ML070160169

Clarification of Alternative Source Term Amendment

ML070160169
Person / Time
Site:	Columbia
Issue date:	02/05/2007
From:	Terao D NRC/NRR/ADRO/DORL/LPLIV
To:	Parrish J Energy Northwest
Fields M, NRR/DORL/LP4, 415-3062
References
TAC MC4570
Download: ML070160169 (4)

Text

February 5, 2007 Mr. J. V. Parrish Chief Executive Officer Energy Northwest P.O. Box 968 (Mail Drop 1023)

Richland, WA 99352-0968

SUBJECT:

COLUMBIA GENERATING STATION - CLARIFICATION OF ALTERNATIVE SOURCE TERM AMENDMENT (TAC NO. MC4570)

Dear Mr. Parrish:

On November 27, 2006, the Nuclear Regulatory Commission (NRC) issued Amendment No. 199 to Facility Operating License No. NPF-21 for the Columbia Generating Station (CGS).

The amendment replaced the previous accident source term used in design-basis radiological analyses with an alternative source term pursuant to Title 10 of the Code of Federal Regulations, Section 50.67 (10 CFR 50.67), "Accident source term." The related Safety Evaluation (SE) provided the details of the NRC staffs review of this license amendment.

Energy Northwest, the CGS licensee, verbally requested the NRC staff provide clarification of the section of this SE that discussed the design basis of the secondary containment.

Specifically, the licensee requested confirmation of its understanding of the requirements for assuring the secondary containment is being maintained in a sufficiently leak-tight condition to preclude exfiltration. The details of the licensees understanding of this issue were provided in its September 11, 2006, letter.

The September 11, 2006, letter provides clarification on what Energy Northwest considers relevant to providing reasonable assurance of secondary containment integrity. It states:

In addition, it is understood that the value of greater than or equal to 0.25 inches of vacuum water gauge is an indication of pressure at one location in the secondary containment and not a value maintained at every surface within the secondary containment. The instrument used to perform this surveillance measures pressure at reactor building elevation 572 in an area that has open communication with the rest of the secondary containment volume.

The NRC staff discussed this issue in Section 3.1.1.3 of the SE, Secondary Containment Drawdown, and concluded that secondary containment integrity is ensured in part by Technical Specification (TS) 3.6.4.1, Secondary Containment and its associated surveillance requirements (SRs).

The design basis dose modeling, which assumes that (1) either all or none of the leakage from the primary containment volume is released to the environment depending upon whether secondary containment integrity is assumed, and (2) conservative modeling of meteorological conditions, is a very conservative approach. It is the NRC staffs engineering judgment that the

J. V. Parrish containment drawn down to a negative 0.25 inch water gauge (w.g.), as determined by a single representative location, is sufficient to demonstrate adequate performance of the SRs in TS 3.6.4.1. Minor amounts of exfiltration under these conditions are expected to have a minimal impact on the radiological consequences and does not present a safety concern.

SR 3.6.4.1.4 is intended to demonstrate that the standby gas treatment system (SGTS) has the capability of drawing down the secondary containment to a negative 0.25 inch w.g. in a 2-minute period of time. The NRC staff finds the acceptance criteria for this SR to be adequate, since a 2-minute draw down will adequately demonstrate the functional capability of the SGTS and because 20 minutes is used as the draw-down time in the loss-of-coolant accident (LOCA) analysis. The significant margin between the SR acceptance criteria of 2 minutes and the assumption of 20 minutes used in the LOCA analysis is sufficient to account for the potential increase in draw-down time due to accident and meteorological conditions.

SR 3.6.4.1.5 is intended to demonstrate that the SGTS is capable of maintaining a negative pressure in the secondary containment for a period of time at a reduced SGTS fan flow rate of 2,240 cubic feet per minute (cfm). SR 3.6.4.1.5 confirms that the SGTS can maintain the negative pressure of 0.25 inch w.g. for an extended period with reduced SGTS flow under test conditions and provides reasonable assurance that the negative pressure can continue to be maintained under adverse conditions when the SGTS would be operating at its full design flow of 4,800 cfm.

Successful completion of these SRs provides reasonable assurance of secondary containment integrity. Changes which reduce required integrity would be detected by increases in draw-down time in successive testing until ultimately the test would fail. An increase in inleakage above the fan flow rate would cause the test to fail and indicate that integrity had degraded.

If you have any questions regarding this letter, please contact me at (301) 415-3317.

Sincerely,

/RA/

David Terao, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-397 cc: See next page

ML070160169 OFFICE NRR/LPL4/PM NRR/LPL4/LA NRR/AADB NRR/ACVB NRR/LPL4/BC NAME MFields LFeizollahi MKotzalas RDennig DTerao DATE 2/5/07 1/25/07 1/24/07 1/25/07 2/5/07 Columbia Generating Station cc:

Mr. W. Scott Oxenford (Mail Drop PE04) Mr. Dale K. Atkinson (Mail Drop PE08)

Vice President, Technical Services Vice President, Nuclear Generation Energy Northwest Energy Northwest P.O. Box 968 P.O. Box 968 Richland, WA 99352-0968 Richland, WA 99352-0968 Mr. Albert E. Mouncer (Mail Drop PE01) Mr. William A. Horin, Esq.

Vice President, Corporate Services/ Winston & Strawn General Counsel/CFO 1700 K Street, N.W.

Energy Northwest Washington, DC 20006-3817 P.O. Box 968 Richland, WA 99352-0968 Mr. Matt Steuerwalt Executive Policy Division Chairman Office of the Governor Energy Facility Site Evaluation Council P.O. Box 43113 P.O. Box 43172 Olympia, WA 98504-3113 Olympia, WA 98504-3172 Ms. Lynn Albin Mr. Douglas W. Coleman (Mail Drop PE20) Washington State Department of Health Manager, Regulatory Programs P.O. Box 7827 Energy Northwest Olympia, WA 98504-7827 P.O. Box 968 Richland, WA 99352-0968 Technical Services Branch Chief FEMA Region X Mr. Gregory V. Cullen (Mail Drop PE20) 130 228th Street, S.W.

Supervisor, Licensing Bothell, WA 98201-9796 Energy Northwest P.O. Box 968 Ms. Cheryl M. Whitcomb (Mail Drop PE03)

Richland, WA 99352-0968 Vice President, Organizational Performance & Staffing/CKO Regional Administrator, Region IV Energy Northwest U.S. Nuclear Regulatory Commission P.O. Box 968 611 Ryan Plaza Drive, Suite 400 Richland, WA 99352-0968 Arlington, TX 76011-4005 Assistant Director Chairman Nuclear Safety and Energy Siting Division Benton County Board of Commissioners Oregon Department of Energy P.O. Box 190 625 Marion Street, NE Prosser, WA 99350-0190 Salem, OR 97301-3742 Senior Resident Inspector U.S. Nuclear Regulatory Commission P.O. Box 69 Richland, WA 99352-0069 August 2006