ML14351A047

Request for Additional Information, Relief Request REP-SI, Alternative for Repair/Replacement Activities for Certain Safety Injection Pump Welded Attachments, Remaining Useful Life +20 Years (TAC Nos. MF4476 and MF4477)

ML14351A047
Person / Time
Site:	Diablo Canyon
Issue date:	12/23/2014
From:	Lingam S P Plant Licensing Branch IV
To:	Halpin E D Pacific Gas & Electric Co
Lingam S P
References
TAC MF4476, TAC MF4477
Download: ML14351A047 (6)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 December 23, 2014 Mr. Edward D. Halpin Senior Vice President and Chief Nuclear Officer Pacific Gas and Electric Company Diablo Canyon Power Plant P.O. Box 56, Mail Code 104/6 Avila Beach, CA 93424

SUBJECT:

DIABLO CANYON POWER PLANT, UNITS 1 AND 2 -INSERVICE INSPECTION PROGRAM REQUEST FOR ALTERNATIVE REP-SI: PROPOSED ALTERNATIVE TO REQUIREMENTS FOR REPAIR AND REPLACEMENT ACTIVITIES FOR CERTAIN SAFETY INJECTION PUMP WELDED ATTACHMENTS (TAG NOS. MF4476 AND MF4477)

Dear Mr. Halpin:

By letter dated July 21, 2014 (Agencywide Documents Access and Management System Accession No. ML 14202A613), Pacific Gas and Electric Company (the licensee) requested relief from the requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, IWA-4000, "Repair/Replacement Activities," including IWA-4130, "Alternative Requirements," and IWA-4131, "Small Items," as corrective action for the four affected Code Class 2, NPS [nominal pipe size] 3/4-inch socket welds on each safety injection (SI) pump at Diablo Canyon Power Plant (DCPP), Units 1 and 2. The licensee submitted lnservice Inspection Request for Alternative REP-SI for U.S. Nuclear Regulatory Commission (NRC) review and approval.

The relief request is related to acceptance of socket welds at the vent and drain lines associated with the three safety injection pumps. Pursuant to Title 10 of the Code of Federal Regulations (1 0 CFR) 50.55a(a)(3)(i), the licensee requested NRC approval to use an alternative from the requirements of the ASME Code,Section XI, for Repair/Replacement rules governing socket welded attachments to safety injection pumps. The NRC staff has reviewed the submittal and has determined that additional information is needed to complete its review. The specific questions are found in the following enclosed request for additional information (RAI). A draft form of these RAis was provided to DCPP licensee staff. During a recent licensing status call on December 9, 2014, between the NRC project manager for DCPP and DCPP licensing staff, it was agreed that no additional licensee clarifications (telecoms) were necessary.

Please respond to the enclosed final RAis no later than 45 days from the date of this letter.

E. Halpin If you have any questions, please contact me at 301-415-1564 or via e-mail at Siva.Lingam@nrc.gov.

Docket Nos. 50-275 and 50-323

Enclosure:

Request for Additional Information cc w/encl: Distribution via Listserv Sincerely, Siva P. Lingam, Project Manager Plant Licensing Branch IV-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 REQUEST FOR ADDITIONAL INFORMATION INSERVICE INSPECTION REQUEST FOR ALTERNATIVE REP-SI ACCEPTANCE OF VENT AND DRAIN SOCKET WELDS AT SAFETY INJECTION PUMPS PACIFIC GAS AND ELECTRIC COMPANY DIABLO CANYON POWER PLANT, UNITS 1 AND 2 DOCKET NOS. 50-275 AND 50-323 By letter dated July 21, 2014 (Agencywide Documents Access and Management System Accession No. ML 14202A613), Pacific Gas and Electric Company (the licensee) requested relief from the requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, IWA-4000, at Diablo Canyon Power Plant (DCPP), Units 1 and 2. The licensee submitted lnservice Inspection Request for Alternative REP-SI for U.S. Nuclear Regulatory Commission (NRC) review and approval.

The relief request is related to acceptance of socket welds at the vent and drain lines associated with the three safety injection (SI) pumps. In order to to complete its review, the NRC staff requests the following additional information.

RAI-EVIB 1.0 The relief request is based on the premise that existing Sl pump vent and drain socket welds may be determined acceptable as-is for continued service. However, the possibility exists that all vent and drain socket welds could fail on an Sl pump. To properly evaluate the relief request, the NRC staff requests that the licensee describe: (a) The safety significance if all vent and drain weld connections are severed on a single Sl pump. (b) In case of failure of all vent and drain weld connections on a single Sl pump, please explain if the safety function of nearby equipment and personnel will be affected.

RAI-EVIB 2.0 The relief request partly bases the acceptability of existing Sl pump vent and drain socket welds on the performance of a welding procedure qualification test with representative type 410 stainless steel (P-6) and type 304 stainless steel (P-8) base materials using type 309 filler metal per the production welding procedure parameters without post-weld heat treatment, and that the qualification test assembly passed the required ASME Code destructive tests. However, for this Enclosure material combination, the possibility exists that untempered martensite may be formed in the P-6 heat affected zone of the qualification weldment.

The NRC staff requests that the licensee discuss the following: (a) Whether hardness testing was performed in the P-6 heat affected zone of the qualification weldment to objectively measure the possibility and extent of untempered martensite formation. (b) Since the destructive test specimens were machined down from 0.375-inch in thickness to 0.300-inch in thickness, please justify that the machined destructive test specimens are representative of the qualification weldment in terms of microstructure.

Discuss whether the possibility exists for detrimental untempered martensite to be formed during welding but removed during the preparation of the destructive test specimens.

RAI-EPNB 1.0 The licensee submitted the relief request under paragraph 50.55a(a)(3)(i) of Title 1 0 of the Code of Federal Regulations (1 0 CFR). The NRC staff believes that the use of the proposed alternative (i.e., continued operation with the existing non-conforming welds) provides a lower level of quality and safety than with ASME Code compliant welds. The NRC staff suggests that it is more appropriate to request the relief pursuant to 10 CFR 50.55a(a)(3)(ii).

Please propose the alternative to the ASME Code under 10 CFR 50.55a(a)(3)(ii) or justify why it is appropriate to submit this relief request under 10 CFR 50.55a(a)(3)(i).

The licensee should also provide hardship justification for not complying with the ASME Code requirements.

RAI-EPNB 2.0 The industry operating experience has shown that socket welds are susceptible to through-wall cracking. (a) Please discuss whether any leakage detection systems are available to detect any potential leak from the subject socket welds and whether the operators in the control room would be notified of the leakage. (b) Please discuss the consequence of a through-wall leak and a complete severance at any of the subject socket welds. RAI-EPNB 3.0 When the safety injection pumps are running; Please discuss whether vibration exists on the drain lines and vent lines. If yes, discuss the potential for the vibration that may cause cracking at the socket welds. Structural Integrity Associates Stress Calculation RAI-EPNB 4.0 Section 2.4, page 2-3, of the stress calculation states that unit axial load of 1000 pounds (lbs). was used as an input. Please discuss where and how 1 000 lbs. was obtained and derived. RAI-EPNB 5.0 Section 3 of the stress calculation states that when analyzing the outside diameter flaw, the methods of the ASME Code,Section XI, Appendix C, C-7300 and American Petroleum Institute, API-579, were used to obtain stress intensity factors. However, when analyzing the inside diameter flaw, it does not appear that the API-579 method was used. Please clarify whether API-579 method was used to evaluate the inside diameter flaw. If not, discuss the reference of the flaw evaluation method. RAI-EPNB 6.0 Section 3.3.2, page 3-8, of the stress calculation states that " ... residual stresses would not contribute to fatigue crack growth ... " The NRC staff believes that although residual stresses are steady state in nature (i.e., constant), they affect the maximum tensile stress and R [stress ratio] and may, therefore, affect fatigue crack growth. Please clarify the above quoted statement.

Discuss whether the above statement is specifically applied to the inside diameter flaw in the subject component.

RAI-EPNB 7.0 Section 4 of the stress calculation discusses fatigue crack growth. Section 4 also discussed a postulated inside diameter initiated flaw. If an inside diameter flaw is postulated, please discuss the likelihood of stress-corrosion cracking in the subject welds. RAI-EPNB 8.0 Page 5-1 of the stress calculation states that the allowable flaw depth for an inside diameter flaw exceeds 80 percent of the wall thickness.

IWB-3643 of the ASME Code,Section XI, 2003 addenda (Code of record) limits the maximum allowable flaw depth to 75 percent through-wall.

Please explain why the allowable flaw depth for an inside diameter flaw exceeds (i.e., non-conservative) the ASME Code,Section XI limitation.

E. Halpin If you have any questions, please contact me at 301-415-1564 or via e-mail at Siva. Lingam@nrc.gov.

Docket Nos. 50-275 and 50-323

Enclosure:

Request for Additional Information cc w/encl: Distribution via Listserv DISTRIBUTION:

PUBLIC LPL4-1 Reading RidsAcrsAcnw_MaiiCTR Resource RidsNrrDeEvib Resource RidsNrrDeEpnb Resource ADAMS Accession No. ML 14351A047 Sincerely, /RAJ Siva P. Lingam, Project Manager Plant Licensing Branch IV-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation RidsNrrDorllpl4-1 Resource RidsNrrLAJBurkhardt Resource RidsNrrPMDiabloCanyon Resource RidsRgn4MaiiCenter Resource *email dated OFFICE NRR/DORL/LPL4-1/PM NRR/DORL/LPL4-1/PM NRR/DORLILPL4-1/LA NRR/DE/EPNB NAME RHaskell SLingam JBurkhardt DAiley* DATE 12/12/2014 12/23/14 12/18/14 10/8/14 OFFICE NRR/DE/EVIB/BC NRR/DORLILPL4-1/BC(A)

NRR/DORL/LPL4-1/PM NAME SRosenberg*

EOesterle SLingam DATE 11/12/14 12/23/14 12/23/14 OFFICIAL RECORD COPY