Summary of the 16th Technical Advisory Committee (TAC) Meetings
Date:
Place:

May 23~May 27, 2022
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,
Prof. Takada, Prof. Yamaguchi
NRRC:
Dr. Apostolakis (Director),
Experts of the Nuclear Risk Research CenterIndustry:
Shikoku EPC, Tokyo EPC HD, TEPSYS, MHI
Proceedings

In the 16th Technical Advisory Committee meetings, the following issues
were reviewed: "Ikata SSHAC study", "PSHA Implementation Guide andRegional SSHAC and Site Response (Future Plan)", "Industry Explanation onRIDM", "Hamaoka Tsunami PRA", “Multi-hazard PRA”, “Seismic PRA projectusing a model plant”, and “Low Power / Shutdown PRA”. In addition to this,opinions were exchanged on "On-Line Maintenance (OLM) Project in Japan".
Monday, May 23, 2022
Topic 1: Ikata SSHAC study

The results of the Ikata SSHAC level 3 project were discussed regarding thequestions addressed by the TAC members after the previous TAC meeting.
 The TAC members commented as follows:- The rationality of the truncation criteria of the seismic motion evaluation
should be considered carefully and should be described appropriately in thePSHA guide.
- When the TI team selects a single model, method, and data in the logic treemodels instead of multiple branches, the team should clearly describe thegrounds for the selection.
Topic 2: PSHA Implementation Guide and Regional SSHAC & Site Response(future plans)

NRRC presented the outline of “PSHA Implementation Guide and Regional
SSHAC & Site Response (future plans)”.
 TAC members commented as follows:- Independent review of the guide should be conducted since the guide is1important for future reevaluation of PSHA by the utilities.
Tuesday, May 24, 2022
Topic 3: Industry Briefing on RIDMNRRC presented "Industry Briefing on RIDM" including the restart status ofJapanese NPP and efforts for strategic and action plans of RIDM.

Wednesday, May 25, 2022
Topic 4: Hamaoka Tsunami PRA - Source term evaluation and uncertainty
analysis -NRRC presented “Outcome of Level 2 PRA on Hamaoka Tsunami PRA Project- Source Term Evaluation and Uncertainty Analysis -”.
 TAC members commented as follows:- The completion of the Level 1 and Level 2 PRA research project to evaluate
the tsunami risk for a model plant is a milestone achievement for theJapanese nuclear industry. It has contributed to the evolution of themethods and modeling tools that enable the analysis of risk in tsunamiprone areas worldwide.
- The models, data, and supporting analyses should be subject to anindependent and in-depth technical review.
- The NRRC should develop tsunami risk assessment guidance for theJapanese utilities and the standards committee.
Topic 5: Multi-hazard PRA

NRRC presented the PRA methodology for the superposed hazard ofearthquakes and tsunamis.
 TAC members commented as follows:- The multi-hazard PRA should demonstrate how much the superposed
hazard of earthquakes and tsunamis differs in magnitude or impact fromthe single-hazard of earthquakes or tsunamis.
- It is essential that one single PRA model can address a seismic hazard, atsunami hazard, and the superposed hazard of seismically-caused tsunamis.
Thursday, May 26, 2022
Topic 6: Seismic PRA using a model plant

NRRC made a presentation on a study of “Update on NRRC Seismic PRA
Project Using A Model Plant.”
TAC members provided the following comments:

2

---

We strongly recommend that NRRC Seismic PRA Project Phase-1 bereviewed by independent experts. A specific plan for an independent peer
review of the Seismic PRA should be drafted and shared with TAC.
NRRC selected/adopted RCW piping as an inter-building piping system,
which can be affected by the inclination of the foundation ground. NRRC
should conduct a specific analysis to identify failure modes and failure
mechanisms of the RCW piping system.
A great number of studies on piping fragility evaluation have been
conducted in the US and recognized as bases for international PRA practice.
Therefore, NRRC should survey international practice further before
conduct studies on the development of piping fragility.

Topic 7: Low Power / Shutdown PRA

The Shikoku Electric Power Company presented “the overseas expert review
results of Low Power / Shutdown PRA” as a part of “the PRA Ikata 3 PilotProject.” TAC members commented as follows:- In the 5th review, the scope of the review was limited to about half of all thesupporting requirements (SRs). Some SRs were considered out of scope
because the shutdown PRA applies the same approach used in the at-PowerPRA. It would be useful to compare those low power and shutdown SRs
against the at-power SRs. If there are differences in the SRs, those SRs
should be examined for the low power and shutdown PRA.
- The scope of the low power and shutdown PRA should include all low power
plant operating states. The at-Power PRA models do not account for uniquesystem alignments, operational activities, and testing that are conductedduring low power modes. (This comment applies to both the Ikata 3 PRA
and the KK 7 PRA.)Tokyo Electric Power Company Holdings presented “the overseas expert
review results of Low Power / Shutdown PRA” as a part of “the PRA KK 7
Pilot Project”.

3