Technical Advisory Committee of the Nuclear Risk Research Center
Central Research Institute of Electric Power Industry
1-6-1 Otemachi, Chiyoda-ku, Tokyo, 100-8126 Japan

November 15, 2018

Dr. George Apostolakis
Head, Nuclear Risk Research Center
Central Research Institute of Electric Power Industry
1-6-1 Otemachi, Chiyoda-ku
Tokyo, 100-8126 JapanSUBJECT:PROPOSED NRRC RESEARCH PLAN FOR FISCAL YEAR 2019

Dear Dr. Apostolakis:
During the tenth meeting of the Technical Advisory Committee (TAC) of the Nuclear
Risk Research Center (NRRC), November 5-9, 2018, we met with the NRRC staff toreview the proposed research plan for fiscal year 2019. The purpose of our review
was to provide comments on the technical merit of the research plan and its
relevance for supporting NRRC's current mission.

CONCLUSION AND RECOMMENDATIONS
1. We did not identify any major research gaps that require immediate attention in
the plan for fiscal year 2019.
2. The guidance and templates for risk-informed decision-making should start withthe decisions that are proposed to be risk-informed. Then for each decision, welldeveloped examples should clearly describe the issue, the needed decision, therisk-informed thought process, and the supporting information. These activities
should be performed with close cooperation from industry stakeholders. Theeffort to develop the examples should begin in fiscal year 2019.
3. The following recommendations do not directly affect the scope of the researchthat is planned for fiscal year 2019. However, they should be integrated into theoverall research program and plans for subsequent years, beginning in fiscal year2020.
•To the extent possible, the probabilistic risk assessments (PRAs) for both
Ikata Unit 3 and Kashiwazaki-Kariwa Unit 7 should be used for trial
applications of all NRRC guidance and analytical methods. The trial
applications should include both the Level 1 and Level 2 elements of each
PRA. This will provide the most effective demonstration of how state-of-the--1-

practice methods are applied to develop high quality fully-integrated plantspecific PRAs.
•The NRRC research program should address methods and guidance for theevaluation of risk during low power and shutdown modes, and the evaluationof risk from events that affect the stored spent fuel.

4. For our future reviews, the presentations for each project should be enhanced.
They should describe the technical needs for each research project and how theproject supports the NRRC short-, intermediate-, and long-term goals. Theobjective of each project should describe the specific reason for the activity, andit should explain how each task is needed to support that objective. This will help
us to better understand the technical motivation and priorities for the research, itsmajor supporting tasks, and their integration.

BACKGROUND
One of the most important objectives of the research plan is to present the technicalcontext of the research needs, including the rationale, current state of knowledge,and potential contributions and significance of the research to the objectives of thecenter. Our review of the research plan focused on the objectives of each research
project and its supporting tasks, the technical relationships and relative priorities
among those activities, and any major needs for additional research. We did notreview the technical details of individual research activities or their completion
milestones, except as needed to understand how those activities are integrated
throughout the plan. We will comment separately on the technical elements ofindividual research projects in our detailed reviews of those projects.

DISCUSSION
The NRRC staff provided a summary of the scope of a strategic plan and a phased
approach for introduction of risk-informed decision-making (RIDM) in the Japanese
nuclear industry. Comprehensive plant-specific probabilistic risk assessments(PRAs) of high technical quality provide the risk information and engineering insightsthat are an essential input for the RIDM process. Therefore, NRRC is conducting
research on improved analytical methods, models, and data for the performance offully-integrated Level 1 and Level 2 PRAs, with extensions to limited-scope Level 3PRAs. The scope of those research activities covers a wide range of technicalissues such as collection and analysis of plant operating experience and data,
human reliability analysis, methods for analyzing internal fires and floods, improved
modeling of severe accident phenomena, and evaluation of the risk from external
hazards such as seismic events, tsunamis, severe winds, and volcanic hazards. In
addition to supporting the development of high quality PRAs, the NRRC researchteam is also developing guidance for the use of PRA as a tool to support the RIDM
process.
During this review, we were briefed on several important research projects, the major
technical tasks in each project, the current status of each task, known or potential-2-

problem issues, and the estimated schedule for completion of each task. The project
timelines and schedules were also useful to illustrate how each activity fits into theoverall research scheme and the context of the NRRC short-, intermediate-, andlong-term goals.
We did not identify any major research gaps that require immediate attention in theplan for fiscal year 2019.
Recommendations for Selected Research Activities
Based on our discussions with the NRRC research team during this review, we offer
the following recommendations for selected elements of the overall research
program. Our first recommendation affects planning for work that will begin in fiscal
year 2019. The second and third recommendations do not directly affect the scopeof the research that is planned for fiscal year 2019. However, they should beintegrated into the overall research program and plans for subsequent years,
beginning in fiscal year 2020.
(1) Guidance for Risk-Informed Decision-Making
Perhaps the most important goal of the near-term and intermediate-term research isto support Japanese utility implementation of a systematic risk-informed decisionmaking (RIDM) framework. We understand that this framework will be used fordecisions at all levels of day-to-day activities at each nuclear power plant. To help
the utilities with their initial efforts to implement this framework, the NRRC
researchers have developed draft guidance and a general template that outlines theelements of an RIDM process. We were briefed on the basic structure of thetemplate during this review meeting.
The guidance and templates for risk-informed decision-making should start with thedecisions that are proposed to be risk-informed. The final scope and content of
those decisions must come from the utility stakeholders who will implement theRIDM process and who need to clearly understand how it will affect their daily
activities.
Therefore, the NRRC researchers should work closely with theircounterparts from the Japanese utilities to develop an initial set of well-defineddecisions and associated examples that demonstrate how the overall RIDM template
can be applied.
Those examples should cover a wide range of practical situations that will benefit
from a systematic consideration of risk. The examples should illustrate the decision
process from beginning to end, starting with a clear description of the issue, theassociated decision, and the options that are faced by the decision-maker. They
should explain the types of risk information that are needed to support that decisionand provide examples of how to most effectively combine quantitative and qualitative
sources of that information, including their associated uncertainties, to support themost effective option.
The effort to develop the examples should begin in fiscal year 2019.

-3-(2) Trial Applications of Guidance and Demonstrations of Methods
During this review, we were briefed on several research projects that have interim
milestones for trial applications of the associated methods and guidance. Those trial
applications are an essential element of each research project. They demonstrate
how the research is applied in a practical risk assessment, and they identify neededrefinements before the methods and guidance are issued for general use. Most ofthese trial applications are not currently scheduled to begin in fiscal year 2019.
However, preliminary planning for some applications has already started.
The Japanese industry is actively supporting the development of high quality PRAs
for two pilot plants: Ikata Unit 3 and Kashiwazaki-Kariwa Unit 7. These PRAs arevery important to the overall goals of the NRRC and the industry. They demonstrate
how current state-of-the-practice methods and models are implemented to achieve acomprehensive assessment of the plant-specific risk and its contributors. They also
provide important experience and lessons for PRA practitioners at all Japaneseutilities, as they update and extend their current models and analyses to achieve thedesired level of quality. The scope of each pilot project is currently focused primarilyon the development of Level 1 and Level 2 PRA models to evaluate the risk frominternal events that occur during full-power operations.
To the extent possible, the integrated Level 1 and Level 2 PRA models for both Ikata
Unit 3 and Kashiwazaki-Kariwa Unit 7 should be used for trial applications of all
NRRC guidance and analytical methods. Those applications will provide the mosteffective demonstration of how each state-of-the-practice method is used to develop
high quality fully-integrated plant-specific PRAs.
That process will also test the guidance and methods in the context of practicalapplications for two different reactor designs, different plant-specific internal
configurations, different site-specific features, and, perhaps, different details of how
the respective PRA models are constructed. This experience is very important toprovide confidence that the final guidance and methods can be used effectively
throughout the Japanese industry as they are adapted and applied for each plantspecific PRA.
As a final comment, it is important to examine how each improved method is applied
for the fully-integrated Level 1 and Level 2 PRA models. Experience has shown thatsegmented trial applications which test methods separately for the Level 1 andLevel 2 portions of the PRA can result in unexpected needs for refinements. For
example, lessons learned during the use of some methods for the Level 2 elementsof a PRA have required inefficient changes to guidance or practical considerations
that affect the Level 1 models and their supporting analyses. To avoid that situation,
the trial applications should include both the Level 1 and Level 2 elements of each
PRA, or the researchers should demonstrate why a more limited trial application will
not affect integrated use of the methods or models in the eventual full-scope PRA.
(3) Risk during Low Power and Shutdown, and Events that Affect Spent FuelTo date, the NRRC research program and individual research projects have focused
almost exclusively on development of methods and guidance for evaluation of the-4-risk from events that occur during plant power operation. Those methods andmodels are important, because they provide a fundamental framework forunderstanding the plant, its systems, its spatial layout and configuration, importantfeatures of the site, and how the operators are trained to prevent or mitigate potential
accident scenarios.
International experience from full-scope PRAs has shown that events which occur
during shutdown modes can be important contributions to overall plant risk.
Furthermore, a complete assessment of the plant-specific risk should also examine
events that affect cooling or damage to the stored spent fuel. In many technicalareas, the methods and models for evaluating these contributions to risk can buildfrom the experience that is gained during development of the full-power PRA models.
However, specialized models and analytical techniques are needed to examine andquantify the risk during a variety of plant operating states, system alignments, andmaintenance configurations that apply during plant shutdown. The frequency andcauses for specific internal initiating events, fires, and floods often vary considerably,
depending on the specific system operating alignments and work activities that areconducted during each plant operating state. Evaluation of human performance
typically requires special attention, due to the need for more manual intervention
when automatic actuation of systems may not be fully available. Integration of theLevel 1 and Level 2 PRA models requires careful coordination to account for thecontainment status during each plant operating state. Activities and system
configurations during reactor defueling and refueling operations can also require
special models and techniques to evaluate the risk from events that may affect fuelin the reactor vessel and fuel in the storage pools.
To provide consistent guidance and state-of-the-practice methods for developmentof high quality full-scope PRAs, the NRRC research program beginning in 2020should address methods and guidance for the evaluation of risk during low powerand shutdown modes, and the evaluation of risk from events that affect the spentfuel.
Recommendations for Future Reviews
We very much appreciate the NRRC researchers' efforts to organize the overview of
the research program and the individual research project summaries in the format
that we requested for this review. That format has improved communications andhelped us to more efficiently focus on the key technical elements of each research
project, discuss potential problems that may warrant special attention, and better
understand how each project is integrated into the overall NRRC research plans andschedules.
To help us better understand the technical motivation and priorities for each research
project, and how the various research activities are integrated, one topic in theresearch summaries would benefit from additional attention. For our future reviews,
the presentations for each project should be enhanced. They should describe thetechnical needs for each research project and how the project supports the NRRC
short-, intermediate-, and long-term goals. The objective of each project should
describe the specific reason for the activity, and it should explain how each task isneeded to support that objective. Additionally, if other considerations affect the-5-

scope, priorities, or schedules for specific technical tasks, the summaries should
inform us of those influences.

We look forward to our continuing interactions with the NRRC research team toreview of the overall research program and individual research projects, and to help
the NRRC and the Japanese nuclear industry achieve their goals of comprehensiverisk-informed decision-making.

Sincerely,

John W. Stetkar
Chairman

REFERENCES
1.

"Overview of NRRC's Activities," Presentation to NRRC Technical Advisory
Committee, November 5, 2018, Proprietary.

2.

"Fire PRA Guide," Presentation to NRRC Technical Advisory Committee,
November 6, 2018, Confidential.

3.

"Internal Flooding PRA – Draft Plan for Pilot Plant PRA," Presentation toNRRC Technical Advisory Committee, November 6, 2018, Confidential.

4.

"L2-3 PRA Related Methodology – FP Behavior in the CV and Reactor
Building," Presentation to NRRC Technical Advisory Committee, November 6,2018, Proprietary.

5.

"Development of Phenomenological Relationship Diagram (PRD) Method,"Presentation to NRRC Technical Advisory Committee, November 6, 2018,Proprietary.

6.

"L2-3 PRA Related Methodology – Environmental Risk Evaluation Method
Development (Level 3 PRA)," Presentation to NRRC Technical Advisory
Committee, November 6, 2018, Proprietary.

7.

"Ikata Unit 3 Project Status Update," Presentation to NRRC TechnicalAdvisory Committee, November 7, 2018, Proprietary.

8.

"KK-7 Project Internal Event Operating Level 1 PRA Model (Level 1.5 PRA
Shutdown PRA Model) Sophistication Progress Report," Presentation toNRRC Technical Advisory Committee, November 7, 2018, Proprietary.

-6-9.

"Establishment of PRA Peer Review Implementation System," Presentation toNRRC Technical Advisory Committee, November 7, 2018, Proprietary.

10.

"Template for Operational Risk-Informed Decision Making," Presentation to
NRRC Technical Advisory Committee, November 7, 2018, Proprietary.

11.

"Research Plan of Seismic PRA – Develop a Procedure How to Implement
NRRC's R&D Outputs in Conducting SPRA," Presentation to NRRC TechnicalAdvisory Committee, November 7, 2018, Proprietary.

12.

"Current Status of Ikata SSHAC Level-3 Project," Presentation to NRRC
Technical Advisory Committee, November 7, 2018, Proprietary.

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