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
  • Risk-Informed Decisionmaking for Nuclear Material and Waste Applications, Rev. 1 (2008)
  • Previous dry cask risk studies (storage)
  • Electric Power Research Institute dry cask PRA (2004)
  • Previous dry cask risk studies (transportation)

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.)

  • 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

  • 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