ML22153A352

Wagnerb-hv-th29-

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 h ave calculated risks to be low additional margin m ay 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

• Re flect 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 staff s 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