Reactor Safety Study

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WASH- 1400

(NUREG 75101 4)

REACTOR SAFETY STUDY

AN ASSESSMENT

O F ACCIDENT RISKS

U.S. COMMERClAL NUCLEAR POWER PLANTS

U.S. NUCLEAR REGULATOR Y COMMISSION

OCTOBER 1975

Foreword

T h is i s t h e f i n a l r e p o r t o f t h e R e a c to r S a f e t y S tu dy "AnAssessme nt o f Ac cide n t Risks i n U.S . Commercia l Nucl ear PowerP l a n t s , " p r e p a r e d u n de r t h e d i r e c t i o n o f P r o f e s s o r Norman C.

R as mu ss en o f t h e M a s s a c h u s e t t s I n s t i t u t e o f T e ch n ol og y . Thew o r k, o r i g i n a l l y s p o n s o r e d by t h e U.S. A to mi c E n er gy C o m i s s i o n ,w as co mp le ted u n d er th e sp o n s o rsh ip o f t h e U.S. N u c lea r R eg u la to -r y C ommission w h ich came i n t o b e in g o n Jan u ary 1 9 , 1 9 75 .

A d r a f t r e p o r t w as p u b l i s h e d i n A u gu st o f 1 9 74 a n d was c i r c u l a t e dt o o b t a i n com ments f ro m a w i de v a r i e t y o f p e o p l e a n d o r g a n i z a -t i o n s . Comments w er e r e q u e s t e d f r om o t h e r a g e n c i e s o f t h e f e d e r -

a l g ov er nm en t, e n v i ro n m e n ta l g r ou p s, gr o up s c r i t i c a l o f n u c l e a rDower. l a w v e r s r e ~ r e s e n t i n s e n v i r on m e n t a l Q ro uD s a nd i n d u s t r v .. > .

and industr ial organizations r e p r e s e n t i n y r e a c c o r m a n u f a c t u r e r s ,a r c h ic e c c c n y i nc c r i ny f lr l r s and e l e c t r i c utilities. I n a d d i c i o nt o t h i s d i s t r i b u t i o n , many r e q u e s t s f o r t h e r e p o r t w ere r e c e i ve dfrom o t h e r i n d i v i d u a l s a n d o r g a n i z a t i o n s . A t o t a l o f a b o ut 90l e t t e r s o f c o m n t w ere re c ei v ed which w ere v e r y h e l p f u l i n t h ep r e p ar a t io n o f t h i s f i n a l r e p o r t . A new Appendix X I h a s b ee na dded t o t h e r e p o r t t o i n d i c a t e t h e s t u d y ' s r es po ns e s t o t h ecomm ents r e c e i v e d a nd t h e r e s u l t i n g c h a ng e s made i n t h e f i n a lr e p o r t .

The R e a c t o r S a f e t y S t u d y w as p e r f o rm e d , a s d e s c r i b e d i n C ha p t e r1, by a n a d h oc g r o up o f p e o p l e i n i t i a l l y a ss e m h le d by t h e Atom icEner gy Commission t o do an i n de p e nd e nt a s s e s s m e nt o f p o t e n t i a la c c i d e n t r i s k s i n U.S. c o m e r c i a l n u c l e a r pow er p l a n t s . When t h e

U.S. N u c le a r R eg u la to ry C o mmission was c re a t ed i n Jan u ary o f 1 97 5t h e work c o n t i n u e d u n d er i t s a u s p i c e s w i t h r e n ew e d r e - e m p h a si s o nt h e i n d e p e n d e n t n a t u r e o f t h e s t u d y gr ou p.

The s t u d y gr ou p w i s he s t o t ha n k a l l t h o s e who c o n t r i b u t e d t o t h es u p p or t o f t h e e f f o r t a n d t h e t e c h n i c a l w ork a s w e l l a s t h o s e whocom mented on t h e d r a f t r e p o r t t o h e l p i mp ro ve t h e q u a l i t y o f t h ef i n a l v e r s i on .

Main Report

Table of Contents

C h a p t e r P a g e N o .FOREWORD................................................................

1.1 I n t r o d u c t i o n ...............................................1 . 2 O b j e c t i v e s o f t h e R e ac t o r S a f e t y S t u d y.....................1 . 3 O r g a ni z a t i o n o f t h e R e a c t o r S a f e t y S t u dy..................................................... 4 O r g a n i z a t i o n o f t h e R e p o rt

1 . 5 T e c h n i c a l A p p e nd i c e s.......................................1 . 6 R e a c t o r S a f e t y S t u d y F lo w C h a r t............................1 .7 F a c t o r s T h at C o n t r i b u te d S i g n i f i c a n t l y i n P e rf o rm i ng t h e

S t u d y.................................................................................. 8 I n s i g h t s G ai ne d D u r i ng t h e S t u d y

1 . 9 L i m i t a t i o n s i n t h e S t ud y...................................1 . 1 0 F i n a l R em ar ks..............................................

2 THE BASIC CONCEPTS OF RISK ................................................................................ 1 M e as u re m en t o f R i s k

2 .2 A t t i t u d e s T ow ard R i s k ......................................2 . 3 R i s k D e t e r m i n a t i o n .........................................

2 .3 .1 H ig h P r o b a b i l i t y E v e n t s.............................2 .3 .2 Low P r o b a b i l i t y E v e n t s..............................

2. 4 P r e s e n t a t i o n o f R i s k E s t i m a t e s .............................REFERENCES.....................3 THE NATURE OF NUCLEAR POWER PLANT ACCIDENTS......................

3 .1 I n t r o d u c t i o n...............................................

3 .2 L o c a t i o n a n d M a g n it u d e of R a d i o a c t i v i t y ....................3 . 3 L o ss o f C o o l an t A c c i d e n t s ................................................................. 3 . 1 LOCA I n i t i a t i n g E v e n t s ................3.2 E f f e c t s o f E n gi n ee r ed S a f e t y F e a t u r e s

3 .3 .3 M ol te n F u e l I n t e r a c t i o n s ............................3. 4 R e a c t o r T r a n s i e n t s.........................................3 . 5 A c c i d e n t s I n v o l v i n g th e S p e n t F u e l S t o r a g e P o ol ............

REFERENCES..............................................................4 RISK ASSESSMENT METHODOLOGY......................................

4 -1 I n t r o d u c t i o n ...............................................4 . 2 Q u a n t i f i c a t i o n o f R a d i o a c t i v e R e l e a s e s ...................... ....... 2 .1 D e f i n i t i o n o f A c c i d e n t S e q ue n c es E v e n t T r e e s

4 .2 .2 P r o b a b i l i t y o f R e l e a s e s .............................4 . 2. 2 .1 F a u l t T r e e s ................................4 .2 .2 .2 F a i l u r e R a t e D a t a ..........................4.2 . 2 .3 Common Mode F a i l u r e s.......................

4 .2 .3 Magn i tude of R e l e a s e s...............................

Table of Contents (Continued)

C h a p t e r P a g e No .4 . 3 C o n s e q u e n c e s of R a d i o a c t i v e R e l e a s e ........................ 49

4 . 3 .1 A t m o s p h e ri c D i s p e r s i o n M od el ........................ 50

4 . 3 .2 P o p u l a t i o n Model 50....................................4 . 3. 3 H e a l t h E f f e c t s a nd P r o p e r t y Damage M od el ............ 5 1

4 .4 O v e r a l l R i s k A s s es s m en t .................................... 5 1

REFERENCES52..............................................................

............................................REACTOR ACCIDENT RISK

5 . 1 I n t r o d u c t i o n a n d Summary...................................5 .2 R a d i o a c t i v e R e l e a s e C a t e g o r i e s ............................................................ 2 . 1 PWR R e l e a s e C a t e q o r i e s ............................... 2. 2 BWR R e l e a s e C a t e g o r i e s...................................... 3 P r o b a b i l i t y o f R e l e a s e

5 . 3 . 1 PWR R e l e a s e P r o b a b i l i t y.............................5 . 3 . 2 PWR D o mi n an t A c c i d e n t S e q u e n c e s.....................

5. 3. 2. 1 L ar ge LOCA (A).............................5 . 3 . 2 . 2 S m a l l LOCA ( S1 ) ............................5. 3. 2. 3 Sm al l LOCA (S2 ) ............................5 . 3 . 2 . 4 R e a c t o r V e s s e l R u p t u r e ( R ).................5 .3 .2 .5 I n t e r f a c i n g S y s t e m s LOCA ( V) ...............5 .3 .2 .6 PWR T r a n s i e n t E v e n t s ( T) ................................................. 3 . 3 BWR R e l e a s e P r o b a b i l i t y

5 . 3. 4 BWR D o m i na n t A c c i d e n t S e q u e n c e s......................................................3 .4 .1 LOCA E v e n t s5 . 3. 4 .2 R e a c t o r V e s s e l R u p t u r e (R ).................5 . 3. 4 . 3 T r a n s i e n t E v e n t s (T)

...................................................... 3. 5 O t h e r I n t e r n a l C a u se s

5. 4 P r o b a b i l i t y o f R e l e a s e s f r om E x t e r n a l C a u se s..................................................... 4 . 1 E a r t h q u a k e R i s k5 .4 .2 Tornadoes ...........................................5 . 4 . 3 F l o o d s ..............................................5. 4. 4 A i r c r a f t I m p a c t s....................................5 . 4 . 5 Tu r b i n e M issiles ....................................5 . 4. 6 O t h e r E x t e r n a l C a u s e s...............................

5 .5 R i s k s f r o m A c c i d e n t a l R e l e a s e s.................................................................. 5. 1 E a r l y F a t a l i t i e s5 . 5 . 2 Ta b u l a r Summary o f R e s u l t s ........................................ 5 . 3 E a r l y I l l n e s s e s

5 . 5. 4 L on g-T er m H e a l t h E f f e c t s ............................5 . 5 . 4 . 1 l a t e n t C an ce rs F a r a l i t i e s ..................5 . 5. 4 .2 Th y r o i d N o d u l e s ............................5 . 5 . 4 . 3 G e ne t ic E f f e c t s............................

5 . 5 . 5 P r o p e r t y Damage.....................................5 . 6 A c c i d e n t R i s k s Due t o 1 0 0 N u c l e a r P ow er P l a n t s.............

C h a p t e r Pa ge No .REFERENCES..............................................................6 COMPARISON OF NUCLEAR RISKS TO OTHER SOCIETAL RISKS ..............

6 . 1 I n t r o d u c t i o n a n d Summary .........................................................2 I n d i v i d u a l R i s k o f F a t a l i t y an d I n j u r y

6 .2 .1 F a t a l i t i e s..........................................6 .2 .2 I n j u r i e s ............................................

6 . 3 S o c i e t a l R i s k..............................................6 .3 . 1 F a t a l i t i e s a nd I n j u r i e s .............................6 . 3 . 2 Ec on o mi c Lo s s e s .....................................

6 . 4 R i s k s F ro m L a r g e C o n se q u en c e E v e n t s ........................6 . 4 . 1 H u r r i c a n e s..........................................6 . 4 . 2 T o r n a d o e s...........................................6 . 4 .3 E a r t h q u a k e s....................................................................................... 4 . 4 M e t e o r s

6 . 4. 5 A i r p l a n e C r a s h e s ....................................6 . 4 . 6 E x p l o s i o n s ..........................................6 . 4 .7 Dam F a i l u r e s........................................6 .4 .8 F i r e s ...............................................6 . 4. 9 H a z a r d o us C h e m i c a l R e l e a s e s .......................................................................................EFERENCES

..............CONCLUSIONS AND RECOMMENDATIONS

.................................................... 1 O v e r v i e w ..............................2 R e s u l t s of t h e R i s k A s s e s sm e n t

7 . 3 F a c t o r s A f f e c t i n g t h e R i s k.................................7 . 3 . 1 P r o b a b i l i t y o f Co re M e l t ............................7 . 3 . 2 L a r g e C o n se q ue n c e A c c i d e n t s .........................

7 .4 O t h e r S t u d y O b j e c t i v e s ............................................................ 4 . 1 R e a l i s m V e r s u s C o n s e r va t i s m

7 .4 .2 M e t h o d o l o g i c a l D e v e l o p me n t s.........................7 . 4. 3 R e s e a r c h S u g g e s t i o n s ................................

7 . 5 F i n a l O b s e r va t i o n s.........................................ADDENDUM An O v e r v i e w of E v e n t T r e e a n d F a u l t T r e e M e th o do l og y a n d

t h e H a n d l i n g o f Common Mode F a i l u r e ..........................EXECUTIVE SUMMARY

APPENDIX I A c c i d en t D e f i n i t i o n a n d U s e o f E v e n t T r e e s

APPENDIX I1 F a u l t T r e e s

APPENDIX I11 F a i l u r e D a ta

APPENDIX IV Common Mode F a i l u r e s

APPENDIX V Quantitative Results of Accident Sequences

APPENDIX VI Calculation of Reactor Accident Consequences

APPENDIX VII Release of Radioactivity in Reactor Accidents

APPENDIX VIII Physical Processes in Reactor Meltdown Accidents

APPENDIX IX Safety Design Rationale for Nuclear Power Plants

APPENDIX X Design Adequacy

APPENDIX XI Analysis of Comments on the Draft WASH-1400 Report

List of Tables

Sor e U.S. Acc iden t Dea th S ta t is t ic s - .1967-1970 ...................Some U.S . Acc iden t Dea th S ta t is t ic s - -196 7-1 968 ...................196 7 F a l l i n g Deaths.. by Age Group ................................T y p i c a l R a d i o a c t i v i t y I n v e n t o r y f o r a 1 0 00 MWe N u c l e a r P ow er..........................................................e a c to r ..............................ummary of A cc id en ts In vo lv in g Core

PWR Dominant Ac cid ent S equence s v s . R e l e a s e C a t e g o r i e s ...........BWR Dominant Acc iden t Sequences o f Each Event Tree v s . R e l e a s e

C a t e g o r y.........................................................C on se qu en ce s o f R e a c to r A c c i d e n ts f o r V a r i o u s P r o b a b i l i t i e sf o r One Re a c to r ..................................................C o ns eq ue nc es o f R e a c t o r A c c i d e n t s f o r V a r i o u s P r o b a b i l i t i e s..................................................o r One Re a c to r

A p pr ox im a te A v er ag e S o c i e t a l an d I n d i v i d u a l R i sk P r o b a b i l i t i e sp e r Y e ar f r om P o t e n t i a l N u c l e a r P l a n t A c c i d e n t s ..................C o ns eq ue nc es o f R e a c t o r A c c i d e n t s f o r V a r i o u s P r o b a b i l i t i e sf o r 1 00 R e a c t o r s .................................................C o ns eq ue nc es o f R e a c t o r A c c i d e n t s f o r V a r i o u s P r o b a b i l i t i e sf o r 1 0 0 R e a c t o r s .................................................R i s k o f E a r l y F a t a l i t i e s f r o m N u c l e a r a nd No n- Nu cl earA c c i d e n t s ........................................................U.S. Fa ta l i t ie s . . by Major Ca te go r i es (1969) ..........I n d i v i d u a l R i s k of E a r l y F a t a l i t y b y V a r i ou s C au se s.I n d i v i d u a l R i s k o f E a r l y F a t a l i t y f ro m N u c l e ar a nd N on -N uc lea r........................................................c c i d e n t s

E s t i m a t e d Av er ag e An nu al R i s k o f I l l n e s s f r o m V a r i o u s A c c i d e n t si n t h e U.S .......................................................A nnu al A c c id e nt F a t a l i t i e s a n d I n j u r i e s i n t h e U.S ......U.S. Economic Losses from Va rio us Causes ....................Consequences o f Major U.S. Hurr icanes 11900-1972) ................Consequences o f Major U.S. Ea rth qu ake s (1900-1972) ....

Page No .1 6

List of Tables (Continued)

Ta ble Pag e No .-10 F a t a l i t i e s i n M a jo r A i r p l a n e C r a s h e s T h ro u gh o ut t h e W orl d

(1960-1973) ..............................................6 - 1 1 E a r l y F a t a l i t i e s i n M a jor E x p l o s i o n s T hr ou gh ou t t h e W o rld

(1925-1971) ...................................................... 1 1 7

6-12 Dam an d L ev ee F a i l u r es i n th e U.S. (1 88 9 -1 9 72 ) ................... 118.................-13 A n nu al R a t es o f F i r e s w i th L arg e E co no mic L o sses 1 1 8

7 -1 A pp ro xi ma te V a l u es o f E a r l y I l l n e s s a nd L a t e n t E f f e c t s f o r1 0 0 R eac to r s ..................................................... 1 4 1

7-2 L an d A rea A f f ec t ed b y P o te n t i a l N u c lea r P ow er P l an t A cc id en t sf o r 1 00 R e a c t o r s................................................. 1 4 1

List of Figures

Figure Page No .1-1 R e a c t o r S a f e t y S t u d y F low C h a r t .................................. 8...........................................-1 A B e n e fi t -R i s k P a t t e r n 1 7

2-2 F a t a l i t y R a te s i n C o m e r c i a l A i r T r a v e l.......................... 17

2-3 F a t a l A c c i d e n t s P e r O p e r a t i o n (L a n di n g o r T a k e o f f ) a s aF u n c t io n o f T ime fo r t h e U.S. A i r C a r r i e r F l e e t .................. 18

F a t a l i t y R a te s i n M otor V e h i c l e T r a v el ...........................U ra ni um D i o xi d e P e l l e t s Use d f o r C o m e r c i a l W a te r C o ol ed N u c l e a rPower P lan ts .....................................................C utaw ay o f F u e l Rod U sed f o r C o m er c i a l Water C o o led N u c lea rPower P lan ts .....................................................S ch emat i c o f R ea c to r C o o lan t S y stem fo r PWR......................S ch emat i c o f BWR R eac to r C o o lan t S y s tem..........................S c he m a ti c o f R e a c t o r C o o l a n t Sy s te m f o r BWR I n s i d e o f t h ePr imary Containment..............................................BWR Rea cto r Bu i ld ing Showing Pr ima ry Containment System.........................................................n c lo sed

Ty pic al PWR Containment ..........................................Power Water Re ac to r Loss of C ool ant Ac ci den t (LOCA) En gin ee redS a f e t y F e a t u r e ( ES F) F u n c t i o n s ...................................Major T ask s o f S tu d y.............................................

4-2 I l l u s t r a t i v e R e l e as e P r o b a b i l i t y V e rs us R e l e a se M ag nitu de........................................................i s togram 53...........-3 S u b t a s k s i n t h e Q u a n t i f i c a t i o n o f R a d io a c ti v e R e l e as e s 54

List of Figures (Continued)

Figure

Page No.

5..........................im p l i f i e d E v en t T ree s f o r a L arg e LOCA ..........................l l u s t r a t i o n o f F a u l t T r e e De ve lo pm en t.

S u b t a s k s i n t h e D e t e r m i n a t i o n o f t h e C on se qu en c es o f R a d i o a c t i v e........................................................e l e a s e s .

H i s t o g r m o f PWR R a d i oa c t iv e R e l e a s e P r o b a b i l i t i e s ...............H i s t o gr a m o f BWR R a d i oa c t iv e R el e a s e P r o b a b i l i t i e s ...............P r o b a b i l i t y D i s t r i b u t i o n f o r E a r ly F a t a l i t i e s p e r R ea ct or

Year .............................................................P r o b a b i l i t y D i s t r i b u t i o n f o r E a r l y I l l n e s s p e r R e a ct o r Ye ar .. .. . .

P r o b a b i l i t y D i s t r i b u t i o n f o r L a t e n t Ca nc er F a t a l i t yI n c i d e n c e p e r R e a c t o r Ye ar .......................................P r o b a b i l i t y D i s t r i b u t i o n f o r Th yr oi d N odule I n c i d e n c e.................................................e r R eac to r Y ear

P r o b a b i l i t y D i s t r i b u t i o n f o r I n c i de n c e o f G e n e ti c E f f e c t s.................................................e r R eac to r Y ear

P r o b a b i l i t y D i s t r i b u t i o n f o r P r o p e r t y Damage p e r R e a c t o rYear .............................................................P r o b a b i l i t y D i s t r i b u t i o n f o r R e l o c a t i o n a nd D ec o nt am i na ti onA rea p e r R eac to r Y ear ............................................P r o b a b i l i t y D i s t r i b u t i o n o f E a r l y F a t a l i t i e s p e r Y ear.................................................o r 100 R e a c t o r s

P r o b a b i l i t y D i s t r i b u t i o n of E a r l y I l l n e s s p e r Year.................................................o r 1 0 0 R e a c t o r s

P r o b a b i l i t y D i s t r i b u t i o n f o r L a t e n t Ca nce r F a t a l i t yI n c i d e n c e p e r Y ea r f o r 100 R e a c t o r s ..............................P r o b a b i l i t y D i s t r i b u t i o n f o r I n c i d e nc e o f G e n e t i c E f f e c t sp e r Ye ar f o r 1 0 0 R e a c t o r s ........................................P r o b a b i l i t y D i s t r i b u t i o n f o r T hy ro id N odule I n c i de n c ep e r Y ea r f o r 100 R e a c t o r s ........................................P r o b a b i l i t y D i s t r i b u t i o n f o r P r o p e r t y D amage p e r Year.....................................o r 1 00 R e a c t o r s

P r o b a b i l i t y D i s t r i b u t i o n f o r R e l o c a t i o n a nd D ec on ta m in at io nA rea p e r Y ear fo r 100 R eac to r s .............................F requ ency of Man-C aused E v en t s In v o lv i n g F a t a l i t i e s ...........F re qu en cy o f N a t u r a l E v e n t s I n v o l vi n g F a t a l i t i e s .................Frequency o f Ac cide n ts Inv o lv ing Pro per ty Damage...............................requency o f H urr i can e Consequences

Figure.-5

Frequency

List of Figures (Continued)

Tornado Consequences .............................................................arthquake Consequences..............................eteorite Consequences .........................irplane Crash Consequences..............................xplosion Consequences ............................am Failure Consequences...................................ire Consequences .............hlorine Accidents Involving Fatalities

Page No .12 3

Chapter 1

Objectives and Organization of the Reactor Safety Study

1.1 INTRODUCTION s y s t e m s h a d n o t b e en w e l l developed .C l ea r ly , even i f t h e r e l i a b i l i t yt e c h ni q u e s n e ed e d f o r r i s k a s se s s m en t

A lt ho ug h n u c l e a r powex p l a n t s h a v e h a d b ee n a v a i l a b l e , t h e e n g i n e e r i n ga d v a n ta g e s o v e r f o s s i l p l a n t s i n m os t i n f o r m a t i o n n e e de d t o d ra w m e a n in g fu la r e a s o f e n v ir o nm e n ta l e f f e c t s a nd i n c o n c lu s i o ns a b ou t t h e p r o b a b i l i t y o ft h e c o s t o f e l e c t r i c i t y , t h e y h av e some a c c i d e n t s i n f u t u r e p l a n t s d i d n o tp o t e n t i a l f o r a c c i de n t s w i th l a r g e r e x i s t .p u b l i c c o ns e qu e nc e s t h an f o s s i l - f u e l e d

- p l a n t s . W hile t h e s a f e t y o f n u c l e a rp l a n t s h a s b ee n much d i s c u s s e d i n F o r t h e s e r e a s o n s , t h e 1 95 7 e f f o r tn u c l e a r c i r c l e s f o r more t ha n t we nt y d e vo te d l i t t l e a t t e n t i o n t o t h e p r o b a -y e a r s , it has o n l y r e c e n t l y a t t r a c t e d b i l i t y o f o c cu rr en ce o f a c c i d en t s . I nw i d e r i n t e r e s t . Much c o n f us i o n e x i s t s t h e p a s t 1 0 y e a r s t h e d ev el op m en t o fi n t h i s a r e a p r i n c i p a l l y b ec au se t h e r e l i a b i l i t y t e ch n iq u es h a s p r og r es s e dp u bl i sh e d r e s u l t s o f e a r l y s t u d i e s 1 h av e c o ns i de r ab l y. F u r t h e r , a s a r e s u l t o fb e en w i d e l y m i s u n d e rs t o o d a n d b e c a u s e n o t h e i n c r e a s e d u s e o f c o mm e rc ia l n u c l e a rr e c e n t a s se ss m en t o f r e a c t o r r i s k s h a s power p l a n t s i n t h e l a s t d ec ad e, a w e l l-b ee n m ade. The p r i n c i p a l p u r p o s e o f d e v e l o pe d a p p r o ac h t o t h e s a f e t y d e s i g n

t h i s s t u dyi s

t o a s s e s s t h e r i s k s t o t h e o f w at er -c oo le d r e a c t o r s a nd s p e c i f i cp u b l i c f ro m p o t e n t i a l a c c i d e n t s i n n u- e n g i n e e r i n g d e s i g n s n e e de d t o i mp le m en tc l e a r pow er p l a n t s o f t h e t y p e b e i n g a q u a n t i t a t i v e a pp ro a ch t o r i s kb u i l t i n t h e U n it ed S t a t e s to da y. It i s a s s e s s m e n t n o w e x i s t s .i n t en d e d t h a t t h e p r e s e n t s t u d y w i l l

p ro du ce a m ore r e a l i s t i c a s s es s m e nt o ft h e s e r i s k s t h a n h a s b ee n p r o v id e d i n

1.2 OBJECTIVES OF THE REACTORSAFETY

e a r l i e r work; it may a l s o h e l p t o d i s p e l STUDY

ome o f t h e e x i s t i n g c o nf u s i on .

A t t h e s t a r t o f t h e R e ac to r S a f e t y Stud y

I t i s i m p o r t a n t t o u n d e r st a n d t h a t t h e i n t h e summer o f 1 97 2, t h e r e was c o n si d -e a r l i e r s t u d i e s o f n u c l e a r p ower p l a n t e r a b l e u n c e r t a i n t y a bo ut t h e a p p l i c a b i l -

a c c i d e n t s w ere p e r fo rm e d w i t h o b j e c t i v e s i t y o f r e l i a b i l i t y t e ch ni qu es t o q u a nt i -

o t h e r t ha n r e a l i s t i c r i s k a ss es sm en t i n t a t i v e r i s k a s s es sm e nt a nd ab ou t t h emind. The A E C ' s m aj or e a r l y s t u dy , a b i l i t y o f t h e s e t e ch n iq u es t o a c hi ev ep u b l i s h e d i n 1 9 57 , was pe rf or m ed b y c r e d i b l e e s t i m a t e s o f t h e o c c u r re n c e o f

B ro ok haven N a t io n a l L ab o r a to ry (BNL) an d ev en t s o f lo w p r o b ab i l i t y . E x p er i en cewas e n t i t l e d " T h e o re t i c al P o s s i b i l i t i e s h ad i n d i c a t e d t h a t a p p l i c a t i o n o f t h e s ea nd C on se qu en ce s o f M ajor A c c i d e nt s i n t e c h n i q u e s g e n e r a l l y l e d t o e s t i m a t e s o fLarge Nuclear Power P l an ts ." I t s f a i l u r e o f e n gi n e e r ed s y st e m s t h a t w e reo b j e c t i v e was t o p r ov i de a n e s t i m a t e o f s o s m a l l a s t o c o n t r a d i c t commont h e u p p er l i m i t t o t h e c o ns e qu e nc e s t h a t e x p e r i e n c e . Much o f t h e u n c e r t a i n t ym ig ht be i n v ol v e d i n s u c h a c c i d e n t s i n t h a t e x i s t e d i s e x h i bi t e d i n t h eo r d e r t o h e l p t h e C ongre ss e n s m e t h a t s t a te m e n t o f o b j e c t i v e s g iv en t o t h el e g i s l a t i o n b e i n g c o n s i d e r e d t o p r o v id e I l e a c to r S a f e t y S t ud y by t h e A tom ic

g ov er nm en t i n d e m n i f i c a t i o n o f t h e p u b l i c Energy Commission on August 4 , 1972:

would be adequate . I t i s o f i n t e r e s tt h a t , a t t h e tim e o f t h e BNL st ud y, on ly "The p r i n c i p a l o b j e c t i v e o f t h e s t u d y i sa fe w v e r y s m a l l m i l i t a r y pow er p l a n t s t o t r y t o r e a c h some m e a n in g fu l c o nc l u-e x i s t e d a n d n o co m m er c ia l n u c l e a r p ow er

s i o n s a bo ut t h e r i s k s o f n u c l ea rp l a n t s w ere i n o p e r a t i o n , a l t h o u g h some a c c i d e n t s u s i n g c u r r e n t t e ch n ol o gy . I t

w e re b e i n g d e s i g n e d a n d c o n s t r u c t e d .i s r e c o g ni z e d , h ow ev er , t h a t t h e p r e s e n t

F u r t h er m o r e , t e c h n i q u e s f o r p r e d i c t i n g s t a t e o f k now le dg e p r o b a bl y w i l l n o tt h e l i k e l i h o o d o f f a i l u r e o f e n g i n e e re d p e r m i t a co mp le te a n a l y s i s o f low-

p r o b a b i l i t y a c c i d e n t s i n n u c le a r p l a n t sw i t h t h e p r e c i s i o n t h a t w ould be d e s i r a -b l e . W here t h i s i s t h e c a s e , t h e s t u d yw i l l c o n s id e r t h e u n c e r t a i n t y i n p r e s e n tk n ow led g e an d th e co n seq u en t r an g e i n

'WASH 1250, Chapter 6 , su mm arize d some t h e p r e d i c t i o n s , a s w e l l a s d e l i n e a t i n go f t h i s e a r l y work. o u t s t a n d i n g p r ob l em s . I n t h i s w ay , a n y

u n c e r t a i n t i e s i n t h e r e s u l t s o f t h i ss t u d y c a n b e p l a c e d i n p e r s p e c t i v e .Thus, a l th o ug h t h e r e s u l t s o f t h i s s t u d yo f n e c e s s i t y w i l l b e i m p r e c i s e i n somea s p e c t s , t h e s t u d y ne v e r t h e l e s s w i l l

p ro v i de a n i m po rt an t f i r s t s t e p i n t h ed ev el op m en t o f q u a n t i t a t i v e r i s k a n a ly -s i s methods."

A s c o n f id e n c e w i t h i n t h e s t u d y g ro up

grew i n t h e a b i l i t y t o a c hi ev e a mean-i n g f u l r i s k a s s es s m e nt , t h e R e a c to rS a f e t y S t u d y a d d ed t h e f o l l o w i n g m ores p e c i f i c o b j e c t i v e s u nd er i t s o r i g i n a l ,b ro a dl y s t a t e d c h a r t e r :

a . P e rf or m a q u a n t i t a t i v e a s se s s m e n t o ft h e r i s k t o t h e p u b l i c from r e a c t o ra c c i d e n t s . T h i s r e q u i r e s a n a l y s e sd i r e c t e d t ow a rd d e t e r m i n i n g b o t h t h ep r o b a b i l i t i e s a nd t h e c o ns e qu en c eso f s u ch a c c i d e n t s .

b . P e rf or m a m ore r e a l i s t i c a s s e s s m e n ta s o pp os ed t o t h e " c o n s er v a t iv e l y -o r i e n t e d " s a f e t y a pp ro ac h t a ke n i n

p r ev i ou s s t u d i e s o f t h i s t y pe andt h e l i c e n s i n g p r oc e s s f o r n u c l e a rp o w e r p l a n t s .

c . D ev e lo p th e m eth o d o l o g ica l ap-p r o a c he s n e ed e d t o pe r fo r m t h e s e

a s s e s s m e n t s a n d g a i n an u n d e r s t a n d -i n g o f t h e i r l i m i t a t i o n s .

d . I d e n t i f y a r e a s i n w hic h f u t u r e

s a f e t y r e s e a rc h m igh t b e f r u i t f u l l yd i r e c t e d .

e . P r o v i d e a n i n d e p e nd e n t c h e ck o f t h ee f f e c t i v e n e s s o f t h e r e a c t o r s a f e t yp r a c t i c e s o f i n d u s t r y an d t h e

government.

1.3 ORGANIZATION O F TH E REACTOR

SAFETY STUDY

T he s t u d y w as o r g a n i z e d t o b e i n de p e n-d e n t o f t h e AEC's o p e r a t i n g a nd

r e g u l a t o r y o r g a n i z a t i o n s . P r o f e s s o rNorman C. Rasmussen o f MIT, a s Dir ec to ro f t h e R e a c to r S a f e t y S t ud y , r e p o r t e d t oth e Commission . Whi le funds and suc ho t h e r a s s i s t a n c e a s w e re n e ed e d we rep ro v id e d b y th e AEC, t h e s tu d y o p er a t edu nd er t h e g e n e r a l c h a r t e r p r ov i de d b yt h e C om m is sio n, b u t r e c e i v e d n o o t h e rd i r e c t i o n f ro m i t . l

To a s s i s t D r . Rasmussen i n t he t e c h n i c a lmanagement o f t h e s tu dy , t h e AEC

' 'This same indep enden ce was pr es er ve d byt h e U . S . Nuclear Regu lato ry Commissionwhen it a ss um e d s p o n s o r s h i p o f t h es t u d y o n J a n u a r y 1 9 , 1 97 5.

a s s i gn e d S a u l L ev in e a s P r o j e c t S t a f fD i r e c t o r . I n a d d i t i o n , one p a r t - t i m ea nd s e ve n f u l l - t i m e p a r t i c i p a n t s w er eAEC emp loyee s. One p a r t i c i p a n t was fromt h e o p e r a t i on a l s i d e o f t h e AEC t oa s s i s t i n m a t t e r s i n v ol v i ng d es ig n andt h e o t h e r s , o n l o a n f r o m t h e AEC'sr e g u la t o ry s t a f f , w ere t e c h n i c a l s a f e t ys p e c i a l i s t s w i t h d e t a i l e d know ledge o fr e a c t o r p l a n t s . A d d it i on a l p a r t i c i p a n t s

w er e f u r n i s h e d by c o n t r a c t o r s a ndn a t io n a l l a bo r a to r i e s t o f u l f i l l t h es p e c i a l i z e d t e c h n i c a l n ee ds o f t h es t u d y . Some o f t h e o r g a n i z a t i o n s a n dt h e i r f i e l d o f e x p e r t i s e w ere:

a . B o e in g C ompany -F au lt t r e e an a l y s i s .

b. Aer oje t Nuclear C o w an y -D ata co l l ec -t i o n , f a u l t t r e e a nd e v e nt t r e ea n a l y s i s .

c. Science Applic at ions , 1nc.-Dataa n a l y s i s , q u a n t i f i c a t io n of f a u l tt r e e s a nd e v e n t t r e e s .

d . Lawrence Livermore L abo rato ry-F au l tt r e e a n a l y s i s .

e. Sandia Laboratories-Data a na ly s is ,f a u l t t r e e an a l y s i s and con sequ en cemodeling.

f . Oak Ridge Nat iona l Laboratory-S ys te m s e n g i n e e r i n g a n a l y s i s .

g. Teknekron-Technical e di ti ng .

h. Hanford Engine eri ng DevelopmentLaboratory-Consequence modeling.

T he w ork by th e abo v e o rg an iza t io n s w as

p er fo rm e d a l m os t e n t i r e l y a tAEC

Head-q u a r t e r s u n de r t h e d i r e c t i o n o f D r .

Rasmussen and M r . Levine.

I n a d d i t i o n , work w as c o n t r a c t e d t oo t h e r o r g a n i z a t i o n s n o t l o c a t e d a tHeadquarters. However, it w a s d i r e c t e di n c o n s id e r a b le d e t a i l by t h e R e ac to rS a f e t y S tu dy . I n c l u d e d w e r e :

a . B a t t e l l e C olumbu s L ab o ra to ry -R a d i o a c t i v i t y r e l e a s e a nd t r a n s p o r t ;a n a l y s i s o f m ol te n f u e li n t e r a c t i o n s .

b. Bat te l l e Pa c i f i c Northwest Labora-

t o r y - R a d i o a c t i v i ty r e l e a s e an dt r a n s p o r t .

c . Oak Ridge Na t io na l Labor ato ry-R a d i o a c t i v i t y r e l e a s e a nd t r a n s p o r t ;s a f e t y d e si g n r a t i o n a l e .

d. Aer oje t Nuclear Company-Radioactivi-t y r e l e a s e a nd t r a n s p o r t .

Reactor Safety Study

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