Perspectives on the Safety of Nuclear
Facilities

George Apostolakis
Head, Nuclear Risk Research Center
apostola@mit.edu
Pacific Rim Forum onThe Earthquake Resilience of Nuclear Facilities
University of California, Berkeley
June 8, 2015
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The Nuclear Risk Research Center
Date of Establishment: Oct 1, 2014
Location: Central Research Institute of Electric Power Industry, Tokyo
Research activities are conducted mainly in Abiko and Komae
Number of members：Approximately 110

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NRRC Mission/Near Term Goals
1.Mission Statement- To assist nuclear operators and nuclear industry tocontinually improve the safety of nuclear facilities bydeveloping and employing modern methods ofProbabilistic Risk Assessment(PRA), risk-informed
decision making and risk communication.
2.Near Term Goals- Review existing PRAs (and improve, as necessary)- Seismic PRA- Tsunami PRA- Infrastructure (HRA/Other (fires, Internal floods,others)/ Risk communication methods)
20153Committees• Technical Advisory Committee
 J. Stetkar, A. Afzali, N. Chokshi, X. Pouget-Abadie, T.
Takada, A. Yamaguchi
 Letter reports and NRRC/industry replies are published inthe website• PRA Promotion Team Senior utility and FEPC managers
 Observers for Mitsubishi, Hitachi, Toshiba, et al Interacts with NRRC management routinely

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Human Reliability Analysis• Utilize the IDHEAS Framework
 Identification and feasibility assessment
 Human Failure Event narrative (crew response tree, crew
failure modes, performance influencing factors)
 Quantification (decision trees)• HRA in extreme environments
 Mobile equipment
 Retrieval, transportation, installation
 Historical record

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Seismic Risk

• Pilot plant: A unit at a site with a second unit next toit
• Interactions between the units will be investigated• SSHAC process for hazard assessment

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Multi-unit Issues• U.S.A.
 Currently at most 3 units Vogtle will have 4
 Adjacent sites: Salem 1&2 and Hope Creek (3 total); Nine
Mile Point 1&2 and FitzPatrick (3 total)• Canada Pickering: 6
 Darlington: 4
 Bruce Power: 8• Japan Kashiwazaki-Kariwa: 7
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Current Situation• General Design Criterion 5: Structures, systems, andcomponents important to safety shall not be shared amongnuclear power units unless it can be shown that such sharing
will not significantly impair their ability to perform their safetyfunctions, including, in the event of an accident in one unit, anorderly shutdown and cooldown of the remaining units.

• U.S. Safety Goals are applied to single units.
• PRAs, with few exceptions, are performed for singleunits.

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CNSC Workshop
November 17-20, 2014
• MUPSA Infrastructure Lack of experience and guidance for performing MUPSA• Selection of Initiating Events
 Most external events involve multi-unit challenges• Accident Sequence Modeling Need to account for multi-unit dependencies including
functional, human, and spatial dependencies
 Need to consider the timing of releases from differentunits• Site Based Risk Metrics
 Need for additional risk metrics beyond CDF and LERF to
fully express the risk profile of a multi-unit site

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CNSC Workshop (continued)• Accident Progression and Source term
Characterization
 Need to define new release categories that adequately
describe the releases from multi-unit accidents. This
includes release magnitudes, energies, and timing fromreactor units, spent fuel storage, and other radiologicalsources• Evaluation of Radiological Consequences Includes consideration of different points of release fromthe plant, possible differences in time of release, andrelease energies for plume rise considerations.

• Site-Based Safety Goals
 Need to define multi-unit site based acceptance criteria
for evaluating the integrated risks from a multi-unit sitePSA
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