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ORNL2890 Reactors Power TID-4500 (15th ea.)

Contract No. W-7405-eng-26

MOETEN-SALT REACTOR PROGRAM QUARTERLY PROGRESS REPORT

For Period Ending October 31, 1959

H. G. MacPherson, Project Coordinator

DATE ISSUED

MAR 8 1960

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

MOLTEN-SALTREACTORPROGRAMQUARTERLYPROGRESSREPORT

SUMMARY Part 1. 1.1

Engineering

and Component Development

Component Development and Testing

Development work on molten-salt-lubricated bearings was continued. In the series of seven concluded tests the start-stop tolerance of ,journal In all but two cases, tests bearings made of INOR- was investigated. Time of operation ranged were carried to seizure or impending seizure. from 3 to 379 hr. The largest number of start-stop 260. Signs of metal-to-metal rubbing were evident

cycles per test was on bearing surfaces.

Serious ingassing was observed during bench tests of the hydrodynamic thrust bearing. Remedial efforts are being continued, and further bench tests are proposed. Two pumps equipped with hydrodynamic bearings were bench tested and Seizure occurred in both after short operation then tested in molten salt. in salt,

and the failures

were attributed

to dry bearings

caused by ex-

cessive restrictions in the suction path of the bearings, No evidence of self-welding was found between INOR- surfaces of dry friction for INORin molten salt at 1200Â°F. Coefficients

immersed on INOR-

8 and for INOR- on stainless steel were found to be fairly constant in the 900 to 1800'F temperature range, a good average value being 0.25. Construction of the Remote Maintenance Demonstration Facility, inThe layout-is being modified cluding the viewing equipment, _was comI$eted. The loop and additional.maintenance tool&are being made as need arises. was tested fork vacuum~tightne'ss~~ .'The~]remote viewing equipment'was modified to improve its reliability s&d&+re quality. A set .of four television ~.~ ,Ali maJor com.'&&e~as provides nearly-%$ - ;:-viewing coverage of the cell. po~~nts:excep~.the,core-vessel-ha~~'been di-sconnected- and reinstalled bye I -~ . remote means &lea~st--&n&c ~~~'Theloop.~will ~~~'The~'loop.~will be-run-with--molten saltafter _.removaland installation of _.'the _-., core~vessel have been successfully accom,; <-. -plished, .: jI- .__ ---~.,.:;:.-"-- .-~ co@leted one year of operating time completed ~Eleven long~term corrosionâ&#x20AC;&#x2DC;loops in this w

quarter.

Tests on two INOR-

minated for metallurgical

examination;

loops and one Inconel loop were terthe results are not yet available.

One loop w a s shut down temporarily due t o pump failure and a subsequent o i l fire.

The t e s t w i l l be continued a f t e r r e p a i r s and reloading.

The

second of three sample i n s e r t s was removed from loop 9354-4 a f t e r 10,000

Two

Findings on t h i s i n s e r t a r e described i n Sec 2.1.

h r of operation.

new INOR-8 loops were s t a r t e d up with BULT-14 s a l t .

These loops have

double-walled i n s e r t s at t h e e x i t of the second resistance heater. The PKP c e n t r i f u g a l pump with Fulton Sylphon bellows-mounted s e a l has logged 17,878 hr of operation i n NaK at 1200°F. w a s observed.

Only negligible leakage

The MF-type c e n t r i f u g a l pump i s operating i n a region of

c a v i t a t i o n i n s a l t 30, and service time of more than 20,000 hr has been recorded t o date.

The average upper- and lower-seal leakage r a t e s amounted

t o 30 and 1 2 cc/day, respectively. Trouble-free operation of t h e small frozen-lead- pump s e a l continued. Total service time i s 12,000 hr. The large frozen-lead-seal test w a s d i s continued. An apparatus f o r t e s t i n g graphite-metal s e a l s i s under construction.

A s e a l i n t h e annulus between a 5-in.-OD graphite tube and a l a r g e r , mating Inconel section w i l l be attempted f i r s t . Sectioning of the f i r s t two i n - p i l e loops w a s completed, and metallographic and a n a l y t i c a l examinations are i n progress.

A t e s t program w a s

launched t o explore t h e behavior of graphite under conditions similar t o those encountered i n graphite-moderated molten-salt reactors.

Bench t e s t s

have been completed, and t h e f i r s t experiment i s scheduled f o r i n s e r t i o n i n the MTR e a r l y i n 1960. 1.2

Engineering Research The v i s c o s i t y of t h e f u e l mixture BULT-14 ( LiF-BeF2-UF4-ThF4, 67-18.5-

0.5-14 mole

4)w a s

determined i n t h e t e q e r a t u r e range from 550 t o 800°C.

Comparison with previous r e s u l t s on other s a l t compositions containing a high percentage of ThF4 shows a maximum deviation of l@ of t h e temperature range.

Enthalpy measurements w i t h t h e BeLT-15 mixture

(LiF-BeF2-ThF4, 67-18-15 mole Btu-1b-l. (

a t the extremes

yielded a heat capacity varying from 0.343

a t 1000°F t o 0.304 Btu-lb-'0 (

a t 1500°F.

The appa-

r a t u s f o r measuring the thermal expansion c o e f f i c i e n t , @, of molten s a l t mixtures was t e s t e d by using HTS (NaN02-NaN03-KN03, 40-7-53 w t

$1.

The

c o e f f i c i e n t @ w a s 3.63 x 10-4/"C between 215 and 315°C; comparison with data obtained from density measurements shows good agreement. iv

-w 5

Preliminary r e s u l t s were obtained f o r heat t r a n s f e r w i t h BUET-14 flow-

ing i n heated Inconel and INOR-8 tubes.

The system w a s operated continu-

ously f o r about f i v e weeks without d i f f i c u l t y .

Axial temperature p r o f i l e s

show the e f f e c t of the laminar-turbulent t r a n s i t i o n i n t h e hydrodynamic boundary l a y e r i n t h e entrance section of the tube.

The heat t r a n s f e r ap-

pears t o be about half t h a t which would be predicted from e a r l i e r studies with molten salts; t h i s discrepancy may r e s u l t from an uncertainty i n t h e value of t h e thermal conductivity f o r BUET-14 used i n the analysis of the data.

A 2 3 difference between t h e r e s u l t s i n the Inconel and INOR-8 tubes

cannot be explained, a t present. Part 2.

2.1

Materials $tudies

Metallurgy I n an e f f o r t t o j o i n graphite t o graphite and graphite t o metal f o r

molten-salt r e a c t o r service, an a l l o y ( 4 6 Ti48qd Zr-44

Be) w a s developed

and had s a t i s f a c t o r y wetting and f l a r i n g c h a r a c t e r i s t i c s .

However, because

of i t s poor corrosion resistance t o molten fluorides, other a l l o y systems a r e being investigated.

Promising a l l o y s i n the Au-Ni-Ta system a r e under study, and a l l o y s i n t h e Ni-Nb, Ni-Mo, Ni-Nb-Mo, Ni-Nb-Ta, Pd-Ni-Ta, and

Pd-Ni-Mo systems a r e being prepared f o r t e s t i n g .

Preliminary work i n

e l e c t r i c - r e s i s t a n c e brazing of graphite t o graphite, using molybdenum as t h e brazing alloy, has a l s o been undertaken. The second of three INOR-8 corrosion i n s e r t s w a s removed a f t e r 10,000

hr from an INOR-8 forced-convection loop. cated t h e i n s e r t t o

Weight-loss evaluations indicorresponds t o a w a l l t h e w a l l i s assumed. which c i r c u l a t e d he loops showed normal at-

t o a depth ranging from o depths ranging from

c i a b l e oxide contamied according t o t h e i r resist-

300'F tests.

i n 100-hr

Grade GT-123 w a s found t o have a bulk-volume permeation of l e s s

than 0.54, t h e m a x i m u m specified f o r the reactor, despite t h e high t e s t V

pressure.

Bismuth has been used t o f i l l the accessible voids i n AGQT

graphite p r i o r t o exposing it t o molten salts.

Tests a r e being conducted

t o determine t o what extent t h e bismuth-permeated graphite w i l l pick up

s a l t s during standard permeation t e s t s . When held i n d i r e c t contact w i t h graphite f o r 20 hr a t 1300째F, LiFBeF2-UF4 (62-37-1 mole nants i n the graphite.

8 ) apparently

gettered completely t h e oxide contami-

No p r e c i p i t a t i o n was detected radiographically i n

t h e LiF-BeF2-ThF4-UF4 (67i18.5-14-0.5 mole '$I) a f t e r it had been i n contact with graphite f o r 500 h r a t 1300째F i n ' a vacuum. INOR-8 specimens showed no metallographic indications that carburiza-

t i o n had occurred a f t e r being i n contact w i t h TSF graphite a t 1000 p s i for 700 h r i n salt environment a t 1300째F. Four braze materials showed good resistance t o f u e l 130 (LiF-BeF2-UF4, 62-37-1 mole $) during a 5000-hr corrosion t e s t i n a thermal-convection loop with a 1300'F hot-leg temperature.

Corrosion t e s t s of 100-hr duration

indicated t h a t t h e usefulness of titanium-, zirconium-, o r beryllium-cont a i n i n g brazing a l l o y s i n f u e l 130 would be limited i n pure nickel o r INOR-

8 containers at 1300'F.

Heavy a t t a c k due t o t h e t r a n s f e r of the r e f r a c t o r y

material t o t h e nickel o r INOR-8 container walls w a s observed. 2.2

Chemistry and Radiation Effects Detailed description of t h e t e n subsidiary binary and ternary systems

incorporated i n the LiF-BeF2-UF4-ThF4 quaternary system i s nearly completed. Among t h e questions as yet incompletely answered by phase-equilibria studies on breeder f u e l s i s t h a t of d e t a i l e d c r y s t a l l i z a t i o n paths f o r compositions of reactor i n t e r e s t . The i d e n t i f i c a t i o n of the isomorphic compounds Na;F-BeF2-3UF4and N@*BeF2*3ThF4i s of e s p e c i a l academic i n t e r e s t since Na;F*BeF2*3UF4has been erroneously reported i n t h e l i t e r a t u r e as NaF*.&W&.. The s o l u b i l i t y of HI? i n molten f l u o r i d e breeder f u e l s has been corr e l a t e d w i t h solvent composition by means' of a concentration scale based on t h e excess or deficiency, i n equivalent per cent, of a l k a l i Kluoride f o r complete coordination of higher-valence cations i n the solvent; t h a t is, Na2BeF4 and Na3ZrF7 correspond t o complete coordination and represent

t h e l i m i t of complexing power of t h e cation. Exchange reactions i n molten fluorides, p a r t i c u l a r l y those that might be of i n t e r e s t i n reprocessing schemes, a r e being explored. vi

Many of the

reactions p o t e n t i a l l y useful f o r removing r a r e e a r t h s a r e subject t o

in-

terference by e s s e n t i a l ingredients i n t h e f u e l . The d i f f u s i o n of chromium, which i s t h e r a t e - l i m i t i n g process f o r long-term corrosion i n molten fluoride breeders, is strongly dependent on grain s i z e , and hence on annealing h i s t o r y .

Under equivalent conditions

there i s no s i g n i f i c a n t difference between t h e d i f f u s i o n c o e f f i c i e n t s of chromium i n INOR-8 and i n Inconel; thus t h e steady-state corrosion rate

i s predicted t o be higher by a f a c t o r of 15/7 i n Inconel, since t h i s i s t h e r a t i o of chromium concentration i n t h e two a l b y s . Except f o r one unexplained and palpably misf'unctioning case, sampled corrosion t e s t loops are demonstrating predictable and s a t i s f a c t o r y behavior i n long-term tests. Exploratory s t u d i e s on t h e hygroscopicity of f u e l s and on t h e possib i l i t y of drying a t low temperatures without extensive hydrolysis have given additional q u a l i t a t i v e evidence of t h e extreme s e n s i t i v i t y of t h e fuels t o moist a i r .

Evidence of formation of a graphite i n t e r c a l q t i o n compound w i t h MoFs was found, but t h i s compound i s not expected t o be encountered i n r e a c t o r operation. Several grades of extruded graphite, but none of t h e molded types, show less than 1 vol $ permeation by breeder fuels a t 60 t o 75 p s i g and

1300'F. About 740 kg of p u r i f i e d f u e l mixtures w a s processed during t h e quarter.

INOR-$ corrosion test capsules have been removed f r o m t h e MTR after

solubilities.

The N02-W system i s a l s o u n a t t r a c t i v e because of t h e low

s o l u b i l i t y of ThF4, although that of UF4 i s higher.

vii

CONTENTS

S~Y............................................................

iii

PART 1. ENGINEERING AND COMPONENT DEVEIDPMENT 1.1.

COMPONENT DEVELOPMENT AND ~ S T I N G . . . . . . . . . . . . . . o o . . o o o o o * o * o o Molten-Salt-LubricatedBearings for Fuel Pumps............... Hydrodynamic Journal Bearings............,......... Hydrodynamic Thrust Bearings.............................. Test of Rrmp Equipped with One Molten-Salt-Lubricated Journal bearing.........................^^........^^^.^. Self-Welding of INOR-8.....................0~..~...00.0~00 Friction Tests on INOR-8........................~..~~s~...

.................................. ..................................*..... Frozen-Lead Pump Seal........................................ Remote Maintenance Demonstration Facility.............. ......

Mechanical Seals for Pumps. MF Performance T-IOop..

Design, Construction, and Operation of Materials-Testing Loops.................................................... Forced-Circulation Corrosion Loops........................ Graphite-Metal Seal Tests..........o.........................

10 1.0

14 14 16

In-Pile Loop................................................. I

1-20 ENGMEERING IIESEARCH..............oooo.o.....o*.........o...o Physical-Property Measurements............................*.. Viscosity................................................. Enthalpy and Heat Capacity.... Thermal Expansion.........................................

t-Transfer S

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

...................... .................... ...................... .. ..........e....

................. ......... ect Contact.... . e ....

el UO...................

19 19 19 20 21

33 33 35 35 43 43 44 45 45

2.2.

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

CHEMISTRY AND RADIATION STC.E Phase Equilibrium Studies The System4 F U . 4 .2 F e B The System BeF2-ThF4 The System NaF.BeF2-W4 Molten-Fluoride Solvents The Compound Nal?*BeF2.3UF4 Gas Solubilities in Molten Fluorides Solubility of KF in Fuel Solvents

......................... ......................... Fission-Product Behavior..................................... Exchange Reactions in Molten Fluorides.................... Chemistry of Corrosion Processes Self-Diffusion Coefficients for Chramium in Nickel Alloys Chemical Analyses of Corrosion Test Loops Solubility of CrF2 in LiF-BeF2 (62-38 Mole $1 Equilibrium Measurements on the Reduction of FeF2 by HZ in LiF-BeF Equilibrium Measurements on the Reduction of CrF2 and FeF2 by H2 in LiF-BeF2 (62-38 Mole $I) Hygroscopic Behavior and Dehydration of Breeder Fuels

................... ..... Graphite Compatibility Studies............................... Penetration of Graphite by Molten Fluorides............... Intercalation of Graphite with Molten Salts............... Diffusion of Rare-Earth Fission Products in Graphite...... Preparation of Purified Materials ............................ Technological Operations.................................. Molten Ammonium Bifluoride as a Reagent................... Radiation Effects............................................ Corrosion Tests Under Radiation........................... 2.3.

49 49 49 49 49

50 52 52

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

.............................................. Thorium Fluoride Solubility in Aqueous NH4F Solutions........ Fuel-Component Solubility in ClF3.HF'. ........................ Fuel-Component Solubility in N02-HF ..........................

FUEL PROCESSING

54 54

55 59 61

62 63 65 65 66 67 67 67 68 69 69 70 70 71

. c

PART 1.

ENGINEERING AND COMPONENT DEVELOPMENT

1.1 COMPONENT DEVELOPMENT AND TESTING

Molten-Salt-Lubricated Bearings f o r Fuel Pumps Hydrodynamic Journal Bearings

Investigations of journal bearings operating i n molten s a l t 130 (LiF-

BeF2-UF4, 62-37-1 mole

8 ) were

continued throughout t h e quarter.

Four

t e s t s were performed t o i n v e s t i g a t e s t a r t - s t o p a b i l i t y of carburized

INOR-8 journals operating a t temperatures from 1200 t o 1500'F

i n INOR-8

bearings having three axial grooves; three were conducted t o investigate performance of t h e three-helical-groove INOR-8 bearing a t 1200'F.

A test,

No. 22, of t h e performance of Inconel f o r comparison with INOR-8 i s i n progress. A l l t e s t pieces were f i t t e d w i t h a r a d i a l clearance of 0.005 i n . (measured at room temperature). A summary of the t e s t conditions i s presented i n Table 1.1.1. Test 15 w a s terminated when impending Geizure became evident upon r e s t a r t i n g t h e run following a 30-min shutdown for r e p a i r s i n t h e o f f gas l i n e .

The support pins were twisted and p a r t i a l l y severed from the

bearing sleeve.

T h i s condition, a r e s u l t of poor a'ttachment, possibly

gave r i s e t o t h e impending failure. Test 16, which w a s a repeat of t e s t 15 w i t h new p a r t s , w a s terminated t

on schedule.

Examination indicated t h a t rubbing damage was somewhat l e s s

than t h a t experienced during a similar test at 1200'F.

Test 17 w a s terminated by seizure during s t a r t - s t o p cycle 129.

The

t e s t pieces exhibited g a l l i n g and metal t r a n s f e r , evidences of rubbing.

Test 20 w a s performed with bearing grooves of the same cross section

as t h a t used i n t e s t 19, but with a flow r e s t r i c t o r over t h e dischazge

".. . .

...___

Table 1.1.1. Hydrodynamic-Journal-Bearing Tests; Summary of Test Conditions

Material

Test

No*

Bearing

Journal

Groove

Speed

Operating Temperature

Configuration*

(rpm)

(OF)

Radial Load (lbf)

Operating Time (hr)

start-stop Cycles

INOR-8

INOR- 8, carburized

Axial

1200

1200 1300

200

21 24

INOR- 8

INOR-8, carburized

Axial

1200

1300

200

123

260

INOR-~

INOR-~, carburized

Axi a1

1200

1400

200

129

INOR-8

INOR-8, carburized

Axial

1200

1500

200

INOR-8

INOR- 8

Helic a1

1200

10-300

136

INOR-8

Helical

1200

10-150

INOR-8

Helic al

1200 600

1200 1200

500

379

106

1200

200

336

Inc one 1

Inconel

Axial

375

*All, bearings contained t h r e e grooves.

c T

end of t h e grooves. The flow r e s t r i c t o r w a s a t h i n d i s k having an inside diameter 0.010 i n . l a r g e r than the inside diameter of the bearing. The t e s t w a s terminated because of a s l i g h t roughness i n t h e drive-motor power t r a c e .

Examination of the t e s t pieces d i d not reveal any apparent

cause f o r t h i s problem. T e s t 2 1 w a s a continuation of t e s t 20, except t h a t the flow r e s t r i c t i o n on t h e bearing grooves w a s reduced by adding a 1/16- by 1/16-in. Vnotch t o t h e shim a t each groove.

The t e s t was terminated by apparent

seizure i n t h e 600-rpm run with 375 l b

load. There w a s s l i g h t evidence

of rubbing between t h e t e s t surfaces. Test 22, now i n progress, i s being performed with an Inconel journal and a three-axial-groove Inconel bearing. Hydrodynamic Thrust Bearings Bench tests were performed on the thrust-bearing t e s t e r with t h e t h r u s t bearing immersed i n o i l .

Gross ingassing w a s found, and a number

of modifications were investigated as possible corrective measures. Seve r a l of these were promising, but f u r t h e r bench t e s t i n g with other modifications i s i n order p r i o r t o hot t e s t s i n molten salt. T e s t of FUnp Equipped w i t h One Molten-Salt-Lubricated Journal Bearing

Bench t e s t s were conducted on t h e o r i g i n a l pump design, shown i n Fig. 1.1.1, t o investigate t h e perfomnance of the overhung motor, of the o i l s l i n g e r i n pumping lubricant t o t h e upper bearing, and of the journal bearing immersed i n o i l . can be reduced t o t o l e r a b l e

flow of l u f

return ports.

UNCLASSIFIED ORNL-LR-WVG 44831

SALT-LI DYNAMIC

Fig.

1.1.1.

Pump with Molten-Salt-Lubricated Journal Bearing and with an Overhung Motor.

i @ J !

UNCLASSIFIED ORNL-LR-DWG 41765A

Fig. 1.1.2. Pump with Molten-Salt-Lubricated Journal Bearing and with a Flexible Shaft Coupling to a Conventional Motor.

Two journal-bearing configurations were t e s t e d i n o i l at room tem-

perature and i n molten salt 130 (LiF-BeF2-UF4, 62-37-1 mole

$1 a t 120O0F.

The o i l t e s t s were performed with t h e pump assembled except f o r the imp e l l e r ; t h e complete assembly w a s operated i n the t e s t s with molten salt. The f i r s t bearing t e s t e d had three a x i a l grooves and was mounted r i g i d l y . The bearing operated successfully i n o i l under load, and the purnp w a s subsequently placed i n operation w i t h molten s a l t .

The punrp w a s r o t a t e d

f o r 10 min a t 1000 rpm and another 10 min a t 1200 rpm; at 1200 rpm the pump delivered a flow of 100 gpm.

The operation w a s terminated as a re-

sult of seizure of the pump r o t a r y element, which i s believed t o have oc-

curred i n the molten-salt-lubricated journal bearing. The other bearing had three h e l i c a l grooves w i t h a flow r e s t r i c t i o n a t t h e discharge (upper) end.

The bearing was mounted f l e x i b l y on gim-

It operated s a t i s f a c t o r i l y i n o i l but subsequently f a i l e d by s e i -

bals.

zure i n operation w i t h molten s a l t . Study of the configuration near the bearing revealed t h a t t h e imp e l l e r hub probably presented too great a r e s t r i c t i o n t o flow of salt i n t o the bearing a t t h e lower end; the bearing therefore pumped i t s e l f dry i n t h e molten-salt t e s t s . f o r both t h e f a i l u r e s .

T h i s condition w a s probably responsible

During t h e o i l t e s t s t h i s condition was not

present, since they were made without the impeller present.

The flow

passage i n t o t h e bearing has been increased by removal of material. from t h e impeller hub and the lower end of the bearing sleeve.

Preparations

a r e being made f o r a t h i r d t e s t . Self-welding of INOR-8 One INOR-8 self-welding experiment w a s performed a t 1200째F, on loosef i t t i n g pins pressing against t h e sides of holes, a condition encountered with gimbal-mounted bearings.

The t e s t w a s performed i n a bath of molten

s a l t 107 f o r 1000 h r under a load of 200 l b f . Examination of the t e s t pieces revealed no evidence of self-welding.

A similar t e s t w i l l be per-

formed a t 1500OF. F r i c t i o n Tests on IN OR-^ F r i c t i o n t e s t s were performed a t MIT' and on INOR-8 against s t a i n l e s s s t e e l . 'E. 8

Rabinowicz.

on INOR-8 rubbing against INOR-8

Four tests were performed, each of

which covered a temperature range of 70 t o 1830째F.

The r e l a t i o n between

the c o e f f i c i e n t of f r i c t i o n and temperature i s shown i n Fig. 1.1.3.

Note

t h a t i n each t e s t t h e c o e f f i c i e n t drops off over the range of 700 t o 900째F and then, i n general, remains a t approximately 0.25 on up t o 1830째F. Mechanical Seals f o r Pumps The modified Fulton Sylphon bellows-mounted s e a l , in a

* undergoing

test

PKP type of c e n t r i f u g a l pump, has accumulated an additional 3048 h r

of operation since t h e previous report period, f o r a t o t a l of 17,878 hr. The pump continues t o operate a t constant conditions of 1200째F loop temperature, 2400-rpm s h a f t speed, and 1200-gpm NaK flow.

The s e a l leakage

i n both t h e test seal and the Durametallic upper s e a l has been negligible. The pump w a s stopped once t o check t h e drive-motor brushes. MF Performance Loop A n MF type of c e n t r i f u g a l pump has continued i n operation2 and has

logged more than 20,000 h r of continuous operation.

Since the previous

r e p o r t period t h e pump has continued operation i n a region of c a v i t a t i o n a t 2700 rpm, 645 gpm, and 2.5 p s i g pump-tank cover gas pressure i n molten

2MSR Quar. Prog. Rep. July 31, 1959, ORNL-2799, p 19.

Coefficient of Fig. 1.1.3. INOR-8 Against Stainless Steel.

Friction vs Temperature for

INOR-8

Against

INOR-8

and for

salt 30 a t 1200'F.

During t h e quarter the pump w a s stopped twice

- once

t o replace the a i r f i l t e r on the motor-generator s e t and once ( f o r 10 min) t o replace the brushes i n the d-c drive motor.

The pump upper- and lower-

s e a l leakage r a t e s have averaged approximately 30 and 12 cc/day, respectively. Frozen-Lead Pump Seal The small frozen-lead pump s e a l being t e s t e d on a 3/16-in.-dia

shaft,

as described p r e v i ~ u s l y ,has ~ operated continuously since the start of i t s operation on June 13, 1958. The accumulated operating t i m e , as of October

31, 1959, was 12,000 h r .

There was slight leakage of lead during t h e f i r s t

100 hr of operation; t h e r e has been no f u r t h e r leakage. Testing of the large frozen-lead pump s e a l w a s discontinued. Remote Maintenance Demonstration F a c i l i t y Construction of the equipment i n t h e Remote Maintenance Demonstration F a c i l i t y w a s completed during July. The e n t i r e loop of piping (made of

3-1/2-

and 6-in. Inconel pipes) w a s stress-relieved a t 1500째F f o r 2 hr.

A check of torque s e t t i n g s on the b o l t s of the freeze flanges a f t e r t h e

s t r e s s - r e l i e v i n g operation revealed t h a t a l l suffered l o s s of tightness; i n some instances the b o l t torque w a s reduced t o a s l i t t l e a s 40$ of the original setting.

To assure constant b o l t torque on the freeze flange

j o i n t s during thermal cycling, t h e use of disk springs was suggested. Three s e t s of Bellville-type springs are presently being t e s t e d f o r t h i s application. A system of controlling the air flow t o the cooling passages of the

freeze flanges was designed, and construction drawings were completed.

It i s believed t h a t such a flow control w i l l eliminate the adverse e f f e c t s of the d i f f e r e n t i a l thermal expansion between t h e Inconel flanges and copper s e a l r i n g s thermal cyclings

and w i l l improve t h e gas-tightness of t h e system during

The loop w a s t e s t e d f o r vacuum-tightness with t h e flange b o l t s t i g h t ened t o t h e i r o r i g i n a l s e t t i n g a f t e r stress-relieving. A pressure r i s e of 52 p w a s recorded i n a 56-hr period with t h e loop i s o l a t e d . The system

w a s o r i g i n a l l y evacuated t o 17 p. 3MSR Qum. Frog. Rep. Oct. 31, 1958, ORNL-2626, p 23.

Television equipment f o r remote viewing of the c e l l has been i n stalled.

The closed-circuit system c o n s i s t s of four remotely operated

cameras.

Two of these, equ

s t e r e o p a i r (Fig. 1.1.4>,

ed w i t h three-lens t u r r e t s and used a s a unted on a d o l l y and are f r e e t o t r a v e l

t h e whole length of t h e c e l l on a r a i l mounted on top of t h e control room.

The other two, with "auto zoom" lenses, a r e mounted i n other locations of the cell. cell.

The complement of cameras allows nearly 90% coverage of t h e A l l four cameras nto a p a i r of monitors mounted on a s t e r e o

viewer above t h e General

manipulator console (Fig. 1.1.5)

The p i c t u r e q u a l i t y and equipment r e l i a b i l i t y were not s a t i s f a c t o r y during e a r l y operation; however, w i t h t h e assistance of a f a c t o r y representative, l o c a l maintenance personnel were able t o correct most of the difficulties.

Upon completion of suggested modifications, t h e frequency

of maintenance on t h e viewing equipment w a s reduced, a t times, from 1 i n 24 h r t o 1 i n 200 h r of operation.

Remotely viewed operation of the General Mills manipulator and overhead crane w a s s t a r t e d i n Se

erriber.

Tasks successfully executed by re-

mote means t o date include removal and i n s t a l l a t i o n of t h e FK salt pump,

Fig. 1.1.4. Stereo Camera Pair for Viewing Operations in the Remote Maintenance Demonstration Facility.

Control Center for General Mills Manipulator Console, Closed-Circuit TeleFig. 1.1.5. vision, and Overhead Crane; Remote Maintenance Demonstration Facility.

i t s motor, the dump tank, t h e freeze valve, the e l e c t r i c heater and i n -

s u l a t i o n u n i t , and the heat exchanger. Numerous modifications were incorporated i n t h e loop, as t h e need arose, e i t h e r t o improve v i s i b i l i t y through the cameras o r t o f a c i l i t a t e maintenance operations.

Removal and i n s t a l l a t i o n of the heat exchanger,

for example, were made practicable by providing guide pins and funnels a t the mating flanges and by adding a screw-jack mechanism t o close and back away t h e heat exchanger (Figs. 1.1.6 and 1.1.7). A v a r i e t y of t o o l s were fabricated and a r e i n use i n conjunction

with t h e overhead crane and t h e manipulator. Remote removal of the core v e s s e l i s scheduled p r i o r t o running molten s a l t through the loop.

Upon completion of the salt run t h e dis-

assembly-assembly cycle w i l l be repeated on a l l components.

V 13

Fig. 1.1.7. Auxiliary Screw Jack for Manipulating the Heat Exchanger in the Remote Maintenance Demonstration Foci lity.

Desim, Construction, and Operation of Materials-Testing MODS Forced-Circulation Corrosion Loops The operation of long-term forced-circulation corrosion-testing loops w a s continued.

Table 1.1.2 gives a summary of 16 loop operations during

t h e period, with accumulated hours of operation a t t e s t conditions.

of t h e loops have operated f o r a f u l l year.

Eleven

(Four other loops with one

year of operation had been terminated e a r l i e r . 4 , Operation of INOR-8 loops Em-8 and -9 and Inconel loop 9377-4 w a s terminated during t h i s period f o r metallurgical examination.

The two

INOR-8 loops had operated without an incident; no dumping o r freeze-up

of the s a l t w a s experienced i n the loops although both sustained a t least f i v e building-power f a i l u r e s .

The LFB pump i n the Inconel loop had been

â&#x20AC;&#x2DC; E R Quar. Prog. Rep. Jan. 31, 1959, ORNL-2684, p 61; Apr. 30, 1959, Om-2723, p 33; J u l y 31, 1959, ORNL-2799, p 31. 1

Comments h m p has been replaced; loop i s awaiting

a new batch of salt Normal operation I n s e r t sample No. 2 removed a t 10,OOO hr; operation resumed Tubing sample removed a f t e r 1 yr; operation resumed Normal operation Terminated Oct. 21, 1959 Terminated Oct. 12, 1959 Tubing sample removed after 1yr; operation resumed Terminated Sept

. 14,

1959

Normal operation

N o m 1 operation Normal operation Normal operation

Normal operation Began operation Oct. 14, 1959

133 LIF-BeF2-ThF4 (71-16-13) 134 LiF-BeF2-ThF4-UFq (62-36.5-1-0.5) 135 NaF-BeF2-ThF4-UF4 (53-45 51-0.5) 136 LiF-BeF2-UF4 (70-10-20) BUI3-14 LiF-BeF2 -ThF4-UF4 (67-18.5-14-0.5 **All tests are operating with a 1300째F high w a l l temperature and a aT of 200째F between high w a l l and low f l u i d temperatures, w i t h one exception: MSRP-15 has a high w a l l temperature of 1400째F.

replaced three times, which required dumping and cooling of the loop. Examination of the loops i s i n progress. INOR-8 loop 9354-3 was shut down i n September when a pump f a i l u r e r e s u l t e d i n an o i l f i r e .

The pump has been replaced, and operation of

the loop w i l l be resumed on r e c e i p t of a new batch of s a l t . INOR-8 loop 9354-4 was shut down i n September, a f t e r 10,000 hr of

operation, f o r the removal of the second of three sample i n s e r t s 5 contained i n t h e hot l e g .

Results of the examination of t h i s i n s e r t a r e

given i n Sec 2.1 of t h i s report.

Operation was resumed with t h e remaining

(third) insert.

INOR-8 loops MSRP-7 and -10 were shut down f o r the removal of tubing sections from t h e hot leg a f t e r 8760 h r (one year) of operation. t i o n s were replaced and operation was resumed.

The sec-

The sections are now being

examined by the Metallurgy Section. Two new INOR-8 loops, MSRP-14 and -15, were placed i n operation with

s a l t BULT-14 i n October.

Both loops contain molten-salt sampling devices

and three jacketed i n s e r t sections.

The double-walled i n s e r t s were placed

a t the e x i t of t h e second resistance-heater section as shown i n Fig. 1.1.8.

The c l o s e - f i t t i n g combination of jacket and i n s e r t was designed t o give t h e same cross section and flow area a s the matching loop tubing.

Loop

MSRP-14 i s operating with a high w a l l temperature of 1300"F, and MSRP-15 with a high w a l l temperature of 1400째F.

Graphite-Metal Seal Tests Several designs f o r graphite-to-metal frozen-salt s e a l s have been proposed.

I n the first of the configurations t o be t e s t e d , the frozen-

s a l t s e a l w i l l be formed i n a narrow annulus between a 5-in.-OD graphite tube and a s l i g h t l y l a r g e r Inconel tube.

Such a s e a l could be used i n

a molten-salt breeder reactor a s the s e a l between t h e f u e l salt and

breeder s a l t .

A sectional view of t h e t e s t - j o i n t design i s shown i n Fig.

1.1.9. Manufacture of p a r t s f o r the s e a l - t e s t apparatus i s nearly complete, and construction of the t e s t loop has been s t a r t e d .

It i s expected t h a t

t h e f i r s t t e s t of the s e a l w i l l be made before the end of November 1959.

51GR Quar. Prog. Rep. Apr. 30, 1959, ORNL-2723, p 33.

UNCUSSIFIED ORNL-LR-DWG 43719 RESISTANCE-HEATER

LUG

INSERT SECTlONS

Fig. 1.1.8.

Double-Walled Insert Sections Installed in INOR-8 Loops MSRP-14 and -15.

In-Pile Loop Sectioning and metallographic examination of the f i r s t MSR i n - p i l e loop are complete. r.

Analysis of the f i e 1 and of radioactive deposits i n

t h e gas passages of the loop i s i n progress.

The second loop has been

sectioned, and some preliminary metallographic examination made.

The

r e s u l t s w i l l be iss f - p i l e tests, i s ning on t h e prop-

UNCLASSIFIED ORNL-LR-PWG 44489

,SALT INLET

0 1

1 .

/ Q

5 ,

SCALE IN INCHES

SALT OUTLET

THERMOCOUPLE\

EXPECTED OPERATING TEMPERATURE:

1300째 F

Fig.

1.1.9.

Graphite-Metal Freeze-Joint Test Apparatus. 4

ENGINEERING F@SEARCH

1.2

Physical-Property Measurements Viscosity The v i s c o s i t y of the f u e l mixture BW-14 (LiF-BeF2-UF4-ThF4, 6718.5-0.5-14 mole viscometer

.’

5 ) vas

obtained by using t h e skirted c a p i l l a r y e f f l u x

The data from t h r e e separate determinations using d i f f e r e n t viscometer cups a r e given i n Fig. 1.2.1. Also p l o t t e d i s t h e c o r r e l a t i n g l i n e derived by a least-squares analysis of these data; i n t h e temperature

range from 550 t o 8OO0C, t h i s analysis yielded the equation p = 0.0812e

4422/T

where p i s the v i s c o s i t y I n centipoises and T i s the absolute temperature The v i s c o s i t y of the BULT-14 mixture i s compared i n Fig. 1.2.2 with

(OK).

on s a l t s 133 (LiF-BeF2-ThF4, 71-16-13 mole $>, 134

earlier

’MSR Quar. Prog. Rep. Jan. 31, 1959, ORNL-2684, p 65. *MSR Qaar. frog. Rep. Apr. 30, 1959, ORNL-2723, p 39.

3MSR Quar. frog. Rep. J u l y 31, 1959, ORNL-2799, p 34, UNCLASSIFIED ORNL-LR-DWG 44490

t, 500 40

I LlOUlDUS

TEMPERATURE

CC)

600

700

800

TEMPERATURE

’

Fig. 1.2.1. Viscosity-Temperature Relationship for the Fuel Mixture BULT-14 (LiF-BeF,UF,-ThF,, 67-18.5-0.5-14 Mole X).

UNCLASSIFIED ORNL-LR-OWG 44494

t. TEMPERATURE ("C) 600

500

450

700

800

; ;20 0)

a .L

C 0

b j 8 > '

0.0014

0.0013

0.0042

0.0044

00040

0.0009

!/r Plo-']

Fig. Mixtures.

1.2.2.

Comparison of the Viscosities of Four Thorium-Containing Molten Salt

(LiF-BeF2-ThF4-UF4, 62-36.5-1-0.5

67-18-15 mole $).

mole $), and BeLT-15 (LiF-BeF2-ThF4,

The v i s c o s i t i e s of the t h r e e high-thorium-content s a l t s

deviate by a maximum of 18$1 ( a t t h e extremes of t h e temperature range). This large v a r i a t i o n i s r a t h e r surprising i n view of t h e small composition change between BeLT-15 and BULT-14; the v i s c o s i t i e s of these two mixtures w i l l be redetermined i n the near future.

Results f o r the BeF2-containing s a l t s studied t o date a r e surmnarized i n Table 1.2.1. Enthalpy and Heat Capacity Analysis of the previously reported data4 on the enthalpy of t h e For t h e s o l i d ( l O W O O 째 C ) ,

BeLT-15 mixture was completed.

t h e enthalpy

( i n cal/g) can be expressed as H~

- H~~

= 4.5

0 . 1 9 ~+ ( 5 . 5 x

, t

Table 1.2.1.

Composition (mole

S a l t No. LiF

V i s c o s i t i e s of BeF2-Containing S a l t s

123

Empirical C on6t ant s*

NaJ?

BeFz

0.0234

5505

UF4

126

0.0104

6487

130

0.0580

4550

133

0.0526

4838

134

36.5

0.0680

4497

136

0.0489

4847

BeLT-15

0.0311

5308

BULT-14

18.5

0.0812

4422

0.5 20

0.5

Wonstants appear i n t h e equation, p = AeB/T

and f o r t h e l i q u i d ( 5 5 W 8 O O " C ) as Ht

- H30

= -38.5

where t i s t h e temperature ("C)

0.418t

- (7.0 x

10-5)t2

The heat of fusion a t 5OOOC was deter-

mined t o be 48 cal/g. Preliminary d a t a on t h e enthalpy of t h e BULT-14 composition a r e given i n Fig. 1.2.3; analysis i s continuing.

Quar. Prog. Rep. June 30, 1958, ORNL-2551, p 39.

UNCLASSIFIED ORNL-LR-DWG 44492

225

-'0

200

175

150

ui (25 W

100 LL

LL 0

I-

0 0

100

200

300

400

500

7CO

600

t, TEMPERATURE ("C)

Fig. 1.2.3.

UF,-ThF,,

Enthalpy-Temperature Relationship for the Fuel Mixture BULT-14 (LiF-BeF267-18.5-0.5-14 Mole %).

where po i s the density a t some base temperature, t o .

The volume c o e f f i -

c i e n t of expansion i s thereby obtained, t o a close approximation, as d(x1 - ~ 2 ) 1 > @ = c + x l dT where x1 i s t h e height of the l i q u i d i n l e g 1 and x2 i s the height of l i q u i d i n l e g 2, both measured above t h e a r b i t r a r y fixed point of the Utube height, c (note Fig. 1.2.6); T i s t h e temperature difference ( " C ) between t h e two legs.

I n practice, it w a s found most convenient t o vary

t h e temperature of one l e g only, the other being held a t some fixed reference temperature. Experimental data from an operational study of t h i s apparatus using the salt mixture HTS ( NaNO2-NaNO,-KNO3,

1.2.6.

40-7-53 w t

'$1

a r e shown i n Fig.

From t h i s figure, t h e slope, dX/dT (where X = xl

t o be 4.808 x

lom3 in./"C; p

- x2),

w a s found

i s then calculated t o be 0.000363 (g/cm3)-

( g / ~ m ~ ) ' ~ . ( " C ) ' ~(22%) over t h e temperature range from 215 t o 315째C. can be compared with t h e value of f3, 0.000378,

obtained from density

This

Fig. 1.2.4.

Apparatus for Determining Thermul-Expansion Coefficient of Molten Salts.

measurements by Vargaftik et a l . 6 Measurements w i t h the BULT-14 mixture were i n i t i a t e d . Heat-Transfer Studies eliminary meas

coefficients 67-18.5-0.5-14 mole $) apparatus, described i n .2.7 and 1.2.8.

minated, a f t e r 24 hr of c i r -

95OF, by an i n t e r n a l leak i n erved during t h i s period t h a t

. Oleshchuk, es,"

Physical Izvest. Vsesoyuz.

7MSR Quar. Prog. Rep. Apr. 30, 1959, ORNL-2723, p 41; MSR Quar. B o g . Rep. July 31, 1959, ORNL-2799, p 39.

UNCLASSlFlED PHOTO 34939

LEVEL PROBES

U-TUBE

Fig. 1.2.5. Apparatus.

Salt Container and Liquid-Level Probes for Thermal-Expansion-Coefficient

-50

Fig. 1.2.6. KNO,, 40-7-53

-40

-30

-20

-10 T = t,-t2

, TEMPERATURE

DIFFERENCE

(OC)

Experimental Data far Thermal-Expansion Coefficient of wt X).

HTS

(NaN02-NaN0,-

t h e heat loss from the piping alone w a s s u f f i c i e n t t o maintain temperat u r e s a t t h e desired l e v e l s , the heat exchanger coolant l i n e s were plugged;

r l e v e l s , p a r t i a l removal of r region s a t i s f i e d t h e addi-

s now operated continuously i n g t h i s period, A t runs akes place under

f a c e ) f o r both The tube-wall sing d a t a from

set so as t o j u s t maintain t h e s a l t passing through t h e t e s t section a t i t s i n l e t temperature.

Under

such e s s e n t i a l l y isothermal conditions, corrections for t h e tube-wall 25

Fig. 1.2.8.

Close-up of lnconel Test Section for Study of Molten-Salt Heat Transfer.

thermocouples can be obtained by comparison with the i n l e t - f l u i d mixedc

mean thermocouple, and the power consumed i s a measure of the system heat

l o s s a t t h e operating temperature.

O f i n t e r e s t i s the unusual shape of

the tube-wall temperature p r o f i l e s of Fig. 1.2.9.

Since the f l u i d e n t e r s

8W. Linke and H. Kunze, Allgem. W h e t e c h . 4 , 7 3 7 9 (1953); see a l s o E. R. G. Eckert and R. M. D r & v !@ansfer, p 213, McGrawH i l l , 1959.

ORNL-LR-

1 200

TUBE OUTSIDE SURFACE

1 180

3 I-

'1 a-

/ -"T -

DWG 44494

Atover-ol I

1160

I W I-

FLUID M E A N

1440

(0)

1420 1280

\TUBE

OUTSIDE SURFACE

0, 1260 W

LT 3 l-

A tover-atl

a a W n

I W

I-

1240

1220 0

x / d , DISTANCE ALONG TUBE

Typical Axial Temperature Profiles as Obtained in the Study of the HeatFig. 1.2.9. (67-18.5-0.5-14 Mole %) Salt Mixture. Transfer Characteristics of an LiF-BeF,-UF,-ThF, (a) Run MA-2, lnconel section, N,,= 7980; (b) run MA-13, INOR-8 section, N,, = 13,940.

v i c i n i t y of x/d = 10.

Further, t h e location of t h i s temperature peak

should be r e l a t e d t o t h e configuration of t h e tube entrance i n t h a t t h e t r a n s i t i o n should occur f a r t h e r downstream f o r a rounded entrance than f o r a sharp-edged entrance.

This may explain the s h i f t i n the location

of the peak between the curves a and b of Fig. 1.2.9; t h i s same difference between t h e temperature p a t t e r n s i n the Inconel and INOR-8 sections has been observed i n all runs made t o date.

Although a sharp-edged entrance

w a s specified f o r both sections, welding of t h e thin-walled tubes i n t o t h e heating lugs (mixing-chamber end p l a t e s ) may have a l t e r e d t h i s s i t u ation.

Thus it i s not possible a t t h i s time t o define exactly t h e en-

trance configuration.

Far downstream (x/d > 4 0 ) t h e temperature curves

assume t h e character observed i n earlier studies with molten saltsg under similar conditions of uniform heat input a t t h e w a l l and established flow and temperature f i e l d s

The results obtained t o date a r e summarized i n Fig. 1.2.10 i n terms of t h e heat-transfer parameter, N - T O m 4 . The wall-to-fluid temperature Nu Pr difference used i n t h e analysis of t h e data was taken i n t h e region of f u l l y developed conditions (as indicated i n Fig. 1.2.9).

The heat f l u x

w a s based on t h e heat gained by t h e f l u i d i n passing through t h e t e s t section; heat balances (corrected f o r e x t e r n a l heat l o s s ) ranged from 0.9 t o 1.2.

The d a t a are compared i n Fig. 1.2.10 with t h e general heat-

t r a n s f e r c o r r e l a t i o n l o f o r normal f l u i d s under moderate A t conditions,

0.8

NNu = 0.023 NRe

0.4 Npr

â&#x20AC;&#x2122;

ak (LiF-Na;F-KF,

11.5-42-46.5

l e $) and 130 (LiFB W - 1 4 salt mixture i n t h e value of i t s thermal

-58-2-40 (Feb. 18, c

12J. C. Amos, R. E. MacPherson, and R. L. Senn, Preliminary Report of Fused S a l t Mixture No. 130 Heat Transfer Coefficient Test, ORNL CF58-4-23 (Apr. 2 , 1958).

conductivity, which w a s assumed t o be 1.3 Btu-hrmating the heat-transfer parameter.

' ft-'

( OF)-'

i n esti-

It i s planned t o determine experi-

mentally t h e thermal conductivity of the B W - 1 4 mixture i n t h e near future.

The discrepancy observed between t h e Inconel and INOR-8 d a t a

(approximately 23$ a t NRe = 10,000) i s not explainable a t present. Future data, obtained a t periodic i n t e r v a l s , w i l l serve t o e s t a b l i s h

whether there e x i s t s a progressive f i l m formation f o r the BUI3-14 salt i n contact w i t h Inconel o r INOR-8. UNCLASSIFIED ORNL-LR-DWG 44495

I i

0 INCONEL SECTION-FLUID TEMPERATURE = l 2 4 7 ' F

------

INOR-8 SECTION- FLUID TEMPERATURE

FLINAK

- HOFFMAN

. to3

104 5 REYNOLDS MODULUS, N R ~

5x104

Fig. 1.2.10. Experimental Results for Heat Transfer with BULT-14 Salt Mixture (LiFBeF ,-UF,-ThF,, 67-18.5-0.5-14 Mole %).

u c

PART 2. MATERIALS STUDIES

2.1

METALLURGY

Graphite Brazing Studies t

Graphite has been proposed f o r use as t h e moderator of a molten-salt reactor.

This material could be placed i n the core i n simple shapes o r

as a complex s t r u c t u r e such as a heat exchanger t h a t would form a section of the primary loop system.

The l a t t e r case would probably require graph-

ite-to-graphite and graphite-to-metal j o i n t s t h a t have s t r u c t u r a l i n t e g r i t y and, t o an extent, leak-tightness. A program has consequently been i n i t i a t e d t o investigate various tech-

niques f o r producing j o i n t s with graphite and t o evaluate t h e i r usefulness f o r molten-salt-reactor

service.

A preliminary l i t e r a t u r e survey revealed

a notable s c a r c i t y of joining techniques applicable t o high-temperaturer e a c t o r technology.

Procedures f o r wetting graphite a r e r e l a t i v e l y well

known, but experience i n producing r e l i a b l e j o i n t s i n complex asseniblies

i s lacking.

One serious problem i s r e l a t e d t o t h e gross differences be-

tween the thermal-expansion c o e f f i c i e n t of graphite and those of comon brazing a l l o y s and s t r u c t u r a l materials. Metals having a strong tendency t o form carbides wet graphite r e a d i l y

when they a r e molten.

Therefore, a l l o y s containing these carbide-forming

metals appear promising as brazing a l l o y s f o r joining graphite t o itself ..

and t o metals.

Zirconium and titanium appear e s p e c i a l l y a t t r a c t i v e , since

t h e i r thermal-expansion c o e f f i c i e n t s are r e l a t i v e l y low (see Table 2.1.1)

as t h e major

Brazed j o i n t s made with t h i s a l l o y appear t o possess good strength and seem promising f o r a v a r i e t y of high-temperature-reactor applications.

Table 2.1.1.

Thermal-Expansion Coefficients of Various Materials

Material

Thermal-Expansion Coefficient [pin. *in."*

Temperature Range

(OF)

Graphite

2-3

Titanium

4Sb

Room

Zirconium

2.8b b 2.7

Room

Molybdenum Sncone1

10.5' b 6.3 d

Type 430 s t a i n l e s s s t e e l

8.3

INOR-8

PanY

32-1800

Room 32-1400 32-1500 32-1800

%he I n d u s t r i a l Graphite Engineering Handbook, National Carbon CombMetals Handbook. C

Engineering Properties of Inconel and Inconel X, I n t e r n a t i o n a l Nickel Company. B e s i g n Data f o r INOR-8 Alloy, Metallurgy Division, ORNL.

For molten-salt service, however, the uses of t h i s p a r t i c u l a r a l l o y a r e limited by i t s poor resistance t o corrosion i n t h i s medium (see "Brazing Material Evaluation i n Fuel 130," t h i s s e c t i o n ) . This development of other brazing-alloy systems i s therefore being

undertaken i n an e f f o r t t o f i n d more compatible materials.

Utilizing

niobium, tantalum, and molybdenum a s t h e primary carbide-forming elements, a number of a l l o y systems a r e being studied i n d e t a i l t o determine t h e i r a p p l i c a b i l i t y f o r joining graphite.

Alloys i n t h e Au-Ni-Ta system have

indicated promising wetting c h a r a c t e r i s t i c s , and several a l l o y compositions f r o m t h e gold-rich corner of the ternary diagram have been selected f o r f u r t h e r study.

The r e l a t i v e l y high thermal-expansion c o e f f i c i e n t s of gold-

r i c h alloys, however, may l i m i t t h e i r use f o r joining graphite. loy systems which w i l l be investigated include Ni-Mo, Ni-Nb,

Other al-

Ni-Nb-Mo,

Ni-Nb-Ta, Pd-Ni-Ta, and Pd-Ni-Mo. Preliminary experiments have a l s o been undertaken t o determine t h e f e a s i b i l i t y of e l e c t r i c - r e s i s t a n c e bonding of graphite t o graphite, using molybdenum as the braze metal.

So far, experiments have been confined t o

UNCLASSIFIED

Graphite T-Joint Brazed with Fig. 2.1.1. flowability are evident.

48% Ti-48%

Zr-4%

Be.

Excellent wetting and

graphite rods of 1/4-in. diameter, o r l e s s , due t o the high-aqerage r e quirements of t h e process.

The j o i n t i s prepared by placing a t h i n d i s k

'MSR Quar. B o g . Rep. J u l y 31, 1959, ORNL-2799, p 59.

Fig. 2.1.2.

Photomicrograph of Graphite T-Joint. As-polished. 12X. UNCLASSIFIED

Fig. 2.1.3.

Graphite Pipe-to-Sheet Joint Brazed with 48% Ti-48% Zr-4% Be.

i n s t a l l e d a t t h e end o

hot-leg section

on the w e i g h t changes

NOR-8 i n contact w

f u e l mixture.

a beryllium-base fluoride

The schedule specified removal of one i n s e r t a f t e r 5000

hr of exposure, another a f t e r 10,000 hr, and t h e t h i r d a f t e r 15,000 hr. Operation of t h e loop began i n July 1958 under t h e conditions:

S a l t mixture

LiF-BeF2-UF'4 (62-37-1 mole

Maximum fuel-metal i n t e r f a c e temperature

1300째F

M i n i m salt temperature

1100째F

200째F

Reynolds No.

1600

Flow r a t e

Examination of t h e second i n s e r t , although not yet complete, indicates t h a t an average weight l o s s of 2.0 mg/cm2 (k3$) occurred along i t s 4-in. length.

If uniform removal of surface metal i s assumed, t h i s weight l o s s

corresponds t o a l o s s i n w a l l thickness of 0.09 mil. No detectable loss i n wall thickness w a s noted i n comparing micrometer measurements of t h e i n s e r t s taken before and a f t e r t e s t . I

The first of t h e i n s e r t s , which w a s removed from the loop after 5000

hr, showed a weight loss of 1.8 mg/cm2 (+2$), o r a l o s s i n w a l l thickness

of 0.08 m i l . '

I 11

The s i m i l a r i t y of these values t o t h e values obtained a f t e r

10,000 h r i n d i c a t e s t h a t no s i g n i f i c a n t weight l o s s occurred a f t e r t h e first 5000 hr of loop operation.

The e r r o r s l i s t e d with these values are

based on estimated limits of precision of the instruments used to measure

from handling

I3 i

I j

1 I %

g t h e surface.

i n s e r t showed t h e surface f i l m t o have increased i n thickness and t h e band

of fine-grained material t o have grown i n s i z e (Figs. 2.1.6 and 2.1.7).

Transverse Section of 5000-hr Insert Removed from INOR-8 Pump Loop 93564. Fig. 2.1.4. Etchant: 3 parts HCI, 2 parts H,O, 1 part 10% chromic acid.

Fig, 2.1.5. Etchant:

Longitudinal Section of 5000-hr Insert Removed from

3 parts HCI, 2 parts H,O, 1 part 10% chromic acid.

INOR-8

Pump Loop

9354-4.

A s previously reported,l a surface l a y e r o r film similar i n appearance t o t h a t found on the 10,000-hr i n s e r t has been noticed on specimens removed from most of t h e long-time INOR-8 thermal- and forced-convection tests. Samples of t h i s film a r e being studied, but no results are available.

The

band of p r e c i p i t a t e s and f i n e grains found along t h e surfaces of t h e i n s e r t s has not been observed i n other t e s t s of INOR-8. A t present it i s not known whether these f i n e grains represent a second phase o r only rec r y s t a l l i z a t i o n of t h e matrix near t h e inside surfaces of t h e i n s e r t . There

i s reason t o suspect t h e l a t t e r p o s s i b i l i t y , since a reaming operation w a s performed on t h e i n s e r t s p r i o r t o service and undoubtedly induced some cold work along t h e inside surfaces.

A review of the r e c r y s t a l l i z a t i o n

properties of INOR-8 indicates t h a t r e c r y s t a l l i z a t i o n of the material can be i n i t i a t e d at 1300°F following p r i o r cold work.2

Grain growth of t h e

r e c r y s t a l l i z e d material would be extremely slow a t t h i s temperature, which would help t o explain t h e extremely f i n e c r y s t a l l i t e s apparent. Examination of Three Inconel Pump Loops.

- Chemical

and metallographic

r e s u l t s have been obtained f o r three Inconel pump loops which completed one year’s operation.

Operating conditions f o r these loops a r e shown i n

Table 2.1.2. Metallographic examination of loop 9344-1, which c i r c u l a t e d salt 123 f o r 8760 h r a t a maximum temperature of 1300°F, showed heavy a t t a c k i n t h e form of intergranular and general voids along both heater legs, a s shown i n Fig. 2.1.8.

I n the f i r s t heater leg, a t t a c k ranged from 18 t o 31 mils

i n depth and i n t h e second leg, from 18 t o 38 mils.. The unheated bend

2J. Spruell, Recrystallization of INOR-8, ORNL CF-57-11-119 (Nov. 25, 1957). Table 2.1.2.

salt LOOP

No.*

Operating Conditions for Three Inconel Forced-Convection Loops

M a x i m u m SaltMetal Interface Temperature (OF)

9344-1 9344-2

123 12

1300 1200

9377-3

131

1300

Minimum Fluid Temperature (OF)

*123: NaF-BeF2-UF (53-46-1 mole $1 12: NaF-LiF-KF 411.5-46.5-42 mole 131: LiF-BeF2-UF4 (60-36-4 mole $1

I I

i j

1100 1100 1100

Flow Rate (OF)

(am)

Reynolds

No.

200

3250

100

2.5

8200

200

3400

Fig. 2.1.8. Specimen Removed from End of Second Heater Leg of lnconel Pump Loop 9344-1, Showing Maximum Attack Found. Loop was operated for 8760 hr with salt mixture NaF-BeF,UF, (5346-1 mole %). Etchant: modified aqua regia.

connecting t h e two l e g s revealed only a few p i t s , not over 1 mil, and t h e cold-leg sections showed only s l i g h t surface roughening and surface p i t d v i s u a l l y o r metallographically. Chemical analyse

sed-salt mixture before and a f t e r circu.1.3.

N6te t h a t an extremely l a r g e

on occurred during t h e t e s t , along with a i c a l examination of t h e salt d i s 1 amounts of U02 and NaF-BeF2.

rmed t h e presence of U02.

Thus

ensive extraneous oxidation e i t h e r before o r d u r i 9344-2, which operated f o r 8760 h r a t a maximum temperature of 1200째F with salt 12, showed moderate a t t a c k

i n t h e form of intergranular and general voids along both heater l e g s . I n 41

t h e first heater leg, a t t a c k ranged from 1 t o 3 mils i n depth and i n t h e second leg, from 4 t o 8 mils.

The cold-leg sections and t h e unheated bend

connecting t h e two hot l e g s revealed l i g h t intergranular voids t o 1 mil. The coolant salt i n t h i s loop w a s replaced t h r e e times because of operating difficulties. A somewhat higher r a t e of a t t a c k occurred i n loop 9377-3, which c i r -

culated salt 131 f o r 8760 hr a t a m a x i m temperature of 1300'F.

Exami-

nation of the heater sections revealed a t t a c k i n t h e form of heavy i n t e r granular and general voids, ranging from 2 t o 8 mils i n t h e f i r s t heater l e g and from 6 t o 14 mils i n t h e second l e g .

The unheated bend connecting

t h e two l e g s showed only l i g h t surface roughening except i n one region where a few i s o l a t e d voids t o a maximum depth of 11 mils were found.

The

cold-leg sections revealed only a few p i t s , all l e s s than 1 m i l . Chemical analyses of salt 131 before and a f t e r c i r c u l a t i o n i n loop

9377-3 are shown i n Table 2.1.4. Except f o r t h e increase i n chromium concentration, these analyses show l i t t l e difference. The present s t a t u s of a l l forced-circulation loop t e s t s now i n progr e s s i s given i n Sec 1.1 of t h i s report.

Table 2.1.3.

Analysis of S a l t 123 Before and After Circulation i n Pump Loop 9344-1 Major Constituents (wt

Sample Taken

$4 Be

Minor Constituents (PPd Ni Cr Fe

Before t e s t

3.40

8.16

140

425

130

After t e s t

2.58

8.25

175

4670

205

Table 2.1.4. Analysis of S a l t 131 Before and After Circulation i n Pump Loop 9377-3 Major Constituents (wt

Sample Taken U

$1 Be

Minor Constituents (ppd Ni Cr Fe

Before t e s t

19.6

7.12

145

345

200

After t e s t

19.5

7.09

860

275

General Corrosion cs 2 I.

Permeation

Studies

of Graphite by Molten Salts

The permeation of various grades of graphite by molten fluoride salts is being investigated in tests3 at 1300°F (704°C) for 100 hr at 150 psig, using the weight increase of the test specimen to calculate the volume of graphite that is permeated by the salt. Table 2.1.5, a summary of results, lists 15 grades of graphite in order of resistance to permeation. These grades were manufactured as low-permeability graphite, with the exception of CT-158, CCN, CEYB, R-0013, AGQT, and TSF. The permeation values for the pipe material are considered high, because no effort was made to seal the ends of the pipe specimens to prevent the exposure of the more continuous and accessible voids produced in the axial direction as a result of fabrication. Pipe specimens with sealed ends are being made to be tested for permeation, since values for them should be more applicable to reactor

designs. Most of the testing was done with LiF-BeF2-ThFb-UF,+ (67-18.5-14-0.5 mole $); however, NsF-ZrFb-UFc, (56-40-4 mole $1 and LiF-BeF*-UFb (62-37-l mole '$) were also used. Under the test conditions the extent of permeation by the three salt mixtures was essentially the same; other test conditions will be investigated. No wetting of the graphite by the salts was observed. Salt permeation studies with additional grades of graphite, including studies to show the effect of exposure time and graphite shape, were begun. An effort is being made to preclude the fuel pickup by initially filling accessible void spaces :.inthe graphite _. -- with bismuth, thus allowing no space for the salt. -Appr&&&tely$G$ of the accessible4 void spaces of AGCT graphite~specimens~,were filledwith bi~smuth when held at 1022°F for 1 -Tests were-begun to determine the extent to which these 4 hr atl25-psig. impregnatea.~~~c~ns.will-.take up salt in- standard permeation tests. ~-.' .- . --.-. , .-.. ;-, .=. ..~: -3w. :g;:; C. o;k :.and.D;.T- .H:~'Jansen,-A Prelim&ry.Summar y of Studies of ~.&OR-8 -~inc~~elr,.-Graphite, ar&.Fluoride Systems for'the MSRP for the Period/May-l,1958-~to .Dec;- 31,~1958j: ORNL.CF-59-l-4, p 1~20; r ~'-. -- .;,&T&,tal~.- accessible~void~lvolume.is‘reporied to be 21.7$ of the bulk -trdlume.of:-AGOT -graphite;:$.~P~ -Eatherly,:M. Janes, and R. L. Mansfield, "Physical Properties of Graphite Materials for Special Nuclear Applications," Second U.N. Intern. Conf. Peaceful Uses Atomic Energy, Geneva, 1958, paper A/Conf 15/P/708, p 4 (June 1958). 43 ‘.

Table 2.1.5.

Permeation of Various Grades of Graphite by - Molten Fluoride S a l t s

A l l percentages axe averages of three w i t h t h e exception of those with numerical superscripts, which denote t h e number of values averaged

Percentage of Bulk Volume of Graphite Permeatgd by Fluoride S a l t s

Graphite Bulk Density

Graphite G rd e

(g/cc 1

Fuel 30

Fuel 130

B u ~ ~ - 1 45U -.

GT -123 -82 R-4

1.93

0.2 1.6

R-0009

1.92

1.8

b CEY-82 R- 0009-RG

1.87 1.90

1.9 2.5

CT-158'

1.77

3.5

186

1.86

CCN

1.92

CEyBb

1.79

4.2 4.3

s-4

1.85

4.8

R-0013

1.87

6.0

mJ-82-RG

1.83

6.4

CS-82 -RG

1.80

8.1

AGGT

1.68

TSF

1.67

1.92

4.9 (1)

14.8

3.8 ( 6 )

4.6 (1) 4.2 ( 2 )

14.8

14.2

13.2 ( 2 )

14.4

a 30: NaF-ZrF4-UF4 (56-40-4 mole $1 130: LiF-BeF2-UF4 (62-37-1 mole $I) BULT-14- .5U: LiF-BeF,-ThF4-UF4 (67-18.5-14-0.5

mole $)

bPipe, nominal dimensions, i n . : 1-1/4 OD x 7/8 I D x 1/2 long. C

Pipe, nominal dimensions, i n . : 25/64 OD x 3/16 I D x 1-1/2 long.

Removal. of Oxide Contaminants from Graphite Previous t e s t s have shown t h a t exposing graphite t o f u e l 130 (LiFBeFz-UF4, 62-37-1 mole $> a t 1300째F ( 7 a " C ) w i l l r e s u l t i n t h e Precipitat i o n of U02, and t h a t t h i s reaction i s e s s e n t i a l l y complete within 5 hr when t h e f u e l i s i n vapor-phase contact o r i n d i r e c t contact with t h e graphite.

This indicated t h a t oxide contamination might be removed from

t h e graphite by vapor-phase o r direct-contact gettering.

Results t h a t

u 2

indicated partial success in two such tests, with fuel 130 as the gettering agent, have been reported.5 A direct-gettering test, which has been completed, was apparently successful in removing oxide contaminants from the graphite. In the test a charge of fuel 130 was in direct contact with an AGCT graphite crucible for 20 hr at 1300째F (704째C) in a vacuum. The ratio of the bulk volume of the graphite to the volume of the salt was 27:l (an arbitrary standard selected for such tests). Radiographic examinations at room temperature indicated that a normal quantity of UO;! had precipitated. The gettering charge of fuel 130 was removed and replaced by a fresh charge of fuel 130, which was held an additional 20 hr at 1300'F. Radiographic examination showed no precipitation, indicating that the preceding gettering operation was successful. Since the cost of fuel 130 would make it an uneconomical gettering agent to use on a full-scale reactor, cheaper gettering agents are also being investigated. A hydrogen test is in progress. Tests similar to those described above are being made with LiF-BeF*ThF4-UF4 (67-18.5-14-0.5 mole $). Three such tests with AGCT graphite have continued for 500 hr, and no precipitation has been detected in the salt by radiographic examinations. Compatibility

of INOR-

and Graphite

in Direct

Contact

The tendency for INOR- to carburize when in direct contact with graphite is being investigated as part of the over-all INOR-&graphitesalt compatibility program. TSF-grade graphite and INOR- specimens were held in contact at 1300"~.at.1b00~~psi. Modified stress-rupture apparatus was used, and the. tests were-held in .salt environments to simulate reactor conditions. Metallographic examination of specimens held for 700 hr in NaF;KF-LFF-.~4--(11.2-41-45.3-2.5 mole $) revealed no evidence of carburization; ~.-Tests for 3400 hr -in NaF-ZrF4;UF4 (50-46-4 mole $> have been completed,..and-the-test specimens are now being examined. r

Brazing&Iaterial-Rvaluation

Since~-a barren-salt-to-fuel-salt for use in the Molten-Salt Reactor, bd

in Fuel 130 heat exchanger is being considered the corrosion resistance of brazing

%SR Quar. Prog. Rep. July 31, 1959, ORNL-2799, p 62.

a l l o y s which may be useful i n the f a b r i c a t i o n of metal-to-metal j o i n t s i n such a heat exchanger

i s being evaluated.

The method used t o subject

brazing a l l o y s t o t h e corrosive environment i n t h e hot l e g of a thermalconvection loop has been described e a r l i e r , 6 and corrosion t e s t r e s u l t s

on a s e r i e s of brazing a l l o y s subjected t o f u e l 130 (LiF-BeF2-UF4, 62-37-1 mole

f o r 1000 h r a t a 1300’F hot-leg temperature i n such a loop have

been reported. The r e s u l t s of a 5000-hr t e s t made under t h e same conditions a r e outl i n e d i n Table 2.1.6.

Copper, gold-nickel, and t h e Coast Metals alloys

showed good corrosion resistance.

A depleted region t o a depth of 3 mils

w a s observed along each of the Coast Metals a l l o y f i l l e t s a f t e r t h e t e s t . Results of e a r l i e r corrosion tests on these a l l o y s i n NaF-ZrF4-base f u e l s and i n l i q u i d metals indicated t h a t t h i s depletion w a s due t o the leaching of the minor constituents boron and s i l i c o n from t h e a l l o y by t h e bath, I

and it appears t h a t boron and s i l i c o n a r e a l s o being leached by f u e l 130. This depletion has no detrimental e f f e c t on the alloy, siiice a nickel-rich, corrosion-resistant matrix i s l e f t .

A 10,000-hr thermal-convection-loop

t e s t on Inconel and INOR-8 l a p j o i n t s brazed with t h e f i v e brazing mat e r i a l s l i s t e d i n Table 2.1.6 i s i n progress. Some refractory-metal-base alloys, being developed by t h e Welding and f

Brazing Group f o r possible application i n joining graphite t o graphite, were given a s t a t i c corrosion t e s t i n f u e l 130 f o r 100 hr a t 1300’F. Nickel, because of i t s comparative inertness t o fluorides, w a s used as the t e s t container material.

Test r e s u l t s , l i s t e d i n Table 2.1.7,

weight losses f o r each a l l o y .

showed large

I n order t o determine t h e alloying element

o r elements responsible f o r t h e heavy attack, the following s t a t i c corrosion t e s t s i n f u e l 130 were conducted a t 1300’F:

(1)titanium w a s t e s t e d

i n containers of titanium, nickel, and INOR-8,

( 2 ) zirconium w a s t e s t e d

i n containers of zirconium, nickel, and INOR-8,

and ( 3 ) beryllium w a s

t e s t e d i n a nickel container.

Large weight l o s s e s (Table 2.1.8) were ob-

served f o r specimens t e s t e d i n nickel o r nickel-base containers, while small weight l o s s e s were found when specimen and container were of the

same metal.

Substituting an INOR-8 (containing 7@ N i ) container f o r one

‘MSR Quar. Prog. Rep. June 30, 1958, ORNL-2551, p 62. 7Met. Ann. Prog. Rep. Sept. 1, 1959, ORNL-2839, p 166-67.

I+

t s of Metallograph-.:

Examinations of Brazing Materials Tested on Loop Circulating Fuel 130 (LiF-BeF2-UF4, 62-37-1 Mole $) conditions:

Hot-leg temperature, 1300째F Cold-leg temperature, llOOOF Time, 5000 h r Metallographic Results:

lOY

omposition ($)

Inconel

Alloy Brazed t o

INOR-8

No a t t a c k

70 Ni-20 Cr-10 Si

Heavy a t t a c k of 16 mils

3-mil a t t a c k

Gold-nickel

82 Au-18 N i

No a t t a c k

Copper

100 cu

No attack; d i f f u s i o n voids 2 mils deep on f i l l e t

No attack; d i f f u s i o n voids 2 mils deep

Coast Metals No. 53

Table 2.1.7.

Results of S t a t i c Corrosion Tests on Refractory-Metal-Base Brazing Alloys i n F u e l 1 3 0 i n Nickel Containers Test conditions:

~ l o Composition y

1300째F, 100 h r

(8)

Weight Change

48 T i 4 8 Zr-4 Be

-4.2

95 Ti-5 Be

-6.5

95 Ti-5 Be

-9.8

($1

u *

Table 2.1.8. Results of S t a t i c Corrosion Tests on Refractory Metals i n Fuel 130 i n Containers of Several Materials Test conditions: Weight Change Material

Nickel

1300"F, 100 hr

($1

When Tested in:

INOR-8

Titanium

Zirconium

Ti Zr

Excessive, portion of sample dissolved

of pure nickel r e s u l t e d i n a weight-loss decrease on the titanium and z i r conium specimens.

Metallographic examination and spectrographic r e s u l t s

on the nickel capsules revealed surface l a y e r s containing titanium, z i r conium, o r beryllium, corresponding t o t h e major component of t h e brazing a l l o y o r metal t e s t e d .

Results of t h e t e s t s indicate t h a t t h e usefulness

of titanium-, zirconium-, o r beryllium-containing brazing a l l o y s i n f u e l

130 would be limited i n systems constructed of nickel o r nickel-base alloys

Phase Equilibrium The,System BeF*-ThFL-UF6 The most favorable fuels

Studies

for breeding with

molten fluorides

are ob-

tained from the LiF-BeFZ-ThFk-UFq quaternary system. Of the ten binary and ternary systems which are incorporated as limiting cases in this quaternary system, only the system BeFz -ThFA-UFc, has not been described previously. Spot checks have shown that only two primary phases, those of BeF2 and of the ThF4-UF4 solid solution, are involved in the BeF2-ThFAUF,: phase diagram. As in the ThF4-UF4 binary system, no minimum exists in the ThFb-UF4 solid-solution liquidus surface in the ternary system. Isotherms for such of the liquidus surface in the ternary system can be approximated by straight ThF4 and BeF2-UF4.

lines

The System BeF2-ThF4 Some of the information

between the bounding binary

on previously

reported1

systems BeF2-

preliminary

phase

diagrams for BeF2-ThF4 was uncertain because BeF2-ThF4 mixtures containing more than 7'5 mole $I BeF2 are too viscous to reach equilibrium, even in periods as long as three weeks. This difficulty is greatly alleviated by small additions of NsF or LiF, and the BeF2-ThF4 binary diagram has now been established with the aid of short extrapolations from work on the ternary systems. Figure 2.2.1, showing a eutectic at 527'C and 2 mole $ ThF,+, is regarded as a final diagram. The System I&'-B~F~-T~Fc Continuing studies of the phase equilibria in the system NsF-BeF2ThF4 have established that this system involves 12 invariant equilibrium Of these, ten have been established to within 1 mole $ and 5'C; -points. these ten are listed in Table~~2.2.1. : ~Molten-Fluoride ~Solvents ~- -A subsidiary interest, as far as breeder fuels tached:to volatility

are concerned,

is at-

a recent search for alternate solvents for use in the fluoridedissolution process, -in which a high solubility of ZrF4 is a

'MSR Quar. Prog. Rep. Oct. 31, 1957, ORNL-2431, p 36. 49

UNCLASSIFIED

ORNL-LR-DWG

4200

29667R

(400

4000 900

800 700

600

500 8eF2

40 ThF,

Fig. 2.2.1.

requisite.

ThG

(mole Z )

The System BeF,-ThF,,

Three mixtures, NaF-ZrF4, N@-LiF, and NaF-LiF-ZrF4, have been

used; of these, NaF-LiF has t h e l a r g e s t capacity f o r ZrF4, but i n t h i s case liquidus temperatures approaching 600째C a r e encountered a t 25 mole

ZrF4.

Exploratory investigations of t h e phase e q u i l i b r i a i n t h e system NaFBeF2-ZrF4 have shown t h a t NU-BeF,

(69-31 mole $) affords a solvent f o r

ZrF4 which w i l l accommodate a s much as 52 mole '$ of ZrF4 i n solution a t temperatures below 550째C and t h a t no liquidus temperatures higher than 570째C w i l l be encountered on the composition path between NaF-BeF2 (69-31 mole '$) and NaF-13eF2-ZrF4 (33-15-52 mole '$). The Compound NaF-BeF2*3UF4 et a1.2 on t h e system NaF-UF4 and more recent atStudies by Barton tempts i n t h i s laboratory t o synthesize a compound NaF*4UF4 by thermalgradient quenches of a substance with t h e composition 20 mole '$ NaF-80 mole '$ UF4 have f a i l e d t o confirm the existence of a compound with t h i s et composition, which w a s reported by Eichelberger gation of t h e system NaF-BeF2-UF4.

i n t h e i r investi-

Moreover, studies a t t h i s laboratory

i n t h e system NaF-BeF2-ThF4 have shown t h a t a primary-phase f i e l d exists corresponding t o t h e "NaF*4UF4" primary-phase f i e l d i n t h e system NaF-BeF2UF4 and t h a t the primary phase i n t h i s case i s NaF.BeF2*3ThF4. This com-

pound i s analogous i n o p t i c a l properties t o t h e so-called "NaF~4UF4"as

2C. J. Barton e t a l . , J. Am. Ceram. SOC.41(2), 63 (1958).

3J. F. Eichelberger e t al., p 110 i n Phase Diagrams of Nuclear Reactor Materials, R. E. Thoma, ed., ORNL-2548 (Nov. 6, 1959). 50

Composition of Liquid (mole $1 NaF

BeF2

TW4

Invaziant Tempera%ure ("C>

Type of Equilibrium

527

TW4, BeF2, and NaF-BeF2-3ThF4

NaF-BeFz,Na;F*2ThF4,and NaF*BeF2-3ThF4

Solid Phases h-esent

365

Peritectic

Na;F*BeF2,N@*2ThF4, and B-NaF *ThF4

320

415

Peritectic

P2-2NU0ThF4,2NaF.BeF2, and B-NaF ThF4

510

Eutectic

B2-2NaF.ThF4, 2NaF-BeF2,and NaP

540

Peritectic

P2-2NaF.ThF4, B-4NaF-ThF4,and NaF

6 83

Peritectic

P2-2NaF-ThF4,3Na;F*2ThF4,and B- N U* TkiF4

740

Peritectic

Na;F*2TkiF4,ThF4, and NaF*BeF2-3ThF4

reported by the Mound Laboratory.

Since a thermal-gradient quench i n t h e

system NaF-BeF2-UF4 at 35-55-10 mole

has produced a primary phase which

i s i s o s t r u c t u r a l , by x-ray d i f f r a c t i o n analysis, w i t h t h e compound NaF. BeF2*3ThF4, it seems probable that t h e compound reported by the Mound Laboratory i s a c t u a l l y NaF-BeF2-3UF4. Gas S o l u b i l i t i e s i n Molten Fluorides

S o l u b i l i t y of HF i n Fuel Solvents

As previously r e p ~ r t e d , ~ ,t h e s o l u b i l i t y of HI? has been measured over wide composition ranges i n both BeF2- and ZrF4-base solvents.

each type of system, compositions r i c h i n a l k a l i f l u o r i d e s showed marked increases i n the s o l u b i l i t y and i n t h e heat of solution of HF.

The t r a n -

s i t i o n t o higher values appeared t o occur as t h e a l k a l i f l u o r i d e content

exceeded t h e stoichiometry f o r complete complexing of t h e Be++ as BeF4

--- , thereby providing

and t h e Zr4+ as ZrF7

"free" f l u o r i d e s f o r forming

Several schemes were examined i n an attempt t o c o r r e l a t e the solub i l i t y of HE' w i t h t h e composition of t h e solvent.

One which works w e l l

i s t h e use of a composition scale i n t e r m s of equivalent per cent f r e e N U as shown i n Fig. 2.2.2.

Compositions corresponding t o Na2BeFQ and

Na3ZrF7 a r e considered t o contain C$ excess NaF.

Other compositions con-

t a i n an excess or a deficiency of NaF; equivalents a r e calculated on t h e b a s i s of 2 f o r Na2BeF4 and 3 f o r Na3ZrF7 i n obtaining equivalent per cent compositions according t o t h i s scheme. Figures 2.2.3,

2.2.4,

and 2.2.5,

applying t o d i f f e r e n t temperatures,

demonstrate the good c o r r e l a t i o n achieved f o r s o l u b i l i t i e s i n NaF-ZrF4 and NaF-BeF2 compositions. l a w constant.

S o l u b i l i t i e s a r e expressed i n terms of t h e Henry's

The curves i n t h e figures a r e logarithmic and give s t r a i g h t -

l i n e p l o t s on semilog paper.

The e f f e c t s of both temperature and compo-

s i t i o n are accommodated i n t h e expression

log

'MSR

(8400 +RT3263 RC - 15.24 +R0.909 RC

Quar. Prog. Rep. Oct. 31, 1958, ORNL-2626, p 85.

'MSR Quar. Prog. Rep. Jan. 31, 1958, ORNL-2474, p 93.

UNCLASSIFIED ORNL-LR-DWG 44497

4 00

120 ‘40

rr UNCLASSIFIED ORNL-LRDWG 4 4 4 9 9

(x to41

T400

I-t

W V

I-

5-1 - 2 5

\ (L

-50

t 40 -75

-400

NoF (mole

4 00

Correlation of Free NaF with Fig. 2.2.2. Mole Fraction of NaF in Mixtures of NaFBeF, and NaF-ZrF, and Na,ZrF,).

(Based

Na,BeF,

VNCLASSIFIEO 4445

(x I 0-61

ORNL- LR-DWG

I80

0 -80

I40

- I

-20

Fig. 2.2.4. Composition Dependence of Henry’s Law Constants for the Solubility of HF in NaF-BeF, and NaF-ZrF, Mixtures at 700OC. UNCLASSIFIED ORNL-LR-DWG 44500

WTW

( x 10-61

I 42O0

IT-

-40

EOUIVALENT PER CENT FREE NoF

160 NoF- ZrF4 CALCULATED \. EXTRAPOLATED FROM MEASUREMENTS TAKEN AT HIGHER TEMPERATURE

-60

0 1

‘2 r

where K = Henry's law constant, moles of HF/( l i t e r of m e l t ) ( a t m )

C = concentration of e f f e c t i v e f r e e fluoride, equivalent per cent, ~

T = temperature,

OK,

R = gas constant.

Calculated values from t h i s equation, denoted by t r i a n g l e s i n Figs. 2.2.3 t o 2.2.5, are within t h e experimental precision of t h e measurements. The a r b i t r a r y concentration scale used here can be r e l a t e d t o a more conventional concentration concept by considering the system N@-BeF2 t o be composed of t h e systems BeF2-Na23eF4 and Na2BeF4-N@; then the postu-

l a t e d free-fluoride model corresponds t o mole $I BeF2 i n t h e former system and t o equivalent per cent N a F i n the l a t t e r system. Similar r e l a t i o n s hold f o r t h e NaF-ZrFb system. Fission-Product Behavior Exchange Reactions i n Molten Fluorides Experiments w i t h exchange reactions f o r reprocessing molten-salt reactor f u e l s have continued.

Important c h a r a c t e r i s t i c s f o r p o t e n t i a l s o l i d

exchange r e a c t a n t s are i n s o l u b i l i t y i n molten f l u o r i d e s and chemical i n e r t n e s s toward reactor f u e l constituents. Studies of oxide reactions i n molten f l u o r i d e s have shown t h a t the rare-earth oxides a r e s u f f i c i e n t l y insoluble t o qualify as possible exchange agents.

The exchange of Ce02 w i t h cerium ion i n the solvent LiF-NaF

(60-40 mole $) and t h e e f f e c t of subsequently added CeF, on the equilibrium Ce*F3(Q) + Ce02(s) e C e q 2 a r e shown i n Fig. 2.2.6.

CeF,

Similarly, i n t h e same solvent, t h e removal of

lanthanum-tracer a c t i v i t y w i t h La203 and the e f f e c t of subsequent additions of CeF3 a r e shown i n Fig. 2.2.7. These experiments, while not c a r r i e d out i n r e a l i s t i c f u e l s , nevertheless i l l u s t r a t e t h e effectiveness of exchange processes i n molten fluorides.

The exchange of lanthanum w i t h cerium i s

i n t e r e s t i n g as a possible method f o r replacing nuclear poisons, such as

samarium, gadolinium, and europium, w i t h more innocuous r a r e earths such as cerium.

Unfortunately, as shown i n Fig. 2.2.8, Ce02 r e a c t s r e a d i l y w i t h

6MSR Quar. B o g . Rep. July 31, 1959, ORNL-2799, p $1.

u *

UF4 in the solvent LiF-NaF (60-40 mole $>. Hence, reprocessing with rareearth oxides would probably be limited to reactor fuels from which uranium had been removed by prior treatment. Figure 2.2.9 illustrates the unfavorable effect of ThF4 and BeF2 on the removal of tracer-cerium activity from solution by exchange with Ce02. Experiments to investigate the exchange properties of carbides are also under way. The results of two experiments to study the removal of hafnium activity with hafnium carbide are shown in Fig. 2.2.10. These results illustrate the unfavorable effect of UF, on the exchange reaction in the solvent LiF-BeF2 (63-37 mole '$). Attempts to remove barium activity with Cr,03 and Be0 from the solvent LiF-BeFz-ThF, (67-18-15 mole $) were not successful. Similarly an attempt to remove cerium activity from the same solvent with Be0 was unsuccessful. The addition of A120, to LiF-BeF,-ThF4 (67-18-U mole 5) containing cerium activity caused the precipitation of ThF4 without any detectable removal of cerium activity from solution. These experiments show that exchange reactions for reprocessing moltensalt reactor fuels are in many cases adversely affected by essential constituents in the fuels. The presence of thorium and beryllium, for example, interferes with exchange reactions involving CeOz and HfC. Further searches for suitable exchange agents will include the rare-earth carbides. Chemistry

of Corrosion

Processes

Self-Diffusion Coefficients for Chromium in Nickel Alloys A preponderance of the evidence ac'cumulated over many years indicates that corrosion of nickel-chromiumalloys by molten fluorides under anisothermal conditions should reach a-~steady-state rate controlled by diffusion reason of chromium in the~metal in the &older part of the system. Forthis the value:of the diffusion coefficient for chromium has been of paramount , interest? Data from- several-,diffusion experiments, employing Cr51 as a tracer, have-been~partially:digested.The -alloy specimens studied may be grouped as follows,.a&ording to the.treatment they received prior to the experiments.~ Inconel annealed at 800째C for 8 to 12 hr, InCone annealed at

7MSR Quar. Frog. Rep. Oct. 31, 1958, ORNL-2626, p 99. 55

UNCLASSIFIED ORNL-LR-DWG 44503

500

400

-P n z 3

300

? -1

2 200 W 0

I2 I6 20 ADDED COMPOUND (9)

IO0

Exchange of Cerium Activity Fig. 2.2.6. with CeO, and CeF, in LiF-NaF (60-40 Mole %) at 75OOC. UNCLASSIFIED ORNL-LR-DWG 44502

0 5

15 TIME (hr)

Reaction of UF, with CeO, Fig. 2.2.8. in LiF-NaF (60-40 Mole %) at 75OOC.

UNCLASSIFIED DWC 44504 ORNL-LR-

IO0

z E

c ? +

a a 0

LiF-BeF2

(63-37mole%l (67-18-45 LiF- NaF 160-40mole7.)

0 LiF-8eF2-ThF4

mole%l

2 3 ADDED COMPOUND (g)

Fig. 2.2.7. Exchange of Tracer-Lanthanum Activity with La 0 and CeF, in LiF-NaF (60-40 Mole %) a t 75030 C.

6 8 CeOp ADDED (gl

Fig. 2.2.9. Removal of Tracer-Cerium Activity by Exchange with CeO, in Molten Fluoride Systems.

UNCLASSIFIED DRNL-LR-DWG 445C

0 0

WITH URANIUM (7 wt%) WITHOUT URANIUM

45 TIME

Fig.

2.2.10. Effect of UF, 76) at 6OOOC.

on the Removal

(hr)

of Hf ‘*’

Activity

with

HfC (5 wt %) in LiF-BeF,

(6337 Mole

1150°C for 2 to 4 hr, and INOR- annealed at 800"~ for 8 to 12 hr. The results given here are over-all coefficients obtained from a comparison between the total amount of Cr51 present in the metal ski the amount in the contacting salt after a given exposure time. A description of the experimental procedures was given in previous reports.7*8 The data presently under discussion are not based on concentration profiles within the alloy. Companion experiments of the latter type will be discussed in a subsequent report; .-the general trends discussed below are reflected by the available profile data, The resultsfor Inconel specimens are presented as curves 5 and 7 on Fig. 2.2.11.'~ Only two 'experimental points for Inconel specimens are shown; however, curve 5 was taken from 19 individual points (34 experiments) at Curves 1 through 4, from various temperatures, and curve 7 from 16 points. 8MSR Quar. Prog. Rep. June 30,

1958,

ORNL-2551, p 95. 57

UNCLASSIFIED ORNL- LR- OWG 44506

TEMPERATURE (OC) 800 750 700

900

-10

650

600

-12

-2 -13

-5 Q

-I4

-15

-16

-I7

- 18

-+-DATA 0 "H"

POINTS FOR INOR-8 INCONEL SPECIMENS

8 t/T

(OK-'

( X $0-4)

Fig. 2.2.1 1. Diffusion Coefficients of Cr5' in Various Nickel-Base Alloys.

a high-temperature investigation conducted on similar a l l o y s by Russian

investigators,9 are shown f o r comparison.

It has been found t h a t grain s i z e , and therefore t h e annealing h i s t o r y p r i o r t o the diffusion experiments, has a marked e f f e c t on t h e d i f f u s i o n coefficients.

For example, photomicrographs of Inconel specimens H1 and

H4 revealed that the average grain s h e was much g r e a t e r i n H4 than i n HI. The e f f e c t of annealing conditions i s e a s i l y seen by cornparing curves 5 and 7 of Fig, 2.2.11 and a l s o t h e individual values f o r H1 and H4.

An ad-

d i t i o n a l annealing e f f e c t i s manifest i n t h e reproducibility of d i f f u s i o n behavior.

The d a t a of curve 7 (specimens annealed a t 800째C) tend t o show

a higher degree of s c a t t e r i n g than those of curve 5 (specimens annealed

a t 115OoC), which suggests that an 800째C annealing temperature f a i l s t o eliminate grain v a r i a t i o n s which might e x i s t between specimens.

'P. L. Gruzin and G. B. Fedorov, Doklady Akad. Nauk S.S.S.R. 264 (1955). 58

105 -

The over-all

diffusion

coefficients

obtained

for INOR-

specimens are

shown as points on curve 6 of Fig. 2.2.11. At temperatures greater than 7OO"C, the INOR- coefficients are of the same magnitude as the Inconel coefficients. This means that the rates of chromium diffusion in INORare approximately 7/15 of the rates in Inconel, at least at higher temperatures. The ratio 7/15 corresponds to the ratio of the chromium concentrations in the alloys. At temperatures below 7OO“C, the INOR- coefficients appear to fall considerably below the Inconel coefficients. This sudden drop might afford a partial explanation of the encouragingly low molten-salt corrosion rates exhibited by INOR- within the 500 to 700°C temperature range. Another point of interest is that observed corrosion results frequently represent considerably faster rates than predicted on the basis of diffusion in the cold zone as the rate-controlling step if the diffusion coefficients from Fig. 2.2.11 are used. This suggests that there is frequently an extended period of uncompensated oxidation, largely extraAn exneous, which precedes the establishment of a steady-state regime. treme example of this

is described

in the next section.

Chemical Analyses of Corrosion Test Loops Periodic sampling to follow the corrosion

behavior

in pumped loop

systems has continued.'O An INOR- loop, containing LiF-BeF,-ThF4-UP, (62-36.5-l-0.5 mole $) has been operating for 9300 hr with a hot-zone temperature of 1300“F and a cold-zone temperature of 1100'F. As shown in Fig. 2.2.12, the chromium content reached a steady-state value of 500 ppm after about 1000 hr. Ssmpling was temporarily discontinued after 5000 hr in order to maintain a sufficient fuel volume in the loop; the scheduled test period for the loop is 15,000 hr. .:This loop appears to be following the predicted behavior. By contrast, an Inconel ioop, operating under the same conditions, has shown a steady increase in chromik concentration in the fuel as illustrated in Fig. 2.2.13: After about-2000 hr some additional fuel was added to compensate for-the depletion due to -sample removals. A slight dilution of the chromium ion concentration was reflected in the analyses. At about 3000 hr a~motor failure

necessitated

draining

the loop into

the

l"MSR Quar. Prog. Rep. July 31, 1959, ORNL-2799, p 88. 59

UNCLASSIFIED ORNL-LR-DWG 44507

800

600 I

-5fi a

400

5 0 LT

200

LOOP: MSRP-12 (INOR-8) SALT : LiF-BeF2-ThF4-UF4 (62-36.5-1-0.5 mole X )

1600

800

Fig.

2.2.12.

2400 3200 TIME (hr)

4000

Chromium Concentration Due to Corrosion of

4800

5600

INOR-8.

UNCLASSIFIED ORNL-LR-DWG 44508

5000

4000

0 TIME (hr)

Fig.

2.2.13.

Corrosion of lnconel Due to an Unidentified Extraneous Source.

sump; t h i s r e s u l t e d i n another d i l u t i o n because, contrary t o intended op-

e r a t i n g procedures, a l a r g e residue of uncirculated s a l t had remained i n t h e sump since t h e o r i g i n a l f i l l i n g .

A s t h e chromium concentration has

increased t o 4730 ppm i n 7000 hr, t h e uranium concentration has dropped

from 2.8 t o 1.5 w t

This i s the behavior predicted f o r continuing ex-

posure t o an extraneous oxidant, such as air, but a rigorous examination of t h e system did not disclose any evidence of a leak o r other means of exposure t o air.

I n another loop, of INOR-8, a s a l t mixture with a higher concentration of uranium, IiiF-BeF2-Wh (70-10-20 mole $), has been pumped under similar conditions f o r 5500 h r .

The analyses suggest, as shown i n Fig. 2.2.14,

t h a t t h e expected steady-state chromium concentration has not yet been reached; t h i s i s somewhat surprising. Three additional t e s t loops, scheduled f o r periodic sampling, were placed i n operation during t h e past quarter. S o l u b i l i t y of CrF2 i n LiF-BeF2 (62-38 Mole

$11

The s o l u b i l i t y of CrF2 i n LiF-BeF2 (62-38 mole $I) was found t o be greater than 7.0 mole

a t 483째C.

Uncombined CrF2 w a s found t o be pre-

c i p i t a t e d f r o m t h e melt, containing 7.0 mole $I CrF2, a t 369 t o 422째C a t Pl

t h e phase boundary between CrF2 and 2LiF-BeF2 primary-phase f i e l d s . Besides indicating t h e extremely high concentration of CrF2 required f o r deposition on heat exchanger surfaces, t h i s information should lead UNCLASSIFIED ORNL-LR-DWG 4451

600 r

TIME ( h r )

Fig.

2.2.14.

Corrosion of

INOR-8 by Fuel Containing

a High Concentration of

UF,. 61

t o an experimental determination of t h e f r e e energy of formation f o r pure CrF2 a t high temperatures (800째C) when combined w i t h the equilibrium cons t a n t s now being obtained f o r t h e reaction CrF2

+ H2 +

Cro

+ 2HF

Equilibrium Measurements on the Reduction of CrF2 and FeF2 by H2 i n LiFBeF2 (62-38 Mole $1 High-temperature experimental equilibrium quotients, l1 Kx, f o r t h e reduction of CrF2 and FeF2 dissolved i n LiF-BeF2 (62-38 mole

46)

are being

obtained from t h e following reactions: CrF2

+ H2 ,-C' 800째C ro

2HF

FeF2

+ H 2700째C , 2 F e 0 +

2HF

A comparison of recent experimental equilibrium quotients obtained f o r the above reactions w i t h those f o r the same reactions i n N@-ZrF4

47 mole

(53-

i s shown i n Table 2.2.2.

The s a t u r a t i n g phase f o r CrF2 i n LiF-BeF2 (62-38 mole $) i s pure CrF2;

a complex compound precipitated on s a t u r a t i n g N@-ZrF4 (53-47 mole $) with "MSR

Quar. B o g . Rep. July 31, 1959, ORNL-2799, p 85.

Table 2.2.2. Effect of Solvent on the Equilibrium Quotients (Atmospheres/Mole Fraction), KX = MoP&/h2PH2

Compound

Temperature ("C)

I n LiF-BeF2

I n NaP-ZrFb a

x 10-4

-45 OOb

6300

FeF2

700

CrF2

750

1.8'

2.21

800

4.1'

6.77

a ANP Quar. B o g . Rep. M a r . 10, 1956, ORNL-2061, p 84.

b2. 88 mole $ FeF2. C

0.53 mole $ CrF2.

CrFz or FeF2. Previous studies have indicated that the saturating phase for FeFz in LiF-BeF2 (62-38 mole $) is pure FeF2; this is still being verified. The smaller equilibrium quotients in LiF-BeF2 result from stronger complexing

in a more basic

solvent.

Hygroscopic Behavior and Dehydration of Breeder Fuels It has been generally recognized that breeder fuels based on LiF-BeF2 as solvent are very hygroscopic and prone to hydrolysis, but no specific experimental evaluation of the problem had been made. Some salts can be dried without quently

extensive hydrolysis, and drying at low temperatures is freTrials were made to explore the prospects for removing helpful.12

Two compositions, LiF-BeF2water from breeder fuels at low temperatures. UF, (62-37-l mole 4) and LiF-BeF,-ThF,-UFh (62-36.5-l-0.5 mole '$), were These preparations were then prepared by melting with ammonium bifluoride. examined by x-ray diffraction and microscopic techniques and found to be typical samples. Only traces of U02 were present. A sample of each, ground to 100 mesh and weighing was placed in a nickel crucible temperature. The initial rate

approximately

10 g,

and exposed to water-saturated air at room of weight increase was 2.9 per day for each

composition. As exemplified in Fig. 2.2.15, for the sample with ThF,, after 40 days the total weight of the sample had increased by 23% and the rate of increase was 0.32$ per day; for the sample without ThF,, the corresponding values were 3O$ and 0.3% per day. These weight percentages are The samples were then placed based on the original weight before exposure. in an oven exposed to air at 133Â°C. Within 24 hr they had returned to the original weights. But on continuing the drying to obtain a constant weight, the samples continued to drop very.slowly to values 0.3 and 0.4$, respectively, below the starting.weight. Unfortunately, the salts at this state could not be distinguished from uncontaminated fuel by either x-ray diffraction or petrographic techniques. The~samples were then melted-â&#x20AC;&#x2DC;in a vacuum dry box at 30 to 50 p, and There was a further weight loss -a release of gas'bubbles was observed. of 0.6 and l$, this

respectively,

for -. then samples with

stage the samplesyere~predominantly

12Argonne National (1959).

Laboratory,

and without

green with

T~FI,.

many small black

Reactor Fuel Processing

L(4),

UNCLASSIFIED ORNL-LR-DWG 43723

E 16 I-I

i2 W

6 b-

TIME (doys)

Fig.

2.2.15.

Li F- BeF ,-Th F,-U

areas.

Hydration-Dehydration Cycle for

F, (62-36.51-0.5 Mol e %).

The green portion had a higher U02 content than the s t a r t i n g ma-

t e r i a l s ; t h e black portions were predominantly U02, and it w a s estimated that from 20 t o 4% of t h e uranium had been converted t o U 0 2 .

Evidently

the uranium had served as an oxide scavenger f o r the melt.

A second p a i r of samples w a s t r e a t e d as above except t h a t the baking i n air was eliminated.

Each sample went d i r e c t l y from the humidifier t o

the vax3uum dry box, where it w a s dried a t 135째C f o r 2 hr a t 30 t o 50 p and then melted.

Bubbling occurred as before, and t h e f i n a l samples were 1.5

and 1$ below the s t a r t i n g weight.

The samples fused a f t e r vacuum drying

were e s s e n t i a l l y i d e n t i c a l w i t h t h e fused sarrlples from t h e first experiment.

It was concluded t h a t t h e weight l o s s e s on prolonged drying were a t least i n p a r t due t o t h e s u b s t i t u t i o n of 0 (wt 16) f o r 2F ( w t 3 8 ) as a

consequence of hydrolysis, and t h a t a s a t i s f a c t o r y reconditioning of fuel

by a simple drying operation i s unlikely.

Graphite Compatibility Studies

Penetration of Graphite by Molten Fluorides Continuing studies13 of t h e permeation of graphite by f u e l mixtures

at approximately 1 a t m l e d t o the following conclusions.

Early experiments, i n which only slight permeation of graphites such c

as AGOT occurred, r e f l e c t e d the e f f e c t of surface oxide i n t h e graphite a s a source of plugging by the formation of insoluble U02. Such r e s u l t s could be a l t e r e d t o give easy permeation by using f u e l s with a l a r g e r oxide s o l u b i l i t y , o r by previously removing t h e oxide by treatment w i t h H2. When easy permeation w a s achieved, the r e l a t i v e composition of the f u e l i n t h e graphite w a s normal, i n contrast t o t h e e a r l i e r behavior which involved complications due t o oxide p r e c i p i t a t i o n . amount of permeation as short ones.

Long-term tests gave t h e same

There w a s good agreement between the

permeation obtained by experiment, i n t h e absence of oxide interference, and t h e permeation calculated on t h e b a s i s of t h e physical i n t e r a c t i o n between a nonwetting l i q u i d and a porous medium. Tests a t lower pressures have been discontinued i n favor of more pert i n e n t s t u d i e s a t 60 psig, corresponding t o reactor conditions.

A t these

higher pressures t h e permeation i s increased i n t h e expected manner, and

differences i n behavior due t o the presence of oxide are usually not apparent.

For example, when dealing w i t h a r e a d i l y permeable graphite, such

as AGOT, l i t t l e e f f e c t i s noted as a r e s u l t of pretreatment w i t h H2.

Attention has recently centered on the amount of permeation t o be exh i t e ; t y p i c a l r e s u l t s a r e shown raphite specimens were baked h r and then l e f t i n contact

i l i c o n carbide w a s accil y , ensuing l a r g e

reached because

f o r comparison.

c2.l

13MSR Quar. B o g . Rep. July 31, 1959, ORNL-2799, p 90. 65

Table 2.2.3.

Permeability of Various Graphites

Permeation conditions:

temperature, 1300'F; Weight Gains

Graphite

pressure, 60 p s i g

($1

LiF-BeF2-ThF4 (67-18-15 mole $)

LiF-BeF2-ThF4-UF4 ( 67.0-18.5 -14.0-0.5 mole $I )

AGOT

17-22

20-23

TSF

R-0013

s-4

4.6-7.0

3.6

21-CT-158

-0.1

18-CT -15 8

-0.1

GT-123

kO.1

50.1

mL- 82

6.2

CEX* (RLM-24)

Not completed

0.1-0.2

Cm** special

1.0

Not completed

*Ektruded tubing, 1-1/4-in. OD x 7/8-in. **Extruded tubing, 1/2-in. OD.

ID.

I n t e r c a l a t i o n of Graphite w i t h Molten S a l t s The p o s s i b i l i t y of i n t e r c a l a t i o n compounds of graphite and molten

f l u o r i d e s i s unlikely, i n view of t h e w i d e experience i n handling f u e l s i n graphite w i t h no evidence of chemical reaction.

However, because of

t h e prevalence of i n t e r c a l a t i o n of chloride w i t h graphite,14 it w a s of int e r e s t t o explore t h e phenomenon. O f the 20 p r i n c i p a l f i s s i o n elements, niobium, technetium, and pos-

s i b l y molybdenum f l u o r i d e s seemed most l i k e l y t o exhibit i n t e r c a l a t i o n w i t h graphite.

Most of t h e other fission-element cations form s t a b l e f l u o r i d e s

which have been included i n melts i n graphite crucibles i n t h e course of other investigations i n t h e Reactor Chemistry Division.

Also, the more

noble metals would be expected t o e x i s t a s t h e f r e e element and therefore would not i n t e r c a l a t e .

While molybdenum i s a l s o l i k e l y t o be uncorribined,

it could possibly form a low-valence fluoride.

Fluorides of molybdenum

w i t h a valence lower than s i x have been studied very l i t t l e .

Niobium forms

14W. &dorff, "Graphite I n t e r c a l a t i o n Compounds," i n Advances i n Inorganic Chemistry and Radiochemistry, H. J. Emelens and A. G. Sharpe, eds., p 223-266, v o l . I, Academic Press, New York, 1959.

a stable

pentafluoride

which has not yet been evaluated

little is known of the chemistry of technetium, rhenium more closely than it does manganese.

but it

in graphite.

Very

seems to resemble

When treated

with molten molybdenum pentafluoride, graphite swelled A graphite tube (3/8-in. OD, l/4-in. ID) was to form an intercalate. sealed in a copper capsule with MoF, and maintained at 100 to 15O'C for 17 hr. The unreacted MoF, was distilled off by heating to 200째C. As a result of the treatment part of the graphite tube had crumbled, outside diameter of the intact portion had increased to l/2 in. to water caused the tube to evolve heat and hydrogen fluoride similar to the behavior of pure MoF5. Molybdenum hexafluoride similar phenomenon has been dizing agents as these could to a lower valence state by

but the Exposure in-a manner

also gave evidence of intercalation, and a noted repeatedly with UFe. Such strong oxinot survive in a reactor, but would be reduced reaction with the containing walls.

Diffusion of Rare-Earth Fission Products in Graphite The development of techniques for the study of diffusion of rare Specimens of graphite are to be imearths in graphite is in progress. pregnated with breeder fuels containing a trace quantity of Eu152*15r,. The activity distribution in the graphite will be determined before and after exposure to clean fuel salt by microcore drilling of small graphite samples from the face of a section of the graphite rod. Tube furnaces, furnace controllers, and Inconel fuel containers for the leaching operation Equipment for microcore drilling has been designed have been procured. and fabricated and the technique tested on graphite samples containing cs137. This technique will be adapted for use in the hot cellto analyze graphite.samples from the MTR .graphite,-fused-salt experiment. A simple 1 glove box for contamination control . is under construction, and a saw for _: sectioning.the graphite rod ison order. Specimens of graphite for the first test were received, ready for impregnation.

were machined to the desired

Preparationlof Technological Operations In order to stock-pile tures

-Purified

sufficient

dimensions,

and are

Materials

quantities

of fluoride

salt

to supply the Molten Salt Reactor Program for the remainder

mixof this 67

f i s c a l year, t h e production f a c i l i t y w a s activated f o r t h r e e weeks, and 600 kg of fluoride s a l t mixes w a s processed.

Small-scale processing op-

e r a t i o n s accounted f o r another 140 kg, making a t o t a l of 740 kg. 4

The increased r a t e of t r a n s f e r and service operations encountered during the previous quarter continued during the f i r s t month of t h i s quart e r ; t h e r a t e then dropped.

Considerable e f f o r t has been devoted t o de-

veloping a technique f o r f i l l i n g recently designed i n - p i l e capsules15 f o r t e s t i n g graphite.

The r e s u l t s obtained t o date are promising but not com-

pletely satisfactory. Molten Ammonium Bifluoride as a Reagent Reactions of molten ammonium b i f l u o r i d e have been u s e f u l f o r prepari n g a large number of metal f l u o r i d e s and ammonium fluometallates.16

Ad-

d i t i o n a l reactions of anrmonium b i f l u o r i d e have been explored. Ammonium dichromate dissolved i n ammonium bifluoride a t 125째C t o form an orange m e l t which vigorously bubbled and rapidly became green a t about 200째C.

Ammonium hexaf luochromate ( 111) had formed by the following reac

tion:

Chromic acid reacted similarly:

C e r i u m t r i f l u o r i d e was prepared by t h e thermal decomposition of a complex, presumably ammonium hexafluocerate( 111), made by r e a c t i n g molten ammonium b i f l u o r i d e w i t h c e r i c oxide:

L i t h i u m hydroxide monohydrate, enriched i n isotope 7, w a s converted

i n t o t h e anhydrous fluoride by fusion with ammonium b i f l u o r i d e and eliminating v o l a t i l e s a t about 350째C. t

I5For t h e ORNL-mR-47 experiment. 16MSR Quar. Prog. Rep. Apr. 30, 1959, ORNL-2723, p 93-94.

Radiation

Effects

Corrosion Tests Under Radiation Two static-corrosion capsules, made of INOR- alloy, were irradiated in the Materials Testing Reactor. Fuel composition and test conditions are summarized in Table 2.2.4. Failure became evident from the release of radioactivity gas from one of the capsules. The two capsules were installed so it was necessary to terminate the test for both capsules.

into the offas a unit;

The Chromel-Alumel thermocouples attached to the capsules showed no sign of failure, and the capsules are being removed from the reactor by a process designed to preserve the thermocouples. examined in the hot cells at ORNL.

The capsules will

Metallographic tests will be made on the metal, chemical analyses will be made on the fuel, and calibrations will be made on the thermocouples.

Table 2.2.4.

Conditions

for 5000&r

Corrosion

Test Under Irradiation

Composition of fuel Melting point of fuel

Li7F-BeF2-U235Fb

(62-37-l

mole $)

Composition

MO, 17%; Cr, 8$; Fe, 5%; Mn, 0.5%; C, 0.06%; bal Ni 1250째F Air-cooled

842째F

of INOR-

Operating temperature Temperature control Weight of fuel per capsule Power'density (initial) Thermal flux Total houk.s.in reactor Total hours above 842'F

0.400 g 1.17 kw/cc l-2 x 1014 neutrons=cm-*a set-l -5508 3392

.-Total-hours not operating (shutdowns, etc.). _Integrated thermal.-flux Estimated:. uranium burnup _

.' 233 -~

2 x 1021 nvt 75%

: .-

2.3

FUEL PROCESSING

Emphasis i s being placed on modification of t h e hydrofluorinatiow v o l a t i l i z a t i o n process f o r application t o MSR salts containing ThF4.

The

process as o r i g i n a l l y developed was s a t i s f a c t o r y f o r t h e recovery of uranium from core and blanket salts i n a two-region r e a c t o r and f o r t h e reThere w a s no provision i n

cycle of Li7F and BeFz used i n t h e core fuel.’

t h i s process, however, f o r t h e handling of thorium, which i s p a r t i c u l a r l y desirable i n core salt, where frequent processing i s necessary.

The hy-

drofluorinationlrolatilization process has as an a t t r a c t i v e f e a t u r e t h e f a c t t h a t t h e processed material remains i n t h e f l u o r i d e form and thus requires l i t t l e f u r t h e r treatment before re-use i n the reactor.

Retention

of t h i s feature i s one objective of t h e work. The use of hot aqueous NH4F solution appears d e f i n i t e l y promising f o r processing ThF4-bearing fuels, and f’urther work i n t h i s d i r e c t i o n seems appropriate.

The p o s s i b i l i t y of using CIJ?,-HF

as a solvent f o r t h e simul-

taneous solution of UF4 and LiF no longer appears a t t r a c t i v e because an appreciable concentration of CIF, represses t h e LiF s o l u b i l i t y and because t h e s o l u b i l i t i e s of UF4 and ThF4 are unsatisfactory.

The N02-HF system

appears a t t r a c t i v e f o r t h e simultaneous d i s s o l u t i o n of LiF, BeF2, and W4, but it does not show s u f f i c i e n t ThFL s o l u b i l i t y . Thorium Fluoride S o l u b i l i t y i n Aqueous NH4F Solutions

An exploratory t e s t indicated that ThF4 w a s soluble t o about 5 w t i n 50 w t 46 aqueous NH4F solution at t h e b o i l i n g point, which i s high enough t o be of i n t e r e s t f o r processing. Typical f u e l s a l t s contain about 60 w t $J $ J

Experimental data indicated increasing ThF4 s o l u b i l i t y with increasing temperature and increasing NH4F concentration, although some d i f f i c u l -

ThF4.

t i e s were encountered i n sampling solutions a t o r near t h e b o i l i n g point. The ThF4 s o l u b i l i t y i n 5@ solution at 105°C w a s 49 mg/ml i n a sample p i -

p e t t e d from a solution i n which the s o l i d s had been allowed t o s e t t l e , and

w a s 43 mg/ml i n a sample f i l t e r e d through s i n t e r e d nickel.

The s o l u b i l i t y

dropped rapidly with decreasing temperature, t o about 12 mg/ml a t 60°C and

4 . 9 m g / m l a t 25°C.

I n 4346 NH4F solution a t 25°C t h e s o l u b i l i t y w a s only

’H. G. MacPherson, Molten S a l t Reactor Program S t a t u s Report, O m 2634 (Nov. 12, 1958). 70

u &

mg/ml.

The solid formed when these N&+F solutions of ThF4 were cooled or diluted was not ThF,+, but rather a compound (or compounds) involving N&+F and ThF&. The compositions of solids formed under various conditions are being determined. The investigation is being extended to measurements of the solubilities of the other fuel components - LiF, BeF2, UF4, and rare earths - both The effect of other components on the ThF4 individually and collectively. 0.4

solubility

has not been measured. Fuel-Component Solubility

in CW3-HE'

Mixed ClF3-HI? solvent appears unsatisfactory for a one-step process to dissolve both uranium and LiF. Further experiments confirmed the observations reported previously' that C1F3 in HF causes a drastic reduction in the LiF and BeF2 solubilities with MSR fuel salt (LiF-BeF2-ThF4-UF4, 62-36.5-l-0.5 mole $). The presence of significant amounts of Cl.F3 in HI? decreased the solubility of LiF from 400 to -20 g/kg, and of BeF2 from Uranium solubilities were generally about 0.25 g/kg; 3G40 to < 5 g/kg. although significant, they are too low to dissolve all the uranium associated with the dissolved LiF and BeF2. Rare-earth and thorium fluorides rare-earth solubilities were in the are very insoluble in these solutions; range 0.0001 to 0.0005 mole $, based on dissolved salt. is probably The U(N), which has a low solubility,

not converted

under

these conditions to the highly soluble U(V1). Operation of the CD',-HF system at a higher temperature and pressure to obtain conversion appears Hence no further work in this direction is planned. impractical. _~ Fuel-Component Solubility in NO;!-HE' Scouting 62-36.5-l-0.5 sion-products)

tests of the sol+ility of fuel salt (LiF-BeF2-ThF4-UF4, mole $, plus 0.05 mole $I rare-earthifluorides and trace fisThe results (Table in NO;!-HF~.solutions were completed.

2.3.1) showthat LiF ,and BeF2 have reasonably good solubility if the NO;! content-is not much higher-than 5 mole $ (above which LiF solubility drops) or much -lower-than probably 2 mole $J (below which BeF2 solubility drops). Uranium solubilities

were generally

about 1 g/liter,

with

some indication

*MSR Quar. Prog. Rep. July 31, 1959, ORNL-2799, p 96. 71

Table 2.3.1.

S o l u b i l i t i e s of Fuel Components and F i s s i o n Products i n N02-HF Solutions

Solubility 11512

(mole

LiF

BeF2

R a r e E a r t h s (mole $>

Major Components (g/kg)â&#x20AC;&#x2122;

Based on C e

Based on Pm Y

2.7

1.0

0.06

0.0013

0.0025

5 .O

0.9

0.15

0.0006

0.001

10.0

1.4

0.04

0.001

0.0003

t h a t values would be higher at NO2 concentrations above 10 mole s o l u b i l i t i e s a r e presumably high i n the absence of L i F and BeF2.

uraniu Thorium

s o l u b i l i t i e s were generally low, and rare-earth s o l u b i l i t i e s were mostly about 0.001 t o 0.002 mole

$, based on dissolved salt ( t h e most reliable

value, from an experiment discussed below, w a s 50-fold l e s s than t h i s ) . With 2.7 mole $ NO2 (Table 2.3.1) t h e BeF2 s o l u b i l i t y w a s unexpectedly high, corresponding almost exactly w i t h t h e NO2 content on a mole basis.

The L i F s o l u b i l i t y was only about half as high a s expected.

The uranium

s o l u b i l i t i e s account f o r about one-third of t h e uranium associated with the dissolved salt except w i t h 10 mole

$ â&#x20AC;&#x2122; NO2, where it accounts f o r a l l

of it. With 5 mole $ NO2 t h e t o t a l salt s o l u b i l i t y i s a l i t t l e over 100 c

g / l i t e r , which i s a reasonable value f o r processing. I n another experiment w i t h approximately 2 mole $ NO;! i n HF, the sol u t i o n w a s decanted f r o m t h e undissolved excess salt and both were analyzed separately.

The LiF, BeF2, uranium, and thorium s o l u b i l i t i e s were 33, 52,

0.5, and 0.04 g/kg, respectively, i n reasonable agreement w i t h t h e values reported above.

The NO2-HF solution dissolved 56$ of t h e LiF, 79$ of t h e

BeF2, 5% of t h e uranium, and 62$ of t h e cesium a c t i v i t y , but only 0.086$ of t h e cerium and 0.05% of t h e promethium.

The much l a r g e r samples per-

mitted more accurate determinations of t h e rare-earth a c t i v i t i e s than i n the experiments reported i n Table 2.3.1.

The t o t a l rare-earth s o l u b i l i t i e s

were 0.000042 mole $ calculated from t h e cerium determination and 0.000029 mole

calculated from t h e promethium determinations, based on dissolved

LiF and BeF2.

43 72

The above r e s u l t s were obtained a t room temperature.

As NO2 w a s added

t o HF, t h e b o i l i n g point rose rapidly t o about 56째C a t about 25 mole $ NO2 and then dropped t o t h e b o i l i n g point of NOz (21OC) w i t h about 60 mole $

NOz, a t which point a second phase appeared. The second phase appeared t o be nearly pure NO2. S a l t s o l u b i l i t i e s would probably be s i g n i f i c a n t l y higher a t t h e b o i l i n g points, since salt s o l u b i l i t i e s i n other HF systems have been observed t o increase w i t h temperature.

ORNL-2890 Reactors - Power TID-4500 (15th ea.)

INTERNAL DISTRIBUTION 1. 2. 3. 4. 5. 6. 7.

8. 9. 10. 11. 12. 13. 14. 15. 16. 17.

R. L. E. D. F. E. A. C. W. G.

M. E. R. W.

D. W. G. 18. C ,

19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34-36. 37. 38. 39. 40. 41. 42. 43.

44. 45. 46.

R. J. F. J. D. L. W. J. D. A. E. J. W. A.

J. W. E. C.

G. A f f e l G. Alexander

Bettis Billington Blankenship Blizard Boch Borkowski Boudreau Boyd Bredig Breeding Briggs Browning Campbell Carr Cathers Center (K-25) Charpie Coobs Culler H. DeVan A. Douglas B. W e t (K-25) K. Ergen Y. Estabrook E. Ferguson P. Fraas A. Franco-Ferreira H. Frye, Jr. R. G a l l T. Gresky L. Gregg R. Grimes Guth S. Harrill R. H i l l S. S. F. P. L. J. F. E. A. J. B. E, 0. H. I. E. A. H. L.

E. Hoffman H. W. Hof A. Hollaende A. S. Householder W. H. Jordan G. W. Keilholtz C. P. Keim E,

M. T. Kelley F. Kertesz B. W. Kinyon M. E. Lackey J. A. Lane R. S. Livingston H. G. MacPherson 54. W. D. Manly 55 E. R. Mann L. A. Mann 55 W. B. McDonald 57 58. H. F. McDuffie 59. J. R. McNally 60. H. J. Metz 61. R. P. Milford 62. E. C. Miller 63. J. W. Miller 64. K. Z. Morgan 65. J. P. Murray (Y-12) 66. M. L. Nelson 67. G. J, Nessle 68. W. R. Osborn 69. P. P a t r i a r c a 70. A. M. Perry 71. D. P h i l l i p s 72. W. D. Reel P. M. Reyling 73 74. J. T. Roberts 75. M. T. Robinson 76. H. W. Savage 77. J. L. Scott 78. H. E. Seagren E. D. Shipley 79 80. M. J. Skinner 81. G. M. Slaughter 82. A. H. S n e l l 83. E. Storto C. D. Susan0 84 85. J. A. Swartout 86. A. Taboada 87. E. H. Taylor 88 R. E. Thoma 89. D. B. Trauger 90. F. C. VonderLage

47. 48 49. 50. 51. 52. 53.

91. G. M. Watson 92. A. M. Weinberg 93. M. E. Whatley 94. J. C. White 95. G. D. Whitman 96. G. C. Williams 97. C. E. Winters

98. J. Zasler 99-102. ORNL Y-12 Technical Library, Document Reference Section 103-142. Laboratory Records Department 143. Laboratory Records, ORNL R.C. 144-145. Central Research Library

EXTERNAL DISTRIBUTION 146. D. H. Groelsema, AEC, Washington 147. Division of Research and Development, AEC, OR0 148-742. Given distribution as shown in TID-4500 (15th ed.) under Reactors-Power category (75 copies OTS)

W 1