ML112580525

Davis-Besse Nuclear Power Station, Unit No. 1 - Review of 30-day Notification Report Regarding Changes to an Emergency Core Cooling System Evaluation Resulting in a Peak Cladding Temperature Difference in Excess of 50 Degrees Fahrenheit

ML112580525
Person / Time
Site:	Davis Besse
Issue date:	09/22/2011
From:	Michael Mahoney Plant Licensing Branch III
To:	Allen B S FirstEnergy Nuclear Operating Co
mahoney, m NRR/DORL/LPLIII-2 415-3867
References
TAC ME4780
Download: ML112580525 (3)

Text

UNITED NUCLEAR REGULATORY WASHINGTON, D.C. 20555*0001 September 22, 2011 Mr. Barry S. Allen Site Vice President FirstEnergy Nuclear Operating Company Davis-Besse Nuclear Power Station Mail Stop A-DB-3080 5501 North State Route 2 Oak Harbor, OH 43449-9760 DAVIS-BESSE NUCLEAR POWER STATION, UNIT NO.1 -REVIEW OF 30-DAY NOTIFICATION REPORT REGARDING CHANGES TO AN EMERGENCY CORE COOLING SYSTEM EVALUATION RESULTING IN A PEAK CLADDING TEMPERATURE DIFFERENCE IN EXCESS OF 50 DEGREES FAHRENHEIT (TAC NO. ME4780)

Dear Mr. By letter to the U.S Nuclear Regulatory Commission (NRC) dated September (Agencywide Documents Access and Management System (ADAMS) Accession ML 102530281),

supplemented by letter dated December 17,2010 (ADAMS Accession ML 103610312), FirstEnergy Nuclear Operating Company (FENOC, the licensee) reported error correction discovered in the emergency core cooling system (ECCS) evaluation that affects the peak cladding temperature (PCT) calculation at the Davis-Besse Nuclear Station, Unit No.1 The letter dated September 2, 2010, was submitted to satisfy the requirements of Title 10 of Code ofFederal Regulations (10 CFR), Paragraph 50.46(a)(3)(ii), which requires reporting of calculated PCT change in excess of 50 degrees Fahrenheit (OF). The reported error was estimated 225 OF increase in PCT for a postulated small break The intent of the 10 CFR 50.46(a)(3)(ii) reporting requirement is to enable the NRC to the safety significance of errors and changes identified in ECCS evaluation models, and to appropriate action if the NRC staff determines that the ECCS evaluation models do not applicable regulatory Based on the letter dated September 2, 2010, the NRC staff was made aware of a error (greater than 50 OF) in the AREVA ECCS evaluation model that is applied to Babcock Wilcox (B&W) nuclear steam supply systems (NSSS), and is applicable to DBNPS. accounting for the error, the corrected PCT for DBNPS was calculated to be 1780 OF. temperature is compared against the acceptance criterion specified at 10 CFR 50.46 which requires the predicted PCT to remain below 2200 The letter dated September 2,2010, did not contain sufficient information to enable determination of the safety significance of the error, as described above. Based on the staffs concerns regarding the safety Significance of the error and the adequacy of the evaluation model, a request for additional information was sent to the licensee. The dated December 17, 2010, provided additional detail regarding the axial power shapes B. in the acceptable evaluation model and how the error impact was estimated using analyses that assumed a more limiting power shape. The error impact was estimated using a conservative, first-principles, based spreadsheet calculation, confirmed by explicit ECCS performance evaluation cases for a B&W-designed NSSS. NRC's Office of Nuclear Regulatory Research performed confirmatory calculations, and the results were found to be consistent with the licensee's estimate of the error impact. In summary, the NRC review of FENOC's letters dated September 2,2010, and December 17, 2010, establish the following: The error-adjusted PCT at DBNPS remain considerably below 10 CFR 50.46(b) acceptance The licensee provided additional information regarding the nature of the error impact evaluation, which indicated that the estimate of the error's magnitude was supported by explicit analyses. The licensee's evaluation is consistent with NRC staff confirmatory calculations. Based on these considerations, the NRC staff has concluded that the error report is not indicative of an immediate, or significant, safety concern and the overall evaluation model, when corrected for this error, appears to remain adequate. The NRC staff review also concludes that the licensee has appropriately submitted a 30-day report pursuant to 10 CFR 50.46(a)(3)(ii), and the analysis results are acceptable. Therefore, the NRC review of the 30-day report is complete, and TAC No. ME4780wili be closed. Please contact me at 301-415-3867, if you have any questions. Michael Mahoney, Project Plant Licensing Branch I Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-346 cc: Distribution via Listserv B. in the acceptable evaluation model and how the error impact was estimated using analyses that assumed a more limiting power shape. The error impact was estimated using a conservative, first-principles, based spreadsheet calculation, confirmed by explicit ECCS performance evaluation cases for a B&W-designed NSSS. NRC's Office of Nuclear Regulatory Research performed confirmatory calculations, and the results were found to be consistent with the licensee's estimate of the error impact. In summary, the NRC review of FENOC's letters dated September 2,2010, and December 17, 2010, establish the following: The error-adjusted PCT at DBNPS remain considerably below 10 CFR 50.46(b) acceptance The licensee provided additional information regarding the nature of the error impact evaluation, which indicated that the estimate of the error's magnitude was supported by explicit analyses. The licensee's evaluation is consistent with NRC staff confirmatory calculations. Based on these considerations, the NRC staff has concluded that the error report is not indicative of an immediate, or significant, safety concern and the overall evaluation model, when corrected for this error, appears to remain adequate. The NRC staff review also concludes that the licensee has appropriately' submitted a 30-day report pursuant to 10 CFR 50.46(a)(3){ii), and the analysis results are acceptable. Therefore, the NRC review of the 30-day report is complete, and TAC No. ME4780 will be closed. Please contact me at 301-415-3867, if you have any questions Sincerely, IRA! Michael Mahoney, Project Manager Plant Licensing Branch 111-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-346 cc: Distribution via Listserv DISTRIBUTION: PUBLIC RidsOgcRp Resource LPL3-2 RlF RidsAcrsAcnw MailCTR Resource RidsNrrSrxb Resource AGuzzetta, NRR RidsRgn1 MailCenter Resource RidsNrrDoriDpr Resource RidsNrrDorllpl3-2 Resouce RidsNrrPMDavis-Besse Resource RidsNrrLASRohrerResource BParks, NRR ADAMS Accession NRR-106 OFFICE LPLlII-21PM LPLlII-2/LA SRXB/BC LPLlII*2/BC NAME MMahoney SRohrer AUlses(SMiranda for) JZimmerman DATE 9/22111 9/22/11 9/20/11 9/22/11 OFFICIAL RECORD COpy