ML20058L655
| ML20058L655 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 08/01/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20058L652 | List: |
| References | |
| NUDOCS 9008070373 | |
| Download: ML20058L655 (6) | |
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EPCLCEU.RE.3 SAFETY EVALUATICI: CY THE OFFICE Of, FU,C,L,EA.R,f,,EA,CT,0.R RECULATION SLTFORTI,H,G,,AT,Ep,0!iENT, p,0,,144, TO FACILITY OPERATING LICEhSE NO. DPR-77 AND-AllENDMENT NO.125..Tp, F,AC,1,LJT,Y,,CF,ER,A, TING LICENSE MO. DPR-79 TEtit!E!!EE YALLEY _A_U,Tp0,RJT,Y S_Ep,00,YAH HUC,LE,AR,,PL,A,NT,,, UNITS 1 (ND 2 DOCXET _NO,S,, 50,.3p7 AMD 50,-),28
1.0 INTRODUCTION
By letter dated ttay 4,1990, the Tennessee Valley Authority (TVA) proposed to n;odify the Sequcyah Nuclear Plant, Units 1 and 2, Technical Specifications (TSs). The' proposed changes are to revise Section 5.0, Design Features, and to add Surveillance Requirement 4.9.1.4 The changes would allow the licensee to increase the maxircurn fuel enrichment for fuel on the site from the current 4.0 weight-percent (w/o)to5.0w/oUranium(U)-235.
In support of these proposed charges to the TSs, TVA submitted by letter dated February 14, 1990, a criticality analysis to justify the proposed increase in the enrichment limit of fuel stored in the Sequcyah spent fuel pool storage racks to 5.0 w/o U-235.
l-The prcposed thonges Eculd allcw a fuel assembly with enrichmert greater than 4.0 w/o U-235 -and burnup less than 7500 MWD /MTU to be placed in locations in the spent fuel pool stcrage racM that face adjacent cells with water 01 fuel assemblies with at let.st 22,004 ND/MTU of burnup.
In its application, TVA also requested changes to the TSs to allow the substitution of Zircaloy-4 or stainless steel filler rods, or of open water channels, for fuel rods in fuel tssemblies. This request is still under staff review and will be the subject of a future evaluation.
The proposed changes do not increase the number of fuel assemblies currently allowed in the spent fuel or new fuel storage racks. The storage capaci'ty cf the spent fuel pool rertains limited to 1386 fuel assemblies and the center-l to-center distance between fuel assemblies in the spent fuel racks renains a 1
nominal 10.375 inches'. The storage of fresh fuel in the new fuel pit storage racks has.rct been reanalyzed and the maximum enrichment limit remains at 4.5 w/o U-235.
The reactivity analysis associated with these proposed changes is delineated below.
2.0 EVALUATION Each core reload is confirmed by TVA to meet all of the design criteria and to be within the bounds of the accident analysis presented in Chapter 15 of 9008070373 900801 PDR ADOCK 05000327 P
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the Sequoyah Final Safety Analysis Report (FSAR) by perforrnance of a reload.
safety analysis prior to fuel loading.
Revisions to this safety analysis for teplacing fuel assentlies may be trade after fuel loading. This analysis considers r;odifications to the plant design and any changes to fuel design, including inct esses in fuel enrichment, for the fuel to be burned during the operating cycle.
The perforrtance of the reload safety analysis ensures that i
the unit, with its specific core design and fuel enrichment, will opt. rate within the prescribed Sequcyah safety limits. 1 9 restricticn on core operation is idertified through the reload safety analysis process. Therefore, operation with this higher enrichment fuel will be justified for each fuel load and operating cycle.
2.1 -Criticality TVA has perforraed a criticality analysis to justify the storage of fuel assemblies in the spent fuel stct age racks at Sequcyah with a maxin.um enrichment of E.0 w/o U-235.
This analysis is an enclosure to TVA letter dated February 14, 1990.
The spent fuel storage rack at Sequcyah is a high density storage rack manufactured by Par, Systems Corporation. The design incorporates the use of the neutron pcison traterial Scral as a means of reducing the center-to-center spacing of the stcragt cells. The spent fuel storage cell consists of two concentric, square stainless steel tubes, seal welded at the ends. The Boral plateris located in the water-tight vcid existing between the tubes. The spent fuel is nortally stored in pool water containing at least 2000 ppm of soluble l
boren which results in a significant reduction in reactivity. However, for conservatisn, the spent fuel rack reactivity is calculated assuming that there is no soluble boren in the water.
The Secucyah spent fuel pool currently is limited to using Westinghouse Electric Corpct ation (Westinghouse) Standard (STD) 17x17 fuel assentlies enriched to less than 4.0 w/o U-235. The new analysis, which takes credit for the reacth tty decrease due to burnup of the stored fuel, evaluates the storage of Westinghcuse 17x17 VANTAGE SH (V5H) fuel assemblies with initial enrichments of up to 5.0 w/o U-235. The analysis is applicable to both the L
STO and V5H fuel assemblies since the V5H fuel results in a higher reactivity-than the STD fuel fcr a given enrichtent and, therefore, is conservative for the STO fuel.
I The analysis uses KEN 0, a three-dimensional tiente Carlo theory computer code for reactivity calculations.
Fewever, since Kell 0 dces not have the capability to deplete fuel asserblies, the CASit0 code was used for burnup-dependent reactivity calculations.
CASi'0 is a two-diniensicnal integral transport theory code. -tleutron cross sectict.s were based on data frota the Ef;DF/B-IV cross secticn library. The anclytical methods and rredels were benchmarked against experimental data with characteristics similar to the Sequoyah spent fuel pcol racks ar.d were fcund to adequatcly reproduce the critical values. The staff concludes that these nethods and redels are acceptable, The design basis for preventing criticality cutside the reactor is that, including ur.cer'.ainties, there is a 95 percent probability at a 95 percent ccnfidence level (i.e.
95/95 probability / confidence) that the effective tultiplication factor (k-eff) of the fuel assembly array will be no greater
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-1 than 0.95. A full, loading in the Sequoyah spent fuel storage recks of fresh fuel assenblies enriched to greater then 4.0 w/o U-235 would violate this 1
bcceptance criterion. Therefore, credit was taken for the reactivity decrease due to bcrrup in order to load V5H assemblies with initial U-235 enrichments greater than 4.0 w/o. Eased en this, an asserably enriched to 4.0 w/c at zero turnup was found tc have a reactivity equivalent to a 5.0 w/o assen.biy with accumulated burnup-of 6750 MWD /MTV.
Therefore, once a 5.0 w/o fuel assembly
.accuttulates at least 6750 MWD /liTU of burnup, it can be stcred anywhere ir. the spent feel storage racks.
This equhaler.t (nrichment concept has been widely used in spcrt fuel rtck analyses and is acceptable, i
-In order to stcre fresh 5.0 w/o fuel with no accumulated burnup in the spent fuel racks, restricticns nust be placed c.r: alhetle storage configurations which (ffccthcly increase the center-to-center spacir.g of the assen.blies.
In Sequcyah, this is acccnplished by requiring a checkerboard configuration for cny fuel asstnblies with initial enrichment greater than 4.0 w/o U-235 and burnup less than C750 MWD /MTV.
i TVA has analyzed the reactivity cf the spent fuel racks for an infinite array of 5.0 w/o frcsh fuel 1catcd in a checkerboard ccnfiguration alternating with 5.0 w/o fuel having accumulated burcup cf 20,000 MWD /tiTU.
The resulting k-eff i'
was 0.94416 including all apprcpriate biases and uncertainties at a 95/95 prob-ability /ccr.fidence level. This netts the t'P.C acceptance criterion ar.d is, therefore, acceptable. Calculatiens also showed that checkerboarding fresh 5.0 w/o fuel assemblies with adjacent cells filled with unborated water (i.e., vacant) dces not increase the reactivity of the system. Therefore, e-Westinghouse STD or V5H 17x17 fuel asserrbly with enrichment greater than 4.0 w/o, but less than 5.0 w/o, and burrup less than 6750 ftWD/MTV may be placed in spent fuel stcrage rack locations that face adjacent cells filled with water or fuel asserrblies with at least 20,000 MWD /tiTV of bumup.
Plant procedures will te relied upor. te deteiniir.c whether or not e., assen.bly ratisfies the burr.up criterion.
In order te allow for uncertainties in the deterrination cf assembly burr.up, the calculated exposure limits will be inct cased by 10 percent.
For exan.ple, the procedures will reflect a criterion cf 22,000 MUD /MTU for the asserblics ibat can be placed adjacent to fresh fuc1 assentlics which exceed 4.0 w/o enrichmect.
The staff finds this.conservatisin appropriate and acceptable.
It is possible to postulate ever.ts which cculd lead to an increase in stcrage rack reactivity, such as a drcpped fuel essembly or misplaced fuel assemblies.
However, for such cvents, credit rray be taken for the 2000 ppm of boron in the spent fuel pcol water by applicetion of the dcuble contingency principle of At;SI in6.1-1975. This states that one is nct required to assure two unlikely, independent, concurrer.t n ents tc provide for protection against a criticality accident.
The staff concludes that this is acceptable since TS 3.9.1 requires tttt the boren concentraticn of the refueling canal (and, therefore, the spent fuel pool) be at 1 cast 2000 ppm during refueling operations.
In additien, prcposed Surycilics.cc Cequirerrent (SP) 4.9.1.4 would require the boron concen-tration ir, the spent fuel pcci to be determined to be no less than 2000 ppm
s !
at lecst once every 72 bcurs ('urir.g fuel movement until the configuration of the assettlies in the stcrage iacks is verified to be correct. The reductior' in k-eff reused by tto Lctited wter core thtn offsets any reactivity additico caused by credibit accidents. Therefore, this change is~acccptable.
2.2 Technical Sp,c,if,ication, Changes Changes to the T!s were proposed in crder to store fuel with enrichcier.ts greater than 4.0 w/o 11-225 in the spent fuel Icol. The proposed th60ges to TS 5.6.1.1. including adding a stattner.t that cry fuel asserbly with enrichtent Steater than 4.0 w/o and burr.Lp less than 7500 PWD/tiTV may be placed in locations in the spent fuel stcrtg t acks providtd that they face adjectr.t cells filitt with weter, er fuel asstn,blies v.ith et least 22,000 MWD /MTV of burnup.
The burrup requiruer.ts discund Ltc.vc have been censervativcly increased by 10 rct(thi ircu GO l.hD/I'Tl' to 7500 PWD/HTU tc allow for uncertainties in the detcrtination cf asserbly hurro;. The in ir.Ln l'-235 enrichtent _ cf stored fuel shall tc liuited to 5.0 w/c.
refcrence to the 1.42 percer.t c' elta k/k uncer-tainty allowance has bcen ircrecstd tu S.Cf pcreent delta L/k to conform to the revised criticality ar.c.bsis for spect fuel stcrage. These prcposed changes to TS 5.6.1.1 are consistent with the criticality analysis and, therefore, are i
acceptabic.
A change has been proposed to TS 5.3.1 to increase the maxitum enrichment cf icicad fuel from 4.0 to 5.0 w/o U-235. This is consistent with the criticality analysis and therefore, is accepteble.
Althcush this is acceptcble frco a spent fuel storage viewpoint, plant operation using the higher entichcd fuel rutt be den.onstrated te be acceptable ty a cycle specific relcad safety evaluaticn prior to each fuel loading.
TVA pretesed to ac'd SF..t.9.1.4 tc> require the bortn concentration in the spe t fuel pec1 tc tc grtoter than cr ec,ual to 2000 ppm at least once per 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> during_ fuel acverent and ortil the. ccr. figuration cf the asserblies in the stcrtg ittks is serified to cceply with the criticality loadir.g criteria trecified in TS 5.6.1.1.c.
This proposed change is consister.t with the double ccntingency prir.ciple of ANSI !!16.1-1975 and with the criticality analysis, and, therefcre, is acceptchie.
Tre. prcrosed change to TS 5.6.1.2 is to delete the statu ont that the rew fuci enrichrent is limited to 4.0 w/o. The criticality ar.alysis supports a new fuel er.richtent of 5.C w/c; therefore, the proposed change is tcccptabic.
Because the stcrage of new fuel in the r.tw fuel stcrage tanks has not been reenalp c.d for higher enrichcd fuel, the maximum enrichraent lictit for the new a
fu i stotest tcnks rereins at 4.5 w/o in TS 5.6.1.2.
2.3 A ccident_A,nalysis in its application, TVA stated that each core reloac' will te within the bounds of each accident analysis presented in Chapter 15 of the Sequoyah FSAR.
These acciderts were evaluated by the staff cnd the consequer.ces were fcund accept-able in Section 15 of NUREG-0011 dated Pfarch 1980, and of Supplement 2 to NUREG-0011 dated August 1980. The NUREG-0011 and its supplerrents were the a
safety evaluaticos that iictnsed Sequoyah, Units 1 and 2.
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-5 The activity inventory in the. fuc1 may increase for long-lived radionuclides of concern as the fuel enrichment increases to 5.0 w/o U-235 and burnup increases to 60,000 MWD /MTU, but, the inventories of short-lived fission products wil' rcirain essentially the same.
It shculd be noted that tha fuel integrity shculd net be cffected by the higher entichment and extended burnup of the fuel.
Therefore, there should not be a significant change to the c' eses calculated for the design basis accidents.
s In reviewing the dose estimates for accidents, the staff agrees with TVA's ccnclusion that increasing the fuel enrichment to 5.0 w/o does not cause the consequences of. the evaluated accidents to 90 tcyctd acceptable values. The' effect of increasing the-feel entichment to 5.0 w/o and burnups to 60,000 MWD /MTU i
would be to only increase the calculated thyroid dose for the postulated fuel handling accident by about 205. There would be no effect on the estimated consequerces of other postulatcd design basis accidents, which scale with power icvel rather than fuel enrichment or burnup. This is documented by the staff in the Environmental Assessrent and Findings of No Significant Impact for Extended Burnup Fuel Use in Comercial Light Water Reactors (LWRs)
(Federal Register, 53 FR 6040 February 29,19EE). Therefore, the staff concludes that the dose conseq,uences for dcsign basis accidents at Sequoyah for enrichrents up to 5.0 w/o and burnups up to 60,000 MkD/HTU are acceptable.
?.5, Conclusion I
4 9
Based on the above evaluation, the staff concludes that the Sequoyah spent fcel stcrage recks can acconn.odate L'estinghouse STD or V5H 17x17 fuel i
essemblies with maximum enrichments of up to 5.0 w/o U-235 and the proposed changes to the TSs to allow up to 5.0 w/o enriched fuel are acceptable.
3.0 ENVIRONMENTAL CCNSIDERATION i
Pursuant to 10'CFR 51.21, 51.32, 51.35, an environmental assessrrent and I
findingof r.o significant impact has been prepared and published in the Federal Register on July 31, 1990 (55 FR 31112).
Accordingly, based upon the environ-rcr.tal cssesstent, the Commission has determined that the issuance of these amendments will not have a significant effect on the quality of the human environment.
4 '. 0 CONCLUSION i
The Corrnission made a proposed detcrmination that the amendment involves no significant hazards consideration which was published in the Federal Register l
(55 FR 24005) on June 13, 1990 and consulted with the State of Tennessee.
No public corrents were received and the State of Tennessee did not have any comments.
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The staff has concluded, based cn the c(nsiderations discussed above, that:
(1) there is aasor:able assurance that the health and safet will not be endengered by operction in the proposed manner,y of the public and (2) such activities will be conducted in cerpliance with the Commission's rcgulations, ar.d the issuance ofathe ar,endn.ents will not be inimic61 to the commen defense and security ncr to the health ar.d safety of the public.
Principal Contritutors:
L. Kopp cnd J. Denchew Dated: August 1,1990 1