Nuclear Risk Research Center (NRRC)
Central Research Institute of the Electric Power Industry (CRIEPI)
1-6-1 Otemachi, Chiyoda-ku, Tokyo, 100-8126, Japan
Dr. George Apostolakis
DirectorJuly 15, 2022
Mr. J.W. Stetkar, Chairman
Technical Advisory Committee
Subject:

TAC Report titled “OUTCOME OF HAMAOKA MODEL PLANT LEVEL 2TSUNAMI PRA PROJECT” dated June 03, 2022

Dear Chairman Stetkar:
We thank the committee for the discussion at the TAC meeting on the Level 2 PRA results in
the Hamaoka Model Plant Tsunami PRA. We also thank the committee for its assessment that"the completion of this project is a milestone achievement for the Japanese nuclear industry,and it has extended the methods and modeling tools that can be used to analyze risk intsunami-prone areas worldwide."
The NRRC responds to TAC's recommendations as follows.
1. Need for independent technical review
We understand the importance and necessity of an independent technical review. Since themethods and the models, data, and supporting analyses developed and used in this project areextensive and vast, we would like to determine the scope of the review and then implement it.
2. Need for targeted sensitivity analysis
We agree with the TAC recommendation regarding the need for a targeted sensitivity analysis.
Since this research project has already been completed, we will discuss the possibility of
conducting a sensitivity analysis in the context of NRRC's in-house research activities.
3. Need to consider how timing considerations are typically modeled throughout the actual1

full scope PRA
We have identified the consideration of the timing of the loss of function of each equipment
during tsunami inundation in the MAAP analysis as one of the medium- to long-term issues inthe actual plant application. We accept TAC's recommendation on this issue. However, sinceresolution of this issue is not a high priority at this time, we do not intend to implement any
immediate action. In the future, when the need to account for the timing of loss of function foreach equipment during the inundation becomes more necessary in the MAAP analysis, weintend to examine how timing considerations are typically modeled throughout the practicalfull-scope PRA in advance, in line with TAC's recommendations.
4. Need to develop tsunami risk assessment guidance
We aim to present the Hamaoka Tsunami PRA assessment case study as an example of aconcrete realization of the requirements of the regulations and guidelines in the PRA standardof AESJ (Atomic Energy Society of Japan), and to position this case study as a technical report
as well. This will enable Japanese utilities to apply the results of this project when conducting
tsunami risk assessments with reference to the tsunami PRA standard of AESJ. For this purpose,
we recognize the need to publish the technologies/methodologies developed in the Tsunami
PRA as publicly available documents. Some of the results have already been made publicly
known as academic papers, and we plan to make other results publicly known sequentially inthe future.
In addition, NRRC members with expertise and experience will actively cooperate with theStandards Committee in the development of tsunami risk assessment guidance.
Sincerely,George Apostolakis

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