Summary of the 18th Technical Advisory Committee (TAC) Meeting
Date:
Place:

May 15(Monday)-19(Friday), 2023
Nuclear Risk Research Center (NRRC),
Central Research Institute of Electric Power Industry and Webex

Participants:
TAC:
Mr. Stetkar (Chair), Mr. Afzali, Dr. Chokshi, Mr. Miraucourt,
Dr. Takada, Dr. Yamaguchi
NRRC:
Dr. Apostolakis (Director),
Research staff of the Nuclear Risk Research Center
Proceedings:
In the 18th Technical Advisory Committee meetings, the following issues were reviewed:• “Overview of NRRC Research Plan for FY2024 –Risk-informed Decision-making (RIDM)
Promotion–”• “Overview of NRRC Research Plan for FY2024 –Risk Assessment Research–”• “Overview of NRRC Research Plan for FY2024 –External Natural Event Research–”• “Good Practice of RIDM” *• “Draft Guidelines for Containment Vessel Leak Rate Test” *• “Draft Guidelines for On-Line Maintenance” *• “PSHA Implementation Guidelines”• “MUPRA research overview - Research plan and current outcomes-” *• “Multi-Hazard PRA (Seismic-Tsunami superposition PRA)”
The following meeting was held closed.
• “Research Initiatives on Risk Integration”
Note: The meetings of the agenda items marked with an asterisk (*) above were also attended
online by electric power companies.
Monday, May 15, 2023
Topic 1 Overview of NRRC Research Plan for FY2024 –RIDM Promotion–
The NRRC presented the overview of the FY2024 Research Plan for “RIDM Promotion.”
TAC’s advice and comments are as follows.
- The RIDM promotion team should develop methodology and guidance for the utilities toutilize PRA to make good decisions.
- To get PRA peer review experience, official peer reviews are not necessary and trial ones
are useful enough. Peer review hands-on experience gives two benefits. The first istraining experienced reviewers. The second is to give feedback to Japanese utilities about
1the current technical quality of PRAs and make them identify areas of improvement inPRAs.
Topic 2 Overview NRRC Research Plan for FY2024 –Risk Assessment Research–
The NRRC presented the overview of the FY2024 Research Plan for “Risk Assessment
Research.” TAC’s advice and comments are as follows.
• SFP PRA- SFP PRA should be intended to be a method for Level 1 and Level 2 for all plant operating
modes. The research plan should explicitly describe that the Level 2 PRA methodology for
SFP will be established considering the plant operating status not only at low power andshutdown but also at full power.
• Fire PRA- There is no need to develop a new methodology for Level 2 Fire PRA since there is nomethodological difference between Level 1 and Level 2 of Fire PRAs in general.
Topic 3. Overview NRRC Research Plan for FY2024 –External Natural Event Research–
The NRRC presented the overview of the FY2024 Research Plan for “External NaturalEvent Research.” TAC’s advice and comments are as follows.
•Seismic PRA- The phase of conducting seismic PRA for a model plant has already been completed. The
next step is the phase of that evaluation for an actual plant, which should be conductedby the utilities. The NRRC should upgrade the assessment methodology of hazard andfragility.
(NRRC) The NRRC will compile methodologies applicable to seismic PRA of actual plants
conducted by the utilities.
(NRRC) We are discussing how to evaluate the capacity of buildings against vertical loads
according to the TAC letter of last November. Based on the request by utilities, we are also
considering cooperating in the development of elastoplastic 3D models for back fitting in
the future.
•Tsunami PRA- The reference tsunami heights and the reference earthquake ground motions areconservative. The NRRC should accelerate before it is too late the implementation of theapplication of rational design in new plant planning, which is one of the long-term goals.
- TAC would like the NRRC to provide the paper on a graded approach to tsunami fragility
assessment.
(NRRC) Since this is a major theme that cuts across different fields, we will consider animplementation system for discussions within not only the NRRC but also the Federation ofElectric Power Companies of Japan.

2•Tornado and High-Wind PRA- Tornadoes and typhoons have common issues in the development of PRA methodology;
therefore, they should be studied concurrently.
•Volcanic ash-fall PRA- The paper on the formulation of the ash-fall hazard curve is quite interesting.
Tuesday, May 16, 2023
Topic 4 RIDM Team Activities
The NRRC presented “Good Practices for RIDM,” “Draft Guidelines for Containment
Vessel Leak Rate Test,” “RIDM activities by the utilities,” and “Draft Guidelines for On-LineMaintenance”. TAC’s advice and comments are as follows.
•Good Practice for RIDM
- The NRRC should continue to consider using the common list of good practice attributes
as bases for consistent evaluation among the utilities.
(NRRC) The NRRC would like TAC to recommend some U.S. utilities for benchmarking daily
RIDM activities.
•Draft Guidelines for Containment Vessel Leak Rate Test
- The estimation of the containment standby failure rate should not use the total industry
exposure times.
- To improve accountability to the regulator, all hazards and all modes should be consideredin risk assessment.
(NRRC) The NRRC will add guidance to CRIEPI study report about the consideration ofuncertainties and PRA scope with reference to RG1.174 and NUREG-1855 and ideas for
LRT test interval extension application.
•Draft Guidelines for On-Line Maintenance- Aggregating the total risk for the whole year is necessary because the sum of the risks canbe unacceptable for OLMs of multiple facilities or multiple times even if each activity iswithin AOT for a short period of time.
- Since plant operation varies depending on the scope of the isolation of the systems, therisk assessment should consider not only the outage of the target equipment but also theimpact of the outage.
- The increase of the initiating event frequencies caused by OLM is addressed by multiplying
the frequencies by rough coefficient factors or using initiating event fault trees.
(NRRC) The fixed version of the Guidelines for On-Line Maintenance will be circulated toTAC members.
Wednesday, May 17, 2023
Topic 5 PSHA Implementation GuideThe NRRC presented the outline of the CRIEPI report on the Probabilistic Seismic Hazard
3

Analysis (PSHA) Implementation Guide and the research progress on Multi-Site SSHAC-Based
PSHA Development. TAC asked questions about the coordination of the PSHA Implementation
Guide with the Atomic Energy Society of Japan Seismic PRA Standard and the way todemonstrate the efficiency of Multi-Site SSHAC/PSHA.
Topic 6 MUPRA research overview-Research plan and current outcomesThe NRRC presented the Research plan and current outcomes of MUPRA. TAC’s advice
and comments are as follows.
- The NRRC needs to exercise caution not to screen out or simplify important scenarios inlevel 2 MUPRA only based on the results of level 1 MUPRA.
- The NRRC needs to provide a big picture of the MUPRA study, considering factors such asPOS, PRA level, and so on.
- The NRRC should avoid using words that may imply the need for new methodologies whenyour objective is not to develop a methodology.
Topic 7 Multi-Hazard PRA (Seismic-Tsunami superposition PRA)The NRRC presented the Research plan and current outcomes of MUPRA. TAC’s advice
and comments are as follows.
- The NRRC should carefully note in the final report that identified superposition events arefor a hypothetical plant along a coast.
Thursday, May 18, 2023
Exit Meeting [Closed]4