ML19098B328

RIC2019 Session T-11, U.S. NRC Operating Experience Data-Applications in Risk Modeling Presentation Title: Common Cause Failure Considerations in Context of Risk Informed Decision Making Presenter: Greg Krueger, NEI

ML19098B328
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Site:	Nuclear Energy Institute
Issue date:	03/12/2019
From:	Nuclear Energy Institute
To:	Office of Nuclear Regulatory Research
John Lane 415-2476
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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

©2019 Nuclear Energy Institute 2 *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

©2019 Nuclear Energy Institute 4 *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 D riven 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

©2019 Nuclear Energy Institute 5 *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 P aper

©2019 Nuclear Energy Institute 6 *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)

• M atrix 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

©2019 Nuclear Energy Institute 9