ML083360191

Response to Request for Additional Information Analysis in Support of Control Rod Insertion Following a Cold Leg Loss-of-Coolant Accident

ML083360191
Person / Time
Site:	Watts Bar
Issue date:	11/25/2008
From:	Riedl C Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
TAC MD9396, TVA-WBN-TS-08-04
Download: ML083360191 (4)

Text

November 25, 2008 TVA-WBN-TS-08-04 10 CFR 50.90 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555-0001 Gentlemen:

In the Matter of ) Docket No. 50-390 Tennessee Valley Authority (TVA) )

WATTS BAR NUCLEAR PLANT (WBN) UNIT 1 - RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION RE: ANALYSIS IN SUPPORT OF CONTROL ROD INSERTION FOLLOWING A COLD LEG LOSS-OF-COOLANT ACCIDENT (TAC NO. MD9396)

The purpose of this letter is to respond to NRCs request for additional information (RAI) dated October 14, 2008 and November 7, 2008.

The first RAI is related to NRCs concerns with regard to the structural integrity analysis of the reactor core and its internals due to the loads created by a postulated rupture of the cold leg accumulator injection line coincident with a seismic event. The second RAI is related to NRCs concerns with the application of the leak-before-break (LBB) methodology to limit large break loss of coolant accidents (LOCAs) to postulated failure of non-qualified LBB piping. TVAs response to these RAIs is provided in the enclosure. There are no regulatory commitments associated with submittal.

If you have any questions concerning this matter, please call me at (423) 365-1742 or Robert Clark at (423) 365-1818.

I declare under penalty of perjury that the foregoing is true and correct. Executed on this 25th day of November, 2008.

Sincerely, C. J. Riedl Manager, Site Licensing and Industry Affairs (Acting)

Enclosure:

cc: See Page 2 E-1 of 2

U.S. Nuclear Regulatory Commission Page 2 November 25, 2008 Enclosures cc:

NRC Resident Inspector Watts Bar Nuclear Plant 1260 Nuclear Plant Road Spring City, Tennessee 37381 Mr. John G. Lamb, Senior Project Manager U.S. Nuclear Regulatory Commission Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation MS 0-8H1A Washington, DC 20555-0001 U.S. Nuclear Regulatory Commission Region II Sam Nunn Atlanta Federal Center 61 Forsyth St., SW, Suite 23T85 Atlanta, Georgia 30303 Mr. Lawrence E. Nanny, Director Division of Radiological Health 3rd Floor L&C Annex 401 Church Street Nashville, Tennessee 37243 E-2 of 2

ENCLOSURE REQUEST FOR ADDITIONAL INFORMATION (RAI)

WATTS BAR NUCLEAR PLANT (WBN) UNIT 1 TECHNICAL SPECIFICATIONS (TS) CHANGE REQUEST TS-08-04 By letter dated August 1, 2008 (ADAMS No. ML082180091), TVA issued a license amendment request to change Watts Bar Nuclear Plant (WBN), Unit 1, Technical Specifications (TS). The proposed request increased the maximum number of Tritium Producing Burnable Absorber Rods (TPBAR) that can be irradiated per cycle from 400 to 2304 rods. It also credited control rod insertion following a cold leg loss of coolant accident (LOCA) and revised the boron requirements for the cold leg accumulators and refueling water storage tank. The combined negative reactivity insertion from these sources ensured that the core would remain subcritical at hot leg switchover (HLSO) due to potential TPBAR failure and sump dilution. These changes were requested in order to increase the TPBAR inventory in the reactor core to support vital national security interests. In response to the August 1, 2008 license amendment request, NRC issued three requests for additional information (RAIs) on October 14, October 28, and November 7, 2008. TVAs response to the RAIs dated October 14, and November 7, 2008 are provided below. The response to RAI dated October 28, 2008 will be provided on the requested schedule.

1. RAI Dated October 14, 2008, Analysis in Support of Control Insertion Following a Cold Leg Loss-Of-Coolant Accident The October 14, 2008 RAI provided thirty questions regarding Westinghouse Topical Report WCAP-16932-P, Control Rod Insertion Following a Cold Leg LOCA for Watts Bar Unit 1. This report analyzed the structural integrity of the reactor core and its internals due to the loads created by a cold leg LOCA coincident with a seismic event. The purpose of the analysis was to demonstrate that the control rods at WBN Unit 1 can be inserted following a postulated rupture of the cold leg accumulator injection line which is a non-qualified LBB piping.

TVA has elected to withdraw WCAP-16932-P from the submittal in order to facilitate review and approval of this license amendment request in time to support the WBN cycle 9 refueling outage. For WBNs cycle 9 refueling outage, TVA will determine the number of TPBARs to be irradiated based on a revised reload safety evaluation that will not require crediting control rod insertion following HLSO to offset the reactivity penalty due to potential TPBAR failure and sump dilution. This new analysis will be provided in a supplement to the original August 1, 2008 license amendment request.

Since TVA is withdrawing WCAP-16932-P from the license amendment request, the questions in the October 14, 2008 RAI, which were associated with the structural integrity of the reactor core and its internals due to the loads created by a cold leg LOCA coincident with a seismic event, are no longer applicable.

2. RAI Dated November 7, 2008, Application of LBB Methodology to Limit Large Break LOCAs to Non-Qualified LBB Piping E-3 of 2

This RAI posed the following NRC question:

Provide justification for the following statement:

With WBN Unit 1 primary loop qualified under the LBB program, control rod insertion capability need only be evaluated for large break LOCAs due to failure of non-qualified LBB piping such as the piping in the RCS auxiliary branch lines TVA Response:

Limiting large break LOCAs to RCS auxiliary branch lines in order to demonstrate control rod insertion capability was based on application of the LBB methodology as described in the WBN UFSAR, Section 3.6B.1. Breaks in the main reactor coolant loop piping (qualified LBB piping) were still postulated for the purpose of sizing the containment, emergency core cooling systems, and environmental equipment qualifications.

However, as discussed above, TVA has elected for this license amendment request not to credit control rod insertion following a large break LOCA. Therefore, the issue regarding large break LOCAs based on failure of qualified LBB piping versus non-qualified LBB piping is no longer relevant to this license amendment request.

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