ML19319E251
| ML19319E251 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 11/29/1976 |
| From: | Reid R Office of Nuclear Reactor Regulation |
| To: | Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| References | |
| NUDOCS 8004010526 | |
| Download: ML19319E251 (7) | |
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- 2 November 29, 1976 DISTRIBUTION:
- 0:chet No. 50 312-ORB #4 Rdg.
s V. Stello T. J. Carter 0 [], n a ~+k R. Reid U [f
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R. Ingram (h r 3O. /
[7 Sacramento Punicipal Utility District V. Rooney
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0 ATTU: ' fir. J. J. Fa tti :ce Jo Guibert Assistant Ger.eral.k.anager Attorney, OELD y
J and Chief Engineer 0I&E(3) f.
6201 S Street D. Eisenhut P. O. Cox 15930 T. B. Abernathy Sacramento, California 95a1,1 J. R. Buchanan AR ACRS (16)
.Centlenen:
Gray File RF.: ' RANCHO SECO NUCLEM GENEP.ATING STATION The'!P.C staff has recer.tly obtained infomation which indicates that fission gas releases fron fuel pellets trith hich burnup r'ay oo under-
. predicted by the current industry models for fission gas release
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As a result, actual end-cf-life fuel roc pressure nay bo higher than that which was consicered in the safety analysis fctr your facility.
Although this situation does not lead us to suspect that fuel design If.cits have been or are currently being exceeded at your facility, the potential nay exist for such an occurrence in the future as higher fuel burnuas are reached.
Consenuently, you are requested to evaluate the effects of increased fission cas releases on tiie safety analysis for ynur facility in accorcance with the schedule specified below.
-If the estinatea date or which any fuel rod in your f9cility vill reach a local exoosure INrnut) of 20,000 Meca,'att-riayt per natric ton of Urenir: (10.2/t9) is sooner than Junc I,1977, provido the f'.lioving infor1ation -i t"in 30 rays of receint of this Ic'ter.
-(If this estinated date is later than June 1,1977, your rescon o ncy ce sub.?.itted withir % days of receipt of tt:is letter),
Tric-estir:ated riate on vnich any fuel red a.
in your facility will reach a local exres*;re (curn:m) of 20,0.iu f:eca.mtt-sys her netric ton of Uraniu1 (ti"J/tt ).
-b.
Usinr the correctly technicae descriW in the ?.tt4ched c9 clos ' c, nodify t e ' fi';;ica ps relem no@l in the therNI wrforma :ce cme for th fuel ir yaar facility and C3lcul?te the fitSicN c':0 rel0Cse, fuel roo pressure, tgel l9 peratur?, etc. _ fe" Ourrirlps Up to an; incluffin?
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-1 target peak-rod burnup. Provide a conp3rison of the results of your calculations with those obtained using the uncorrected fission pas release model.
c.
Describe the ir'oact (if any),of larger fission pas releases on the. l.CCA analysis and other 53fety analyses for your facili ty.
d.. If internal fuel rod pressures, as calculated using the aoove-nontioned fissio.n gas release correction, are predicted to exceed tbs no'.'inal. systen pressure for your facility, ~ provide the date that this is anticipated to occur and discuss the inplications of operating under both normal and accident
. conditions with fuel claddine tensile stresses.
I!e have advised all 0. 5. fuel manufacturers by separate correspondence i
that this ir.formtion recuest is being sent to licensees of operating power reactors.
In our letter to the fuel nanufacturers, we have indicated that boundine calculations for appropriate plant groupinos would be acceptable.
This renuest for generic information was approved by GAD under a blanket cledrance nunber B-180225 (20072); this clearance expires July 31,1977. Three sicned originals and 40 copies r.,f your resoonse will be reauired.
Sincerely, Pobert l!. Poid, Chief Operating 4eactors 3 ranch 44 Division of Operatino Reactors Enclusore:
turnup-Dependent Correcticn for Fission Gas Release.
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Sacramento: 'eun c pal Utility District-ii
- cc: David S. Kaplan', Secretary and General ' Counsel
- m 6201 S Street
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Post ~ 0ffice Box 15830
-Sacranento, California 95813 Business and P,unicipal Department i
Sacranento City-County Library 828'I Street-Sacranento, California 95814 4
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Enclosure.1 Recent ANS standards activities (1-2) lead us to believe that high
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burnup gas releases are underpredicted by current LWR industry models. We s;
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have previously (1) looked for a burnup dependence and found none for LWRs M
in the burnup range from 400 to 18,300 mwd /tU.
hus, we incorrectly pre-sumed that the' strong burnup dependence exhibited by LMFBR data (5.) was not representative of LWR fuels during their shorter burnup lifetimes.
New high burnu'p UO2 data mentioned by Westinghouse to the ANS group (2.)
and discussed with the NRC (1) show, however, that the sharp release increase seen in LMFBR data occurs also in LWR fuels.
Therefore, in the absence of a complete analysis of high burnup LWR UO2 data, we will assume that the burnup dependence is the same in LWR and LMFBR oxide fuels. This assumption, however, will be applied only in the high burnup region above 20,000 mwd /tU since'the current industry models have been checked with the data base (1) ranging to 18,.300 mwd /tU.
The following correction has ';een derived to give an increased release fraction F'(Bu,T) as a function of burnup and the uncorrected release-prediction F(T)..Burnup Bu is the lo al burnup in megawatt-days per metric ton of uranium (mwd /tU), and T, which is not an explicit variable in the correction,'is temperature.
(1 - exp[-0.435 x 10 (Bu-20000)])
F'(Bu,T) : F(T) i- (1-F(T)]
(1)
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, Figure 1 shows schematically how this correction would be applied to the GAPCON gas release model, which.is independent of burnup. In the event i+:
an' existing codel contains a burnup dependence, F(T) would be the predicted
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release fraction under the temperature conditions of interect, but with the
'nup variable set equal to 20,000 mwd /tU.
Equation 1 is a-replication of the Dutt and Baker (1) LMFBR correla-lon, walch'is an updated version of the correlation in Ref. 5 Equation 1 was'derkved'byassumingaconvenientfunctionalformdependingonF(T)and Bu and fitting it to the Dutt and Baker curves using a non-linear regression
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Fi ure 2 shows procedure. No conservatism has been intentionally added.
5 how closely Eq. i reproduces the Dutt and Baker curves.
References 1.
-R. C. Meyer (NRC), cemorandum to P. S. Check, " Summary of Meeting of
'ANS-5.4 Working Group on Fuel Plenum Gas Activity," February 25, 1976.
2.
R. 0..Meyer (NRC), cemorandum to P. S. Check, " Summary of ANS-5.1 (Decay. Heat)'and ANS-5.4 (Fission Gas Release) Activities," June 22, 1976.
3 R. O. Meyer (NRC), cemorandum to P. S. Check, " Summary of ANS-5.4 Meeting en Fission Gas Release," October 6, 1976.
4 C. E..Beyer and C. R. Hann, " Prediction of Fission Gas Release from UO Fuel," Battelle report, BNWL-1875, November 1974.
5 D. S. Dutt, D. C. Bullington, R. B. Baker, and L. A. Pember,
'"A Correlated Fission Gas Release Model for Fast Reactor Fuels," Trans.
Am. Nucl.~~ Soc. 15., 193 (1972).
6.
R. C..Meyer (NRC), ce=orandum to P. S. Check, " Summary of Meeting with
~ Westinghouse on Fuel Rod Pressures," September 22,.1976.
.7
- 3. S. Dutt and R. B. Baker, "Siex:
A Correlated Code for the Prediction-of Liquid Metal Fast Breeder Reactor (LMFBR) Fuel Thermal Performance,"
WestinEnouse Hanford report,:HEDL-TME 74-55,' June 1975 pw
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