Summary of the 19th Technical Advisory Committee (TAC) Meetings
Date:

November 13(Monday) -16(Friday), 2023

Place:

Nuclear Risk Research Center (NRRC), Central Research Institute ofElectric Power Industry and Webex

Attendees:
TAC:

Mr. Stetkar (Chair), Mr. Afzali, Dr. Chokshi,
Mr. Miraucourt, Dr. Takada, and Dr. Yamaguchi

NRRC:

Dr. Apostolakis (Director) and the research staff of the NRRC

Proceedings:
In the 19th Technical Advisory Committee meeting, the following issues werereviewed:
Topic 1: Draft Guidelines for Containment Vessel Leak Rate Test
Topic 2: Good Practices in Risk-Informed Decision-Making by the JapaneseUtilities
Topic 3: Fire Hazard Research Activities (Fire Event Data and Ignition
Frequencies and Recent Regulatory Response)
Topic 4: Seismic Fragility Analysis Methods
The following meetings were held behind closed doors:-Recent Activities by Risk-Informed Decision-Making Promotion Team-Use of Risk Information in Aging Management and Life Extension-Use of Artificial Intelligence (AI) and Machine Learning (ML) for Risk-InformedApplications-Big Picture for Future NRRC Research Projects

Monday, November 13th, 2023
Topic1: Draft Guidelines for Containment Vessel Leak Rate Test(NRRC) The NRRC has decided to incorporate the demand-based model, consistent
with EPRI’s method, instead of the time-based model for the CV failure probability
estimation.
(TAC) Let’s assume that one test was performed 7 years after fifteen annual
periodical tests. In this case, one of the possible approaches to consider outliers
is to average the data per plant rather than accumulating test counts for all plants.
(NRRC) Our approach exempts outliers as anomaly data due to long-term
shutdowns and counts only data for normal-test frequencies of one test everyoutage or one test every three outages. Thus, considering the data for the twopatterns is quite a logical treatment.
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(TAC) When the industry adopts this approach, three things should be considered.
‐CDF must be evaluated for full-scope (i.e. for all hazards and all modes) PRA.
‐Evaluated values must have certain margins covering uncertainties.
‐Criteria acceptable to the Japanese industry are needed.
(NRRC) The Guidance should be developed to show how to assess CDF and CFF
with the current PRA model of the limited scope.
(TAC) A utility that applies to increase the test interval according to this Guidanceshould not face the risk that they must reduce the test interval when they complete
their full-scope PRA. For example, a utility may use a limited-scope PRA to justify
an increase to 15 years. If the CDF from their full-scope PRA is much higher, theutility would need to revise their request, because they can only justify a shorter
test interval. That would reduce utility and NRA confidence in the risk-informed
basis for this application.
(NRRC) Is an all-hazard, all-mode PRA model necessary for this evaluation? Are thelimited-scope PRA models that the utilities have today not appropriate to use?
(TAC) The guidance must consider the total risk impact. Many plants in the U.S.
were approved to implement test interval extensions with only PRAs that quantified
internal-event CDF. These cases required quantitative evaluation from their PRA,
supplemented with bounding quantitative estimates and qualitative considerationof the CDF contributions from hazards and operating modes that were not includedin their PRA model.
Monday, November 13th, 2023
Topic 2: Good Practices in RIDM by the Japanese Utilities(TAC) Are these activities introduced in this meeting commonly implemented by all
the Japanese utilities?
(NRRC) The educational programs are conducted by each utility, but we are unsure
if the other activities are conducted by all the utilities.
(TAC) TAC wants to understand what kind of RIDM guidance the NRRC plans todevelop to realize high-quality RIDM programs conforming to the international
standard for all Japanese NPPs. TAC is interested in how the NRRC will take theleadership to develop the guidance for all the utilities to implement the activities
that have not been shared among the industry. One way for the NRRC to develop
the guidance is to sort out the best practices among all the activities conducted bythe utilities. In addition, there are probably some activities that no utility has
implemented that should be implemented.
The NRRC presented some good examples of risk-informed activities implemented
by individual utilities; however, the presentation does not show what is the best
and what should be applied to all the utilities.
2(TAC) TAC knows the Atomic Energy Society of Japan has developed the IRIDMStandard. What are the contents?
(NRRC) The Standard contains reference information for the utilities’ risk-informedapplications. However, some parts of it are not yet sufficient for practical use.
(TAC) The guidance for the industry must show the basic elements of RIDM, thatis, "WHAT (to do) " before everything and not "HOW (to do)." The overall framework
and programs must be provided instead of specific numbers or detailed calculation
methods. The guidance is used to confirm the consistency of the utilities’ programsin, for example, the scope of the applications, no matter how they are implemented.
(TAC) What impedes the promotion of RIDM in Japan? In the previous TAC
discussion, the NRRC said that was because the regulator won’t support RIDM.
However, while individual utilities have some voluntary RIDM activities, why is theintroduction of RIDM not progressing for all utilities?
(Director) The NRA is certainly an impediment, but it is not the only problem. Along history of taking a deterministic approach hinders a deterministic culture
from changing. Thus, activities to deepen understanding of PRA such as what it isand what benefits it offers are required. It is also important to organize andpromote what can be done without NRA approval.
(TAC) The utilities did not seem to be able to convince the NRA of the benefits ofRIDM at the recent NRA-CNO Opinion Exchange Meeting.
(TAC) The Japanese utilities seem to be inward-looking and to be working
separately on their programs.
(Director) The NRRC needs to work closely with ATENA and JANSI. The NRRC also
needs not only to develop the guidance but also to promote and implement RIDM
together with the whole industry.
(NRRC) How advanced does TAC think the Japanese utilities are in the RIDM
activities compared to the other countries?
(TAC) RIDM in Japan is not necessarily lagging globally but is certainly far behindthat in the U.S. However, even in the U.S., each utility used to separately conduct
its activities. Nevertheless, the U.S. has corrected this situation by having INPO
evaluate utilities on RIDM and publicize best practices. In Japan, it is important for
the NRRC not to get too caught up in the development of PRA and RIDM
methodology, but to keep insisting that the utilities actively utilize RIDM.
(TAC) In Europe, the organization called WANO considers how to correct thesituation in which each utility separately conducts its own activities. In Japan,WANO peer review can be one of the effective measures. It is also effective toestablish a system of cooperation among the utilities if they can conduct
activities voluntarily.
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(TAC) It is not appropriate for TAC to judge if each of the Japanese RIDM activities
is good or bad. That is not our role as technical advisors to the NRRC. However, AllTAC can point out is that simply sharing information doesn’t make all the utilities
implement good practices. The first step in promoting RIDM is to identify goodpractices from the utilities’ activities and have all the utilities implement them. In
addition, a certain degree of internal regulation and control is necessary for all
utilities to implement good practices. To do this, the NRRC must first take the leadin developing the guidance on what the utilities should do. Then, it is necessary todecide who will take the initiative in having utilities implement good practices(ATENA or the NRRC?)

and who will provide oversight of the implementation

status (INPO plays the role in the U.S. Then, JANSI or the NRRC in Japan?)(TAC) Incentives for RIDM as well as enforcement are important for the utilities toperform good practices. TAC suggests that the NRRC should encourage the mostinfluential organizations to have the utilities implement RIDM by giving them clear
incentives.
Tuesday, November 14th, 2023
Topic 3: Fire Hazard Research Activities (Fire Event Data and Ignition Frequencies
and Recent Regulatory Response)(TAC) Fire events that involve human-caused fires and transient combustibles
should be counted separately by the plant operational state because workload andworkplaces are different in between the shutdown state and the at-power state of
the plants.
(TAC) Fire ignition frequencies should be classified by location because thefrequencies, especially human-caused and transient combustible fire frequencies,differ between the turbine buildings and the reactor buildings.
(TAC) Why does the database not quantify electrical cabinet fire frequencies
according to the detailed cabinet categories in the NRRC Fire PRA Guide?
(NRRC) This analysis does not classify the electric-cabinet fire events by
combustible material quantity or size. This is reasonable to avoid too many firesource categories with zero events.
(TAC) The hierarchical Bayesian method is used to quantify fire ignition
frequencies in the United States. In general, a hierarchical Bayesian analysis will
typically result in larger uncertainties than the empirical Bayesian method. This isbecause the hierarchical method better accounts for the plant-to-plant variability
in the data.

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Wednesday, November 15th, 2023
Topic 4: Seismic Fragility Analysis Methods(TAC) If the seismic fragility analysis demonstrates piping-system failures can bescreened out from major risk sources, that will greatly contribute to theadvancement of PRA. Updated estimations of piping-system seismic capacities torealistic values probably result in the more risk importance of other equipment
failures than that of piping-system failures. The NRRC should utilize RIDM in its
research planning to prioritize research subjects appropriately.
(NRRC) We have determined that the research program of seismic fragility analysis
has a high priority as a result of RIDM. We will use the RIDM process to decide on
appropriate research targets to avoid consuming too many resources for research
prioritization.
Thursday, Ｎｏｖｅｍｂｅｒ 16th, 2023
EXIT Meeting (minutes undisclosed)5