ML12296A227

Severe Accident Management Alternative (SAMA) Review

ML12296A227
Person / Time
Site:	Watts Bar
Issue date:	10/17/2012
From:	Hruby R Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
TAC MD8203
Download: ML12296A227 (2)

Text

Tennessee Valley Authority, Post Office Box 2000, Spring City, Tennessee 37381-2000 October 17, 2012 10 CFR § 50.4 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555-0001 Watts Bar Nuclear Plant, Unit 2 NRC Docket No. 50-391

Subject:

WATTS BAR NUCLEAR PLANT (WBN) - UNIT 2 - SEVERE ACCIDENT MANAGEMENT ALTERNATIVE (SAMA) REVIEW (TAC NO. MD8203)

Reference:

TVA letter dated January 31, 2011, "Watts Bar Nuclear Plant (WBN) -

Unit 2 - Request for Additional Information Regarding Severe Accident Management Alternative Review (TAC No. MD8203)"

The purpose of this letter is to modify commitment 9 in Enclosure 2 of the reference. This commitment stated the following:

For SAMA 293 and SAMA 294, the identified carbon steel piping is currently planned to be replaced with stainless steel piping. This was the reason these SAMAs were dispositioned as already committed to implement. However, the lower leak frequencies corresponding to stainless steel piping were incorporated in the October 2010 SAMA model, and these two flood scenarios still contributed to CDF significantly. Rerouting of the pipes outside the areas was impractical due to interferences in the area. Therefore, flood detection is also currently planned to be installed at WBN for areas 772.0-A8 and 772.0-A9. Flood detection in these areas will permit the operators to recognize that isolation of the break is needed and to take action if needed. (RAI 4.f Response)

TVA is revising its commitment to provide flood detection and piping change from carbon to stainless steel in the WBN Auxiliary Building areas 772.0-A8 and 772.0-A9 to only providing flood detection in those areas.

The rationale for revising the prior commitment came from a bounding evaluation of the change in core damage frequency (CDF) for multiple electrical board areas including the specified areas showing that changing both the pipe material and the addition of flood detection equipment provided a very small increase in benefit as compared to the change

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U.S. Nuclear Regulatory Commission Page 4 October 17, 2012 in risk from either modification by itself. A change from carbon steel to stainless steel piping would be expected to reduce the CDF by about 1.5E-5/yr. The addition of flood detection alone would result in an expected CDF reduction of approximately 1.6E-5/yr. The expected CDF reduction from taking both actions is approximately 1.7E-5/yr. Therefore, TVA determined that installation of flood detection sufficiently reduced CDF without replacement of the existing piping.

There are no new regulatory commitments contained in this letter. If you have any questions, please contact Gordon Arent at (423) 365-2004.

I declare under penalty of perjury that the foregoing is true and correct. Executed on the 1 7th day of October, 2012.

Respectfully, Raymond A. Hruby, Jr.

General Manager, Technical Services Watts Bar Unit 2 cc:

U. S. Nuclear Regulatory Commission Region II Marquis One Tower 245 Peachtree Center Ave., NE Suite 1200 Atlanta, Georgia 30303-1257 NRC Resident Inspector Unit 2 Watts Bar Nuclear Plant 1260 Nuclear Plant Road Spring City, Tennessee 37381