ML071170021

Review of 10 CFR 50.46 Notifications of ECCS Evaluation Model Changes

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, 2007 Mr. Preston D. Swafford Interim 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 50.46 NOTIFICATIONS OF ECCS EVALUATION MODEL CHANGES (TAC NO. MD1235)

Dear Mr. Swafford:

This letter documents the U.S. Nuclear Regulatory Commission (NRC) staff review of two reports 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, TVA submitted 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 leakage in 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 licensees 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 were estimated to be significantly lower than the 10 CFR 50.46 PCT limit of 2200 oF. Therefore, the NRC 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 annual report 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 (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 analysis and 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, the NRC 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 assess whether its procedures need to be updated:

• The NRC staff reviewed the LOCA PCT summary tables for best estimate large break and 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 changes were greater than 50EF for six LOCA cases presented in the annual report. As previously 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 reassesses the effects on PCT for SBLOCAs, if the change in PCT is greater than 50EF, current regulations require that the licensee report the change even though it is an improvement in the margin.

This completes the NRC staffs actions for TAC No. MD1235. If there are any questions, please contact me at (301) 415-3974.

Sincerely,

/RA/

Brendan T. Moroney, Project Manager Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-390 cc: See next page

ML071170021 OFFICE LPL2-2/PM LPL2-2/LA SRXB/BC LPL2-2/BC NAME BMoroney RSola GCranston TBoyce by email DATE 4/26/07 4/27/07 4/26/07/07 4/27/07

Preston D. Swafford Tennessee Valley Authority WATTS BAR NUCLEAR PLANT cc:

Mr. Ashok S. Bhatnagar, Senior Vice President Mr. James D. Smith, Acting Manager Nuclear Operations Licensing and Industry Affairs Tennessee Valley Authority Watts Bar Nuclear Plant 6A Lookout Place Tennessee Valley Authority 1101 Market Street P.O. Box 2000 Chattanooga, TN 37402-2801 Spring City, TN 37381 Mr. Larry S. Bryant, Vice President Mr. Michael J. Lorek, Plant Manager Nuclear Engineering & Technical Services Watts Bar Nuclear Plant Tennessee Valley Authority Tennessee Valley Authority 6A Lookout Place P.O. Box 2000 1101 Market Street Spring City, TN 37381 Chattanooga, TN 37402-2801 Senior Resident Inspector Mr. Michael D. Skaggs, Site Vice President Watts Bar Nuclear Plant Watts Bar Nuclear Plant U.S. Nuclear Regulatory Commission Tennessee Valley Authority 1260 Nuclear Plant Road P.O. Box 2000 Spring City, TN 37381 Spring City, TN 37381 County Executive General Counsel 375 Church Street Tennessee Valley Authority Suite 215 6A West Tower Dayton, TN 37321 400 West Summit Hill Drive Knoxville, TN 37902 County Mayor P. O. Box 156 Mr. John C. Fornicola, Manager Decatur, TN 37322 Nuclear Assurance Tennessee Valley Authority Mr. Lawrence E. Nanney, Director 6A Lookout Place Division of Radiological Health 1101 Market Street Dept. of Environment & Conservation Chattanooga, TN 37402-2801 Third Floor, L and C Annex 401 Church Street Mr. Robert H. Bryan, Jr., General Manager Nashville, TN 37243-1532 Licensing and Industry Affairs Tennessee Valley Authority Ms. Ann P. Harris 4X Blue Ridge 341 Swing Loop Road 1101 Market Street Rockwood, TN 37854 Chattanooga, TN 37402-2801 Ms. Beth A. Wetzel, Manager Corporate Nuclear Licensing and Industry Affairs Tennessee Valley Authority 4X Blue Ridge 1101 Market Street Chattanooga, TN 37402-2801