ML102980689

Request for Additional Information Related to the Review of the Diablo Canyon Nuclear Power Plant, Units 1 and 2, License Renewal Application (TAC Nos. ME2896 and ME2897) - Time Limited Aging Analysis

ML102980689
Person / Time
Site:	Diablo Canyon
Issue date:	11/02/2010
From:	Ferrer N License Renewal Projects Branch 2
To:	Conway J Pacific Gas & Electric Co
Ferrer, N B, NRR/DLR, 415-1045
References
TAC ME2896, TAC ME2897
Download: ML102980689 (6)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555'()001 November 2,2010 Mr. John Conway Senior Vice President Generation and Chief Nuclear Officer Pacific Gas and Electric Company 77 Beale Street, MC B32 San Francisco, CA 94105

SUBJECT:

REQUEST FOR ADDITIONAL INFORMATION RELATED TO THE REVIEW OF THE DIABLO CANYON NUCLEAR POWER PLANT, UNITS 1 AND 2, LICENSE RENEWAL APPLICATION (TAC NOS. ME2896 AND ME2897) - TIME LIMITED AGING ANLYSIS

Dear Mr. Conway:

By letter dated November 23, 2009, Pacific Gas & Electric Company submitted an application pursuant to Title 10 of the Code of Federal Regulations Part 54, to renew the operating licenses for Diablo Canyon Nuclear Power Plant, Units 1 and 2, for review by the U.S. Nuclear Regulatory Commission (NRC or the staff). The staff is reviewing the information contained in the license renewal application and has identified, in the enclosure, areas where additional information is needed to complete the review.

The request for additional information was discussed with Mr. Terry Grebel, and a mutually agreeable date for the response is within 30 days from the date of this letter. If you have any questions, please contact me at 301-415-1045 or bye-mail at nathaniel.ferrer@nrc.gov.

Sincerely, Nathaniel Ferrer, Project Manager Projects Branch 2 Division of License Renewal Office of Nuclear Reactor Regulation Docket Nos. 50-275 and 50-323

Enclosure:

As stated cc w/encl: Distribution via Listserv

Diablo Canyon Nuclear Power Plant, Units 1 and 2 License Renewal Application Request for Additional Information Set 30 Time Limited Aging Analysis - Clarification on Responses Based on the U.S. Nuclear Regulatory Commission (NRC or the staff's) review of Pacific Gas and Electric Company (PG&E or the applicant's) response dated September 24,2010, please provide responses to the following:

RAI4.7.5-2 (follow up)

By letter dated September 24, 2010, in response to request for additional information (RAI) 4.7.5-2, item 4, the applicant stated that the indication in residual heat removal piping WIC-95 is connected to the inside surface and that the flaw was characterized as a construction-related flaw and was not service induced.

Questions:

1. The staff noted that the original flaw may be a fabrication defect embedded in the wall thickness. However, the flaw appears to have grown to the pipe surface. Therefore, the flaw should be considered service-induced. Without loading from system operations, the flaw would not have grown to the surface. Explain why an inside surface-connected flaw is not considered to be a service-induced flaw.

2. Explain the degradation mechanism that appears to have caused the flaw to open to the pipe surface.

3. The flaw evaluation in the applicant's submittal dated May 7, 1997, as shown in the Plant Aging Management Document Retrieval and Research System does not provide a detailed discussion on the flaw growth calculation. It appears that the flaw evaluation dated May 7, 1997, was based on only the fatigue degradation mechanism. However, as the flaw has reached the inside surface of the pipe, the flaw growth appears to be caused by degradation mechanisms other than fatigue.

(a) Justify why the fatigue degradation mechanism is adequate for the surface connected flaw without considering the stress corrosion cracking degradation mechanism which has a higher growth rate than the fatigue mechanism.

(b) Justify the flaw growth rate used in light of the actual flaw growth based on the operating experience.

(c) Discuss the flaw growth calculations in detail.

(d) Provide the flaw growth rate used in the calculation and its reference.

4. Provide the flaw evaluation of the subject pipe as shown in PG&E Letter DCL-97-086 dated May 7, 1997.

5. Provide the nominal pipe size, the pipe wall thickness, outside diameter of the pipe, pipe material specification, material specification of weld WIC-95.

ENCLOSURE

- 2 RAI 4.7.5-3 (follow up)

By letter dated September 24, 2010, in response to RAI 4.7.5-3, item 2, the applicant stated that the indication in the Unit 2 auxiliary feedwater piping line 567 was surface-connected, not embedded. Discuss whether the indication is connected to the inside surface or outside surface of the auxiliary feedwater pipe.

RAI4.7.5-3 (follow up)

By letter dated September 24, 2010, in response to RAI 4.7.5-3, item 4, the applicant stated that it has no plans to conduct any further inspections on the Unit 2 auxiliary feedwater line 567 because (1) it [the additional inspection1 is not required, (2) the flaw is a fabrication defect and is not service-related, and (3) a follow-up examination showed there was no change in the flaw.

Questions:

1. A fabrication defect usually is embedded in the pipe or weld wall thickness. If the flaw reaches the surface, it is driven by service-induced loading. Explain why the flaw is not service related.

2. The staff does not agree with the applicant's reasons for not inspecting the Unit 2 auxiliary feedwater line 567. The applicant stated that the flaw is a fabrication defect and is not service-related. The staff does not agree with this assessment because the applicant indicated that the flaw is connected to the pipe surface. If a flaw is connected to the surface, the flaw propagation is most likely to be service-related. A fabrication flaw would not be connected to the pipe surface because a surface-connected fabrication defect would have been removed during the construction to satisfy the requirements of the ASME Code,Section III. The applicant stated that a follow-up examination showed there was no change in the flaw. Even though there was no growth in the follow-up examination, this result does not imply that the flaw would not grow in the future. In the future, the flaw may extend to an unfavorable stress region of the pipe wall and the flaw growth may initiate at a later date. The subject flaw is connected to the pipe surface which means that environmental impact on the flaw may exacerbate its growth in the long term. The staff does not believe the original flaw evaluation included the environmental impact on the flaw growth.

In light of the above concerns, the applicant's response to RAI4.7.5-3, item 4, does not provide a reasonable assurance that the flaw in the Unit 2 auxiliary feedwater piping line 567 would not grow and that the structural integrity of the subject piping will be maintained in the future. Provide additional technical basis for not examining the surface-connected flaw.

- 3

3. It appears that the flaw evaluation of the Unit 2 auxiliary feedwater line 567 dated October 22, 1999, was based on only the fatigue degradation mechanism. However, as the flaw has reached to the surface of the pipe, the flaw growth appears to be caused by degradation mechanisms other than fatigue.

(a) Justify why the fatigue degradation mechanism is adequate for the surface connected flaw without considering the stress corrosion cracking degradation mechanism which has a higher growth rate than the fatigue.

(b) Justify the flaw growth rate used in light of the actual flaw growth based on the operating experience.

(c) Provide the flaw growth rate used in the analysis and associated reference.

November 2, 2010 Mr. John Conway Senior Vice President Generation and Chief Nuclear Officer Pacific Gas and Electric Company 77 Beale Street, MC B32 San Francisco, CA 94105

SUBJECT:

REQUEST FOR ADDITIONAL INFORMATION RELATED TO THE REVIEW OF THE DIABLO CANYON NUCLEAR POWER PLANT, UNITS 1 AND 2, LICENSE RENEWAL APPLICATION (TAC NOS. ME2896 AND ME2897) - TIME LIMITED AGING ANLYSIS

Dear Mr. Conway:

By letter dated November 23, 2009, Pacific Gas & Electric Company submitted an application pursuant to Title 10 of the Code of Federal Regulations Part 54, to renew the operating licenses for Diablo Canyon Nuclear Power Plant, Units 1 and 2, for review by the U.S. Nuclear Regulatory Commission (NRC or the staff). The staff is reviewing the information contained in the license renewal application and has identified, in the enclosure, areas where additional information is needed to complete the review.

The request for additional information was discussed with Mr. Terry Grebel, and a mutually agreeable date for the response is within 30 days from the date of this letter. If you have any questions, please contact me at 301-415-1045 or bye-mail at nathaniel.ferrer@nrc.gov.

Sincerely, IRA!

Nathaniel Ferrer, Project Manager Projects Branch 2 Division of License Renewal Office of Nuclear Reactor Regulation Docket Nos. 50-275 and 50-323

Enclosure:

As stated cc w/encl: Distribution via Listserv DISTRIBUTION:

See next page ADAMS Accession No'.. ML102980689

• concurrence via e-mail OFFICE' LA:DLR PM:RPB2:DLR BC:RPB2:DLR PM:RPB2:DLR NAME IKing

• NFerrer DWrona NFerrer DATE 10/27/10 10/28/10 11/02/10 11/02/10 OFFICIAL RECORD COpy

Letter to J. Conway from N. Ferrer dated November 2, 2010

SUBJECT:

REQUEST FOR ADDITIONAL INFORMATION RELATED TO THE REVIEW OF THE DIABLO CANYON NUCLEAR POWER PLANT, UNITS 1 AND 2, LICENSE RENEWAL APPLICATION (TAC NOS. ME2896 AND ME2897) - TIME LIMITED AGING ANL YSIS DISTRIBUTION:

HARD COPY:

DLRRF E-MAIL:

PUBLIC RidsNrrDlr Resource RidsNrrDlrRpb1 Resource RidsNrrDlrRpb2 Resource RidsNrrDlrRarb Resource RidsNrrDlrRapb Resource RidsNrrDlrRasb Resource RidsNrrDlrRerb Resource RidsNrrDlrRpob Resource RidsOgcMailCenter Resource NFerrer KGreen AStuyvenberg DWrona AWang MPeck, RIV TBrown, RI GMiller, RIV NO'Keefe, RIV ICouret, OPA VDricks, OPA WMaier, RIV JWeil,OCA EWiliiamson, OGC SUttal,OGC RRihm, EDO