ML20215B188

Safety Evaluation Re Util 860902 Submittal of CEN-335(c)-P, Waterford Unit 3,Cycle 2,Shoulder Gap Evaluation Rept, in Response to License Condition 2.c.7.Shoulder Gaps in All Fuel Acceptable Through Cycle 2

ML20215B188
Person / Time
Site:	Waterford
Issue date:	12/08/1986
From:	Office of Nuclear Reactor Regulation
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Shared Package
ML20215B089	List: ML20215B087 ML20215B188
References
NUDOCS 8612120067
Download: ML20215B188 (3)

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ENCLOSURE 1

SAFETY EVALUATION OF SHOULDER GAP REPORT LOUISIANA POWER AND LIGHT COMPANY WATERFORD STEAM ELECTRIC STATION, UNIT 3-

DOCKET NO.'50-382

1.0 INTRODUCTION

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License Condition 2.c.7 to Facility Operating License NPF-38 for Unit 3 of'the Waterford Steam Electric Station requires justification that suf-

-ficient shoulder gap clearance will be available in all existing fuel assemblies to be irradiated in the next cycle of operation (Cycle 2).

Pursua'nt to this requirement, Louisiana Power and Light (LPL), the licensee, has submitted the.Waterford Unit 3, Cycle 2, Shoulder Gap Evaluat'onreport,CEN-335(c)-P,byletterfromK.W. Cook _(LPL)to Georg'e W. Knighton (NRC) dated September 2, 1986. The evaluation pre-sented in CEN-335(c)-P is based on an empirical evaluation of data

. obtained from Arkansas Nuclear One Unit 2 (ANO-2) and San Onofre Nuclear Generating Station Unit 2 (SONGS-2).

2.0 EVALUATION The'Waterford-3 Cycle 2 core will be comprised of 61 Batch B, 64 Batch C, and 92 Batch D 16 x 16 fuel assemblies. The Batch B and C assemblies i will have one cycle of previous exposure and the Batch D assemblies will be fresh (unirradiated).

In the licensee's prediction of minimum available shoulder gaps at

end-of-cycle 2 (EOC 2), several conservatisms were applied to the analysis. The analysis assumed the following

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- 1. - The nominal initial. design gap at the beginning of life pre-service condition was reduced to' account for uncertainties arising

- from component dimensional tolerances, elastic compression of the guide tubes,'and differential thennal expansion between fuel . rods and guide tubes. This is conservative and acceptable.

2. The minimum predicted guide tube growth was selected as the growth associated-with the lower 95/95 probability / confidence level measured SONGS-2 growth rate through two. cycles.and the high end of the fluence range. No credit was taken for additional guide tube growth in Waterford-3 due to its' higher fuel-rod fluence than SONGS-2. The use of SONGS-2 data to predict Waterford-3 data is acceptable.since both contain fuel assemblies with the same guide tube dimensions, material, and holddown spring forces and are, therefore, expected to have the same guide tube growth rates.

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3. . The limiting fuel rod growth rate was observed on 16 x 16 Batch C

! fuel in ANO-2 and this rate was assumed to be bounding for Waterford-3 i.-

. fuel rods. The Batch C fuel rods exhibited essentially a linear gr'cwth rate while all the other fuel types inspected have exhibited a decrease in fuel rod growth rate at increasing exposures. Although l the decreasing growth behavior is expected for the Waterford-3 fuel, I

the more conservative linear growth rate of the limiting ANO-2 Batch C fuel was used in the shoulder gap justification for Waterford-3 Cycle 2 and is, therefore, acceptable.

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An empirical evaluation 'of ANO-2 and SONGS-2 data based on the above-mentioned assumptions has demonstrated that the shoulder gaps in all the Waterford-3 fuel, including the unmodified Batch B design, are acceptable through Cycle 2, Additional assurance of the shoulder gap adequacy of the Batch B fuel was obtained using the SIGREEP model. Although SIGREEP has not been officially approved by the NRC, comparisons of measured Cycle 2 shoulder gap changes in SONGS-2 Batch C fuel with SIGREEP predictions showed that the model can conservatively predict shoulder gap changes through Cycle 3 of SONGS-2. The SIGREEP evaluation of the unmodified Batch B assemblies for Waterford-3 showed acceptable shoulder gaps for fuel rod fluences well in excess of the peak EOC 2 rod fluence.

3.0 CONCLUSION

The staff has reviewed the Shoulder Gap Evaluation report, CEN-335(c)-P, submitted in response to License Condition 2.c.7 for Waterford-3. Based on the discussed technique, which employs an existing measured data base, as well as on the additional evaluation using the SIGREEP analytical model, the staff concludes that the shoulder gaps in all the Waterford-3 fuel are acceptable through Cycle 2. The report also satisfies License Condition 2.c.7 to the Waterford-3 facility operating license.