ML071170021
| ML071170021 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 04/27/2007 |
| From: | Moroney B NRC/NRR/ADRO/DORL/LPLII-2 |
| To: | Swafford P Tennessee Valley Authority |
| Moroney B, NRR/DORL, 415-3974 | |
| References | |
| TAC MD1235 | |
| Download: ML071170021 (5) | |
Text
April 27, 2007Mr. Preston D. SwaffordInterim Chief Nuclear Officer Nuclear Support Tennessee Valley Authority 6A Lookout Place 1101 Market Street Chattanooga, TN 37402-2801
SUBJECT:
WATTS BAR NUCLEAR PLANT, UNIT 1 - REVIEW OF 10 CFR 50.46NOTIFICATIONS OF ECCS EVALUATION MODEL CHANGES (TAC NO. MD1235)
Dear Mr. Swafford:
This letter documents the U.S. Nuclear Regulatory Commission (NRC) staff review of tworeports for Watts Bar Nuclear Plant Unit 1 that were submitted by the Tennessee Valley Authority (TVA, the licensee) pursuant to Title 10 of the Code of Federal Regulations (10 CFR),Section 50.46, "Acceptance criteria for emergency core cooling systems [ECCS] for light-water nuclear power reactors."By letter dated August 16, 2005, as supplemented by letter dated September 11, 2006, TVAsubmitted a 30-day report pursuant to 10 CFR 50.46(a)(3)(ii), which requires such a report if a change in an ECCS evaluation model results in a significant change (greater than 50 degrees Fahrenheit (oF)) in peak cladding temperature (PCT). The 30-day report indicated that leakagein the piping relief valves could result in a loss of up to 30 gallons per minute (gpm) in safety injection (SI) flow to the pressurizer relief tank when the SI system was in operation. The licensee assessed the effects of the reduced SI flow on the analysis of record (AOR) for the large-break (LB) and small-break (SB) loss-of-coolant accidents (LOCAs). The licensee's assessment showed that the PCT remained unchanged for the LBLOCA, while it increased by
120 oF for the limiting SBLOCA with a 4-inch diameter pipe break. The resulting PCTs wereestimated to be significantly lower than the 10 CFR 50.46 PCT limit of 2200 oF. Therefore, theNRC staff agreed with the licensee that the AOR for the LOCA with the PCT penalties to account for a reduction of 30 gpm in SI flow remained valid.By letter dated April 12, 2006, TVA submitted the annual report for 2005. The 2005 annualreport indicated that eight changes were made to the "best estimate large break code." The changes were:(1)revised iteration algorithm for calculating the average fuel temperature;(2)pellet radial profile option; (3)improved automation of end of blowdown time; (4)general code maintenance; (5)thermodyamic properties from THERMO; (6)pressurizer fluid volume; P. Swafford-2-(7)vessel unheated conductor noding; and(8)containment relative humidity assumption.The licensee assessed the impact of the model changes on the PCTs for the LBLOCA analysisand showed that the impact was very small, and the resulting LBLOCA PCT remained essentially unchanged. The NRC staff did not review the acceptability of the model changes and the impact analysis; however, the staff noted that the limiting PCT for the LBLOCA (1790 oF) was significantly lower than the 10 CFR 50.46 PCT limit of 2200 oF. Therefore, theNRC staff agreed with the licensee that the AOR for the LBLOCA, with consideration of the effects of the model changes, remained valid.The following additional comments and observations are provided so that TVA can assesswhether its procedures need to be updated:*The NRC staff reviewed the LOCA PCT summary tables for best estimate large breakand found that the LBLOCA analysis had not been reanalyzed for both cases with the original steam generators and replacement steam generators since 1998. Many model changes or error corrections were made since then. *The NRC staff also found that the sums of the absolute magnitudes of the PCT changeswere greater than 50F for six LOCA cases presented in the annual report. Aspreviously noted, 10 CFR 50.46(a)(3)(ii) requires this to be reported within 30 days.*When the leakage in the piping relief valves is corrected and the licensee reassessesthe effects on PCT for SBLOCAs, if the change in PCT is greater than 50F, currentregulations require that the licensee report the change even though it is an improvement in the margin. This completes the NRC staff's actions for TAC No. MD1235. If there are any questions,please contact me at (301) 415-3974.Sincerely,/RA/Brendan T. Moroney, Project ManagerPlant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor RegulationDocket No. 50-390 cc: See next page
ML071170021OFFICELPL2-2/PMLPL2-2/LA SRXB/BCLPL2-2/BCNAMEBMoroneyRSola GCranston by emailTBoyceDATE 4/26/074/27/07 4/26/07/074/27/07 Preston D. SwaffordTennessee Valley AuthorityWATTS BAR NUCLEAR PLANT cc:Mr. Ashok S. Bhatnagar, Senior Vice President Nuclear Operations Tennessee Valley Authority 6A Lookout Place 1101 Market Street Chattanooga, TN 37402-2801Mr. Larry S. Bryant, Vice PresidentNuclear Engineering & Technical Services Tennessee Valley Authority 6A Lookout Place 1101 Market Street Chattanooga, TN 37402-2801Mr. Michael D. Skaggs, Site Vice PresidentWatts Bar Nuclear Plant Tennessee Valley Authority P.O. Box 2000 Spring City, TN 37381General CounselTennessee Valley Authority 6A West Tower 400 West Summit Hill Drive Knoxville, TN 37902Mr. John C. Fornicola, ManagerNuclear Assurance Tennessee Valley Authority 6A Lookout Place 1101 Market Street Chattanooga, TN 37402-2801Mr. Robert H. Bryan, Jr., General ManagerLicensing and Industry Affairs Tennessee Valley Authority 4X Blue Ridge 1101 Market Street Chattanooga, TN 37402-2801Ms. Beth A. Wetzel, ManagerCorporate Nuclear Licensing and Industry Affairs Tennessee Valley Authority 4X Blue Ridge 1101 Market Street Chattanooga, TN 37402-2801Mr. James D. Smith, Acting ManagerLicensing and Industry Affairs Watts Bar Nuclear Plant Tennessee Valley Authority P.O. Box 2000 Spring City, TN 37381Mr. Michael J. Lorek, Plant ManagerWatts Bar Nuclear Plant Tennessee Valley Authority P.O. Box 2000 Spring City, TN 37381Senior Resident InspectorWatts Bar Nuclear Plant U.S. Nuclear Regulatory Commission 1260 Nuclear Plant Road Spring City, TN 37381County Executive375 Church Street Suite 215 Dayton, TN 37321County Mayor P. O. Box 156 Decatur, TN 37322Mr. Lawrence E. Nanney, DirectorDivision of Radiological Health Dept. of Environment & Conservation Third Floor, L and C Annex 401 Church Street Nashville, TN 37243-1532Ms. Ann P. Harris341 Swing Loop Road Rockwood, TN 37854