ML22153A343

Thaggardm-hv-t8

ML22153A343
Person / Time
Issue date:	03/08/2022
From:	Mark Thaggard NRC/RES/DRA
To:	Office of Nuclear Reactor Regulation
References
Download: ML22153A343 (13)

Text

Perspective on Safety Improvements for Commercial Nuclear Power Plants Mark Thaggard, Director Division of Risk Analysis Office of Nuclear Regulatory Research, U.S. NRC

Overview

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2

RES Considerations in Looking at Different Measures of Performance

• What timeframe should we consider?

• 20 years (2000+)

• 30 years (1990+)

• Advancements make it difficult to compare performance measures over time

• Measures of performance may need to be interpreted using engineering judgment 3

1988-2000 Plant Safety Improvements

• The period of interest impacts overall conclusions

• Many safetysignificant actions/changes were made 4

1988-2000 Plant Safety Improvements Significant Events 5

2000-Present: Plant Safety Improvements

• Improvements made during this period are not as significant as those in the 1990s

• Not all changes have been fully realized 6

RES Categories of Performance Measures Operational trends Plant risk due to internal events/internal floods Plant risk due to other hazards NRC studies, orders, models, etc.

Industry studies, standards, models, etc.

Other 7

• 51 measures Safety Measure Trends

• Negative Trends

• Loss of offsite power (LOOP) recovery time 1

• Positive Trends measure

• Annual scrams

• NRC reactive inspections

• Accident sequence precursor (ASP) results

• Radiation exposure

• Performance indicators 8

• Internal events core damage frequency (CDF) measures

• Reactor coolant pump (RCP) seal performance

• Loss of offsite power (LOOP) frequency 8

Remaining SafetyRelated Measures

• Apparent favorable trends

• Lower conditional probability that a radiological release would lead to prompt or latent health effects

• Improvements related to flooding and seismic hazard reevaluations

• Mitigating strategies improvements (FLEX) 9

• Risk insights from the StateoftheArt Reactor Consequence Analyses (SOARCA)

• Generic Issues Program improvements

• B.5.b improvements

• Improvements in consensus standards and regulatory guidance

• Pressurizedwater reactor steam generator performance improvements

• Improvements in PRA development tools

• 32 neither favorable or negative trend 9

Some Observations

• Large reduction in average core damage frequency (CDF) (since the IPE results)

• Limited to contributions from internal events

• External event hazards can add significantly to plant risk, so it is important to include in discussion of safety trending

• Reduction in performance issues

• Risk below NRC safety goals

• Both the uncertainties and external hazards need to be considered when looking at the safety goal impacts 10

Conclusions

• Performance measures appear to show improvements in nuclear power plants

• Could be attributed to initiatives and rules addressing key safety issues (e.g., station blackout (SBO) rule, greater use of riskinformed decisionmaking)

• Plant safety improvements implemented since the year 2000 have shown a gradual increase in safety, but to a smaller extent than during the previous 10 years

• Not all safety measures moved in the same positive direction

• External event impacts are important, and significant uncertainties still exist 11

Questions 12

Points of Contact Mehdi.Reisifard@nrc.gov Branch Chief, Division of Risk Analysis, RES Matthew.Humberstone@nrc.gov Senior Reliability and Risk Analyst Division of Risk Analysis, RES 13