ORNL-TM-2032 by Jon Morrow

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JAN 10 1968

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O A K RIDGE NATIONAL LABORAT operated by

UNION CARBIDE CORPORATION NUCLEAR DIVISION

1 %

for the

US. ATOMIC ENERGY COMMISSION

ORNL- TM- 2032 COPY

NO. -

DATE

November 1,

CLOSED-CIRCUIT TELEVISION VIENING I N MAINTENANCE O F RADIOACTIVE SYSTEMS AT O m *

R . L . Moore

ABSTRACT Considerations a f f e c t i n g t h e u s e of c l o s e d - c i r c u i t t e l e v i s i o n i n r a d i o a c t i v e systems a r e discussed. Equigment used f o r c l o s e d - c i r c u i t t e l e v i s i o n viewing at t h e Hcjmogeneous Reactor T e s t and a t t h e Molten-Salt Reactor Experiment i s described. The r e s u l t s of a r a d i a t i o n t e s t of a miniature, r a d i a t i o n r e s i s t a n t t e l e v i s i o n camera are presented.

*Paper p r e s e n t e d at t h e Winter Meeting of t h e American Nuclear Society, Oct 31-Nov. 3, 1966, P i t t s b u r g h , Pa.

NOTICE This document contains information of a preliminary nature and was prepared primarily for internal use a t the Oak Ridge National Laboratory. It i s subiect to revision or correction and therefore does not represent a final report. *Tt?.,

1967

LEGAL NOTICE T h i s report was prepored os on occount of Government sponsored work.

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Makes any worronty or representation, expressed or implied, w i t h respect t o the accuracy, completeness, or usefulness of the information contained i n t h i s report, or thot the use of any

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6. Assumes ony l i a b i l i t i e s w i t h respect to the use of, or for damages resulting from the use of any informotion, opporotus, method, or process disclosed i n t h i s report. As used i n the above, "person

octing on behalf of the

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h-,

CONTENTS Page Introduction..............................

Underwater Viewing i n t h e Homogeneous Reactor Test............................

Core Inspection i n t h e Homogeneous Reactor Test............................

Radiation Tests on a Miniature, RadiationResistant Tv Camera.....................

Remote Maintenance Viewing i n t h e MoltenS a l t Reactor Experiment..

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

Conclusions...............................

IN'JXOIKJCTION c

The ease with which maintenance of radioactive systems can be performed i s strongly dependent on t h e a b i l i t y t o view t h e operations. I n systems such as the Molten-Salt Reactor Experiment (MSRE), t h e radiation levels i n portions of t h e system a r e very high and viewing must be accomplished d i r e c t l y through highdensity windows or indirectly by means of optical devices or closed-circuit television. A t ORNL, the use of windows or optical devices i s t h e preferred method of viewing; however, i n some cases, supplementary viewing with closed-circuit television i s e i t h e r necessary or desirable. Radiation damage i s t h e most important consideration affecting t h e selection of television f o r viewing of maintenance operations. Other considerations a r e t h e ruggedness and r e l i a b i l i t y of t h e equipment. The radiation levels encountered i n many of t h e ORNL viewing operations a r e high i n comparison w i t h permissible biological dose rates, but low i n comparison t o the dose t h a t conventional electronic c i r c u i t r y can withstand. Commercial grade equipment i s used f o r these applications and l i t t l e , i f any, attempt i s made t o make the equipment radiation r e s i s t a n t . I n other cases t h e radiation l e v e l s a r e much higher, and radiation r e s i s t a n t equipment is required.

'1,

UNDEliWATER VIEWING I N "HE HOMOGENEXIUS REACTOR TEST -.

L Figure 1 shows a camera used f o r underwater viewing i n Hmogeneous

Fig. 1. HRT U n d e r w a t e r TV Camera Assembly.

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Reactor T e s t (HRT) maintenance operations. This assembly consisted of a standard Dage Models.lL2 AR camera, a flange$ tube, a Lucite face plate, and a Tygon tube. The Tygon tube enclosed t h e camera cable t o a point w e l l above t h e pool l e v e l and provided mechanical protection as w e l l as water-proofing. To keep t h e camera temperature within t h e recommended l i m i t , an a i r purge w a s supplied t o t h e camera through a small polyethylene tube and returned through t h e Tygon tube. The camera w a s manipulated manually by means of a r i g i d pipe and a p l a s t i c l i n e . Because of t h e shielding provided by t h e water and t h e variety of locations of t h e camera, no exact data were obtained on t h e dose which t h e camera accumulated. However, we estimate t h a t t h e dose r a t e varied ' from negligible t o 106r/hr and t h a t the total dose was about lo4 r. Some lens browning occurred, and more than t h e usual amount of trouble w a s encountered with t h e electronic c i r c u i t s . However, most of t h e trouble w a s routine o r was caused by shock and vibration. The only electronic trouble attributable t o radiation damage w a s t h e failure of several electrolytic condensers i n t h e camera. Replacement of these condensers restored the camera performance. CORE INSPEC'ZLON I N THE HOMOGENFDUS REACTOR TEST

Figure 2 shows a camera assembly developed f o r use i n locating and inspecting a hole i n the HRT core. The camera assembly, developed by

Fig. 2.

HRT Miniature TV Camera and Preamplifier.

6 Dage Electronics Division of Thompson Products t o ORNL specifications, consists of a camera equipped with a non-browning lens, a camera preamplifier, and a 10-f't interconnecting cable. A mirror and lighting assembly, consisting of a polished S t e l l i t e , right-angle mirror and a 50-cp spotlight bulb, w a s added at ORNL. The outside diameter of t h e camera i s 2 in., and t h e length (exclusive of lens, mirror, and lamp) i s 7-3/4 in. The only electronic cmponents i n t h e camera head a r e a type 6198A vidicon tube, a deflection c o i l assembly, one carbon resistor, and one ceramic capacitor. A l l other electronics a r e located i n t h e preamplifier or in t h e camera control unit. Separation of t h e camera and t h e preamplifier resulted in a considerable reduction i n s i z e of t h e assembly t o be inserted i n t h e reactor core and permitted t h e radiationsensitive components of t h e preamplifier t o be located i n a region of much lower activity, outside t h e reactor core. This camera was designed t o be interchangeable with the underwater camera previously described and used the sane camera control unit and monitors.

L) P

Figure 3 shows t h e camera assembly i n s t a l l e d on an articulated manipulator i n a remote maintenance mock-up of the HRT core and blanlcet vessels. Hydraulic control of t h e three manipulator joints, together with rotation of the camera by means of an e l e c t r i c motor, enabled t h e operator t o view any part of t h e exterior surface of the reactor core vessel. c

Figure 4 shows a mardpulator and camera assembly constructed f o r use i n viewing t h e i n t e r n a l surface of the HRl' core vessel. The assembly shown here i s foreshortened, as evidenced by t h e lines above and below t h e preamplifier. The actual distance from t h e preamplifier t o t h e camera i s 10 f't, and t h e overall length i s approximately 20 f't. The camera w a s required t o pass through a 2-in. diameter hole, i n a reactor access flange, located 14 f't below t h e t o p of a portable maintenance shield. I

In the manipulator shown i n Fig. 3, a fixed-focus lens w a s used, and focusing w a s accomplished by moving the camera. In t h e assembly shown i n Fig. 4, camera motion w a s r e s t r i c t e d t o v e r t i c a l motion along the centerline of t h e reactor, and remote focusing w a s required. This w a s accmplished with a remotely operated spur-gear mechanism, shown a t r i g h t of t h e camera. To permit insertion i n t o the reactor, t h e mechanism w a s designed t o r e t r a c t and fold inside a 2-in. diameter cylindrical surface which w a s concentric with and p a r a l l e l t o t h e outer surface of t h e canera. After the camera was inserted, t h e mechanism w a s lowered and rotated t o engage a spur gear on t h e camera-lens focusing ring.

Fig. 3.

HKC Miniat

Fig. 4.

ra and Articulated Manipulator.

HRT Miniature Tv Camera and Linear Manipulated.

a W I A T I O N TESTS OF A , I M RADIATIONm 1 m m Tv CAMERA ,

* .

Fortunately f o r t h e project (but unfortunately f o r our Tv camera program) the hole i n $he HKT core w a s found and inspected by semidirect optical means, and thege remotely manipulated TV camera systems were not needed. However, we did gain experience i n developing and operating these devices and w e did obtain some useful data. As part o f t h e camera evaluation, we i n s t a l l e d t h e camera i n t h e waterproof container shown i n Fig. 5 and exposed it t o intense gamma radiation produced by 'OCo slugs i n the canal at the Oak Ridge Graphite Reactor. During these t e s t s , the camera w a s focused on a miniaturized resolution chart, and performance w a s observed during i n i t i a l insertion and prolonged operation. The gamma dose r a t e was monitored with Ce(S04), dosimeters.

In the first t e s t , thescamera w a s equipped with a standard lens and lowered i n t o a 1.5 x 10 r/hr gamma f i e l d . There w a s no observable i n i t i a l effect as the camera w a s lowered i n t o t h e f i e l d ; however, t h e a x i m u m t a r g e t voltage after 20 min picture faded rapidly and required m of operation. After 1 hr of additional exposure i n a reduced f i e l d of approxima,tely 5 x 1 0 ' r'hour, t h e picture w a s not readable. An additional 18 hr of exposure w a s accummulated a t t h i s lower l e v e l before the camera w a s removed from t h e radiation field. The t o t a l dose w a s 5 x lo6 r. Subsequent examination showed no visual damage other than glass-browning of t h e lens and t h e vidicon tube. m e r replacement of t h e lens, %he

Fig.

5. HRT Miniature TV Camera Radiation Test Assembly.

camera operated s a t i s f a c t o r i l y w i t h only a slight loss of sensitivity. camera was equipped with a nonbruwning ' I n t h e second t e lens and lowered i n t o a 3,.9 x 106 r/hr gamma f i e l d . The only effect observed w a s a gradual loss of sensitivity, which w a s compensated by adjustment of the t a r g e t control. The duration of the t e s t was approximately 250 hr, and t h e t o t a l integrated dose received by t h e camera w a s approximately lo8 r. A t t h e end of t h e t e s t , the t a r g e t control had been advanced t o i t s maximum position, and there w a s a s l i g h t l o s s i n picture resolution. Subsequent t e s t s showed that approximately 20$ of the loss of s e n s i t i v i t y w a s due t o browning of t h e camera lens and t h e lamp bulbs. The remaining 8 6 w a s apparently due to browning of t h e vidicon faceplate. Replacement of t h e vidicon, t h e lens, and t h e lamps restored the o r i g i n a l s e n s i t i v i t y of t h e equipment. Because of t h e time and expense involved, and because t h e lo8 r dosage obtained exceeded the dose expected i n t h e HF?P viewing operation, no attempt w a s made t o determine the ultimate l i f e of t h e camera. REMOTE MAINTENANCE VIEWING I N THE NOLTEN-SfiT REACTOR MPERIMENT

Figure 6 shows a Kintel, model 2511 radiation-resistant camera presently used i n mairrtenance operat ions a t t h e Molten-Salt Reactor Experiment ( M S ~ ) .The use of television i n MSRE maintenance operations

Fig. 6.

MEW Remote Maintenance TV Camera and Preamplifier. \

is presently limited t o those operations associated with removal of large camponents. For these operations large cell-access openings a r e required, and t h e Wntenance operations must be performed remotely from a shielded maintenance control room. To supplement the d i r e c t view available through windows i n t h e maintenance control roam, indirect, orthogonal viewing of these operations w i l l be provided by two cameras mounted on portable stands which can be moved by use of an overhead crane. A t h i r d camera i s also provided f o r use as an operating spare. The cameras are radiation and shock resistant, and w i l l withstand continuous exposure t o 1-Mev gamma radiation at a dose r a t e of about, lo5 r/hr f o r 100 hr without degradation of performance. Replacement of t h e vidicon tube and the lens w i l l restore t h e camera erformance u n t i l the camera has accumulated a radiation dosage of 108 r. Each camera i s connected by 50 ft of radiation-resistant cable t o a preamplifier which, i n turn, i s connected by a 100-f't cable t o a camera control unit. The preamplifier i s not radiation r e s i s t a n t and must be shielded f r o m high-level radiation. The camera control units f o r the t h r e e cameras a r e mounted i n a console i n t h e maintenance control room together w i t h t h e monitors and associated camera controls. Figure 7 shows the assembled console. Although three camera systems a r e i n s t a l l e d , only two monitors a r e used. A video switching system permits t h e operator t o display t h e signal fran any of t h e three cameras on e i t h e r or both monitors. The joy s t i c k control mounted on t h e front of t h e console t a b l e enables t h e operator t o control pan, tilt, focus, and zom motions with wrist-and finger actions. Other l e s s frequently

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used controls and adjustments are located on t h e sloping panel i n front of t h e operator. Space was provided on t h e t a b l e f o r t h e addition of crane controls. ' Except f o r t h e vidicon tube and a small'(nuvistor) vacuum tube i n t h e camera, the system uses solid-state components throughout.

The complete system produces high-quality pictures, and performance i s stable over a wide range of variation of l i n e voltage, l i n e frequency, ambient temperature, and humidity. Ekcept f o r a few minor f a i l u r e s which occurred during t h e f i r s t few weeks of acceptance testing, t h e r e l i a b i l i t y of t h e system has been excellent. The design o f t h i s system and the selection and procurement of components w a s strongly influenced by prior experience at ORNL w i t h the use of closed-circuit television i n maintenance operation a t t h e HIZT and i n t h e MSRF, remote-maintenance demonstration f a c i l i t y . CONCLUSIONS

The HRT operations demonstrated t h a t t h e use of television f o r viewing i n high-level radiation environments w a s practical. The t e s t s performed i n t h e maintenance demonstration f a c i l i t y demonstrated t h a t orthogonal viewing w a s preferred t o three-dimensional viewing f o r MSRE maintenance operations. Both operations demonstrated that systems used f o r remote maintenance must be rugged and easy t o operate and must have a high degree of performance and r e l i a b i l i t y . "he conclusions drawn f r o m t h i s experience have been supported and supplemented by t h e experience gained by uthers i n similar operations. Since viewing equipment must be operable when needed, maintenance personnel have been understandably reluctant t o use t h e low-reliability equipment available i n t h e past. This equipment used vacuum tube c i r c u i t r y throughout, ive t o shock and vibration, and r e l i a b i l i t y ranged f r o m n a l t o poor. It i s m y belief t h a t t h e t television has now advanced t o t h e s t a t e of t h e art of c r e l i a b i l i t y of presently available point where t h e perfomanc t h e requirements f o r remote maintenance equipment are commensurate viewing and t h a t the system i n s t a l l e d at t h e MSRE w i l l be a useful and v i t a l t o o l i n mure maintenance operations.

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