Technical Advisory Committee of the Nuclear Risk Research Center
Central Research Institute of Electric Power Industry
1-6-1 Otemachi, Chiyoda-ku, Tokyo, 100-8126 JapanMarch 26, 2021
Dr. George Apostolakis
Head, Nuclear Risk Research Center
Central Research Institute of Electric Power Industry
1-6-1 Otemachi, Chiyoda-ku
Tokyo, 100-8126 JapanSUBJECT:DETAILS OF ENVISIONED RISK-INFORMED DECISION-MAKINGFRAMEWORK

Dear Dr. Apostolakis:
In our February 16, 2021 letter on the Nuclear Risk Research Center (NRRC)
research plan for fiscal year 2021, we concluded that 1) most of the NRRC research
activities have achieved adequate maturity and sophistication to warrant theirpractical use and 2) the needs and priorities for development of increasingly detailed
models for specific hazards and damage mechanisms are highly dependent on theirintended applications.
This letter aims at clarifying information about the elements of a risk-informed,performance-based (RIPB) decision-making framework that are necessary to enable
us to provide more refined and focused recommendations on specific research
programs.
CONCLUSION
The intended applications of probabilistic risk assessments (PRAs) within a RIPBdecision-making framework should provide the primary motivation and structure for
the NRRC research. As a result, prioritization of the different research areas,planning of the corresponding research details, and publication of the resulting
application guides should be consistent with those needs of the industry that areplanned to be addressed using risk-informed, performance-based initiatives.
We are requesting a more formal, comprehensive, and detailed briefing on how thescope and details of each research project are carefully tailored to meet the timing,
scope, and structure of the utilities' needs for integrated risk management. A
thorough discussion and a better understanding of these issues will help us to more
effectively focus our reviews of specific research projects and our recommendations
for how that research supports an integrated risk-informed decision-making (RIDM)
framework.

-1-The present request is an extension of our November 19, 2019 letter report thatrequested a briefing on the industry readiness for implementation of the riskinformed Reactor Oversight Process (ROP). Unfortunately, due to the pandemic, it
was not possible to have that briefing. The items discussed in that letter report could
be integrated into this requested briefing.
BACKGROUND
As noted in our February 16, 2021 letter report:"Since 2014, the NRRC research has made important advances in the scientificand engineering state of knowledge about events, phenomena, and accident
scenarios that contribute to the risk from a nuclear power plant. The PRA is avital tool to support effective risk-informed decision-making (RIDM) programs andpractices that focus on the most important sources of risk at each nuclear powerplant site. Therefore, it is essential that the scope and details of each research
project are carefully tailored to meet the utilities' needs for integrated riskmanagement. We will comment on the current status of the integration of NRRC
research activities with the utilities' RIDM programs in a separate letter report."
DISCUSSION
For the last several years, appropriately, as part of each research program summary,the overall scope of research and the technical objectives of the individual projects
are related to the NRRC short-, intermediate-, and long-term goals. These goals, inturn, are established according to the following mission and vision of the NRRC:"Mission Statement
To assist nuclear operators and the nuclear industry in their continuous effort toimprove the safety of nuclear facilities, that is, to manage the relevant risks, bydeveloping and employing modern methods of Probabilistic Risk Assessment(PRA), risk-informed decision making and risk communication.""Vision Statement
To become an international center of excellence in PRA methodology and risk
management method, thereby gaining the trust of all the stakeholders."
Also, the Technical Advisory Committee mission is to provide:"…independent oversight, reviews, and recommendations to ensure that all
NRRC research programs and work products maintain the highest standards oftechnical excellence."
Based on the above missions and vision, as well as NRRC's significant progress indeveloping PRA methods and models since 2014, it is now the right time for us to be
more actively engaged in a robust and detailed conversation on the timing, scope,and methods of the envisioned RIPB decision-making framework in Japan, as well-2-

as the relationship between those programs and the sophistication of the PRA
models (scope and level of detail). This will help us and the NRRC research teams
to better focus our collective efforts in delivering "the highest standards of technicalexcellence" in areas that best serve the Japanese operators.
Our conclusion is based on the following perspective, which is consistent with theU.S. Nuclear Regulatory Commission definition of RIDM:"An approach to regulatory decisionmaking, in which insights from probabilistic
risk assessment are considered with other engineering insights."
A robust RIPB decision-making framework involves the following distinct
components:
Risk Analysis Component – Uses tools (e.g., PRA models) and rules (e.g.,standards) to analyze what could go wrong, how often, and its consequences.

Risk Integration Component – Uses the insights from the Risk Analysis
Component in combination with other considerations to develop a relationshipbetween the risk and a set of acceptable risk levels. In other words, itestablishes the relationship between the risk analysis results and a set ofperformance objectives to be used by the decision makers. In this component,performance objectives for the major plant elements (e.g., functions,structures, systems, and components) that are evaluated in the Risk Analysis
Component are established for monitoring.

Risk Management Component – Uses the results from the Risk Integration
Component to make decisions on many topics, including the following:o Risk Reduction – Take temporary or permanent measures to reduce
the risk.
o Risk Prioritization – Prioritize activities to proactively or reactively, butholistically, manage the risk.
o Risk Monitoring – Monitor plant performance and provide reasonableassurance that the risk remains below the risk acceptance targets.

These three components are highly inter-related and do not effectively function
without the other. That is, to achieve the NRRC vision of becoming "…aninternational center of excellence in PRA methodology and risk management
method [emphasis added]", the following needs to be achieved:
Risk Analysis Component (e.g., PRA models) with sufficient scope and levelof detail needed by the Risk Integration Component to provide an adequate
and appropriate picture of a plant's risk profile.

Risk Integration Component to evaluate the risk profile that is used toestablish the overall plant performance objective(s) that the Risk Management
Component is trying to achieve.

Thus, although the Risk Analysis Component is the foundation of the overall RIDM
process (ground zero), it has to be focused on the objective(s) of the Risk

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Management Component, with full awareness of how the Risk Integration
Component is formulated.
Finally, the Risk Analysis Component, by itself, has many beneficial attributes. For
example, it 1) identifies and provides understanding of potential failure modes, 2)
identifies and justifies sources and levels of uncertainties, 3) provides a tool toimprove the effectiveness of corrective and compensatory measures, 4) provides atool for evaluating the cost-effectiveness of different options, 5) provides a tool for
quantifying engineering judgment and transparently communicating technical issues
with the stakeholders, 6) provides a basis for development and communication of thesafety case for regulators and the public, etc. However, to fully benefit from all ofthese features, the other two components (Risk Integration and Risk Management)
have to be adequately developed to provide the necessary context for the Risk
Analysis Component.
Most of our discussions with the NRRC research teams to date have focused
primarily on detailed technical elements of the Risk Analysis Component of the RIDM
framework. To better help the NRRC and the Japanese nuclear industry achieve
their goal of comprehensive RIPB decision-making, we need to more fully
understand how the Risk Integration Component and the Risk Management
Component of that framework are being envisioned, the timing of their development
and implementation, and key elements of their supporting infrastructure. A thoroughdiscussion with representatives of the organization responsible for coordinating
industry RIDM programs and initiatives, members of the RIDM Promotion Team, andNRRC management responsible for integration of the center's research programs
and priorities will help us to more effectively focus our reviews of specific research
projects and our recommendations for how that research best supports an integrated
RIDM framework.
Sincerely,

John W. Stetkar
Chairman
REFERENCES
1.

Technical Advisory Committee of the Nuclear Risk Research Center,"Proposed NRRC Research Plan for Fiscal Year 2021," February 16, 2021.

2.

Technical Advisory Committee of the Nuclear Risk Research Center,"Framework and Infrastructure for Supporting Industry Readiness for ROP
Implementation," November 19, 2019.

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3.

U.S. Nuclear Regulatory Commission, Basic References, Glossary, RiskInformed-Decisionmaking,www.nrc.gov/reading-rm/basic-ref/glossary/riskinformed-decisionmaking, accessed March 14, 2021.

4.

U.S. Federal Energy Regulatory Commission, Office of Energy Projects –Division of Dam Safety and Inspections, "Interim Guidance, Risk-Informed
Decision Making (RIDM) Risk Guidelines for Dam Safety," Chapter 1,"Introduction to Risk-Informed Decision Making," Version 4.1, March 2016.

5.

Zio, E. and N. Pedroni, "Risk-Informed Decision-Making Processes, An
Overview," Report 2012-10, Foundation for an Industrial Safety Culture(FonCSI), Toulouse, France, December 2012.

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