Risk-Informed Decision Making

George Apostolakis
Head, Nuclear Risk Research Center
Presented to NRA Chairman T. Fuketa andCommissioner S. Yamanaka
September 10, 201811

Overview• Risk-informed decision making• PRA quality• Safety goals

2Our Main Thesis• Neither the traditional process that focuses on“deterministic” requirements nor a risk-based
decision-making process is sufficient for rational
decision making.
 The U.S. NRC-sponsored WASH-1400 identified the risk
significance of human actions and support systems
 The U.S. industry-sponsored Zion/Indian Point PRAs
pointed out the significance of external events• We must use the best attributes of both processes,
i.e., a risk-informed decision-making process (RIDM).
• Risk is plant-specific. Only PRA can provide useful
insights about unique plant features.
• Large variability of CDFs in the U.S., even though allplants were licensed under the same system.
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Major Challenges• Both the regulators and the industry have been
focusing on regulatory-compliance for a long time.
• Moving to a risk-informed culture is not easy andtakes time.
• An important first step is the ROP that will be
implemented in Japan in 2020.
• Another important step is the issuance of theStrategic and Action plans by the industry.

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Risk-Informed Decision-Making

From: Strategic and Action Plans for the Implementation of Risk
Information Utilization at Nuclear Power Plants, February 8, 2018.

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PRA Quality• A plant-specific PRA is the essential element for
RIDM and the ROP.
• Such a PRA is a complex combination of logic
models, experimental and statistical evidence, andjudgment.
• The uncertainties for some initiators may be verylarge (however, they are not quantified in the“deterministic” system).
• An exhaustive review was performed for theindustry-sponsored Zion/Indian Point PRAs bySandia National Laboratories on behalf of the NRC.
• This review was unique and very resource intensive.
• A practical solution was needed.
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Assuring PRA Quality in the U.S.
• U.S. scientific societies (ASME and ANS) issuedstandards.
• The NRC issued reports and regulatory guides
endorsing the standards (with exceptions, asappropriate).
• NEI issued guidance on peer reviews.
• NRC and ACRS staff observed several peer reviews.
• NRC approved the NEI peer review process.
• Compliance with these documents has eased theNRC’s burden regarding PRA reviews.
• The NRC receives a PRA summary but staff mayreview as much of the industry’s PRA as they wish.
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Uncertainties in RIDM (RG 1.174)••

The analysis is subject to increased technical review and management
attention; …the numerical values associated with defining the regions in thefigure are to be interpreted as indicative values only.
The decision-making process combines risk insights and defense in depth; itis inherently subjective.
8Japanese Industry’s Efforts on PRA Quality• Improving the infrastructure NRRC Guides on HRA, Fire PRA, Data Collection
 Models for external events, including the SSHAC process Multi-unit PRA• NRRC’s Technical Advisory Committee (TAC) highlevel review of Ikata 3 PRA
 Expanding the list of Initiating Events, e.g., adding loss ofinstrument air system
 Improving plant-specific data collection• International expert reviews following the ASME/ANSstandards and the NEI process Ikata 3: Torri, Lin, Fleming (U.S.), Boneham (U.K.)
 KK 7: Chapman, Wachowiak (U.S.), Nusbaumer (Switzerland)• NRA staff are welcome to observe these meetings,
the resulting actions, and relevant documents
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NRRC Training Courses
１．PRA and risk information utilization course

For beginners
Preparing for implementation in FY2018

２．Risk professional course (supported by EPRI)

Mainly L1 internal events PRA
For utility’s PRA practitioners and regulatory staff
Started in FY2018

３．Risk information utilization course

 For decision makers (NPP managers)
 Preparing for a trial offering in FY2018.

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Safety Goals• SGs contribute to answering the question: How safe
is safe enough?
 “Continuous risk management” versus “continuoussafety improvement”• Easier to communicate the level of safety to allstakeholders
 They replace the obscure statement “the plants will besafe if they meet the regulations”• They are an essential part of RIDM
• The SGs are indicative values.
• “Informal” Goals in Japan CDF < 10-4 per reactor year CFF < 10-5 per reactor year
 Frequency of release of more than 100 TBq of Cs 137<10-6 per reactor year11

Establishing Safety Goals• Because of their significance, formal SGs should be
the result of deliberation among the regulators,industry, scientific societies, and the public• Safety Goals can be in different forms
 U.S.: Point values for CDF and LERF
 Proposed safety improvements are evaluated using the Backfit
Rule (adequate protection vs. safety improvement).

 U.K.: Two values for individual risk of death Basic Safety Level (10-4), not allowed to be exceeded Basic Safety Objective (10-6), “the BSO doses/risks have been set ata level where ONR considers it not to be a good use of its
resources or taxpayers’ money, nor consistent with a targeted andproportionate regulatory approach, to pursue further improvements
in safety.”
 Between BSL and BSO, cost-benefit analysis evaluates
improvements
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A Broader Proposal from the IAEA

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Final Remarks• RIDM is the rational way to proceed both for theindustry and regulators• PRAs should be plant-specific• We need to move from a regulatory-complianceculture to a risk-informed culture• The ROP and the industry’s strategic and actionplans are significant steps forward• PRA quality is improved by issuing standards,
regulatory guidance, and implementing peer reviews• RIDM is an inherently subjective process requiring
substantial training• The deliberative process for establishing safety
goals should start soon
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