ML18348A736

Letter Results of Burnup Study

ML18348A736
Person / Time
Site:	Palisades
Issue date:	05/23/1978
From:	Hoffman D Consumers Power Co
To:	Ziemann D Office of Nuclear Reactor Regulation
References
Download: ML18348A736 (3)

Text

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• Power company General Offices: Z12 West Michigan Avenue, Jackson, Michigan 49201 , Area Code 517 788-0550 C')

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ES --i CJ Director, Nuclear Reactor Regulation 2:

Att: Mr Dennis L Ziemann, Chief Operating Reactors Branch No 2 US Nuclear Regulatory Commission Washington, DC 20555 DOCKET 50-255 - LICENSE DPR PALISADES PLANT - FISSION GAS RELEASES FROM FUEL PELLETS In your letter of November 29, 1976, you requested information concerning fission gas releases from fuel pellets with high burnups at the Palisades Plant. By letter dated February 14, 1977, we addressed item (a) of your request. The remaining items were not included in our power increase re-g_uest (Technical Specification Amendment No 31) as preYiously indics.ted.

The following is provided to complete our response.

The NRC fission gas correction, as described in the attachment to the November 29, 1976 letter, was applied to the release fractions calculated with Exxon Nuclear Company's fuel densification model (G.APEX) for burnups greater than 20,000 MWD/MTM. The increased moles of gas in the fuel rod re-sult in higher internal rod pressures at steady state operation. During a LOCA, the higher internal pressures result in earlier clad ruptures with significant changes in the ballooning characteristics of the clad. The*

effect of ballooning becomes important in the heatup analysis when the re-flood rate is less than one inch per second, at which point a steam cooli.ng model is invoked. During steam cooling, flow diversion around the rupture plane reduces the downstream steam flow and the heat removal rate from the clad, resulting in higher. Peak Cladding Temperatures (PCT). Above one inch per second, no heat transfer penalty is taken for subchannel flow blockage due to rod ballooning.

Table 1 sUillillarizes the effects of the modified fission gas release model on fuel rod performance during normal operation. Fuel average temperatures, rod pressures and moles of gas released are given as a function of peak pel-let burnup with and without the NRC correction. Peak pellet burnups up to and including the target peak pellet burnup for Batch D and Batch E fuels are considered. The internal rod pressures are well below the primary sys-tem operating pressure of 2060 psia for all cases.

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• For Batch D and Batch E fuels, the increased fission gas release predicted by the NRC correction results in higher PCTs than would have been predicted using Exxon Nuclear Company's approved models.

For. peak pellet burnups less than . 35,000 MWD/MTM with the NRC fission gas re-lease model, PCT does not exceed the 2,200°F LOCA limit for both D and E fuels.

However, for Batch E fuel, PCT was found to exceed the 2,200°F LOCA limit for a peak pellet burnup 45,000 MWD/MTM. To reduce PCT below 2,200°F,.the Linear Heat Generation Rate (LHGR) would have to be reduced by 6% from its Beginning-of-Life (BOL) value of 14.39 kW/ft. Thus, for Batch E fuel, the allowable LHGR would have to decrease linearly from 14.39 to 13.53 kW/ft for peak pellet burnup from 35,000 to 45,000 MWD/MTM, respectively, to ensure PCT 2_ 2,200°F.

The Batch*D exposure study was limited to the anticipated discharge peak pellet exposure of 35,000 MWD/MTM.

David P Hoffman Assistant Nuclear Licensing Administrator CC: JGKeppler, USNRC

TABLE 1 RESULTS OF BURNUP STUDY Steadi State Conditions (1) Rod Pressure Change in Exposure Gas Release Gas Released Fuel Average (MWD/MTM) Model (Gm Moles) TemEerature (°F) (Psia) PCT (°F)

. ENC BATCH E FUEL ( 2 )

0 GAPEX .0180 2325 994 0 (Ref'erence) 20,000 GAP EX .0203 1762 851 -117 35,000 GAPEX .0206 1765 921 - 54 45,000 GAPEX .0209 1767 989 - 55 35,000 NRC .0220 1773 983 - 12(3) 45,000 NRC .0269 1797 1259( 3 ) + 19 CE BATCH D FUEL( 4 )

0 GAPEX .0253 2247 907 0 (Ref'erence) 20,000 GAPEX .0264 1687 851 -150 35,000 GAPEX .0266 1688 917 -102 45,000 GAPEX .0267 1689 934 - 81 35,000 NRC .0274 1691 934 - 82 (l)Moles Predicted by GAPEX (+NRC Correction)

( 2 )LHGR = 14.39 kW/Ft Unless Otherwise Noted

( 3 )LHGR = 13.53 kW/Ft

( 4 )LHGR = 13.84 kW/Ft