Summary of the 9th Technical Advisory Committee (TAC) Meeting
Date:
Place:

May 21 – 25, 2018
Nuclear Risk Research Center (NRRC), Central ResearchInstitute of Electric Power Industry

Participants:
TAC:
Mr. Stetkar (Chair), Mr. Afzali, Dr. Chokshi, Mr. Miraucourt,
Prof. Takada, Prof. Yamaguchi
NRRC:
Dr. Apostolakis (Head), Experts of the Nuclear Risk ResearchCenterIndustry:
Experts of TEPCO Holdings, TEPCO SYSTEMS, Shikoku
EPCO for respective topics
Proceedings
All the topics were discussed in full session. In addition, an open discussion
took place on research for Level 2 and Level 3 PRA.

May 21 (Mon.)
Topic 1: NRRC R&D Roadmap
 NRRC presented “NRRC R&D Roadmap as of February 2018”.
 TAC members commented as follows:- The risk from all hazards should be evaluated in a single integrated
PRA. NRRC should promote research to establish the best way tointegrate different models to evaluate various hazards.
- To coordinate its research well, it is important for NRRC to have abig picture for the development of a good quality PRA which
addresses all hazards in all of the operating modes at a reasonably
consistent level of detail.
- Risk communication would benefit from connecting NRRC’s various
R&D activities and their outcomes. Also, we would like to know
NRRC’s specific research activities on risk communication because ofits importance.
- TAC’s role is to discuss R&D activities of NRRC, but we are also
highly interested in the actual application of PRA results. We would
appreciate more inputs about related developments including
activities of relevant organizations.

1（Handouts）
1-1. NRRC R&D Roadmap as of February 2018
Topic 2: Risk Assessment Research: Thermally-Induced SGTR NRRC presented current R&D status on “Thermally Induced-SGTR”.
 TAC members commented as follows:- TI-SGTR, which was thought not to be important in past PRAs, may
have a large contribution to risk of an NPP. It is a higher priority toimplement TI-SGTR modeling in PRA rather than to refine estimatesof the conditional TI-SGTR probability based on domestic SG flaw
data.
- The US NRC ACRS pointed out that there are some scenarios which
resulted in High/Dry/Low conditions in addition to the scenarios
derived from the approach of the draft version of NUREG-2195
Appendix L. So it is important for utilities to consider on their own
all conditions that can result in H/D/L.
- TI-SGTR does not contribute to the Level 1 PRA results, but it may
be dominant when Level 3 PRA is considered. Japanese utilities
should not screen it out without any risk assessment even though theconditional TI-SGTR frequency is small.
（Handouts）
2-1. Safety Research on Thermally Induced-SGTR
Topic 3: Pilot Projects for PRA Improvement
 Shikoku EPCO presented the current status of the Ikata 3 pilot project.
TEPCO Holdings and TEPCO SYSTEMS presented the current status of
the Kashiwazaki-Kariwa (KK) 6/7 pilot project.
 NRRC presented the establishment of a PRA peer review
implementation system.
 TAC members commented as follows:- In the US, utilities use findings of peer reviews as learning material.
You can find some gaps and learn from them by comparing a peer
review result and your self-assessment result.
- When utilities share their PRA models with NRA in developing thenew inspection process, it is important to share expectations on bothsides and to reach a common understanding about the required PRA
2-quality.
The definition and interpretation of “safe and stable state” have to beconsistent in the industry at large.
The data collection and analysis methods should also be consistent.
For example, should the standby failure rate model be used forcomponent demand failures?

（Handouts）
3-1. Ikata Unit3 Project Status Update3-2. Attachment: Comment resolution plan for the 1st external expert review
3-3. KK-7 Project Internal Event Operating Level 1 PRA ModelSophistication Progress Report
3-4. Attachment: 1st - 3rd Expert Review Comments
3-5. Establishment of PRA peer review implementation system
May 22 (Tue.)
Topic 4-A: Risk Assessment Research: Fire PRA Guide NRRC presented the current R&D status of “Fire PRA Guide”.
 TAC members commented as follows:- It is useful to identify fire/flooding sources in a seismic PRA
walk-down. Japanese utilities can refer to EPRI seismic PRA
walk-down guide in developing their good PRA.
- There are very limited research activities on seismically induced fire
PRA internationally. When NRRC can start a research in this field, it
will be a great contribution.
- The fire events should be classified by their severity with focus onfire ignition sources rather than plant response because the lattercan depend on the plant characteristics.
- The guidance for treatment of incipient fire detection should becoordinated with the guidance for collection and screening of fire
event data. The fire event screening process and the fire PRA
models should not "double account" for the effects of incipient firedetection.
(Handouts)
4-1. Fire PRA Guide
4-2. Fire PRA Guide Overall Progress and Roadmap

3Topic 4-B: PRA Data Collection
 NRRC presented the current R&D status of “PRA Data Collection”.
 TAC members commented as follows:- In order to develop a generic database for the Japanese PRAs, thescope of the components and failure modes for collection should not
be limited to the ones of the PRA models for the individual plants but
be broad enough to cover the models of the whole industry. TAC
recommends that the Japanese industry determine the scope of theirdata collection based on a "master list" of components and failuremodes. NUREG/CR-6928 is a good reference for that list.
(Handouts)
4-3. Development of PRA parameter database
4-4. Implementation Guide on Data Collection for PRA
4-5. Development of PRA parameter database - supplement
May 23 (Wed.)
Topic 5: External Natural Event Research NRRC presented the current R&D status of “Tsunami PRA”,“Probabilistic Seismic Hazard Analysis (PSHA)” and “Seismic Fragility”.
 TAC members commented as follows:- When Tsunami PRA becomes practically applicable, it is expectedthat utilities will be able to gain new insights from results ofTsunami PRA, especially by comparing PRA results such as CDFs ofthe plant before and after the installation of Tsunamicountermeasures based on lessons learned from Fukushima-Daiichi
accident.
- NRRC should make a practical PSHA guide for utilities withconsideration of efficiency in terms of cost and duration forimplementation.
- Site response characteristic is one of the key issues in ground motion
estimation, especially in the case of utilization of GMPE (GroundMotion Prediction Equation). NRRC should conduct research anddevelopment regarding these site characteristics related to groundmotion estimation considering the treatment of uncertainty.
- NRRC should develop a quantitative methodology to select andassign weights when it uses several GMPEs in evaluating groundmotion.
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-EPRI has provided excellent research results on seismic fragility, sowe recommend NRRC to refer to them.

（Handouts）
5-1. Tsunami PRA Level 1 (Accident sequence evaluation) and Level 2
5-2. Tsunami PRA Hazard and Fragility (outdoor) assessment
5-3. PSHA Enhancement in Japan Based on Lessons Learned from Ikata
Level-3 SSHAC Project
5-4. Seismic Fragility
May 24 (Thu.)
Topic 6: Open Discussion
 A discussion session took place on research for Level 2 and Level 3 PRA.
(Handouts)
6-1. L2PRA and L3PRA related research
Topic 7: Exit Meeting
TAC and NRRC had a discussion on how to organize future meetings.
May 25 (Fri.)
Committee internal meeting.

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