Summary of the 10th Technical Advisory Committee (TAC) Meeting
Date:
Place:
Participants:
TAC:
NRRC:
Industry:

Nov. 5 – 9, 2018
Nuclear Risk Research Center (NRRC), Central Research Institute ofElectric Power Industry
Mr. Stetkar (Chair), Mr. Afzali, Dr. Chokshi, Mr. Miraucourt, Prof.
Takada, Prof. Yamaguchi
Dr. Apostolakis (Head), Experts of the Nuclear Risk Research Center
Experts of TEPCO Holdings, Shikoku EPCO for respective topics

Proceedings
All the topics were discussed in full session. In addition, an open discussion session
took place. The open discussion included a lecture by Mr. Afzali on “Technology
Inclusive Risk-Informed Performance-Based Licensing Basis Foundation.”
November 5 (Mon.)
Topic 1: Overview of NRRC R&D Goals
 NRRC presented “Overview of NRRC R&D Goals”.
 TAC members commented as follows:- The Technical Advisory Committee (TAC) understands that this presentation
covers the research projects that are considered as high priority by NRRC, andthus NRRC explained those projects. For the next presentation, TAC would like
NRRC to explain all research programs in the same format (by making a one-pagesummary). It is possible that TAC may consider some topics that are currently
deemed low-priority by NRRC as deserving a higher priority, but the current style
may result in the loss of TAC opportunities to point out such matters.
1. Risk-Informed Decision Making (RIDM)- Phase 2 of the strategic plan should clarify specific objectives and priorities forusing RIDM (for example, the introduction of Risk-informed In-service Inspection(RI-ISI), On-Line Maintenance (OLM), etc.) and the action plan for thoseobjectives.
2. PRA Method Improvement- Considering the RIDM comments, priorities for the necessary NRRC research anddevelopment items (for example, Low Power and Shutdown PRA, spent fuel poolrisk, external events other than natural phenomena) and the research schedule
for those items should be examined, based on the industry action plan.
- Referring to NRRC resources, a system that can provide usefulness of outcomes1

--or incentives for researchers should be considered, for example, by thinking about
the priority of research topics from the viewpoint of overall risk significance, anddetermining the direction of the research plan for FY 2019 and after.
Even though it is important for NRRC to issue original guidance for specific use
in Japan, adoption of proven guides that have been used in Japan and foreigncountries should also be positively considered from the viewpoint of resourcesaving.
In developing pilot studies for internal flooding, internal fires, and multi-unit PRA,
the quality of the PRA model that is used for those studies should be strictlyexamined, so that the pilot studies maintain consistency with current progress forthe development of a "good quality" PRA.

3. Natural External Events- It is important to consider the fragility assessment with regards to the whole
facility including the ground, buildings and equipment taken into account for theSeismic PRA.
- Floating debris should be considered comprehensively regardless of its size for theTsunami PRA. The influence of intake plugging by waste such as entrained rubble,
plastic bags, and silt, as well as impacts by ships on the ocean, should also beconsidered.
- A simultaneous tsunami and seismic disaster should be considered throughcollaboration among the seismic-related personnel.
November 6 (Tue.)
Topic 2: Fire PRA Guide NRRC presented current R&D status on “Fire PRA Guide”.
 TAC members commented as follows:- The Fire PRA guide drafted by NRRC includes the US knowledge appropriately
and has been improved greatly compared with NUREG/CR-6850. The guideclarifies a process that can detail risk-significant scenarios without applying
predetermined screening criteria, and thus we can expect improved and more
efficient implementation.
- TAC understands the necessity of the activities concerning fire frequency basedon domestic operating experience, but it is difficult to quantify appropriate
frequencies for the detailed categories, if the assessment period of the operation
status is short and data is insufficient. The initial use of international data ishighly recommended. Bayesian analysis methods can be used to update theinternational experience as more Japanese industry data are collected.
- The guide would be more useful by improving details such as providing guidance
for walk-downs consistently and providing evidence for specific numerical values
2-introduced by the guide.
A pilot study should be conducted, feedback concerning the guide provided, andrevisions made to improve practical use of the guide and to provide high quality
and realistic risk insights.

Topic 3: Internal Flooding NRRC presented the current R&D status on “Internal Flooding”.
 TAC members commented as follows:- If the internal flooding simulator is described in the guide, its functions andanalytical accuracy should be examined.
- Takahama Unit 3 is considered as a pilot site, but the pilot study should be done
at multiple plants with different configurations. Carrying out multiple pilot
studies leads to the enhancement of the general usability of the guide.
 Many of the PWRs are already restarting, but the BWRs are still in the process of thebusiness licensing stage. NRRC is planning to carry out the pilot study targeting asingle unit in a PWR plant first, considering the resources of NRRC and electricutilities.
- How large is the framework for collecting data on flooding frequency? In particular,
detailed information such as the flood source (affected system, pipe rupture orconnection failure, etc.), cause of the flood (pipe break, human error, etc.), waterleakage modes, the amount of leakage, etc. is necessary for category setting.
 NRRC has established a framework where NRRC and utility members participate.
However, information such as leakage rates and calibers seems to be highly limited.
NRRC has been collecting detailed information to the maximum possible extent.
- According to the project schedule, the plant walk-down is planned after the desk
study, but it would be more effective to do the plant walk-down first. In the plant
walk-down, the survey should be done also from the viewpoint of seismicallyinduced flooding.
- Does the Human Reliability Analysis (HRA) guide issued by NRRC apply to HRAtasks in the internal flooding analysis guidance?
 Currently, NRRC’s HRA guide has not been referred to explicitly. NRRC wants todeal with this issue during the revision of the guide.
- TAC is concerned that practical application of methods to derive the Zone ofInfluence (ZOI) of flooding would be complicated due to many combinations ofparameters.
 NRRC will try to add an additional appendix on how to apply this method practicallyduring the revision of the guide.

3

Topic 4: Level 2-3 PRA related methodology
 NRRC presented current R&D status on “Level 2-3 PRA related methodology”.
 TAC members commented as follows:＜Level 2 PRA＞
- Benchmark analysis of fission product behavior in containment vessels andreactor buildings, and accumulation of experimental verification data are timeconsuming issues requiring a large budget. These activities should be promoted
in an international framework.
 NRRC is participating in the Benchmark Study of the Accident at Fukushima Daiichi
Nuclear Power Station (BSAF) project promoted by OECD / NEA, and conducting
research activities related to verification analysis using the MAAP code in theinternational framework. Regarding the experimental research for fission productbehavior in the building shown in the Phase 2 research after 2022, we would like tojudge implementation carefully in light of the results of the research conducted up
until the year 2021, and trends in international collaborative research.
- Regarding the Level 2 PRA methodology in the Phenomenological Relationship
Diagram (PRD) method, NRRC should describe and demonstrate the effectivenessand usefulness of this methodology, such as the point that the Level 2 evaluation
can be carried out simply without conducting large-scale thermal-hydrauliccalculations using the MAAP code.
＜Level 3 PRA＞
- As for the local topography effect on Level 3 PRA results, its influence may growdepending on the combination of risk indices (Latent Cancer Fatality (LCF) and
Early Fatality (EF)) and the evacuation model. Although it depends on decisions
by electric utilities, NRRC should apply the Level 3 PRA methodology at a specificsite and carefully investigate the practical value of insights.
November 7 (Wed.)
Topic 5: PRA Pilot Project (Ikata Unit 3)
 NRRC presented the current status of the “PRA Pilot Project, Ikata Unit 3”.
 TAC members commented as follows:- The comments from the external expert review to be considered not only in PWRs
but also BWRs should be shared and addressed throughout the industry.
- The topic of “Perform best estimate success criteria analyses” was discussed at
past TAC meetings. NRRC should store up such topics so that you can keep theseissues in mind for reviews of other PRAs to be conducted in the future.
- Regarding the success criteria, was there any difference between the comments
received in the external review and the results of the self-review conducted in4

advance? When there are differences between them, it is important to consider
the reason for the differences, not only in this example.
Topic 6: PRA Pilot Project (KK Unit 7)
 NRRC presented the current status of the “PRA Pilot Project, KK Unit 7”.
 TAC members commented as follows:- You should perform a documented self-assessment to learn from the disparities
with the results of the external review.
 The current expert reviews are being conducted during our model enhancement. We
are planning to conduct a self-assessment before the peer review after the As-Is model
is completed.
Topic 7: PRA Peer Review Guide NRRC presented the current status of the “PRA Peer Review Guide”.
 TAC members commented as follows:- The PRA standard to which the peer review guide conforms should be clarified. It
is confusing to refer to both the ASME / ANS standard and the AESJ standard.
The guide should not refer to both standards until it is confirmed that the AESJ
standard is consistent with the ASME / ANS standard.
- It is most important to clarify at an early stage the definition of the PRA peer
review.
- Consideration of the PRA standard and peer review guide will doubtless continue,but, in parallel, pilot applications of the peer review process should be conducted.
- Currently, external expert review is based on the ASME / ANS standard, but inthe long term, domestic PRAs will comply with the AESJ standard. For thispurpose, the AESJ standards committee is examining the definition of "What todo" as a standard In collaboration with the ASME / ANS Joint Committee onNuclear Risk Management (JCNRM) through the Japan International Working
Group (JIWG), consistency with the ASME / ANS standard will be discussed.
From this point of view, the peer review guide should be configured according tothe AESJ standard.
 Clarify the objective of the draft guide, since it is not clear whether to aim for a shortterm perspective or prepare for a long-term response.
- How is the regulatory authority going to be involved in PRA peer review?
 The PRA of the utilities will be disclosed to the regulators. Regarding the review ofPRA to be disclosed, the regulators are reserving their intent, but utilities arerequesting that the PRA be reviewed by peer review consistent with the reviews in theUnited States.
 Since it will take time for improvement of utilities' PRAs, spot-like reviews byregulators may be conducted during that time.
5 In the United States, NRC Regulatory Guide 1.200 is based on the ASME / ANS
standard. So, above all, it is necessary to identify the subject standard and certify it
mutually with the regulators.
Topic 8: RIDM Template NRRC presented current the R&D status of the “RIDM Template”.
 TAC members commented as follows:- Increase the number of specific cases so that personnel at the nuclear power plantcan easily understand them. This is very important.
- Clarify the purpose of the template. Clarify how to use it.
Topic 9: Seismic Level 1 PRA
 NRRC presented the current status of the “Seismic Level 1 PRA”.
 TAC members commented as follows:<Project Plan of Seismic PRA>
- Though it is required to enhance details of each technical issue in the R&D of PRA,
it is also preferable to proceed with the R&D to expand the range of PRA
applications. For example, add PRA for fire caused by seismic events in addition
to the fire PRA.
- You should proceed with the scope of the seismic PRA with a view to Level 2 PRA.
A valid reason why it is limited to Level 1 PRA is required.
<Fragility Analysis: Equipment>- Research of fatigue as a failure mode is interesting. If there will be any further
progress, we would like it to be introduced at future TAC meetings.
- We would like to hear about the progress of the seismic experience database at
the next TAC meeting.
<Discussion Point>- It is inevitable that different kinds of PRA software are used at each site. Whenmultiple sites are subject to a model project for seismic PRA, the particular
software used at each site should be utilized for the seismic analysis. A particularplant should always use the same PRA software for all models (e.g., internalevents, internal fires, internal floods, seismic events, tsunamis, high winds, otherexternal events, etc. for full-power, low power, and shutdown modes). It isextremely important that the same system logic models and basic event names
must be used throughout the entire PRA.

6

<Current status of Ikata SSHAC level-3 project>
After finishing the Senior Seismic Hazard Analysis Committee (SSHAC) project
for the Ikata NPP, the next step will be conducted, including what kind of guide
should be prepared with a view to expansion of SSHAC to other sites.
November 8 (Thu.)
Topic 10: Exit Meeting
TAC and NRRC had a discussion on how to organize future meetings.
November 9 (Fri.)
Committee internal meeting7