DCL-15-040, Response to NRC Request for Additional Information Regarding Unit 1 Reactor Vessel Inspection Interval Extension from 10 to 20 Years

Response to NRC Request for Additional Information Regarding Unit 1 Reactor Vessel Inspection Interval Extension from 10 to 20 Years

ML15089A595
Person / Time
Site:	Diablo Canyon
Issue date:	03/30/2015
From:	Allen B Pacific Gas & Electric Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
DCL-15-040
Download: ML15089A595 (4)

Text

Pacific Gas and Electric Company Barry S. Allen Diablo Canyon Power Plant Vice President, Nuclear Services Mail Code 104/6 P. 0. Box 56 Avila Beach, CA 93424 805.545.4888 March 30, 2015 Internal: 691.4888 Fax: 805.545.6445 PG&E Letter DCL-15-040 u~s. Nuclear Regulatory Commission 10 CFR 50.55a ATTN: Document Control Desk Washington, DC 20555-0001 Docket No. 50-275, OL-DPR-80 Diablo Canyon Power Plant Unit 1 Response to NRC Request for Additional Information Regarding Unit 1 Reactor Vessel Inspection Interval Extension From 10 to 20 Years

References:

1. PG&E Letter DCL-14-074, "ASME Section Xllnservice Inspection Program Request for Alternative RPV-U 1-Extension to Allow Use of Alternate Reactor Inspection Interval Requirements," dated August 18, 2014 (ML14230A618)

2. NRC Letter, "Diablo Canyon, Unit 1 - RAis for ASME Section XI lSI Program Request for Alternative RPV-U 1- Extension to Allow Use of

• Alternate Reactor Inspection Interval Requirements (TAC No.

MF4678)," dated February 24, 2014

Dear Commissioners and Staff:

In Reference 1, Pacific Gas and Electric Company (PG&E) submitted Relief Request for NRC approval to extend the Diablo Canyon Power Plant (DCPP)

Unit 1 reactor vessel inspection interval from 10 to 20 years in accordance with WCAP-16168-NP-A, Revision 3, "Risk-Informed Extension of the Reactor Vessel In-Service Inspection Interval."

The NRC Staff provided a request for additional information (RAI) via an e-mail dated February 24, 2014 (Reference 2). The Enclosure to this letter provides PG&E's responses to the RAI questions.

This communication does not contain regulatory commitments (as defined by NEI 99-04).

If you have any questions or require additional information, please contact Mr. Philippe Soenen at (805) 545-6984.

A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway

• Diablo Canyon

• Palo Verde

• Wolf Creek

Document Control Desk PG&E Letter DCL-15-040 March 30, 2015 Page 2 Sincerely, Bar;;:z 5. ~

Vice President- Nuclear Services rntU4231/50621143 Enclosure cc: Diablo Distribution cc/enc: Marc L. Dapas, NRC Region IV Administrator Thomas R. Hipschman, NRC Senior Resident Inspector Siva P. Lingam, NRC Project Manager Gonzalo L. Perez, Branch Chief, California Department of Public Health State of California, Pressure Vessel Unit A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway

• Diablo Canyon

• Palo Verde

• Wolf Creek

Enclosure PG&E Letter DCL-15-040 PG&E Response to NRC Request for Additional Information Regarding Relief Request REP-51 NRC Question RAI-1:

Table 1, "Critical Parameters for the Application of Bounding Analysis for DCPP Unit 1,"states that DCPP Unit 1 is bounded by 7 heatup/cooldown cycles per year. Please cite the plant design basis for heatup/cooldown cycles per year.

PG&E Response:

Table 5.2-4 in Updated Final Safety Analysis Report (UFSAR),

Revision 21 lists the summary of all Reactor Coolant System (RCS) design transients, including the number of RCS heatup/cooldown design transients. The 7 heatup/cooldown cycles per year (for a period of 80 years) assumed for the Westinghouse pilot plant study in WCAP-16168-NP-A, Revision 3 (Reference 1) provides a bounding fatigue crack growth value for the Diablo Canyon Unit 1 RCS design transients listed in UFSAR Table 5.2-4 .

The projected number of RCS transient cycles for 60 years of operation are provided in Table 4.3-2 of the Diablo Canyon Unit 1 License Renewal Application (Reference 2), which is less than the number of RCS design transients listed in UFSAR Table 5.2-4. Diablo Canyon Unit 1 is therefore bounded by the 7 heatup/cooldown cycles per year assumed for the Westinghouse pilot plant study in WCAP-16168-NP-A, Revision 3.

NRC Question RAI-2:

In Table 3, the licensee's calculated 11T 3o, RTMAX-XX, and TWCF95-XX values were inconsistent with the calculations performed by the NRC staff. Please provide further detail on how 11T30 was calculated. In particular, please provide the Reactor Coolant System Temperature, P

[wt%,], and Mn [wto/o] values used to perform the calculations~

PG&E Response:

WCAP-16168-NP-A, Revision 3 (Reference 1) contains the U.S. NRC Safety Evaluation Report (SER) provided for the WCAP-16168-NP topical report. Paragraph 3.4, Item 1 of the U.S. NRC SER states the following:

1

Enclosure PG&E Letter DCL-15-040 The RTMAX-X and the shift in Charpy transition temperature produced by irradiation defined at the 30 ft-lb energy level, L1 T3o, must be calculated using the methodology documented in the latest revision of RG 1.99, "Radiation Embrittlement of Reactor Vessel Materials, " or other NRC-approved methodology.

The 11T 30 values for the Diablo Canyon Unit 1 reactor vessel materials were calculated using the Regulatory Guide (RG) 1.99, Revision 2 methodology (Reference 3). Specifically, the 11T 30 values were determined per Equation 2 of RG 1.99, Revision 2:

11T 30 = /1RT NDT = (CF) f 0 '28 - 1

0. 0iogf)

The chemistry factor (CF) values are a function of copper and nickel content, and are provided in Table 3 of the request (Reference 4) for each of the materials. The RCS temperature as well as the weight percent of phosphorus (P) and manganese (Mn) contents are not needed to calculate the 11T 30 values in accordance with the RG 1.99, Revision 2.

The neutron fluence (f) values used to calculate the 11T 30 values for each of the materials are also provided in Table 3 of the request.

References:

1. Westinghouse Report WCAP-16168-NP-A, Revision 3, "Risk-Informed Extension of the Reactor Vessel In-Service Inspection Interval," October 2011 (ADAMS Accession Number ML11306A084)

2. "License Renewal Application Diablo Canyon Power Plant Unit 1 and Unit 2," Facility Operating License Nos. DPR-80 and DPR-82 (ADAMS Accession Number ML093340086)

3. NRC Regulatory Guide 1.99, Revision 2, "Radiation Embrittlement of Reactor Vessel Materials," U.S. Nuclear Regulatory Commission, May 1988

4. PG&E Letter DCL-14-074, "ASME Section Xllnservice Inspection Program Request for Alternative RPV-U 1-Extension to Allow Use of Alternate Reactor Inspection Interval Requirements,"

August 18, 2014 (ADAMS Accession Number ML14230A618) 2