ML12353A130

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Request for Alternative No. RI-ISI-INT3 to ASME Code Requirements for Class 1 and 2 Piping Welds, Third 10-Year Inservice Inspection Interval
ML12353A130
Person / Time
Site: Diablo Canyon  Pacific Gas & Electric icon.png
Issue date: 01/16/2013
From: Markley M
Plant Licensing Branch IV
To: Halpin E
Pacific Gas & Electric Co
Sebrosky J
References
TAC ME7854, TAC ME7855
Download: ML12353A130 (8)
v • d • e


Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555*0001 January 16, 2013 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, UNIT NOS. 1 AND 2 -APPROVAL OF AN ALTERNATIVE TO THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS BOILER AND PRESSURE VESSEL CODE SECTION XI EXAMINATION REQUIREMENTS FOR CLASS 1 AND 2 PIPING WELDS (TAC NOS. ME7854 AND ME7855)

Dear Mr. Halpin:

By letter dated January 20,2012 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML12025A084), as supplemented by letter dated September 6, 2012 (ADAMS Accession No. ML12250A815), Pacific Gas and Electric Company (PG&E, the licensee), submitted a request for U.S. Nuclear Regulatory Commission (NRC) approval for continued use of risk-informed (RI) inservice inspection (lSI) process developed based on Electric Power Research Institute (EPRI) Topical Report TR-112657, Revision B-A, as an alternative to the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),

Section XI requirements for lSI of Class 1 and 2 (Categories B-F*, B-J, C-F-1, and C-F-2) piping welds for Diablo Canyon Power Plant (DCPP), Units 1 and 2. The licensee stated that the proposed alternative will provide an acceptable level of quality and safety as required by Title 10 of the Code of Federal Regulations (10 CFR), paragraph 50.55a(a)(3)(i). The request is for the third 10-year lSI interval, which is scheduled to end on May 6,2015, for DCPP, Unit 1, and March 12,2016, for DCPP, Unit 2. The DCPP RI-ISI program was initially submitted to the NRC by letter dated February 16, 2001, and was approved by the NRC for use in the second 10-year lSI interval by letter dated November 8,2001 (ADAMS Accession No. ML012970223).

The NRC staff has completed its review of the request and determined that the proposed alternative provides an acceptable level of quality and safety. Accordingly, as set forth in the enclosed safety evaluation, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a, and is otherwise in compliance with the ASME Code requirements. Therefore, pursuant to 10 CFR 50.55a(a)(3)(i),

the NRC staff authorizes continued use of the RI-ISI Program at DCPP, Units 1 and 2, for the third 10-year lSI interval.

All other ASME Code,Section XI requirements for which relief was not specifically requested and approved remain applicable, including third-party review by Authorized Nuclear Inservice Inspector.

E. Halpin - 2 If you have any questions. please contact Joseph M. Sebrosky at 301-415-1132 or via e-mail at joseph .sebrosky@nrc.gov.

Sincerely, Michael T. Markley. Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-275 and 50-323

Enclosure:

As stated cc w/encl: Distribution via Listserv

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION ALTERNATIVE TO THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS BOILER AND PRESSURE VESSEL CODE, SECTION XI, EXAMINATION REQUIREMENTS FOR CLASS 1 AND 2 PIPING WELDS FOR THIRD 10-YEAR INSERVICE INSPECTION INTERVAL DIABLO CANYON POWER PLANT, UNITS 1 AND 2 DOCKET NOS. 50-275 AND 50-323

1.0 INTRODUCTION

By letter dated January 20. 2012 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML12025A084). as supplemented by letter dated September 6.2012 (ADAMS Accession No. ML12250A815). Pacific Gas & Electric Company (PG&E. licensee),

requested U.S. Nuclear Regulatory Commission (NRC) authorization to extend the risk-informed inservice inspection (RI-ISI) program plan for Diablo Canyon Power Plant (DCPP), Units 1 and 2, to the third 10-year inservice inspection (lSI) interval. The licensee initially submitted the DCPP RI-ISI program to the NRC by letter dated February 16, 2001 (ADAMS Accession No. ML010570163), and supplemented by letter dated August 24,2001 (ADAMS Accession No. ML012490110). The DCPP RI-ISI was reviewed and approved by the NRC for use in the second 10-year lSI interval by letter dated November 8,2001 (ADAMS Accession No. ML012970223).

The licensee has considered relevant information since the development of the original program. and reviewed and updated the RI-ISI program. The current PG&E submittal proposed the continuation of the updated RI-ISI program during the third 10-year lSI interval.

2.0 REGULATORY EVALUATION

Pursuant to paragraph 50.55a(g) of Title 10 of the Code of Federal Regulations (10 CFR), the American Society of Mechanical Engineering Boiler and Pressure Vessel Code (ASME Code)

Class 1, 2, and 3 components (including supports) shall meet the requirements, "except design and access provisions and preservice examination requirements" set forth in the Code to the extent practical within the limitations of design, geometry. and materials of construction of the components. Paragraph 10 CFR 50.55a(g) also states that lSI of the ASME Code, Class 1, 2.

and 3 components is to be performed in accordance with Section XI of the ASME Code and applicable addenda, except where specific relief has been granted by the NRC.

Enclosure

-2 The regulations also require, during the first 10-year lSI interval and during subsequent intervals, that the licensee's lSI program complies with the requirements in the latest edition and addenda of Section XI of the ASME Code incorporated by reference into 10 CFR 50.55a(b) 12 months prior to the start of the 120-month interval, subject to the conditions listed therein.

DCPP is currently in its third 10-year lSI interval.

Pursuant to 10 CFR 50.55a(g), a certain percentage of ASME Code Category B-F*, B-J, C-F-1, and C-F-2 pressure retaining piping welds must receive lSI during each 10-year lSI interval.

The ASME Code requires 100 percent of all B-F* welds and 25 percent of all B-J welds greater than 1-inch nominal pipe size be selected for volumetric or surface examination, or both, on the basis of existing stress analyses. For Categories C-F-1 and C-F-2 piping welds, 7.5 percent of non-exempt welds are selected for volumetric or surface examination, or both. According to 10 CFR 50.55a(a)(3), the NRC may authorize alternatives to the requirements of 10 CFR 50.55a(g), if an applicant demonstrates that the proposed alternatives would provide an acceptable level of quality and safety, or that compliance with the specified requirement would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

The NRC staff has developed the following documents to evaluate proposed RI-ISI programs:

  • RG 1.178, Revision 1, "An Approach for Plant-Specific Risk-Informed Decisionmaking for Inservice Inspection of Piping," September 2003 (ADAMS Accession No. ML032510128), and

January 2007 (ADAMS Accession No. ML070240001).

RG 1.174, Revision 2, provides guidance on the use of probabilistic risk analysis (PRA) findings and risk insights in support of licensee requests for changes to a plant's licensing basis.

RG 1.178, Revision 1, describes an RI-ISI program as one that incorporates risk insights that can focus inspections on more important locations while at the same time maintaining or improving public health and safety. RG 1.200, Revision 1, describes one acceptable approach for determining whether the quality of the PRA. in total or the parts that are used to support an application, is sufficient to provide confidence in the results, such that the PRA can be used in regulatory decision-making.

- 3

3.0 TECHNICAL EVALUATION

3.1 Licensee's Proposed Alternative to ASME Code The licensee is proposing to continue use of the DCPP RI-ISI program plan in the third 10-year lSI interval as an alternative to the current ASME Code,Section XI, 2001 Edition through the 2003 Addenda, examination requirements for Class 1 Examination Category B-F* and B-J piping welds and Class 2 Examination Category C-F-1 and C-F-2 piping welds. The risk informed lSI program approved for use in the second 10-year inspection interval was submitted by the licensee by letters dated February 16 and August 24,2001. The proposed alternative is sought for the DCPP third 10-year lSI interval, which is scheduled to end on May 6,2015, for Unit 1 and March 12, 2016, for Unit 2.

The licensee's process used to develop the initial RI-ISI program was based on Electric Power Research Institute, Inc. (EPRI) Technical Report TR-112657, "Revised Risk-Informed Inservice Inspection Evaluation Procedure," Revision B-A, December 1999 (ADAMS Accession No. ML013470102).

3.2 NRC Staff Evaluation The NRC staff has reviewed and evaluated the licensee's proposed RI-ISI program, including those portions related to the applicable methodology and processes, based on guidance and acceptance guidelines provided in RGs 1.174 and 1.178, in Section 3.9.8, "Risk-Informed Inservice Inspection of Piping" (ADAMS Accession No. ML032510125) of NUREG-0800, "Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants:

LWR Edition" (SRP), and in EPRI TR-112657, Revision B-A. An acceptable RI-ISI program plan is expected to meet the five key principles discussed in RGs 1.174 and 1.178, SRP Section 3.9.8, and the EPRI TR-112657, Revision B-A, as stated below:

1. The proposed change meets the current regulations unless it is explicitly related to a requested exemption (Le., a specific exemption under 10 CFR 50.12, "Specific Exemptions").
2. The proposed change is consistent with a defense-in-depth philosophy.
3. The proposed change maintains sufficient safety margins.
4. When proposed changes result in an increase in CDF [core damage frequency]

or risk, the increases should be small and consistent with the intent of the Commission's Safety Goal Policy Statement.

5. The impact of the proposed change should be monitored by using performance measurement strategies.

The first principle is met in this relief request because an alternative lSI program may be authorized pursuant to 10 CFR 50.55a(3)(i) and, therefore, an exemption request is not required.

-4 The second and third principles require assurance that the alternative program is consistent with the defense-in-depth philosophy and that sufficient safety margins are maintained, respectively.

Assurance that the second and third principles are met is based on the application of the approved methodology and not on the particular inspection locations selected. In its submittal, the licensee stated that it is using the same methodology as the original RI-ISI submittal. In addition, the licensee stated that as part of the 1O-year code update, Auxiliary Feedwater piping was added to the program. The approved methodology was applied to the piping added in accordance with the 2001 Edition through the 2003 Addenda of ASME Code,Section XI. Since the methodology used to develop the RI-ISI program for the third 1O-year interval is unchanged from the methodology approved for development of the RI-ISI program used in the second 10-year lSI interval, the NRC considers the second and third principles to be met.

The fourth principle, that any increase in CDF and risk are small and consistent with the Commission's Safety Goal Policy Statement, requires an estimate of the change in risk. The change in risk estimate is dependent on the location of inspections in the proposed lSI program compared to the location of inspections that would be performed using the requirements of ASME Code,Section XI. The NRC staff has previously determined that it is not necessary to develop a new deterministic ASME program for each new 10-year interval but, instead, it is acceptable to compare the new proposed RI-ISI program with the last deterministic ASME program. The licensee stated that a new risk impact analysis was performed, and the revised program continues to represent a risk reduction when compared to the last deterministic ASME Code,Section XI inspection program. The revised program represents a reduction of 1.22E-07 in regards to CDF and 1.22E-09 in regards to large early release frequency (LERF).

The fourth principle also requires demonstration of the technical adequacy of the PRA. As discussed in RGs 1.178 and 1.200, an acceptable change in risk evaluation (and risk-ranking evaluation used to identify the most risk significant locations) requires the use of a PRA of appropriate technical quality that models the as-built and as-operated plant. The Diablo Canyon PRA (DCPRA) received a Westinghouse Owners Group (WOG) Peer review in May 2000. The

. team found two "A" Facts and Observations (F&Os) relating to human reliability analysis (HRA).

An upgrade of the HRA model was performed following the peer review, and a subsequent focused scope peer review was performed to review the upgrade. In addition to the WOG Peer review and HRA focused scope peer review, two limited scope and independent assessments of the DCPRA Level 1 and Level 2 models were performed by industry PRA experts. The Diablo Canyon Internal Flood PRA was reviewed by Scientech/Jacobsen Engineering by using an approach that compared the method of implementation and documentation of the existing internal flooding PRA with the requirements of the ASME/American Nuclear SOCiety (ANS)

Standard. The NRC staff reviewed outstanding issues associated with this review and found no open issues to have an impact on the risk results of this application.

In response to an NRC request for information (RAI) dated August 8,2012 (ADAMS Accession No. ML12221A367), the licensee addressed the risk impact at DCPP for external events including seismic and fire. The licensee highlighted EPRI TR-112657, Revision 8-A, which qualitatively addresses external events. The conclusion from this technical report regarding the impact on external events is that inclusion of external hazard groups in the quantification would not alter the results of the comparison with the acceptance guidelines. For extreme loading

- 5 such as seismic, the NRC concluded in its safety evaluation on EPRI TR-112657, Revision B-A, dated October 28, 1999 (ADAMS Accession No. ML993190477), that "additional analyses for extreme loading events are not needed because the relevant information (pipe rupture safety significant and plant-specific service experience) is addressed and additional evaluation will not change the conclusions derived from the RI-ISI program."

The fifth principle of risk-informed decision-making requires that the impact of the proposed change be monitored by using performance measurement strategies. The RI-ISI program is a living program and, as such, is subject to periodic reviews. The licensee indicates that, to satisfy the periodic review requirements, an evaluation and update was performed in accordance with the Nuclear Energy Institute document 04-05, "Living Program Guidance to Maintain Risk-Informed Inservice Inspection Program for Nuclear Power Plant Piping Systems,"

published in April 2004 on an ASME period basis as required by the initial submittal. These periodic reviews have resulted in changes in consequence rankings and the addition/deletion of welds based on plant modifications. Also, as part of the living program aspect of the RI-ISI program, the DCPP lSI Program has been augmented by incorporating the requirements of ASME Code Case N-770-1, "Alternative Examination Requirements and Acceptance Standards for Class 1 PWR [Pressurized Water Reactors] Piping and Vessel Nozzle Butt Welds Fabricated with UNS N06082 or UNS W86182 Weld Filler Material With or Without Application of Listed Mitigation Activities," consistent with 10 CFR 50.55a(g)(ii)(F)(1).

Based on the above, the NRC staff concludes that the five key principles of risk-informed decision making are ensured by the licensee's proposed third 10-year RI-ISI program and, therefore, the proposed program for the third 10-year lSI interval is acceptable.

4.0 CONCLUSION

As set forth above, the NRC staff determines that the proposed alternative provides an acceptable level of quality and safety. Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a, and is otherwise in compliance with the ASME Code requirements. Therefore, pursuant to 10 CFR 50.55a(a)(3)(i), the NRC staff authorizes continued use of the RI-ISI Program at DCPP, Units 1 and 2, for the third 10-year lSI interval.

All other ASME Code,Section XI requirements for which relief was not specifically requested and approved remain applicable, including third-party review by Authorized Nuclear Inservice Inspector.

Principal Contributors: K. Hoffman, NRR/DE/EPNB J. Patel, NRR/DRAIAPLA Date: January 16, 2013

ML12353A130 *SE memo dated OFFICE NRR/DORULPL4/PM N RR/DORULPL4/LA NRRlDRAlAPLAlBC NRR/DE/EPNB/BC NRRlDORULPL4/BC NAME JSebrosky JBurkhardt DHarrison* TLupold* MMarkley DATE 1/16/13 1/10/13 11/19/12 11/19/12 1116113

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