ML19064B075
| ML19064B075 | |
| Person / Time | |
|---|---|
| Issue date: | 01/30/2019 |
| From: | Jonathan Evans, Hartle B NRC/NRR/DRA |
| To: | |
| References | |
| Download: ML19064B075 (22) | |
Text
Risk-Informed Technical Specification Initiative 4b: Risk-Informed Completion Times Brandon Hartle, Reliability and Risk Analyst Jonathan Evans, Reliability and Risk Analyst PRA Licensing Branch A, Division of Risk Assessment, NRR NEI Lessons-Learned Workshop, January 30 - 31, 2019
Executive Summary
- TSTF-505 Rev. 1 suspended November 2016
- Revision resolves issues, except Loss of Function Conditions
Initiative 4b Overview
- Risk-Informed process to extend TS CTs based on plant configuration
- Risk evaluation using current configuration to calculate a specific CT called Risk-informed Completion Time (RICT)
- Frontstop = existing TS CT
- Backstop = 30 day maximum
- Applies to planned and emergent conditions 3
Initiative 4b Overview
- NEI 06-09 Rev. 0
- Introduced term PRA Functional as an alternative to Operable and allowed a RICT for all PRA Functional configurations
- This replaces design basis analysis requirements with PRA success criteria in the TSs
- Restricted definition of PRA Functional as capable of meeting design basis analysis requirements or appropriate disposition or programmatic restriction will be provided
- A RICT can only apply to (restorative) TS Required Actions that are not Mode changes or unit shutdown 4
Attributes of a RICT Program
- Integrates Plant Risk
- Manage multiple SSC outages
- Manage broader scope of SSCs (TS and non-TS)
- Flexible Configuration Management
- Decisions include real-time risk insights
- Focus on repair, not necessarily shutdown
- Emergent problems
- Ongoing/continuous risk awareness 5
Description of TSTF-505 Rev. 1
- Defined Conditions, Required Actions, and CTs within scope
- Added a new program in TS Chapter 5, "Administrative Controls," entitled the "Risk-Informed Completion Time Program."
- Provided additional clarity for RICT entry using PRA Functional to extend CT for loss of function (LOF) mode change conditions (e.g., 3.0.3 conditions) 6
Early Challenges for TSTF-505 Rev. 1
- Vogtle pilot 4b review on-going in 2016
- 5 other TSTF-505 reviews submitted before pilot completed
- Implementation of the TSTF in these LARs would have resulted in indeterminate and potentially substantive reduction in safety margin 7
Issues With TSTF-505 Rev. 1
- Included PRA Functional to extend CT for configurations with loss of capability to achieve design basis success criteria
- Added new TS 3.0.3 Conditions and Required Actions to replace default TS 3.0.3 entry and included PRA Functional to extend CTs in the new TS
- Included (in model TSTF-505 SE) justification for adequate defense-in-depth and safety margin which relied on assuming NRCs restricted definition of PRA Functional, without additional disposition or programmatic restrictions for TS 3.0.3 and mode change CTs 8
TSTF-505 Rev. 1 Suspension
- NRC staff suspended approval of TSTF -505, Rev.1, explaining concerns identified during review of plant-specific LARs:
- Definition of PRA Functional
- SE on NEI 06-09 limited use of PRA Functionality by requiring remaining performance capability to meet design basis analysis requirements (e.g., maintain functional capability to perform at level of one operation train)
- TS Conditions Involving Mode Changes or Unit Shutdowns
- SE on NEI 06-09 a RICT can only apply to (restorative) TS Required Actions that are not Mode changes or unit shutdown 9
TSTF-505 Rev. 1 Condition B does not meet design basis analysis requirements, therefore, would not meet intent of SE for NEI 06-09 1
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TSTF-505 Rev. 2 1
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TSTF-505 Rev. 2 Changes
- Removed Loss of Function Conditions
- Staff concerned with maintaining adequate defense in depth and safety margins
- The conditions in Table 1 require additional justification that those are not Loss of Function
- Newly Developed PRA Method Administrative Control Constraint
- Conditions not modeled in the PRA are in scope
- Can be plant specific, PRA model dependent
- Table 1 in Model application requires additional justification 1
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TSTF-505 Rev. 2 Changes
- Common Cause Failures (CCF)
- Included in the TS Admin Section to address emergent failures
- CCF PRA Modeling to be handled on a plant specific basis
- All hazards require technically adequate dispositions
- External hazards need to be systematically considered
- Addressing only the impact on baseline risk is insufficient
- Impact on configuration specific change in risk should be addressed 1
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Initiative 4b Loss of Function Considerations
- 4b allows the use of PRA Functional and calculation of RICT when all trains are Inoperable
- But available equipment can provide design basis success parameters upon demand OR
- Define and justify adequate defense in depth and safety margins when available equipment can only provide PRA success parameters
- Change in Backstop for CT upon Inoperability of all trains from 30 days to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />
- Consistent with approved and used TSTF-426 which allows a maximum of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> when all trains are Inoperable 1
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Initiative 4b Loss of Function Considerations
- Using design basis success criteria for PRA Functional for loss of all trains alleviates need for justifying PRA success criteria, i.e.,
- Use only SSCs relied on in the original TS specified safety function
- Ensure design basis success criteria for parameters are met for all design basis initiators
- May deviate by requesting TS changes for Inoperability of all trains using PRA Functional with supporting information
- This review may be complex and resource intensive
- Suggest only using on a limited basis 1
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TSTF-505 and 4b LAR Content 4b, Risk-Informed Completion Times
- More flexibility for technical 50.69 SSC Categorization licensee robustness, and plant representation 5b, Risk-Informed
- More complex staff Surveillance Frequencies review Risk-Informed Inservice Inspection 1
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- Scope, level of detail, and technical adequacy of PRA are to be commensurate with application
- Requires confidence in plant specific PRA models
- Up-to-date full-scope PRA peer reviews
- Supporting Requirements assessed to Capability Category II for all PRA hazards
- Facts and Observations (F&Os) resolved or dispositioned prior to LAR submittal
- Deviations from NRC accepted guidance and pilot applications add to review time and resources 1 7
4b Application Review Best Practices
- Pre-submittal meetings
- Familiarizes staff with licensees strategy and goals
- Allows for clarifications to reduce acceptance review pitfalls
- Reviewing recent submittals
- Helps licensee anticipate and address common RAIs
- Minimizes deviations from acceptable approaches/templates
- F&O Closure Observations
- Audits
- Assists with NRC review of complex 4b applications
- Clarifies information in the LAR to reduce RAIs 1
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Conclusions
- Revision resolves issues, except for loss of function conditions
- 3 Initiative 4b LARS in house; 3 SEs issued
- 3 LARs in house for TSTF-505 Rev. 2
- Complex reviews that rely on the technical adequacy of the PRA
- High quality submittals needed to support efficient review by the NRC
- Progress/Path forward
- With issuance of the SE for TSTF-505 Rev. 2, we expect a large number of submittals in 2019
- Reviewing previous submittals and using best practices will facilitate efficient NRC review 1
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List of Acronyms
- CC - Capability Category
- CCF - Common Cause Failure
- CDF - Core Damage Frequency
- CT - Completion Time
- F&O - Facts and Observations
- LAR - License Amendment Request
- NRC - Nuclear Regulatory Commission
- RAI - Request for Additional Information
- RICT - Risk Informed Completion Time
- SE - Safety Evaluation
- SR - Supporting Requirement
- SSC - Systems, Structures, and Components
- TS - Technical Specification
References
- TSTF-505, Revision 1, Provide Risk-Informed Extended Completion Times
- RITSTF Initiative 4b, June 14, 2011, and Model Application dated January 31, 2012 (ADAMS Accession No. ML120330410).
- Draft Revised Model Safety Evaluation of TSTF-505, Revision 2, Provide Risk-Informed Extended Completion Times - RITSTF Initiative 4b, May 1, 2018 (ADAMS Accession No. ML17290A005).
- Letter from Timothy J. McGinty, U.S. Nuclear Regulatory Commission, to Technical Specifications Task Force, Issues With Technical Specifications Task Force Traveler TSTF-505, Revision 1, Provide Risk-Informed Extended Completion Times - RITSTF Initiative 4B, dated November 15, 2016 (ADAMS Accession No. ML16281A021).
- Final Safety Evaluation For Nuclear Energy Institute (NEI) Topical Report (TR) NEI 06 09, Risk-Informed Technical Specifications Initiative 4b, Risk-Managed Technical Specifications (RMTS) Guidelines, May 17, 2007 (ADAMS Accession No. ML071200238). 2 1
References
- Topical Report NEI 06-09, Revision 0-A, Risk-Informed Technical Specifications Initiative 4B, Risk-Managed Technical Specifications (RMTS) Guidelines, October 2012 (ADAMS Package Accession No. ML122860402).
- Regulatory Guide 1.174, Revision 3, An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis, January 2018 (ADAMS Accession No. ML17317A256).
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