Risk-Informed Decision Making

George Apostolakis
Head, Nuclear Risk Research Center, Tokyo
apostola@mit.edu
Presented at theMETI Working Group Meeting
September 26, 2016

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Risk-Informed Decision Making (1)• Decision making must be based on the current stateof knowledge of the decision maker (DM) The current state of knowledge regarding design,operation, and regulation is key.
 The current state of knowledge is informed by science,engineering, and operating experience, including past
incidents.

• What we know about plant behavior is not easily
available to the DM Accident sequences, human performance, risk
significance of systems, structures, and components, etc
 Example: Until the Reactor Safety Study, thesignificance of support systems and human errors had
not been appreciated2

Risk-Informed Decision Making (2)• PRAs provide this information to the DM
 PRAs do not predict the future PRAs tell us what we know now regarding potential accident
sequences, their likelihood, and consequences• Since decision making should be based on thetotality of our knowledge, the characterization “riskinformed” would appear to be superfluous A fuzzy concept that may be abused• However, it is useful as a communication tool amongindustry and regulatory staffs.
3Communication with the Public• The traditional “deterministic” regulatory systemdoes not communicate well
 Saying that plants are safe because they meet theregulations is a mystifying message to the public Even communication among experts is impeded• Risk metrics such as core damage frequency (CDF)
and large release frequency (LRF) communicate
clearly the risks that are being managed• Understanding the concept of residual risk isimportant No industrial activity or facility imposes zero risk
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Evolution of RIDM in the U.S.A.
• The NRC’s 1995 PRA Policy Statement encourages(but does not require) increased use of PRA
methods to promote regulatory stability andefficiency.
• The use of PRA should be increased to the extent
supported by the state of the art and data and in amanner that complements the defense-in-depth
philosophy.
• PRA should be used to reduce unnecessaryconservatisms associated with current regulatory
requirements.
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NRC Policy Statement on the USE of
PRA in Regulations (1995)• Deterministic approaches to regulation consider alimited set of challenges to safety and determine
how those challenges should be mitigated.
• A probabilistic approach to regulation enhances andextends this traditional, deterministic approach, by:(1) Allowing consideration of a broader set of
potential challenges to safety,(2) providing a logical means for prioritizingthese challenges based on risk significance, and(3) allowing consideration of a broader set ofresources to defend against these challenges.
6Experience with RIDM in the U.S.A.
• Supplementing the traditional regulations
 Station Blackout Rule (10 CFR 50.63)
 Its significance identified by PRA

 Maintenance management (10 CFR 50.65)
 Fire protection (10 CFR 50.48(c) Voluntary•

New reactor certification and licensing (10 CFR52.47 and 52.79)• Changes in the plant licensing basis (RegulatoryGuide 1.174 )• Prioritization of issues according to risk significancehas saved resources thus improving safety
indirectly
7Reactor Oversight Process• Motivation
 The previous inspection, assessment and enforcement
processes were not clearly focused on the most safety
important issues and were overly subjective• Challenges

Hundreds of affected NRC and industry staff
Development of performance indicators using plant data
Quality of the licensee PRAs
Establishing the Action Matrix• Outcomes Improves the consistency and objectivity of inspections
 Provides explicit guidance on the regulatory response toinspection findings
 Focuses NRC and licensee resources on those aspectsof performance that have the greatest impact on safe
plant operation8

Realizing the Full Benefits of RIDM inJapan• The establishment of ROP is a major step forward• It is not the final goal
• Establishing RIDM is a major undertaking for both
the regulator and the industry• We need a roadmap to identify the needs andsolutions in a systematic way, including: Infrastructure development (people, organizations,standards; peer reviews; safety goals)
 “Good” PRAs meeting international standards of practice Developing acceptable PRA models for hazards of greatinterest in Japan (earthquakes, tsunamis, volcanos) Developing processes for risk-informing regulations(would the regulator use its own PRAs or rely on thepeer-reviewed industry PRAs?)
20169

NRRC Activities• Position paper for proper application of RIDM inJapan Establishment of RIDM Promotion Team Pilot projects for establishing “Good” PRAs: Ikata Unit 3,
Kashiwazaki-Kariwa Units 6 and 7• White paper on RIDM applications in the U.S.A.
 What was the motivation?
 How can Japan benefit from the U.S. experience?

• Research projects
 Human Reliability Analysis
 Seismic PRA
 SSHAC process for Ikata Unit 3 (Senior Seismic Hazard Analysis
Committee)

 Fire PRA
 Volcano PRA
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Summary• Decision making should be based on the current
state of knowledge
 PRA results are an essential part of this knowledge• PRAs provide metrics that facilitate communication
with the public• PRAs consider a broader set of potential challenges
to safety and prioritize these challenges based onrisk significance (we can’t do everything)• RIDM allows more effective and efficient use ofresources, thus improving safety indirectly• A roadmap is needed for developing RIDM
processes in a systematic way11