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Experience with glovebox inert atmosphere control system
NUCLEAR ENGINEERING AND DESIGN 6 (1967) 213-216. NORTH-HOLLAND PUBLISHING COMP.. AMSTERDAM
EXPERIENCE WITH GLOVEBOX I N E R T ATMOSPERE CONTROL SYSTEM * W i l l i a m F. HOLCOMB Argonne National Laboratory. Idaho Dit,ision, Idaho Falls. Idaho. USA
Received 26 June 1967
The handling and preparation of sodium for fuel elements at the Fuel Cycle Facility for the Second Experimental Breeder Reactor requires the use of a glovebox equipped with a recirculating inert atmosphere of high parity. The argon gas purification system consists of a palladium catalyst for removing oxygen, molecular sieve dryer for removing water, and a canned blower for circulating the gas. The purification system serves a 250 ft 3 glovebox complex and with continuous operation can maintain an atmosphere with oxygen impurities of 2 ppm and water impurities of 6 ppm at an inleakage rate of 0.002 ft3/hr of air while operating the gtovebox complex at a negative pressure of I in. of water.
1. ~ T R O D U C T I O N The F u e l Cycle F a c i l i t y , built as p a r t of the Second E x p e r i m e n t a l B r e e d e r R e a c t o r c o m p l e x (EBR-II) for the r e m o t e r e p r o c e s s i n g and r e f a b r i c a t i n g of r e a c t o r fuel, r e q u i r e s an i n e r t a t m o s p h e r e glovebox s y s t e m for handling and p r e p a r i n g sodium. The sodium is used as a bond between the u r a n i u m fuel pin and s t a i n l e s s s t e e l j a c k e t used f o r encapsulation. The glovebox s y s t e m c o n s i s t s of two 2 module, 1½ t i e r g l o v e b o x e s c o n n e c te d to each o t h e r by a t r a n s f e r p o r t and c o m m o n c i r c u l a t i n g l i n e s . Fig. 1 shows the glovebox c o m p l e x and fig. 2 shows a s c h e m a t i c of the p u r i f i c a t i o n and a n a ly ti c a l i n s t r u m e n t a t i o n s y s t e m s attached to the g l o v e b o x e s . The b o x e s have 49 g l o v e s , two t r a n s f e r locks, and n u m e r o u s p e n e t r a t i o n s for the p u r i f i c a t i o n , a n a l y t i c a l i n s t r u m e n t a t i o n and p r e s s u r e c o n t r o l s y s t e m s . The v o l u m e of the g l o v e boxe s and a s s o c i a t e d gas handling e q u ip m e n t is about 250 ft 3 ( ~ 7 ra3). During c o n s t r u c t i o n , all piping and gas handling s y s t e m s w e r e c h e c k e d for l e a k s by Halium M a s s S p e c t r o m e t e r . Any d e t e c t a b l e leak was repaired. Argon was chosen as the i n e r t gas b e c a u s e it is easy to contain and c o m p r e s s . A ls o , it is * This work was performed under the auspices of the United States Atomic Energy Commission under contract with the University of Chicago.
a l r e a d y piped throughout the building at v a r i o u s p r e s s u r e s to m e e t the r e q u i r e m e n t s of the F u e l Cycle F a c i l i t y and i t s argon a t m o s p h e r e hot cel l , and is thus r e a d i l y a v a i l a b l e in the l a b o r a t o r i e s .
2. ARGON PURIFICATION
SYSTEM
The argon p u r i f i c a t i o n s y s t e m c o n s i s t s of four i t e m s of equipment a r r a n g e d in this o r d e r : 1. A f i l t e r s e c t i o n built into the glovebox which is connected with the c i r c u l a t i n g l i n es of the cat al y z e r and d r y e r section. 2. A p al l ad i u m c a t a l y s t bed which r e m o v e s the oxygen p r e s e n t in the gas s t r e a m by combining it with added h y d r o g e n to f o r m w a t e r . The bed contains 36 pounds (16 kg) of c a t a l y s t and has an infinite life u n l e s s poisioned. 3. An e i g h t - s t a g e c e n t r i f u g a l b l o w e r which c i r c u l a t e s the gas f r o m the g l o v e b o x e s through the c a t a l y z e r and d r y e r and back to the g l o v e boxes. Its flow r a t e is a p p r o x i m a t e l y 10 f t 3 / m i n (0.3 m 3 / m i n ) at a s t a t i c p r e s s u r e of 14 in. of w a t e r . The b l o w e r is i n s t a l l e d in a s m a l l g a s tight e n c l o s u r e to o v e r c o m e leakage p r o b l e m s . 4. A m o l e c u l a r si ev e d r y e r which r e m o v e s w a t e r f r o m the c a t a l y t i c r e a c t i o n of oxygen and the w a t e r i n i t i al l y in the gas s t r e a m . The d r y e r v e s s e l contains 80 pounds (36 kg) of s i e v e s which have a capacity of 16 pounds (7 kg) of w a t e r at n o r m a l o p e r a t i n g conditions. I n t e g r a l l y a s s o c i a t e d with the p u r i f i c a t i o n
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ADDITION SOLENOID I PS~G~ DING AI SUPPLY
TO BLD'G l
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I r . ~ I' VENT m. - - ~ SOLENOID GLOVE BOX #1 TRANSFER LUCK
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Fig. 2. Glove boxes atmosphere control system. s y s t e m a r e t h r e e srLb-systems: (1) hydrogen addition; (2) a n a l y t i c a l i n s t r u m e n t a t i o n ; and (3) dryer regeneration. The hydrogen addition s e c t i o n c o n s i s t s of a hydrogen gas manifold and flow m e t e r for m e t e r i n g the hydro~:en for the catalytic c o m b i n a tion with oxygen to f o r m water. The hydrogen manifold i s built to act as a safety m e a s u r e to p r e v e n t a c o m b u s t i b l e quantity f r o m e n t e r i n g the g].oveboxes. The manifold cons i s t s of a h i g h - p r e s s u r e 220 ft 3 (~6 m 3) gas bottle connected to :t s m a l l h i g h - p r e s s u r e 30 ft 3 (~ 0.9 m 3) gas bottle. Through a s e r i e s of p r e s s u r e r e g u l a t o r s and v a l v e s , the s m a l l e r gas bottle is p e r i o d i c a l l y c h a r g e d with gas f r o m the l a r g e r gas bottle. ,~:fter i s o l a t i n g the l a r g e r bottle the s m a l l e r bottle can then be opened to the p u r ification s y s t e m . By u s i n g the p r e d e t e r m i n e d size bottle, the amount e,f gas which could e n t e r the boxes upon a r e g u l a t o r f a i l u r e can be controlled. This has p r o v e n v e r y s u c c e s s f u l where total quantities can be c a l c u l a t e d beforehand then
allowed to e n t e r the gloveboxes unattended. During n o r m a l o p e r a t i o n s , the hydrogen flow rate n e c e s s a r y to r e a c t s t o i c h i o m e t r i c a l l y with the oxygen p a s s i n g through the c a t a l y z e r is det e r m i n e d f r o m the oxygen c o n c e n t r a t i o n of the glovebox a t m o s p h e r e , r e a d on the oxygen m e t e r , and the known p r o c e s s i n g flow r a t e . The h y d r o gen rate i s adjusted to 85% of the s t o i c h i o m e t r i c flowrate. The a n a l y t i c a l i n s t r u m e n t a t i o n section takes its sample from each glovebox and feeds it to a sample header via a diaphragm p r e s s u r e - v a c u u m pump. The i n s t r u m e n t a t i o n c o n s i s t s of a 0-10% n i t r o gen in argon t h e r m a l conductivity a n a l y z e r , an e l e c t r o l y t i c water a n a l y z e r , and an e l e c t r o l y t i c oxygen a n a l y z e r (with m a x i m u m r a n g e s of 0 - I 0 0 0 ppm) connected to the sample h e a d e r . Continuous s a m p l e s a r e drawn through the i n s t r u m e n t s by m e a n s of a d i a p h r a g m p r e s s u r e - v a c u u m pump which exhausts to the building exhaust s y s t e m . The d r y e r r e g e n e r a t i o n section r e g e n e r a t e s
216
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the d e s i c c a n t in the d r y e r when it b e c o m e s satu r a t e d with m o i s t u r e to such an extent that the efficiency of the d r y e r is reduced. Saturation is indicated by a r i s e of water c o n c e n t r a t i o n in the atmosphere. During r e g e n e r a t i o n , the c a t a l y z e r and d r y e r u n i t s a r e isolated f r o m the gloveboxes, and air with a dewpoint of l e s s than - 6 0 ° F (-51°C) is heated to 600°F (315°C) as it p a s s e s through the d r y e r v e s s e l . During the r e g e n e r a t i o n period, the c a t a l y z e r and d r y e r a r e i n o p e r a t i v e . A d r y e r bypass valve was i n s t a l l e d to p e r m i t b e t t e r control of the amount of water r e m o v e d , thus m a i n t a i n i n g the water content of the gloveboxes a t m o s p h e r e r e l a t i v e l y constant. It also p e r m i t s the c a t a l y z e r and d r y e r s y s t e m s to be r e t u r n e d to s e r v i c e after a d r y e r r e g e n e r a t i o n by allowing the d r y e r to be b y p a s s e d while it is cooling down. 3. PRESSURE CONTROL Control of glovebox p r e s s u r e is a c c o m p l i s h e d through differential p r e s s u r e switches connected for operating at a p r e s s u r e negative to the a m bient a t m o s p h e r e . The p r e s s u r e c o n t r o l l e r section c o n s i s t s of t h r e e d i f f e r e n t i a l p r e s s u r e switches, a p r e s s u r e gauge, an addition line, and a vent line controlled by solenoid valves (see fig. 2). N o r m a l box p r e s s u r e is approximately -1.0 in. of water with p r i m a r y control on either side to vent or add gas as r e q u i r e d . Should the p r e s s u r e r i s e to -0.28 in. of water (caused by glove i n s e r t i o n , gas leaks, or a t m o s p h e r i c p r e s s u r e drop), a dual d i f f e r e n t i a l p r e s s u r e switch c l o s e s , e n e r g i z i n g a solenoid vent valve that vents gas to the building exhaust s y s tem. The vent line is a side s t r e a m connected to the outlet of the c i r c u l a t i n g blower, thus c r e a t i n g sufficient d r i v i n g force to vent sufficient quantit i e s of argon when needed. Should the p r e s s u r e drop to -1.5 in. of water (caused by leaks in the vacuum lock s y s t e m s e r v i c i n g the box, glove withdrawal, a t m o s p h e r i c p r e s s u r e r i s e , or s a m pie withdrawal) the s a m e dual differential p r e s s u r e switch c l o s e s , e n e r g i z i n g a solenoid gas addition valve, adding argon to the box f r o m the F C F building 1 psig argon supply s y s t e m . If the p r e s s u r e were to continue to r i s e , at +0.5 in. water, a high a l a r m p r e s s u r e switch would close, e n e r g i z i n g an a l a r m c i r c u i t c o n s i s t i n g of an ann u n c i a t o r a l a r m in the o p e r a t i o n s c o n t r o l r o o m of the F C F and an a l a r m bell in the glovebox room. If the p r e s s u r e were to continue to drop, at -2.0 in. water, a low a l a r m p r e s s u r e switch would close, e n e r g i z i n g an a l a r m c i r c u i t con-
HOLCOMB
s i s t i n g of an a n n u n c i a t o r a l a r m in the o p e r a t i o n s control room of the F C F and an a l a r m bell in the glovebox room. An i n t e r l o c k c i r c u i t , used with the low p r e s s u r e a l a r m , d e - e n e r g i z e s any vacuum pumps which a r e s e r v i c i n g the vacuum locks and p r o c e s s equipment in the box.
4. OPERATING EXPERIENCE The a t m o s p h e r e is e s t a b l i s h e d by purging about 1200 ft 3 (34 m 3) of argon into the boxes with the c i r c u l a t i n g blower operating and the vent solenoid activated, thus continually diluting the a i r - a r g o n m i x t u r e until the air c o n c e n t r a t i o n is about 2.7%. Then the hydrogen addition s y s t e m is operated to d e c r e a s e the oxygen content. During the hydrogen addition some p u r g i n g with argon is continued. It r e q u i r e s about 20 h o u r s of p u r g i n g to reduce the a i r content so that the catalyst may be placed in operation. The d r y e r r e q u i r e s r e g e n e r a t i o n about once every 7 weeks. The r e g e n e r a t i o n r e q u i r e s 8 hours, during which the p u r i f i c a t i o n s y s t e m is inoperative. During the cooling period (6 hours), the p u r i f ication s y s t e m is r e t u r n e d to operation although the d r y e r b y p a s s valve is opened allowing the m a j o r i t y of the gas flow to bypass the d r y e r until it has cooled down to a m b i e n t t e m p e r a t u r e . The c i r c u l a t i n g blower and d r y e r (or d r y e r bypass) are operated continuously. The hydrogen addition s y s t e m is n o r m a l l y operated only during the day shift, although the hydrogen addition s y s t e m can be operated unattended with very low feed r a t e s over night or over a weekend. The lowest a i r inleakage o b s e r v e d during the past 4 y e a r s was 0.001 f t ~ / h r (0.00003 m 3 / h r ) at a box p r e s s u r e of -1.0 in. of water, while the a v e r a g e a i r inleakage rate is about 0.004 f t 3 / h r (0.0001 m 3 / h r ) at -1.0 of water. Continuous operation of the gas p u r i f i c a t i o n s y s t e m has shown a capability of m a i n t a i n i n g an a t m o s p h e r e with oxygen i m p u r i t i e s of 2 ppm and water i m p u r i t i e s of 6 ppm at a box inleakage r a t e of 0.002 f t 3 / h r (0.00006 m 3 / h r ) of a i r while o p e r a t i n g in the range of -0.8 to -1.0 in. of water. However, r e s u l t s f r o m e x p e r i m e n t s indicate that sodium extruding and handling is c o n s i d e r a b l y i m p r o v e d by m a i n t a i n i n g the water in the a t m o sphere at 30-50 ppm and the oxygen at 10-25 ppm; t h e r e f o r e , the glovebox a t m o s p h e r e is m a i n t a i n e d at these l e v e l s . The p u r i f i c a t i o n s y s t e m has operated over 34000 h o u r s without the need for m a i n t e n a n c e on any of the components.
EXPERIENCE WITH GLOVEBOX I N E R T ATMOSPERE CONTROL SYSTEM * W i l l i a m F. HOLCOMB Argonne National Laboratory. Idaho Dit,ision, Idaho Falls. Idaho. USA
Received 26 June 1967
The handling and preparation of sodium for fuel elements at the Fuel Cycle Facility for the Second Experimental Breeder Reactor requires the use of a glovebox equipped with a recirculating inert atmosphere of high parity. The argon gas purification system consists of a palladium catalyst for removing oxygen, molecular sieve dryer for removing water, and a canned blower for circulating the gas. The purification system serves a 250 ft 3 glovebox complex and with continuous operation can maintain an atmosphere with oxygen impurities of 2 ppm and water impurities of 6 ppm at an inleakage rate of 0.002 ft3/hr of air while operating the gtovebox complex at a negative pressure of I in. of water.
1. ~ T R O D U C T I O N The F u e l Cycle F a c i l i t y , built as p a r t of the Second E x p e r i m e n t a l B r e e d e r R e a c t o r c o m p l e x (EBR-II) for the r e m o t e r e p r o c e s s i n g and r e f a b r i c a t i n g of r e a c t o r fuel, r e q u i r e s an i n e r t a t m o s p h e r e glovebox s y s t e m for handling and p r e p a r i n g sodium. The sodium is used as a bond between the u r a n i u m fuel pin and s t a i n l e s s s t e e l j a c k e t used f o r encapsulation. The glovebox s y s t e m c o n s i s t s of two 2 module, 1½ t i e r g l o v e b o x e s c o n n e c te d to each o t h e r by a t r a n s f e r p o r t and c o m m o n c i r c u l a t i n g l i n e s . Fig. 1 shows the glovebox c o m p l e x and fig. 2 shows a s c h e m a t i c of the p u r i f i c a t i o n and a n a ly ti c a l i n s t r u m e n t a t i o n s y s t e m s attached to the g l o v e b o x e s . The b o x e s have 49 g l o v e s , two t r a n s f e r locks, and n u m e r o u s p e n e t r a t i o n s for the p u r i f i c a t i o n , a n a l y t i c a l i n s t r u m e n t a t i o n and p r e s s u r e c o n t r o l s y s t e m s . The v o l u m e of the g l o v e boxe s and a s s o c i a t e d gas handling e q u ip m e n t is about 250 ft 3 ( ~ 7 ra3). During c o n s t r u c t i o n , all piping and gas handling s y s t e m s w e r e c h e c k e d for l e a k s by Halium M a s s S p e c t r o m e t e r . Any d e t e c t a b l e leak was repaired. Argon was chosen as the i n e r t gas b e c a u s e it is easy to contain and c o m p r e s s . A ls o , it is * This work was performed under the auspices of the United States Atomic Energy Commission under contract with the University of Chicago.
a l r e a d y piped throughout the building at v a r i o u s p r e s s u r e s to m e e t the r e q u i r e m e n t s of the F u e l Cycle F a c i l i t y and i t s argon a t m o s p h e r e hot cel l , and is thus r e a d i l y a v a i l a b l e in the l a b o r a t o r i e s .
2. ARGON PURIFICATION
SYSTEM
The argon p u r i f i c a t i o n s y s t e m c o n s i s t s of four i t e m s of equipment a r r a n g e d in this o r d e r : 1. A f i l t e r s e c t i o n built into the glovebox which is connected with the c i r c u l a t i n g l i n es of the cat al y z e r and d r y e r section. 2. A p al l ad i u m c a t a l y s t bed which r e m o v e s the oxygen p r e s e n t in the gas s t r e a m by combining it with added h y d r o g e n to f o r m w a t e r . The bed contains 36 pounds (16 kg) of c a t a l y s t and has an infinite life u n l e s s poisioned. 3. An e i g h t - s t a g e c e n t r i f u g a l b l o w e r which c i r c u l a t e s the gas f r o m the g l o v e b o x e s through the c a t a l y z e r and d r y e r and back to the g l o v e boxes. Its flow r a t e is a p p r o x i m a t e l y 10 f t 3 / m i n (0.3 m 3 / m i n ) at a s t a t i c p r e s s u r e of 14 in. of w a t e r . The b l o w e r is i n s t a l l e d in a s m a l l g a s tight e n c l o s u r e to o v e r c o m e leakage p r o b l e m s . 4. A m o l e c u l a r si ev e d r y e r which r e m o v e s w a t e r f r o m the c a t a l y t i c r e a c t i o n of oxygen and the w a t e r i n i t i al l y in the gas s t r e a m . The d r y e r v e s s e l contains 80 pounds (36 kg) of s i e v e s which have a capacity of 16 pounds (7 kg) of w a t e r at n o r m a l o p e r a t i n g conditions. I n t e g r a l l y a s s o c i a t e d with the p u r i f i c a t i o n
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ADDITION SOLENOID I PS~G~ DING AI SUPPLY
TO BLD'G l
UST FILTERS
TO BLDg. SUSPECT ~ HRUST DUCT
I r . ~ I' VENT m. - - ~ SOLENOID GLOVE BOX #1 TRANSFER LUCK
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Fig. 2. Glove boxes atmosphere control system. s y s t e m a r e t h r e e srLb-systems: (1) hydrogen addition; (2) a n a l y t i c a l i n s t r u m e n t a t i o n ; and (3) dryer regeneration. The hydrogen addition s e c t i o n c o n s i s t s of a hydrogen gas manifold and flow m e t e r for m e t e r i n g the hydro~:en for the catalytic c o m b i n a tion with oxygen to f o r m water. The hydrogen manifold i s built to act as a safety m e a s u r e to p r e v e n t a c o m b u s t i b l e quantity f r o m e n t e r i n g the g].oveboxes. The manifold cons i s t s of a h i g h - p r e s s u r e 220 ft 3 (~6 m 3) gas bottle connected to :t s m a l l h i g h - p r e s s u r e 30 ft 3 (~ 0.9 m 3) gas bottle. Through a s e r i e s of p r e s s u r e r e g u l a t o r s and v a l v e s , the s m a l l e r gas bottle is p e r i o d i c a l l y c h a r g e d with gas f r o m the l a r g e r gas bottle. ,~:fter i s o l a t i n g the l a r g e r bottle the s m a l l e r bottle can then be opened to the p u r ification s y s t e m . By u s i n g the p r e d e t e r m i n e d size bottle, the amount e,f gas which could e n t e r the boxes upon a r e g u l a t o r f a i l u r e can be controlled. This has p r o v e n v e r y s u c c e s s f u l where total quantities can be c a l c u l a t e d beforehand then
allowed to e n t e r the gloveboxes unattended. During n o r m a l o p e r a t i o n s , the hydrogen flow rate n e c e s s a r y to r e a c t s t o i c h i o m e t r i c a l l y with the oxygen p a s s i n g through the c a t a l y z e r is det e r m i n e d f r o m the oxygen c o n c e n t r a t i o n of the glovebox a t m o s p h e r e , r e a d on the oxygen m e t e r , and the known p r o c e s s i n g flow r a t e . The h y d r o gen rate i s adjusted to 85% of the s t o i c h i o m e t r i c flowrate. The a n a l y t i c a l i n s t r u m e n t a t i o n section takes its sample from each glovebox and feeds it to a sample header via a diaphragm p r e s s u r e - v a c u u m pump. The i n s t r u m e n t a t i o n c o n s i s t s of a 0-10% n i t r o gen in argon t h e r m a l conductivity a n a l y z e r , an e l e c t r o l y t i c water a n a l y z e r , and an e l e c t r o l y t i c oxygen a n a l y z e r (with m a x i m u m r a n g e s of 0 - I 0 0 0 ppm) connected to the sample h e a d e r . Continuous s a m p l e s a r e drawn through the i n s t r u m e n t s by m e a n s of a d i a p h r a g m p r e s s u r e - v a c u u m pump which exhausts to the building exhaust s y s t e m . The d r y e r r e g e n e r a t i o n section r e g e n e r a t e s
216
W.F.
the d e s i c c a n t in the d r y e r when it b e c o m e s satu r a t e d with m o i s t u r e to such an extent that the efficiency of the d r y e r is reduced. Saturation is indicated by a r i s e of water c o n c e n t r a t i o n in the atmosphere. During r e g e n e r a t i o n , the c a t a l y z e r and d r y e r u n i t s a r e isolated f r o m the gloveboxes, and air with a dewpoint of l e s s than - 6 0 ° F (-51°C) is heated to 600°F (315°C) as it p a s s e s through the d r y e r v e s s e l . During the r e g e n e r a t i o n period, the c a t a l y z e r and d r y e r a r e i n o p e r a t i v e . A d r y e r bypass valve was i n s t a l l e d to p e r m i t b e t t e r control of the amount of water r e m o v e d , thus m a i n t a i n i n g the water content of the gloveboxes a t m o s p h e r e r e l a t i v e l y constant. It also p e r m i t s the c a t a l y z e r and d r y e r s y s t e m s to be r e t u r n e d to s e r v i c e after a d r y e r r e g e n e r a t i o n by allowing the d r y e r to be b y p a s s e d while it is cooling down. 3. PRESSURE CONTROL Control of glovebox p r e s s u r e is a c c o m p l i s h e d through differential p r e s s u r e switches connected for operating at a p r e s s u r e negative to the a m bient a t m o s p h e r e . The p r e s s u r e c o n t r o l l e r section c o n s i s t s of t h r e e d i f f e r e n t i a l p r e s s u r e switches, a p r e s s u r e gauge, an addition line, and a vent line controlled by solenoid valves (see fig. 2). N o r m a l box p r e s s u r e is approximately -1.0 in. of water with p r i m a r y control on either side to vent or add gas as r e q u i r e d . Should the p r e s s u r e r i s e to -0.28 in. of water (caused by glove i n s e r t i o n , gas leaks, or a t m o s p h e r i c p r e s s u r e drop), a dual d i f f e r e n t i a l p r e s s u r e switch c l o s e s , e n e r g i z i n g a solenoid vent valve that vents gas to the building exhaust s y s tem. The vent line is a side s t r e a m connected to the outlet of the c i r c u l a t i n g blower, thus c r e a t i n g sufficient d r i v i n g force to vent sufficient quantit i e s of argon when needed. Should the p r e s s u r e drop to -1.5 in. of water (caused by leaks in the vacuum lock s y s t e m s e r v i c i n g the box, glove withdrawal, a t m o s p h e r i c p r e s s u r e r i s e , or s a m pie withdrawal) the s a m e dual differential p r e s s u r e switch c l o s e s , e n e r g i z i n g a solenoid gas addition valve, adding argon to the box f r o m the F C F building 1 psig argon supply s y s t e m . If the p r e s s u r e were to continue to r i s e , at +0.5 in. water, a high a l a r m p r e s s u r e switch would close, e n e r g i z i n g an a l a r m c i r c u i t c o n s i s t i n g of an ann u n c i a t o r a l a r m in the o p e r a t i o n s c o n t r o l r o o m of the F C F and an a l a r m bell in the glovebox room. If the p r e s s u r e were to continue to drop, at -2.0 in. water, a low a l a r m p r e s s u r e switch would close, e n e r g i z i n g an a l a r m c i r c u i t con-
HOLCOMB
s i s t i n g of an a n n u n c i a t o r a l a r m in the o p e r a t i o n s control room of the F C F and an a l a r m bell in the glovebox room. An i n t e r l o c k c i r c u i t , used with the low p r e s s u r e a l a r m , d e - e n e r g i z e s any vacuum pumps which a r e s e r v i c i n g the vacuum locks and p r o c e s s equipment in the box.
4. OPERATING EXPERIENCE The a t m o s p h e r e is e s t a b l i s h e d by purging about 1200 ft 3 (34 m 3) of argon into the boxes with the c i r c u l a t i n g blower operating and the vent solenoid activated, thus continually diluting the a i r - a r g o n m i x t u r e until the air c o n c e n t r a t i o n is about 2.7%. Then the hydrogen addition s y s t e m is operated to d e c r e a s e the oxygen content. During the hydrogen addition some p u r g i n g with argon is continued. It r e q u i r e s about 20 h o u r s of p u r g i n g to reduce the a i r content so that the catalyst may be placed in operation. The d r y e r r e q u i r e s r e g e n e r a t i o n about once every 7 weeks. The r e g e n e r a t i o n r e q u i r e s 8 hours, during which the p u r i f i c a t i o n s y s t e m is inoperative. During the cooling period (6 hours), the p u r i f ication s y s t e m is r e t u r n e d to operation although the d r y e r b y p a s s valve is opened allowing the m a j o r i t y of the gas flow to bypass the d r y e r until it has cooled down to a m b i e n t t e m p e r a t u r e . The c i r c u l a t i n g blower and d r y e r (or d r y e r bypass) are operated continuously. The hydrogen addition s y s t e m is n o r m a l l y operated only during the day shift, although the hydrogen addition s y s t e m can be operated unattended with very low feed r a t e s over night or over a weekend. The lowest a i r inleakage o b s e r v e d during the past 4 y e a r s was 0.001 f t ~ / h r (0.00003 m 3 / h r ) at a box p r e s s u r e of -1.0 in. of water, while the a v e r a g e a i r inleakage rate is about 0.004 f t 3 / h r (0.0001 m 3 / h r ) at -1.0 of water. Continuous operation of the gas p u r i f i c a t i o n s y s t e m has shown a capability of m a i n t a i n i n g an a t m o s p h e r e with oxygen i m p u r i t i e s of 2 ppm and water i m p u r i t i e s of 6 ppm at a box inleakage r a t e of 0.002 f t 3 / h r (0.00006 m 3 / h r ) of a i r while o p e r a t i n g in the range of -0.8 to -1.0 in. of water. However, r e s u l t s f r o m e x p e r i m e n t s indicate that sodium extruding and handling is c o n s i d e r a b l y i m p r o v e d by m a i n t a i n i n g the water in the a t m o sphere at 30-50 ppm and the oxygen at 10-25 ppm; t h e r e f o r e , the glovebox a t m o s p h e r e is m a i n t a i n e d at these l e v e l s . The p u r i f i c a t i o n s y s t e m has operated over 34000 h o u r s without the need for m a i n t e n a n c e on any of the components.