DCL-07-077, Mitigation of Alloy 600/82/182 Pressurizer Butt Welds in 2008

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

ML072970461
Person / Time
Site:	Diablo Canyon
Issue date:	08/07/2007
From:	Keenan J Pacific Gas & Electric Co
To:	Dyer J Office of Nuclear Reactor Regulation
References
600/82/182, DCL-07-077
Download: ML072970461 (3)

Text

Pacific Gas and ElectricCompany" John S. Keenoan 77 3oalq Street, Miailco~dn BI Se*iliJr Vice PIresidont Sani F:rancisco, CA 94105 Goeir aiti i . Chief NuclearW O1fic er Ha'iling A ddrass Moil Code R1B32, 40,ou3235 August 7, 2007 - Fo, CA 94177 416.97*3.46 84 PG&E Letter DCL-07-077 Interal; 223,4684 F 415,97.3,2313 Mr. James E. Dyer Director, Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Docket No. 50-323, OL-DPR-82 Diablo Canyon Unit 2 Mitigation of Alloy 600/82/182 Pressurizer Butt Welds in 2008

References:

1. PG&E Letter DCL-07-009 from John S. Keenan, Senior Vice President - Generation and Chief Nuclear Officer of Diablo Canyon Power Plant, to U. S. NRC, "Inspection and Mitigation of Alloy 600/82/182 Pressurizer Butt Welds," dated January 31, 2007

2. PG&E Letter DCL-07-019 from John S. Keenan, Senior Vice President - Generation and, Chief Nuclear Officer of Diablo Canyon Power Plant, to U. S. NRC, "Additional Commitments Related to Inspection and Mitigation of Alloy 600/82/182 Pressurizer Butt Welds," dated February 20, 2007

3. Letter from James E. Dyer, Director of Office of Nuclear Reactor Regulation (U. S. NRC), to John S. Keenan, Senior Vice President -

Generation and Chief Nuclear Officer of Diablo Canyon Power Plant, "Confirmatory Action Letter,-Diablo Canyon Power Plant, Unit No. 2 (TAC No. MD4150)," dated March 15, 2007

4. Electric Power Research Institute Final Report, "Advanced FEA Evaluation of Growth of Postulated Circumferential PWSCC Flaws In Pressurizer Nozzle Dissimilar Metal Welds, (MRP-216):

Evaluations Specific to Nine Subject Plants," EPRI, Palo Alto, CA:

2007; 1015383 dated July 31,.2007

5. Nuclear Energy Institute Letter to James E. Dyer, Director of Office of Nuclear Reactor Regulation (U, S. NRC), "Transmittal of EPRI e*

Report," dated August 1, 2007 A member of the STARS (Strategic TePamng and Resource Sharing) Alitance Callaway , Comanche Peak a Diablo Canyon

• Palo Verde

• South Texas Project *Wolf Creek

Document Control Desk PG&E Letter DCL-07-077 August 7, 2007 Page 2 In the Reference 1 submittal, Pacific Gas and Electric (PG&E) provided the plans and schedule for the mitigation of pressurizer Alloy 600/82/1.82 butt welds for Diablo Canyon Power Plant (DCPP) Unit 2. In that submittal, PG&E stated that, based on the current refueling outage schedule, PG&E would complete the. mitigation action during the DCPP Unit 2 Fourteenth Refueling Outage (2R14) currently scheduled to begin February 4, 2008 (i.e., beyond the industry-sponsored Materials Reliability Program MRP-139 Implementation deadline of December 31, 2007).

Reference 2 provided regulatory commitments regarding the DCPP Unit 2 schedule for mitigation actions, enhanced reactor coolant system (RCS) leakage monitoring, and Inspection reporting requirements, Also, specific to DCPP Unit 2, a commitment was made to accelerate the mitigation actions, currently scheduled during the 2R14 outage, into 2007 if the results of ongoing analytical work do not demonstrate to the NRC that the current schedule is adequate. These regulatory commitments were confirmed in the Reference .3 Confirmatory Action Letter (CAL).

EPRI's advanced finite element analysis, Reference 4, was recently completed and submitted by Reference 5. The analysis, which is applicable to DCPP Unit 2, assumed the existence of large circumferential cracks in all the analyzed locations.

This assumption Is very conservative considering industry field inspections and experience that has shown a relatively low number of primary water stress corrosion cracking (PWSCC) indications inthese 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. The rolled and welded stainless steel liners within the spray, safety, and relief nozzles, which are designed to seaf the low alloy steel nozzle and dissimilar metal weld from the pressurizer vapor space, have not been credited inthe analysis.

This letter confirms that the Reference 4 EPRI Advanced Finite Element Analysis report bounds the DCPP Unit 2 pressurizer Alloy 82/182 welded pipe/nozzle components. PG&E has reviewed the report and verified that the inputs address DCPP Unit 2 weld configurations and loads, that the analysis and conclusions are applicable to the DCPP Unit 2 design, and that all welds representative of DCPP Unit 2 are adequately addressed by the crack.growth analyses and associated sensitivity cases. Finally, the analytical results applicable to DCPP Unit 2 satisfy the leakage evaluation criteria presented in the report.

Therefore, PG&E concludes the analytical results presented in Reference 4, and the current DCPP Unit 2 enhanced leakage monitoring program, provide a reasonable and adequate basis for performing mitigation activities during DCPP 2R14, currently scheduled to begin February 4, 2008, as committed to in Reference 2, after which time DCPP Unit 2 will fully satisfy the MRP-139 inspection/mitigation requirements for pressurizer Alloy 600/821182 components.

A member of the STARS (Strategic Tearning and R.esoorco Sharing) Alliance Callaway o Comanche Peak

• Olablo c*anyon a Palo Verde

• South Texas Project o Wolf Creek

Document Control0Desk PG&E Letter DCL-07-077 August 7, 2007 Page33 If you have any questions concerning this submittal, please contact. Stan Ketelsen.at 805&545-4720.

Sincerely, n S, Keenan

• enfor Vice President- Generationand Chief NuclearOfficer kjse/4328 cc. Michael A. Brown, DCPP NRC Resident Inspector Bruce S. Mallett, NRC Region IV Sandra Shewry, Director, California. Department of Health Services Alan B. Wang, Project Manager,. Office of Nuclear Reactor.R egulation Diablo Distribution