S t a b i l i a e n t o d i ISPIiA EURA'I'O'i . . 15.5 ,75

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. . . RAPi'?!?R D I LAVOW

. . E.X?ERIil3N'l'AL DGTEXXIi\lAi'I3N OF INTEGRAL C A T U R E

. . CROSS SECTI22NS OF STRUCTURAL ilATERTAbS I N FAST . .

S?EC+RA.. OGRESS R E ; ? ? R T , T9 A P R I L 1 5 t h 1 975

PREFACE

This r e p o r t . was o i r i t t en . on r e q u e s t of t h e ~ d v i s o r ~ C o r n i t t e e on ProgranTe .:kna.ge.nent (cCMGP) f o r t h e I n f o r q a t i o n Anal.,rsis Se rv i ces an.d i s a t r m s c r i . ~ t i o n of t h e t a l k g i v e n a t t h e CC'G:? meeting hg ld st CCE I s p r a on ' larch 17-1 9, 1975

Onlv work done a f t e r ' t h e CC%? mketing i n 9c tobe r 1971 i s m e s e n t e d wi th t h e e w e p t i o n o f sollze p o i n t s , e s s e n t i a l t o t h e u n d e r s t m d i n g of t h e given r e s u l t s , which ; . r e r e c a l l e d i n t h e t e x t . ,Thus i t i s assumed t h a t t h e i n f o r a s t i o n ~ r e v i o u s l v r e l eaked i n w r i t t e i for;-, ( annua l Progress r e p o r t s , e t c . ) i s knoum . Resu l r s s h o w n a r e i n a p r e l i ~ i n a r v form, n o t v e t r e v i s e d , and p o s s i b l v s u b i e c t t o change; t hey a r e updated t o t h e s t a t u s of t h e work a t iniddle Apr i l 1975.

The i s s u e of t h e r e o o r t was soyewhat dela-red t o i n c l u d e r e s u l t s n o t v e t a v a i l a b l e a t t h e t iw of t h e t a l k , i.e, c f d c a p t u r e fiss fission" .neasurments ( s e c t i o n 5 ) .

. .

I t i s re.minded t h a t t h i s urork i s done wi th in a c o l l a b o r a t i o n agreeqent avong CCF. I s p r a , A G I ? Nucleare and CNEN.

1A. P r i n c i p l e of t h e e?per iment Goal of t h e e:periaent i s t h e de te rmina t ion of t h e neu t ron c a p t u r e c r o s s s e c t i o n of e l eTen t s used a s s t r u c t u r a l ; n a t e r i a l s i n f a s t r e a c t o r s ( a s Fe, C r , x i ) , averaged over neu t ron energ.r s p e c t r a -which n a x i n i z e t h i s ci i3ture i n t h e energ17 ra-nge (1-100 K ~ v ) where t h e p r e s e n t u n c e r t a i n t i e s i n t h e qeasured d i f f e r e n t i a l c r o s s s e c t i o n s a r e h i g h e r .

The wmsurenents a r e ln%de b y t h e "void-nul l r e a c t i v i t v i ' V.F thod (PCTK method), i n . redia c o n s i s t i n q of :-iicros?heres of F i s s i l e - w t e r i ? l (u? wi tn 93X U235 en r i chven t ) and q r a p h i t e co-;.tzininq t h e moun t o? boron r e q u i r e d t o reduce k-inf of t h e rnedj.u~? t o mi t v .

The "void-nul l re ; l c t iv i t r i " w t h o ? i s based on t h e elem?nt;.rv p r i n c i p l e t h a t r e p l x e ~ e n t by vo id , of a p o r t i o n of an i - n f i n i t e hornoc;eneous wdiu:? v i t h ~ u l t i a 1 i c i ; t i o n f a c t o r equa l t o .~.r,i t v , does n o t 7iodify i t s r e ? , c t i v i t y . For n r a c t i c a l reasons the, co:nposit ion of .the sample, which vhen r ep l aced by vo id c;ives

A i? n u l l - r e a c t i v i t y v r i r i a t i on , i s deterxif led bv l i n e a r i n t c r ?o - l a t i o n of r e a c t i v i t v s i g n ? l s ob ta ined hv s a m l e s v i t h v ; n v i n ~ poison c o n t e n t ,

In rea.l.it:r : n u l t i ~ l v i n g inedi? m e f i n i t e , a ? d even a t t h e i r - . c e n t p r sove r e s i d u a l mismatch of t h e l o c a l s o e c t r u q with r r s p e c t t o t h e i n f i n i t e medium s p e c t r u v .?z.v occur ; a l s o , nPutron leaka(7e 3a.v ' i n t r o d u c e a cu rva tu re i n t h e f l n r d i s t r i b u t i o n w t e n d i n ? t o t h e nedium c e n t e r . Thus, t h e m e d i u ~ v i t h i ' n u l l - r e a c t i v i t v con?os i t i onu has a k-inf = l / ( l - E ) , G b c i n s t h e c o r r e c t i o n f :r non a s - m 7 t o t i c spec t ru? c o n d i t i o n s -7nd lczlcage, u s u a l l y c a l c u l a t e d by a f i r s t o rde r p e r t u r b a t i o n f,or.n?.li.svi.

'The e v p e r i ~ c n t i s based on ?I s e t of two indeoendent q~void- .nul l r e a c t i v i t v " neasuremeritc ; t h e f i r s t 716th ;I test--nedi.cn c o n t a i n i n g . on lv f i s s i l e m d moderator p m t i c l e s ( r e f ernncc mediu*) , t h e second wi th ? t es t -mediu :~ which a l s o i n c l u d e s homogeneousl\r d i spe r sed :nicrosohcres of t h e m i t e r i a l under i nvcs t . i ga t ion .

The resolvin .7 equa t ions a rp shown uri-th c-ondensed. not;.ti.on i n Table 1 ; equa t ion 1 r e f c r s t o t h e reference t e s t -med im

. eaua t ion 2 r e f e r s t o t h e a t e s t - m e d i u ~ wi th added Fe p .7r t i c les .

1ia.vinfldeternined t h e n u l l - r e a c t i v i t ~ r c o m o s i t i o n and c;ll.cu- l a t c s t h e c o r r e c t i o n f a c t o r E, one i n f e r s k-inf = I,(?.-.::) p e r t a i n i n g t o t h e i n f i n i t e ilediu? !!ria t h a t c o ? ~ o s i t : i o n , The neu t ron b?. lmce shown ?t t h e r i g h t s i d e of eqs .1 , 2 i s thus , f o r t h e as:mptotic ( i n f i n i t e vediu?) s2ectrum c o n d i t i o n s .

P e The s o l u t i o n of eqs.1 and 2 f o r R = CW IF5 i s shown .n cq.3. ~Fe ,&5 i s then t h e r e s u l t of t h e e r a e r i v e n t and i s t h e v?, lur p e r t a i n i n g t o t h e i n f i n i t e mediuv. s a ~ c t r u m .

? a r t of t h e q u ~ n t i t i e s ~ a t t h c r i g h t s i d e of eq.3 a r c t i l T c c t l . ~ :-fieasured , namely . . .. . . . . ... . .

rJ g ' 5 8 - 3 5. . a sj n u l l r e a c t i v i t v c o m ~ o s i t i o n s , _R=C /F , Fi = C . ' r " , F :'I'

The u r a n i u ~ of t h e a c t u a l t c s t 3edi .m be ing h i g h l v enr iched (93% u235) , -the :Last two q u a n t i t i e s can a l s o be c a l c u l a t e d , wi thout a f f e c t i n g t h e u n c e r t z i n t y of t h e e x p e r i ~ e n t a l va lue o-f RFe

Silice t h e messwed o u m t i t i e s a r e detern.ined i n t h e l o c a l spectrum ( i . e . thc spec t ruq a t t h e c e n t e r of t h e t e s t vedium), t hey v u s t be conver ted i n t o t h e corresponding a s m p t o t i c sFectrum v a l u e s , b y c a l c u l a t e d convers ion f a c t o r s of t h e kind , a '?'n~"local , e t c .

--5 8 . 5 C ' The o t h e r q u a n t i t i e s , ntine1.i - v , 7? ,ig , 1: a r e t heo re t i c ' l l v c a l c u l a t e d f o r t h e . i n f i n i t e rnediuln s p e c t r m .

I t f o l l o v ~ s t h a t an accu ra t c t h e o r e t i c a l c a l c u l a t i o n i s e s s e n t i a l , bo th f o r t h e des ign and t h e i n t e r p r e t a t i o n of t h i s kind of experirqent .

done a t CCR IsDrz., u s ing E N D F / R ? , 2 d a t a f i l e s and t h e 27-group: I-dimension, t r a n s p o r t code ANISN ( f o r i n s t a n c e , t h i s c a l c u l a t i o n le?d t o t h e cho ice of t h e a t o v i c r a t i o C/~235 = 153 f o r t h e r e f e r e n c e t e s t w d i u n , a s t h a t g i v i n g t h e b e s t s p e c t r a l c o n d i t i o n s ) ,

The i n t e r p r e t a t i o n of t h e exper iment i s a t p r e s m t c a r r i e d o u t by CNEN, Centro d i Calcolo d i Bologna; t h e d a t a and codes

0 s o f a r used a r e :

d a t a f i l e c r o s s s e c t i o n averaging code

c a l c u l a t i o n code

EKDF/E.? GAV2 (103 groups) , ANISN ( t r a n s n o r t , I -d , 27 groups)

2 UX-B ..K (2030 groups) A L C I ( d i f f u s i o n , 2.-d, I 0 groups) . .

Seve ra l combinations were t e s t ed . ( e g. ENDF.3-GA?I 2 - AELTISN V S , G N D F / B ~ - : ; Ic~ -- AN1SN) r each ing t h e cdnc lus ion t o s e l e c t

2 t h e !IC group-cross s e c t i o n s gene ra t ion code f o r t h e d e f i n i t i v e i n t e r p r e t a t i o n of t h e e7per iment : however most c a l c u l a t i o n s were o r i g i n a l l y m d e us ing t h e G.41 2 code, 2nd t h e i r r e s u l t s are. o f t e n s h o w f o r comparison v4.th neasured d a t a o re sen ted i n t h i s r e p o r t .

A s q u a n t i t a t i v e l ? ! sho~inn i n a d e t a i l e d e r r o r a n a l v s i s ? resen ted p rev ious ly , t h e two b a s i c condi t i o n s t o reduce t h e e:merirncn:al e r r o r ( r e f . eq., 3 ) a r e a ) c lo senes s of l o c a l soectrum t o t h e c o r r e s ~ o n d i n g asvnpt .ot ic

spec t run ; b ) c lo senes s of t h e a s v ~ p t o t i c s p e c t r a of t h e r e f e r e n c e t c s t

1

mediu~. and t h e t e s t medim con ta in ing t h e s t r u c t m a l . m a t e r i a l ( ~ e , i n eq .3 ) .

'To which e ~ t e n t t h e f i rs t cond i t i on i s ;net f o r t h e " r e f e rence" . 3 mediun i s evidenced i n Table 2 , shoving r e s u l t s of an E?JD:;'/i;3-?C--

A N I S N c a l c u l a t i o n made f o r t h e i n f i n i t e n e d i u ~ and t h c c m t y . a l zone of t h e same xediun i n t h e P , B ~ / ~ " v r=_ac to r . A s s p e c t r a l i n d e r e s a r e taken t h e sane f i s s i o n s (~u .240 , Pu239, U233, ~ 1 2 3 5 ) measured bv q i n i a t u r i z e d chambers ( s e e s e c t i o n ,I-) , a s nc:~!. a s q u a n t i t i e s r e l e v m t t o t h e neu t ron ba-lance (ca/p5, CY5) ,

0

I n o r d e r t o ~ e e t t h e second c o n d i t i o n , t h e . a s v ~ p t o t i c spac:t-.um of t h e t e s t mediu-n con ta in ing t h e s t r u c t u r a l m . t c r i a l (l7e :in t h e a c t u a l c a s e ) was:-'matched t o t h a t of t h e " re fe rence : ' nediuq c h a r a c t e r i z e d by the: atomic r a t i o C,/U'235 = .-. 159? bv varyinn i t s ~ 1 ~ 2 3 5 va lue keeping c o n s t a n t t h e F e / C va luc . .

(=3.:t, s o a s t o have a s i g n i f i c a n t f r a c t i o n of t o t 5 1 cz.ptvrc by Pe, which w a s r e q u i r e d bv t h e above nent ioned e r r o r m a l i r s i s ) . A s na t ch ing p a r m e t e r s were taken t h e s m e q u a n t i t i e s s p e c i f - e d above.

I n . Table 3 a r c presented t h e r e s u l t s r o f a CARNAVAL 3 (c;::A, ~ r a n c e ) c a l c u l a t i o n (Fe ic=3 .5) which shoui t h a t t h e b e s t n7:.;?tc:h i s obta ined when C/~235=123. A s i m i l a r c a l c ~ ~ l a t i o n car r i~r r ! o u t by CNEN f o r ? ~ / C = O , . ; , gave 2 s l i g h t l y lower ~,/U?35 v a ? w (1 l o ) , which was chosen f o r t h e t e s t samples . actual1:r i>.s::d,

EXPERIHENTAL FACILIT"

A h o r i z o n t a l c ros s - sec t ion of t h e e x p e r i w n t a l f a c i l i t y i n . t h e RB2/TV r e a c t o r i s shourn i n Fiu .1 . 'The d iameters o f thc 60 c a l l e d f a s t zone ( loaded wi th t h e r e f e r e n c e medium) x d b u f f e r zone (lo?d.ed v i th arrairs of iVTR f u e l p l a t e s wi th 9?! enr iched U and vedged g r a ~ h i t e s l a b s , w i th ~/U235=150) arc. 100 and 600 ma, r e s p c c t i v e l v .

A v c r t i c a l c ros s - sec t ion i s shoum i n F ig ,2 : t h e h e i g h t s of t h e f a s t and b u f f e r zonc a r e 733 mm and 950 mm, ressectiva:.ir. Also s h o v ~ i s t h e c e n t r a l (53--mm?--dia) o s c i l l a t e d e1eTen-i- u e d t o r e p l a c e t h e t e s t sample (130--m?-high) bv vo id ,

The " r e fe rence" medium c o n s i s t s of a nivture.0f.l.-7i'n-diz~; pyrocarbcln coated; f i s s i l e p a r t i c l e s ( U O enr ichcd t o 93::

2 ~ 2 3 5 ) and g r a p h i t e p a r t i c l e s wi th B con ten t r e q u i r e d t o poison .. . t h e k- inf of t h e ?zediun t o uni tv; t h e tes t med?.m c o n t ? i n s a l s o 3.75-mis-dia Pe ~ a r t i c l e s .

Boron i s conta ined on lv i n ? a r t of t h e g r a p h i t e p z r t i c l e s , t o allo\v a f i n e 3djustement of t h e R con ten t of t h e mediu-n. I n o r d e r t o be a b l e t o r c c o w r t h e boron loaded from t h e pure gra-phi te p a r t i c l e s f o r f u r t h e r u s e , t h e two kinds of

: . p a r t i c l e s were :mnufirctured wi th di'ferent mew d e n s i t i e s . ( I -32 vs . 1 .57) and narrow dens i t v d i s t r i b u t i o n curves ( s e f Fig .3) s o t h a t an e f f e c t i v e s e p a r a t i o n (n ,99x) bias a t t a i n s b l e bu heavv l i a u i d s rn i r tu res (dibromoethane ilid a l c o h o l ) . The main c h a r w t e r i s t i c s of t h e p a r t i c l e s ( f i s s i l e , g r a p h i t e , boron loaded g r a p h i t e ) m e l i s t e d i n t h e Apaendir.

The li~2/T~ r e a c t o r v i t h t h e above exper imental f a c i l i t v reached i t s f i r s t c r i t i c a l i t 7 1 on Sept .3 rd , 197.4, A sunmar.r of t h e s e t of t e s t s performed t o meet t h e u s u a l s a f e t y requi rements , and. of t h e resu-lt-s o b t a i n e d (2s p re sen ted i n - t h e 1'374. P rog res s Report ) i s given i n t h e ~ p p e n d i : ~ .

3A. ?;echanical o s c i l l h t o r : neu t ron d e t e c t i o n e q u i ~ m e n t and - .

d?.ta a n a l v s i s method .- The p i l e o s c i l l a t o r ( ~ i g . 4 ) i s a wheel-ca.n tvpe engine , t r a n s m i t t i n g l v i 2 a c r o s s head running on a r a i l , a v e r t i c a l n o t i o n t o t h e o s c i l l a t e d e i c n e n t . 3ving t o t h e long r e s t t : i w r e l a t i v e t o t h e t r a n s i t t iw, t h e o s c i l l a t i o n a~pro?.i!v.ates a square uiave func t ion . Yain f e a t u r e s : run Os200 cm, t r a n s i t time l i n sec / run , ?ia: . induced a c c e l e r a t i o n 2 0 - 3 g,

Thc o s c i l l a t e d ele,nent (63-nm-di a, 4.~30-mm-long) c o n s ~ s t s of a t r a i n of t ube - segments, c o n t ~ i n i n g s p a r t i l , l e mi'.ture w i th t h e saxe composi-t ion.of t h e " r e f e rence" medium, and t v o 130--mn-high s e ~ ~ p l ~ ~ s , space:! by 1500 m;n (liiqh and lour sample)

. .

The i n s t r u n e n t a t i o n f o r t h e a i l e d e n s i t y modu1;ition d e t e c t i o n c o n s i s t s of a gamma-conpensated i o n i z 6 t i o n c h m b e r (p laced i n s i d e t h e g r a p h i t e r e f l e c t o r ) , wi th c d i b r a t e d zero supvres s ion , convers ion t o f requencv, double s c a l e r u n i t ( k l t c r n a t e c o u n t i n n ) , t a p e puncher.

Thc d a t a a n a l v s i s y i e l d s t h e r a t i o of t h e f i r s t h?.rmonic a-flplitude of t h ~ Four i e r s e r i e s e v ~ a n s i o n of t h e s i g n a l devided bv t h e vean power l e v e l (A//:?, i n s h o r t n o t a t i o n ) ,

?relimin;lrv t e s t s -- Pre l iminarv t e s t s w r e performed t o chcck t h c , i n s t r u n f n t a t i o n and s e l e c t t h e b e s t o s c i l l a t i o n cond i t i ons . The v a r i e d p r i r a ~ e t e r s were o s c i l l a t i o n per iod (60, 120 and 2'7.0 s ~ c ) r e a c t o r power ( 1 , 1 ) and 39 1,') s i n g l e rea.ding'- t ime ( 3 . 2 , 2'4, 1 s ~ c ) , e t c . The c o n d i t i o n s chosen, viere . pe r i cd 59 s c c , p o w r 1 I.';rcading time 1 s e e ,

c a r e f u l t e s t s .were a l s o c a r r i e d ou t t o v e r i f v some esse : i t i ? . l c o n d i t i o n s as :

&) s t a b i l i t - i of t h e p a r t i c l e s .n ivture honogenei tv t o v ib r? - t i ons induced du r ing o s c i l l a t i o n ;

b ) r e p r o d u c i b i l i t y of i. omogencitv and composit ion of mi>:tx-e i n t e s t sample;

c ) s e n s i t i v i t v t o B and U235.

Condi t ions a ) and b ) were v e r i f i e d v i t h i n t h f euper i .venta l e r r o r ( a s I 5.') A/? = 6 ~ 1 0 - 5 ; t h e mcasured s c n s i t i v i t i e ( c ) vicre 0.01 g r B and 0 , l g r U235, r e s p e c t i v e l y .

Nul l -- r e ? c t i v i t v measurements -- ( r e f e r e n c e nedium) Four t e s t samDles, wi th varv ing B con ten t around t h e t h ( ~ x ~ t i - c a l va lue f o r k-inf = 1 , were confcc t ioncd wi th c o m ~ o s i - t i o n s a s shown i n 'i'a\le 4. Thc n a r t i c l e 7 i i r t u re s were c h r i r x - t c r i z c d by t h e i r va.lTae oP B / ~ 2 3 5 ( i n a toms) , Ont n o t e s a smal l (1r:ss than 1 % ) v a r i a t i o n of t h e t o t a l urcight of p a r t i c l e s conta ined i n t h e s?mpl@s, due .to- ? . . v a r i a t i o n of t h c par-t:ic;les vo id c o e f f i c i e n t ( t h e o r ~ t i c a l l v 3.17 f o r Equal d i a n e t ~ . r sphe re s , measured m a n va lue : 0.37) .

The de te rmina t ion of t h e r e a c t i v i t v ( b e t t e r s a i d A/? v;?l.u::) of a tcs t -sample r e s u l t e d from t h e ~ c r f o r n m c e of two ;nensurements, v i i t h t h e f o l l o v i n g o s c i l l a t e d . e l c n e n t conoosi t i o n : 1 ) o s c i l l a t c d elernent wi th t e s t - s , a m ~ l e h igh , voided-sam1.c low 2 ? I voided I ' I 1

Sub t r ac t ion of t h e r e s u l t s (=A/?) of t h e t vo measurewnts gave A/P ( t e s t - s m p l e ) -A/P (voided. s m p l e ) , i . c , thc. r c a c t i - v i t y due t o t h e re!?lacemcnt "test-aediam v s . vo id" , having e l i n i n a t e d s ~ u r i o u s s i g n a l s ( a s A / P ) from non homogene:i.t:i.c:!; of t h e o s c i l l a t e d column, smpl i : c o n t a i n e r s , deirived nc:.l.trons (most p m t o f ) , e t c ;

Th:: r e s u l t s of thc; measureinents mii ' shoon i n Fig .5 . Tlic va lues p re scn tcd a r e from mca~surements ?t 1 w porit.r ;.I??

o s c i l l a . t i o n p e r i o d s of 59, 123 a.nd 240",

Tht: composit ion of t h c f o u r samples o s c i l l a t e d i s s h o w in 'i 'zblc 5 . One ~ a \ r n o t e t h a t ; due t o i:xproveil p r i . c t i c e , thc sprefid i n t h e vo id c o e f f i c i c n t ( o r t o t a l w i g h t of t h e s;?-n?le) o s reduccd t o 9.2!< nay.

~ h c r e s u l t s of t h e lneasuremmts, ca . r r ied ou t a t 1 r ' p o w r and 69" o s c i l l a t i o n p e r i o d , a r e p re sen ted i n Fig.6. Agilin the a.lignment of t h e w a s u r e d v a l u e s A/:? on t h e s t r s i g h t l i n e r c s l i l t i n g f r o v t h e f i t i s good. Thf. obse rv? .~ ion t h a t t h e s l o p e of t h e l i n e i s c l o s e t o t h a t of t h e correspon- d ing l i n e (50" p c r i o d ) through t h e d a t a , .7,.. f o r t h e ureferc..nc::"

- / . ' 3) incdiuli, could si?.ggist t h a t ( ~ 7 : ~ ~ <. D: as c l o s e l v t b c si . ;c : v z lue i n t h e two CASCS,

3E. Dettrnin,s . t ion of -. t h e o s c i l l a t e d sanples composit ion The funda.menta1 importance of t h e accurate: knowledge of thr . medium conpos i t i on , r "~r t h e c o r r c c t i n t e r p r e t a t i o n of thj.3 kind of rncasurenen-ts, i s ?n r s t ~ b l i s h e d f a c t , T ~ E o s c i l l a t e d s a m l e s a r c c o n f ~ c t i o n c d s t a r t i n g from lio~orjt-neous l o t s of t h e ? ? r t i c l c s q i r t u rc : c o m o n e n t ( f i r ; r : i . l : , pure gr i lyhi tc , b o r m l o a d ~ d g r a p h i t e , i r o n ) . 'Th:: a n a l j ~ s e s ~ c a r r i e d o u t on s t a . t i s t i c r . 1 s?m?lcs taken C r o n t k i n d i v i d u a l lo;s , m e r

XATERI AS AXALYSI S ACCURACY

f i s s i l e

boron loaded +2.2:: -

-1wiqhing t h e r e c p i r i d amounts of t h e :n ix turc cornponcnts (e. 9. f i s s i l e , q r m h i t e , boron loaded g r m h i t e ) , with p r e c i s i o n +0.01 g r ; - . . .

-:nixing by an a i r - j e t dev ice t o achieve an honogeneous mix ture , accordin: . t o a r o u t i n e e s t a b l i s h e d through a previous stud7? ( s e e 1973 Progress ~ e p o r t ) ;

- f i l l i n g sanp le c o n t a i n e r , d rv ing , se:aling cover .

8v combining t h e l o t s s n a l v s i s d a t a 3nd the mi::ture coi?~onc.nts wci<lhts , t h e sanplc-s c o ~ ~ ~ o s i t i o n i s i n f e r r e d crsscntii.ll..r 1,r.i t t h c orccis i .on speci . f ied f o r t h e zbove ana1:rscs..

To improve t h e c o n f ' i d ~ n c e l e v e l of t h e samples c o a p o s i t i o n , z f t c r o s c i l l a t i o n 29r t h e nu l l - r eac t i v i t vae ' t 6 r ? ina t i on , t h e f'issilc: p a r t i c l c s con t s ined i n each s m p l e . are s t p a r a t c d by t h e heavy l i q u i d s technique (100;:; e f f i c i e n c y ) and t h e B con ten t of t h e gr ; i?hi te i s xcasured k i n g a s t a t i s t i c z l

.. . s3npl€ taken f r m t h c "PUE g r a ~ h i t e p1;rs boron loaded g r 3 . p h i t ~ " . phase.

I t i s no ted th3.t t h c p r e c i s i o n by which th:: samples c o m ~ o s i t i o n i-s t hus m a s u r e d i s we l l w i t h i n t h e l i m i t s sssuqed f o r t h e + - p r i o r i e r r o r m a l v s i s of t h e experiment ( s e e Progrcss Ecoort 1972) : e .9 . t h e B c o n t m t i s mcasuzed t o v i t h i n +0.2;;, v s . - t h e +0.5iL value assuncd f o r t h e e r r o r a a l v s i s . -

4. SE'ECTRUN I N D E X :4EASUBE.'IENTS

4A, - P r i n c i p l e of t h e me?surement A complete ma.?pinc; ( r a d i z l a ?d a r i a l ) of t h e f a s t zonc co:ntaining t h e micros:, h r e s i s performed , f o r each t e s t - medi.um composi t ion, usin. m i n i a t u r i z , ~ d f i s s i o n c h m b e r s mi.th va r ious s p w t r u T s e n s i t i v e de?osi . t s ,

The spec t run indc: i s thus :neasv.rerl do not e n t e r dirc.ct1.i i ~ t o t h e r e s o l v i n g (.quation f o r t h e experiment ( ~ f i b l e 1 , G q . 3 ) , bu t n rov idc u s e f u l i n f o r : l a t i o n -to t e s t t h ~ s p e c t r m n,?tchiny; t o t h e ?.symptotic v ~ ~ l u e , a s \vcl l a s t h e r e l i a . b i l i t v of t h e t h e o r e t i c a l c a l c u l a t i o n codes used f o r t h e i n t e r - p r c t z t i o n of the: c-.::perirr,cnt. The. spectrum s e n s i t i v e d e p o s i t s ;ire U235, iT238,. Pu239 and Pu.240; t h e d e p o s i t s t h i c k n e s s 3x6 i s o t o p i c composit ion a r e l i s t e d . i n Tzble 5 .

The f i s ~ i o n ? ~ b l e (~u2 . :0 , ~ 2 3 9 ) d e p o s i t s a r c s?ilted wi th snla l l m o u n t s of' 2 i s s i l e i s o t o p e s ( ~ ~ 2 3 ' 3 , U235), t o nor..?aliz3c t h e chamb::rs c?f ic j .cnci t -s (c. q , U238 t o ~ 2 3 5 ) b'r interc?.l-i- br?. t ion i n a thermal s ?ec t ruq . Thc r a t i o s o f t n e ~ f f c c t i v r : ( f a s t zone) c r o s s s e c t i o n s a r e then infc-rrcd from equa t ions

i<ormal izat ion of t h e Pu239 and U235 chamber e f f i c k e n c i e s

.;a, -~ ,Shc:rm?.l colunin c h ~ ~ . i ? . ~ . c t e r i z a t i o n Thi thermal spcctrum i n tlic t h e r m l c o l m n coil~1E.d t o thi: 2Tt2 re:?.ctor vras nc.?sured bv a s t andz rd f o i l a c t i v a t i o n at:iAod. Anc%u.rerncnt 01 Pu233, I n m d Cu - i c t i va t ions on t n t thi~i-~na!. co1.v.mn ~ r i s , shouicd r ? ? o n c n t . a l v a r i ; i t i o n s . wi th pra~ctirr7L!v j.dcntici.1 e r p o n c - t s f o r t h c t h r c e d i f f ~ r e n t s p e c t r u x .'

s e n s i t i v e detectors ( F i g . 7 ) , evidencing t h z t t h e Ycstco.K parmc. tc rs a r e const,=.nt over ,an ~': ' trndcd s p 8 . c ~ in tc rv? l . .

A mr.:;isurmc?nt of thc ,T, r p-ra : i~cters a t an intcrincdiatc: p o s i t i o n i n t hc colui?,n (by q ? ~ t i v r 7 t i o n of ?u23'), I n m i '.i?3', de - t cc to r s , norlnzlj..c.ed by s i iw l t ancous i r r a d i a t i o n of t l x s m i d e t e c t o r s i n t hc tlhcrmzl vicll o i ' t t h fE.ZSJ1"'II rezcto-: s t CESNEP, X i l an ) g;ive t h e .Followin$; va!.ues

Fi?om the: VESTCOTT p m x w t c r s t ? b l c s f o r Pu239 sncl U235 on:

4 In s t rumen ta t ion --- <,'I . . ..a% f i s s i o n ch?whi:rs used h ~ v c 1 . 5 mm o u t c r d i ame te r , 1-2 ;::.,: sc ins i t ivc he.iglit, 2nd a r e intc?ra.tixl -iiith c r t c n s i o n i i i l c . i i ,

c:L?.d by s t z i n l e s s s t i : c l , t o 2. t o t a l lc?n$gth of about 2030 r-::;:.

Elcct i" ica1 insu la . t ion i s provided bTi -7 0.2-nim-thick tr.Ploi.1 t~1.b~:

Jnln - ,.iLi: chambers ?.re in t roev.c td i n thc. f a s t zone throu-k. c~ 2.2.-mw-di?~O.l--!i1ui~--.t!!1:i?lclc, ? .~i?l staj.nl::ss s t c : c l . :.',:s, a t v a r i o u s rzdip .1 ~ ? o s i t i o n s ,=s shovn i n 7ig.8. Each chamber i.s , x r z , - c t cd rto i . t s p r c s n o l i f i f r , f o r pro!?(.:: s i n n a l t r a n s x i s s i o n t o t h c inst :wmcntation rack , ~ 1 1 ~ ~?:23:*,1?lj.-

f i c r s are i n t t r c - ! i b r ? ~ t e d t o an accu.r?.cj? of +0.22. - 'J'hc f i s s i o n chanbcjrs s c a i ~ n i n g and coiln-tinq s v s t i ~ i s sko>~i ?.s a block d i ~ g r z m ic F i - . 3 .

Si.n.u.ltancou sc?,iininr! oir tk? ??st zonc bv ~ i c ~ i t cEZmb: 1-5 ::.:: perforifled throush ;i mechai ic i : dcvic::,, via. 2 :;erp'..ti:?.l 51-.:?:.v!

drivc.9 b-: S:OS':l\! s t ?pp inc Totor ( v i b r a t i o n f r e e ) , fc",:?; ,

170 Fiz , p u l s e gc?nc.r?tor, A..ial position in^: ~f thi: ck'.-'i:l,rP.'r. i.:: ?c:cur?te t o w i t h i n i - 0 , l :m, ".

The. scznning seqi imcc i s ?redetermined bv a coded a ro9 ran on punched t a y , r ead v i s 3 TELE'TVPG u i i t and f e d t o ?~ d i 3 i t s . l rro$p?;.nnin.' u i i i t , cihich supplies t h e rcquircci nu-nbcr o : ou.lscs t o t h e SLOSVN motor ( a 0.4 m axia.1 desplacement corresponds t o 1.39.. p u l s e s s u p p l i ~ d t o thc n o t o r ) ,

'The c ~ . i s s i o n sp'ecltr? of tkic U235 ?;id Pu239 c h x b c r s ?rc shovn i n 5 . g . 7 3 ; thc r e s o l u t i o n of t h e gross f i s s i o n product pc?k

i s ijood, 'The w i s s i o ~ . s ? c . c t r u n i s thc s m c f o r c h m b c ~ exsosure t o t h c i h ~ r ? s l and f z s t zone ne~l.'tron spcctr? . ,

.??D. B e s u l t s of :Y.O~U.~~~-<X~ Tvpica l r e s u l t s of n?.,:asurenents of t h c a - i a l ai?d radi2 . l d i s t r i b u t i o n s of f- i .ssions i n t h e f a s t zonc (preliminar:r nn,-,Lysis of da.t;..) ?i.e shokin i n F iq . 1 I t o 13.

/ fac. ?I ~v.easu.rcments were per forncd a.t 15 a x i s 1 l e v c i s , i , e , ovt-r

+I40 mm from t h c c o r e i?..idplane ( n o t c t h a t t h e s m p l c h c i p h t - i s 1-53 mm fro-, the; n i d p l m c : ) , 3t 30 ::! r e a c t o r pow??, c o m t i n a - time from 103 s t o 600 s. .~,,h,. . , e;weriment;.l c r ~ o r f o r rich da-ca poi-nt , i n tem- 03: 1 C ,

.. , . .. . . . . . .. . . . . . . . ,. . . . . i s t : - ~ ? i c ? , l l y l + l a !~- ' .! 0 - '.,' ' -

Fig . 1 I shovs the: :i?i?surc.d w i a ~ l d i s t r i b u t i o n s of f i s s i o n s ( ~ 2 3 5 , ~ 2 3 8 , Pu231, l u 2 ~ 0 ) , norm1izi .d t o un i t7 : ?-i: thc- c o r e :nidpl-?ne, Sccond. dc g ree curve-s (cont inuous 1i r .c) ,zrc f i t - t c d t ) t h e d ? t ? bir t h e l e a s t s q l ~ . ~ c s method,

Also shovm' a r c the? : ~ o r ' w l i z i . d c.d.rvts (do.t tc4 lire) c ? l c ~ r i ? t c d b:r the-. cha in G.&I 2 -.- ALCT. 'The ?.crccment betnreen e:ipeyi.w,ental

. - ?nd c,~. lcxl ; l ted curvcis czn 5c cons~c.c.:c:d good ?or; a 11 i s c t c , z s . Note th?.t the d i s t r j ~ b u t i o n s >.re f 3 ~ 3 t over t h e t e s t s-?!?pl,; h e j . ~ h t (~t.59 - v:n f r o n t h c ~iii--:.?.nc 1 ,

Shoiriii i n Fig . 1 :! i r e th,: neasured 2nd ca.lcul.atcd s?cctru;i: indcues d i s t r i b u t i . o n s i n f crrccl' f.roa ths d ? t a of F i g . 1 I . Ac~ain thc: c w v c s m::. f l z t and th i . zgrcemsnt b c t v c m exa : . r i .xn t m d theorv i s good,

%'hi. ne.su.red m d c ~ . l c u l ? t c d (GA? 2- ALCI:) r z d i a l distrfii.)ui:ions of f : i s s ions , norm,-lized t o u&tv on t h e c o r i . x i s , a r c s h o v i n Fig .13. 3nc n o t c s th?,t t h e curvatuwe of t h c d i s t r j -bu- t ions i s h iqhe r and th.t some d i s c r e . ..i.ncy b2tu~?e% inc-7sure:nen.i: ?iid theorv a.>vew; tovard t h e o u t r r b o u n d ~ r y of t h e f ,?.st zmc:

,.;:2,?,:;,,::~(.:.< ::.. Absolutc va lucs f o r t h e experimental indwc : s ( 6 )/.. ~ . t?:) + ...

? . as i n f e r r e d from t h e f i s s i o n chambcrs count r:?.tes ?t TI?;. f<?.st z,onc c e n t e r m d i n t h e t h e m , - l co3.u.mn (p re l i rn inxv . r c : s u i t s ) , ? r c given i n T~?blc 7 m d compared wi th va1uc.s c.;lcu- l s t c d bv t h e GAV 2 A L C I and .1c2 - AiVISN cha ins .

'Thi: incasu.rcd v,?.lucs l i c w i th in t h e range of calculate-d v;.ilj.ci: produced b.7 thc. -two c a l c u l a t i o n s c h e m s , hu t ? t t h i s s t - -. t h e comparison n u s t bc cons.di:ii.ed on1.v 3s inc1i:-3.tivc.. I_

s tudy of t h e s c n s i t : l v i t y of t h ~ considcrcc! s>cctr .m i.:ici:..- c.5,

t o neu t ron energy snectrum v a r i a t i o n s , i n t h e oresc.nt Pi-?:

zonc. c o n f i g u r a t i m , i s und~rv.r?v.

5A. -. In . s t runcnt? t ion -- m d r rpc . r iment? i techniauc: -- ,n i h c :-i:asurcd quantitv:~gllc?~turc/~23",ission" i n t h r tcis-:

s m ? l e i s d i r e c t l y c n t c r c d i n t o t h e resolving cquz t ion :;F t h e exptlr inent ('i'3.b~~ 1 , E.r.3) and i t s u n c c r t ? i n t v i s t h . ~ r?j.n scurci-. of m r o r i n t h i erpcr i .nent ( re f . 1 972 ?ro<jj?(:.ss Repor t ) .

The mc?surement i s made bv R co? t ed , rcs7.U235 c c a t c d , c l i~mbers wi th fo l lowing c h ? z ~ c t i . . r i s t i c s

2 dcposi t thickness 5 3 , m ~ / c m i s o t o p i c composi~tioii : 9Ii' 90;, r e sp . U215 9 3 . Y chambers s truct: ir?. l :n;itcri- sl : zircofiiu;z chambers o u t e r d i ? , : .+ j-;.m

s e n s i t i v e , p m t heic;h.t : 1 3 mm

Thi: c h m b e r s ?.rc ~ l x c d :?t t h c c c n t i y of ?. test s sap l~ , identical t o t h c s m p l e used f o r t h e n u l l r c a c t i v i t v dcter:ili- nzti.on, bu t providcti oiith a 5-m!n-inner d i z n e t e r , , 0.1 - m - t h i c k s t a i n l e s s tub? on i t s ?.xis, . . .

ill^ .n, , chamber i n t c g r a t c d e r t e n s i o n l i n e goes i n s i d e a 2,2.-mri?-dia, 0.1.--mm-thick t u b e , throug?' t h c a r i s of -the upper s e c t i o n of t h e c c n t r a l f u e l e l c q e n t ,

G l c c t r i c ? l i n su l> . t i on i s provided bv two t h i n t e f l o n r i n q s iit t h c ends of t h c ciizltber ( a v w from t h e sensitive zone) ?ad ?, 3,2-am-thick t e f l o n tubc cover ing t h e e t e n s i o n l i n e , Each c h m b e r i s counted a . l t e r n a t i v e l y a t thk tcs t sample c c n t c r ?nd a t m a c c u r ? t e l v r e p r o d u c i b l i p o s i t i o n i n t h c , t h e r n a l column coupled t o t h e I ? R ~ / ' T v r e a c t o r . - ...

The chamber count ing i s normalized t o t h s s imul taneous me?.surement of t h e count ra. te .,f 2 1 .5-rnm-di a , 11235 f i s s i o n c h m b c r p1acc.d ,it a f i x e d p o s i t i o n i n t h e t h e r n a l colmmi'l, Dur t o t h e h igh c o u n t i n g . s t a t i s t i c s (up t o 2,530.300 p u l s e s c o l l e c t e d ) and t b c use of v r r y s t z b l e components f o r thc c o u n t i n r l i n c , t h e e r r o r in t roduced bv t h i s norrnaliza.tion i s i n s i g n i f i c a n t ,

Neutron c a p t u r e by l3lO v i e l d s a L i 7 nuc leus sild an a lpha p ~ r t i c l e . Owing t o t h e r e l ? ~ t i v e l v low energy of t h e

emi t ted p m t i c l e s , ' h igh i v n p l i f i c a t i o i ?.nd x c u r a . t e p u l s e shr?.ping i s r e q u i r e d f o r an e f f e c t i v e d i s c r i m i n a t i o n frorn background n o i s e , i n a d d i t i o n p a r a s i t e re? .c t ions ( n , p t vpe , by high-cncrgv n e u t r o n s ) w i th t h e c h m b e r v a l l and gmmz pi le-up occur and must be x c o u n t e d f o r .

To t h i s e f f e c t t h e count r a t e of dumw chambcrs ( i . 2 . v:itliout t h e B d e p o s i t ) i s m c a s . ~ r ~ d ?<nd p r o p e r l v subtrz.ctcrd Crox t h e B c h m b c r s count r - t e s . A t v p i c a l emiss ion spc.ctrua or" t h e 9 chamber; ;.s .w;.surcd i n t h e t!flcrmal colunn, i s sl.ovn i n I Thc r s s o l u t i o n of t h c Li7 ( l e f t ) a-9.d ~ lp l ?? . n i & s i s s - l t i s f a c t o r y .

The measureaent y i e l d s t h e r ? t i o of t h e e f f e c t i v e c r o s s sec t i .ons , sveraocd i n t h e f a s t zone s?ectrIwn, a s : .,I 3 ! 3 ; 9 ; t i ~.. 3 k>

(.,. - .-?- - - I . \- L-i:'.; ,-., i s . ~ ~ - -7T, - 3- ' -

Li C-- ' . : ; ' :.: 35 t is :, . ..

here C i s t h e chamber, count r a t e n o r m l i z c d t o t h e oni it or count r z t e and c o r r c c ? ~ ~ : ~ f o r dead t imc , f l u x dep res s ion , s e l f - s h i e l d i n , , e t c . For t h e a c t u a l t h c r ~ a l colunln c o n d i t i o n s

~ h c q u a n t i t y t 3 be i.ntroducc:i i n t h e r e s o l v i n g e r r ~ a t i . - , - ~ of t h e e x p e r i r e n t (TzSle 1 , en , ? ) , nl rwlv !';31" cmtu re / i ; - .35 f i s s i o n u i n t h e t c s t sarnD1e. i~ obtained as . . -. ,'.. 5h3,;- &!:.:>, : , - .- i..: - I . . . , , / , , , , . . .<- \

.-

i '-- /' i : - - _ L j. / ':IG , " ' .; i ,'

5B. Xe?.sureaents and r e s u l t s . ie.suri.wnts w r e done i n the- follou!in$j t e s t - s m p l e s 3.t -i:h< Fas t zone c e n t e r

I otc!st ss.ri?lc cont8 in inq t h c r c f e r e n c e med:lu;n v i t h " 3 ~ : .

re ; ic t iv i t , r : ' c o ? ~ o s i t i ~ n j

2 . t e s t sm?!.e con ta in ing t h e t n s t w d i u ~ wi th Fc ( ~ / ~ 2 3 5 = l l 0 , Fe/C=3.;) :~?i thMnu. l l r f , ? .c t iv i t . ?" c o ~ m o s i t i o n ;

A,Ci.in;rd t iw of t h e c:?-irihfrs ( r ~ l a t i v ~ t o t h e : non i to r ) ; R , f 1u.v p e r t u r b a t i o n csuser! bv t h e 9. I -mT-thick s t e e l t~;.br.

con ta in ing t h e c h m b e r s p laced i n t h e t e s t s m p l e ; C , e f f e c t of u n c e r t a i n t v i n t h e p o s i t i o n of t he c h a ~ b e r ,

vhen pl?ct?d i n t h e t h e r w l coluxii, on chanber count ~ ~ . t : .

A J h c d e a d ti:ne of t h e chanbcrs v?s i n f e r r c d from rne?.sur::*~cnts of normalised count r ? t e s . o f t h c ch?-ibers ? l aced i ~ n ti:lc therr ia l column, ;-t f o u r d i f f e r e n t r e a c t o r p o w r s , nr;l-rl . .

33, 20, 1 3 and 5 'The va lues obt?.in::d:for t h e B c h m b e r s 'C =1+1..3,us; ?o? - t h f U235 c h m b e r s , ;. = 2+3.2 ,us. -

The w a s u r e d e f f e c t vas 3.a:L p c r m.,n d i s p l x e m e n t . S ince t h e -ictu?.l u n c ~ r t ? . i n t v i n t h e c h m b e r p o s i t i o n mzs + 0 . 2 ~ n n , t h e cor resaonding count r a t e u n c e r t ? i n t v t!ii?s - l i m i t e d t o +0 ,1 . L o - . .

Thc r e s u l t s of .?c?sure%ents 1 ,2 m d 3 ( p r e l i n i n a r ~ m a l y s i s o f d a t ? ) m e ~ r e s e n t c d i n Teble 8. Thc va lues given i n c l u d e corrections f o r ch?mhber dead t i n c , f l u x ~ e r r u r b a t i o i l b:: conta innent tube i n t e s t - s n m l e , s e l f - s h i e l d i n g of c h m b e r d e p o s i t ( s i g n i f i c m t f o r chamber ~ l . ; i c c d i n then131

c o l u m ) , f l u - deoress ion around c h m b ~ r ( s i g n i f i c ? . n t i n t h e r w l c o l u . m ) , " e s t c o t t T , r p - i r . m e t ~ r s n ~ n s u r c d i n t h e t h e r ~ . ? ~ l c o l u m , h?ckground of ( n , p ) ?nd ( n , ~ , ) r ea . c t i ons y:ith thc. 813 c h m b e r w a i l s ( a s qeasured by/ t h ~ dumny.. c h ? . ~ b e r ) ,

Ti.ie eva lua . t ion of t h c cha.7tbc.r s e l f - s h i e l d i n g m d f l u x d e ~ r e s s i o n c o r r e c t i o n f a c t o r , m p l i e d t c ~ t h e v a l u c s of Tz.ble 8, i s a. ve rv ~ r e l i r n i n 3 r y oni.. An .?.ccura.te t r a n s p o r t c ,?lcuic?tion, ss we l l ?s a d i r e c t e w e r i v ? n t ? . l de temin ; . t ion of t h e s e c o r r e c t i o n s , a r e und6ru~w.

A t t h e p r e s e n t s t z g e of t h e d,ata an? . lv s i s , t h? u n c c r t a i n t v of t h e r c s u i t s p re sen ted i n T?ble 8 i s roughlv esti::l;itcd a.3 +2i. - One can n o t e t h a t t h e r e s u l t s of mcasurenents 1 and 2 ( " r e f e m n c e " n c d i u . ~ and test-medium wi th F C ) a r e m i t e c l o s e ; t h i s f;.ct t c n d s t o .con.€ir;n t h e valid it:^ of t h e cho ice ~ / ~ 2 3 5 = 113 f o r t h e t e s t - m e d i m v i t h Fe ( s c : ~ s e c t i o n 1B).

?'iainl.r t o t e s t e i t h e r t h e n u c l e a r d ~ ~ t a . f i l e s and t h e ~ T ~ U D -

c r o s s s e c t i o n s g tner? . t ion codes , a. s e r i e s of 1:-inf c?lcu- 1. t ions mas nerform.ed, us'lnq t h e E N D F / B ~ ( E N D F ~ ~ I f o r Ye, s i n c e r e c e n t c o ~ p a r i s o n s sugges t t h a t t h e v e r s i o n 1 d ? t ? f o r Fe ? r e b e t t e r ) ?XI? ir::NDL f i l e s , v i t h t h e GA'12, YC2 and. PRAVDA c r o s s s e c t i o n ?vcraging codes, L-inf vas

caLcu1ati.d f o r bo th tht? r e f e r e n c e .mcdiun and the: t e s t qediurn wi th Fee

?he r c s u l t s , p r c s c n t c d in, Tzble 9 , -?re i n v f r v good ?greemen-t (with-ir,. s o w hundrcd ~ c m ) f o r the r e f e r e n c e qediu?!, v i t h t h e exception of t h e va lucs ob t? ined bv CAY 2 (conf i r -n inc t h a t t h i s code i s n o t & ? c i u ? t c ) ,

S i g n i f i c m t d i s c r c p m c i r s w e i n s t c 6d observed monrr the! k-inf v?luc;s calcul; . ted f o r t h e test-ncdiuxi niitlc F::, l i k e l v oliring t o t h e larqi ' u n c e r t ? i n t y i n th; Fe cro?i;-- s e c t i o n da.t?, Xeportcd belol.; i s ? co.n?arison S e t w e n I<-inf c ; i lcv .P. - t i o n s b.7 t h e E I L I D F ' B ~ - 'IC' - A N I S N cha in a.nd CARMAVA. 3 ( Z E A , France),

Ag3.i.n one n o t e s are e x c e l l e n t aqretrncnt f o r t he r??i:.rcncc: medim ?nd a large: d i s c r e o m c v f o r t h e m d i u a w i t h 7 c , On t h e b a s i s of t h e ?.bovc evidence, t h ~ E N D F , ~ ? ( B I Co!?

2. ?'e)-Yc cha in v . s chosen t o o b t a i n t h e group-cross s ~ c t i o n s used i n tlii' c ? l ~ u l ~ t i o n s f o r t h c i n t e r n r c t . t i m of t h e exper imint . Thf c ? l c u l . t t d q u m t i t i e s m d correction f , ?c to r s cnt::r::c! i n t o t h e resolving ecpa t ion of t h e e ? e r i m e n t ( ' 7 " b l ~ 1 , ea .3 ) a r c i n f e r r c d rn?inlv bv 27-group A N I S N c a l c u l r t ? o n s (w i th group-bucklings obt,?incd throur;h 3 f i t t o t h c 1 0 - g r o w - 7 ~ i a . l f l u x d i s t r i b u t i o n s c , ??cu l~ . t ed b,r ALC':) ,,

?'::.c c o r r e c t i o n E ( f l u x ' h i sna t ch and lea.kaqe e f f e c t s ) i:; c a l c u l ~ t c d fo l lo r r ina the: OLDE'CO? pcr tv . rh?t ion Cor:.ialj.!',. * i n d i f I u s i o n , 2. dimensions, u s i n ? 8 itnd ?/ vaI.ues (10 groups) gene r s t cd bv A L C I c d c u l a t i o n c . A one-dimension t r a n s p o r t c ~ l c u l a t i o n (27-grcups, pe . r turba. t ive) bv t h e DTFIV-DACI codes i s non O P F T A ~ ~ ~ V C

,ad i s hi-in-i comp~red with t h i ?bow sche~ne f o r t h c d .e tc rn in? t ion of thc c o r r e c t i o n f a c t o r E.

The r e p o r t on t h e s t a t u s of t h e e - ~ e r i a e n t , uod?.ted t o A p r i l 1 5 t h , 1975, i s concluded a t t h i s q o i n t . A i m of t h e r e p o r t x r ? ~ t o out i n evidencc how t h e exue r imtn ta l t echniques , equ ipqents m d procedures , r e q u i r e d t o supply the d a t a used t o i n f e r t h e f i n a l c r p e r i n e n t a l r e s u l t ( s e e T.?ble 1 , eq , 3) arer? developed, te-sted and o u t i n t o one ra t ion .

Tynica l results of ? co?mlete s e r i e s of ; ne?su rmen t s h ~ v e : a l s o been p re sen ted , bu t i t i s s t r e s s e d t h a t t h e

d3t. r e d u c t i o n and m a l v s i s y i e l d i n v h e ?hove r e s u l t s ? r e i n gene r?~ l 3 r e l i n i n a r ~ and n o t coqp le t e .

On t h e whole, t h e r e s u l t s obta.ined were cons idered s a t i s f x t o r v , bo th f r o a t h e o o i n t of vicur of t h e i n t e r n a l cons i s t ency of t h e d ? t a snd of t h e correspondencc between t h e c : p e r i : ~ e n t a l e r r o r va lues found and t h e a - p r i o r i v;ilues ?.ssu-ncd i n t h e r r r o r a n a l v s i s e s t a b l i s h e d f o r t h e assessment of t h e in e v e r i n e n t z l p a r m c t c r s . The i n t c r a r c t a t i o n of t h e r e s u l t s ( e , g , s o l u t i o n of e q , ? , Table 1 ) r c q u i r c s a c .? re fu l r e v i s i o n of e i t h e r t h c erperiment?. l m c l c a l c u l a t e d q m n t i t i e s in t roduced i n t h e e c u a t i o n , vrhich i s under\?sxr ( d a t e d Apr i l I j t h , 197,;).

The program of t h e I I ~ ~ . / T V vork i n 1975 f o r e s e e s t h e perfor-nance of complete s e t s of me:?sureaents, ss desc r ibed i n t h i s r e o o r t , f o r

- •’;\st zone and tcs t -sample c o g t a i n i n g Fe p m t i c l e s ( l i k e l v w i t l i test:-sawples wi th vary ing Fe con ten t m d ~/U235 v a l u e s )

- fa .s t zone con ta in ing Fe ? a r t i c l e s and t e s t - s m p l e c o n t s i n i n q iq i articles ( l i k e l y v i t h ' va rv ing X i con ten t and ~./:!235 v a l u c s )

- s i q i l a r c o n f i g i i r a t i o n s ' w i t h t e s t - s m p l e s containin:: s t a i n l e s s s t c : e l m d C r p s r t i c l e s ,

APPENDIY

1 . COATED PARTICLTS C2AXACTEBI S T I C S

A, FISSILE PARTICLLS

mate r i 21s UO kerni 1s c o a t ~ d bv oyror mbon 2

k c r n e l d i a - 606+5 ,u " dcns i t y 10.52' ' I U con ten t 83.15 w t .!

i s o t o n i c composit ion U U234 9 . 7 ~3'3

(ai-t ,i) U235 93.16+3.32 U235 0.235- U738 5"82

c o + t i n ? t h i c k n e s s 200 + 4,u " dcns i t v 1.7 ; OL02 -

p a r t i c a l e di mctc_r I !3713+? ,v. ,, dcns i t.7 .3.5i+3.0

- !I 1: c m t m t 55.599 v t '! I t-I, conten t

C 8 D D ? ~

t o t ? ? w i g h t U 13.1'38 kg

n . G R A P H I T E PABT? CLE S

m a t e r i a l s d i a . dcns i t ; r

~ u r i t v 5 con tcn t

2

g r ? ~ h i t e k e r n c l r o a t f d b->? plrrocmbon 1320 + 79 :u - 1.322 n u c l e a r crnde 100 pp:n.

C. 30E0M LOADED GRA?H LTS PARTICLFS

d i ? * dens i t v B con ten t p u r i t y H con tcn t 2

g r ? ~ ? h i t e k e r n r l con ta in ing B C ./i

co.ated b-;r pyrocarbon 1020 + 70,~. I -553- 4--53 + 3.01 ? l i t .: - n u c l e w grad? I 90 ppn

2, CORE LOADINS AND SAFETY TESTS

A, TEST ZONE LOADING

f i s s i l e p a r t i c l e s 0.55 kg (2235 5 kg) q r s p h l t c o a r t i r l C s 2 3 . 9 kg boron lox i ed

su red s a f e t y 1i jn . j - t

--- -- (PC?) - -- ('3~71) .-

c o n t r o l rods i n s e r t i o n 21 53 . :: q 599

c o l d c l c a n corc. c r c e s s r c a 3 i v i . t ; ~ 1 8 O ( ~ t 20•‹C) :< 503

void coefP i< : icn t of d r i v e r zoni- -0 . 1 7,./c?i 3 - -0. I 5 i c m 3

.-

f -is t l i r a t c r dw?p from d r i v e r zons. 8503 -- -> -- 5001)

Table 9 - Resolving equations for t h e experiment

5 5 i f , +&,.

inf inite m e d i u m s p e c t r u m

5 8 5 Calculated quantities: LfI2 b2 %,2 1 4 f 1 2 p

13 neutron , R U233 p 2 . 3 3 , pu2.q

C 2 J / 3235 , 5'235 F F :7

/ F,G235 e spectrum \ -----.L-

. . :dB, Ths valucs ;>,re in t e n s 3f' .xic:r~~canic cross-sections

rn ic rosphcres w i g h t s ( g r ) ,T. t on s m p l c

araphi . t r r z t - i o s ( n ) S o t ? l g r a p h i t c V i t h )j f i s s i l e 3235 ' S'u235

a

2 t 0% rnficrosphcrc.~ v r - i a h t s ( g r )

samplt- c ; ~ i r p h ~ . r e - r:?-tios ( n ) t o t 3 1 q r ~ p h i t ~ . >:'ith R f i s s i l ? FE U235 9 3;ir235

vcid 2,27

FIG. 1

b o r o n

FIG. 4

T e s t m e d ' *urn

f i g . Axid di5tribnt;on of activations r n e a s ~ ~ w d inthe RB2/7V Thermal Cdum

Rad ; a / a r r a n g e r n e n C of Fi ~ s ; o n c l r a m b a r s . in f a s t z o n e

I

i I

MULTI C H A WEL RNALYZER

PRINTER K I

PRINTER P O F J C H G R

F ; s s ; o n c h a m b e r s c o u n f ; n g s j s f e m I

F I G . 1 0 T Y P I C A L E M I S S P U 2 3 9 MINIATU

3N SPECTRA OF THE U 2 3 5 AND I Z E D F I S S I O N CHAMBERS.

- Measured

A xin 1 d;stribu/ions of 5pectrum indexes

FIG. 14 TYPICAL E>lISS13iV :;PECr?I<UX OF' THE B 1 0 CHA?IBEii