ML111530443
| ML111530443 | |
| Person / Time | |
|---|---|
| Site: | Pilgrim |
| Issue date: | 06/01/2011 |
| From: | Pilgrim Watch |
| To: | Atomic Safety and Licensing Board Panel |
| SECY RAS | |
| Shared Package | |
| ML111530440 | List: |
| References | |
| RAS 20407, 50-293-LR, ASLBP 06-848-02-LR | |
| Download: ML111530443 (4) | |
Text
UNITED STATES ATOMlC ENERGY COMMlSSlON WASHINGTON. P.C. 20545 September 20, 1972 2 , F, O'teary, L F. E, Kzuesi, RO L. Rogers, RS Xere is an idea to kick around, PI cc: E, G , c&, L J. M. Hendrie, L D, F. Knuth, L R. L, Tedesco, L V, Stello, L
. . G. Lainas, L
'F'ressure-Suppression Containments Recent e v e n t s have h i g h l i g h t e d t h e s a f e t y d i s a d v a n t a g e s of pressure-sup-p r e s s i o n containments- While they a l s o have some saSety advantages, on balance I b e l i e v e t h e disadvantages a r e preponderant. I recommend t h a t the .GC adopt a p o l i c y of discouraging f u r t h e r u s e o f pressure-suppression containments, and t h a t such designs n o t be a c c e p t e d f o r c o n s t r u c t i o n per-mits f i l e d a f t e r a d a t e t o be decided (say two y e a r s a f t e r t h e p o l i c y is adopted),
2, Discussion A pressure-suppression containment system h a s some means o f absorbing t h e heat of v a p o r i z a t i o n o f t h e steam i n t h e f l u i d r e l e a s e d t o t h e containment volume, I n a l l t h r e e GE models, t h e .steam i s f o r c e d t o bubble through a pool of w a t e r and i s condensed. I n t h e Westinghouse design, t h e steam i s condensed by flowing i t over i c e cubes. The o b j e c t i v e i s t o reduce the pressure i n t h e containment through "suppressing" t h e p a r t i a l p r e s s u r e o f t h e steam by condensing i t . To b e ' e f f e c t i v e , p r e s s u r e suppression must t a k e piace concurrent w i t h t h e flow of steam i n t o t h e containment, and i t s e f f e c t i v e n e s s i s t h e r e f o r e dependent on t h e r a t e a t which steam i s generated o r r e l e a s e d , I f some unexpected e v e n t s6ould result i n steam generation o r flow g r e a t e r than t h e suppression c a p a b i l i t y , then t h e steam that i s n o t condensed would add an increment o f containment pressure, S i n c e t h e o b j e c t i v e of p r e s s u r e suppression i s t o permit u s e of a smaller con-tainnent, r a t e d a t lower p r e s s u r e than would b e required without suppres-s i o n , then incomplete suppression would l e a d t o o v e r p r e s s u r i z i c g a p r e s s u r e -
suppression contaiomenE s o d e s i g r t d .
It may be noted t h a t t h e Stone and Webster "subatmospherict1 d e s i g a has l i t t l e e f f e c t on t h e i n i t i a l containment p r e s s u r e r i s e due t o an a c c i d e n t ,
and i s therefore,not a "pressure-suppression containment" f o r t h e p r e s e n t discussion. I n t h i s d e s i g n , c h i l l e d w a t e r s p r a y s a r e used t o reduce 'the containment p r e s s u r e , and t h e r e f o r e t h e containment leakage, quickly a f t e r ti p o s t u l a t e d LOCA, The p r e s s u r e c a p a b i l i t y and v o ~ u m eare designed t o take the f u l l a c c i d e n t , without c r e d i t f o r condensation.
Like all containments, the pressure-suppression d e s i g n s are required t o include margins i n c a p a b i l i t y . Experiments have been conducted by GE and Westinghouse t o e s t a b l i s h t h e r a t e of steam g e n e r a r i o n that can be accommodated, The pressure-suppression pools, ice condenser, etc,, a r e then s i z e d f o r t h e double-ended break steam flow, with margins f a r un-'
equal d i s t r i b u t i o n of steam t o t h e many modular u n i r s of which =he c-on-denser i s composed, The r a t e and d i s t r i b u t i o n margins a r e probably ade-qua te, More d i f f i c u l t t o a s s e s s . i s t h e margin needed when applying t h e e x p e r i -
cleats1 d a t a t o t h e r e a c t o r design, Recently w e have r e e v a l u a t e & t h e 10-year-old CE t e s t r e s u l t s , and decided on a more c o n s e r v a t i v e i n t e r p r e -
t a t i o n than h a s been used a l l t h e s e y e a r s - b y GE (and accepted bp us) We
now b e l i e v e t h a t t h e former i n t e r p r e t a t i o n was i n c o r r e c t , u s i n g d a t a fro= t e s t s not a p p l i c a b l e t o a c c i d e n t conditions.
We are r e q u i r i n g an independent e v a l u a t i o n of t h e i c e condenser d e s i g n and i t s bases t o make less probable any comparable m i s i n t e r p r e t a t i o n of t h i s design.
Sizce t h e pressure-suppression c o n t a i m e n t s a r e s m a l l e r t h a n conventional "b" containments, t h e same amount of hydrogen, formed i n a p o s t u l a t e d acclden:, would c o n s t i t u t e a h i g h e r voluine o r weight p e r c e n t a g e of t h e c o n t a i m e n t atmosphere. Therefore, such hydrogen g e n e r a t i o n tends t o be 8 more s e r i o u s problem i n pressure-suppression containments. The small G"c designs (both t h e light-bulb-and-doughnut and t h e over-under configura-t i o n s ) have t o be i n e r t e d because t h e hydrogen assumed ( p e r S a f e t y Guide 7) would immediately f o r n an e x p t o s i v e L i x t u r e , The GE Mod 3 and t h e Westing-house i c e condenser designs ( t h e y have equal volumes) r e q u i r e high-flow c i r c u l a t i o n and mixing systems t o ensure even d i l u t i o n of t h e hydrogen t o avoid f l a w a b l e mixtures i n one or' more compartments ( s e e following f o r an a d d i r i a n a l s e r i o u s disadvantage o f ' t h i s needed r e c i r c u l a t i o n and i t s v a l v e s ) a By c o n t r a s t , t h e d r y containments only r e q u i r e recombination o r purging s t a r t i n g weeks a f t e r t h e a c c i d e n t . ,
/
A 1 1 pressure-suppression containments a r e d i v i d e d i n t o two ( o r more) major volumes, t h e steam flowing from one t o t h e o t h e r through t h e condensing w a t e r o r i c e , Any steam t h a t flows from one of t h e s e volumes t o t h e o t h e r without being condensed i s a p o t e n t i a l source of unsuppressed p r e s s u r e .
N e i t h e r t h e s t r e n g t h n o r t h e leakage r a t e of t h e d i v i d e r (between t h e voIumesJ i s t e s t e d i n t h e r u r r e n t l y approved programs f o r i n i t i a l o r period-i c i n s e r v i c e t e s t i n g . Some e f f o r t i s now underway t o d e v i s e a legkage t e s t , b u t none h a s s o f a r been accomplished, Because of l i n i 6 d s t r e n g t h a g a i n s r c o l l a p s e , t h e "receiving" volume tias t o be provided w i t h vacuum r e l i e f , In a l l d e s i g n s e x c e p t GE Mod 111, t h i s f u n c t i o n i s p ~ , s f o m e dby a group o f v a l v e s , Such a v a l v e s t u c k open i s a l a r g e bypass of t h e condensation scheme; t h e amount o f steam that t h u s escapes condensation can o v e r p r e s s u r i z e t h e containment, Valves do n o t have a v e r y good r e l i a b i l i t y record, R e c e n t l y , f i v e o f t h e vacuum r e l i e f v a l v e s f o r t h e pressure-suppression containment of Quad C i t i e s 2 were found s t u c k p a r t l y open. Moreover, t h e s e v a l v e s had been modified t o include redundant "valve-closedf' p o s i t i o n i n d i c z z o r s a d test-i n g d e v i c e s , because of r e c e n t Reg concerns, The redundant posLtion i n -
d i c a t o r s were found n o t t o i n d i c a t e c o r r e c t l y the p a r t i c u l a r p=cly open s i t u a t i o n that obtained on t h e f i v e f a i l e d valves. W e have only r e c e h t l y begun t o pay s e r i o u s a t t e n t i o n t o t h e s e v a l v e s , s o p r e v i o u s :.~-rveillance programs have n o t g e n e r a l l y included them, The GE Mod li; desLga h a s an e l e g a n t water-leg s e a l t h a t o b v i a t e s t h e need f o r vacuum reltef v a l v e s .
T5.e high-capacity atmosphere r e c i r c u l a t i o n systems provided for hydrogen mixing involve a d d i t i o n a l v a l v e s which, i f open a t t h e wrong t i n e , would c o n s t i t u t e a s e r i o u s steam bypass and thus a p o t e n t i a l s o u r c e o f containment
o v e r - p r e s s u r i z a t i o n . These v a l v e s a r e l a r g e , and must open q u i c k l y and r e l i a b l y when r e c i r c u l a t i o n i s needed. I n o t h e r engineered s a f e t y f e a t u r e s ,
no s i n g l e valve i s r e l i e d on f o r such s e r v i c e , y e t redundancy h a s n o t been I',,
provided even f o r s i n g l e f a i l u r e s , open and c l o s e d , of t h e s e v a l v e s . This -
i s a s e r i o u s mission, s i n c e opening a t t h e wrong time l e a d s t o over-pressur-i z a r f o n , while f a i l u r e t o open when needed i n h i b i t s r e c i r c u l a t i o n .
The snaller s i z e of t h e pressure-suppression containment, p l u s t h e r e q u i r e -
nect f o t t h e primary system t o be contained i n one of t h e two volumes, h a s l e d t o overcrowding and l i m i t a t i o n of a c c e s s t o r e a c t o r and primary system c o n p n e n t s f o r s u r v e i l l a n c e and i n - s e r v i c e t e s t i n g . S e p a r a t e s h i e l d i n g of con?cnents has tended t o s u b d i v i d e i n t o compartments t h e volume occupied .
by che primary system. (Some coinpartmentation of d r y containments a l s o occurs.) A pipe break i n one o f these-compartments c r e a t e s a p r e s s u r e d i f f e r e n t i a l ; each compartment must Be designed t o w i t h s t a n d t h i s pressure.
A method of t e s t i n g such d e s i g n s h a s n o t been developed.
Wnat a r e t h e s a f e t y advantages of p r e s s u r e suppression, a p a r t from t h e c o s t saving. GE people t a l k about a decontamination f a c t o r o f 30,000 from scrubbing o f i o d i n e o u t of t h e steam by t h e w a t e r . T h i s i s h a r d t o swallow, b u t som? decontamination undoubtedly occu"rs, One wonders why GE d o e s n ' t do an experiment t o measure i t , and g e t c r e d i t f o r it. The i c e -
condenser decontamination i s measurable b u t n o t s i g n i f i c a n t .
R e c i r c u l a t i o n of t h e containment atmosphere' through t h e i c e h a s the p o t e n t i a l for r a p i d l y reducing t h e containment p r e s s u r e by c o o l i n g i t s atmosphere, 2ut i n t h e p r e s e n t design t h e r e ' s not ezmzg;Fr l e s for "bt,, =e J s p r a y s a r e f u r n i s h e d (in both volumes), j u s t a s i n d r y c ~ n t a i ~ e n t s Re- .
c i r c u l a t i o n through t h e water i n t h e GE d e s i g n s seems n o t t o have been t r i e d , b u t may be necessary i n Mod 111 f o r hydrogen c o n t r o l . We have ng a n a l y s i s w h e t h e s a y s i g n i f i c a n t cooling w i l l r e s u l t .
It i s by no means c l e a r t h a t t h e pressure-suppression contai3ments a r e , over-a i l , s i g n i f i c a n t l y cheaper than d r y c o n t a i a n e n t s when . a l l c o s t s a r e ' i n c l u d e d ,
Information on t h i s p o i n t would be u s e f u l i n e v a l u a t i n g c o s t s a d b e n e f i t s ,
and-should be obtained. '