ML20076C874
| ML20076C874 | |
| Person / Time | |
|---|---|
| Issue date: | 03/23/2020 |
| From: | Michael Montecalvo NRC/NRR/DRA/APOB |
| To: | Antonios Zoulis NRC/NRR/DRA |
| References | |
| Download: ML20076C874 (5) | |
Text
March 23, 2020 MEMORANDUM TO: Antonios Zoulis, Chief PRA Operations Branch Division of Risk Assessment Office of Nuclear Reactor Regulation FROM: Michael Montecalvo, Senior Reactor Analyst /RA/
PRA Operations Branch Division of Risk Assessment Office of Nuclear Reactor Regulation
SUBJECT:
PEER REVIEW FOR RISK ASSESSMENT TO SUPPORT DIFFERING PROFESSIONAL OPINION OF STAFFS RESPONSE TO OCONEE TASK INTERFACE AGREEMENT 2014-04 The purpose of this memorandum is to document an additional peer check of the risk analysis that was completed associated with a differing professional opinion (DPO) submitted on July 11, 2018, in accordance with Management Directive 10.159, The Nuclear Regulatory Commission Differing Professional Opinions Program (Agencywide Documents Access and Management System (ADAMS) ML15132A664). The DPO, titled Oconee Task Interface Agreement 2014-04
- U.S. Nuclear Regulatory Commission (NRC) Staffs Response Concerning Degraded Voltage Protection (ADAMS Accession No. ML19136A282), concerns the staffs response to Oconee Task Interface Agreement (TIA) 2014-04 associated with degraded voltage protection (ADAMS Accession No. ML18051B257). The DPO Ad Hoc Review Panel issued their report, Differing Professional Opinion Panel Report on the Oconee Task Interface Agreement 2014-04, NRC Staffs Response Concerning Degraded Voltage Protection (ADAMS Accession No. ML19347B523) to the Office of Nuclear Reactor Regulation (NRR) Director on December 12, 2019, after reviewing the applicable documents, conducting internal interviews with relevant individuals, completing a risk assessment, and completing their deliberations. Subsequently, the NRR Office Director issued a memorandum titled Directors Decision for Differing Professional Opinion Oconee Task Interface Agreement 2014 NRC Staffs Response Concerning Degraded Voltage Protection (ADAMS Accession No. ML20027C726) describing the issue, the Directors decision, and follow-up actions that were directed to be taken. A DPO response appeal was submitted on February 28, 2020. Our review concluded the analyst used NRC guidance to appropriately model the issue of concern and this additional review of the risk assessment did not identify any issues that would impact the results or the regulatory decision.
Enclosure:
Peer Check of Risk Assessment for DPO on TIA 2014-04 CONTACT: Michael Montecalvo, NRR/DRA 301-415-1678
ML20076C874 *via email NRR-106 OFFICE NRR/DRA NRR/DRA/APOB NAME MMontecalvo AZoulis DATE 03/12/20 3/23/2020 PEER CHECK OF RISK ASSESSMENT FOR DIFFERING PROFESSIONAL OPINION ON OCONEE TASK INTERFACE AGREEMENT 2014-04 The purpose of this enclosure is to document an additional peer check of the risk analysis that was completed associated with a differing professional opinion (DPO) submitted on July 11, 2018, in accordance with Management Directive 10.159, The Nuclear Regulatory Commission Differing Professional Opinions Program (Agencywide Documents Access and Management System (ADAMS) ML15132A664). The DPO, titled Oconee Task Interface Agreement 2014-04
- NRC Staffs Response Concerning Degraded Voltage Protection (ADAMS Accession No. ML19136A282), concerns the staffs response to Oconee Task Interface Agreement (TIA) 2014-04 associated with degraded voltage protection (ADAMS Accession No. ML18051B257). The DPO Ad Hoc Review Panel issued their report, Differing Professional Opinion Panel Report on the Oconee Task Interface Agreement 2014-04, NRC Staffs Response Concerning Degraded Voltage Protection (ADAMS Accession No. ML19347B523) to the Office of Nuclear Reactor Regulation (NRR) Director on December 12, 2019, after reviewing the applicable documents, conducting internal interviews with relevant individuals, completing a risk assessment, and completing their deliberations. Subsequently, the NRR Office Director issued a memorandum titled Directors Decision for Differing Professional Opinion Oconee Task Interface Agreement 2014 NRC Staffs Response Concerning Degraded Voltage Protection (ADAMS Accession No. ML20027C726) describing the issue, the Directors decision, and follow-up actions that were directed to be taken.
A DPO response appeal was submitted on February 28, 2020 stating that the DPO response contained inaccurate technical and regulatory bases to conclude that Oconee meets its licensing basis. Concerning the risk assessment performed to support the DPO panels recommendation and the Directors decision, the submitter claimed:
The risk evaluation performed for the degraded voltage protection issue has never been modeled by the NRC. Therefore, the uncertainties and assumptions made in the evaluation cannot be validated.
And:
I am concerned that an unsupported risk assessment was used to screen a generic safety issue as low safety significance.
The risk assessment discussed above was completed by a Regional Senior Reactor Analyst and subsequently peer checked by an independent Regional Senior Reactor Analyst prior to being presented for review to the DPO ad hoc review panel. The DPO panel then included the risk analysis in their report to the NRR Office Director for review. In response to the DPO response appeal, it was requested that an additional headquarters peer check of the risk analysis be completed. The process provided in ADM-504, NRR Technical Work Product Quality and Consistency was used to assure the quality and consistency of the risk analyses completed by the Regional staff and the additional peer check being performed. The following Enclosure
guidance documents were used in the review to ensure that sound, state of the art probabilistic risk analysis methodologies were utilized while modeling the issue of concern:
Risk Assessment of Operational Events Handbook, Volume 1 - Internal Events (Adams Accession No. ML17348A149)
NUREG-1855, Guidance on the Treatment of Uncertainties Associated with PRAs in Risk-Informed Decisionmaking (Adams Accession No. ML17062A466)
NUREG/CR6823, Handbook of Parameter Estimation for Probabilistic Risk Assessment (Adams Accession No. ML032900131)
NUREG/CR-5485, Guidelines on Modeling Common-Cause Failures in Probabilistic Risk Assessment (Adams Accession No. ML070570062)
Additionally, the following references were reviewed for their applicability to the risk-informed decision with specific reference to the thresholds for regulatory action:
- NRC Enforcement Manual, Appendix F, Notices of Enforcement Discretion (Adams Accession No. ML)
- RG 1.174, An Approach for Using Probabilistic Risk Assessment in Risk Informed Decisions on Plant Specific Changes to the Licensing Basis (Adams Accession No. ML)
- LIC-504, Integrated Risk-Informed Decisionmaking Process for Emergent Issues (Adams Accession No. ML19253D401)
An iterative approach was used by the analyst and was appropriate due to the modeling features of PRA (in this case the Oconee SPAR model) and the regulatory issue being decided.
In this iterative approach, the scenarios were initially analyzed using conservative modeling assumptions. Scenarios could be further analyzed using progressively more realistic assumptions based on the level of effort required and the results of each stage of the analysis.
Analyst knowledge and experience are key to balancing the need for more analysis with the preciseness required and the impact to the regulatory process. Individual sub-components are not usually modeled in a PRA when the failure of the overall component is adequate to capture the plant impact (e.g. a pressure switch resulting in a pump failure would not need to be explicitly modeled if the pump failure to start or failure to continue to run is adequately modeled and captures that failure mode). A more robust analysis at the component level could be completed but would be inappropriate in this case due to the resources that would be expended for the effort and the de minimis impact on the regulatory decision being made. The methodology used was sound with three different scenarios analyzed and a graded approach to equipment failures and the resulting plant operational state. The analyst used plant specific empirical data when possible but relied on conservative assumptions for failures which was appropriate for providing input to the regulatory decision. Additionally, there was an appropriate consideration of uncertainty given in the analysis used to support the decision and in the interpretation of the findings of the analysis.
In conclusion, the analyst used NRC guidance to appropriately model the issue of concern while balancing level of effort with the appropriate level of precision. This additional review of the risk assessment did not identify any issues that would impact the results or the regulatory decision.