Summary of the 15th Technical Advisory Committee (TAC) Meeting
Date:
Place:

Nov. 16, 19 and Dec. 9, 2021
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 Center
Observers:
Shikoku Electric Power Company (in the SSHAC meeting)
Proceedings

NRRC Risk Assessment Research Plan and External Natural Event
Research Plan for FY 2022 were discussed.
Of the NRRC Research Plan for FY 2022, “NRRC’s activity to promote riskinformed applications” and “The results of the Ikata SSHAC Level 3 Project by
Shikoku EPC and the SSHAC-based research of probabilistic seismic hazard
analysis (PSHA) activities in Japan” were discussed.
Tuesday, November 16, 2021
Topic 1: Overview of NRRC Risk Assessment Research Plan for FY 2022

The NRRC presented the overview of the Risk Assessment Research Plan for
FY 2022.
 TAC members commented as follows:
Current Status of PRA Method Improvement / Planning R&D-Shutdown PRA sometimes has as much contribution to the risk as at-power
PRA, but the present material may lead to a misunderstanding that
shutdown risk is negligible. The material contents should be consistent withthe way of prioritizing the research items in NRRC.
Level 1 PRA-TAC would like the NRRC to share the English report of the internal-event
LOOP MUPRA. TAC does not rush NRRC to finalize the report, expecting toreceive it after the director’s approval.
Fire PRA-In the U.S., the issue related to HEAF has a significant regulatory impact.
We hope that the HEAF guideline will be developed also in Japan for effective
discussion on the subject.

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Multi-Unit PRA-

The method for calculating the joint failure probability considering seismic
response correlation is an important issue that is also common to single unit
seismic PRA.
Risk Communication-

This is a very important program and an objective worthwhile to pursue. We
would like to discuss it soon again at the end of the research phase in FY2024.
General comments---

It is a very good idea to have a seminar on HRA. It would be better to share
the knowledge with not only the people in NRRC but also those outside
including NRA. We recommend that similar lectures be held for otherresearch subjects such as uncertainty.
Since some new challenging issues have been identified, the NRRC needs tobalance the overall research scope and prioritize research problems. It should
be time to comprehensively review the research issues in terms of risk
significance, level of technical/empirical knowledge, available resources,
regulatory necessity, and social interest.
Since nuclear power is finding its way back as the best value for money inenergy generation, focused and resource-intensive research by the NRRC
must be useful in the future.

Friday, November 19, 2021
Topic 2: Overview of NRRC External Natural Event Research Plan for FY 2022

The NRRC presented the overview of the External Natural Event Research
Plan for FY 2022.
 TAC members commented as follows:
Current Status of PRA Method Improvement
---In the future, Multi-Hazard PRA for the combined hazards in addition toseismic and seismic-induced tsunamis will have to be developed.
Seismic PRA
After the fragility evaluation results based on the seismic experience databaseare summarized, we would like them to be presented in future TAC meetings.
High-Wind PRA
The current tornado countermeasures have been conservatively and heavily
armored. High-Wind PRA should continue to be developed for optimizing
countermeasures by analyzing the safety margins as well as the robustness ofthe countermeasures against tornadoes.

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--Volcanic ash-fall PRA

Since the volcanic ashfall can last for days or weeks, the research team needs
to demonstrate a comprehensive methodology to quantify the risk of long-term
reactor cooling after shutdown due to volcanic ashfall in addition to the usual
short-term cooling for both full power and shutdown modes.
It is better to perform PRA and evaluate risks for not only volcanic ashfall but
also other various volcanic impacts.

Friday, November 19, 2021
Topic 3: Overview of NRRC Research Plan on Risk-Informed applications for FY
2022

The NRRC presented the overview of the Research Plan on Risk-Informed
applications for FY 2022.
 TAC members commented as follows:- In the US, when practicing the application of 10CFR50.69, the utilities use
the guideline developed by EPRI etc. The utilities have an advisory board,which coordinates at the management level to determine what organizationof NEI, EPRI, ASME, etc. is to develop the guideline to avoid duplication.
This coordination is essential. The NRRC, as a research institute, develops
various kinds of guidelines but they seem to be poor in coordination. TAC
would like to discuss the role of the NRRC from the perspective of the USutilities.
- I think that the NRA's involvement is necessary when the NRRC conducts apilot study. The NRRC should propose a pilot study of a specific application
to the utilities and the NRA. However, the situations in Japan and the US
can be different. I am not sure the NRA would respond to the NRRC’s proposal.
I suggest that the NRRC consider well the manner and the system in Japanto realize the pilot study.
- I understand that the KK7 PRA review was similar to the peer reviews
conducted in the US in that international experts check whether the PRA
meets the ASME/ANS standards. TAC would like to confirm that this fact has
been stated in the report. TAC also would like to discuss this topic in the next
TAC meeting.
- OLM does not necessarily improve safety. Even so, it can be done within theacceptable risk increase.
- The US utilities claim that OLM improves safety because it reduces humanerrors by using maintenance personnel with full knowledge of the plants.
That is, the risk during refueling outage decreases.
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Thursday, December 9, 2021
Topic 4: The results of the Ikata SSHAC Level 3 Project by Shikoku EPC and theSSHAC-based research of probabilistic seismic hazard analysis (PSHA)
activities in Japan NRRC presented the results of the Ikata SSHAC Level 3 Project by Shikoku
EPC and the SSHAC-based research of probabilistic seismic hazard analysis(PSHA) activities in Japan.
 TAC members commented as follows:- Though it is concluded that the probability of exceedance of 1000 gal is of theorder of 10-5 -10-6 in the executive summary, the mean value of the probability
for the period of 0.02s is about 7×10-5. The summary should be carefully made---in terms of periods and uncertainties so as not to mislead the readers.
The usage of the BPT model in logic trees and the difference between the BPTmodel and the Poisson process should be discussed in another meeting.
Ikata3 is located on a very stiff hard rock site and can have risk-significant
components with a natural frequency of 100Hz. Is the reason for no
consideration of the period of 0.02 sec or less in the Ikata SSHAC Project
because there is no regulatory requirement for that in Japan?
One of the reasons might be that the time history of ground motion is obtainedat only 0.01s intervals and it is difficult to evaluate the response of equipmentwith natural frequencies of more than 50Hz.
We plan to issue the TAC letter about the Ikata SSHAC Level 3 Project. The
TAC members will discuss the contents of the letter and ask necessary
questions on the Ikata SSHAC report for writing the letter.

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