DCL-12-084, Response to NRC Request for Additional Information Regarding Request for Approval of an Alternative to the ASME Boiler and Pressure Vessel Code Section XI Examination Requirements for Class 1 and 2 Piping Welds
| ML12250A815 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 09/06/2012 |
| From: | Welsch J Pacific Gas & Electric Co |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| DCL-12-084 | |
| Download: ML12250A815 (6) | |
Text
Pacific Gas and Electric Company James M. Welsch Diablo Canyon Power Plant Station Director Mail Code 104/5/502 P. O. Box 56 Avila Beach, CA 93 424 September 6, 2012 805. 545.3242 Internal: 691. 3242 Fax: 805.545.4234 PG&E Letter DCL-12-084 Internet: JMW1@pge.com u.S. Nuclear Regulatory Commission 10 CFR 50.55a ATTN: Docu ment Control Desk Washington, DC 20555-0001 Docket No. 50-275, OL-DPR-80 Docket No. 50-323, OL-DPR-82 Diablo Canyon Units 1 and 2 Response to NRC Request for Additional Information Regarding Request for Approval of an Alternative to the American Society of Mechanical Engineers (ASME)
Boiler and Pressure Vessel Code Section XI Examination Requirements for Class 1 and 2 Piping Welds
Reference:
- 1. PG&E Letter DCL-12-007, "Request for Approval of an Alternative to the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code Section XI Examination Requirements for Class 1 and 2 Piping Welds," dated January 20, 2012 In Reference 1, Pacific Gas and Electric Company (PG&E) submitted a request for approval to use an alternative to the ASME Section XI Code examination requirements for inservice inspection of Class 1 and 2 piping welds (Categories B-J, C-F-1, and C-F-2) for Diablo Canyon Power Plant (DCPP)
Units 1 and 2.
The NRC Staff provided a request for additional information (RAI) via e-mail, dated August 8, 2012. The Enclosure to this letter provides PG&E's response to the NRC RAI.
PG&E makes no regulatory commitments (as defined by NEI 99-04) in this letter.
If you have any questions or require additional information, please contact Mr. Tom Baldwin at (805) 545-4720.
Sincerely,
--L_~ A wdL
)i~:S~. Welsch Interim Site Vice President A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway
- Comanche Peak
- Diablo Canyon
- Palo Verde
- San Onofre
- South Texas Project
- Wolf Creek
__ Document Control Desk PG&E Letter DCL-12-084
~&~ September 6,2012 Page 2 RNTT14231/50505234 Enclosure cc: Diablo Distribution cc/enc: Elmo E. Collins, NRC Region IV Dean H. Overland, NRC Senior Resident Inspector Michael S. Peck, NRC Senior Resident Inspector Joseph M. Sebrosky, NRR Project Manager State of California, Department of Occupational Safety and Health, Pressure Vessel Unit A member of the STARS (Strategic Teaming and Resource Sharing) Alliance Callaway
- Comanche Peak
- Diablo Canyon
- Palo Verde
- San Onofre
- South Texas Project
- Wolf Creek
Enclosure PG&E Letter DCL-12-084 PG&E Response to NRC Request for Additional Information Regarding Request for Approval of an Alternative to the American Society of Mechanical Engineers (ASME)
Boiler and Pressure Vessel Code Section XI Examination Requirements for Class 1 and 2 Piping Welds NRC Question 1:
The NRC issued rulemaking on June 21, 2011 which requires licensees to follow an augmented inservice inspection program in accordance with ASME Code Case N-770-1, "Alternative Examination Requirements and Acceptance Standards for Class 1 PWR Piping and Vessel Nozzle Butt Welds Fabricated With UNS N06082 or UNS W86182 Weld Filler Material With or Without Application of Listed Mitigation Activities," and limitations listed in Title 10 of Code of Federal Regulations SO. SSa (g) (6) (U) (F). In addition, the NRC held a public meeting to discuss the June rulemaking and the implementation of Code Case N-770-1 on July 12, 2011.
Agencywide Document Access and Management System (ADAMS) accession number # ML112240818 documents the NRC summary of that meeting. The NRC staff's concern is that, the welds required to be examined in accordance with the augmented program required by SO. SSa(g) (6)(U) (F) should not be counted as exams selected to satisfy the RI-ISI program. Please describe how DCPP will address the requirements of the June 2011 rulemaking and ASME Code Case N-770-1 in implementing Relief Request RI-ISI-INT3-U1 &2.
PG&E Response:
ASME Code Case N-770-1 is implemented separately from the Risk Informed Inservice Inspection (RI-ISI) Program in accordance with the requirements of 10 CFR 50.55a(g)(6)(ii)(F). No inspections of Code Category B-F welds that are susceptible to primary water stress corrosion cracking (PWSCC) alone are credited under the RI-ISI Program. As such, examinations performed in accordance with Code Case N-770-1 will not be credited under the RI-ISI Program. However, if in the future any of these welds are selected for examination due to their susceptibility to another degradation mechanism, at that time they may undergo a separate examination for this degradation mechanism and be credited under the RI-ISI Program.
The RI-ISI Program alternative for the third 1O-year lSI interval will have no impact on the implementation of requirements for Code Case N-770-1.
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Enclosure PG&E Letter DCL-12-0B4 NRC Question 2:
Please describe how the proposed RI-ISI program will satisfy the requirements of IWB-2412 and IWC-2412 for percentage of examinations completed.
PG&E Response:
The examinations are scheduled in accordance with ASME Section XI, Code Paragraphs IWB-2412 and IWC-2412 requirements. The distributions for weld examinations completed will satisfy the requirements of Table IWB-2412-1 for Class 1 piping exams and Table IWC-2412-1 for Class 2 examinations.
NRC Question 3:
IWB-2420(a) and IWC-2420(a), "Successive Examinations" require that "the sequence of component examinations which was established during the first inspection interval shall be repeated during each successive inspection interval, to the extent practical."
This requirement is to ensure components are examined on a once per 1O-year frequency to the extent practical. Please discuss how the proposed RI-ISI program satisfies this requirement.
PG&E Response:
Risk informed examinations are scheduled in accordance with Successive Examination IWB-2420(a) requirements for Class 1 welds and Successive Examination IWC-2420(a) for Class 2 welds and the sequence of component examinations established during the first risk informed interval application are being repeated in this interval. Allowing the application of the risk informed process for this interval has permitted repeating the sequence of examinations established during the initial risk informed interval for all welds that remain in the program. The high risk category welds that were front loaded in the initial two periods of the first interval are being examined in the initial two periods of this interval.
Note that periodic Living Program Review and Updates of the RI-ISI Program may identify deletions, additions or changes to the items selected for examination. In the case where changes are implemented, future examinations of newly selected items will be scheduled per the requirements of IWB-2420(a) and IWC-2420(a), as applicable.
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Enclosure PG&E Letter DCL-12-084 NRC Question 4:
The original RI-ISI program required 10% of the ASME Class 1 piping non-socket rd welds, is this requirement retained by the 3 interval RI-ISI program? The -1 and Attachment 1-2 tables do not identify any ASME Section XI Item Numbers making it impossible for the NRC staff to determine)f this requirement was retained.
PG&E Response:
The commitment to examine 10 percent of the ASME Class 1 piping nonsocket welds is retained by the third interval RI-ISI Program.
NRC Question 5:
The original RI-ISI program stated that RI-ISI examination locations were selected such that >90% coverage is attainable. Was this requirement retained in the examination locations selected for the proposed program?
PG&E Response:
In the proposed program, the RI-ISI examination locations were selected such that greater than 90 percent coverage is attainable. The weld selections for the original RI-ISI Program were predicated on achieving greater than 90 percent coverage for the examination. In field practice, some welds were found to have limitations to this coverage due to configuration, obstructions, etc. When possible, these welds were substituted in the RI-ISI Program by different welds in the same risk segment, or if not possible, these welds were substituted by different welds in the same risk category and with the same degradation mechanism to achieve greater than 90 percent coverage.
This is reflected in the proposed RI-ISI Program.
NRC Question 6:
As a living program the original RI-ISI program required a review of the program on an ASME period basis. Is this requirement retained in the proposed RI-ISI program?
PG&E Response:
The prescribed reviews have been conducted and results factored into the revised RI-ISI Program and the requirement is retained in the proposed RI-ISI Program.
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Enclosure PG&E Letter DCL-12-084 NRC Question 7:
Risk informed applications must address external events as specified in Regulatory Guide 1.200 Revision 2. Please provide an assessment for how external events, including seismic events, at Diablo Canyon Power Plant affect the results of the risk impact analysis for the third ten-year interval inservice inspection program plan.
PG&E Response:
Risk informed applications must address the impact of external events as addressed in Parts 4 through 9 of the ASME/ANS Probabilistic Risk Assessment (PRA) Standard.
Electronic Power Research Institute Technical Report (TR) 1021467 qualitatively addresses external event impacts to the RI-ISI application. The conclusion from this TR regarding the impact of 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 internal fire, the NRC safety evaluation (SE) of this TR states that fire events may challenge piping integrity but that such challenges are expected to be less frequent and not significantly different than challenges caused by the random occurrence of internal initiating events. As such, the impact of the internal fire PRA results does not have a significant impact on the conclusions from the RI-ISI application.
For external events that may subject piping to extreme loading (seismic, flooding, high winds), the NRC SE for the TR concludes that "additional analyses of 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." Therefore, Diablo Canyon Power Plant has concluded that the results from such external event PRAs do not significantly impact the RI-ISI application.
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