ML20082T447

Sar:Use of H-451 Graphite in Fort St Vrain Fuel Elements

ML20082T447
Person / Time
Site:	Fort Saint Vrain
Issue date:	12/20/1977
From:	GENERAL ATOMICS (FORMERLY GA TECHNOLOGIES, INC./GENER
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ML20082T428	List: ML20082T427 ML20082T447 ML20082T465 ML20082T482
References
GLP-5588, NUDOCS 8312160021
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{{#Wiki_filter:.. A_ n L. - t } t,. l' } GLP-5528 5 e. u SAFETY ANALYSIS REPORT USE OF H-451 GRAPHITE IN FORT ST. VRAIN FUEL ELEMENTS i 6 p t-t i 5 r. GENERAL ATOMIC COMPANY DECEMBER 20,1977 T 0312160021 831202 PDR ADOCK 05000267 P PDR Ii = = - - - -..

=. - - - - - - l ~.& O 4 + c I i A r-TOPICAL REPORT EVALUATION l I = l Report Nc=ber: GL*-5588 Report

Title:

Safety Analysis Rep:rt--Use of H-451 Graphite in Fort St. Vrain i l' ?- Fuel Elements Report Data: Dece==er 20, 1977 1; l il Origina.ing C gant:ation: General At:mic C:cpany 1 i l Reviewed by: Reactor Fuels Ser.icn, Core Perf:rmance Branch, Division of Systems Safety, March 1379. [ l l i Summarv ef Tecical Recer l 1 This t:pical report was submitted by General At:mic C:mpany (GA) via letter h (G. L. Wessman (GA) to R. P. Denise (NRC), Mar:n 28,1978). In that lettar we i z. were requested to review the report and cencur with GA's opinion that the

• substitutien of type'li-45T'gra;htia in the' For. St.' Vrain (FSV) reactah ~cere for t.he. type (H-327) cu-ently in use,is a::eptacle. T.he reasons for.cesiring to su:stitute M-451 for M-327 graphite in FSV were stated to be as f:llows:

i + 1. General Atomic is contractually obligated to supply Public Service Ccapany of Colorado (PSC)' with fuel elements. - l: 6 2. It appeared to Gd that 11-327 gra:hita, the type currently used, e would nct be availahle in the future. f i i 4 ~l l 1 i -t--

l t ^ X.. l I, I 3. General At:mic believes tnat H-451 gra:htte is superi:r :: H-327, f I i both in ter=s Of.di=ensienal s. ability uncer irradia.icn, as well as s rangth. I Thus, NE's approval of H-451 gra;nita for use in the FSV reac :r was soli:itec j i so that the reference core H-307 ;raphite fuel and refle:. r elements c:uld be replaced with H-451 ; a;hite elements curing future relcads; the first potential i substituti:n c:uld begin with relcad " segment 5," currently scheduled f r ' early 1581. f The t::ical re; rt was stru::ured int: three :ajor sections: (1) a perf:rmanca I analysis cf the H-451 elements, enc: passing the nu: lear, ther:al, and structural i f: cesign, (2) a safety analysis of the effect of the H-451 elements en a::idents i l t that had been censidered in the F5V F5AR, and (3) a su= mary cf catarial pre;erty j data for H-451 graphita. In general, the a;proach used was to c:: pare the g r i analytical results based on H-327 graphita with the results obtained with the jl l assumptions cf H-451 graphite as the core material. The objective was t: ~ ~ demonstrat's. that H-451 was'a bettet structural r.aterial thh H-327_ and that, ~ the use of H-451 wcul'd (a) result. in negligible. changes in the nuclear and. j . th....l' behavier c.f the c:re, and (b) net resuTt in aducad safety margins cr erma ... ~ reliability ::.sared : the reference H-307 c:re. I. i j The core nuclear perfor=ance analysis adcressed fuel loading and ex:ess rea:tivity, I i I power distributien, fuel burnup and ex:esure, shutdown margins and reacter' I-8 I control, and red withdrawal ac:idents. The -cd withdrawal ac:icent was given I special attention because it is icentified in tne F5V F5AR as the worst-case reactivity initiated ac:icent; c:nt ci red ejection ac:icents are not censicered .h l l

e-k .. :- - ~- . = = - - 5 t I t i credible f r -he F5V res:.:r and, therefore, the =nsecuen:es =f a r:d eje:tien ? l a::ident are net.analy:ed. ~ i - i e I I The._ccre ther=al analysis addressed the fact that the thermal concuctivity cf l I H-451 gra:hite is appr:ximately a fact:r of 1.2 greater than ' hat cf H-227 t i graphita. The better ther=al c:nductivity was predicted : result in a smaller ' tempera?.ure rise acr:ss tne gra:hite web and in 1cwer feel :entarline tc=e-- atures. The expected reducti:n in fuel te=peratures was ex;ected als: :: rescit in negligible changes in metallic fission pr: duct release and a rece:tien i in gaseous fission product release. i. I The graphite structural analysis re:crt section addressed'(a) the =echanical I properties of H-327 and H-451 graphites in a c:=parative way, (b) stress I t i analyses for both types of gra:ihite, and (c) graphite irradiation-induced t ;: dimensienal changes. The H-451 graphite has higher strength than H-327, but i the H-451 fuel element would have higner stress levels. Design stress margins I, l. 6 6 were, hewever, asserted to be i=preved by the inclusien of H-451 graphite

2..~

elements in the F5V c:re because the imprevements in strength were more tnan s required te meet the increase in stress. i f I j The tcpical report's " safety analysis" section was used to examine events and I ~ ~ accidents previously analyzed in Chaptar XIV cf the FSV FSAR te determine.if j. the substitution of M-451 graphite in FSV retcad ::res c:uld altar the con-sequences of pestulated ac:idents. Events given a re-examinati:n included fuel element "malfunctiens," loss of normal shutd:wn :: cling, ::is ure inleakage, 9 1 l-p l' I T

s-n r v 4-1 I pemanent less of for:ad circulati:n, rapid de:ressuri:a.icn, and the r:d withdrawal event mentic.Gd aseve. It was ::n:1uced in :ne report that F existing 75AR results of a::f dent analyses ::nservatively beund any pertur:a-tions resulting fr m the intr:cu: tion of H-451 gra; nite fuel elements. l l Summarv of :lecuitterv Evaluatien l Curing the ::urse cf cur review of GL?-5555, recuests f:r additi:nal I l information were resp:nded to by GA in writing (Refs. 2 :: 5). Our in::uiries i and GA's res;cnses will be ine:rporated into GLS-5555 via amen ment. i t Our review fccussed pri=arily on six aspects of H-451 graphite perforcance l relative t: H-327 graphite perf rmance in the Fort St. Vrain :cre: i (1) material reproducibtitty; (2) corrosien (exidatien); (3) mechanical and lt physical pr:perties; (4) irradiation-induced dimensional changes; (5) 'I i fission product talease and transport; and (6) post-trradiation examination L and surveillance requirements. These subjects will be discussed in crder j i t below. K n s. Gra:htte Re:recutibili v - This has been a c:ntinuing ::ncern in H7GR fuel g system reviews (Ref. 6) be:ause (a) the properties and performance of graphite t materials are strongly dependent upon the nature of the precursor matarials and methods used in manufacture, and (b) the gra:hite used in FSV is not manu-factured by General At:mic. Graphite grades H-227 and H-451 are manufactured l by the Great Lakes Carbon Corporation; only the ma:hining and fuel loacing of 1 i 1 {) a ph69m.w we Wb6 6. 69 W i t

L t ? i t the as-fa:ricated gra-hite bic:ts are perf: mec :y General At:mic. A:::r:ingly, we asked GA t: indicata h:w acetuate assurance cult be previded that (a) the I H-451 gra;hite to be used in future F5V reloads is the same as that subjected [ ~ to the qua'lification test pr: gram, and (b) if different precursces or fabrication I l para:eters were used fer future relcad =aterial, the same (or predictable l 5 changed in) pr:;erties and thermai/irradiatien :hanges would be cbtained as with the test qualified material. I i The majer thrust of the resp nse to this questien (see resp:nse to C251.la) was that, for F5V reicad seg=en.s, the H-451 legs will be manufactured fr:m -l L. ii near-isctropic : ke taken fr:s the same batch as that used fer the manufacture - 'l l' i cf a prepecduction let that is used as a standard fcr production f the F5V reload ele =ents and that is to be used for future H-451 production. This same i .I preproduction lot has also been well characterf ted for pr:pe-ties and irradiation {j i behavicr, and the data ettained are used in the design data package for the 1 yc H-451 fuel elements.< ~ The H-451 purchase specification further assures repro. i 5 r. J ducibility of ccke structure by requiring the fabrication and testing of the I c efficient of the-cal expansien (CTI) of calculated c:ke sa=:les. The C-~ test =eth:d is specified (Ref. 7). Thus, severai ste:s ara aken to ensure i that the same c:ke will be used in the future F5V reload H-451 graphite blocks l as was used in the H-451 qualificatien test program. In addition, the H-451 !I purchase specification iequires that the binder shculd be a c 41 tar. pitch of j I the same type used to manufacture ;r:tstype, propr:ductien or procu tion icgs of i j H-451 graphite and that the impregnant shall be a type co-tified to the purenaser. I ) t 1 3 \\ s 1 7 I. .i .mem...

==m em ) . ~ _

__= s r~- Q. ~ - -. ~ e /. !i We, therefore, ::nciuca that acequa a assuran:e has been proviced ::n:arning

i the reproducittlity of the H-451 gra

:hite fer FSV, so long as the precursor E'

materials and ;rocessing remain unchanged. Should the pre:ursor materials j or fabrication process be changed, however (for example, should the current I i' >t near-iset cpic c ke supply be exhausted, thereby necessitating the pr:ductica 4 i of a new bat:h with ;ctentially different cualities), we will require GA :: 1 f ' provide evidence te support the perfer=ance predictier.s for the gra: nite elements produ:ed ft:m the altered materials er pr: cess parameters. l i r A secondary c:ncern regarding the effact =f fabricati:n process en material perfomance invc1ved the method used..to fabricate the fuel r:ds that are c:n-I I t..ined in ver.ical holes drilled int the hexag:nal graphite fuel blocks. Two i l processes have been develcped: (1) an out-of-block forming and curing prc:ess;

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and (2) a cure-in place process, sometimes called "in-block carb:nization". 1 The cure-in place process can result in a stronger bond between the coated + 1 1 fuel particles and the fuel rod matrix; this has been observed't: cause tears j,i,- I j in the outer pyrocarbon coatings due tu differential irradiatten-induced shrinkage. On tne other ha.nd, the... cure-in-place proces.s i:,.,r',ves, heat transfer

s..

between the fuel red and graphite bicek because the gap is closed during the j i t curing pr: cess. In response to our q'vestion (Q:31.1b), GA jndicated that the t. e cure-in place process was not being considered at this time for the fuel rods to be used in the H-451 fuel elements, and that if the cure-in place process t' 1: 4 were te be adepted in the future, a se;,arate safety calysis. and re;crt wculd i be subsitted., i I t f. s, 4 11 s \\

r r' ( k l

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e r ll ,y, 4 i l Gra:hite :r esi:n - This subja:t is i=;ertant fr:: the stane:: int f neat l generation, ;r:cu:tien ' f fla==able gas mixtures, potential fission product I* o I l release, burnable ;cison oxidation, fuel particle hydrolysis, and effe:ts on 5-r graphite physical and mechanical pr:perties (and ;ctantial effset, therefore, on core integ-ity). Our review fccused, in particular, en ne data base for i H-451 graphite, the effect of c talysts on H-451 graphite exidati n rate, and 4 l ' a general c:=; arisen of the effects f H.451 versus H-227 gra:hite oxicatica f i en c:re perf: :anca. One review questien (q131.10), for exa=:le, ac:ressed i the effe:: of gra;hite type en the rir: tion rata as a fun:ti:n cf percent g 3 i l graphite burnoff; this questi n also addressed the Overall effect of H-451 1 graphite cxidation rate en the predicted ac:ident ::nsecuences discussed in ((g. the report safety anaiyses. Ancther questien (Q221.11a) adcressed the relationship bet een graphite reaction rata, fuel hydrolysis rate, and (: t associated release of ncble gas fission products. } The respenses t: the abeve questicas are contained in reference 2. Experi-i i l ( mental data on a variety of graphites were cited as evidence that the chemical l' j reactivities cf H-451 and H-327 graphites are similar. Parametric calcula-j tions were perf:r:ed :: cetermine the sensitivity of tne exicatien effects e (hydrolysis rates, for example) ts the coolant canditions (suca r F nure t t-j levels). The results of these calculations are documented in refere. q: 4. ~ j~ Results of the parametric calculations showed that a factor of ten increase in 3: l' reaction rata decreased the acble gas release due to hydrelysis by 15::, wnile j a threefeld ce rease in reaction rate increased the noble gas release by atcut \\ 4 1 J s1 1 'I 'l r*. <- r -r-4

{ -{-- - ~~~ .g. j 4 20%. 7hese are relatively s all effects when c:=;arec : ne assumed Orcar:f- ~ l l magnitude change in reacticn rate. The t:tal a:cun't cf gra: nite exiciced t throughout a simulatec reacter steem ingress accicent, calculated using the i i OXIDE-3 computer code (Ref. 9), varied by atout a fact:r of two for a tenfeld change in reaction rate (:ur CXIDE-3 review conclusions are reperted in j !. i reference 10). We c:nclude, therefore, that ce substitution cf H-451 graphite for H-227 grachite in the FSV c:re will not significantly alter the :xidati:n j characteristics and c:nsequences as predieted in ce 75V FSAR. l L i Mechanical and 5vsical 7-::erties and Stress-St sin Relati:nshi:s - Secti:n a i E l t of the t:pical report listed un materials pr:perty data for both the H-451 1 il It I and H-327 gra;:hites. Our review c:n'centratad en the H-A51 graphite data tase, i j + 8 ue c:m; arisen cf H-451 graphite pr:perties with ucse f:r H-327 graphite, and the en going and planned experimental program. These mechanical pr:perties i i t; I that are identified in G1*-5588 as the ones that deter =ine the element stresses, stress-strength margins, and element deformations are (1) modulus of elasticity, l (2) tensile strength, (3) creep properties, (a) irradiation-induced dimensional j. .E changes, (5) thermal expansion, and (5) t.*iermal c:nductivity. As ; art cf our i review, we asked GA (Q231.5) t: illustrate ne relative impertance of these properties to the calculatics of the. abcve parameters. Dimensional changes are discussed separately below, i i t t i GA's respense was in terms.cf the effect of material pr:perty charges at the ! i I time of maximum stress, for both cperating and shutdown c:nditions, and at the time of maximum dimensienal change. This appr:ach was fellowed because ef. the f .I v w ,--c.,

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ecmplexity cf the effe: cf matarial property variaticns en stress, design 5 margins, etc., i.e. the effect of any specift: variatica is cependent uten the ~ i intera: tion with varicus other preperties whi:h vary with time. Thus, the { l -maximum-eperating stress was reported to cc:ur at :ere days and was due *c startup thermal stresses. At that time there are no creep effects, and any I change.in creep parametars, therefore, has no effect en stress and stress cargins. Although, as indicated in reference 3, at end cf life in the element, a a *2C variation in the stancy-state :rees coeffteient :an result in a -23 f, in:rease in%ating s ress, the cperating stress at this time is re:crtec to be sufficiently 1cw that even this 2 5 increasa precu:es a stress of only one quartar the stress during initial startup. We, therefore, conclude, based j f cn a calculatten of the maximum str'sses during normal operation and using the available H-451 prcperty data, that there is reasenable assurance that the H-451 graphite element design will ac:c::medate the maximum stress with adequate [ I margin. f ~ As indicated earlier, the off-ncrmal case that produces the maximum graphite i e stress (negie: ting, for the mement, sets:fic censidera.f ens) is the maximum-worth 1. t red withdrawal event. This event pr: duces the greatest temcera.ure differences I across the web between fusi and coolant hcles and, therefore, results in the .l. l' greatest thermally induced stress. However, as indicated in the response te [ questien Q7.31.8, the H,451 fuel elements retain censiderable margin (* 1550 [ i i psi and

• 1150 psi in the axial and radial directions, respectively) for the

{ wors. case r:d withdrawal. These margins are greatar than'these calculated for the H-38 graphite elements (* 100 and

• 700 psi, respectively).

a 4 I t. I [ . l D ~._

.s =. - - - L .w. 1 I e s 1 { The ateve-dis: ssed :alculatiens f =perating and snu-d:wn stress anc strain distributiens were perf:rmed using the ::e; uter pr: grams FESIC anc SAFE / GRAPHIT, whien were used in the design and analysis cf the F5V Initial ::re. t '. t 4 As noted in cur evaluation of the FULTON plant (Ref.11), we had not yet [ t l reviewed FESI: cr SAFI/GRAPHIT, and since these c: des have been suter:eded by t core recent 0: des, we still have net reviewed them. FE5I: and~SAFI/GRAPHIT

• have been cr:ss-:he:ked, however, by hand calculattens and c:m: arisen with these newer ::ces. Therefore, we find tnat the use of FE5IC and SAFE /GRAPHIT are a::eptable in this appli:stien.

I I j Regarding the acquisition and current availability cf H-451 graphite mechanical i and physical property data, a censiderable bccy cf such data exists, as shown 4 in section 4 of GLP-558. This information was generated fer the c:ost part ) i i under CCE-funded programs. The details of the tast procedures and results i are provided in the quarterly progress reports on the "hTGR Fuels and Care 1 Development Pr: gras." These quartarly repcrts are supplemented by extensive i 1 suusary reports. H-451 graphite property measurements are continuing in ce-tain areas (n=tably, c sep), but the data acquisition schedule has been stretched out be:ause of the redirectica of the HTGR ::mmer:iali.ati:n effert I in recent years. The creep tests en H-451 graphite will not be ::::pleted until late-1982, whereas H-451 graphite reload segments could be placed in FSV I by early 1981. The creep tests wfil lead the FSV elements in irradiation 3 exposure, however, sc that full-expcsure : es; data will be available ver the range of temperatmres. expected in FSV (see GA response to Q231.21 (Ref. 4)). ? d ..a _. =_ e w

/- r ( L l ... t. u. 1 l f We will require General At:mic :: provide timely re::r s :n the results and j future test pr:Jec-icns for the H-451 grapnite test ;rogram, which incluces i not only creet tests but other mechanical and irradiation tests as well. j4 l 4 2 l With regard to seismic stresses and analysis and their relationship to H-451 l mechanical preperties, GA indicated in res; nse to our review questi:ns that 1 H-451 fuel elements weuld be expected to see increased seis=ic leading c:m:ared with H-327 because Of H-451's higher elastic ecdulus in the radial cirection i (see modulus data in repert tables 4-3 and 4-9). Using simple s: ring / mass j k relations, H-451 fuel element impact forces were expected to be 3C% greater

• I than that cf H-327 elements. Eecause H-451 fuel slemen.s have mere than !!%

l., higher radf ai strength, however, the seismic structural damage petantial for o H-451 elements is less than that fer M-327 elements. The method of analysis .l-used to detemine the seismic stresses in the graphite fuel and reflector i elements was essentially the same as that used for t.'e FSV FSAR. Testing of !l i full scale. structures under simulated seismic loadings have also been conducted j I to ' substantiate the strength of the fuel elementa. We conclude that adequa.e I i assurance has been provided that ne H-451 g. a:hite ele *ments seismic res; case is at leas:' equal to or tetter than that of the referenca M-327 elements. i l I ( The fatigue behavior of H-451 graphite is addressed in the topical report in 5 i i, l terms of the homologous st ess, which is defined as maximum applied fatigue il , Il 4 stress diviced by tensile strength. In response ta staff question Q120.1, GA 'l asserted that both primary and sec ndah (tiermal) loadings are below.he i, l i t 1 .? .Il !( -l .i -._#,r -y .p

_s- .u. hemoleg:us stress limits, and snat no fatigue anaiysis -as ne: essa y, tnere-fore, f:r the H-451 elemer.ts. The resp:nse :: a su':se;uent questien (Q130.2) I cn the relationship of hemolog us ilmits = per:en survival indi:ated that i 1 j both see:n'dary and primary limits have been calculated to be. well balcw the l stress ilmits for 99% survival. Cycli: fatigue behavier =f near-isctrepic graphite is discussed in detail in reference 12. T-radiatien-fnduced Dimensi:nal Chances - Irradiati:n =f gra:hite causes l damage en an at:mic scale (lattice defects) nat is manifested in tulk dimensional 3 I changes which vary as a function net only of irradiati:n tamperature and fluence, but which are also sffectad by graphite struct5rai variables. A l facter that usually determines the usefulness f a ;raphite in remeter design 7 is the maximum radial c:ntracti:n, which influences the stability of a gra:hite stack. Another fa:ter that recuired censideraticn in cur review was the f dimensional c:mpatibility of H-451 graphite elements with H-327 elements since. only one-sixth of the : re would be replaced at each refueling. In addition, l' t because cf the current theories relating the power fluctuations in TSV to gap

f si

es between "uel c:1umns and regi ns, we recuired an assessment cf the j

potential for c:mponen damage that might se caused by gap ficw-induced mo i:n j and ac::unting for the different dim'ensional change behavior cf H-451 and H-327 graphites (see Q231.5). I: a c ] In respense to our questions regarding the effe: s of i-adiation-induced l dimensional changes, GA pointed out the following pertinent facts: (1) The transition t: H-451 graphite fuel elements will take place en a region :- g i i l 1 - I. j i l 5 -A'$'% - ~ ',.a.._... x "~~) ) a

^ m

• i,

(. \\ 1 1 j regten basis. H-451 and H-327 gra:hite elements will, ineref:re, n

e mixe-in the same layer within a regi:n during tne transiti:n.

(2) The =axi=us l radial shrinkages =f the H-227 and H-451 fuel elements are calculated :: differ by abcut 9.1%. Theref:re, the characteristics of the power fluctua-i tiens (assuming that they are related te cpening and closing f inte--regional J gaps, as postulated in referenca.13) should be unaffected. (3) P:tential i inpact leads calculated for the H-451 elements were 21% higher than the f1'uctua-tien 1 ;act 1: ads f r M-?27 elements. Secause H-151 graphite has a 55% greater I radial strength than H-227, h wever, the likelthece cf damage cue to flu nuati:n-i i induced leadings is decreased with the su:stitutien cf H-451 fer H-227 gra: nite. l We thus c:nclude, based en the above reas:ning, that the su stitutten of H-451 s s j graphite should net have any =easurable adverse effects due :: irradiation-i induced dimensional changes en the charactaristics of care fluctuatiens er [ i ) on the overall stability of the cere. 3 l i j Fission P oduct Release and Trans:cet - The improved thermal c:nductivity of Il i e j H-451 graphite relative : tha Of H-327 is cited by GA as reasen :: expect a I r slight reducticn in gasecus fissi:n pr:duc releasa. Metallic fission pr cuct ~! releases are nct se directly assessable, however. In centrast t: lig..: water t' reacters, metallic fission products do not proceed directly fr:m failed fuel i d to the primary c olant, but must migrate thr: ugh the fuel red ntrix material r d and graphite element web : the graphite-helium inter.f. ace Metallic fission + e 1 9 0 !l i I 8 g-G e,- w*we

r e n r ( 's 1 t l g i i l l 1 l ,,r: duct trans::rt fr:m failed fuel particles is tnus a multi-ste; ;r::ess I wht:n is, in part, a functicn cf the scr;tivity and diffusivity of tne fission h i. I t product in gra: nite, j I i j In GLo-5588, GA claimed that the fission pr: duct retentien characteristics of f H-451 graphite are similar :: H-327. In general, h: wever, most of the fission j product trans;:rt data have teen chtained en the current reference H-327 -l graphite, not :n H-451. In s me cases, no data exist fer H-451; f:r exas:le, I there are ne data fer the diffusien cf str:ntium in H-451 gra: nite. We, J therefore, asked GA to ;r: vide additicnal support f r their claims regarding I l fission pr: duct transport in H-451 graphita. I GA respended wita some previcusly unpublished data (en sceptivity of :esium en ,} H-327 graphita; ses response to Q231.12). By c:mparing data in ter=s of I general ft: functions (Fig. 2 of respcase to Q231.12), they showed that there [ i, was no significant difference in sorptivib cf Cs en H-327 and H-451 graphites. I I j I. j Data on serptivity of strentium en H-327 gra; nite (provided in 7 ables I thr ugh { -III of the GA res ense) were cec:ared wi.h data en H-451 in Fig.1 cf GA's 4 3 respense te sn:w that there is reass'na:1e agreement ::etween the serption 4 8 Ii isotherms for H-327 and H-451 graphites.. Although no data exist en the dif-1i 1 I j fusion of Sr on H-451 graphita, data were presented. (Table VII and Figure,3 of { j GA's respense) that indicated that'there is ne dependence on graphite type. '!I y I.] These and ether results discussed at length in GA's responses t: questions 3 i i Q231.12 and Q23I.22 lead us :: ::ncluda that there is reasenable assurance J d 1 1 7 1 g g a j 0 I y 7

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n e l e ( y i n- / 1 1 I 1 that fissicn pr: duct trans:crt behavier has been ecdeled c:nse-vatively. As t I indicated in the, resp:nse tc Q221.22 m, for example, even if the Cs-127 l; I* sour:e tem is increased by about a fact:r of seven, the two-neur exclusion-i area-bcundary bene dose fer FSAR " Design Basis Accident No. 2" (Rapid Depressurizatien E1:wd:wn) is increased by enly about 0.5 res. This is still ~ well belcw 10 CFR 100 timits and is the only dese significantly affected by I the hypotheticaT ine ease in Cs invent:ry. i i I post-Ir-adiation Examinati:n and surveillance - Although there is a c:nsid-erable bcdy of experimental cata c:ncerning the behavier of H-451 graphite, j g ii surveillance, including intaris and,; cst-irradiation exa'minations, is required, j } te c:nfim the safety analysis of any new fuel design feature. We have in recent months issued several pcsttten statemen.s regarding surveillance and i1; E PIE cf both test and reference fuel in F5V; e.g., Refs.14 and 15. These j statements ddress, in part, the planned insertion of eight test elements (Ref.16), c:cpesed of.H-451 graphite, in ' reload." segment 7" (currently being I 8 loaded into the reacter during the spring 1979). Although we had no formal i I 1 survet11ance requirement for the eight te": elements as a c:ndition of this I j insertien, we have n:ted (Ref.14) that safety analyses su;perted by results l I l cf such pcst-irradiatien survalilance may be required for future leads of fuel cf new designs. Thus, befers final approval cf future reloads of H-451 graphite. j can be granted, we will require (a) results of surveillance examinations en j I l the eight H-451 test elements, and (b) a commt ment to perferz ?!E :n future t r large-scale H-451 relcad eiements. With regard :: the eight tes elements 9 t ].- l 3

r r. '. j } ? l i FT5-1 :nr ugn FTI-3, the :urrently planned C05-fun ec post-irradiati:n pr: gras described in Amendment 2-(A;;endix A) of reference 15, shculd pr:vice a ::n-i "i siderable a unt cf ::nfir:a. ry infer: nation and should pr: vide sufficient I inf:r:ation for licensing purposes. k Reeulat:rv *esition ~

• We have ::cpleted our review cf t pical report GL -5528, which is intended :

i serve as a reference t: ;tevide the basis for allcwing.ne substitution of i Ii nea--isotrepi: H-451 gra:hite fuel and reflect:r elements f:r the curren-j l needle-::ke H-327 grapnita elements in the Fert St. Vrain rea Or. In cu. ,I evaluation we f :used pri=arily en six aspects of H-451'gra:hite performance I relative to H-327 graphita perfer:ance in the FSV ::re: (1) graphite repr:du:- ibility; (2) corresion (exidation); (3) mechanical and physical properties; j b i (4) irradiatien-induced dimensional enanges; (5) fissien produ:: release and' j t transport; and (5) ; cst-irradiation examination and surveillance requirements. Based on cur evaluation cf the information provided in the topical report and the responses to our requests for additional information, we ::n:1ude that k reasonable assurance has been provided that tne substitution cf H-451 for ~ t ? H-327 graphite elements in the FSV care will (a) result in negligible cnanges in the nuclear and thermal behavice of the care, and (b) will not result in~ i i ! I reduced safety margins or reliability compared to the reference H-327 care. lj t 6 9 f 1 Because data acquisition en H-451 properties and themal tr adiation perform-ance is engoing (via 00E-funded programs involving test-react:r irradiations and test elements to b'e irradiated in FSV), we will require, as part of any 1 j s e 4 1

l 1 e ( i 17 i i t I I future applicati:n f:r insertion of rel:ad M-451 elements, that General A ::ic Cc:pany pr:vice, timely reports en tast results involving H-ail graphita. I' Specifically, we will require that reports be previced en the results Of (a) i I the cn going f r adiation reep pr: gram and (b) post-irradiation examinations !I L l e j and surveillanca en the eight H-451 elements that are being insertad as p?rt cf reload Segment 7. In additien, shculd changes be mace in the c:ke er I methods of fabricatien of the H-451 gra hite biccks, we will recuire GA u provideevidencetesupporttheperfermancapredicti:nsf:rtnegra:r.ita t l elements pr:duced f-:= the altered =atarials :r pr::ess parameters. i This evaluatien a: plies nly to H-451 graphite :: be used in the port St. Vrain - l; reacter, because the analyses were performed in tor =s of 'the transier.t ~ analysis fer F5V and the c:=parative effect of H-451 versus the F5V reference j ,i H-327 graphite. A separate analysis would be required for any application =f H-451 graphite in a high temperature gas-c:cled reacter having a design differing fr a Fort St. Vrain's. .l I I e i t-s - 1 j l t 1 I l I I l 1 ..t .q 6 S ~~.

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c-. - ^ [. (' k I .n. [ i i q t Refarences i I f 1. G. L Wessman (GA), letter t: R. P. Denise (NRC), Mar:5 23, 1978

2. - G. L Wess=an (GA), letter to William Gammill (NRC), 0:::cer 30,1973.

' 3. G. L Wessman (GA), letter t Villiam Gumill (NRC), Nevuber 17, 1973. t, i i 1. l 4. G. L Wess=an (3A), letter :: William Ga: mill (NRC), February 5,1979. 3 l 5. G. L Wess=an (GA), letter t: Villiam Gammill (NRG, Fe:ruary 15, 1979. i .j 6. Victor Stells, Jr. (NRC), Memorandum t: Ray G. Smith, " Comments on ERDA l Division of Rea:t r Research and Devele;mett Draft Standard RDT-1, f Near-Isotropic Petroleum-Coke Based Graphites fer High 7emperature , Gas Cooled React:r Core C:mpenents," June 9, 1975. I i g i i: 7. RDT Stancard Ei-17, "Near-Isetr:pic Petroleum-C ke Based Gruhite fer I High-7emperature Cas-C:cled Rea ::r C:re Cem;cnents," 0:tcher 1977. J 8. A.' W Barse11 and M. 3. Peroomian, Censequences of Water Ingress 1 into the K7GR Primary C alant," General At:mic Report GA-A12171, e f April 15, 1975. I'. 1 t l t a 1 . j j l

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s..

e k +

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j, j

-u-I e t f 9. M. E. Pere mian, A. W. Earsell, and J. C. Saeger, "0XIDE-3: A .l'i ~ Computer Cmde f:r Analysis =f H7GR 5 team er Air Ingress Accidents," General At:mic Re; rt GA-A12tS2, January 15, 1974. 1 e i 10: D. L Ross (NRC), Me:crandum t: R. P. Denise, " Support t: GASSAR !!ER " ~ December 15, 1975. i

11. " Safety Evaluatten =f the Fult:n Generating Station, Units 1 anc 2,"

NUREG-75/015, March 1575. l, i e g 12. R. J. Price, " Cyclic Fatigue c' Near Is:t :pic Graphite: Influence of 1 I 3 i Stress Cycle and Neutren I. radiation," General At:=ic Report GA-A1452E, I i November 1977. I i 1 i J ! i l! 1

13. "Cere Fluctuation Investigatten Status and Safety Evaluation Report,"

. transmitted via lettar ?-78137 from J. K. Fuller (PSC) to William ) Gammill (NRC), August 11, 1978. t I 14. R. L Tecese: (N?.0), Me: rancum :: W. J. Gamill, "Fuei Surveillance y Pol. icy--Applicati n t: Fort St.'Vrain," Decem:er 13, 1978. g I i i 15. R. L. Tedesco (NRO) Memorandum t: W. Gammill, "Fert St. Vrain Fuel Surveillance," February 15, 1979. l i g O 1

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15. Saf ety Analysis Ra;;:r: for F:rt St. Vrain Kelca:! Tes-Elements FTE-1 i

througn FTE-2, General At:=t: Raccr GL. -5494, Juna 30, :577. j 1 [ ? & i k o i t e g e a n ' Ii I f ,f. I i 4 l l i 6 i t I 1 a g t a f -g f t j t. e . g 4 t l tj. f-G t 8 8 a e I- - ~ ~ !

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