ML060820402
| ML060820402 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 03/31/2006 |
| From: | Fields M Plant Licensing Branch III-2 |
| To: | James M. Levine Arizona Public Service Co |
| Fields M , NRR/DORL,415-3062 | |
| Shared Package | |
| ML060820427 | List: |
| References | |
| IR-04-014, STN 50-528, STN 50-529, STN 50-530 | |
| Download: ML060820402 (5) | |
Text
March 31, 2006 Mr. James M. Levine Executive Vice President, Generation Mail Station 7602 Arizona Public Service Company PO Box 52034 Phoenix, AZ 85072-2034
SUBJECT:
PALO VERDE NUCLEAR GENERATING STATION, UNITS 1, 2, AND 3 -
TRANSMITTAL OF FINAL ACCIDENT SEQUENCE PRECURSOR ANALYSIS OF EMERGENCY CORE COOLING SYSTEM PIPING VOID ISSUE
Dear Mr. Levine:
Enclosed for your information is the final Accident Sequence Precursor (ASP) analysis of the Emergency Core Cooling System (ECCS) piping void issue that was identified in July 2004.
This event was documented in Nuclear Regulatory Commission (NRC) Inspection Report 05000528/2004014, 05000529/2004014, and 05000530/2004014, dated January 5, 2005.
Condition Summary On July 31, 2004, Arizona Public Service Company (the licensee) notified the NRC that a voided condition existed in a section of ECCS recirculation piping in all three units, such that both ECCS trains in each unit were affected. Specifically, the section of recirculation piping between the closed inboard containment isolation valves and the associated train sump recirculation check valves (downstream of the outboard containment isolation valves) were void of water for both ECCS trains. The relevant air volume was about 100 ft3 per train. Of this volume, approximately 90 ft3 of air was caught between the inboard and the outboard containment isolation valves, with the remaining 10 ft3 existing between the outboard containment isolation valve and the train sump recirculation valve.
The voided condition apparently existed since 1992, when a modification to the recirculation piping leak testing procedure was put in place without proper analysis. This modification involved draining the recirculation piping section, each time the leak test with demineralized water was completed. In addition, even prior to 1992, quarterly stroke testing of the containment isolation valves left part of the suction piping in the partially voided condition.
ASP Summary This event was modeled as a conditional assessment with the recirculation function unavailable following a transient or a small loss-of-coolant accident (LOCA). The unavailability of the recirculation function following a medium LOCA was treated with a probability distribution developed through an expert elicitation process. The analysis considered the one year period prior to discovery of condition, as per ASP program convention.
Results: The ASP analysis calculated a mean change in core damage probability (CDP) of 1.4x10-5, with 5% and 95% uncertainty bounds of 3.7x10-6 and 4.4x10-5, respectively.
J. Levine Significance Determination Process (SDP)/ASP comparison: This condition was analyzed as a YELLOW finding by a Phase 3 SDP analysis. The NRC staff found and the licensee agreed that the recirculation function was not available following a transient or small LOCA.
However, based on laboratory testing and analysis, the licensee stated that the recirculation function was available (i.e., nominal equipment unavailabilities) following a medium LOCA. The NRC staff working on the SDP analysis reviewed the licensees testing and analysis, and concluded that availability of the recirculation function could not be assured following a medium LOCA. The SDP Phase 3 analysis calculated a CDP of in the mid-10-5 and issued a YELLOW finding. The ASP analysis took a different approach to the recirculation function unavailability following a medium LOCA, and used a recently developed, simplified expert elicitation approach. The result was a factor of 3 lower CDP in the ASP analysis. The ASP analysis is consistent with the SDPs YELLOW analysis finding.
If you have any questions, please contact me at 301-415-3062.
Sincerely,
/RA/
Mel B. Fields, Senior Project Manager Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. STN 50-528, 50-529 and STN 50-530
Enclosure:
Final ASP Analysis cc w/encl: See next page
Pkg No.: ML060820427 OFFICE NRR/LPL4/PM NRR/LPL4/LA NRR/LPL4/BC NAME MFields DJohnson DTerao DATE 3/31/06 3/31/06 3/31/06
Palo Verde Generating Station, Units 1, 2, and 3 cc:
March 2006 Mr. Steve Olea Arizona Corporation Commission 1200 W. Washington Street Phoenix, AZ 85007 Mr. Douglas Kent Porter Senior Counsel Southern California Edison Company Law Department, Generation Resources P.O. Box 800 Rosemead, CA 91770 Senior Resident Inspector U.S. Nuclear Regulatory Commission P. O. Box 40 Buckeye, AZ 85326 Regional Administrator, Region IV U.S. Nuclear Regulatory Commission Harris Tower & Pavillion 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-8064 Chairman Maricopa County Board of Supervisors 301 W. Jefferson, 10th Floor Phoenix, AZ 85003 Mr. Aubrey V. Godwin, Director Arizona Radiation Regulatory Agency 4814 South 40 Street Phoenix, AZ 85040 Mr. Craig K. Seaman, General Manager Regulatory Affairs and Performance Improvement Palo Verde Nuclear Generating Station Mail Station 7636 P.O. Box 52034 Phoenix, AZ 85072-2034 Mr. Hector R. Puente Vice President, Power Generation El Paso Electric Company 310 E. Palm Lane, Suite 310 Phoenix, AZ 85004 Mr. John Taylor Public Service Company of New Mexico 2401 Aztec NE, MS Z110 Albuquerque, NM 87107-4224 Mr. Thomas D. Champ Southern California Edison Company 5000 Pacific Coast Hwy Bldg D1B San Clemente, CA 92672 Mr. Robert Henry Salt River Project 6504 East Thomas Road Scottsdale, AZ 85251 Mr. Jeffrey T. Weikert Assistant General Counsel El Paso Electric Company Mail Location 167 123 W. Mills El Paso, TX 79901 Mr. John Schumann Los Angeles Department of Water & Power Southern California Public Power Authority P.O. Box 51111, Room 1255-C Los Angeles, CA 90051-0100 Mr. Brian Almon Public Utility Commission William B. Travis Building P. O. Box 13326 1701 North Congress Avenue Austin, TX 78701-3326
Palo Verde Generating Station, Units 1, 2, and 3 cc:
March 2006 Ms. Karen O'Regan Environmental Program Manager City of Phoenix Office of Environmental Programs 200 West Washington Street Phoenix AZ 85003 Mr. Matthew Benac Assistant Vice President Nuclear & Generation Services El Paso Electric Company 340 East Palm Lane, Suite 310 Phoenix, AZ 85004