ML19098B328
| ML19098B328 | |
| Person / Time | |
|---|---|
| Site: | Nuclear Energy Institute |
| Issue date: | 03/12/2019 |
| From: | Nuclear Energy Institute |
| To: | Office of Nuclear Regulatory Research |
| John Lane 415-2476 | |
| References | |
| Download: ML19098B328 (9) | |
Text
Common Cause Failure Considerations in the Context of Risk Informed Decision Making March 12, 2019 Greg Krueger Senior Technical Advisor Nuclear Energy Institute T11 - U.S. NRC Operating Experience Data Applications in Risk Modeling
©2019 Nuclear Energy Institute
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- The current quantitative-focused CCF approach in evaluating performance issues emphasizes numerical results with limited consideration of recent operational processes or performance
- A quantitative focus leads to significant application of analytical resources when treatment of CCF drives a Significance Determination Process (SDP) result
- Gaining alignment on how to risk-inform CCF insights in an event/condition assessment would improve decision making and clarity of performance assessment outcomes Common Cause Failure Considerations in the Context of RIDM
©2019 Nuclear Energy Institute 3 Unprecedented Industry Performance Reliability
>90%
Capacity Factor Sustained Safety 10-Fold Reduction in Average CDF Excellence Highest Performance Record Ever Oversight Fewest NRC Performance Issues Ever Margin Fleet
~100 Times Safer Than NRC Goals Exceptional Safety Culture
>90%
10x Top Performing Best Ever 100x
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- Current component failure events and common cause failures are not representative of the improvement in industry wide performance over the most recent 10 years
- Recent industry evaluation of the average number of failure events associated with Motor Driven Pumps (MDPs) and Emergency Diesel Generators (EDGs) shows a significant decrease from the period 1996 to 2005 compared to 2006 to 2015
- For example, a reduction of up to 1/3 fewer pump failure to start events in the most recent 10 years has been observed
- While MDP failure rates have generally decreased over time, the rate of decrease in CCF is more dramatic (40% to 60% decrease).
Common Cause Failures - Data
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- Expand the framework for crediting observed defense against common cause qualitatively independent of the quantitative risk analysis Recommendation 1: Perform sensitivities between baseline or nominal CCF calculation and conditional CCF calculation to illustrate the quantitative range of results Recommendation 2: Expand Ground Rule 3 in the Risk Assessment of Operational Events Handbook (RASP Handbook) to reflect use qualitative factors to reflect utility defenses employed to limit CCF Industry CCF White Paper
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- Use of qualitative CCF factors within the existing regulatory performance assessment process has potential to:
Improve characterization of performance deficiencies Better focus on higher organizational deficiencies Optimize resource expenditures by focus on performance rather than quantitative refinements Add perspective to the evaluation of a performance deficiency Increase the recognition and use of common cause defenses by utilities, thereby promoting improved good practices Common Cause Failures - Qualitative Factors
©2019 Nuclear Energy Institute 7
- A suggested application table reflecting the strength of defense against CCF is suggested for incorporation into the RASP handbook Common Cause Failures - Qualitative Factors Strength of Defenses Qualitative Factor Complete Nominal or baseline CCF Superior Nominal CCF - 0.5 Conditional CCF Moderate 0.5 Conditional CCF - Conditional CCF Weak Conditional CCF (Current NRC quantitative process)
- Matrix could be used in conjunction with quantitative SDP results to reflect utility action taken to prevent the potential for common cause
©2019 Nuclear Energy Institute 8
- The combined impact of improved data and defenses employed to reduce common cause events will result in a reduction of resources used to evaluate performance issues
- Industry performance and improved processes should influence the evaluation of CCF using an integrated RIDM approach Conclusions
Contact:
Greg Krueger gak@nei.org
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