ML22153A352
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ML22153A352 | |
Person / Time | |
---|---|
Issue date: | 03/08/2022 |
From: | Brian Wagner NRC/RES/DRA |
To: | Office of Nuclear Reactor Regulation |
References | |
Download: ML22153A352 (10) | |
Text
Risk-Informing Dry Cask Reviews:
Current Research Brian Wagner, Reliability and Risk Engineer Division of Risk Analysis, Office of Nuclear Regulatory Research, U.S. NRC
Overview
- Background
- Benefits and challenges to risk-informing dry cask reviews
- Current research
Background
- Guidance
- Probabilistic Risk Assessment (PRA) Policy Statement (1995)
- Risk-Informed Decisionmaking for Nuclear Material and Waste Applications, Rev. 1 (2008)
- NUREG-2150, Risk Management Task Force (2012)
- Previous dry cask risk studies (storage)
- NUREG-1864 (2007)
- Electric Power Research Institute dry cask PRA (2004)
- Previous dry cask risk studies (transportation)
- NUREG-0170 (1977)
- NUREG/CR-4829 (1987)
- NUREG/CR-6672 (2000)
- NUREG-2125 (2014)
Benefits to Risk-Informing Cask Reviews
- Dry cask PRAs have calculated risks to be low additional margin may exist
- Reduce regulatory burden on less risk-significant aspects
- Focus resources on more risk-significant aspects
- PRAs use a systematic process creates a framework to
- Identify more risk-significant aspects and areas where additional data and analyses would be useful
- Test the sensitivity of analysis results to key assumptions
- Evaluate the significance of new failure mechanisms
Challenges
- Limitations of previous studies (data, scope, cask type, site, etc.)
- Lack of failure data (behavior of spent fuel under accident conditions, potential for very low probability accidents and events)
- PRAs rely on generic analyses and, when necessary, conservative assumptions and parameters when data are not available
- Caution: Worker protection can be a significant consideration due to the limited energy in release scenarios limiting offsite releases
Current Research: Level 3 PRA Project
- Full-scope, comprehensive site Level 3 PRA
- Directed in SRM-SECY-11-0089 (2011)
- Objectives
- Reflect technical advances since NUREG-1150, new scope considerations (e.g., spent fuel pools, dry cask storage)
- New insights
- Enhance staff PRA capability
Current Research: Level 3 PRA Project (cont.)
- Dry cask PRA model improvements (based on NUREG-1864 model)
- Detailed event identification
- Refined analysis of several scenarios
- Additional structural analysis
- Enhanced consequence analysis
- Results
- Generally consistent with past dry cask PRAs
- Provide updated insights on main risk contributors
- Provide basis for additional analysis as needed
- Status
- Technical work essentially complete
- Report under review, aiming to release a draft publicly this year
Current Research: Spent Fuel Storage Job Aid/Risk Tool
- Goal is to use risk information to focus license amendment reviews
- Risk tool (ADAMS Accession No. ML20350B659) includes risk insights from available risk studies, safety margin investigations, selected NRC safety evaluation reports, and input from NRC senior technical reviewers
- Tree diagram: Provides preliminary estimation of risk significance (on a component-by-component basis)
- Rationale: More detailed description of risk information
- Job aid provides a step-by-step approach for using the risk tool
- Status:
- Pilot application reviews ongoing
- Reviewing insights from pilots
- Continuing risk-informing discussions and implementing in safety reviews to ensure appropriate risk focus
Current Research: Spent Fuel Storage Job Aid/Risk Tool Current Research: Risk-Informing Chloride-Induced Stress Corrosion Cracking
- Enhance the staffs understanding of important technical issues key to successful aging management of chloride-induced stress corrosion cracking (CISCC)
- Understand the effects of materials and environmental parameters on CISCC growth rates
- Assess mitigation and repair methods
- Investigate risk-informing CISCC
- Review literature relevant to CISCC evolution and risk sequence
- Evaluate risk and consequence assessments to identify critical parameters for CISCC
- Perform a CISCC probabilistic assessment
- Can inform inspection frequencies