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CRNL-TM-25 78

Contract No. W-7405-eng-26 Chemical Technology Division

PROCESSING OF THE MSRE FLUSH AND FUEL SALTS

R. B . Lindauer

AUGUST 1969

OAK RIDGE NATIONAL LABORATORY Oak Ridge, Tennessee operated by UNION CARBIDE CORPORATION for the IJ. S. ATObiIC ENERGY COPDIISSION

iii CONTENTS Page

............................. 1 . Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 . Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 . Process Description . . . . . . . . . . . . . . . . . . . . . 3.1 Fluorination . . . . . . . . . . . . . . . . . . . . . . 3 . 2 Reduction . . . . . . . . . . . . . . . . . . . . . . .

Abstract

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

4. Equipment Description and Performance

. . . . . Shielding . . . . . . Fuel Storage Tank . . NaF Trap . . . . . . . Caustic Scrubber . . . Mist Filter . . . . . Soda-Lime Trap . . . . Charcoal Traps . . . . Off-Gas Filter . . . .

4.1 Plant Layout 4.2 4.3 4.4 4.5 4.6

4.7 4.8

4.9

. . . . . . . . .

... 4.11 UF6 Absorbers . . . . . 4.12 Salt Sampler . . . . . . 4.10 Gas Supply System

4.13 Salt Filter

5.5 e m

5.6

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

. . . .

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

. . . .

6 6 8

13 15 17 17 17 20

21 22 22

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

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

. . . . . Fluorination of the Flush Salt . Reduction of the Flush Salt . . Fluorination of the Fuel Salt . Reduction of the Fuel Salt . . .

5.2 Caustic Scrubber Tests 5.4

Operating History . . . . . . . . . 5.1 Fluorine Reactor Tests . . . 5.3

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

4.14 Special Instrumentation 5

. . . . .

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

30 30

39 41 43 44 47

Page

..................... 6.1 Fluorine Utilization . . . . . . . . . . . . . . . . . 6.2 Corrosion . . . . . . . . . . . . . . . . . . . . . . . 6.3 Molybdenum . . . . . . . . . . . . . . . . . . . . . . 6.4 Plutonium . . . . . . . . . . . . . . . . . . . . . . . 6.5 Niobium . . . . . . . . . . . . . . . . . . . . . . . . 6.6 Iodine and Tellurium . . . . . . . . . . . . . . . . . 6.7 Uranium Absorption . . . . . . . . . . . . . . . . . . 6.8 Uranium Product Purity . . . . . . . . . . . . . . . . 6.9 Reduction o f Metal Fluorides . . . . . . . . . . . . . 7 . Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 8 . References . . . . . . . . . . . . . . . . . . . . . . . . . 6

Discussion of Data

50 50 53

56 57 57 62 64 66 70

PROCESSING OF THE MSRE FLUSH AND FUEL SALTS R . B. Lindauer

ABSTRACT The MSRE Fuel P r o c e s s i n g P l a n t , shakedown t e s t s of equipment and p r o c e d u r e s , and t h e uranium r e c o v e r y o p e r a t i o n a r e d e s c r i b e d . The MSRE f l u s h and f u e l s a l t b a t c h e s were f l u o r i n a t e d t o r e c o v e r 6 - 5 and 216 kg of uranium, Y e s p e c t i v e l y . Known l o s s e s d u r i n g p r o c e s s i n g were less t h a n 0 . 1 % . Gross b e t a and gamma decontamination f a c t o r s of 1 . 2 x l o 9 and 8 . 6 x lo8 were o b t a i n e d . Corrosion averaged about 0 . 1 m i l l h r . The c o r r o s i o n product f l u o r i d e s were reduced and f i l t e r e d t o p r o v i d e a c a r r i e r s a l t having a lower c o n c e n t r a t i o n of m e t a l l i c contaminants t h a n t h e o r i g i n a l c a r r i e r s a l t , 1.

INTRODUCTION

The Molten S a l t Reactor Experiment (MSRE) i s an 8-Mw c i r c u l a t i n g l i q u i d f u e l r e a c t o r o p e r a t i n g a t 1200째F.

The o r i g i n a l f u e l c o n t a i n e d

65 mole % L i F 4 , 30 mole % BeF2, 5 mole % Z r F 4 and 0 . 9 mole %

238-235UF:4.

The r e a c t o r f i r s t went c r i t i c a l on June 1, 1965, and began f u l l - p o w e r o p e r a t i o n i n May 1966.

P r i o r t o shutdown on March 26, 1968, t h e r e a c t o r

had o p e r a t e d f o r s l i g h t l y more t h a n one e q u i v a l e n t f u l l - p o w e r y e a r , o r 72,400 Mwhr. The MSRE Fuel P r o c e s s i n g F a c i l i t y was c o n s t r u c t e d i n a small c e l l i n t h e r e a c t o r b u i l d i n g f o r two p u r p o s e s : o x i d e s i n t h e f u e l o r f l u s h s a l t by H,-HF

(1) t o remove any accumulated s p a r g i n g , and ( 2 ) t o r e c o v e r

t h e o r i g i n a l uranium charge from t h e s a l t t o permit t h e a d d i t i o n of t h e 2 3 3 U f u e l charge f o r t h e second phase of r e a c t o r o p e r a t i o n .

The p l a n t

had been o p e r a t e d once b e f o r e , i n 1965, t o remove oxide (115 ppm) from t h e f l u s h s a l t b e f o r e t h e r e a c t o r went c r i t i c a l . '

S i n c e t h a t time t h e

oxide c o n t e n t s of b o t h t h e f l u s h s a l t and t h e f u e l s a l t have remained c o n s t a n t ; t h e r e f o r e , i t a p p e a r s u n l i k e l y t h a t such an o p e r a t i o n w i l l be required i n the future. A d e s i g n and o p e r a t i o n s r e p o r t d e s c r i b i n g t h e MSRE Fuel P r o c e s s i n g 2

Plant

was w r i t t e n b e f o r e t h e i n i t i a l t e s t run; it was r e v i s e d i n

December 1967 to reflect the modifications being made to permit handling

of short-decayed fuel salt. The present report covers the modifications made to the plant during the final plant testing operations and describes the results of these tests and of the flush and fuel salt processing.

2. SUMMARY The uranium recovery process consists of fluorine sparging to volatilize the uranium, followed by decontamination o f the gas stream with a 750'F

NaF bed and absorption of the UF6 on the 200'F

NaF beds. The excess

fluorine is removed by an aqueous scrubber. The corrosion product fluorides are reduced to the metals, which are filtered from the salt before the salt is returned to the reactor system. After four months of testing and modifications, during which the fluorine disposal system was changed from the gas-phase reaction with

SO2

t o the aqueous KI-KOH scrubber, processing of the blSRE flush salt (66 mole % LiF - 34 mole % BeF2) began.

The flush salt was fluorinated to recover

6 . 5 kg of uranium. About 216 kg of uranium was recovered from the MSRE

fuel salt. Corrosion of the fuel processing tank during fluorination of the fuel salt averaged about 0.1 mil/hr. The mast accurate calculations were based on the corrosion of nickel (0.04 mil/hr) and chromium (0.14 mil/hr).

Fluorine utilization averaged 7.7% during fluorination of the

flush salt bnd 39% during fluorination of the flush salt) and 39% during fluorination of the fuel salt. Reduction and filtration produced carrier salt containing less impurities than the original salt. The recovered uranium was decontaminated from fission products by gross gamma and gross beta decontamination factors of 8 . 6 x lo8 and 1.2 x lo9, respectively. Identifiable uranium losses were l e s s than 0.1%.

3. PROCESS DESCRIPTION 3.1

Fluorination

The flowsheet used is shown in Fig. 1. The.molten salt was forced from the drain tank under pressure, through a freeze valve in the drain Y

ORNL-DWG

200°F

NaF

ABSORBERS

68-8994

IN CUBICLE

”

FUEL

ACTIVATED

CHARCOAL

-Ll%lD TO VENT AND

FLUSH

MIST FILTER

TRAP \

‘CAUSTIC NEUTRALIZER

\CHARCOAL

TANK

Fig.

MSRE Fuel Processing

System.

TRAP

t a n k c e l l , through a m e t a l l i c f i l t e r (back-flow) and a n o t h e r f r e e z e v a l v e i n t h e processing c e l l t o t h e f u e l storage tank.

The t r a n s f e r was made a t

1000 t o l i 0 0 " F , a t e m p e r a t u r e t h a t i s well above t h e f r e e z i n g p o i n t of t h e s a l t b u t n o t h o t enough t o reduce t h e s t r e n g t h of t h e m e t a l l i c f i l t e r e l e -

ment below a s a f e l i m i t .

The t r a n s f e r was made with t h e lowest p o s s i b l e

p r e s s u r e i n o r d e r t o minimize stress on t h e f i l t e r element as t h e gas blew through a t t h e end o f t h e t r a n s f e r and a l s o t o minimize e n t r a i n m e n t of

s a l t o r a c t i v i t y from t h e f u e l s t o r a g e t a n k . The s a l t was t h e n cooled t o w i t h i n 50째F of t h e l i q u i d u s t e m p e r a t u r e t o minimize c o r r o s i o n and f i s s i o n product v o l a t i l i z a t i o n d u r i n g f l u o r i n a t i o n . The sample l i n e was purged w i t h helium t o p r e v e n t c o n d e n s a t i o n of UF6 a t t h e c o l d upper end.

The s a l t was sparged w i t h e i t h e r p u r e f l u o r i n e o r a

f l u o r i n e - h e l i u m mixture a t a r e l a t i v e l y h i g h flow r a t e (%40 l i t e r s / m i n ) t o

c m e r t t h e UFL, t o U F 5 .

F l u o r i n e u t i l i z a t i o n was h i g h d u r i n g t h i s p e r i o d .

When a l l t h e UF:, had been converted t o UF5, UF6 began t o form and v o l a t i l i z e , a s i n d i c a t e d by a t e m p e r a t u r e r i s e i n t h e f i r s t a b s o r b e r and by 3

r i s e on t h e i n l e t mass flowmeter ( s e e S e c t . 4 . 1 4 ) .

When t h i s o c c u r r e d ,

t h e f l u o r i n e flow was reduced t o 15 o r 25 l i t e r s / m i n t o i n c r e a s e t h e a b s o r b e r r e s i d e n c e time f o r more e f f i c i e n t a b s o r p t i o n and t o i n c r e a s e t h e fluorine utilization. The g a s l e a v i n g t h e f u e l s t o r a g e t a n k c o n s i s t e d of UF6, e x c e s s f l u o r i n e , helium, bfoFo and some CrF:, o r C r F 5 from c o r r o s i o n , I F 7 , and t h e f l u o r i d e s of some o t h e r f i s s i o n p r o d u c t s such as t e l l u r i u m , niobium, ruthenium, and antimony.

The gas passed through a 750째F sodium f l u o r i d e t r a p where t h e

chromium f l u o r i d e and most of t h e v o l a t i l i z e d f i s s i o n p r o d u c t s , e x c e p t i o d i n e and t e l l u r i u m , were r e t a i n e d .

A small f l u o r i n e flow was i n t r o d u c e d

upstream o f t h i s bed t o e n s u r e an e x c e s s of f l u o r i n e and t o p r e v e n t any n o n v o l a t i l e U F g from forming and remaining on t h e h e a t e d NaF i n t h e e v e n t t h a t t h e f l u o r i n e u t i l i z a t i o n was n e a r 100%. Although t h e f l u o r i n e u t i l i z a t i o n was n o t high enough t o r e q u i r e t h i s a d d i t i o n a l f l u o r i n e stream, a small flow was maintained t o p r e v e n t d i f f u s i o n and c o n d e n s a t i o n of UFg i.n the line. The gas s t r e a m , which now c o n s i s t e d of UF6, f l u o r i n e , helium, bloF6, IF7, T e F 6 , and a t r a c e of o t h e r f i s s i o n p r o d u c t s , l e f t t h e s h i e l d e d c e l l W

5 and passed through f i v e NaF a b s o r b e r s i n a s e a l e d c u b i c l e i n t h e operating area.

These a b s o r b e r s were h e a t e d t o 200 t o 250째F t o i n c r e a s e t h e

r e a c t i o n r a t e and t o minimize MoF6 a b s o r p t i o n . t o a t l e a s t 140'F

The UF6 p i p i n g was h e a t e d

t o p r e v e n t condensation of UF6.

As t h e UF6 began t o

l o a d on a g i v e n a b s o r b e r and t h e t e m p e r a t u r e s t a r t e d t o r i s e , t h e c o o l i n g

a i r was t u r n e d on t h a t p a r t i c u l a r a b s o r b e r t o l i m i t t h e t e m p e r a t u r e t o a maximum of 350째F.

High t e m p e r a t u r e reduced t h e uranium l o a d i n g by promot-

i n g s u r f a c e a b s o r p t i o n and reducing p e n e t r a t i o n of t h e UFg t o t h e i n s i d e of t h e p e l l e t s .

The f i n a l a b s o r b e r was o p e r a t e d below 250"F, where t h e

p a r t i a l p r e s s u r e of UFg over t h e UF6.2 NaF complex allowed only a n e g l i g i b l e amount of uranium t o r e a c h t h e c a u s t i c s c r u b b e r . I f t h e gas stream l e a v i n g t h e a b s o r b e r s c o n t a i n e d g r e a t e r t h a n 50% f l u o r i n e , i t was d i l u t e d w i t h helium b e f o r e r e a c h i n g t h e c a u s t i c s c r u b b e r . T h i s allowed a smooth r e a c t i o n i n t h e s c r u b b e r without t h e p r o d u c t i o n of

a flame o r p r e s s u r e o s c i l l a t i o n s .

- KOH 1300 l i t e r s of 2 M

The c a u s t i c s c r u b b e r was charged w i t h

0.33 M - KI c o n t a i n i n g 0.2 M- K ~ B Q O ~which , was

added as a s o l u b l e n e u t r o n p o i s o n .

The r e a c t i o n t h a t o c c u r r e d i n t h e

scrubber i s :

6 F 2 + 1 2 KOH + K I

1 2 KF + 6 H 2 0 + 3 / 2 02 + KIO3.

The s c r u b b e r s o l u t i o n was r e p l a c e d b e f o r e one-half o f t h e KOH had been consumed, as determined by f l u o r i n e flow and c a l c u l a t e d u t i l i z a t i o n , because d i p t u b e c o r r o s i o n was i n c r e a s e d when t h e OH- c o n c e n t r a t i o n was l e s s t h a n

1 FI.

Besides f l u o r i n e , most of t h e molybdenum and i o d i n e were removed i n

the scrubber. A h i g h - s u r f a c e - a r e a f i l t e r l o c a t e d downstream of t h e s c r u b b e r removed

any p a r t i c u l a t e m a t t e r from t h e s c r u b b e r .

During t e s t r u n s , h y d r a t e d

o x i d e s of molybdenum c o l l e c t e d a t s h a r p bends i n t h e l i n e from t h e s c r u b b e r . A soda-lime t r a p (a m i x t u r e of sodium and calcium h y d r a t e s ) provided a

means f o r d e t e c t i n g f l u o r i n e and a means f o r removing t r a c e s o f f l u o r i n e from t h e s c r u b b e r o f f - g a s b e f o r e i t reached t h e c h a r c o a l a b s o r b e r s .

The

t r a p was o p e r a t e d a t room t e m p e r a t u r e , and t h e t e m p e r a t u r e s were monitored. A c t i v a t e d impregnated c h a r c o a l t r a p s s o r b e d any i o d i n e t h a t was n o t removed i n t h e c a u s t i c s c r u b b e r .

The gas l e a v i n g t h e c h a r c o a l t r a p s con-

s i s t e d of o n l y helium and oxygen t h a t was

produced i n t h e c a u s t i c

s c r u b b e r ; t h e oxygen amounted t o about 25% o f t h e f l u o r i n e flow t o t h e scrubber.

This gas flowed through a flame a r r e s t e r and t h e n through an

absolute f i l t e r before being routed t o t h e c e l l exhaust.

I t was moni-

t o r e d f o r gamma a c t i v i t y and i o d i n e b e f o r e being mixed w i t h t h e rest o f t h e b u i l d i n g exhaust g a s , which passed through a d d i t i o n a l f i l t e r s and was f i n a l l y d i s c h a r g e d from a 1 0 0 - f t - t a l l s t a c k . When t h e r e was no longer any evidence of a b s o r b e r h e a t i n g , t h e f l u o r i n e flow was stopped and t h e s a l t was sampled and a n a l y z e d .

The uranium

c o n c e n t r a t i o n i n t h e s a l t was expected t o b e less t h a n 50 ppm a t t h i s time

. 3.2

Reduction

Before t h e s a l t could be r e t u r n e d t o t h e r e a c t o r system, t h e N i F 2 , F e F 2 , and C r F 2 produced b y c o r r o s i o n of t h e Hastelloy-N f u e l s t o r a g e t a n k had t o b e removed from t h e s a l t (hIoF6 i s v o l a t i l e ) .

Because t h e c o n c e n t r a -

t i o n o f n i c k e l i n Hastelloy-N i s h i g h e r t h a n t h a t of chromium o r i r o n , t h e c o n c e n t r a t i o n of N i F 2 was h i g h e r t h a n t h a t of C r F 7 o r F e F ? i n t h e f u e l salt.

S i n c e n i c k e l i s more noble t h a n i r o n o r chromium, i t was reduced

by hydrogen s p a r g i n g a t 1225'F.

A f t e r t h e r e d u c t i o n of N i F 2 was complete,

as i n d i c a t e d by f i l t e r e d s a l t samples, p r e s s e d zirconium metal s h a v i n g s were added t o t h e s a l t and hydrogen s p a r g i n g was continued t o reduce t h e In t h i s o p e r a t i o n , t h e Z r F b c o n c e n t r a t i o n of t h e s a l t was

FeF2 and C r F F ,

i n c r e a s e d by a n e g l i g i b l e amount (.1%). The reduced metals were removed by a f i b r o u s metal f i l t e r , and t h e e f f i c i e n c y of t h e f i l t r a t i o n was v e r i f i e d by sampling t h e f i l t e r e d s a l t . 4.

EQUIPMENT DESCRIPTION AND PERFORMANCE

This s e c t i o n d e s c r i b e s t h e performance of equipment n o t i n c l u d e d i n the discussion i n Sect. 6. 4.1

P l a n t Layout

Most o f t h e p r o c e s s i n g equipment i s l o c a t e d i n t h e f u e l p r o c e s s i n g c e l l ( F i g . 2 ) , which i s 13 x 13 x 1 7 f t deep and i s s i t u a t e d j u s t n o r t h of t h e r e a c t o r d r a i n t a n k c e l l .

This p r o c e s s i n g c e l l c o n t a i n s t h e f u e l

+d i

a, 3

cv M 0.

.rl

s t o r a g e tank ( f l u o r i n a t o r ) , t h e 750'F KaF t r a p , t h e c a u s t i c s c r u b b e r , two remotely-operated a i r v a l v e s , t h r e e s a l t f r e e z e v a l v e s , and t h e blower f o r t h e a b s o r b e r c u b i c l e . The c e l l t o t h e e a s t ("spare c e l l " ) i s a l s o 13 x 13 x 1 7 f t and c o n t a i n s t h e o f f - g a s equipment

- - m i s t f i l t e r , soda-lime t r a p , c h a r c o a l

t r a p s , and o f f - g a s f i l t e r - - which i s l o c a t e d downstream of t h e c a u s t i c scrubber. The p l a n t i s o p e r a t e d from t h e high-bay a r e a over t h e s e two c e l l s . T h i s a r e a c o n t a i n s t h e absorber c u b i c l e , i n s t r u m e n t c u b i c l e , i n s t r u m e n t panelboard, sampler and sampler panelboard, hydrogen and oxygen m o n i t o r s , and r a d i a t i o n d e t e c t i o n i n s t r u m e n t s . The g a s supply s t a t i o n , which c o n t a i n s t h e f l u o r i n e manifold (where two 1 5 , 0 0 0 - l i t e r f l u o r i n e t a n k s mounted on t r a i l e r s can be c o n n e c t e d ) , t h e hydrogen manifold, and t h e p r e s s u r e and flow i n s t r u m e n t a t i o n a s s o c i a t e d w i t h t h e s e two g a s e s , i s s i t u a t e d o u t s i d e t h e b u i l d i n g , t o t h e s o u t h west of t h e b u i l d i n g .

The helium f o r purging and s p a r g i n g comes from t h e

r e a c t o r system s u p p l y . 4.2

Shielding

The s h i e l d i n g around t h e f u e l p r o c e s s i n g c e l l was designed t o l i m i t t h e r a d i a t i o n l e v e l t o 5 mrad/hr when a f u l l y i r r a d i a t e d , 3-day-decayed f u e l b a t c h was i n t h e f u e l s t o r a g e t a n k .

To meet t h i s requirement, new

roof p l u g s k e r e i n s t a l l e d , and t h e e a s t and west walls of t h e c e l l were backed up by an a d d i t i o n a l 2 f t of s t a c k e d b a r y t e s b l o c k . A d d i t i o n a l s h i e l d i n g was designed f o r 30-day-decayed f u e l , b u t was n o t i n s t a l l e d because t h e p l a n t t e s t i n g r e q u i r e d more time t h a n e x p e c t e d . This s h i e l d i n g consisted o f : (1)

c h a r c o a l beds i n t h e s p a r e c e l l - t o

permit l i m i t e d e n t r y f o r main-

tenance; (2)

UFg a b s o r b e r s i n t h e o p e r a t i n g area

-to

reduce t h e background a c t i v -

i t y from i o d i n e and t e l l u r i u m i n t h e gas s t r e a m ; (3)

an NaF t r a p i n t h e f u e l p r o c e s s i n g c e l l - t o

shield the electrical

i n s u l a t i o n and v a l v e diaphragms f o r absorbed "Nb. The s h i e l d i n g used i s summarized i n Table 1.

Table 1 ,

S h i e l d i n g f o r t h e Fuel P r o c e s s i n g System Thickness (in. )

Lo c a t i o n

Mater i a 1

Fuel p r o c e s s i n g c e l l 24

Normal c o n c r e t e High-D c o n c r e t e

South w a l l

36 12

hormal c o n c r e t e tigh-D c o n c r e t e

West wall

12 24

iiormal c o n c r e t e Iiigh-D c o n c r e t e

North wall

Normal c o n c r e t e

Roof

High-D c o n c r e t e

Sa 1t s amp 1e r

East wall

4,3

1,ead

Fuel S t o r a g e Tank

The c o n s t r u c t i o n of t h e f u e l s t o r a g e t a n k , o r f l u o r i n a t o r ( s e e F i g . 3 )

i s similar t o t h a t of t h e r e a c t o r d r a i n t a n k s , except t h a t t h e f l u o r i n a t o r i s 30 i n . t a l l e r t o p r o v i d e about 38% f r e e b o a r d above t h e normal l i q u i d level.

T h i s e x t r a h e i g h t minimized s a l t c a r r y o v e r d u r i n g gas s p a r g i n g .

The t a n k i s suspended i n s i d e t h e h e a t e r and i n s u l a t i o n assembly t o m i n i -

m i z e t h e weigh c e l l t a r e weight.

There i s no p r o v i s i o n f o r c o o l i n g s i n c e

t h e h e a t l o s s l i m i t s t h e t e m p e r a t u r e t o less t h a n 1200'F a f t e r two weeks' decay ( F i g s . 4 and 5) The f u e l s t o r a g e t a n k i s h e a t e d by f o u r s e t s of h e a t e r s , which p r o v i d e

5 . 8 kw on t h e bottom, 1 1 , 6 kw on t h e lower s i d e s , 5 , 8 kw on t h e upper s i d e s , and 2 kw on t h e t o p . separate powerstat.

Each group of h e a t e r s i s c o n t r o l l e d by a

During t h e p e r i o d i n which UF4 was converted t o UF5

(when t h e f l u o r i n e u t i l i z a t i o n was h i g h ) , t h e h e a t of r e a c t i o n , p l u s t h e a f t e r h e a t , p r o v i d e d s u f f i c i e n t h e a t t o m a i n t a i n t h e s a l t a t 850'F0

About

1 2 kw of e l e c t r i c a l h e a t was r e q u i r e d d u r i n g t h e r e d u c t i o n o p e r a t i o n a t

1225째F.

0 R N L- DW G 65- 25 09 R

SAMPLER LINE ULTRASONIC L E V E L PROBE TO TRANSDUCER

-O

GAS OUTLET

INyT GAS

SALT INLET AND OUTLET LINE

SUPPORT RING,+

I' I

SUPPORT) COLUMN

LIQUID LEVEL

1 7'in.

1 1 i in.

6 2 in. I I

I1 II

I I

1 ;

STABILIZER n

Fig. 3.

50 in.

Fuel Storage Tank.

I-

ORNL-DWG

Fig. 4.

20 50 DECAY TIME ( d a y s )

100

MSRE After Heat.

200

69-6779

500

O R N L - DWG 69-6780

.7I

FLUSH SALT R E DUC T I 0Nb o /

COOL DOWN RUN NO 3 RUN NO 4

100

300

Fig. 5.

700 900 FST TEMPERATURE (OF)

500

1100

Fuel S t o r a g e Tank Heat Loss.

.I300

The gas i n l e t l i n e f o r t h e f u e l s t o r a g e t a n k has a normal submergence of 64 i n . , and t h e d i f f e r e n t i a l p r e s s u r e between t h i s l i n e and t h e gas s p a c e p r o v i d e s an i n d i c a t i o n o f l i q u i d l e v e l ,

The tank i s equipped with

an u l t r a s o n i c probe ( S e c t . 4.14) t o check t h e weigh c e l l c a l i b r a t i o n d u r i n g t h e f i l l i n g and emptying o p e r a t i o n s . S e v e r a l s a f e t y i n t e r l o c k s a r e provided on t h e f u e l s t o r a g e t a n k :

The gas s p a r g e l i n e i s a u t o m a t i c a l l y vented i f t h e p r e s s u r e i n t h i s l i n e d e c r e a s e s t o t h a t of t h e gas s p a c e .

This prevents accidental

backup o f molten s a l t i n t h e c o l d gas i n l e t l i n e . 2.

An a u t o m a t i c v a l v e w i l l open i n t h e tank o f f - g a s l i n e i f t h e t a n k p r e s s u r e r e a c h e s 50 p s i g .

An alarm sounds a t 5 p s i g , which i s a

p r e s s u r e h i g h e r t h a n t h a t normally found d u r i n g o p e r a t i o n . 3.

F l u o r i n e flow t o t h e tank i s stopped i f t h e helium purge flow down t h e sampler l i n e s t o p s .

This minimizes t h e amount of f l u o r i n e , UF,,

o r r a d i o a c t i v e g a s e s which could d i f f u s e i n t o l i n e s l e a v i n g t h e c e l l

i n t h e event t h a t t h e helium supply i s l o s t . 4.

The f l u o r i n e supply v a l v e i s designed s o t h a t it must b e c l o s e d b e f o r e t h e s a l t sampler v a l v e can be opened. 4.4

NaF Trap

The NaF t r a p , shown i n F i g . 6 i s o p e r a t e d a t 750 t o 800"F,

In t h i s

t e m p e r a t u r e r a n g e , v o l a t i l e ruthenium, niobium, antimony, and chromium f l u o r i d e s a r e absorbed, while uranium and molybdenum h e x a f l u o r i d e s p a s s through.

The s l i g h t l y o v e r s i z e d l i n e from t h e f u e l s t o r a g e tank i s a l s o

h e a t e d t o 750째F t o p r e v e n t t h e a b s o r p t i o n of uranium a t t h e t r a p i n l e t . The t r a p h a s two s e t s of h e a t e r s t h a t a r e s e p a r a t e l y c o n t r o l l e d , 2 , 2 5 kw i n t h e c e n t e r p i p e and 9 kw on t h e s i d e s .

There a r e t h r e e thermocouples

l o c a t e d i n w e l l s a t t h e i n l e t , c e n t e r , and o u t l e t o f t h e t r a p , r e s p e c tively,

which a r e m a i n t a i n e d a t t e m p e r a t u r e s w i t h i n 1 0 째 F o f each o t h e r ,

With 4 i n . of i n s u l a t i o n , t h e h e a t l o s s i s about 1270 w a t 775'F. Before we had determined t h a t most of t h e niobium l e f t t h e s a l t d u r i n g r e a c t o r o p e r a t i o n , we were concerned t h a t t h e 3 x l o 5 c u r i e s of g5Nb i n t h e f u e l s a l t would cause o v e r h e a t i n g of t h e t r a p .

With t h e

extended decay t i m e , we c a l c u l a t e d t h a t 1 x l o 5 c u r i e s of gsNb would b e

O R N L - D W G 65-2511R

ING B A I L

-OUTLET

INLET

I I

I 18 in.

I I I

I1 I I I I

HEATING '

I PIPE

1 I I I

OPEN^

AT TOP ONLY

I I

I I I

I I I I I I

I I

BAFFLE

12 in.

20 in.

A Fig. 6. Sodium Fluoride Trap.

15 i n t h e s a l t a t t h e time of p r o c e s s i n g .

Apparently, however, most of t h e

niobium e i t h e r p l a t e d o u t o r was c a r r i e d out i n t h e r e a c t o r o f f - g a s stream s i n c e no d e t e c t a b l e h e a t i n g of t h e t r a p was d e t e c t e d d u r i n g f l u o r i n a t i o n and t h e c e n t e r p i p e a i r c o o l i n g system was n o t r e q u i r e d . We were a l s o concerned t h a t t h e t r a p might become plugged w i t h v o l a t i l i z e d chromium f l u o r i d e s . replaceable.

For t h i s r e a s o n , t h e t r a p was designed t o be

The p i p i n g a s s o c i a t e d w i t h t h e t r a p i s f l a n g e d , with pro-

v i s i o n f o r remote leak d e t e c t i o n , and t h e h e a t e r and thermcouple l e a d s a r e provided w i t h d i s c o n n e c t s .

Because o f t h e a n t i c i p a t e d h i g h r a d i a t i o n

l e v e l , a d e f e c t i v e t r a p would be disconnected and moved t o an empty space w i t h i n t h e c e l l i n s t e a d o f b e i n g removed from t h e c e l l .

However, we d i d

n o t d e t e c t any i n c r e a s e i n p r e s s u r e drop between t h e f u e l s t o r a g e tank and t h e absorber i n l e t .

Chromium f l u o r i d e v o l a t i l i z a t i o n was expected as t h e

uranium c o n c e n t r a t i o n i n t h e s a l t d e c r e a s e d ; b u t such v o l a t i l i z a t i o n was a p p a r e n t l y almost i n s i g n i f i c a n t u n t i l t h e c o n c e n t r a t i o n became as low as 20 ppm. 4.5

C a u s t i c Scrubber

The c a u s t i c s c r u b b e r shown i n Fig. 7 was used f o r d i s p o s a l o f e x c e s s f l u o r i n e and of t h e HF produced d u r i n g N i F 2 r e d u c t i o n .

The Flonel s p r a y

r i n g d i s t r i b u t o r o r i g i n a l l y i n s t a l l e d i n t h e tank was r e p l a c e d with two d i p l i n e s , each with t h r e e 3 / 8 - i n . h o l e s , as shown i n t h e f i g u r e .

The

d i p l i n e s have s h u t o f f v a l v e s w i t h e x t e n s i o n h a n d l e s t o p e r m i t a l t e r n a t i n g t h e l i n e s when plugging o c c u r s .

The new d i p l i n e s a r e made o f I n c o n e l ,

which has a h i g h e r c o r r o s i o n r e s i s t a n c e ( t h a n Monel) t o t h e KOH-KI-F2 action.

re-

The s c r u b b e r and o t h e r i n t e r n a l p i p i n g were o r i g i n a l l y c o n s t r u c t e d

of Inconel.

The c o o l i n g water t o t h e c o i l i s n o t metered; however, o n l y

a f r a c t i o n of t h e f u l l flow was r e q u i r e d t o c o n t r o l t h e temperature d u r i n g fluorination.

On one o c c a s i o n , i n which t h e temperature was allowed t o

i n c r e a s e from l e s s t h a n 8 0 째 F t o g r e a t e r t h a n 100"F, no d e c r e a s e i n plugging

was n o t e d . The c a u s t i c s c r u b b e r was equipped w i t h a c o n t a c t microphone s i m i l a r t o t h e one used f o r t h e f u e l s t o r a g e t a n k .

I t was used i n t e r m i t t e n t l y as

a check on t h e gas flow r a t e through t h e d i p l i n e s .

During a 2-hr p e r i o d

i n r u n 6 , u n u s u a l l y loud, r a p i d n o i s e s , accompanied by r a p i d b u t small

O R N L - D W G 65-2513R

GAS

TH ERMoWELL

LEVEL BUBBLER TUBE

84 in.

18 in.

F i g . 7.

C a u s t i c Scrubber.

p r e s s u r e f l u c t u a t i o n s i n t h e l i n e t o t h e s c r u b b e r , were h e a r d .

Switching

d i p t u b e s r e s t o r e d t h e normal bubble flow sound.

Mist F i l t e r

4.6

The m i s t f i l t e r i s a h i g h - e f f i c i e n c y F i b e r g l a s a i r f i l t e r c o n s i s t i n g of f i f t y - f i v e 9-1/2-in.-diam

by 2 8 - i n . - l o n g bags hanging v e r t i c a l l y i n a

30-in.-diam by 4 - f t - h i g h s t a i n l e s s s t e e l v e s s e l . about 50 f t 2 .

The t o t a l f i l t e r area i s

The f i l t e r , which i s mounted i n an opening i n a h o r i z o n t a l

s u p p o r t p l a t e n e a r t h e t o p of t h e v e s s e l , was caulked t o p r e v e n t b y p a s s i n g . The t a n k i s h e a t e d w i t h steam c o i l s t h a t a r e wrapped around t h e tank t o p r e v e n t condensation of t h e m o i s t u r e t h a t i s c a r r i e d over from t h e c a u s t i c scrubber.

A thermowell i n s t a l l e d i n t h e gas space above t h e f i l t e r was

used t o a d j u s t t h e amount of i n s u l a t i o n i n o r d e r t o p r e v e n t o v e r h e a t i n g and damage t o t h e f i l t e r b i n d e r .

4.7

Soda-Lime Trap

The soda-lime t r a p , shown i n Fig. 8, was charged with a c t i v a t e d alumina when i t was used as t h e f l u o r i n e d i s p o s a l backup t r a p f o r t h e SO2 system.

When t h i s d i s p o s a l method was abandoned i n f a v o r o f t h e aqueous

s c r u b b e r , t h e t r a p was recharged w i t h soda-lime, which i s very e f f e c t i v e f o r t h e removal of f l u o r i n e a t room t e m p e r a t u r e b u t cannot be used with SO,.

To p r e v e n t e x c e s s i v e p r e s s u r e drop w i t h a gas having a h i g h f l u o r i n e

c o n t e n t , t h e soda-lime was mixed w i t h an e q u a l volume of 4- t o 8-mesh alumina, which has a very slow r e a c t i o n r a t e a t low t e m p e r a t u r e s .

To p r e -

v e n t condensation of water vapor i n t h e gas from t h e s c r u b b e r , t h e soda-

lime t r a p was i n s u l a t e d and t r a c e d w i t h low-temperature steam t u b i n g ? Thermocouples were i n s t a l l e d n e a r t h e i n l e t and n e a r t h e o u t l e t . During t h e p r o c e s s i n g of t h e f l u s h and f u e l s a l t s , no t e m p e r a t u r e r i s e

was observed.

Thus it appears t h a t no u n r e a c t e d f l u o r i n e escaped from t h e

caustic scrubber.

4.8

Charcoal Traps

The c h a r c o a l t r a p s shown i n F i g . 9 were c o n s i d e r a b l y overdesigned t o p e r m i t t h e h a n d l i n g o f t h e l a r g e amount of i o d i n e t h a t i s p r e s e n t i n 30-daydecayed f u e l , and t o allow f o r t h e u n c e r t a i n t i e s a s s o c i a t e d w i t h a gas

ORNL-DWG 68-2730A

OUTLET

c H ARG I NG/ FLANGE

30 in.

6 - in.

F i g . 8.

Soda-Lime Trap.

ORNL-DWG

GAS IN LET

F i g . 9. Charcoal T r a p s .

68-!3777

20 stream c o n t a i n i n g SO;! and S02F2.

The o r i g i n a l t r a p ( i n l e t ) was i n i t i a l l y

charged with r e p l a c e a b l e c a n n i s t e r s , each of which had a t o t a l bed depth The f i n a l c a p a c i t i e s and r e s i d e n c e times a r e shown i n Table

of 1 - 1 / 2 i n . 2.

Table 2 .

Trap

Diameter (in.)

Length (in. )

Charcoal Traps

Volume (liters)

Residence Time a t Average Flow of 16 s t d l i t e r s / m i n (set>

Inlet

5.84

Backup

3.17

9.01

Total

The t r a p s a r e steam-traced i n t h e same manner as t h e soda-lime t r a p . S u r f a c e thermocouples (TE) a r e l o c a t e d a t t h e i n l e t of t h e f i r s t t r a p and

a t t h e i n l e t and t h e o u t l e t of t h e backup t r a p .

Temperatures were main-

t a i n e d between 175 and 205째F d u r i n g p r o c e s s i n g , and no a d d i t i o n a l h e a t i n g

was d e t e c t e d a t any t i m e . Four i o n chambers, l o c a t e d a t t h e i n l e t and t h e o u t l e t of each t r a p were used t o d e t e c t t h e accumulation of i o d i n e ; however, because t h e f u e l had been allowed t o decay f o r such a l e n g t h y p e r i o d , none o f t h e r e a d i n g s increased during processing.

Five chambers (CT-A-E) as shown i n F i g . 9 ,

were used d u r i n g t h e f l u o r i n e r e a c t o r t e s t s d e s c r i b e d i n S e c t . 5 . 1 . 4.9

Off-Gas F i l t e r

The f u e l p r o c e s s i n g c e l l v e n t i l a t i o n a i r and t h e gas stream from t h e c h a r c o a l t r a p s p a s s through a 2 - i n . - d e e p ,

24- by 2 4 - i n . F i b e r g l a s p r e -

f i l t e r and a 1 l - 1 / 2 - i n . - d e e p y 24- by 2 4 - i n . F i b e r g l a s a b s o l u t e f i l t e r b e f o r e p a s s i n g through t h e r e a c t o r system containment f i l t e r s and t h e containment s t a c k .

There a r e t h r e e 2-in.-diam b u t t e r f l y v a l v e s f o r i s o -

l a t i o n and f o r bypassing t h e f i l t e r s d u r i n g replacement of t h e l a t t e r . v

Since these valves do not have soft seats, it was necessary to blank the bypass valve in order to obtain a satisfactory DOP test. A locally mounted differential-pressure transmitter indicates the pressure drop across the filters on the fuel-processing system panelboard. During the processing described in this report, the differential pressure varied between 1/2 and 1 in, H 2 0 .

This variation was probably the result

of variable flow rates rather than a buildup of solids on the filter. 4.10 Gas Supply System The fluorine and hydrogen manifolds and associated instrumentation are located outside the building. Space and piping are available to connect two 15,000-liter fluorine tanks mounted on trailers simultaneously, Each tank holds sufficient fluorine to volatilize the uranium that would normally be loaded on one group of absorbers; piping is provided for purging the connecting piping before and after a tank is used. The tanks can be initially loaded with fluorine under a pressure of 70 psig. This pressure is reduced to 18 psig by a throttling valve that is controlled automatically from the operating panelboard, The fluorine then passes through a NaF trap for removal of HF before being metered through an orifice. Another throttling valve regulates the flow rate of fluorine to the fuel storage tank. The fluorine flow downstream of the fuel storage tank is regulated by a manual throttling valve and measured by an integral-orifice flowmeter. The hydrogen manifold consists of two banks of two cylinders each. The manifold has a two-stage pressure regulator containing an interstage pressure relief valve. This pressure regulator is set to provide a constant 15-psig pressure upstream of the flow control valve (which is controlled from the panelboard). The flow is measured by an orifice meter. High-purity hydrogen was used to prevent oxide contamination of the salt during the reduction step. Spark-proof tools were used for changing the cylinders, and joints were leak-tested after each change. Helium is obtained from the reactor system helium supply, which consists of a 39,000-ft3 tank mounted on a trailer. The 2400 psig pressure is reduced to 20 psig at the fuel processing system panelboardThe helium is analyzed for moisture and oxygen before and during usage.

22 4.11

UF6 Absorbers

Five a b s o r b e r s ( s e e F i g . l o ) , connected i n s e r i e s , are l o c a t e d i n a

9 f t 4 i n . x 2 f t 4 i n . x 2 f t 2 i n . s e a l e d c u b i c l e l o c a t e d i n t h e operat i n g a r e a above t h e p r o c e s s i n g c e l l .

The c u b i c l e i s v e n t e d t o t h e c e l l ,

where a blower i s l o c a t e d f o r p r o v i d i n g a d d i t i o n a l n e g a t i v e p r e s s u r e [below t h e - 0 . 3 i n . H 2 0 i n t h e c e l l ) when a i r i s being used t o cool t h e absorbers.

T h i s blower f a i l e d d u r i n g f u e l s a l t run 1 ( S e c t . 5 . 5 ) .

When

loaded t o w i t h i n 1 / 2 i n . o f t h e t o p , each a b s o r b e r h o l d s about 25 kg of

NaF.

The minimum c r o s s - s e c t i o n a l area ( o u t l e t s i d e ) i s 0 . 4 6 f t 2 .

The

i n l e t and t h e o u t l e t Hastings mass flowmeters ( S e c t . 4.14) a r e a l s o l o c a t e d i n the cubicle. Each a b s o r b e r i s mounted i n an i n s u l a t e d can with a removable i n s u l a t e d cover.

An a i r c o o l i n g c o i l and an e l e c t r i c h e a t e r a r e p o s i t i o n e d

below each a b s o r b e r .

A s e p a r a t e thermocouple on t h e bottom p l a t e of each

h e a t e r i n d i c a t e s o v e r h e a t i n g o r burnout of a h e a t i n g e l e m e n t .

Each

h e a t e r was used t o h e a t each a b s o r b e r t o about 200째F b e f o r e t h e s t a r t o f UF6 a b s o r p t i o n .

When a b s o r p t i o n began, t h e h e a t was t u r n e d o f f and a i r

was t u r n e d on. A l l a b s o r b e r p i p i n g l o c a t e d upstream of t h e f i n a l a b s o r b e r i s h e a t e d

and i n s u l a t e d t o p r e v e n t condensation of U F 6 .

The a b s o r b e r s a r e connected

w i t h removable jumpers having r i n g - j o i n t f l a n g e s . t e s t e d before the absorber c u b i c l e i s sealed.

The f l a n g e s a r e leak-

Copper r i n g s a r e u s e d , and

a t o r q u e wrench i s employed t o e n s u r e t h a t t h e p r e s s u r e on t h e r i n g s i s

uniform. 4.12

S a l t Sampler

The f u e l s t o r a g e tank i s provided w i t h a s a l t sampler s i m i l a r t o t h e s a m p l e r - e n r i c h e r used w i t h t h e r e a c t o r f u e l pump ( s e e F i g . 1 1 ) .

The

sampler, which i s mounted on a semipermanent r o o f p l u g n e a r t h e i n s t r u m e n t panelboard, i s connected t o t h e t a n k by a v e r t i c a l 1 - 1 / 2 - i n . p i p e .

s e p a r a t e i n s t r u m e n t panelboard f o r t h e sampler i s l o c a t e d i n t h e same area.

During p r o c e s s i n g , t h e sampler l i n e was purged by a minimum o f 5

s t d l i t e r s of helium p e r minute, mainly t o p r e v e n t t h e c o n d e n s a t i o n of

UFF, on t h e c o l d s u r f a c e s .

Two thermocouples on t h e sampler l i n e showed

23 ORNL- DWG 65-2544R

THERMOWELL

---

MATERIAL: CARBON STEEL

AIR COOLING PIPE

REMOVABLE

F i g . 10.

UF6 Absorbers.

24 ORNL-DWG 63-5848R

SAMPLER-ENRICHER SCHEMATIC

Fig. 11.

MSRE Sampler-Enricher.

t e m p e r a t u r e s of 550째F and 130"F, r e s p e c t i v e l y , a t p o s i t i o n s 3 f t above t h e t a n k and 6 f t above t h e tank (near t h e bottom of t h e r o o f p l u g s ) . IJnder t h e c o n d i t i o n s p r e v a l e n t d u r i n g t h e p r o c e s s i n g of t h e f u e l s a l t , condensation of U F g would n o t occur above a t e m p e r a t u r e of 115"F, which would probably b e n e a r t h e t e m p e r a t u r e of t h e i s o l a t i o n v a l v e i n t h e o p e r a t i n g area. The sampler was used f o r 33 sampling o p e r a t i o n s and f o r charging zirconium c a p s u l e s f o r t h e s t r u c t u r a l m e t a l f l u o r i d e r e d u c t i o n .

The o n l y

d i f f i c u l t i e s experienced involved t h e f i l t e r c a p s u l e s ; t h e s t a n d a r d "dip" samples were t a k e n r e l i a b l y .

On some o c c a s i o n s , t h e vacuum i n t h e f i l t e r

c a p s u l e s was l o s t due t o premature m e l t i n g of t h e f r o z e n s a l t p l u g s which were designed t o r e t a i n t h e vacuum.

When t h e temperature d i f f e r e n t i a l

between t h e s a l t and t h e f r e e z i n g p o i n t was t o o low, t h e c a p s u l e s f a i l e d t o provide s u f f i c i e n t f i l t e r e d s a l t . A r a d i a t i o n d e t e c t o r was mounted on t h e sample l i n e n e a r t h e i s o l a -

t i o n v a l v e below t h e sampler.

I t was s e t t o alarm when t h e r a d i a t i o n

l e v e l reached 100 m r / h r . 4.13

Salt Filter

The s a l t f i l t e r i s i n s t a l l e d i n t h e f u e l p r o c e s s i n g c e l l between t h e c e l l wall and t h e f r e e z e v a l v e f o r t h e f u e l s t o r a g e t a n k .

The r e p l a c e a b l e

f i l t e r element, which r e s t s on a s p h e r i c a l s e a l , i s mounted i n a h e a t e d , i n s u l a t e d 6-in.-diamY 7-ft-long pipe.

The 4 - f t - l o n g f i l t e r c o n s i s t s o f

two c o n c e n t r i c f i b r o u s m e t a l c y l i n d e r s with a t o t a l f i l t e r a r e a o f 8 65 ft2.

The s a l t e n t e r s t h e s i d e of t h e f i l t e r housing, j u s t above t h e

f i l t e r element and l e a v e s through a bottom o u t l e t ( s e e F i g . 1 2 ) " The upper 3 f t o f t h e f i l t e r housing i s normally unheated and p r o v i d e s a t r a n s i t i o n zone from t h e molten s a l t t o t h e c o o l r i n g j o i n t s e a l f l a n g e , which c o n t a i n s a c o n t i n u o u s l y p r e s s u r e d l e a k m o n i t o r ,

A helium purge

connection a t t h e t o p i s normally used t o purge t h e f i l t e r of a i r ; however, it can a l s o be used f o r blowing out r e s t r i c t i o n s i n t h e connecting p i p i n g i f necessary.

B a f f l e s a r e i n c l u d e d i n t h e gas s p a c e t o p r e v e n t s a l t from

s p l a t t e r i n g on t h e r i n g j o i n t s e a l . The c e n t e r of t h e f i l t e r element i s a s e a l e d can t o l i m i t t h e volume o f s a l t runback t h a t i s u n a v a i l a b l e f o r p r o c e s s i n g ( 0 . 5 6 f t 3 ) on t r a n s f e r

ORNL-DWG

LEAK DETECTOR PRESSURE7

68-13779

RING JOINT FLANGES \

HELIUM PURGE

UPPER HEATED ZONE

SPACER

E-6

TE-5

(3 FINS EQUALLY SPACED)

TE-4

LIFTING B A I L FOR REPLACEABLE FILTER ELEMENT

PTE-3 SALT FROM FUELSTORAGE TANK

' S P H E R I C A L SEAT'

F E LT M ETA L FILTER ELEMENTS

LOWER HEATER

' 1' Fig. 12.

Salt Filter.

SALT TO DRAIN TANK

27 W

This volume a l s o r e d u c e s t h e weight of t h e

t o t h e f u e l s t o r a g e tank.

element when i t i s submerged i n s a l t and p r e v e n t s t h e f i l t e r from b u r s t i n g when s a l t i s t r a n s f e r r e d from t h e d r a i n tank through a r e s t r i c t e d f i l t e r element.

The element w i l l l i f t o f f t h e s e a t when a s a l t p r e s s u r e of about

1 p s i (depending on s a l t d e n s i t y ) i s a p p l i e d under t h e s e a t .

element has a b u r s t s t r e n g t h of 25 p s i a t 1200'F.

The o u t e r

A possible f i l t e r col-

l a p s e when t h e f u l l gas p r e s s u r e i s a p p l i e d t o t h e f i l t e r a t t h e end of a

t r a n s f e r i s p r e v e n t e d by a p e r f o r a t e d Inconel backup p l a t e p l a c e d on t h e i n s i d e of each f i l t e r c y l i n d e r .

This p l a t e provides a c o l l a p s e s t r e n g t h

o f 131 p s i , which i s w e l l above t h e maximum t r a n s f e r p r e s s u r e of about 30 p s i .

More d e t a i l s on t h e f i l t e r d e s i g n can be found i n r e f . 3 .

During f i l t r a t i o n of t h e f l u s h and f u e l s a l t s , no p r e s s u r e drop a c r o s s t h e f i l t e r was d e t e c t e d , even though s a l t s c o n t a i n i n g about 10 kg o f r e F i l t r a t i o n time was about 2 h r f o r each b a t c h .

duced m e t a l s were f i l t e r e d .

L a t e r , 2 f t 3 o f f u e l s a l t was r e t u r n e d t o t h e p r o c e s s i n g t a n k t o be used f o r a s a l t d i s t i l l a t i o n experiment.

A sample of t h i s s a l t , a f t e r s p a r g i n g ,

r e v e a l e d t h a t much of t h e reduced metals had remained i n t h e t a n k . 4.14

Special Instrumentation

I n a d d i t i o n t o t h e s t a n d a r d o r i f i c e flowmeters and t e m p e r a t u r e , p r e s s u r e , l i q u i d l e v e l , and r a d i a t i o n i n s t r u m e n t s , s e v e r a l s p e c i a l i n s t r u ments were used d u r i n g t h e p r o c e s s i n g of t h e f l u s h and f u e l s a l t .

These

i n s t r u m e n t s a r e d e s c r i b e d below. H a s t i n g s Mass Flowmeters.

- These

i n s t r u m e n t s , which i n d i c a t e t h e

p r o d u c t of h e a t c a p a c i t y and mass flow r a t e of t h e gas s t r e a m , were i n s t a l l e d upstream and downstream o f t h e a b s o r b e r c h a i n i n o r d e r t o p r o v i d e

a s e n s i t i v e i n d i c a t i o n of t h e UFg (which h a s a h i g h h e a t c a p a c i t y ) concent r a t i o n i n t h e gas stream.

Two d e t e c t o r s (0 t o 2 and 0 t o 10 e q u i v a l e n t

cfm o f a i r ) were r e q u i r e d upstream t o o b t a i n b o t h range and s e n s i t i v i t y , w h i l e one 0- t o 2-cfm d e t e c t o r was r e q u i r e d downstream. ging o f t h e 0.03-in.

To p r e v e n t p l u g -

c a p i l l a r i e s by NaF p a r t i c l e s , t h e primary elements

are p r o t e c t e d by 36-u F e l t m e t a l f i l t e r s .

The two i n l e t m e t e r s a r e h e a t e d

by a h e a t i n g t a p e ( t h a t i s c o n t r o l l e d s e p a r a t e l y from t h e r e s t o f t h e g a s l i n e h e a t e r s ) t o p r e v e n t t h e t e m p e r a t u r e on t h e e l e c t r i c a l i n s u l a t i o n from W

exceeding 2 0 0 째 F .

The r e a d i n g s a r e n o t a f f e c t e d by t e m p e r a t u r e changes.

28 These flow m e t e r s agreed w i t h i n +4% o f t h e helium r o t a m e t e r s when only helium was p r e s e n t .

However, unaccountably h i g h r e a d i n g s were

o b t a i n e d i n t h e last t h r e e r u n s , e s p e c i a l l y on t h e e x i t meter from t h e A t t h e end of r u n 6 , t h e e x i t meter i n d i c a t e d a MoF6 (which

absorbers.

a l s o has a h i g h h e a t c a p a c i t y ) r a t e corresponding t o a molybdenum c o r r o s i o n r a t e of almost 1 m i l / h r , w h i l e t h e i n l e t meter throughout t h e r u n i n d i cated a corrosion rate only s l i g h t l y g r e a t e r than t h e 0.2-mil/hr rate assumed f o r molybdenum.

Soon a f t e r t h e f l u o r i n e flow was s t o p p e d , b o t h

meters agreed c l o s e l y with t h e helium purge flow. These meters a l s o provided a s e n s i t i v e i n d i c a t i o n of i n c i p i e n t p l u g ging i n t h e c a u s t i c s c r u b b e r d i p l i n e s . The UFg flow a t a given time could be c a l c u l a t e d from t h e f o l l o w i n g formula, assuming a MoF6 flow r a t e e q u i v a l e n t t o a molybdenum c o r r o s i o n r a t e of 0 . 2 m i l / h r : UF6 flow

x A = Absorber I n l e t Meter Reading

(F2 f e e d r a t e x B

1 / 2 UFg flow)

or UF6 flow =

where A = B =

I n l e t Meter Reading - 0.0362 x F 2 f e e d r a t e , 0.1525 Meter r e a d i n g = 0.1706, s t d l i t e r s o f UFg/min Meter r e a d i n g s t d l i t e r s of FZ/min

0.0362, and t h e

i n l e t meter i s c o r r e c t e d f o r helium, n i t r o g e n , MoF6, and f l u o r i n e i n t r o duced downstream o f t h e f l u o r i n a t o r .

Fluorine u t i l i z a t i o n s calculated

from t h e s e UF6 flows n e a r t h e end of each r u n were h i g h e r t h a n t h o s e c a l c u l a t e d from a b s o r b e r weight i n c r e a s e because of t h e b u i l d u p o f dense

UF6 i n t h e f u e l s t o r a g e t a n k gas s p a c e . Hydrogen Monitor. - T o

v e r i f y t h a t t h e system has been completely

purged a f t e r hydrogen r e d u c t i o n , a hydrogen monitor was i n s t a l l e d t o a n a l y z e a sample of t h e gas downstream of t h e c h a r c o a l b e d s .

A commercial

i n s t r u m e n t , which determines t h e p a r t i a l p r e s s u r e o f hydrogen by measuring t h e p r e s s u r e i n s i d e a p a l l a d i u m - s i l v e r a l l o y membrane, was u s e d .

The

sample l i n e c o n s i s t s of about 50 f t of 1 / 4 - i n . t u b i n g , which p r o v i d e s a

29 W

flow of about 100 cc/min through t h e i n s t r u m e n t w i t h t h e d i f f e r e n t i a l p r e s s u r e a v a i l a b l e from t h e c h a r c o a l t r a p s t o t h e v e n t i l a t i o n header i n the operating area,

Because of t h e long l i n e and low flow r a t e , t h e o v e r -

a l l r e s p o n s e time i s s e v e r a l m i n u t e s . Oxygen Monitor. - T h e '

oxygen monitor, a commercial i n s t r u m e n t based on

t h e paramagnetism o f oxygen, was valved i n t o t h e same sample l i n e on which t h e hydrogen monitor was l o c a t e d .

This i n s t r u m e n t was i n s t a l l e d , prima-

r i l y t o determine t h a t oxygen was completely purged from t h e system b e f o r e t h e s a l t was t r e a t e d with H2-HF t o e f f e c t oxide removal.

In t h e f l u s h and

f u e l s a l t p r o c e s s i n g o p e r a t i o n s d e s c r i b e d i n t h i s r e p o r t , t h e hydrogen r e d u c t i o n s t e p immediately followed t h e f l u o r i n a t i o n s t e p ; t h e r e f o r e t h e r e

was l i t t l e danger of forming an e x p l o s i v e gas m i x t u r e . S i n c e oxygen was produced i n t h e f l u o r i n e d i s p o s a l r e a c t i o n (equival e n t t o about o n e - f o u r t h of t h e r e a c t e d f l u o r i n e ) , i t was hoped t h a t t h e oxygen monitor c o u l d p r o v i d e an i n d i r e c t measure of f l u o r i n e u t i l i z a t i o n . However, d u r i n g t h e f l u o r i n a t i o n of t h e f l u s h s a l t , t h e r e l a t i v e l y low f l u o r i n e u t i l i z a t i o n caused t h e oxygen t h a t was produced t o exceed t h e range of t h e instrument ( 1 0 % ) . A malfunction of t h e i n s t r u m e n t prevented

i t s use during f u e l processing. U l t r a s o n i c Level Probe. - T h e

f u e l s t o r a g e t a n k c o n t a i n s an u l t r a s o n i c

l e v e l probe t o p r o v i d e a s i n g l e p o i n t check on t h e weigh c e l l c a l i b r a t i o n . T h i s probe h a s a l/Z-in.-diam s e n s i n g element, which i s b e t t e r s u i t e d t o t h e c o r r o s i v e c o n d i t i o n s d u r i n g f l u o r i n a t i o n t h a n t h e t h i n - w a l l e d conduct i v i t y - t y p e probes used i n t h e r e a c t o r d r a i n t a n k s .

The u l t r a s o n i c energy

i s t r a n s m i t t e d through two f o r c e - i n s e n s i t i v e mounts, one on t h e tank and a n o t h e r a t t h e c e l l wall p e n e t r a t i o n , t o t h e u l t r a s o n i c g e n e r a t o r , t r a n s -

m i t t e r , and r e c e i v e r l o c a t e d j u s t west of t h e f u e l p r o c e s s i n g c e l l . g e n e r a t o r produces a s i g n a l i n resonance w i t h t h e system.

The

When t h e s a l t

c o n t a c t e d t h e p r o b e , i t caused a d e c r e a s e i n t h e r e f l e c t e d s i g n a l , t h u s operating a r e l a y switch. D i f f i c u l t y was experienced w i t h t h e d r i f t i n g o f t h e s i g n a l frequency away from t h e r e s o n a n t peak; t h i s r e s u l t e d i n a s i g n a l even though c o n t a c t w i t h s a l t had n o t been made.

A similar d i f f i c u l t y had been experienced i n

1965 d u r i n g t h e f l u s h s a l t t r e a t m e n t ; i n t h a t i n s t a n c e , a s a t i s f a c t o r y L

30 s i g n a l was o b t a i n e d when t h e s a l t was t r a n s f e r r e d t o t h e t a n k b u t n o t when i t l e f t t h e t a n k .

I n 1966, t h e s t a b i l i t y of t h e g e n e r a t o r was i m -

proved by r e w i r i n g t h e u n i t w i t h h i g h - s t a b i l i t y components.

During t h e

r e c e n t p r o c e s s i n g o p e a t i o n , a s i g n a l was a g a i n o b t a i n e d when t h e f l u s h

s a l t was t r a n s f e r r e d t o t h e f u e l s t o r a g e t a n k , b u t n o t when t h e s a l t l e f t t h e tank.

No s i g n a l s were o b t a i n e d f o r t h e f u e l s a l t .

For p r o p e r opera-

t i o n , t h e g e n e r a t o r would probably r e q u i r e a c o n s t a n t t e m p e r a t u r e e n v i r o n ment o r a much b r o a d e r s i g n a l o u t p u t . The s a l t weights o b t a i n e d a t probe c o n t a c t are compared i n Table 3 . Table 3 .

Performance of t h e U l t r a s o n i c Level Probe S a l t Weight a t Probe Contact ( l b ) Weigh C e l l Bubbler Instrument

Year 1965

7880

Readings n o t t a k e n

1968

6550a

7950

The weigh c e l l r e a d i n g s t a k e n i n 1968 were u n r e l i a b l e . They were cons i s t e n t l y 5 t o 10% lower t h a n t h e b u b b l e r i n s t r u m e n t r e a d i n g s and a l s o t h e comparable r e a d i n g s i n t h e r e a c t o r d r a i n t a n k s .

5. 5.1

OPERATING HISTORY F l u o r i n e Reactor Tests

I n A p r i l 1968 (about two weeks a f t e r t h e r e a c t o r shutdown), t h e f l u o r i n e supply and excess f l u o r i n e d i s p o s a l systems, which had n o t p r e v i o u s l y been o p e r a t e d , were t e s t e d .

According t o t h e o r i g i n a l d e s i g n of

t h e d i s p o s a l system, t h e e x c e s s f l u o r i n e was expected t o r e a c t w i t h s u l f u r d i o x i d e i n a f l u o r i n e r e a c t o r (Fig. 13) a t t e m p e r a t u r e s above 400'F t o form s u l f u r y l f l u o r i d e , S02F2, a r e l a t i v e l y i n e r t gas t h a t c o u l d b e s a f e l y passed through F i b e r g l a s f i l t e r s and d i s c h a r g e d t o t h e atmosphere. A backup alumina bed, o r i g i n a l l y unheated, had been i n s t a l l e d between t h e

f l u o r i n e r e a c t o r and t h e c h a r c o a l t r a p s t o d e t e c t and t o remove traces o f unreacted f l u o r i n e .

ORN L- DWG 65- 254 5R

s o 2 F2 OUTLET

5-in. MONEL PIPE.ni -2--- . ,

00 in.

i RMOW E L L S

STEAM OUTLET

'1 2 0 in.

PIPE

17 HEAT TRANSFER RODS

I=:

SO2 AND F2 PR E H E AT ERS

STEAM

INLET

\EIGHT

318-in. DISTRIBUTOR HOLES FOR F2

2 F2 INLET

&JSO2

INLET

F2 REACTOR

F i g . 13.

44 in.

I 18 in.

F l u o r i n e Reactor and P r e h e a t e r s .

R e s u l t s o f f o u r f l u o r i n e d i s p o s a l t e s t r u n s a r e summarized i n Table 4 and Fig. 14.

The f i r s t r u n was s t a r t e d on A p r i l 2 , b u t was i n t e r r u p t e d

a f t e r about 1 - 1 / 2 h r by f l u o r i n e i g n i t i o n of two Teflon p l u g v a l v e s .

t o t a l of 900 l i t e r s of f l u o r i n e had been used; however, t h e flow r a t e was very e r r a t i c because of t h e d i f f i c u l t y encountered i n b l e n d i n g a low f l u o r i n e flow r a t e ( ~ 7 . 5s t d l i t e r s / m i n ) with a h i g h helium flow r a t e ( ~ 8 5s t d l i t e r s / m i n ) t o o b t a i n d i l u t e f l u o r i n e f o r c o n d i t i o n i n g t h e system.

During

t h e time t h a t t h e f l u o r i n e was flowing, t h e r e was no evidence of a r e a c t i o n i n t h e f l u o r i n e r e a c t o r although t h e alumina bed was h e a t e d h i g h e r t h a n 250'F.

We b e l i e v e t h a t SO2 had condensed i n t h e s u p p l y l i n e because of

e x c e s s i v e back p r e s s u r e from check v a l v e s .

After t h e flow o f SO2 and

f l u o r i n e was s t o p p e d , t h e temperature of t h e f l u o r i n e r e a c t o r r o s e t o 520'F. SO2,

This t e m p e r a t u r e r i s e was probably caused by t h e e v a p o r a t i o n of and i t s subsequent flow through t h e leaky check v a l v e s and r e a c t i o n

with f l u o r i n e b e i n g purged from t h e f u e l s t o r a g e t a n k . The t e s t was resumed t h r e e days l a t e r , a f t e r t h e p l u g v a l v e s had been replaced.

When t h e helium purge was s t a r t e d , t h e t e m p e r a t u r e of t h e

alumina t r a p a g a i n r o s e a s t h e r e s u l t of r e s i d u a l f l u o r i n e i n t h e system. A r e a c t i o n was a l s o observed i n t h e f l u o r i n e r e a c t o r , p r o b a b l y from a

small amount of SO2 remaining i n t h e system.

When t h e SO2 and f l u o r i n e

flows were s t a r t e d , t h e r e a c t o r t e m p e r a t u r e r e a d i n g went o f f s c a l e (>lOOO째F)

because o f i n s u f f i c i e n t c o o l i n g from low-pressure steam.

The

alumina t r a p t e m p e r a t u r e s d e c r e a s e d , p r o b a b l y because t h e bed was exh a u s t e d and because some of t h e f l u r o i n e had r e a c t e d w i t h t h e c h a r c o a l t r a p s , causing an i n c r e a s e i n p r e s s u r e drop i n t h e system. The f i r s t t e s t i n d i c a t e d t h e need f o r t h e f o l l o w i n g : (1) Finer-mesh alumina and a h e a t e d alumina bed t o i n c r e a s e t h e c a p a c i t y

and t h e r e a c t i o n r a t e ; a d d i t i o n a l thermocouples t o p e r m i t t h e consumption of f l u o r i n e i n t h e bed t o b e f o l l o w e d . (2) An SO2 flow u n t i l a l l f l u o r i n e has been purged from t h e system. ( 3 ) A g r e a t e r e x c e s s of SO2 t o compensate f o r poor flow c o n t r o l

(4) I n c r e a s e d steam p r e s s u r e on t h e f l u o r i n e r e a c t o r c o o l i n g c o i l f o r g r e a t e r cooling capacity. (5) Check v a l v e s w i t h lower p r e s s u r e d i f f e r e n t i a l i n t h e SO2 supply l i n e . Y

Table 4. Fluorine Flow Aver. Liters Time Per (min) Liters (min)

Fluorine Reactor Max. Steam Temp. Pressure (OF) (Psi)

Summary of Fluorine Reactor Test Runs

Max. Temp. (OF)

Alumina Trap Bed Penetration Material

Run

Date

41 2

100

900

520

2250

%1/2

1/4-in. b a l l s

4/5

210

5100

>lo00

7250

To CTa

1/4-in. b a l l s

511

130

2650

%loo0

>loo0

%2/3

35 40 50

5/3

160

3900

>lo00

35 o r

5/20

102

5/21

202

4400

aCT

charcoal t r a p s .

b M T = a c t i v a t e d alumina t r a p .

Run i n t e r r u p t e d by i g n i t i o n of two Teflon plug valves. b AAT r e a c t i o n t o o slow; replaced AATb with f i n e r AA and i n s t a l l e d h e a t e r s and more thermocouples. Increased steam p r e s s u r e f o r b e t t e r FLR cooling. Improved i n s u l a t i o n i n s t a l l e d on SO, and Fp p r e h e a t e r s and l i n e s . Replaced SO2 check valves. System performed s u f f i c i e n t l y w e l l t o permit t e s t i n g o f i o d i n e r e t e n t i o n on charcoal i n next run. Improved S o p Cylinder heating.

>lo00

To CTa

I n l e t 2/3, 8-14 mesh; o u t l e t 1/3, 60-100 mesh.

b Iodine r e t e n t i o n s a t i s f a c t o r y . AAT heating major problem; p r e h e a t e r s added t o AATb and FLRC i n l e t s . FLRC steam c o i l bonding damaged; added Thermond bypassed FST f o r next run.

I n l e t 2/3, 8-14 mesh; o u t l e t 1/3; 60-100 mesh.

Remarks and Modifications Made A f t e r Run

>loo0

50-30 - 10

>1500

%1/2

I n l e t 2/3, 8-14 mesh; o u t l e t 1/3, 60-100 mesh.

Run suspended when AAT temperature exceeded 1500Â°F, near end of f l u o r i n e conditioning, t o allow cooling and readjustment of a l l temperatures.

1440

0-25

1480

To CTa

I n l e t 2/3, 8-14 mesh; outlet 1/3, 60-100 mesh.

Fluorine r e a c t o r operation good, b u t alumina t r a p heating continued. Piping t o be temporary modified f o r c a u s t i c scrubber test.

â&#x20AC;&#x2DC;FLR

= fluorine reactor.

dHeat t r a n s f e r cement.

w w

ORNL-DWG 69-5399

1600

*-.

800

-P

OFF

400

' 5

5 1600 W

1200

SCALE 3 1 2

800

*oo

RUN

ti.

16 17 16 14 15 4-2-68 1A

48 19 20 2 ? 23 24 01 0 2 0 3 46

4-5-66 IB

Fig. 14.

5-1-68 2

48 49 20 21 13 5-3-68 3

14 15 16 17 14 5-20-68 48

Temperatures During Fluorine Reactor Tests.

16 17 18 5-24-68 48

19 2 0

The above equipment and p r o c e d u r a l changes were e f f e c t e d , and t h e c h a r c o a l c a n n i s t e r s ( i n t h e i n l e t c h a r c o a l b e d ) , which had r e a c t e d w i t h f l u o r i n e , were r e p l a c e d .

T e s t r u n 2 was t h e n s t a r t e d on May 1, 1968.

About 1 / 2 h r a f t e r t h e s t a r t of f l u o r i n e flow, t h e r e a c t o r i n l e t temperat u r e s t a r t e d t o r i s e , i n d i c a t i n g a r e a c t i o n ; however, t e m p e r a t u r e p o i n t s 16 i n . and 32 i n . downstream b u t s t i l l i n t h e r e a c t i o n zone) showed p r a c t i c a l l y no h e a t i n g .

I t i s b e l i e v e d t h a t t h e i n c r e a s e d flow of steam

overcooled t h e r e a c t i o n zone, t h e r e b y c a u s i n g t h e r e a c t i o n r a t e t o dec r e a s e and a l l o w i n g u n r e a c t e d f l u o r i n e t o r e a c h t h e alumina t r a p .

The

alumina t r a p was b e i n g h e a t e d a t t h e r a t e of about 80°F/hr, b u t t h e t e m p e r a t u r e a t a p o i n t 8 i n , down t h e bed r o s e s h a r p l y , from 400°F t o > l O O O ° F i n less t h a n 15 min, about 2 h r a f t e r t h e s t a r t of f l u o r i n e flow.

The f l u o r i n e flow was t h e n stopped, b u t t h e SO2 flow was continued w h i l e t h e system was b e i n g purged w i t h helium.

Two hours l a t e r , t h e t e m p e r a t u r e

measured a t p o i n t s f a r t h e r down t h e alumina bed r o s e from about 800°F t o >lOOO°F.

S i n c e t h e f l u o r i n e flow r a t e t o t h e r e a c t o r should have been

low a t t h i s t i m e , it appears t h a t t h e second t e m p e r a t u r e r i s e was due t o an SOzFz r e a c t i o n . ( L a t e r , such a r e a c t i o n was shown t o occur above 800'F.) However, because a t t h i s time we were unaware of t h e SOZF2-alumina r e a c t i o n , e f f o r t s were d i r e c t e d t o improving SO2 and F2 flow c o n t r o l .

One of t h e main o b j e c t i v e s of t h e f l u o r i n e d i s p o s a l t e s t s was t o demonstrate t h a t i o d i n e could b e r e t a i n e d on c h a r c o a l when SO2 and S02F2 were flowing through t h e b e d s .

I n t h e e v e n t t h a t t h i s could n o t b e demon-

s t r a t e d , an a l t e r n a t i v e f l u o r i n e d i s p o s a l method would have t o be found. T h e r e f o r e , a l t h o u g h o p e r a t i o n of t h e system was s t i l l n o t s a t i s f a c t o r y , as shown by t h e t e s t s d e s c r i b e d above, i t was f e l t t h a t t h e alumina t r a p had s u f f i c i e n t r e s i d u a l c a p a c i t y t o remove any u n r e a c t e d f l u o r i n e and t h a t i o d i n e would be r e t a i n e d on t h e c h a r c o a l t r a p s . I n t h e t h i r d r u n , a s a t i s f a c t o r y h e a t o f r e a c t i o n was o b t a i n e d i n t h e f l u o r i n e r e a c t o r ; t h i s i n d i c a t e d t h e p r o d u c t i o n o f S02F2.

Since heating

was observed a t t h e c e n t e r o f t h e alumina bed, b u t n o t a t t h e e x i t , i t appeared t h a t no f l u o r i n e was l e a v i n g t h e bed.

About 100 min a f t e r t h e

s t a r t of f l u o r i n e flow, 30 mc o f C H 3 l 3 I I was i n j e c t e d i n t o t h e gas stream upstream o f t h e c h a r c o a l t r a p s . V

The l o a d i n g of t h e i o d i d e was followed

36 by d e t e r m i n a t i o n of t h e r a d i a t i o n l e v e l s w i t h r a d i a t i o n monitors ( s e e Fig. 15).

Although f l u o r i n e flow was stopped 1 h r a f t e r t h e s t a r t of

i o d i d e i n j e c t i o n , t h e f l u o r i n e r e a c t o r temperature remained above 400°F f o r 4 a d d i t i o n a l hours (from purged f l u o r i n e ) .

A f t e r t h e f i r s t 72 min

of t h e 2-hr i o d i d e i n j e c t i o n p e r i o d , t h e summation of t h e l e v e l s i n d i c a t e d by t h e f i v e r a d i a t i o n monitors on t h e c h a r c o a l t r a p s reached a maximum and l e v e l e d o f f , i n d i c a t i n g a l l t h e i o d i d e had been loaded.

During

t h e t h i r d and f o u r t h hour, t h e r e was a v e r y s l i g h t i n c r e a s e i n r a d i a t i o n a t p o i n t s CT-D and CT-E ( s e e F i g . 9) and a c o r r e s p o n d i n g , r e d u c t i o n a t CT-C.

During t h i s t i m e , t h e temperature a t t h e o u t l e t o f t h e alumina

exceeded 1000°F, and t h e r e was some h e a t i n g o f t h e c h a r c o a l , i n d i c a t i n g

a r e a c t i o n with f l u o r i n e (probably from S02F2 decomposition).

The s l i g h t

s h i f t i n t h e l o c a t i o n of t h e i o d i d e c o u l d have been caused by f l u o r i n e r a t h e r t h a n S02F2.

The almost immediate p e n e t r a t i o n o f some o f t h e

i o d i d e through t h e f i r s t 1 2 i n . o f c h a r c o a l w a s n o t unexpected, as t h i s t y p e of behavior has been noted p r e v i o u s l y f o r o r g a n i c i o d i d e s . A f t e r t h e t h i r d r u n , t h e i n s u l a t i o n was removed from t h e f l u o r i n e r e a c t o r t o allow t h e c o o l i n g c o i l s t o be examined.

[The copper c o i l s

were bonded t o t h e blonel r e a c t o r w i t h E-Z flow s o l d e r (flow p o i n t , 1328°F) c o n t a i n i n g cadmium.

A t t e m p e r a t u r e s above 1300"F, a l l o y i n g , a l o n g with

t h e formation of c r a c k s and weakening of t h e m e t a l , can o c c u r . ]

In runs

1 and 3 , t h e thermowell t e m p e r a t u r e s exceeded 1000°F (maximum r e c o r d e r

temperature) f o r 3-1/2 h r and f o r 40 min, r e s p e c t i v e l y .

Examination r e -

v e a l e d t h a t t h e s o l d e r had m e l t e d , l e a v i n g t h e middle t h i r d o f t h e 4 4 - i n . c o i l unbonded.

Dye-checking r e v e a l e d some c r a c k s i n t h e Monel.

However,

a p r e s s u r e t e s t showed t h a t t h e r e a c t o r s t i l l had adequate s t r e n g t h t o permit t h e remaining t e s t r u n s t o be made.

A high-temperature h e a t

t r a n s f e r cement was a p p l i e d around t h e c o i l s , and t h e r e a c t o r was r e i n sulated. Run 4A was s t a r t e d on May 2 0 , 1968,

A p r e h e a t e r had been i n s t a l l e d

on t h e f l u o r i n e r e a c t o r i n l e t t o p r o v i d e i n l e t t e m p e r a t u r e s above 400°F t o e n s u r e a r e a c t i o n a t low f l u o r i n e flows as w e l l as a t t h e s t a r t o f f l u o r i n e flow.

A p r e h e a t e r had a l s o been i n s t a l l e d a t t h e alumina t r a p

i n l e t t o o b t a i n more s a t i s f a c t o r y t e m p e r a t u r e d i s t r i b u t i o n and t o improve t h e e f f i c i e n c y a t t h e bed i n l e t ( i n r u n 3 no r e a c t i o n o c c u r r e d i n t h e

37 ORNL-DWG 68-5494

30mc Me1 ADDITIONI

P 2

,ICT-C 1

IO2

IO'

CT-D

CT-E

I J

loo

0 V

Fig. 15.

6 8 TIME (hr)

Charcoal Trap Radiation Levels During Addition of CH31311.

The r a n g e s on t h e two t e m p e r a t u r e r e c o r d e r s

i n l e t half of t h e bed).

were i n c r e a s e d from 0 - 1000 t o 0 - 1500 and 0 - 2000'F.

A temporary

bypass l i n e was i n s t a l l e d around t h e f u e l s t o r a g e t a n k t o e l i m i n a t e i t s 120-ft

volume between t h e f l u o r i n e s u p p l y and t h e f l u o r i n e r e a c t o r .

This l i n e had t o b e c o n d i t i o n e d w i t h d i l u t e f l u o r i n e , which involved manual flow c o n t r o l .

Control was e r r a t i c ; however, t h e f l u o r i n e r e a c t i o n

s t a r t e d immediately and, soon t h e r e a f t e r , t h e alumina t r a p i n l e t began t o h e a t up.

The h e a t e d zone proceeded t o t h e second thermowell, and t h e

f l u o r i n e flow was stopped when an o f f - s c a l e r e a d i n g of 1500'F was o b t a i n e d a t t h i s point.

We decided t o allow t h e alumina bed t o c o o l and t o resume

t h e r u n t h e next day.

The system was c o n d i t i o n e d s o t h a t a u t o m a t i c flow

c o n t r o l of 100% f l u o r i n e could t h e n b e used. The f o u r t h t e s t was resumed on May 2 1 ; our e f f o r t s were c e n t e r e d on t r y i n g t o determine t h e cause of t h e alumina t r a p h e a t i n g .

To e n s u r e a

complete r e a c t i o n of t h e f l u o r i n e w i t h S O 2 , t h e f l u o r i n e r e a c t o r i n l e t was p r e h e a t e d s o t h a t t h e temperature of t h e r e a c t i o n zone was about steam c o o l i n g was delayed u n t i l t h e r e a c t o r t e m p e r a t u r e reached

600'F; 1000째F.

Then t h e steam p r e s s u r e was c a r e f u l l y a d j u s t e d t o m a i n t a i n a l l

temperatures above 400째F.

A maximum f l u o r i n e flow of 25 s t d l i t e r / m i n

was used, w i t h a minimum of 50% e x c e s s SO2.

The flow c o n t r o l was good.

In s p i t e of s a t i s f a c t o r y o p e r a t i o n i n t h e r e a c t o r , t h e alumina t r a p t e m p e r a t u r e s a g a i n i n c r e a s e d as soon as t h e r e a c t i o n s t a r t e d .

We con-

cluded t h a t t h e s e i n c r e a s e s could only have been caused by S02F2 decomposition.

When t h e e x i t of t h e alumina t r a p reached about 1000째F,

i o d i d e began t o move down t h e c h a r c o a l bed.

Most of t h e i o d i n e l e f t

t h e f i r s t 1 2 i n . of bed and accumulated a t t h e i n l e t o f t h e backup t r a p . F l u o r i n e flow was stopped 20 min a f t e r t h i s m i g r a t i o n began, and t h u s no i o d i n e l e f t t h e t r a p .

About 5 mc of i o d i d e s t i l l remained a t t h i s

time . Laboratory t e s t s 4 were made by W. S. Pappas* t o v e r i f y t h e decompos i t i o n of S02F2.

While t h e s e t e s t s showed no gaseous decomposition

p r o d u c t s l e a v i n g t h e alumina bed, t h e l a b o r a t o r y bed was n o t completely exhausted as was t h e c a s e a t t h e MSRE.

The cause of t h e i o d i n e movement

i n t h e l a s t run could, t h e r e f o r e , have r e s u l t e d e i t h e r from u n r e a c t e d

ORGDP

39 f l u o r i n e p a s s i n g through t h e exhausted alumina bed o r from S02F2 decompos i t i o n p r o d u c t s l e a v i n g t h e exhausted b e d ,

The movement was probably n o t

due t o S02F2 s i n c e Pappas' work showed o n l y p a r t i a l t r a p p i n g o f S02F2 below 1200째F.

Also, S02F2 was produced f o r 2 h r b e f o r e t h e alumina bed

t e m p e r a t u r e reached 1200째F, and no i o d i n e movement was observed d u r i n g t h i s time. With steam c o o l i n g o f t h e f l u o r i n e r e a c t o r , it was n o t p o s s i b l e t o m a i n t a i n t h e r e a c t o r walls above 400'F. t r a c e s o f f l u o r i n e could n o t b e e n s u r e d .

Thus t h e complete r e a c t i o n of I f work had been c o n t i n u e d on

t h e SO;! system, we would have i n s t a l l e d c o n t r o l l e d e l e c t r i c h e a t over t h e e n t i r e 8 f t o f t h e r e a c t o r i n s t e a d of steam h e a t o v e r t h e f i r s t 3-2/3 f t . F u t u r e work would a l s o have involved d e c r e a s i n g a c t i v a t e d alumina t r a p t e m p e r a t u r e s ( t o 700 t o 750'F)

t o p r e v e n t t h e S02F2 r e a c t i o n .

Some means

of c o o l i n g would probably have been r e q u i r e d t o p r e v e n t a small f l u o r i n e r e a c t i o n from h e a t i n g t h e bed above t h e S02F2 r e a c t i o n t e m p e r a t u r e . A f t e r t h i s l a s t f l u o r i n e r e a c t o r t e s t , i t was thought t h a t t h e r e a c t o r c o u l d b e o p e r a t e d a t h i g h e f f i c i e n c y ; however, t h i s could n o t be r e a d i l y demonstrated.

S i n c e no h i g h l y e f f i c i e n t backup t r a p was a v a i l -

a b l e f o r t h e d e t e c t i o n and removal of t r a c e s of f l u o r i n e i n t h e p r e s e n c e of SO2 and S02F2, we decided t o make a t e s t r u n with KOH-KI s o l u t i o n i n the caustic scrubber.

Temporary p i p i n g changes were, t h e r e f o r e , made t o

p l a c e t h e backup alumina t r a p downstream o f t h e c a u s t i c s c r u b b e r t a n k . 5.2

C a u s t i c Scrubber T e s t s

Two weeks a f t e r t h e l a s t f l u o r i n e r e a c t o r t e s t was completed, t h e p i p i n g was modified t o t e s t d i s p o s a l , u s i n g t h e s c r u b b e r .

The s c r u b b e r

was charged w i t h a 2 M KOH -- 0 . 3 3 M - K I s o l u t i o n , and 30 mc of CIi3'3'-I

was a g a i n loaded on t h e c h a r c o a l t r a p s .

The backup alumina t r a p m a t e r i a l

was r e p l a c e d , and t h e t r a p was h e a t e d t o 700-800째F.

Fluorine diluted t o

less t h a n 50% w i t h helium was used t o c o n d i t i o n t h e s c r u b b e r - - an operat i o n requiring several hours.

After about 50 min of c o n d i t i o n i n g t h e new

o r r e c e n t l y exposed p i p i n g w i t h d i l u t e f l u o r i n e t h e f l u o r i n e flow r a t e was s t a b i l i z e d a t 35 s t d l i t e r s / m i n and d i l u t e d w i t h an e q u a l flow of helium upstream of t h e s c r u b b e r .

A s soon as t h e f l u o r i n e flow began, t h e t e m p e r a t u r e n e a r t h e e x i t o f t h e alumina t r a p ( c o n t a i n i n g 5-mesh alumina) began t o i n c r e a s e s l o w l y . There was no i o d i n e movement; t h e o t h e r alumina bed t e m p e r a t u r e s were s t e a d y ; and a gas sample downstream of t h e s c r u b b e r showed o n l y a f a i n t t r a c e of f l u o r i n e .

The temperature r i s e , was t h e r e f o r e , a t t r i b u t e d t o This

t h e i n c r e a s e d gas flow due t o oxygen f o r m a t i o n i n t h e s c r u b b e r .

was v e r i f i e d two days l a t e r by i n j e c t i o n of 6 s t d l i t e r s o f oxygen p e r minute i n t o t h e system, u s i n g a helium flow equal t o t h a t used d u r i n g t h e test run.

The temperature r i s e was d u p l i c a t e d .

Further confirmation

was o b t a i n e d by r e p e a t i n g t h e f l u o r i n e flow t e s t ; no a d d i t i o n a l temperat u r e r i s e was o b t a i n e d . Following t h e s u c c e s s f u l t e s t a t t h e MSRE, t h e Fuel Processing P l a n t was converted from t h e SO2 system t o t h e s c r u b b e r method o f f l u o r i n e disposal.

The f l u r o i n e r e a c t o r , gas p r e h e a t e r s , and a s s o c i a t e d

p i p i n g were removed from t h e c e l l .

The Monel i n l e t d i s t r i b u t o r r i n g i n

t h e c a u s t i c s c r u b b e r was blanked and r e p l a c e d by an Inconel d i p t u b e . (Laboratory t e s t s had shown t h a t Inconel had much g r e a t e r c o r r o s i o n r e s i s t a n c e t h a n Monel.)

S i n c e d i p t u b e plugging (by c o r r o s i o n p r o d u c t s )

had o c c u r r e d i n l a b o r a t o r y t e s t s ,

s p a r e d i p t u b e was i n s t a l l e d .

Ex-

t e n s i o n handle v a l v e s were s u p p l i e d t o p e r m i t d i p t u b e s t o b e s w i t c h e d from t h e o p e r a t i n g a r e a .

A c o n t a c t microphone was i n s t a l l e d on t h e

s c r u b b e r t a n k t o d e t e c t any abnormal r e a c t i o n such as t h a t which o c c u r r e d i n l a b o r a t o r y t e s t s when a f l u o r i n e c o n c e n t r a t i o n o f g r e a t e r t h a n 50% was used. A second s c r u b b e r t e s t was made on J u l y 4 , 1968.

The f u e l s t o r a g e

t a n k bypass l i n e was removed, and t h e tank was h e a t e d t o 1100째F f o r a pressure t e s t .

The t a n k was m a i n t a i n e d a t t h i s t e m p e r a t u r e d u r i n g t h e

scrubber t e s t .

A f t e r 70 min o f f l u o r i n e flow, t h e p r e s s u r e upstream of

t h e scrubber s t a r t e d t o i n c r e a s e .

The flow was, a t f i r s t , reduced from

35 t o 25 s t d l i t e r s / m i n and, t h e n , had t o b e stopped completely 15 min

l a t e r t o p r e v e n t t h e s o l u t i o n from l e a v i n g t h e s c r u b b e r t a n k .

After

t h e system had been purged o v e r n i g h t w i t h helium a t a low flow r a t e , t h e gas l i n e from t h e s c r u b b e r was removed and found t o be almost comp l e t e l y r e s t r i c t e d by a w h i t e s o l i d c o n t a i n i n g a h i g h p e r c e n t a g e o f molybdenum

Laboratory t e s t s u s i n g MoF6 and KOH-KI s o l u t i o n produced a heavy

m i s t t h a t could b e removed from t h e gas s t r e a m by a F i b e r g l a s f i l t e r .

5 0 - f t 2 f i l t e r was, t h e r e f o r e , i n s t a l l e d downstream o f t h e s c r u b b e r t o

To p r e v e n t plugging o f t h e connecting l i n e , t h e

remove such m a t e r i a l .

s i z e of t h e l i n e was i n c r e a s e d from 3 / 4 - i n . bends were e l i m i n a t e d .

t o 1 - 1 / 2 i n . , and a l l s h a r p

The alumina backup t r a p was r e l o c a t e d downstream

o f t h e F i b e r g l a s f i l t e r , and t h e alumina was r e p l a c e d w i t h soda-lime, which removes f l u o r i n e e f f e c t i v e l y a t low t e m p e r a t u r e s .

Both t h e f i l t e r

and t h e soda-lime t r a p were steam h e a t e d t o p r e v e n t condensation of t h e s a t u r a t e d gas stream from t h e s c r u b b e r . Another equipment change r e s u l t i n g from t h e e x p e r i e n c e of t h e second s c r u b b e r t e s t was t h e a d d i t i o n of means f o r h e a t i n g t h e UFg a b s o r b e r s . The MoF6 was expected t o b e r e t a i n e d on t h e s e a b s o r b e r s , which were a t room t e m p e r a t u r e , i n s t e a d of p a s s i n g through t o t h e s c r u b b e r .

Follow-up

l a b o r a t o r y t e s t s showed a much slower r e a c t i o n r a t e f o r b o t h MoFg and U F g w i t h l o w - s u r f a c e - a r e a NaF t h a n w i t h t h e h i g h - s u r f a c e - a r e a material used i n previous v o l a t i l i t y processing.

Heating and i n s u l a t i n g t h e a b s o r b e r s

provided two a d v a n t a g e s : (1) t h e amount of UFg l e a v i n g a p a r t i c u l a r abs o r b e r b e f o r e t h a t a b s o r b e r i s f u l l y loaded was reduced, and (2) t h e amount of coabsorbed molybdenum was minimized. 5.3

F l u o r i n a t i o n of t h e Flush S a l t

On August 1, t h e f l u s h s a l t was t r a n s f e r r e d by gas p r e s s u r e , from t h e f u e l f l u s h tank i n t h e d r a i n c e l l t o t h e f u e l storage tank i n t h e f u e l processing c e l l .

The t r a n s f e r r e q u i r e d about 1 1 - 1 / 2 h r .

Following

t h i s t r a n s f e r , t h e i s o l a t i o n freeze v a l v e s were f r o z e n and l e a k - t e s t e d , and t h e f l u s h s a l t was sampled.

Analyses showed t h a t f u e l s a l t had been

r e t a i n e d by t h e f l u s h s a l t d u r i n g t h e seven f l u s h e s of t h e r e a c t o r system. Each of t h e s e f l u s h i n g o p e r a t i o n s c o n t r i b u t e d about 200 ppm ( o r 1 kg) o f uranium t o t h e f l u s h s a l t , f o r a t o t a l o f about 6-1/2 kg o f uranium. P e r t i n e n t i r r a d i a t i o n and decay d a t a are shown i n Table 5 . F l u o r i n a t i o n of t h e f l u s h s a l t was s t a r t e d on August 2 .

The s a l t

was sparged w i t h 25 s t d l i t e r s o f f l u o r i n e p e r minute d i l u t e d w i t h 20 s t d l i t e r s of helium p e r minute.

An a d d i t i o n a l 15 s t d l i t e r s o f helium p e r

minute was used t o purge t h e sample l i n e .

The r e a d i n g on t h e i n l e t mass

Table 5 .

Fuel System Flushes

Decay a t T i m e o f F l u o r i n a t i o n (months)

Flush No.

Fuel I r r a d i a t i o n a t Time of Flush (Mwhr) <1

7 ,800

a9,500

20-1/2

% l o ,000

14-314

33,000

%40,000

7 2 ,400

4-1/4

flowmeter r o s e r a p i d l y and reached a maximum a f t e r 48 min of f l u o r i n e sparging.

The peak r e a d i n g corresponded t o a f l u o r i n e u t i l i z a t i o n of

about 15%. The r e a d i n g s of t h e thermocouples on t h e No. 1 and No. 2 a b s o r b e r s r o s e , b u t lagged t h e i n i t i a l r i s e i n t h e mass flowmeter r e a d i n g by 20 t o 30 min.

The r e a d i n g on t h e e x i t mass flowmeter r o s e as

expected as t h e f l u o r i n e u t i l i z a t i o n decreased from i t s peak, b u t a t t a i n e d

a much h i g h e r r e a d i n g t h a n e x p e c t e d .

When t h e r e a d i n g f o r t h i s meter

went o f f - s c a l e , we decided t o bypass t h e f l u o r i n e around t h e s a l t w h i l e we i n v e s t i g a t e d t h e r e a s o n f o r t h i s high r e a d i n g .

There was some concern

t h a t a uranium breakthrough had o c c u r r e d ; however, no t e m p e r a t u r e r i s e had been observed on any of t h e l a s t t h r e e a b s o r b e r s .

I t was f i n a l l y con-

cluded t h a t MoFF, was t h e cause of t h e h i g h r e a d i n g ; t h e r e f o r e , f l u o r i n e s p a r g i n g was resumed a f t e r 95 min.

A f t e r a t o t a l of 5 h r o f f l u o r i n e

s p a r g i n g , t h e f l u o r i n e supply was exhausted.

S i n c e t h e r e a d i n g on t h e

i n l e t flowmeter had almost become c o n s t a n t , w e decided t o sample t h e s a l t w h i l e t h e f l u o r i n e t r a i l e r and t h e c a u s t i c s c r u b b e r s o l u t i o n were being replaced.

F l u o r i n a t i o n was resumed a f t e r t h e c a u s t i c s o l u t i o n was re-

p l e n i s h e d ; it was t h e n t e r m i n a t e d when a uranium a n a l y s i s of 24 ppm was o b t a i n e d f o r t h e f l u s h s a l t , s i n c e f l u o r i n e s p a r g i n g had been c a r r i e d o u t f o r an a d d i t i o n a l 109 min and t h e r e a d i n g of t h e i n l e t mass flowmeter had become c o n s t a n t ,

Analysis o f a second s a l t sample, t a k e n a t t h i s time

i n d i c a t e d a uranium c o n c e n t r a t i o n of o n l y 7 pprn ( d e s i r e d <10 pprn).

43 The a b s o r b e r s were loaded w i t h low-surface-area NaF f o r t h e f l u s h

s a l t p r o c e s s i n g and were h e a t e d t o 200

r a t e (see S e c t . 6 . 7 ) .

250째F t o i n c r e a s e t h e r e a c t i o n

S i n c e t h e amount of uranium i n t h e f l u s h s a l t was

o n l y about h a l f t h e c a p a c i t y of one a b s o r b e r , v e r y l i t t l e uranium was exp e c t e d t o be d e p o s i t e d on t h e l a s t f o u r a b s o r b e r s .

However, almost 30%

was c o l l e c t e d on t h e second a b s o r b e r and p o s s i b l y 3% on t h e t h i r d , a l though no t e m p e r a t u r e r i s e was d e t e c t e d on t h e l a s t t h r e e a b s o r b e r s .

For

t h e f u e l s a l t r u n s , i t was, t h e r e f o r e , decided t o use only h i g h - s u r f a c e a r e a m a t e r i a l i n t h e f i n a l t h r e e a b s o r b e r s t o permit o p e r a t i o n with o n l y one backup a b s o r b e r . 39'F;

The temperature r i s e on t h e f i r s t a b s o r b e r was o n l y

t h u s c o o l i n g a i r was n o t r e q u i r e d . Although some plugging of t h e c a u s t i c s c r u b b e r d i p l i n e s o c c u r r e d ,

s w i t c h i n g t o t h e s p a r e l i n e f o r s e v e r a l minutes always c l e a r e d t h e l i n e . 5.4

Reduction of t h e Flush S a l t

A f t e r t h e a n a l y s i s of t h e f i r s t f l u o r i n a t i o n s a l t sample (uranium,

24 ppm) was o b t a i n e d , h e a t u p of t h e s a l t f o r hydrogen r e d u c t i o n was started,

During t h e h e a t u p , t h e c a u s t i c s c r u b b e r d i p l i n e s were checked

and found t o b e f r e e o f p l u g s .

The c a u s t i c s o l u t i o n was l e f t i n t h e t a n k

t o n e u t r a l i z e t h e HF formed d u r i n g N i F 2 r e d u c t i o n .

A p e r i o d of 43 h r a t

maximum w a t t a g e was r e q u i r e d t o r a i s e t h e s a l t temperature from 860 t o 1220째F.

August 5 , 1968, hydrogen s p a r g i n g was s t a r t e d .

A m i x t u r e of

hydrogen (30 s t d l i t e r s / m i n ) and helium (20 s t d l i t e r s / m i n ) was used i n c o n j u n c t i o n with a 1 0 - s t d - l i t e r j m i n helium sample l i n e p u r g e ,

The hydro-

gen monitor i n t h e o f f - g a s l i n e downstream o f t h e c h a r c o a l beds was observed i n o r d e r t o determine t h e time a t which hydrogen consumption by NiF2 ceased.

A f t e r 2 h r , t h e r a t e of i n c r e a s e of t h e monitor was e s s e n -

t i a l l y z e r o , which i n d i c a t e d a n i c k e l r e d u c t i o n r a t e o f l e s s t h a n 3 ppmjhr. Hydrogen s p a r g i n g was continued f o r a t o t a l of 10.8 h r . Zirconium was t h e n added through t h e s a l t sampler t o reduce t h e FeF2 and C r F 2 , as well as t h e remainder o f t h e N i F 2 .

Three l - i n . - d i a m c y l i n -

d e r s of p r e s s e d zirconium s h a v i n g s , weighing 604 g t o t a l , were dropped through t h e sample l i n e with t h e m a n i p u l a t o r .

The c o n t a c t microphone on

t h e f u e l s t o r a g e t a n k provided an a u d i b l e v e r i f i c a t i o n o f t h e passage of W

t h e c y l i n d e r down t h e l e n g t h of t h e sample l i n e .

Although t h e r e was some

44 concern t h a t t h e c y l i n d e r s would b e h e l d up by t h e v a l v e o r t h e b e l l o w s , t h i s did not occur.

The s a l t was t h e n sparged w i t h a m i x t u r e o f hydrogen

(30 s t d l i t e r s / m i n ) and helium (10 s t d l i t e r s / m i n ) .

An a d d i t i o n a l flow

of helium (20 s t d l i t e r s l m i n ) was used t o purge t h e sample l i n e .

After

9 h r of s p a r g i n g , t h e hydrogen flow was stopped; t h e n t h e system was

purged w i t h (75 s t d l i t e r s / m i n ) f o r 85 min b e f o r e t h e s a l t was sampled. Two samples were o b t a i n e d : a s t a n d a r d d i p sample, and a f i l t e r e d sample, u s i n g a c a p s u l e s e a l e d w i t h l i t h i u m - b e r y l l i u m f l u o r i d e s a l t ("freezeAnalyses of t h e samples i n d i c a t e d t h a t , a l t h o u g h t h e

valve capsule'').

n i c k e l c o n c e n t r a t i o n had been reduced t o less t h a n 50 ppm, t h e r e had o n l y been a s l i g h t r e d u c t i o n i n t h e i r o n and chromium c o n c e n t r a t i o n s .

a d d i t i o n a l 470 g of zirconium was added, and t h e s a l t was sparged w i t h t h e same hydrogen-helium mixture ( s e e above) f o r an a d d i t i o n a l 16 h r . A f t e r f a i l u r e t o o b t a i n a sample w i t h t h e f r e e z e - v a l v e c a p s u l e , t h e s a l t was t r a n s f e r r e d through t h e f i l t e r t o t h e d r a i n t a n k .

In the drain tank,

t h e s a l t was s u c c e s s f u l l y sampled by u s i n g a new t y p e of c a p s u l e , designed by A . I . Krakoviak,* t h a t r e l i e s on t h e vacuum produced by t h e c o o l i n g c a p s u l e t o p u l l t h e s a l t sample through t h e f i l t e r .

This eliminates t h e

danger of l o s i n g vacuum by t h e m e l t i n g of t h e f r o z e n s a l t s e a l i n t h e freeze-valve capsule.

A n a l y s i s of t h e f i l t e r e d p o r t i o n of t h e s a l t showed

t h a t r e d u c t i o n was adequate and t h a t t h e f i l t e r had removed t h e reduced metals. 5.5

F l u o r i n a t i o n o f t h e Fuel S a l t

R e s u l t s o b t a i n e d d u r i n g t h e p r o c e s s i n g of t h e f l u s h s a l t p o i n t e d o u t t h e need f o r s e v e r a l equipment and p r o c e d u r a l changes b e f o r e t h e much more r a d i o a c t i v e f u e l s a l t was p r o c e s s e d .

These changes, which r e q u i r e d

about two weeks, c o n s i s t e d of t h e f o l l o w i n g :

(1)

Enough h i g h - s u r f a c e - a r e a NaF (1400 l b ) was p r o c u r e d from ORGDP t o l o a d t h e l a s t t h r e e a b s o r b e r s i n each r u n , and t h e f i r s t two abs o r b e r s i n t h r e e of t h e s i x r u n s , t o o b t a i n a comparison between t h e performance o f t h e two t y p e s of NaF.

(2)

Piping was i n s t a l l e d t o p e r m i t t h e helium d i l u e n t ( r e q u i r e d t o l i m i t t h e f l u o r i n e c o n c e n t r a t i o n t o t h e c a u s t i c s c r u b b e r t o less t h a n 50%) t o b e i n t r o d u c e d downstream of t h e a b s o r b e r s i n s t e a d o f i n t o t h e

Reactor D i v i s i o n .

45 fuel storage tank.

This change i n c r e a s e d t h e r e s i d e n c e time i n t h e

a b s o r b e r s , t h u s p e r m i t t i n g more e f f i c i e n t a b s o r p t i o n . (3)

The flow r a t e of t h e sample l i n e purge gas was reduced from 15 t o 10 s t d l i t e r s / m i n i n run 1 and t o 5 s t d l i t e r s / m i n t h e r e a f t e r t o

f u r t h e r increase the absorber residence time. (4)

For more e f f i c i e n t a b s o r b e r purging, a connection was provided a t t h e a b s o r b e r i n l e t t o permit purging w i t h pure helium i n s t e a d of purging through t h e f u e l s t o r a g e t a n k .

(5)

A small soda-lime t r a p was i n s t a l l e d i n t h e a b s o r b e r c u b i c l e t o

allow t h e a b s o r b e r s t o b e vented t o atmospheric p r e s s u r e i n s t e a d of t h e s c r u b b e r l i q u i d head. (6)

Purge flow r a t e s f o l l o w i n g f l u o r i n a t i o n were k e p t low t o a l l o w more e f f i c i e n t a b s o r p t i o n o f UF6, which was being purged from t h e gas space. While t h e above changes were i n p r o g r e s s , t h e f l u s h s a l t was r e -

t u r n e d t o t h e r e a c t o r system and c i r c u l a t e d t o t e s t t h e f u e l pump sampler.

The t r a n s f e r o f t h e f u e l s a l t t o t h e p r o c e s s i n g c e l l was s t a r t e d on August 17, 1968, a f t e r a d i f f i c u l t y w i t h a r e s t r i c t i o n i n t h e l i n e a t t h e c e l l wall p e n e t r a t i o n was r e s o l v e d .

The s p a r e h e a t e r s a t t h e p e n e t r a t i o n

were e n e r g i z e d , t h e r e b y r a i s i n g t h e temperature from 1108째C t o 1 2 5 ~ 5 째 C b~ u t However, when t h e d r a i n t a n k was p r e s s u r i z e d ,

the restriction persisted.

t h e h o t s a l t e v i d e n t l y thawed t h e p l u g , and t r a n s f e r was s t a r t e d . o p e r a t i o n r e q u i r e d about 11 h r a t an average r a t e of 15 lb/min.

This After the

t r a n s f e r , a r a d i a t i o n l e v e l of about 2 r / h r was d e t e c t e d a t t h e f i l t e r l o c a t e d upstream o f t h e i n l e t mass flowmeter i n t h e a b s o r b e r c u b i c l e ,

This

r a d i o a c t i v i t y was caused by c a r r y o v e r o f m e t a l l i c 95Nb d u r i n g t h e gas blowthrough a t t h e end of t h e s a l t t r a n s f e r .

The f i l t e r was decontami-

n a t e d t o approximately 100 mr/hr t o minimize contamination o f t h e uranium product d u r i n g f l u o r i n a t i o n .

Analysis o f t h e decontamination s o l u t i o n s

confirmed t h a t t h e p r i n c i p a l a c t i v i t y p r e s e n t was 95Nb. The c a u s t i c s c r u b b e r was emptied, r i n s e d , and r e c h a r g e d ; t h e n s e v e r a l

s a l t samples were t a k e n .

The low-surface-area NaF i n t h e t r a p f o r remov-

i n g HF from t h e f l u o r i n e supply was r e p l a c e d w i t h h i g h - s u r f a c e - a r e a m a t e r i a l s i n c e agglomeration of p e l l e t s i n t h e f i r s t f l u s h s a l t a b s o r b e r

i n d i c a t e d t h e p r e s e n c e of c o n s i d e r a b l e HF i n t h e gas stream.

This HF

could have r e s u l t e d from t h e r e a c t i o n of f l u o r i n e w i t h t h e Be(0H)z remaining i n t h e f l u s h s a l t a f t e r t h e p r e v i o u s H2-HF t r e a t m e n t . Because t h e f l u o r i n e supply system had been opened, it seemed a d v i s a b l e t o c o n d i t i o n t h i s equipment w i t h d i l u t e f l u o r i n e ( t h i s was s t a r t e d on August 23).

Conditioning and a p e r i o d of s t e a d y flow t o check t h e

Hastings mass flowmeter r e a d i n g s were completed, and t h e n s a l t s p a r g i n g

was s t a r t e d .

After 30 min a t a flow r a t e of 20 s t d l i t e r s / m i n , t h e

f l u o r i n e flow was i n c r e a s e d t o 40 s t d l i t e r s / m i n f o r t h e conversion of UFb t o U F g .

F l u o r i n e u t i l i z a t i o n was very high ( ~ 7 0 % d) u r i n g t h i s p e r i o d .

For almost 6 h r , t h e a b s o r b e r i n l e t and o u t l e t meters r e a d t h e same, i n d i c a t i n g t h a t no a b s o r b a b l e compounds were v o l a t i l i z e d .

For t h e n e x t

100 min, t h e r e a d i n g s on b o t h meters r o s e ( t h e i n l e t meter a t t h e f a s t e r r a t e ) , b u t no a b s o r b e r h e a t i n g was n o t e d .

This was i n t e r p r e t e d t o i n d i -

c a t e MoF6 (from Hastelloy-N by c o r r o s i o n ) v o l a t i l i z a t i o n and e i t h e r dec r e a s i n g f l u o r i n e u t i l i z a t i o n o r incomplete a b s o r p t i o n of t h e MoF6 on t h e NaF.

A f t e r 7 - 1 / 2 h r , UFg a b s o r p t i o n was i n d i c a t e d by a t e m p e r a t u r e r i s e

on t h e f i r s t a b s o r b e r .

F l u o r i n e flow was d e c r e a s e d t o i n c r e a s e f l u o r i n e

u t i l i z a t i o n and a b s o r b e r r e s i d e n c e t i m e .

Twenty minutes b e f o r e UF6 ab-

s o r p t i o n began, t h e p r e s s u r e i n t h e a b s o r b e r c u b i c l e r o s e above t h e alarm p o i n t (-1 i n . H20).

I t was found t h a t t h e blower which normally m a i n t a i n s

a n e g a t i v e p r e s s u r e i n t h e c u b i c l e was i n o p e r a b l e , a p p a r e n t l y because of

a mechanic21 r a t h e r t h a n an e l e c t r i c a l m a l f u n c t i o n .

However, s i n c e t h e

blower was l o c a t e d i n t h e f u e l p r o c e s s i n g c e l l , i t c o u l d n o t b e r e p a i r e d . By c a r e f u l adjustment of t h e c o o l i n g a i r , t h e p r e s s u r e i n t h e c u b i c l e was kept from exceeding atmospheric p r e s s u r e . To e n s u r e t h a t e s s e n t i a l l y no uranium was l o s t t o t h e c a u s t i c

s c r u b b e r , we decided t o u s e t h e f i f t h a b s o r b e r o n l y as backup and n o t f o r c o l l e c t i n g uranium.

Consequently, t h e f i r s t r u n was t e r m i n a t e d when

uranium broke through t o t h e t h i r d a b s o r b e r .

S i n c e no t e m p e r a t u r e r i s e

was observed f o r t h e f o u r t h a b s o r b e r d u r i n g p u r g i n g , t h e second r u n was continued u n t i l uranium broke through t o t h e f o u r t h a b s o r b e r .

The t h i r d ,

f o u r t h , and f i f t h r u n s were t e r m i n a t e d a f t e r 6 0 , 75, and 95 min, r e s p e c t i v e l y , of l o a d i n g on t h e f o u r t h a b s o r b e r without any t e m p e r a t u r e r i s e b e i n g observed on t h e f i f t h a b s o r b e r .

The s i x t h r u n completed t h e

o p e r a t i o n ; no uranium was found on t h e f o u r t h o r f i f t h a b s o r b e r .

Fluorine

flow was stopped when t h e i n l e t mass flowmeter showed no f u r t h e r d e c r e a s e f o r an hour ( s e e F i g . 1 6 ) .

End p o i n t d e t e r m i n a t i o n was somewhat d i f f i c u l t

because of t h e almost continuous b u i l d u p of r e s t r i c t i o n s i n t h e s c r u b b e r d i p t u b e s , accompanied by an i n c r e a s e i n system p r e s s u r e and a d e c r e a s e i n f l u o r i n e flow.

The i n c r e a s e i n t h e r e a d i n g of t h e e x i t meter a t t h e

end o f t h e r u n was probably due t o MoF6 b e i n g desorbed s i n c e t h e r e a d i n g

was t o o h i g h t o b e accounted f o r by helium and f l u o r i n e .

The n e u t r o n

c o u n t e r n e a r t h e f u e l s t o r a g e tank provided a n o t h e r s e n s i t i v e i n d i c a t i o n of t h e end p o i n t .

The n e u t r o n count r a t e f e l l r a p i d l y d u r i n g t h e l a s t

few hours of f l u o r i n a t i o n b u t had become c o n s t a n t by t h e time t h e f l u o r i n e flow was s t o p p e d . After r u n 6 , a n a l y s i s of a f u e l s a l t sample i n d i c a t e d 26 ppm, o r about 130 g, of uranium remaining i n t h e s a l t .

This i s a v e r y a c c e p t a b l e

The s a l t was, t h e r e f o r e , h e a t e d t o 1225OC t o reduce t h e s t r u c t u r a l

loss.

metal f l u o r i d e s . 5.6

Reduction of t h e Fuel S a l t

The t e m p e r a t u r e of t h e f u e l s a l t reached 1225'C on August 31, 1968 and a 3 0 - s t d - l i t e r / m i n hydrogen s p a r g e was s t a r t e d a t t h i s time.

A low-

flow hydrogen s p a r g e had been used d u r i n g t h e p r e v i o u s 15-hr h e a t u p ,

h i g h r a d i a t i o n r e a d i n g n o t e d a few hours l a t e r a t t h e a b s o r b e r c u b i c l e appeared t o be c e n t e r e d a t t h e m e t a l l i c f i l t e r upstream of t h e i n l e t mass flowmeter. 80 r / h r .

The u n s h i e l d e d r a d i a t i o n l e v e l a t t h e c u b i c l e w a l l w a s a b o u t

The s o u r c e of t h i s r a d i a t i o n was l a t e r i d e n t i f i e d as 95Nb ( S e c t .

6.5).

I t i s known t h a t niobium e x i t e d i n t h e m e t a l form d u r i n g r e a c t o r o p e r a t i o n and t h a t , i n t h i s form, most o f it p l a t e d out o r l e f t i n t h e gas stream. decay.

After r e a c t o r shutdown, t h e 95Nb grew back i n from 9 5 Z r

After a decay p e r i o d of f i v e months, less t h a n 0 , 1 % of t h i s 95Nb

would be r e q u i r e d t o produce t h e observed r a d i a t i o n l e v e l .

The r e s t o f

t h e niobium probably p l a t e d o u t on t h e d r a i n t a n k o r on p r o c e s s i n g equipment s u r f a c e s , o r was v o l a t i l i z e d d u r i n g f l u o r i n a t i o n .

About 60% o f t h e

i b F 5 formed d u r i n g f l u o r i n a t i o n would be c a r r i e d from t h e s a l t by 60,000 v

l i t e r s of gas f l o w .

ORNL-DWG 69-540f

2.0

4.8 ._ L

4.6

c 0

4.4

a W

E E

w 4.2

c W

J LL

FLUORINE FLOW OFF

4.0

m m a

z 0.8

0.6 2200

2400

0200 TIME, 8-29-68

F i g . 16.

End o f Run No. 6 .

0400

Because of t h e h i g h e r c o n c e n t r a t i o n of c o r r o s i o n p r o d u c t s i n t h e f u e l s a l t ( t h a n i n t h e f l u s h s a l t ) , a 24-hr hydrogen s p a r g e was s p e c i f i e d ; however, f r e q u e n t s c r u b b e r d i p l i n e plugging caused t h e s p a r g e t o b e stopped a f t e r 17 h r .

A t t h i s t i m e , t h e s c r u b b e r s o l u t i o n t h a t had been

used d u r i n g t h e l a s t f l u o r i n a t i o n run was r e p l a c e d w i t h a KOH s o l u t i o n c o n t a i n i n g no K I o r K2B407.

Because of f r e q u e n t plugging o f t h e l i n e s ,

t h e flow r a t e s were reduced below t h e planned 30 s t d l i t e r s / m i n f o r about 70% of t h e t i m e .

A f i l t e r e d s a l t sample was t a k e n and analyzed

w h i l e t h e s c r u b b e r s o l u t i o n was b e i n g r e p l a c e d .

As expected, t h e r e was

no evidence of r e d u c t i o n of chromium o r i r o n ; however, t h e a n a l y s i s showed t h a t t h e n i c k e l c o n c e n t r a t i o n had i n c r e a s e d from 840 ppm t o 1540 ppm. T h i s i n c r e a s e i n n i c k e l c o n c e n t r a t i o n was thought t o be t h e r e s u l t of contamination by n i c k e l o x i d e , o r i g i n a t i n g from p o o r l y purged welding o f t h e n i c k e l f i l t e r element i n t h e f r e e z e - v a l v e c a p s u l e .

After another

1 7 h r of s p a r g i n g , t h e n i c k e l c o n c e n t r a t i o n had only d e c r e a s e d t o 520 ppm; a g a i n no chromium o r i r o n was reduced.

A t h i r d p e r i o d of s p a r g i n g f o r

17-1/2 h r d e c r e a s e d t h e n i c k e l c o n c e n t r a t i o n f u r t h e r t o 180 ppm.

The

remaining r e d u c t i o n was accomplished w i t h zirconium m e t a l . Twenty-seven zirconium s l u g s , weighing an average of 180 g each, were charged through t h e sampler; two o t h e r s r o l l e d beyond t h e r e a c h of t h e m a n i p u l a t o r and could n o t be charged t o t h c s a l t a t t h i s time. Approximately 5 kg o f zirconium was added, and t h e s a l t was sparged f o r 24 h r w i t h hydrogen a t t h e r a t e of 10 s t d l i t e r s / m i n ,

A n a l y s i s of a

f i l t e r e d sample of s a l t taken a t this t i m e showed t h e n i c k e l t o be completely reduced and t h e chromium and i r o n reduced t o about 100 ppm. The s a l t had been a g i t a t e d w i t h helium p r i o r t o t h e sample a n a l y s i s and t h e n was sparged f o r 8 a d d i t i o n a l h r w i t h hydrogen.

D i f f i c u l t i e s again

p r e v e n t e d sampling b e f o r e f i l t r a t i o n . The f u e l s a l t was f i l t e r e d w i t h o u t d i f f i c u l t y ,

A d i p sample from

t h e d r a i n t a n k showed t h e chromium c o n c e n t r a t i o n t o b e 34 ppm; a second f i l t e r e d sample showed o n l y 29 ppm of chromium i n s o l u t i o n . on t h e r e d u c t i o n a r e g i v e n i n S e c t . 6 .

More d e t a i l s

50 6.

6.1

DISCUSSION OF DATA Fluorine Utilization

The e f f i c i e n c y o f t h e f l u o r i n a t i o n r e a c t i o n i s measured by t h e p e r centage of t h e f l u o r i n e ( a f t e r s u b t r a c t i n g t h e f l u o r i n e consumed by c o r r o s i o n ) t h a t i s used i n t h e r e a c t i o n w i t h t h e uranium.

The f l u o r i n e

consumed by c o r r o s i o n i s assumed t o be c o n s t a n t a t 2.5 s t d l i t e r s / m i n . C o r r e c t i o n i s a l s o made f o r t h e i n e r t g a s e s p r e s e n t (assumed t o b e n i t r o gen) i n t h e f l u o r i n e supply and t h e e f f e c t of t h e reduced gas d e n s i t y on t h e o r i f i c e flowmeter.

F l u o r i n e u t i l i z a t i o n i s a f u n c t i o n of m e l t temper-

a t u r e , f l u o r i n e flow r a t e , uranium c o n c e n t r a t i o n , and d i p t u b e submergence. Laboratory t e s t s had shown a d e c r e a s e i n u t i l i z a t i o n from 8 . 0 t o 3.8% as The h i g h e r u t i l i z a t i o n

t h e temperature was reduced from 930'F t o 840'F.'

(average, 39%) d u r i n g t h e f u e l s a l t p r o c e s s i n g was probably due b o t h t o lower gas v e l o c i t i e s by a f a c t o r o f 5 and g r e a t e r d i p t u b e submergence (by a f a c t o r o f 15) t h a n used i n l a b o r a t o r y t e s t s .

U t i l i z a t i o n was v e r y h i g h

b e f o r e t h e s t a r t o f UF6 v o l a t i l i z a t i o n (average, 71%) and, a f t e r t h a t , seemed t o be r e l a t i v e l y i n s e n s i t i v e t o uranium c o n c e n t r a t i o n u n t i l n e a r l y

a l l t h e uranium was v o l a t i l i z e d ( s e e F i g s . 17 and 1 8 ) .

The h i g h e s t aver-

age u t i l i z a t i o n d u r i n g UF6 v o l a t i l i z a t i o n o c c u r r e d i n t h e f i f t h r u n ( s e e Table 6 ) . U n t i l 90 min b e f o r e t h e s t a r t of UFg v o l a t i l i z a t i o n , t h e r e a d i n g s o f t h e a b s o r b e r i n l e t and o u t l e t mass flowmeters were e q u a l , i n d i c a t i n g t h e absence of any a b s o r b a b l e c o n s t i t u e n t s i n t h e gas s t r e a m .

These flow-

meters were used t o c a l c u l a t e t h e f l u o r i n e u t i l i z a t i o n , as shown i n F i g . 18.

The u t i l i z a t i o n decreased when t h e f l u o r i n e flow r a t e was i n c r e a s e d

and a l s o when MoF6 and UF6 began t o be v a p o r i z e d .

I t i s t h u s assumed t h a t

t h e f l u o r i n e u t i l i z a t i o n does n o t change, when t h e f l u o r i n e flow i s s t e a d y , u n t i l v o l a t i l i z a t i o n begins.

During t h e FloF, v o l a t i l i z a t i o n p e r i o d ( b e f o r e

UF, v o l a t i l i z a t i o n began), t h e u t i l i z a t i o n was c a l c u l a t e d by d i f f e r e n c e , u s i n g t h e u t i l i z a t i o n s i n t h e two p r e v i o u s p e r i o d s and assuming t h a t a l l t h e UF, was c o n v e r t e d t o UF, p r i o r t o uranium v o l a t i l i z a t i o n .

The f l u o -

r i n e flow rates a r e a d j u s t e d f o r t h e f l u o r i n e t h a t was consumed by c o r r o sion.

During t h e v o l a t i l i z a t i o n of UF6, t h e f l u o r i n e u t i l i z a t i o n was

c a l c u l a t e d from t h e i n c r e a s e i n a b s o r b e r w e i g h t s .

The i n l e t mass Y

ORNL-DWG 69-5407

z Q

20 W

J IJ-

I J - 0

10 20 30 40 FLUORINE SPARGE TIME AFTER UFG BREAKTHROUGH ( h r )

Fig. 17.

Fluorine Flow Rate vs Utilization.

'\ \

rr----j

Fig. 18.

4 5 6 FLUCQINE SPAQGE TIME (hr)

Fluorine Utilization at the Start of Run 1.

53 Table 6 , Fluorine Utilization Corrected F2 Flow (std liters/min)

Percent agc F2

Utilization 7.7

Flush salt

19.8

Fuel salt, overall

18.8

Run 1 - Before MoFg Volatilization

17.1

- Before MoF6 Volatilization

36 .O

- During MoFg Volatilization

31.5

- During UFg Volatilization

26 2 e

Run 2 - During UFg Volatilization

15,3

Run 3 - During UFg Volatilization

16.7

Run 4

During UF6 Volatilization

16,2

Run 5 - During UFg Volatilization

13.5

Run 6 - During UFg Volatilization

16 -9

flowmeter indicated a high utilization toward the end of each run because of the stratification of the dense UFg in the fuel-storage-tank gas space, The fluorine flow rates calculated from the decrease in pressure in the fluorire trailers agree reasonably well with the results obtained with the orifice flowmeter except in runs 2 and 5. In run 2 a fluorine flow of 90% of the rate indicated by the flowmeter was used since this produces: (1) utilizations in reasonable agreement with those observed in the other

runs, (2) an integrated UFg flow from the inlet meter that is in agreement with the absorber weight increase, and (3) a reasonable amount of MoFg leaving the absorbers as calculated from the outlet meter.

In run 5 a

fluorine f:ow of 110% of the rate indicated by the flowmeter was used, 6.2 Corrosion One o i the major problems encountered during processing was the corrosion of the fuel storage tank. Coupon testing in the Volatility Pilot 6

Plant and at Battelle Memorial Instituteâ&#x20AC;&#x2122; had shown Hastelloy-N to be

54 s u p e r i o r , as a material of c o n s t r u c t i o n , t o n i c k e l (mainly because of

t h e absence of i n t e r g r a n u l a r c o r r o s i o n ) and as r e s i s t a n t t o c o r r o s i o n as any o f t h e o t h e r m a t e r i a l s t e s t e d ; however, t h e c o r r o s i o n r a t e was s t i l l much h i g h e r t h a n d e s i r e d .

The c o r r o s i o n r a t e s shown i n Table 7 were c a l -

c u l a t e d from t h e i n c r e a s e i n C r y F e y and N i c o n t e n t s o f t h e s a l t and from t h e amount of MoF6 v o l a t i l i z e d . Table 7 .

Corrosion During F l u o r i n a t i o n

Corrosion (mi l s / h r ) , Based on : Ni Fe Cr

Flush S a l t Fuel S a l t

QO. 2

Aver

0.10

0.2

0.15

0.11

0.04

0.2

0.14

0.09

a e

a Weighted f o r c o n c e n t r a t i o n i n Hastelloy-N.

The c o r r o s i o n r a t e s c a l c u l a t e d d u r i n g f l u s h s a l t p r o c e s s i n g may b e h i g h s i n c e t h e y i n c l u d e a 2-hr c o n d i t i o n i n g p e r i o d a t 1125'F w i t h f l u o r i n e . A l l o t h e r f l u o r i n e exposures were a t 850 t o 860'F.

The c o r r o s i o n r a t e ,

based on molybdenum, was c a l c u l a t e d from t h e r i s e o f t h e r e a d i n g o f t h e i n l e t mass flowmeter p r i o r t o t h e temperature r i s e i n t h e f i r s t a b s o r b e r (Fig. 19).

I t i s b e l i e v e d t h a t t h i s r i s e was due t o t h e p r e s e n c e of MoF6,

which i s more v o l a t i l e t h a n UF6 and has almost as l a r g e a h e a t c a p a c i t y , The c o r r o s i o n due t o molybdenum i n t h e f l u s h s a l t could n o t b e c a l c u l a t e d d i r e c t l y because of t h e s h o r t time i n t e r v a l (20 min) between t h e two i n d i cations.

The e q u i v a l e n t t i m e i n t e r v a l f o r t h e f u e l s a l t was 90 min; t h u s

t h e c a l c u l a t i o n i n t h i s c a s e should be r e a s o n a b l y a c c u r a t e .

A 15-min time

l a g i n t h e temperature r e s p o n s e was assumed i n t h e c a l c u l a t i o n s .

With t h e

f u e l s a l t t h e r e was a s i m u l t a n e o u s , b u t s m a l l e r , r i s e on t h e e x i t flowmeter r e a d i n g .

T h i s i s b e l i e v e d t o be caused mainly by t h e i n c r e a s i n g

amount o f u n r e a c t e d f l u o r i n e due t o reduced u t i l i z a t i o n .

The average e x i t

meter r e a d i n g agreed reasonably well with t h e c a l c u l a t e d r e a d i n g f o r 43% f l u o r i n e u t i l i z a t i o n ( s e e Table 6 ) .

The h i g h e r c o r r o s i o n r a t e , based on

molybdenum, i s probably due t o s u r f a c e l e a c h i n g and r a p i d v o l a t i l i z a t i o n of t h e h i g h l y v o l a t i l e MoF6.

ORNL-DWG 6 9 - 5 4 0 5

4 /

FLUORINE OFF FOR TRAILER CHANGE

120

150

TIME ( m i n )

Fig. 19.

Mass Flowmeter Readings Before Start of Volatilization

of UF6 from Fuel Salt.

56 6.3

Molybdenum

During r e a c t o r o p e r a t i o n , c o r r o s i o n product and f i s s i o n product molybdenum e x i s t s as f i n e l y d i v i d e d metal.

I n t h i s form, most o f it

l e a v e s t h e s a l t , e i t h e r i n t h e gas stream o r by d e p o s i t i o n on t h e g r a p h i t e and metal s u r f a c e s .

During f l u o r i n a t i o n , t h e molybdenum i n t h e H a s t e l l o y -

N f u e l s t o r a g e t a n k i s a t t a c k e d and converted t o MoF6.

Molybdenum i s t h e

o n l y major c o n s t i t u e n t of t h e f u e l s t o r a g e tank forming a h i g h l y v o l a t i l e fluoride.

(Chromium f l u o r i d e i s n o t v o l a t i l i z e d u n t i l e s s e n t i a l l y a l l of

t h e UFg has been v o l a t i l i z e d . ) v o l a t i l e than UFg.

A s seen i n Table 8 , M O F 6 i s somewhat more

The molybdenum complex, MoF6-3 NaF, i s much l e s s s t a b l e

t h a n t h e uranium complex, UF6.3 N a F . Table 8 . . Comparison Between MoF6 and UF6

B o i l i n g p o i n t a t 760 mm, "F P a r t i a l p r e s s u r e over NaF a t 2 0 0 째 F , mm

UF 6

MoF,

147

0,001

A t t h e s t a r t of f u e l s a l t f l u o r i n a t i o n , it i s l i k e l y t h a t non-vola-

t i l e MoF3 i s formed and i s n o t converted t o bloF, u n t i l most o f t h e UF4

i s converted t o U F 5 .

Because of t h e h i g h e r v o l a t i l i t y o f MoF6, v o l a t i l i -

z a t i o n would b e expected t o b e g i n b e f o r e UF6 b e g i n s t o v o l a t i l i z e .

This

was v e r i f i e d by t h e i n c r e a s e i n t h e r e a d i n g on t h e a b s o r b e r i n l e t mass flowmeter about 1 - 1 / 2 h r b e f o r e an a b s o r b e r t e m p e r a t u r e r i s e was noted (see Fig. 1 9 ) ,

During t h i s p e r i o d of MoF, v o l a t i l i z a t i o n , t h e r e a d i n g on

t h e a b s o r b e r o u t l e t meter i n d i c a t e d t h a t no MoF6 was p r e s e n t i n t h e e x i t gas stream u n t i l n e a r t h e s t a r t of U F g a b s o r p t i o n .

After UF, began t o v o l a t i l i z e , t h e a b s o r b e r o u t l e t mass flowmeter

was used t o c a l c u l a t e t h e amount o f bloF6 l e a v i n g t h e a b s o r b e r s .

The

molybdenum i n t h e a b s o r b e r o u t l e t stream was a l s o c a l c u l a t e d by two o t h e r methods: from t h e gas flow and t h e MoF6 vapor p r e s s u r e , and by s u b t r a c t i n g t h e amount of MoF6 r e t a i n e d on t h e a b s o r b e r s from t h e amount o f MoF6

produced by c o r r o s i o n .

A good c o r r e l a t i o n of t h e d a t a , except i n r u n 6,

was o b t a i n e d , showing t h a t t h e amount of absorbed MoFg i n c r e a s e s as t h e amount o f UFg passed through t h e NaF i n c r e a s e s . approximations, a r e compared i n Table 9 .

The d a t a , which a r e only

This t a b l e a l s o shows t h e amount

of molybdenum found i n t h e c a u s t i c s c r u b b e r s o l u t i o n s .

The r e a s o n f o r

t h e e x c e s s i v e amount o f MoFg l e a v i n g t h e a b s o r b e r s i n r u n 6 i s n o t c l e a r . The amount of molybdenum t h a t passed through t h e s c r u b b e r i s n o t known. There was no accumulation o f s o l i d s i n t h e l i n e from t h e s c r u b b e r as was experienced d u r i n g t h e second s c r u b b e r t e s t r u n ( S e c t . 5 . 2 ) ; however, t h e

m i s t f i l t e r was n o t examined, From t h e random samples of NaF analyzed f o r molybdenum, t h e followi n g o b s e r v a t i o n s have been made concerning t h e a b s o r p t i o n of MoF6: (1)

Absorption i s h i g h e r on h i g h - s u r f a c e - a r e a NaF t h a n on low-surfacea r e a NaF.

(2)

Absorption i s h i g h e r on p e l l e t s t h a n powder, probably because MoF6

i s trapped inside the p e l l e t s . (3)

Absorption i s h i g h e r on NaF t h a t has been exposed t o U F g , and i n c r e a s e s w i t h t h e UFg c o n c e n t r a t i o n i n t h e gas s t r e a m .

Run 6 a p p e a r s

t o b e an e x c e p t i o n i n t h i s r e s p e c t . 6.4

Plutonium

S i n c e t h e MSRE f u e l s a l t c o n t a i n e d 66 w t % 238U, amount of 239Pu was produced.

a significant

A t t h e time of r e a c t o r shutdown, t h e p l u -

tonium c o n c e n t r a t i o n i n t h e f u e l s a l t was c a l c u l a t e d t o b e 1 1 2 ppm (560 g ) . Five s a l t samples withdrawn a f t e r f l u o r i n a t i o n , a f t e r r e d u c t i o n , and a f t e r r e t u r n of t h e s a l t b a t c h t o t h e r e a c t o r d r a i n tank showed an average conc e n t r a t i o n o f 110 ppm.

T h i s confirms t h e e x p e c t a t i o n t h a t plutonium would

n o t b e v o l a t i l i z e d under t h e r e l a t i v e l y mild c o n d i t i o n s r e q u i r e d f o r u r a nium v o l a t i l i z a t i o n . 6.5

Niobium

Figure 20 shows t h e amounts o f f i s s i o n product f l u o r i d e s c a l c u l a t e d t o be v o l a t i l i z e d d u r i n g f l u o r i n a t i o n of t h e f u e l s a l t .

The i o d i n e and

t e l l u r i u m f l u o r i d e s ( S e c t . 6 . 6 ) p a s s through b o t h NaF beds t o t h e c a u s t i c

Table 9 .

D i s p o s i t i o n of V o l a t i l i z e d Molybdenum Molybdenum (g) In Absorber Out l e t Stream Amount Produced Minus Amount From Flow and Ab sorbed Vapor P r e s s u r e

From Mass Flowmeter

Produced by Corros iona

Ab s o r b ed on NaFb

990

962

940

26 0

Run 1

1270

130

1140

246

670

107

Run 2

739

2 10

5 19

427

364

Run 3

86 8

330

538

257

26 7

Run 4

914

375

5 39

132

8 70

Run 5

1131

425

706

271

663

Run 6

1114

112

1002

399

3120

T o t a l Fuel

6036

1582

4444

1732

5954

373

Total

7026

1610

5406

2672

Flush S a l t

In Caustic Scrubber

Fuel S a l t

633

a A t a c o n s t a n t c o r r o s i o n r a t e of 0.2 m i l s / h r . bFrom a c o r r e l a t i o n o f absorbed Mo v s UFb through NaF. C

Unable t o c a l c u l a t e .

59 ORNL-DWG

106

69-5402

VAPOR PRESSURE >106rnm: MoF6, I F 7 , T e F g

1 ~

404 I)

cn cn

0 - 5

103

0 20 40 60 00 I oc PERCENT VOLATILIZED DURING F U E L SALT FLUORINATION

Fig. 20.

Calculated Fission Product Volatilization During Fuel

Salt Fluorination.

60 s c r u b b e r and c h a r c o a l t r a p s .

Because of t h e five-month decay t i m e , 99ivi0

was not p r e s e n t i n d e t e c t a b l e amounts,

Ruthenium, niobium, and antimony

e x i s t a s metals d u r i n g r e a c t o r o p e r a t i o n and, as such, are c o n t i n u o u s l y removed by d e p o s i t i o n o r by t h e o f f - g a s stream.

S i n c e ruthenium i s formed

d i r e c t l y by f i s s i o n and s i n c e r a d i o a c t i v e antimony has no l o n g - l i v e d p r e c u r s o r s , t h e amounts of t h e s e i s o t o p e s i n t h e p r o c e s s e d s a l t were small as compared w i t h niobium, which grows i n from n o n v o l a t i l e 9 5 Z r . Figure 2 1 shows t h e b u i l d u p o f 95Nb a f t e r r e a c t o r shutdown and t h e b u i l d u p a f t e r f l u o r i n a t i o n , assuming complete v o l a t i l i z a t i o n .

Also shown

i s a comparison between t h e amount o f niobium found i n s a l t s a u p l e s t a k e n b e f o r e and a f t e r f l u o r i n a t i o n and t h e amount of niobium which should have been p r e s e n t from zirconium decay (assuming no niobium p r e s e n t a t sainple time) when t h e sample was analyzed s e v e r a l months a f t e r p r o c e s s i n g ,

Since

t h e sample p r i o r t o f l u o r i n a t i o n showed less niobium t h a n would have grovn i n from z i r c o n i u n decay, i t i s i n p o s s i b l e t o s a y whether t h e r e was any a p p r e c i a b l e amount of niobium i n t h e s a l t b e f o r e f l u o r i n a t i o n .

R t least

60% o f t h e grown-in niobium must have been l o s t d u r i n g sample p r e p a r a t i o n (before a n a l y s i s ) ,

T h i s l o s s d i d n o t occur i n t h e p o s t - f l u o r i n a t i o n

samples, a s seen i n F i g . 2 1 , when t h e s a l t was i n an o x i d i z e d s t a t e .

The

c l o s e agreement between t h e c a l c u l a t e d amount and t h e sample a n a l y s i s probably i n d i c a t e s t h a t t h e r e was very l i t t l e niobium l e f t i n t h e s a l t after fluorination. Figure 20 i n d i c a t e s t h a t approxil,iately 60% o f t h e n i o b i m i n t h e f u e l s a l t v o l a t i l i z e d duriiig f l u o r i n a t i o n

I t i s n o t k n m n , however, how much

niobium was p r e s e n t i n t h e s a l t a t t h a t t i m e ,

From t h e lack of h e a t gen-

e r a t i o n i n t n e NaF t r a p , t h e v o l a t i i i z e d niobium i s b e l i e v e d t o c o n s t i t u t e l e s s t h a n 10% o f t h e 9 x l o L c u r i e s w?iich would have grown i n a f t e r r e a c t o r shutdown.

(A temperature r i s e oi' 2 0 째 F would have been observed from

t h e h e a t g e n e r a t i o n from 9000 c u r i e s of 9 5 h % . )

The temperature of t h e

t r a p , remained c o n s t a n t ; t h a t i s , no h e a t e r adjustment was r e q u i r e d throughout t h e s i x runs.

Apparently, most o f t h e niobium was removed from t h e

s a l t by d e p o s i t i o n i n t h e d r a i n t a n k o r i n back-flowing through t h e s a l t

f i l t e r during s a l t t r a n s f e r ,

A t t h e end of t h i s t r a n s f e r , t h e t r a n s f e r

gas blowthrough c a r r i e d a small amount of m e t a l l i c niobium t o t h e a b s o r b e r f i l t e r (see S e c t . 5 . 5 ) .

Alt,iough t h i s f i l t e r was decontaminated p r i o r t o

3 I

F i g . 21.

Buildup of "Nb

from "Zr

Decay.

62 f l u o r i n a t i o n , undoubtedly some of t h e niobium was d e p o s i t e d on t h e upstream p i p i n g .

During f l u o r i n a t i o n , t h i s niobium would be converted t o

v o l a t i l e NbF5 and c o l l e c t on t h e UFg a b s o r b e r s (any niobium upstream of T h i s i s probably t h e s o u r c e

t h e NaF t r a p s h o u l d be absorbed on t h e t r a p ) .

of t h e niobium on t h e a b s o r b e r s ( S e c t . 6 . 8 ) r a t h e r t h a n niobium t h a t was v o l a t i l i z e d from t h e s a l t p a s s i n g through t h e NaF t r a p . Two days a f t e r t h e end of f l u o r i n a t i o n , a t t h e beginning o f hydrogen r e d u c t i o n , a l a r g e amount o f niobium ( e s t i m a t e d t o be 15 t o 20 c u r i e s ) was S i n c e 9 5 N b should have grown i n a t t h e r a t e

found on t h e a b s o r b e r f i l t e r .

of about 1000 c u r i e s p e r day, a p p a r e n t l y less t h a n 1%o f t h e niobium i n t h e s a l t was c a r r i e d t o t h e a b s o r b e r c u b i c l e .

A gamma s c a n , made of t h e

f i l t e r on March 10, 1969, i s shown i n F i g . 2 2 . t h a t of g5Nb a t 0 . 7 7

MeV.

The o n l y d e f i n i t e peak i s

Very small amounts of 125Sb, lo3Ru, and

could be t h e cause of t h e b u l g e i n t h e curve between 0 . 4 and 0.55 6.6

MeV.

Iodine and Tellurium

During f l u o r i n a t i o n , v o l a t i l e I F 7 i s formed and p a s s e s through b o t h NaF beds; i t i s removed by t h e c a u s t i c s c r u b b e r by r e a c t i o n w i t h t h e KOH

and by exchange w i t h t h e K I .

A t o t a l of 404 m c of 1311 was c a l c u l a t e d t o

be i n t h e f u e l s a l t a t t h e s t a r t of p r o c e s s i n g .

Analyses o f t h e c a u s t i c

s c r u b b e r s o l u t i o n s showed t h a t 288 m c was c o l l e c t e d d u r i n g r u n 1 and 10 m c

was c o l l e c t e d d u r i n g run 2 f o r a 74% a c c o u n t a b i l i t y .

T h i s i s i n reason-

a b l e agreement w i t h t h e r e s u l t s of i o d i n e a n a l y s e s of f u e l s a l t (during r e a c t o r o p e r a t i o n ) , which showed about 65% o f t h e c a l c u l a t e d amount.

The

d i s c r e p a n c y between t h e c a l c u l a t e d amount and t h e analyzed amount is caused by t h e l o s s of m e t a l l i c 13'Te b e f o r e decay.

There was no i n d i c a -

t i o n t h a t any i o d i n e c o l l e c t e d on t h e c h a r c o a l beds downstream o f t h e scrubber. Tellurium e x i s t s p r i m a r i l y i n t h e m e t a l l i c s t a t e d u r i n g r e a c t o r o p e r a t i o n and, as such, i s removed from t h e s a l t by d e p o s i t i o n and by t h e o f f - g a s stream.

salt.

Freeze-valve samples showed less t h a n 1%remaining i n t h e

S i n c e 129Te h a s no l o n g - l i v e d p r e c u r s o r , t h e a c t i v i t y w i l l n o t grow

back i n after r e a c t o r shutdown.

Any t e l l u r i u m remaining i n t h e s a l t w i l l

b e converted t o t h e v o l a t i l e TeFg d u r i n g f l u o r i n a t i o n .

MPC f o r 129mTe

Because o f t h e low

pc/cC), a t l e a s t 94% o f t h e remaining 1%would have

ORNL-DWG 69-5404

io3)

-t

Fig. 22.

0.2

0.4 0.6 GAMMA ENERGY ( M e V )

0.77

0.0

Gamma Scan of Absorber Cubicle F i l t e r .

1.o

t o be removed from t h e g a s stream b e f o r e t h e stream i s d i s c h a r g e d from the stack.

Tellurium h e x a f l u o r i d e i s n o t absorbed on NaF a t any tempera-

t u r e and removal i n t h e c a u s t i c s c r u b b e r i s not v e r y e f f i c i e n t .

However,

s i n c e a n a l y s e s of t h e s c r u b b e r s o l u t i o n s showed t e l l u r i u m t o b e below t h e l i m i t of d e t e c t i o n , i t i s p r o b a b l e t h a t less t h a n 1%was p r e s e n t i n t h e

s a l t a t r e a c t o r shutdown.

Any t e l l u r i u m p a s s i n g through t h e s c r u b b e r

would have been removed by t h e a c t i v a t e d aluminaâ&#x20AC;&#x2122; 6 7

i n t h e soda-lime t r a p .

Uranium Absorption

A s mentioned i n S e c t . 5 . 5 , two t y p e s of NaF were used: a h i g h - s u r f a c e -

a r e a (HSA) m a t e r i a l (1 m2/g), prepared a t ORGDP by h e a t i n g NaHF2 p e l l e t s , and a low-surface-area (LSA) m a t e r i a l (0.063 m2/g, p r e p a r e d a t t h e UCNC Paducah P l a n t , from NaF powder and water and s i n t e r e d a t 70OoC.

The LSA

m a t e r i a l was o r i g i n a l l y s p e c i f i e d f o r t h e MSRE Fuel P r o c e s s i n g P l a n t because of i t s h i g h e r c a p a c i t y f o r b o t h C r F 5 (on t h e 750Â°F NaF t r a p ) and f o r UF6.

(This high c a p a c i t y i s due t o t h e slower s u r f a c e r e a c t i o n and

g r e a t e r p e n e t r a t i o n t o t h e i n s i d e of t h e p e l l e t s . )

When t h e f l u o r i d e

d i s p o s a l method was changed from t h e SO2 gas-phase r e a c t i o n t o t h e aqueous s c r u b b e r , a more c o n s e r v a t i v e approach toward p o s s i b l e uranium breakthrough from t h e a b s o r b e r s became n e c e s s a r y .

The low MoF6 r e t e n t i o n observed

during t h e f i n a l f l u o r i n e disposal t e s t (Sect, 5 , 2 ) suggested t h a t t h e r e a c t i o n r a t e with UFg might b e t o o slow f o r complete uranium a b s o r p t i o n 10 under t h e planned o p e r a t i n g c o n d i t i o n s Subsequent l a b o r a t o r y t e s t s confirmed t h e much slower r e a c t i o n r a t e w i t h t h e LSA material

The ab-

s o r b e r s were, t h e r e f o r e , h e a t e d t o i n c r e a s e t h e r e a c t i o n r a t e , and t h e LSA NaF was r e s t r i c t e d t o t h e No

1 and No

2 p o s i t i o n s o f t h e group of f i v e

absorbers. A comparison of t h e r e s u l t s o b t a i n e d with t h e two t y p e s o f NaF i s

shown i n F i g . 23.

Three a b s o r b e r s loaded w i t h each t y p e of m a t e r i a l were

used i n t h e f i r s t p o s i t i o n , and t h r e e were used i n t h e second p o s i t i o n , during t h e s i x runs.

I n t h e f i r s t p o s i t i o n , t h e NaF was exposed t o a

h i g h e r UF6 c o n c e n t r a t i o n ; t h i s r e s u l t e d i n a lower l o a d i n g t h a n i n t h e second p o s i t i o n where t h e slower r e a c t i o n r a t e p e r m i t t e d deeper p e n e t r a t i o n of t h e p e l l e t s .

Except i n one c a s e , h i g h e r l o a d i n g s were o b t a i n e d W

ORNL-DWG 6 8 - 11623

14.5

14.C

13.5

13.c h

- 12.5 4 Y

\ N0.2

POSITION

11.0

10.5

10.0

9.5 160 Fig. 23.

200 240 280 AVERAGE TEMPERATURE ( O F ) Comparison of LSA and HSA NaF Loading.

320

66 a t lower t e m p e r a t u r e s ; i n t h a t p a r t i c u l a r c a s e , t h e a b s o r b e r had been

used i n a p r e v i o u s run where a s m a l l amount of uranium was absorbed. In s p i t e of t h e f a c t t h a t t h e LSi" NaF a b s o r b e r s were o p e r a t e d a t h i g h e r temperatures ( t o compensate f o r t h e s l o w e r r e a c t i o n r a t e ) , t h e t o t a l loading was 13 t o 14% h i g h e r .

The maximum uranium l o a d i n g o b t a i n e d

was 0 . 5 6 g p e r g of NaF, as compared with 0 . 4 9 g p e r g o f NaF f o r t h e HSA material.

Both of t h e s e a b s o r b e r s were i n t h e second p o s i t i o n .

The t h r e e

lowest l o a d i n g s shown i n F i g . 23 f o r t h e LSA NaF c o n t a i n e d from 11 t o 18% HSA (added l a t e r t o more f u l l y charge t h e a b s o r b e r s ) , which undoubtedly reduced t h e loading on t h e s e a b s o r b e r s . The time r e q u i r e d f o r a breakthrough of UF6 from a given a b s o r b e r t o t h e subsequent a b s o r b e r v a r i e s d i r e c t l y with t h e r e s i d e n c e time of t h e gas stream i n t h e a b s o r b e r , as shown i n F i g . 2 4 .

The f i r s t a b s o r b e r i n

r u n 1 had an u n u s u a l l y s h o r t breakthrough time (25 s e c ) , which was possi b l y caused by a b s o r p t i o n o f NoFg t h a t had been v o l a t i l i z e d b e f o r e t h e

s t a r t of UF6 v o l a t i l i z a t i o n (Sect

6.3).

The c o n d i t i o n s and l o a d i n g s a r e summarized i n Table 10.

These load-

i n g s a r e h i g h s i n c e no allowance was made f o r absorbed MoF6. 6,8

Uranium Product P u r i t y

The i n l e t of t h e f i r s t a b s o r b e r i n each r u n was analyzed f o r g r o s s b e t a and gamma a c t i v i t y about 1 2 days a f t e r f l u o r i n a t i o n ; t h e r e s u l t s a r e shown i n Fig

25.

The a c t i v i t y a s s o c i a t e d w i t h uranium d a u g h t e r s a t t h e

same time i s a l s o shown.

A t t h e time of t h e a n a l y s e s , t h e 2 3 5 U d a u g h t e r s

had reached e q u i l i b r i u m , w h i l e t h e 2 ? 8 U d a u g h t e r s had a t t a i n e d o n l y about 30% o f e q u i l i b r i u m .

The o n l y a c t i v i t i e s a p p r e c i a b l y above background were

t h e gamma a c t i v i t y i n t h e f i r s t run and t h e gamma a c t i v i t y on t h e f i r s t a b s o r b e r o f t h e second r u n .

(The a c r i v i t y i n t h e f e e d s a l t b e f o r e f l u o r i -

n a t i o n , counted a t t h e same t i n e , was 2.66 x 1013 g r o s s gamma and 3 . 8 x l O I 3 g r o s s b e t a c o u n t s p e r minute p e r gram of uranium.)

The average g r o s s b e t a

and gamma decontamination f a c t o r s (DF) f o r t h e s i x a b s o r b e r s a n a l y z e d , a f t e r c o r r e c t i o n f o r uranium daughter a c t i v i t y , were 1 . 2 x

lo9

and 8 . 6 x

lo8 respectively,

The Gnly a c t i v i t y c o l l e c t e d i n any measurable amount on t h e NaF abs o r b e r s w i t h t h e UF6 was 9 5 h i n Most of t h i s a c t i v i t y was p r o b a b l y c a r r i e d

ORNL-DWG 69-5400

160

140

c ._

I (3

3 0 K

+ Y

a W

m LL W

m K

2o 0

Fig. 24.

10 15 20 ABSORBER RESIDENCE TIME (sec)

Absorber Residence Time vs UF6 Breakthrough Time.

68 Table 1 0 ,

Summary o f U F

Aver Temp. I

Run Flush

Absorption Data

Flow Through Absorber Minus N 2 Iie and Unreacted F 2 Superficial Corrected Gas Flow Rate Velocity (std liters/min) (fps1 20.0 0.038

Average Gas Residence Time (Excluding UF6) (set) 18.3

Uranium Absorbeda (kg) 4.65

Absorber 1

Type NaF LSA

LSA

226

20 .o

0.037

18.7

1.83

LSA

210

20.0

0 036

19.2

0.15

227

20 .o

0.037

18.7

6.63

Aver Fuel-1

(OF)

244

LSA

26 1

39.4

0.077

9.1

12.53

HSA

258

28.5

0.055

12.6

9.80

HSA

258

28.5

0.055

12.6

3.49

LSA

255

21.2

0.041

17.0

11.98

LSA

282

17.9

0.036

19.3

12,86

HSA

265

17.0

0.033

20.8

8.36

HSA

25 3

17.0

0.033

21.2

0.61

â&#x201A;Ź]SA

252

18.7

0.036

19 3

10.66

LSA

263

18.8

0.037

18.9

13.14

HSA

258

18.8

0 '037

19 * 1

ll"91

HSA

2 74

18.9

0.038

18.6

5.73

HSA

193

19.5

0.034

20.2

11,42

HSA

218

19.5

0.036

19.5

11.55

M A

217

19.5

0 036

19.5

11,24

HSA

2 20

19.5

0.036

19.4

9,83

LSA

238

16,O

0.030

23.0

13.51

LSA

243

15.1

0.029

24.2

14 45

HSA

188

15.1

0.026

26.3

12.37

HSA

207

15.1

0,027

25.5

8.94

HSA

207

38.7

0.070

10 .o

10.45

HSA

200

38.7

0.069

10.1

12 47

IlSA

179

38.7

0.067

10.4

0 -55

236

22.7

0.043

18.0

217 85

Aver a

These weights i n c l u d e absorbed MoF6

bTotal weights.

ORNL- DWG 69 - 5406

to5) 3

.=“2 .E L

a v) +

GROSS

0 3

IN U PRODUCT

L ow0 ---- E---

p ACTIVITY

u UP

;HTER y ACTIVITY ’

GROSS

IN U PRODUCT,

100

150

URANIUM VOLATILIZED (kq)

Fig. 25.

Gross Activity i n Uranium Product.

2oc

70 from t h e s a l t i n t o t h e p i p i n g and equipment between t h e f u e l s t o r a g e tank and t h e m e t a l l i c f i l t e r upstream of t h e a b s o r b e r s a t t h e end of t h e s a l t t r a n s f e r when t h e p r e s s u r e of t h e t r a n s f e r gas was r e l e a s e d ( S e c t s . 5 . 5 and 6 . 5 ) ,

Because of t h i s dpm p e r gram of U 95% ( dpm p e r gram of U on niobium- v o l a t i l i z e d d u r i n g

contamination, t h e decontamination f a c t o r f o r i n salt ) was lower t h a n t h e a c t u a l DF from absorber f l u o r i n a t i o n and c o l l e c t e d on t h e a b s o r b e r s a

The DF was lower a t t h e s t a r t of r u n 1 when most o f t h e niobium between t h e NaF t r a p and t h e a b s o r b e r s was f l u o r i n a t e d and c o l l e c t e d on t h e f i r s t absorber.

The D F â&#x20AC;&#x2DC; s v a r i e d from 5 x

end o f f l u o r i n a t i o n .

lo6

a t t h e s t a r t t o 1 x 10â&#x20AC;?

a t the

T h e r e f o r e , n o t w i t h s t a n d i n g t h e p i p i n g contamination,

a c o n s i d e r a b l y h i g h e r niobium DF was o b t a i n e d i n t h e s e r u n s t h a n i n t h e V o l a t i l i t y P i l o t P l a n t (5 x l o 7 ) f o r 30-day-decayed uranium, The a c t i v i t y of t h e uranium p r o d u c t , i n e x c e s s of t h e uranium daught e r a c t i v i t y , would be expected t o b e n e g l i g i b l e a f t e r d e s o r p t i o n of t h e UF6 from t h e NaF.

L a b o r a t o r y - s c a l e runs have shown decontamination f a c 11 t o r s of 10 t o l o 3 f o r t h i s o p e r a t i o n , The o n l y n o n r a d i o a c t i v e contaminant of any consequence expected t o b e found w i t h t h e absorbed uranium was molybdenum (from c o r r o s i o n of t h e Hastelloy-N d u r i n g f l u o r i n a t i o n ) .

The a c t u a l amount on t h e a b s o r b e r s

could n o t be determined u n t i l t h e UF6 was desorbed.

The b e h a v i o r of

molybdenum d u r i n g t h e p r o c e s s i n g i s d i s c u s s e d i n S e c t , 6 . 3 , 6.9

Reduction o f Metal F l u o r i d e s

The c o n c e n t r a t i o n s of t h e s t r u c t u r a l m e t a l f l u o r i d e s i n t h e f l u s h and f u e l s a l t s d u r i n g v a r i o u s s t a g e s o f p r o c e s s i n g a r e shown i n Table 11, C a l c u l a t i o n s of t h e hydrogen and zirconium u t i l i z a t i o n s were o n l y approximate f o r t h e f o l l o w i n g r e a s o n s : (1)

D i f f i c u l t i e s i n o b t a i n i n g f i l t e r e d samples

(2)

Large s t a n d a r d d e v i a t i o n i n i r o n a n a l y s e s .

(3)

Unreliable nickel analyses using f i l t e r capsules with nickel f i l t e r s , Oxidation of t h e f i l t e r d u r i n g f a b r i c a t i o n caused a h i g h n i c k e l a n a l y -

s i s f o r a t l e a s t one sample. S i n c e t h e f l u s h s a l t was n o t sampled a f t e r r e d u c t i o n of N i F 2 , t h e hydrogen u t i l i z a t i o n d u r i n g r e d u c t i o n could n o t be c a l c u l a t e d .

The

71 Table 11.

S t r u c t u r a l Metal F l u o r i d e Concentrations

Con c e n t r a t i o n (ppm) C r 2 10 Fe 2 40 N i 5 15 Flush s a l t a I n r e a c t o r system

Before f l u o r i n a t i o n

104

After f l u o r i n a t i o n

133

loob

210

516

174b

50b

No sample taken

After 1074 g o f Z r and 25 h r o f H2 s p a r g i n g After f i l t r a t i o n

No sample t a k e n

After 1 0 . 8 h r of H2 s p a r g i n g A f t e r 604 g o f Zr and 9 h r o f H2 s p a r g i n g

150

76b

141b

130

Before f l u o r i n a t i o n

170

131

After fluorination

4 20

400

840

A f t e r 1 7 . 1 h r of H2 s p a r g i n g

420b

430b

A f t e r 33.5 h r of H2 sparging

420b

400b

5 20b

After 5 1 . 1 h r o f H2 sparging

460b

380b

A f t e r 5000 g of Z r and 24 h r of H2 sparging

loob

1l o b

180b b <lo

Fuel s a l t a I n r e a c t o r system

A f t e r 5100 g o f Z r and 32 h r of H2 sparging After f i l t r a t i o n a

H2 s p a r g i n g times a r e cumulative.

b F i l t e r e d sample. C

Contaminated sample.

No sample taken 34

110

72 hydrogen utilization during fuel salt reduction, however, was calculated to be 1.9% overall, as shown in Table 12. This is somewhat higher than 12 the utilization experienced in test runs with a 48-liter batch of salt. In the test runs, the utilization was less than 1% when the nickel fluoride concentration in the salt was less than 500 ppm. The higher utilization during fuel salt reduction is probably due to greater dip tube submergency (64 in. vs 26 in.).

Apparently, a high hydrogen concentration

is more important for efficient reduction than a high gas sparge rate.

The minimum hydrogen utilization during flush salt reduction was calculated by assuming complete reaction of the zirconium and an iron reduction equal to the chromium reduction. The maximum utilization assumes complete NiF2 reduction by the hydrogen. Table 12 summarizes the nickel reduction step. Since the NiF2 reduction of the fuel salt (and probably also in the case of the flush salt) was incomplete after hydrogen sparging, the remainder of the NiF2 was reduced by addition of zirconium. The reduction step after zirconium was added to the salt is summarized below in Table 13. A zirconium utilization of only 40% during the flush salt processing would have been required if all the NiF2 had been reduced during the hydrogen sparge.

7. ACKNOWLEDGMENTS Much of the credit for the successful processing of the MSRE fuel belongs to the following: G , I. Cathers for laboratory-scale work in support of the fluorination, absorption, and fluorine disposal operations;

E. L. Nicholson for assistance in design of final modifications to the plant; W , H. Carr, G. I. Cathers, and E. L , Nicholson for around-theclock technical assistance during the fuel salt fluorination; R. H. Guymon, T. L, Hudson, and A. I. Krakoviak for supervision of operations; and W. S. Pappas, ORGDP, for specification of special instrumentation and assistance during testing and final operation.

73 Table 1 2 .

Reduction of Nickel F l u o r i d e Hydrogen Sparge Aver. H2 Flow Rate (std liters/min) % H2 -I_-__.

T o t a l H2 Flow (liters)

% Hydrogen Utilization

Salt

Sparge Time (hr)

Flush

10.8

36.2

23,500

2 . 2 - 3.6

Fue 1

17.1

21.4

21,860

1.1

16.4

34.0

33,470

17.6

10.8

11,420

21.8

Fuel Aver.

Table 13.

5.7 1.9

Reduction o f Chromium and

I r o n F l u o r i d e s After Addition of Zirconium Zirconium Added

Sparge Gas Flow Rate fstd liters/min)

Salt

(e)

Sparg e Time (hr)

Flush

604

4 70

11.5

18.5

100

Aver. Fue 1

Aver.

5000

0 (He)

13.2

% Zr Utilization

> 40

79 5 6

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