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 JapanMay 27, 2017
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:

CURRENT STATUS OF FIRE PRA RESEARCH ACTIVITIES

Dear Dr. Apostolakis:
During the seventh meeting of the Technical Advisory Committee of the Nuclear Risk
Research Center (NRRC), May 22-26, 2017, we met with representatives of theNRRC staff and their contractor to discuss the current status of the Fire Probabilistic
Risk Assessment (FPRA) research activities. The purpose of the presentation wasto discuss the NRRC's approach and to get early feedback on the suitability of theproposed activities and the resulting near-term and long-term products.
CONCLUSIONS AND RECOMMENDATIONS
1. The scope of the proposed guidelines (i.e., what needs to be done) is consistent
with the state of practice FPRA guidance available internationally.
2. Due to the acknowledged changes in the NRRC guidance compared to thatprovided in NUREG/CR-6850, potential changes to the fire frequency and heatrelease rate estimates, and the first use of these methods in Japan, a full andintegrated pilot application of the proposed guidelines should be conducted
before they are issued for general use.
3. The proposed fire frequency and fire severity enhancement activities are very
important. The guidance document should provide cautions against prematurescreening of the fire events. Additionally, the updated fire frequency and fireseverity estimates should be compared to and contrasted with similar estimatessuggested by other internationally recognized guidance documents (such as theupdated estimates in NUREG/CR-6850, Supplement 1), and justifications for all
significant differences should be provided.

-1-BACKGROUND
Fire hazard has been recognized to be a major challenge to safe operation ofnuclear power plants. As a result, for many years both prescriptive and risk-informed
methods have been used to minimize the risk of fires. The use of a risk-informed
approach in the U.S., as part of the transition to a fire protection program based on
NFPA-805, has been recognized by both industry and the NRC to have resulted insignificant safety improvements. However, those efforts have also demonstrated
that the FPRA methods, as delineated in the 2005 version of NUREG/CR-6850,include many conservatisms that result in unrealistic characterization of the fire risk.
As a result, NRC and EPRI have taken advantage of documents produced throughthe NFPA-805 Frequently Asked Question (FAQ) process to (1) update theNUREG/CR-6850 guidance in a number of areas, including fire heat release rate(HRR) and fire frequency estimates and (2) are continuing work on additional
enhancements.
In consideration of this experience, the NRRC is working on improving methods andproviding additional guidance and refinements for conducting FPRA in Japan. Our
briefing on these activities included a discussion of the following topics:
1. Fire PRA Guide Development
2. Fire Event Frequency for Japanese NPPs
3. Current status of recommendations from TAC meeting #3
This letter report provides our observations and recommendations on the first twotopics.
DISCUSSION
The following observations and comments are based on the summary overview
material presented during our meeting and our discussions of that material with theNRRC staff and their consultants.
Fire PRA Guide Development
It was explained that the Japanese utilities plan to perform an internal FPRA as partof their future state-of-the-practice PRAs. This FPRA will be used in a yet to be
developed risk-informed decision making process for safety improvements, as wellas risk-informed operational decision making. To support consistent conduct ofthese studies, NRRC is developing a fire PRA guide that will assist in developing
realistic FPRAs. It was also stated that, although NUREG/CR-6850 will be used as astarting platform for developing this guideline, the NRRC is changing the breakdownof the NUREG/CR-6850 structure. The presentation included the proposed changes
to the structure, but limited information was presented on the technical content of theguidance. These changes include a phased approach (Phase A and Phase B), as
well as changes to the order of tasks to be performed compared to the steps
provided in NUREG/CR-6850. The stated objective of the proposed changes is toimprove the efficiency of conducting a FPRA. One example of a reorganized task isdevelopment of a Fire-Induced Plant Response Model (NUREG/CR-6850, Task 5).

-2-However, based on the discussions during the presentation, it was not clear how the
proposed changes would result in the desired outcome (i.e., improve efficiency).
Additionally, we are concerned that such a change from a well-established andexercised practice may result in unintentional complexity and inefficiency, and may
not be warranted. However, we acknowledge that the briefing material presents only
a rather high-level concept, and we encourage the NRRC team to provide moredetails when the approach is fully developed. Considering these changes and thefact that these methods have never been used in Japan, a full pilot application
should be conducted to assess the practicality and reasonableness of the proposedguidance, as well as other related work such as improvements of the fire frequency
and HRR estimates.
Fire Event Frequency for Japanese NPPs
It was reported that the NRRC intends to use fire event frequency data from theNuclear Information Archives (NUCIA) database, which contains records of theJapanese nuclear power plant operating experience. We were also informed thatNRRC plans to conduct confirmatory interviews and research to develop
supplemental plant-specific fire event data and fire frequency estimates. A relatively
detailed description of the proposed guidelines for the fire event analysis, including
the data in NUCIA and an event screening approach, was presented. Systematic
examination of the operating experience in Japan is highly beneficial. However, it isdifficult to assess the reasonableness of the outcome without a detailed review of thefully developed guidelines, the quality of the data provided in NUCIA, and the contentof the confirmatory activities. Additionally, it seems that the proposed screeningapproach may incorrectly remove some events from the database. That practice
could result in fire event frequency estimates that are not consistent with actual
operating experience. For example, screening criteria that are based on selected
plant locations and specific systems do not seem consistent with criteria that areused to compile similar fire event data in other countries.
It would be very beneficial for NRRC to fully brief us on the proposed fire event datacollection methods and screening criteria before they are implemented throughout
the industry. Additionally, the updated fire frequency and fire severity estimatesshould be compared to and contrasted with similar estimates suggested by otherinternationally recognized guidance documents (such as the updated estimates inNUREG/CR-6850, Supplement 1), and justifications for all significant differences
should be provided.
Sincerely,John W. Stetkar
Chairman-3-

REFERENCES
1.

"Current Status of the Fire PRA Research Activities," NRRC Staff
Presentation to NRRC Technical Advisory Committee, May 23, 2017(confidential).

2.

U.S. Nuclear Regulatory Commission and Electric Power Research Institute,"EPRI / NRC-RES Fire PRA Methodology for Nuclear Power Facilities,"NUREG/CR-6850, EPRI 1011989, September 2005.

3.

U.S. Nuclear Regulatory Commission and Electric Power Research Institute,"Fire Probabilistic Risk Assessment Methods Enhancements," NUREG/CR6850, Supplement 1, EPRI 1019259, September 2010.

4.

National Fire Protection Association, "NFPA 805: Performance-BasedStandard for Fire Protection for Light Water Reactor Electric Generating
Plants", 2001 Edition, February 2001.

5.

Electric Power Research Institute, "Fire PRA Methods Enhancements:Additions, Clarifications, and Refinements to EPRI 1019189," EPRI 1016735,
Interim Report, December 2008.

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