f e r t o the documents and drawings l i s t e d . For d e t a i l s on the operation of the system from the reactor operator's viewpoint, r e f e r t o item 11 i n t h e Reference L i s t , Computer Manual f o r MSHE Operators. lInterim Report t o Oak Ridge National Laboratory Relating t o a Digital D a t a Acquisition System f o r Use with the Homogeneous Reactor Test F a c i l i t y , CF-60-3-159, R. K. Adam e t al. (Mar. 29, 1960). 2Final ReDort t o O a k Ridge National Laboratorv Relating u --v - u t o a D i g i t a l Data Collecting and Computing Svstem f o r t h e RPXS Test Loop Facility, R. K. Adams e t al. (June LL, ~ r o u ) . ~

3MSRE Data Collecting and Handling Requirements, A Study Report, MSR-61-ll2, G. H. Burger (Aug. 15, 1961).

4Specification f o r a D i g i t a l Data Collecting and Computing System f o r t h e Molten S a l t Reactor Emeriment Located a t Oak Ridne National Laboratory, O a k Ridge, Tennessee, JS-81-170 (May 1, 1962). v

%se of On-Line Computer i n MSm Operation, CF-62-3-26, Haubenreich and J. R. Engel ( M a r . 6, 1962).

P. N.

6Toward Closed Loop Control i n Nuclear Plants, Nucleonics, 71 (June 1962). 7High Speed Monitor f o r Closed Loop Control, Colin G. Lennox and Albert Pearson, Nucleonics, 73 (June 1962). %nput Signal Functional Tabulation, SC-I&C-EGM-6230. 'MSRE Digital Data Collecting and Computer System Calculations, May 17, 1963. 'OTRWC Proposal f o r a TRW-340 D i g i t a l Data Collecting and Computing System, TRWC-63 157.

Womputer ~ a n u a fl o r MSRE Operators. 12Cross Reference Listing of MSRE Instrumentation and Control System Drawings, CF-63-2-2, R. L. Moore. 13MSRE Data Logger Signal Interconnection Wiring, ORNL Drawings D-HE-B-57456, 57457, 57458, 57459, 57460, and 57461.

L8E

388

k 0

m Q)

k PI

;;f

389

ORNL-DWG 6 4 - 6 4 e l A R

3 LOGGING TYPEWRITERS

ANALOG SIGNALS TO REMOTE INDICATORS.CONTROLLER*S,ETC.

INPUT KEYBOARD

OPERATOR CONSOLE INDICATING LIGHTS,

TYPEWRITER

ALARMS 36 ANALOG OUTPUTS

3 2 DIGITIZED OUTPUTS

REACTOR SYSTEM INSTRUMENTS

350 ANALOG INPUT SIGNALS

442 "ON-OFF'' SIGNALS

INPUT-OUTPUT EOUIPMENT

4-i

AND AMPLIFIERS)

CONTROL AN0 PROGRAM

t INSTRUCTIONS NO CONTROL DIGITAL INPUT

DIGITAL COMPUTER

CONTROL

: INFORMATION

2 MAGNETIC TAPE UNITS

Fig. 2.12.3. Computer System.

Block Diagram of MSFE Digital Data Collecting and

390

ORNL-DWG 64-628R

~. L

SPARE PARTS STORAGE

: \\

TABLE

DESK

POWER PANEL

c .c +

1/0 NO. 1

ANALOG SIGNAL INPUT

POWER SUPPLIES

DRUM MEMORY

POWER SUPPLIES

t .-e

0 r +

MAGNETIC TAPE

II MAGNETIC TAPE

PAPER TAPE PUNCH AND READER

Fig. 2.12.4.

X-Y PLOTTER

Layout of Data Room.

391

ORNL DWG. 67-1821

5-1

5.6

5 5

5-3

CONTROLSWITCHES

Fig. 2.12.5.

Computer Operator Console.

5-2

5.1

393

ib, I

2.13

MSRE Beryllium Monitoring System'

Atmospheric beryllium concentration i s monitored by 15 a i r sampling s t a t i o n s located a t s t r a t e g i c places throughout t h e reactor building. The beryllium content of the a i r i s monitored by drawing a i r through f i l t e r papers which a r e then collected and analyzed f o r beryllium content. The radiator a i r stack a i r i s monitored by an arc spectrograph. A i r is drawn through t h e spectrograph f o r a s e t period and then analyzed by t h e l i g h t spectrographic method. The r e s u l t of t h e analysis i s printed on a recorder located i n t h e spectrograph cabinet. The spectrograph i s equipped with a manual switch s o t h a t the coolant c e l l can be monitored during reactor maintenance operations.

'N. E. Bolton and T. C Whitson, Revised Beryllium Control Program f o r MSRE, ORNL-CF-63-11-44. (Supersedes ORNL CF-63-7-63. )

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134. 135. 136. 137. 138. 139. 140.

141. 142.

143.

144. 145. 146. 147. 148-1451. 150.

H. H. C. C. J. L. H. A. R. R. C.

H. P. J. E. L. R. C. P. A. T. H. J. B. G.

Koger Krakiovak Krewson Kryter Lamb Lane Lin Lindauer P. Litman H. Llewellyn L. Long I. Lundin N. Lyon G. MacPherson E. MacPherson L. Manning D. Martin H. Mauney McClain W. McClung E. McCoy F. McDuffie K. McGlothlan J . McHargue R. McWherter E. McNeese J . Metz S. Meyer R . Minue L. Moore A . Mossman W. I. W. C. E. A. S. B.

A. Nelms D. Neumann

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