ML20085F931
| ML20085F931 | |
| Person / Time | |
|---|---|
| Site: | Robinson  |
| Issue date: | 02/20/2020 |
| From: | Milton Valentin-Olmeda NRC/NRR/DORL/LPMB |
| To: | Grzeck L Duke Energy Corp |
| Valentin-Olmeda M | |
| References | |
| Download: ML20085F931 (4) | |
Text
From: Valentin-Olmeda, Milton To: Grzeck, Lee Cc: Philpott, Stephen
Subject:
Robinson SPRA - SPR Audit Questions - 2nd batch Date: Thursday, February 20, 2020 3:52:00 PM
- Lee, Please include the following new questions with the ones in the original email.
There is a portion of these new questions that are associated with a previous question (Topic # 16, Question 5 sent on 2/3/2020).
Those are highlighted below to prevent confusion and are needed to address topics #8, #13, #14 and
- 16 of the checklist.
The other questions are also new and are in addition to those sent on 2/3/2020.
Let me know if we need to discuss these and please let me know if it would be reasonable to have responses to all questions by 3/31/2020.
Respectfully, Milton Valentín, PM Beyond Design Basis Management (Fukushima)
US NRC NRR/DORL/LPMB Milton.Valentin@nrc.gov 301-415-2864 From: Valentin-Olmeda, Milton Sent: Monday, February 03, 2020 12:29 PM To: Grzeck, Lee <Lee.Grzeck@duke-energy.com>
Cc: Philpott, Stephen <Stephen.Philpott@nrc.gov>
Subject:
Robinson SPRA - SPR Audit Questions Greetings Lee, Based on the review of the H.B. Robinson Nuclear Plant, Unit 2, (RNP) seismic probabilistic risk assessment (SPRA) submittal (ADAMS Accession No. ML19346E204, non-public), please answer the following questions to support the staff in completing the technical checklist (ADAMS Accession No. ML18173A017) topics #14, #15, and #16 and make responses available in the electronic portal for staff audit:
Topic #16 - Review of Plant Modifications and Licensee Actions, If Any
- 5. Section 6 of the December 12, 2019 submittal states that a sensitivity for the modification mentioned in Table 6-1 of the submittal resulted in SCDF and SLERF reductions to be approximately 40 percent and 30 percent, respectively. The submittal does not provide enough information to understand the details to understand the basis for the risk reduction. For that reason;
- a. Explain the assumptions for determining the potential risk reduction from the proposed modification. Discuss the consideration of potential failure modes of the proposed modification such as liquefaction, seismically-induced failures of the SSCs involved in the modification, seismically-induced failure of enclosures or structures housing the equipment, failure of human actions, and random failures. The discussion should provide a summary of how the corresponding failure probabilities were determined.
- b. If failure modes and events, such as those mentioned in item (a), for SSCs involved in the modification were not considered in the evaluation for determining the potential risk reduction from the proposed modification:
- i. Justify their exclusion by performing sensitivity study(ies) and demonstrating that the results can be considered representative of the risk reduction from the modification. Alternately, update the results of the expected risk reduction from the proposed modification by including the failure modes and events for SSCs involved in the modification.
ii. Provide an explanation of how the design of the proposed modification can achieve the reduction estimates in Table 6-1 of the submittal given the unique site-specific failure modes that can impact the efficacy of the proposed modification.
- c. Provide the results (i.e., updated Tables 5.4-1, 5.4-2, 5.4-3, 5.4-4, 5.5-1, 5.5-2, and 5.5-3) of a sensitivity study for the proposed modification that results in the reductions of about 40% and 30% for SCDF and SLERF, respectively, as discussed in Section 6.0 of the submittal.
- d. Using the results of the sensitivity study provided in item 5(c) above,
discuss the impact of the results of the sensitivity on Question 3 including the impact of any new dominant risk contributors and potential modifications to address them.
- e. Provide the results (i.e., updated Tables 5.4-1, 5.4-2, 5.4-3, 5.4-4, 5.5-1, 5.5-2, and 5.5-3) of an aggregate sensitivity study that includes the guaranteed failure of SDAFW conditional on the Class III TB failure and the planned plant modification.
Topic #13 - Question 10 -Evaluation of LERF (SPID Section 6.5.1)
According to Appendix 15 of RNP-F-PSA-0062, Revision 4, reviewed during the audit of the SPRA submittal, the 2010 peer review of the IEPRA identified F&O LE-E1-1 to provide appropriate justification for parameter values selected for equipment and operator response in the accident progression analysis and for the RNP containment event tree. The 2017 IAT left this F&O open because "the response to the LE-E1-1 F&O is not specific enough to be able to verify the requested improvements." Previous risk-informed license amendment requests for Robinson (e.g., NFPA 805, 10 CFR 50.69, ILRT) have indicated that many of the Level 2 PRA parameters are based on expert judgement. While not discussed in the SPRA submittal, this appears to be a source of uncertainty.
- a. Provide a listing of the LERF model parameters that were developed based on expert judgement, and those which have a significant source of uncertainty and corresponding significantly impact the SLERF results,
- b. Justify the treatment of each of these parameters in the SPRA based on the impact of the uncertainty in each of these parameters on the results and insights presented in the submittal.
Topic #14 - Question 11 -Peer Review of the SPRA, Accounting for NEI 12-13 (SPID Section 6.7)
Section 5.1 of the submittal states that the SPRA was developed using the June 2015 IEPRA model of record. The response to NRC Question 9 provided during the audit stated that, with the exception of the six open Findings, most of relevant F&Os were appropriately resolved/closed so that they would not adversely affect the Robinson SPRA. According to Appendix 15 of RNP-F-PSA-0062, Revision 4, reviewed during the audit of the SPRA submittal, the IAT assessment of the resolution to the F&Os from the peer review of the IEPRA was conducted in 2017. The NRC staff observed that several of the F&O dispositions involved making changes to the IEPRA model that could impact the SPRA (e.g., F&O DA-C8-1, LE-C2-1, LE-C9-1, LE-C11-1, SY-A11-1, SY-A11-2). It is unclear to the NRC staff that these model updates were incorporated into the SPRA. Address the following:
- a. Clarify if the resolutions to the IEPRA F&Os that were reviewed by the IAT were incorporated into the SPRA used to develop the quantification results reported in the SPRA submittal.
- b. If not, identify the F&Os that resulted in changes to the IEPRA model and justify that the resolutions to these F&Os do not materially impact the SPRA quantification results (i.e., SCDF, SLERF, SCDF and SLERF importance analysis).
Topic #14 - Question 12 - Peer Review of the SPRA, Accounting for NEI 12-13 (SPID Section 6.7)
The disposition to F&O 24-1 is that no changes were made to the SPRA model based on the review of the IEPRA assumptions. Table 5-12 of the SPRA Model Notebook, which was reviewed during the audit, identifies the following internal events assumption that was not changed in the SPRA model:
"An operator action is included in the PSA model for taking the necessary actions to align deepwell water for AFW supply (OPER-18A). The additional set of steps required to restore a deepwell pump aligned in containment cooling mode is not considered to significantly change the likelihood of success because of the long time available."
Provide justification for the disposition given that seismic events may limit the time available to perform this action and the importance of providing water to the AFW pumps in the planned plant modification.
Topic #8 - Question 13 -Screening by Capacity to Select SSCs for Seismic Fragility Analysis (SPID Section 6.4.3)
The disposition to F&O 29-1 provided in Table A-2 of the Submittal describes a comprehensive review of both safety and non-safety valves for the purpose of assessing the appropriateness of the assigned fragilities. The fragility for one safety-related valve, FCV-6416, was revised/reduced as a result of this review. Section 1.41 of the SPRA F&O Resolution Notebook, which was reviewed during the audit, identifies several non-safety-related valves in which the fragilities were revised/reduced as a result of this review.
However, the Representative Fragility Notebook and Seismic Fragility Notebook, which were also reviewed during the audit, do not reflect the revised fragilities in most cases. As a result, it is unclear to the NRC staff if the changes made to the SPRA to address the SPRA peer review F&Os were incorporated in the SPRA used in the Submittal. Provide the following: