ML22040A138
| ML22040A138 | |
| Person / Time | |
|---|---|
| Issue date: | 03/08/2022 |
| From: | Mike Franovich Office of Nuclear Regulatory Research |
| To: | |
| References | |
| Download: ML22040A138 (13) | |
Text
Making Effective Decisions in Using Defense in Depth, Safety Margins, and Risk!
Technical Session T8 Michael X. Franovich Director, Division of Risk Assessment Office of Nuclear Reactor Regulation
AGENDA High Energy Arc Fault (HEAF)
New Reactors Historical Background Derecho Analysis 2
Meeting the Challenge of Becoming a More Modern Risk-Informed Regulator
- Risk assessment technology continues to mature and is used increasingly in regulatory matters to support safety decisions.
- Risks are dynamic. Effective risk management relies on vigilant assessment and use of operating experience.
- Risk technology and insights complement traditional defense in depth to achieve an acceptable level of residual risk.
- Transformation is in progress to further risk-inform.
3
Organization Learning Continual Value Added Pursue a common understanding of risk ( and +) and communication of risk information across the agency.
- Enhanced decisionmaking, more efficient use of resources, and reduction of unnecessary burden Objectives of the Commission policy on probabilistic risk assessment (PRA)
- Improved mission delivery, reduced costs, and focused corrective actions towards key risks Objectives of the Office of Management and Budget policy requiring enterprise risk management
- Agile, adaptive, and enhanced efficiency NRC Futures Assessment 4
Major Policies Shaping Risk-Informed Thinking for the NRC 1975 1985 1995 Reactor Safety Study (WASH-1400)
Severe Accident Risks (NUREG-1150)
Individual Plant Examinations (IPE) for Severe Accident Vulnerabilities (GL 88-20, NUREG-1560)
IPE of External Events (GL 88-20 Supp. 4, NUREG-1742)
Station Blackout (NUREG-1032)
Indian Point
& Zion Probabilistic Safety Studies 1980 1990 PRA Policy Statement Severe Accident Policy Statement Safety Goal Policy Statement TMI Accident Shutdown /
Low Power (NUREG-1449)
The use of PRA technology should be increased in all regulatory matters to the extent supported by the state-of-the-art in PRA methods and data and in a manner that complements the NRC's deterministic approach and supports the NRC's traditional defense-in-depth philosophy.
X 1998 Risk-Informed, Performance-Based Regulation SECY-98-144 5
Integrated Decisionmaking (RG 1.174)
- 1. Change meets current regulations unless specifically related to a requested exemption
- 2. Change is consistent with defense-in-depth philosophy
- 3. Sufficient safety margins are maintained
- 4. Changes in risk are small and consistent with NRC Safety Goal Policy Statement
- 5. Monitor change with performance measurement strategies Integrated Decisionmaking Principles All elements of Integrated Decisionmaking should be considered more than just the numbers alone.
Integrated Decisionmaking is a place for critical thinking and dialogue.
6
Background on the LIC-504 Process LIC-504 (ADAMS Accession No. ML19253D401) was created to address recommendations in the Government Accountability Office (GAO) report, GAO-04-415, Nuclear RegulationNRC Needs to More Aggressively and Comprehensively Resolve Issues Related to the Davis-Besse Nuclear Power Plants Shutdown, issued 2004 The major revision of LIC-504 (Rev. 5, 2020) included several significant changes prompted by previous uses of the process (e.g., considering enterprise risk and exposure to workers, guidance on how to consider risk significance to recommend generic communications).
- 1. Determine whether prompt regulatory actions are necessary.
- 2. Use best available information to develop risk-informed recommendations for management consideration; specifically including the following:
Use conservative assumptions in the absence of information Use best available information Rely on performance monitoring (NUREG/CR-1855) to address uncertainties LIC-504 evaluations result in two distinct outcomes:
The way LIC-504 teams develop recommendations has evolved to accommodate some key elements of the Be riskSMART (NUREG/KM-0016) framework.
7
Example 1LIC-504 Duane Arnold Derecho PROBLEM:
- Derecho highlighted a combined event not modeled in PRAs (weather-related loss of offsite power (LOOP) coincident with potential loss of emergency service water); potential for generic issue with previously unknown risk.
APPROACH:
- Using LIC-504 guidelines, determine whether prompt regulatory actions (i.e., orders to shut down or impose compensatory measures) were needed.
SOLUTION:
- Communicate risk insights within the NRC and with industry.
- Update Standardized Plant Analysis Risk (SPAR) models to improve realism and review team recommendations for further updates.
KEY TAKEAWAYS:
- Review the combined event effects and generate risk-informed recommendations that could help enhance plant safety and future regulatory processes.
8
Example 2Aluminum High Energy Arc Fault PROBLEM:
APPROACH:
- Evaluate operating experience.
- Develop the strategies for a risk-informed resolution (Be riskSMART).
- Continue communication and outreach.
SOLUTION:
- Perform LIC-504 review and communicate risk insights.
KEY TAKEAWAYS:
- Plants are safe; however, HEAF events are credible.
- Use LIC-504 to continue to identify any potential safety issues that may be applicable to operating light-water reactors and develop risk-informed options to disposition them.
San Onofre 4160 V (2001) 9
Example 3New ReactorsNuScale PROBLEM:
- Review inadvertent actuation block (IAB) valves and consider passive components and applicability of the single-failure criterion (SFC).
APPROACH
- SFC is one element of a defense-in-depth approach.
- SECY-05-0138, Risk-Informed and Performance-Based Alternatives to the Single-Failure Criterion (ADAMS Accession No. ML051950619)
(1) Eliminate unlikely sequences and postulated single failure (2) Risk-inform based upon safety significance (3) Take a blended approach of diversity, redundancy, and unreliability SOLUTION:
- Assess options (including regulatory certainty and timeliness) through SECY-19-0036, Application of the Single Failure Criterion to NuScale Power LLCs Inadvertent Actuation Block Valves, (ADAMS Accession No. ML19060A081).
- Conduct review using risk-informed decisionmaking (RIDM) and the 1995 PRA Policy Statement as directed by the Commission in SRM-SECY-19-0036 (ADAMS Accession No. ML19183A408).
KEY TAKEAWAYS:
- SRM-SECY-19-0036 provides direction on the appropriate application and interpretation of both regulatory requirements in 10 CFR Part 50 and risk-informed principles for the NuScale IAB valve. The NRC has some discretion, in fact-or application-specific circumstances, to decide when to apply SFC. The NuScale decision is similar to those in previous Commission documents that addressed the use of SFC and clarified when to apply it.
10
Three Key Messages The NRC supports and advances RIDM through its programs and activities to help enhance safety and focus resources on what is most safety significant.
The NRC is leveraging the use of risk assessment approaches in RIDM in a manner that complements defense in depth, safety margins, engineering judgment, and enterprise risk.
The NRC is continuing to increase the use of risk insights through Be riskSMART and other initiatives to expand the use of PRA technology to other business lines to further support other regulatory matters.
Organization Learning Continual 11
Questions?
12
13 Points of Contact Antonios.Zoulis@nrc.gov Branch Chief, Division of Risk Assessment, NRR Lundy.Pressley@nrc.gov Reliability and Risk Analyst Division of Risk Assessment, NRR