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
HeadJanuary 15, 2020
Mr. J.W. Stetkar, Chairman
Technical Advisory Committee
Subject:

TAC Report titled “PROPOSED NRRC RESEARCH PLAN FOR FISCAL YEAR
2020” dated November 19, 2019

Dear Chairman Stetkar:
We appreciated the discussions throughout the review of our research plan and theCommittee’s insights. The NRRC reply to the TAC recommendations is as follows.
1. Research plan for fiscal year 2020
In the subject report, the Committee stated: “We did not identify any major gaps in the overall
research plan for fiscal year 2020.” We are gratified to receive this comment.
2. Practical demonstrations to support the development of good quality PRAs
The committee expressed the view that some research activities are about to reach maturity
and can be practically verified.

We have the same opinion and hope to move steadily to thedemonstration stage after discussions with power companies.
3. Recommendations for specific activities
With regard to nine recommendations for specific research activities, we will reconsider theplans for fiscal year 2020 and beyond for those research activities.

In that case, in addition toresource constraints, we would like to confirm the needs of electric power companies andmake efforts to make the results more effective in practical use at nuclear power plants.
Responses to each recommendation are as follows.

1(1) Methods and Guidance for Evaluating Risk during Low Power and Shutdown Modes
By analyzing the results of the expert reviews (including interviews with PRA analysts, ifnecessary) in fiscal year 2020, we will consider setting up an appropriate research program infiscal year 2021, if the NRRC finds common research issues concerning the LPSD risk
assessment.
(2) Methods and Guidance for Evaluating Risk from Events that affect Stored Spent Fuel
By analyzing the results of the expert reviews (including interviews with PRA analysts, ifnecessary) in fiscal year 2020, we will consider set-up an appropriate research program in fiscalyear 2021, if the NRRC finds common research issues to be implemented concerning the spent
fuel risk assessment.
(3) Demonstration of PRA Methods and Models for Evaluating the Risk from Combined
Effects of Earthquakes and Tsunamis
NRRC has been conducting a study which aims at developing methods of hazard and fragility
evaluations against superposed seismic and tsunami events. We are planning to investigate
and determine whether we need to conduct a full-scope PRA (risk quantification) against thesuperposed external events for a specific site while continuing the development of the related
studies addressed above. We have also recognized that screening of external hazards is a keyissue.
(4) Scope of Multi-Unit PRA Research
We will consider our resources and technical issues required for integrated assessment ofLevel 1 and Level 2 risks in fiscal year 2020.
(5) Planned Use of the Fire PRA Guide
A revised version of the NRRC Fire PRA Guide will be released on the NRRC web site by the end offiscal year 2019. Therefore, the practical use by electric power companies is expected. Moreover,
we are discussing a plan for a model plant analysis using the Guide starting in fiscal year 2021.

(6) Seismic PRA Demonstration ProjectNRRC has been conducting various R&D activities on seismic hazard evaluation and seismic
fragility evaluation of SSCs (e.g., ground foundation, surrounding slopes and reactor buildings)
using model plants.

2Utilities will perform Seismic PRAs using pilot plants the internal PRA of which will be“state-of-the practice” and implementing the output from the NRRC’s project mentioned
above. This approach will allow utilities to obtain a more comprehensive seismic risk profile.
(7) Level 2 PRA Demonstration Project
Regarding the Level 2 target plant, in consideration of the future practical implementation ofLevel 2 pilot applications among utilities, we will select an appropriate model plant, including
the optimal use of the pilot plant PRA model for Ikata Unit 3 or Kashiwazaki-Kariwa Unit 7.
(8) High Wind Prediction Tool
Basically, we are conducting research based on the needs of utilities, but we will check again.
(9) Phenomenological Relationship Diagram (PRD) Methodology
Basically, we are conducting research based on the needs of utilities, but we will investigate
again the usefulness of the proposed PRD methodology and the needs of the utilities. If
deemed necessary, we will conduct the comparison of PRD methodology with theconventional methods, such as MAAP etc.
Sincerely,

George Apostolakis3