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 JapanMay 30, 2023
Dr. George Apostolakis
Director, Nuclear Risk Research Center
Central Research Institute of Electric Power Industry
1-6-1 Otemachi, Chiyoda-ku
Tokyo, 100-8126 JapanSUBJECT:PRELIMINARY NRRC RESEARCH PLAN FOR FISCAL YEAR 2024

Dear Dr. Apostolakis:
During the 18th meeting of the Technical Advisory Committee of the Nuclear Risk
Research Center (NRRC), May 15-19, 2023, we met with the NRRC staff to review
the proposed preliminary research plan for fiscal year 2024. The purpose of ourreview was to provide comments on the technical merits of the research plan and its
relevance for supporting the NRRC's current mission.
This letter report marks a change to the schedule for our research plan reviews. Our
discussions with the NRRC management and research staff have provided us with abetter appreciation of the time and effort that are involved with development of theannual research plan, including consultations and approvals by the Japaneseindustry sponsors. We understand that our technical input and recommendations
will be more timely and effective when they are provided while the research plan is in
its formative stages. This is especially important for your consideration of our initialtechnical input on proposed innovative methods and major new research projects.
Therefore, beginning with this report, we will now conduct our annual review of the
proposed preliminary research plan in May, rather than November.
CONCLUSIONS AND RECOMMENDATIONS
1. The overall scope of the preliminary research plan for fiscal year 2024 and thetechnical objectives of the individual projects within each major research area
remain consistent with the NRRC short-, intermediate-, and long-term goals.
2. We are pleased that the preliminary plan includes our recommended research
activity to develop methods and practical guidance for the integration of PRA
models and aggregation of results to provide a full-scope assessment of theoverall plant risk and its contributors. This is a challenging task. The guidance
will enhance the utilities' consistent use of the PRA to support their risk-informed
decision-making programs, discussions with the Nuclear Regulation Authority,-1-and communications with the public. We look forward to regular interactions withthe research teams as this project progresses.
3. During our review, we identified three individual research activities that meritadditional attention in the preliminary plans for fiscal year 2024 and subsequent
years. Our recommendations for those activities are summarized in theDiscussion section of this report.
BACKGROUND
One of the most important objectives of the research plan is to present the technicalcontext of the research needs, including the rationale for prioritization and scope ofthe research, current state of knowledge, and potential contributions and significanceof the research to the goals of the center. Our review of the preliminary researchplan focused on the objectives of each research project and its supporting tasks, thetechnical relationships and relative priorities among those activities, and any major
needs for additional research. We did not review the technical details of individual
research activities or their completion milestones, except as needed to understandhow those activities are integrated throughout the plan. We will comment separately
on the technical elements of individual research projects in our future detailed
reviews of those projects.
DISCUSSIONDuring this review, we were briefed on continuing and planned projects in eachresearch area, the major technical tasks in each project, the current status of eachtask, known or potential problem issues, and the estimated schedule for completionof each task.
A relatively short time has passed between our November 2022 review of the final
research plan for fiscal year 2023 and the research teams' efforts to begin
preparation of the preliminary plan for fiscal year 2024. Therefore, details of mostresearch projects and supporting tasks have not changed significantly, with only
updates to their progress and completion schedules. During our discussions, theresearch teams confirmed that specific research tasks will incorporate
recommendations from our November 27, 2022 letter report. The overall scope ofresearch for fiscal year 2024 and the technical objectives of the individual projects
within each major research area remain consistent with the NRRC short-,intermediate-, and long-term goals.
Based on our review of the preliminary research plans and our discussions with theresearch teams, we offer the following recommendations for further assessments ofthree individual research activities.

-2-(1) Development of Risk-Informed Decision-Making Guidance
A continuing research activity involves the development of guidance for the utilities'
implementation of an infrastructure and programs that will support integrated riskinformed decision-making (RIDM) in all aspects of plant operations and management.
RIDM is an effective process in which risk insights obtained from a PRA model areused in combination with prescriptive and deterministic inputs as well as goodengineering practices, consideration of operating experience, and soundmanagement oversight to improve safety while increasing operational flexibility. In
the United States, there are a number of different programs that benefit from theRIDM concepts, practices, and principles. The two main categories are:•Category 1 - Voluntary and required Risk-Informed Performance-Based(RIPB) programs that are used to meet regulatory requirements. Examples ofvoluntary programs include Risk-Informed Inservice Inspection (RI-ISI), RiskInformed Allowed Completion Times (also known as "RIPB AOT" or "Initiative4b"), RIPB Surveillance Frequency Program (also known as "Initiative 5b"),
RIPB Fire Protection Program, Risk-Informed Categorization of Structures,Systems, and Components (SSCs), etc. Use of a voluntary RIPB program tomeet regulatory requirements necessitates Nuclear Regulatory Commission(NRC) approval via a License Amendment and is typically undertaken whenan NRC-endorsed RIPB program is available. An example of a regulatoryrequired RIPB program is the suite of programs that are needed to support
meeting the 10 CFR 50.65 Maintenance Rule requirements.

•Category 2 - Voluntary RIPB programs that do not require regulatory approvaland are primarily used to improve efficiency and enhance the safety-focused
effectiveness of operational programs. Examples of such programs include
use of risk insights for (a) operator training, (b) prioritizing items in thecorrective action program, (c) internal quality control related inspections,(d) plant staff awareness of risk-sensitive plant configurations, etc.

Utilization of the voluntary Category 1 RIPB programs is subject to a regulatory
framework that is still maturing in Japan. The NRRC should continue its support forenabling the currently-envisioned voluntary Category 1 RIPB programs, while
monitoring regulatory framework evolution.
We recommend that the NRRC research team should focus their near-term activities
on the development of guidance to enable utilities to take advantage of Category 2
RIPB programs. These are equally important as Category 1 voluntary RIPB
programs and can be implemented sooner. These processes provide a consistent,transparent, and balanced approach to safety and operational flexibility, whileallowing optimization of resources. Improved safety is achieved by providing
information that increases the plant staff's awareness of factors that influence overallplant risk (e.g., equipment failures, personnel actions, maintenance configurations,etc.).
A comprehensive understanding of a plant's risk profile also allows
prioritization and effective use of resources to address the more risk-significant
SSCs and issues, while conserving resources that might be inappropriately applied
to less risk-significant concerns. Development of guidance for Category 2 RIPB-3-

programs and implementation of those programs at each plant will also allow theNRRC research team, the utilities, and industry organizations to become
experienced in the practical use of RIDM concepts and the supporting programmaticelements such as use of an integrated decision-making panel.
(2) Spent Fuel Risk Assessment
We are pleased that the preliminary research plan includes a more explicit activity forthe development of methods and guidance for an evaluation of the risk from damage
to stored spent fuel. The scope of these analyses includes fuel damage (Level 1risk) and offsite releases (Level 2 risk). A trial application of the methods is currently
planned to begin in fiscal year 2026.
The preliminary plan and individual research tasks continue to focus on evaluation of
the risk only during low power and shutdown plant operating states. In our letter
reports for the fiscal year 2022 and 2023 research plans, we explained why it isimportant for the scope of this research to integrate the analyses of spent fuel risk
with the PRA models for damage to fuel in the reactor core during full power, lowpower, and shutdown modes. Beginning in fiscal year 2024, the scope of thisresearch should include development of methods and models for an integrated
evaluation of the risk from spent fuel damage during all plant operating modes.
(3) High Wind Risk Assessment
The research teams confirmed that they have completed the development ofmethods and models for the evaluation of hazards from high winds and missiles thatare generated by tornadoes. The preliminary research plan for fiscal year 2024
includes development of methods to evaluate those hazards from typhoons. The
preliminary plan also indicates that one task for fiscal year 2024 involves a trial
application of a detailed PRA for tornado damage at a Japanese plant site.
Experience has shown that integration of the high-wind analyses into a full-scope
PRA requires similar analysis techniques and models for tornadoes and typhoons.
To demonstrate these techniques and to gain important practical experience for theanalyses of both hazards, the scope and schedule for the planned trial application
should include an evaluation of the risk from both tornadoes and typhoons.
We look forward to our continuing interactions with the NRRC research team toreview the overall research program and individual research projects, and to help theNRRC and the Japanese nuclear industry achieve their goals of comprehensive riskinformed decision-making.
Sincerely,

John W. Stetkar
Chairman-4-REFERENCES
1.

"NRRC Overview: Preliminary Research Program for FY2024, RIDM
Promotion," Presentation to NRRC Technical Advisory Committee, May 15,2023, Proprietary.

2.

"NRRC Overview: Research Program for FY2024, Risk Assessment,"
Presentation to NRRC Technical Advisory Committee, May 15, 2023,
Proprietary.

3.

"NRRC Overview: Research Program for FY2024, External Natural Events,"
Presentation to NRRC Technical Advisory Committee, May 15, 2023,
Proprietary.

4.

Technical Advisory Committee of the Nuclear Risk Research Center,"Proposed NRRC Research Plan for Fiscal Year 2023," November 27, 2022.

5.

Technical Advisory Committee of the Nuclear Risk Research Center,"Proposed NRRC Research Plan for Fiscal Year 2022," December 30, 2021.

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