L-97-313, Provides Notification of Error Discovered in Use of Acceptable SBLOCA Evaluation Model,Which Calculates Cooling Performance of Plant Eccs.Rept Submitted Per 10CFR50.46
| ML17229A555 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 12/17/1997 |
| From: | Stall J FLORIDA POWER & LIGHT CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| L-97-313, NUDOCS 9712230078 | |
| Download: ML17229A555 (4) | |
Text
CATEGORY 1 REGULA Y INFORMATION DISTRIBUTI
, YSTEM (RIDS)
'ACCT'SSION NBR:9712230078 DOC.DATE: 97/12/17 NOTARIZED: NO FACIL:50-335 St. Lucie Plant, Unit 1, Florida Power
& Light Co.
AUTH.NAME AUTHOR AFFILIATION STALL,J.A.
Florida Power
&. Light Co.
RECIP.NAME RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)
DOCKET ¹ 05000335
SUBJECT:
Provides notification of error discovered in use of acceptable SBLOCA evaluation model, which calculates cooling performance of plant ECCS.Rept submitted per 10CFR50.46.
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Florida Power & Light Company, 6351 S. Ocean Drive, Jensen Beach, FL 34957 December 17, 1997 L-97-313 10 CFR 50.46 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Re:
St. Lucie Unit 1 Docket No. 50-335 Error in the Application ofSBLOCA Evaluation Model; 30Da 10 CFR50,46Re ort Ref:
(1) Report EMF-96-176, Revision 1, St. Lucie Unit 1 Small Break LOCA Analysis with 30%
Steam Generator Tube Plugging: Siemens Power Corporation; December, 1996 (Docketed as enclosure to FPL letter L-96-333, December 20, 1996).
(2) Report EMF-1987, Revision 1, St. Lucie Unit 1 Small Break LOCA Analysis With Asymmetric HPSI Flow: Siemens Power Corporation; December, 1997.
This report is submitted pursuant to 10 CFR 50.46(a)(3)(ii) to provide notification ofan error discovered in the use of an acceptable small break loss ofcoolant accident (SBLOCA) evaluation model which is employed to calculate cooling performance of the St. Lucie Unit 1 emergency core cooling system (ECCS).
The error involved the non-conservative assumption of symmetric safety injection flow throughout the event, and led to lesser values ofpeak cladding temperature (PCT) than should have been calculated in the SBLOCA analysis ofrecord (Reference 1). Specifically, it was assumed for the analysis that 1/4 ofthe total high pressure safety injection (HPSI) flow is distributed to each ofthe four reactor coolant system (RCS) cold legs.
The limitingbreak size was determined to be 0.1 ft'hich yielded a calculated PCT of 1804 'F.
In response to an industry operating experience feedback issue involving HPSI flow during accident mitigation, FPL performed a plant specific evaluation and determined that asymmetric flow distributions may occur in the St. Lucie Unit 1 HPSI system which could result in more safety injection flow(than was assumed) to be released from the RCS break during a LOCA event.
The amount of asymmetry was calculated to be from 1% to 2%, indicating that less than the previously assumed 75% oftotal HPSI flow would be available for core cooling. For the SBLOCA,,the depth ofcore uncovery would be greater than previously calculated and as a result, the assumption ofsymmetric HPSI flow is,non-conservative.
The SBLOCAwith 30% steam generator tube plugging was re-analyzed for St. Lucie Unit 1 (Reference 2), and the analysis was performed with an asymmetric distribution ofHPSI flowto the cold legs. The highest flowdelivery (approximately 26% ofthe HPSI total mass fiowrate) was assigned to the broken cold leg to conservatively model the loss ofHPSI flow out ofthe break.
The analysis was performed using the revised guidelines that force the broken loop seal to remain plugged, and SBLOCAbreak I
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St. Lucie Unit 1 Docket No. 50-335 Error in the Application ofSBLOCAEvaluation Model; 30Da 10 CFR 50.46 Re ort 4
L-97-313 Page 2 of2 spectrum calculations were performed for break sizes of.04,.05, and 0.1 ft~. Due to the reduced total HPSI flow available for recovery of core inventory, the size of the limiting break changed from the previously identi6ed value of0.1 ft'o.05 ft', which yielded a calculated PCT of 1953 'F. Although the PCT increase of 149 'F is significant as defined in the regulation, the analysis demonstrates that all 10 CFR 50.46 criteria are met for the limitingSBLOCA case.
The results ofthis complete re-analysis will be documented as the SBLOCA analysis ofrecord for St. Lucie Unit 1.
It should be noted that the limitingLOCAfor St. Lucie Unit 1 ECCS cooling performance remains the large break (LBLOCA). Please contact us ifthere are any questions.
Very truly yours, J. A. Stall Vice President St. Lucie Plant JAS/RLD cc:
Regional Administrator, Region II, USNRC.
Senior Resident Inspector, USNRC, St. Lucie Plant.
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