Summary of the 11th Technical Advisory Committee (TAC) Meeting
Date:
Place:

May 20 – 23, 2019
Nuclear Risk Research Center (NRRC), Central Research Instituteof 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 Research CenterIndustry:
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 on research for “Low power shutdown PRA and SFP PRA” as well as“RIDM Phase 2 action plan”.
May 20 (Mon.)
Topic 1: Overview of NRRC’s Activities NRRC presented “Overview of NRRC’s activities”.
 TAC members commented as follows:- In the next TAC meeting, the R&D status of Multi-Unit PRA (MUPRA) should
be included. In addition, for MUPRA, not only Level 1 PRA, but Level 2 PRA
should be included.
- As for seismic PRA, a very important point is how the current regulations
would be changed to rational ones.
- As for the completed R&D items, the outcome and how to utilize the researchshould be included in overview papers.
- Two areas for possible consideration as future R&D items are dynamic PRAand guidance for the evaluation of human errors of commission.
Topic 2: Utilization of fire PRA and history of fire protection regulation, andCurrent status of Fire PRA draft guide NRRC presented “Utilization of fire PRA and history of fire protection
regulation, and current status of Fire PRA draft guide”.
 TAC members commented as follows:- As a Fire PRA (FPRA) is an effective tool to demonstrate the safety of a nuclear
power plant in a quantitative manner, the FPRA should have a sufficient levelto identify vulnerabilities of the fire protection measures. If NRRC can provide1--a good technical basis for the FPRA, the PRA should be feasible in Japan to get
key risk insights.
In the U.S., when a new requirement is enforced, a back-fit analysis isconducted including costs and benefits based on the FPRA. So, it is a goodstrategy to inform the Japanese utilities about the usefulness and necessity of
the FPRA for relaxation of back-fit issues and to support more rational
potential future enforcement of the fire protection requirements.
TAC would like to know if NRRC needs a formal review of the FPRA Guide.

May 21 (Tue.)
Topic 3: Development of technical foundation for good Level 2 and Level 3 PRA
 NRRC presented “Development of technical foundation for good level 2 andlevel 3 PRA”.
 TAC members commented as follows:- In the last TAC meeting, we specifically requested that the technical basis for
the Phenomenological Relationship Diagram (PRD) method should beexplained during this meeting. It was not. We ask you for the explanation again.
- For the source term uncertainty analysis method, be sure to fully understandthe Sequoia case studies conducted by NRC's State-of-the-Art Reactor
Consequence Analysis (SOARCA) project.
- The uncertainty of the parameters is not only that which can be obtained as asmooth curve. When you determine the distribution of uncertainty in aphysical parameter, the opinion of experts in the field should be reflected.
- It should be noted that the specific parameters selected in the Level 3 PRA
WinMACCS uncertainty analysis may vary from site to site.
Topic 4: PRA Pilot Projects (Ikata Unit 3)
 NRRC presented Updated Ikata Unit 3 PRA Pilot Project Status.
 TAC members commented as follows:- Systems Analysis (SY), Data Analysis (DA), and Quantification (QU) should bein the scope of the 5th Ikata review, because these elements have important
points which are unique to the shutdown PRA model.
- In human reliability analysis (HRA), qualitative analysis for human failure
events (HFEs) is extremely important before quantification with the HRA
Calculator, so it is necessary to properly perform that according to the latestmethod based on the HRA guide.
- It is necessary for utility engineers and staff to maintain, modify and utilize
PRA models in-house as soon as possible.

2-A PRA model should be able to evaluate not only internal events but also
flooding, fire, seismic, tsunami, etc. with a single model or models which areconsistent to each other.
The Ikata project team should make it clear that the current expert reviews
are not a formal peer review when asked by NRA.
Integrated thermal-hydraulic and neutronic analyses are important for therisk of re-criticality in the core during zero-flow in the RCS, refueling, etc.

-Topic 5: PRA Pilot Projects (KK Unit 7)
 NRRC presented “PRA Pilot KK7 Projects- Progress Report-”.
 TAC members commented as follows:- What is the difference between the "As-is" model and others?
The equipment configuration is fixed, but the modification work is still on going and thedetail has not been finalized. "As-is" model will be developed based on fixed information(as-built, as-operated). (TEPCO)-When you have the peer review conducted, what will the peer review team use
as the basis of the PRA standard?
We are going to be reviewed by international experts, so we will have the peer review
based on ASME/ANS PRA standard perspective. (TEPCO)-Is seismic PRA included in the SAR?
Seismic and tsunami PRA will be included in the SAR. (TEPCO)

May 22 (Wed.)
Topic 6: Fragility development of equipment based on seismic experience data NRRC presented “Fragility development of equipment based on seismicexperience data”.
 TAC members commented as follows:- Floor responses of buildings are required in fragility estimation. Response
analyses of the buildings are needed to overcome a shortage of earthquake
motion records.
- It is desired that the outline of the EPRI fragility estimation method be sharedwith TAC members.
- Systematic estimation of seismic experience data is good activity. There is anapprehension that formal inspection reports of utilities do not include every
case of equipment damage. Additional survey of equipment damage is desired.
- Failure modes of electrical components should not be considered only as theloss of support function, but the loss of active function (electrical function) also.
Further organization of a way of thinking about failure modes of equipment is3

---desired. Required functions of the same type of equipment might be different
at different plants. Even if the same physical damage occurs to two electricalcomponents, it is possible that the damage may produce different judgments
about functional failure from a PRA viewpoint (e.g., effects from open circuits,
spurious signals, etc.). Careful attention must be paid for descriptions andexamples of failure conditions.
Failure distribution among plants is very important. If equipment failures areconcentrated in a specific plant, it is required to take the specific condition of
the plant into account. Bayesian methods can be used to account for plant-toplant variability in the experience data.
Installed numbers and locations of equipment should be efficiently collected incooperation with the plant-specific data collection project and the fire PRA
project of NRRC.
Loss of offside power (LOOP) must be evaluated in consideration of variouselements. Current experience data seems to be insufficient for entire
evaluation of LOOP.

Topic 7: Progress of Tsunami PRA project NRRC presented “Progress of tsunami PRA project”.
 TAC members commented as follows:- Current status of Tsunami PRA (Hamaoka-4) should include the utilization ofthe outcome and the degree of uncertainties of Tsunami PRA.
- To keep in mind when showing quantitative results of the tsunami PRA for
Hamaoka-4, those results may be misinterpreted as a general recommendationof NRRC regarding the concept of model development and screening criteria,etc. It should be emphasized that the screening analyses and results apply onlyto Hamaoka, and different site-specific models may be needed for other sites.
- The screening analyses should account for the tsunami effects on the Level 2
PRA, in addition to the Level 1 PRA.
- In the explanation of the overview model, it is better to clarify and justify what
you are evaluating, rather than emphasize the screening process. The
explanation should emphasize the viewpoint of using the PRA to find andexamine site-specific issues in the plant design and operation, not only as atool to screen out items.
Topic 8: HRA application method in Hamaoka Tsunami PRA
 NRRC presented “HRA application method in Hamaoka Tsunami PRA and theeffectiveness of HRA improvement in PRA results”.

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TAC members commented as follows:
In 2014, TAC suggested that THERP is not a correct way to assess humanreliability. Cognitive performance should be assessed, and considerations ofhuman characteristics are important to define and evaluate PRA scenarios.
The 2017 NRRC HRA guide was developed to reflect those concepts. However,the 2018 HRA guide has removed most of them.
TAC asks NRRC to re-examine the 2018 HRA guide. Individual TAC members
have comments on the 2018 HRA guide. NRRC should consider thosecomments, and, in the next TAC meeting, we should discuss them.

May 23 (Thur.)
Topic 9: Trial of risk information utilization exercise
 NRRC presented “Trial of risk information utilization exercise”.
 TAC members commented as follows:- During the course program, when explaining a case, it should be shown again
many times where it corresponds to the Figure A.1 (Three-ball diagram) in theStrategic plan.
- RIDM templates help to identify issues in implementing RIDM. The important
thing is that they not checklists. It should be clearly explained in the coursethat the RIDM process has not been completed until all the template items
have been covered.
- Among the pre-tasks are the reading of white papers and the review of US
cases, but also the RIDM strategic plans should be included.
- Treatment of uncertainty and expert evaluation are key factors in decisionmaking. It should be emphasized and demonstrated in the course that theycannot always be determined quantitatively.
Topic 10: Exit Meeting
As the result of discussion by the TAC members, they decided not to create a TAC
report on any specific research topics at this time.
TAC and NRRC had a discussion on how to organize future meetings.

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