ML24303A221
| ML24303A221 | |
| Person / Time | |
|---|---|
| Site: | Nuclear Energy Institute |
| Issue date: | 10/29/2024 |
| From: | Nuclear Energy Institute |
| To: | Office of Nuclear Regulatory Research |
| References | |
| Download: ML24303A221 (1) | |
Text
©2024 Nuclear Energy Institute
©2024 Nuclear Energy Institute l 1 CCF and SDP Realism NRC Public Meeting October 30, 2024
©2024 Nuclear Energy Institute 2 Overview Improved realism furthers transparency and efficiency Elimination of unnecessary conservatism decreases burden on both NRC and licensees Notable progress made with GREATR project Key Areas for CCF Design defense strategies Extent of condition Stakeholder engagement in CCF data update
©2024 Nuclear Energy Institute 3 Licensees often have known conservatisms in the common cause approach in their base model for simplicity, as results on total CDF are trivial SPAR models have similar simplifications Event-specific assessments substantially magnify the impact of these conservatisms, and the common cause modeling approach should be refined to reflect knowledge of the event condition to the extent practical Common Cause Failure Realism Base model impact*
Event specific impact*
- Illustrative example only - not tied to a specific plant PRA or event assessment
©2024 Nuclear Energy Institute 4 Recognize inherent conservatism in both NRC and licensee CCF factors Often drives SDP outcomes when conservatisms remain in event specific assessment Example: Keeping turbine driven and motor driven pumps in one common cause group Example: Grouping together components when one failed due to a modification that was not performed on all components in the group Common cause may not be zero, but full alpha factor should not be applied if factors can be excluded Qualitative arguments are sufficient for reduction and detailed CCF reevaluation should not be required Credit for CCF Design Defenses
©2024 Nuclear Energy Institute 5 Knowledge of extent of condition can decrease CCF impact for a specific event Information provided by licensees should be given due consideration Potential to decrease CCF impact when failure mode is not seen on redundant components Use of component specific priors when available For SDPs involving RICT, RMAs required by the RICT should be credited in the SDP evaluation Justification for Decrease in CCF in Event Assessments
©2024 Nuclear Energy Institute 6 Interested in seeing draft of the revised RASP handbook to understand how this is incorporated Extensive guidance on use should be provided to SRAs Parameters for identification of cause should be clearly stated Accurate completion of root cause is vital to success Need to evaluate draft RASP handbook revisions and run cases to understand impacts Application of Causal Alpha Factor Method
©2024 Nuclear Energy Institute 7 Industry is interested in an ongoing review cycle to avoid inappropriate data from getting into evaluations Would be useful to evaluate raw data involved in CCF factor generation to better understand assumptions behind values and relevance to specific event assessments Long term potential benefit for NRC and industry via reduction in event-by-event refinements and discussions Stakeholder Engagement in INL/NRC Data Updates
©2024 Nuclear Energy Institute 8 Next Steps Identifying areas of excess conservatism and pursuing realism improvement results in a more effective regulatory process Public availability of draft RASP handbook revisions for stakeholder feedback Stakeholder engagement in data update process can prevent extensive disagreements over CCF impact during event assessments
©2024 Nuclear Energy Institute 9 Discussion/Questions