ML023100039
| ML023100039 | |
| Person / Time | |
|---|---|
| Site: | Dresden, Sequoyah, Arkansas Nuclear  |
| Issue date: | 11/11/2002 |
| From: | Mary Johnson NRC/NRR/DSSA/SPSB |
| To: | Bahadur S NRC/ACNW, Advisory Committee on Reactor Safeguards |
| Harrison D, NRR/SPSB, 415-3587 | |
| References | |
| RG-1.174 | |
| Download: ML023100039 (6) | |
Text
November 11, 2002 MEMORANDUM TO Dr. Sher Bahadur, Associate Director for Technical Support Advisory Committee for Reactor Safeguards Advisory Committee for Nuclear Waste FROM: Michael R. Johnson, Branch Chief/RA/
Probabilistic Safety Assessment Branch Division of Systems Safety and Analysis Office of Nuclear Reactor Regulation
SUBJECT:
EXAMPLES OF RISK-INFORMED LICENSING ACTIONS During a meeting with the Advisory Committee for Reactor Safeguards (ACRS) Subcommittee on Probabilistic Risk Assessment (PRA) on September 9, 2002, it was suggested that the ACRS would benefit from being able to examine and discuss examples of risk-informed licensing actions completed by the Office of Nuclear Reactor Regulation (NRR). Therefore, attached are various examples of staff risk reviews of license applications that requested to implement: 1) a risk-informed inservice testing (RI-IST) program for selected valves, 2) a risk-informed inservice inspection (RI-ISI) program, 3) a risk-informed technical specification (RI-TS) change to extend the allowed outage time (AOT) for the emergency diesel generators (EDGs), and 4) a RI-TS change to extend the integrated leak rate test (ILRT) interval. In addition, attached is the risk-related portion of an extended power uprate (EPU) license application and the staff review. Although EPU applications are not identified as risk-informed licensing actions, licensees address, and the staff reviews, the risks associated with the EPU.
Note that the EPU Safety Analysis Report (ADAMS Accession # ML010080145) contains GE proprietary information and thus, should not be released to the public and should only be provided to those with a need-to-know to conduct official business. This document, which was provided previously to the ACRS during the Dresden EPU license amendment review, is identified in the attached summary, but is not enclosed with this transmittal. A copy of this document will be made available upon request.
The aim of providing these examples is to provide the ACRS with a sense of the information provided in the original licensee submittals, the level and focus of staff reviews, and how the staff has implemented the guidance contained in Regulatory Guide (RG) 1.174 and the associated Chapter 19 of the Standard Review Plan (SRP), as well as the application-specific regulatory guides and SRP sections. We would appreciate the opportunity to discuss these examples with the ACRS PRA subcommittee at a time that is convenient.
CONTACT: Donald Harrison, SPSB/DSSA/NRR 415-3587
Dr. S. Bahadur 2 If you or your staff have any questions, require additional information, or would like to arrange a meeting time to discuss these examples, please feel free to contact me at 415-3183 or Donnie Harrison of my staff at 415-3587.
ATTACHMENT: Enclosures (5)
Dr. S. Bahadur 2 If you or your staff have any questions, require additional information, or would like to arrange a meeting time to discuss these examples, please feel free to contact me at 415-3183 or Donnie Harrison of my staff at 415-3587.
ATTACHMENT: Enclosures (5)
DISTRIBUTION without
Enclosures:
SPSB R/F CAHarris GMHolahan CIGrimes WDBeckner MACunningham MSKelton SDuraiswamy MPRubin MLWohl SCDinsmore MRSnodderly DGHarrison ACCESSION NO.: ML023100039 TEMPLATE NO.: NRR-106 DOCUMENT NAME: C:\ORPCheckout\FileNET\ML023100039.wpd To receive a copy of this document, indicate in the box C=Copy w/o attachment/enclosure E=Copy with attachment/enclosure N = No copy OFFICE SPSB:DSSA C SC:SPSB:DSSA C C:SPSB:DSSA C NAME DGHarrison MPRubin MRJohnson DATE 10/17/02 10/29/02 11/06/02 OFFICIAL FILE COPY
SUMMARY
OF ENCLOSURES Sequoyah Nuclear Plant Units 1 & 2 RI-IST This license amendment is an example of a request to implement a risk-informed inservice testing (RI-IST) program, in which the staff did not grant the request. Although the licensee did provide some quantitative risk information, the staff determined that the information provided was not complete and did not address some important elements of an acceptable RI-IST program, as presented in Regulatory Guide 1.175. The licensee formally withdrew their application following discussions with the staff regarding the information that would be needed to complete and grant the application. Since the licensee withdrew their application, the staff requests for additional information (RAIs) were not formally issued. However, the staff did document their initial review effort through a Safety Evaluation (SE) that identified the areas in the original submittal that were incomplete. The SE identifies a number of issues with the licensees submittal that would need to be resolved to grant the application, including: 1) providing additional information, such as the determination of the safety significance of the selected valves, 2) performing additional quantitative risk calculations, such as the calculation of the aggregate risk due to implementing the proposed RI-IST program and the impact of various plant/system operating configurations, 3) explaining differences in the materials available to the staff, such as the differences in the operating descriptions and configurations of some of the systems in the individual plant examination (IPE) versus this application, and 4) addressing tradition engineering considerations, such as defense-in-depth and safety margins. Without resolving the numerous issues identified in the SE, the staff could not determine if the supporting PRA was of adequate quality, scope, and detail for this specific application and thus could not accept the licensees quantitative results.
ADAMS Accession # Subject Date ML003718350 Licensee Submittal April 27, 2000 ML011000080 Licensee Withdrawal March 30, 2001 ML011240271 Safety Evaluation May 4, 2001 Dresden Station Units 2 & 3 RI-ISI This license amendment is an example of a request to implement a risk-informed inservice inspection (RI-ISI) program. The licensee submitted relief requests for Dresden, Braidwood, Byron, and Quad Cities. In the Dresden submittal, the licensee was the first to use the Monti-Carlo method (i.e., Markov model), but they did not use it exactly as provided for in the Safety Evaluation approving the Electric Power Research Institute (EPRI) methodology, which is documented in EPRI TR-112657, Revision B-A. Thus, this departure from the approved methodology, and its risk impacts, became a main focus of the staffs review. During the review, it was also noted that the report on the Monti-Carlo method that is referenced in the EPRI topical report did not include a clear description of the equations to be used and only discussed it as part of the method development. The licensee identified the Monti-Carlo techniques used in the submittal and, following staff review of the licensees approach, the use of the analysis as requested by the licensee was eventually approved. The licensees process for evaluating the potential change in risk was determined to be acceptable because it accounted for the change in the number and location of elements inspected, recognized the differences in degradation mechanisms related to failure likelihood, and considered the synergistic effects of multiple degradation mechanisms within the same piping segment. Further, the calculated increase in risk associated with the implementation of the RI-ISI program was small and consistent with the guidelines of RGs 1.178 and 1.174.
ADAMS Accession # Subject Date ML003762371 Licensee Submittal October 18, 2000 ML010570133 RAI Response February 19, 2001 ML012050103 Safety Evaluation September 5, 2001 ATTACHMENT
Arkansas Nuclear One Unit 2 RI-TS EDG AOT This license amendment is an example of an one-time risk-informed technical specification (RI-TS) allowed outage time (AOT) extension request. The licensee requested to extend the AOT from 3 days to 10 days for an emergency diesel generator (EDG) to provide the licensee with needed flexibility in performing maintenance during power operation. In addition to the EDGs, the licensee had previously installed an alternate ac diesel generator (AACDG) that is completely independent from offsite power and the EDGs, except for the bulk fuel oil storage system. The one-time AOT extension for the EDGs is conditioned on the availability of the AACDG. The licensee addressed the risks associated with the one-time AOT extension, as well as the quality of their probabilistic risk assessment (PRA). However, at the time of the submittal, the licensee had not had a peer review of their PRA. The staff determined that the AOT extension was acceptable due to the licensees requirement that the AACDG be available, the licensees risk management program, and the low risk results.
ADAMS Accession # Subject Date ML011690265 Licensee Submittal June 12, 2001 ML012190033 RAI Response July 31, 2001 ML012640398 RAI Response September 19, 2001 ML012700225 Follow-up Submittal September 25, 2001 ML012880265 Safety Evaluation October 15, 2001 Sequoyah Nuclear Plant Unit 2 RI-TS ILRT This license amendment is an example of a RI-TS request to extend the integrated leak rate test (ILRT) from a 10-year interval to a 15-year interval. However, in this case, the staff did not grant the requested extension to a 15-year interval, but instead, granted an extension of one operating cycle, approximately an 11.4-year interval.
The shorter interval was justified since the risk analysis results indicated that the increase in large early release frequency (LERF) was in the range of 10-7 to 10-6/year, which was due to the fact that not as much of the containment is visually inspectable due to the ice beds. RG 1.174 states that when the calculated increase in LERF is in the range of 10-7 to 10-6/year proposed changes will be considered if the total LERF, including external events, is less than 10-5/year. The licensee did not have a full scope probabilistic risk assessment (PRA) that addressed external events and they were unable to demonstrate that the total LERF was less than 10-5/year.
However, the extension to an 11.4-year interval was determined to be acceptable per the RG 1.174 acceptance guidelines since it could be shown by the licensee that allowing this interval would not increase the LERF value by more than 10-7/year, indicating that this is only a very small increase.
ADAMS Accession # Subject Date ML012890474 Licensee Submittal October 9, 2001 ML020530292 RAI Response February 14, 2002 ML020870238 RAI Response March 13, 2002 ML012530113 Referenced RI-ISI RAI Response August 31, 2001 ML021010066 RAI Response April 9, 2002 ML021140405 Follow-up Submittal April 11, 2002 ML021280455 Safety Evaluation May 7, 2002 2
Dresden Station Units 2 &3 EPUs This license amendment is an example of an extended power uprate (EPU) request. Though not identified as a risk-informed licensing action, these submittals do address the risks associated with implementing the EPU. The licensee submitted EPU license amendments for Dresden and Quad Cities, requesting a 17 to 18 percent increase in their original licensed power levels. Through the staff review, a number of issues were identified that resulted in the licensee providing additional information and performing additional analyses. In particular, the licensee performed some simplistic seismic risk analyses to ensure that the conditions and modifications credited in their seismic margins analysis, though not implemented, were not risk-significant. Since this issue had the potential to raise a question regarding adequate protection, this area became a main focus of the staff review.
Note that the EPU Safety Analysis Report (ML010080145) contains GE proprietary information and thus, should not be released to the public and should only be provided to those with a need-to-know to conduct official business. It is not enclosed with this transmittal, but will be made available upon request.
ADAMS Accession # Subject Date ML010080047 Licensee Submittal December 27, 2000 (Letter & Selected Attachments)
ML010080145 Licensee Submittal of Extended Power December 31, 2000 (Sensitive - Contains Uprate Safety Analysis Report GE Proprietary (Attachment E to ML010080047)
Information)
ML010470076 RAI Response February 12, 2001 ML012330383 RAI Response August 14, 2001 ML012550410 RAI Response September 5, 2001 ML012640178 RAI Response September 14, 2001 ML012680224 RAI Response September 19, 2001 ML012760060 RAI Response September 26, 2001 ML020140022 RAI Response November 30, 2001 ML013510595 NRC Approval December 21, 2001 (Letter with Enclosures 1 & 2)
ML013540187 Safety Evaluation December 21, 2001 (Enclosure 3 to ML013510595) 3