ML20151A656
| ML20151A656 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 11/26/1976 |
| From: | Schwencer A Office of Nuclear Reactor Regulation |
| To: | Groce R YANKEE ATOMIC ELECTRIC CO. |
| References | |
| NUDOCS 8011030825 | |
| Download: ML20151A656 (6) | |
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Yankee Atomic Electric Company.
Eji a ATTH: Mr. Robert H. Groce Licensing Engineer 20' Turnpike Road Westboro, Massachusetts - 01581 THIS DOCUMENT CONTAINS' Gentlemen:
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YANKEE-ROWE
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The !!RC' staff has recently obtained information which indicates that fission cas releases from fuel pellets with high burnup may be under-predicted by' the current industry nodels for fission gas release.
As a result, actual end-of-life fuel rod pressure may be higher than that which was considered in the safety analysis for your facility.
Although this situation does not 1ead us to suspect that fuel design limits have been or are currently being exceeded at your facility, the potential nay exist 'for such ~an occurrence in the future as higher fuel burnuns are reached. Consequently, you are recuested to evaluate the effects of increased fission cas releases on the safety analysis for your facility in accordance with the schedule specified below.
If tre estiraated date on which any fuel rod in your facility will recch a local exposure (hurnup) of 20,000 l'co.twett-days per metric n'
ton of Uraniun (ru0/tU) is sooner than June 1,1977, provide t%
followin-) information within 30 days of receipt of this letter.
(If this estimated d3te is later than June 1,1C77, your responm nay be sub1ittoc' within 90 days of receipt of this letter).
a.
The estincted date on which any fuel rod in your facility will reach a. local exposure (burnuo) of 20,000 i'egawatt-cays por cetric ton of Uranium (!n!D/tll).
b.
Usinc the correction technioue described in the attached enclosure, nodify the fission cas release nodel in thc' f
. thernal perfor. ance code for the fuel in your facility and 7
calculate the fission cas releese, fuel rod pressure, fuel temperature, etc. for burnups un to and ircluding the
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target peak-rod burnup.
Provide a comparison of the results of your calculations with those obtained using.
In) the uncorrected fission gas release nodel.
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Describe the ' impact (if any) of larger fission gas releases
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on the LOCA analysis and other safety analyses for your
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facility.
d.
If internal' fuel rod pressures, as calculated using the above-nontioned fission gas ralease correction, are predicted to exceed the nominal system pressure for your facility, provide
-the date that this is anticipated to occur and discuss the implications of operating under both nomal and accident conditions with fuel cladding tensile stresses.
- We have advised all U. E. f ue; manufacturers by separate correspondence that this infomation request is being sent to licensees of operating power reactors.
In our letter to the fuel manufacturers, we have indicated.that bounding calculations for approcriate plant ' groupings
- would be. acceptable.
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This request inr generic infomation was approved by GA0 under a L':
blanket clearance number B-180225 (R0072); this' clearance expires 1
July 31, 1977.
Three signed originals and 40 cooies of your response vill be required.
Sincerely, Is Original signed by A. Schwencer, Chief Operating Reactors Branch (1 Division of Operating Reactors
Enclosure:
DISTRIBUTION U
Ournup-Derandent Correction Dockrt 01&E(3)
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for Fiss'an Gas Release NRC PDR ACRS(16)
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b Recent ANS standards activities (1-1 lead us to believe that high We burnup gas releases are underpredicted by current LWR industry models.
have previously (1) looked for a ournup dependence and found none for LWRs in the burnup range from 400 to 18,300 mwd /tu.
Thus, we incorrectly pre-sumed that the strong burnup dependence exhibited by LMFBR data (1) was not representative of LWR fuels during their shorter burnup lifetimes.
data mentioned by Westinghouse to the ANS group (2)
New high burnup UD2 and discussed with the NRC (6) 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 This assumption, however, dependence is the same in LWR and LMFBR oxide fuels.
will be applied only in the high burnup region above 20,000 mwd /tU since the industry models have been checked with the data base (1) ranging to-current 18,300 mwd /tU.
t l
The following correction has been derived to give an increased release f
fraction F'(Bu,T) as a function of burnup and the uncorrected ralease Burnup Bu is the local burnup in megawatt-days per cetric prediction F(T).
ton of uranium (mwd /tU), and T, which is not an explicit variable in the ccrrection, is temperature.
(1 - exp(-0.436 x 10 "(Bu-20000)))
(1)
F(T) + [1-F(T))
F'(Bu,T)
4
. Figure 1 shows schematically how this correction would be applied to In the event the GAPCON gas release model, which is independent of burnup.
an existing model contains a burnup dependence, F(T) would be the predicted release frac lon under the temperature cosiltions of interest, but with the e
burnup variable set equal to 20,000 Mh'd/tU.
Equation 1 is a replication of the Dutt and Baker (1) LMFBR correla-tion, which is
'.a updated version of the correlation in Ref. 5 Equation 1 eerived by assuming a conven ent functional form depending on F(T) and i
Bu and fitting it to the Dutt and Baker curves using a non-linear regression er procedure. No conservatism has been intentionally added.
Figure 2 shows how closely Eq. 1 reproduces the Dutt and Baker curves.
References
- 1. '
R. O. Meyer (NRC), cemorandum to P. S. Check, " Summary of Meeting of ANS-5.4 Working Group on Fuel Plenum Gas Activity," February 25, 1976.
R. O. Meyer (NRC), memorandum to P. S. Check, " Summary of ANS-5 1 l
2.
(Decay Heat) and ANS-5.4 (Fission Gas Release) Activities," June 22, 1976.
R. O. Meyer (SRC), memorandum to P. S. Check, " Summary of ANS-5.4 3
Meeting on Fission Gas Release," October 6, 1976.
UO C. E. Beyer and C. R. Hann, " Prediction of Fission Gas Release frc 4.
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. J5, 198 (1972).
6.
R. O. Meyer (NRC), memorandon to P. S. Check, " Summary of Meeting with Westinghouse on Fuel Rod Pressures," September 22, 1976.
D. S. Dutt and R. B. Baker, "Siex:
A Correlated Code for the Prediction 7
of Liquid Metal Fast Breeder Reactor (LMFBR) Fuel Tnermal Performance,"
Westinghouse Hanford report, HEDL-TME 74-55, June 1975
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