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

June 11, 2018
Revision 1

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:

IMPLEMENTATION GUIDE ON DATA COLLECTION FOR
PROBABILISTIC RISK ASSESSMENT

Dear Dr. Apostolakis:
During the ninth meeting of the Technical Advisory Committee of the Nuclear Risk
Research Center (NRRC), May 21-25, 2018, we met with representatives of theNRRC staff to discuss the status of guidance for the collection of equipment
performance data at Japanese nuclear power plants. This letter report documents
our review of the draft "Implementation Guide on Data Collection for Probabilistic
Risk Assessment (PRA)".

CONCLUSION AND RECOMMENDATIONS
1. The current scope of the guidance covers the collection of plant operating
experience that is needed to derive component failure rates. The format of thedocumentation for the individual plant data collection records is consistent withstate-of-the-practice methods that provide traceability of decisions regarding theequipment condition, the basis for categorizing specific events, and the derivationof relevant operating and testing exposure data.
2. The data collection guidance should clearly state that historical operating
experience should be compiled from all nuclear power plants, including plantsthat have restarted, plants that are planned to restart, and plants that will remain
shutdown permanently. That practice will provide the best possible generic
database for use in all Japanese PRAs.
3. The guidance should be improved to better define the scope of the systems,
component types, and failure modes for which data will be collected at all nuclear
power plants. This will ensure that the database will consistently support thedevelopment of high-quality plant-specific and generic data for the Japanese-1-nuclear industry. The Discussion section of this report contains our suggestions
about how to achieve these improvements.

BACKGROUND
To support the development of high-quality probabilistic risk assessments (PRAs)
and to establish a comprehensive database that can be maintained and updated asadditional operating experience is compiled, the NRRC has developed draft
guidance for the collection of data at each Japanese nuclear power plant. The
current guidance addresses the compilation of operating experience that will be used
to derive individual component failure rates (i.e., component failure events and thecorresponding number of component demands, operating hours, and test intervals).
Additional guidance is planned for the compilation of operating experience that will
support the development of data for common cause failure parameters andequipment unavailability due to maintenance and other causes.
The version of the draft report that was provided for our review did not contain theannexes, which describe details for specific elements of the guidance, databaserecords, and documentation. Therefore, our observations and recommendations inthis letter report are limited to the material in the main body of the draft guidance,supplemented by our discussions with the NRRC experts during our meeting.

DISCUSSION
The overall guidance is generally consistent with state-of-the-practice methods forthe collection of plant-specific operating experience that will be used to derive
individual component failure rates (e.g., failures to function on demand and failuresduring operation). In particular, the systematic documentation of decisions by plant
personnel regarding the technical basis for categorizing specific events provides afully-traceable record of the assessed extent of the equipment condition, without theneed to re-examine all details of the original operating and maintenance records.
The documentation of the equipment exposure data similarly provides a clear
summary of the operating experience, testing records, and methods that are used toderive the relevant number of component demands, operating hours, and standby
equipment test intervals.
We understand that the detailed documentation of these tasks will be retained byeach plant, and only the relevant records of component failures and exposure data
will be submitted to the NRRC. The NRRC data analysis experts will then use theevidence from each plant to derive the component failure rates. The data from allplants will also be used to develop a comprehensive and consistent generic
database that applies for the entire Japanese industry.
Realistic and consistent operating experience from all Japanese nuclear power
plants is needed to support the development of a comprehensive database that will
be used in high-quality full-scope Level 1 and Level 2 PRAs that evaluate the risk
from all internal and external hazards during all plant operating modes. To support
development of a fully inclusive generic database, relevant data should be collected-2-from as many plants as possible. We understand that no formal decision has yet
been made regarding the collection of data from plants that will remain shutdown
permanently. The historical data from those plants are equally relevant to theindustry experience before March 2011 as the historical data from plants that haverestarted or plan to restart. Therefore, the data collection guidance should clearlystate that historical operating experience should be compiled from all nuclear power
plants, including plants that have restarted, plants that are planned to restart, andplants that will remain shutdown permanently. That practice will provide the best
possible generic database for use in all Japanese PRAs.
We and the NRRC data experts clearly recognize the fact that a very substantial
amount of effort is needed to collect this information. Furthermore, that effort
requires critical involvement of valuable plant personnel who are most familiar with
their own plant's operating, testing, and maintenance records, and who can interpretthe available information to understand the extent to which a component's condition
was affected during a particular event. It is essential that these activities are
performed efficiently to make the best use of the available resources and to ensurethat all relevant operating experience is compiled consistently at each plant. This isespecially true for the initial efforts to collect the historical operating experience,
before the establishment of plant programs and data management systems that will
be used for regular compilation of future data.
Our review of the guidance identified some areas where the screening criteria andexamples seem to be too narrowly focused. These criteria seem to require that theplant data collection engineers must make difficult decisions regarding theapplicability of specific failure modes for individual components in each system as
they review their plant's operating experience.
Different interpretations andapplications of these detailed criteria may result in significant plant-to-plantdifferences in the ways that data are collected for specific systems, component types,
and failure modes. Those differences would then result in gaps or inconsistencies in
the operating experience that is used to support a comprehensive and traceable
generic Japanese industry database. Furthermore, the need for difficult screening
decisions by each plant data collection engineer will increase the effort that isneeded to compile and document the operating experience that consistently
correlates data for specific failure modes with the corresponding equipment
exposure data.
To avoid potential gaps and inconsistencies, the guidance should be improved tobetter define the scope of the systems, component types, and failure modes forwhich data will be collected at all nuclear power plants. We offer the following
suggested enhancements for two elements of the guidance.
Scope of Systems and Components for Data Collection
It is very useful for the guidance to contain a "master list" of the systems for which
every plant will compile their operating experience. This generic master list should
contain every system that is included in the PRA models for any nuclear power plantin Japan. The master list improves confidence that each plant data collectionengineer clearly knows "what is in" and "what is out" of their scope of work.

-3-Selection of the master list of systems is a critical element of the guidance. Theauthors of the guidance should develop a preliminary list, based on their experiencefrom a broad variety of PRAs that have been performed for operating PWRs andBWRs. The authors should then confer with the PRA analysts at each Japanese
nuclear power plant to understand the scope of the systems that are included in theircurrent PRA models and systems that may be added as the PRA scope is extended.
In practice, the master list may contain a small number of systems that are notincluded in the current scope of a particular plant-specific PRA. Some of thosesystems may be added to the models as the PRA is extended to evaluate additional
hazards and operating modes, and to evaluate the risk from offsite releases. Othersystems may not be directly relevant for the particular plant PRA, but the data forequipment in those systems are relevant for other plants. In any case, regardless ofthe details in a particular plant-specific PRA model, the actual equipment operating
experience from that plant is directly relevant to the development of acomprehensive, consistent, and traceable database that can be used throughout theJapanese industry. Therefore, the data should be collected to support the generic
database.
Within this framework, each plant data collection engineer will compile data for all
equipment in each system in the master list. The plant data collection engineers do
not need to have a detailed understanding of the plant-specific PRA, its current
scope, possible future extensions, assumptions about models for specificcomponents and failure modes, etc. The engineers can then focus their efforts on
their specific area of expertise – efficient compilation and understanding of the plant
operating experience.
This practice improves overall efficiency of the data collection effort, and it retains aconsistent focus on the systems and components that are potentially important toplant risk. It also avoids sources of inconsistency that may arise if individual datacollection engineers have different interpretations of the potential relevance ofspecific systems or components at each plant.
Scope of Component Types and Failure Modes
The plant data collection engineers should compile the operating experience for allcomponent types and failure modes in every system from the master list. This effort
should not apply distinct screening criteria for individual component failure modes.
For example, the plant-specific PRA models may include only the "fail to open"
failure mode for a particular motor-operated valve. However, the operating
experience for that valve will include evidence for both the "fail to open" and the "failto close" failure modes. The evidence for both failure modes is relevant to the data
for similar motor-operated valves at that plant, and it is relevant to the data for similar
motor-operated valves at other plants. Therefore, the plant data collection engineers
should not screen out the operating experience for specific failure modes.
Again, experience has shown that this practice improves overall efficiency, improves
consistency within the plant-specific data, and improves consistency andcompleteness in the generic industry data. That is because each plant datacollection engineer does not need to make sometimes difficult decisions about subtle-4-

details of a specific event, how those details might affect the PRA models, and how
those considerations affect the final categorization of the event.
The guidance in NUREG/CR-6928, "Industry-Average Performance for Components
and Initiating Events at U.S. Commercial Nuclear Power Plants," contains a list ofcomponent types and failure modes that are used in many PRAs performed in theU.S. It may be useful for the authors of the NRRC data collection guidance to referto that report to ensure that the scope of the data collection effort does not
inadvertently omit plant operating records for specific component types and failuremodes. However, care must be exercised when the lists in NUREG/CR-6928 arecompared with the data needs for Japanese PRAs. In particular, the component
boundaries that are defined in NUREG/CR-6928 are slightly different from those incurrent Japanese PRA models. Those differences will affect how the data arecompiled and analyzed for some types of components, such as circuit breakers,
instrumentation, relays, elements of solid state or digital control circuits, etc. The
guidance should contain clear examples to ensure that the plant data collectionengineers understand these distinctions and to ensure that the operating experience
for these types of components and failure modes is not inadvertently omitted fromthe database.

We look forward to continuing our review of this important guidance for plant datacollection, as it is extended to include other types of data. We also look forward toreviewing the guidance and methods that will be used by the NRRC data analysis
experts to develop the Japanese industry generic database and to combine theplant-specific and generic data for use in each plant's PRA.

Sincerely,

John W. Stetkar
Chairman

REFERENCES
1.

Nuclear Risk Research Center (NRRC), Central Research Institute of ElectricPower Industry (CRIEPI), "Implementation Guide on Data Collection forProbabilistic Risk Assessment (PRA)," Revision 1, Draft (without Annexes),April 2018.

2.

"Development of PRA Parameter Database (Implementation Guide on Data
Collection for PRA)," NRRC Staff Presentation to NRRC Technical Advisory
Committee, May 22, 2018 (confidential).

3.

"Development of PRA Parameter Database - Supplement," NRRC Staff
Presentation to NRRC Technical Advisory Committee, May 22, 2018(confidential).

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4.

U.S. Nuclear Regulatory Commission, "Industry-Average Performance forComponents and Initiating Events at U.S. Commercial Nuclear Power Plants,"
NUREG/CR-6928, February 2007.

5.

U.S. Nuclear Regulatory Commission, "Industry-Average Performance forComponents and Initiating Events at U.S. Commercial Nuclear Power Plants,"
NUREG/CR-6928, Component Reliability Data Sheets, 2015 Update,available at https://nrcoe.inel.gov/resultsdb/AvgPerf.

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