ML072410203

Mitigation of Alloy 600/82/182 Pressurizer Butt Welds in 2008

ML072410203
Person / Time
Site:	Palo Verde
Issue date:	08/02/2007
From:	Hesser J Arizona Public Service Co
To:	Dyer J Office of Nuclear Reactor Regulation
References
102-05727-JHH/RJR, TAC MD4169, TAC MD4170, TAC MD4171, NRR-07-004
Download: ML072410203 (3)

Text

CAL No. NRR-07-004 L---N A subsidiaryof Pinnacle West Capital Corporation John H. Hesser Mail Station 7605 Palo Verde Nuclear Vice President Tel: 623-393-5553 PO Box 52034 Generating Station Nuclear Engineering Fax: 623-393-6077 Phoenix, Arizona 85072-2034 102-05727-JHH/RJR August 02, 2007 Mr. James E. Dyer Director, Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555ý0001

References:

(1) Letter 102-05640-CDM/TNW/RJR, dated January 31, 2007, from C. D.

Mauldin, Arizona Public Service Company (APS), to NRC, "Mitigation of Alloy 600/82/182 Pressurizer Butt Welds" (2) Letter NRRý07-004, dated March 15, 2007, from J. E. Dyer, NRC to Randall K. Edington, APS, "Confirmatory Action Letter ý-Palo Verde Nuclear Generating Station, Units 1, 2 and 3 (TAC NOS. MD4169, MD4170, AND MD4171)"

(3) Electric Power Research Institute (EPRI) final report, dated July 31, 2007, from C. Harrington, EPRI, to J. Riley, Nuclear Energy Institute (NEI), "Advanced FEA Evaluation of Growth of Postulated Circumferential PWSCC Flaws in Pressurizer Nozzle Dissimilar Metal Welds, (MRP-216): Evaluations Specific to Nine Subject Plants, 1015383" (4) Letter dated August 1, 2007, from A. Marion, NEI, to J. E. Dyer, NRC, "Transmittal of EPRI Report 'Advanced FEA Evaluation of Growth of Postulated Circumferential PWSCC Flaws in PresSurizer Nozzle Dissimilar Metal Weld (MRP-126 [216]): Evaluations Specific to Nine Subject Plants"'

Subject:

Palo Verde Nuclear Generating Station (PVNGS)

Unit 2 Docket No. STN 50-529 Mitigation of Alloy 600/82/182 Pressurizer Butt Welds in 2008 In the Reference 1 submittal, Arizona Public Service Company (APS) provided the plans and schedule for the mitigation of pressurizer Alloy 600/82/182 butt welds for Palo Verde Units 1, 2 and 3. In that submittal, APS stated that, based on the current refueling outage schedule, Palo Verde Unit 2 would complete the mitigation action in the A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Aj Callaway 0 Comanche Peak 0 Diablo Canyon 0 Palo Verde 0 South Texas Project 0 Wolf Creek

Mr. James E. Dyer Director, Office of Nuclear Reactor Regulation PVNGS Unit 2 -Mitigation of Alloy 600/82/182 Pressurizer Butt Welds in 2008 Page 2 spring of 2008; i.e., beyond the industry-sponsored Materials Reliability Program MRP-139 implementation deadline of December 31, 2007.

Reference 1 also provided regulatory commitments regarding the Palo Verde Unit 2 schedule for mitigation actions, enhanced Reactor Coolant System (RCS) leakage monitoring, and inspection reporting requirements. Also, specific to Palo Verde Unit 2, a commitment was made to adopt contingency plans to shut down by December 31, 2007 to perform weld overlays, if technical information, being developed by EPRI through advanced finite element analyses, does not provide reasonable assurance to the NRC that primary water stress corrosion cracking (PWSCC) conditions will remain stable and not lead to rupture without significant time from the onset of detectable leakage. These regulatory commitments were confirmed in the Reference 2 Confirmatory Action Letter (CAL).

EPRI's advanced finite element analysis, Reference 3, was recently completed and submitted to the NRC by Reference 4. The analysis, which is applicable to Palo Verde Unit 2, assumed the existence of large circumferential cracks in all the analyzed locations. This assumption is very conservative considering field inspections and experience which has shown a relatively low number of PWSCC indications in these components. With this conservatism, the analysis concluded that there is significant time for crack growth between the onset of detectable leakage and development of critical flaw size.

This letter confirms that Reference 3 bounds the Palo Verde Unit 2 pressurizer Alloy 82/182 welded pipe/nozzle components. APS has reviewed the report and verified that the input addresses Palo Verde Unit 2 weld configurations and loads, that the analysis and conclusions are applicable to Palo Verde Unit 2 design, and that all welds representative of Palo Verde Unit 2 are adequately addressed by the crack growth analyses and associated sensitivity cases. Finally, the analytical results applicable to Palo Verde Unit 2 satisfy the leakage evaluation criteria presented in the report.

Therefore, APS concludes that the analytical results presented in Reference 3, and the current plant enhanced leakage monitoring program, provide a reasonable and adequate basis for performing mitigation or inspection activities during the scheduled refueling outage in the spring of 2008 as committed to in Reference 1, after which time Palo Verde Unit 2 will fully satisfy the MRP-1 39 inspection/mitigation requirements for pressurizer Alloy 600/82/182 components.

p4; Mr. James E. Dyer Director, Office of Nuclear Reactor Regulation PVNGS Unit 2 -Mitigation of Alloy 600/82/182 Pressurizer Butt Welds in 2008 Page 3 This letter contains no new commitments. If you have any questions about this submittal, please contact Glenn A. Michael at (623) 393-5750.

Sincerely, JHH/GAM/RJR/gt cc: B. S. Mallett NRC Region IV Regional Administrator M. T. Markley NRC NRR Project Manager G. G. Warnick NRC Senior Resident Inspector for PVNGS U.S. NRC Document Control Desk