The Nuclear Risk Research Center

George Apostolakis
Head, Nuclear Risk Research Center
apostola@mit.edu
Idaho National Laboratory
April 30, 2015

2015

11

Nuclear Safety in Japan• Deterministic approach• Few PRAs were done prior to Fukushima• After Fukushima, the Nuclear Regulation Authority
issued very conservative deterministic regulations• All 48 units are currently shutdown• A local court blocked the restart of Takahama 3 and4 over the approval of the NRA.
• “It is internationally recognized that our newregulatory regime is one of the strictest . . . but that
was apparently not understood (by the judge),”
Chairman of the Nuclear Regulation Authority (NRA)
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

2015

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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-informeddecision making and risk communication.
2.Near Term Goals- Review existing PRAs (and improve, as necessary)- Seismic PRA- Tsunami PRA- Infrastructure (HRA/Other Ies ( fires, Internal floods,others)/ Risk communication methods)
20154

Role of the NRRC
To support utilities, NRRC will
- Develop modern PRA methodologies and infrastructure- Investigate mechanism, frequency and consequences ofexternal natural hazards- Continuously be aware of and identify new risks

NRRC R&D outcomes
Stakeholders

NRRCUtilities

state-ofpracticestate-of-the-art

Gap AnalysisIssues to be solved tocontinuously improvesafetyInstitutions-Internationaldomestic

Identify what should be doneby NRRC and whenDevelop researchplan/roadmap

NRRC
resources

Do R&D

Information
release

Produce R&D outputs
Confirm utilities’ efforts

Stakeholder
trust

Utility’s Risk Management
process
Utilize NRRC’s R&D
outputs to risk-informed
decision making

model
knowledge
Skilled researchers

methodology

dataContinuoussafety
5 improvement

NRRC Website

http://criepi.denken.or.jp/en/nrr
c/index.html

http://criepi.denken.or.jp/jp/nrrc/index.html6

Committees• Technical Advisory Committee
 J. Stetkar, A. Afzali, N. Chokshi, X. Pouget-Abadie, T.
Tamada, 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

2015

7

PRA Upgrades• TAC Letter The event sequence models that have been developed tosupport the planned restart of lkata Unit 3 do not
represent the as-built, as-operated plant Differences in the designs, normal system
configurations, and operating practices at lkata Unit 2and Unit 3
 Failure rates should be plant-specific lkata plant personnel should be actively involved in thedevelopment and review of the PRA models• Industry Reply
 We agree with the recommendations

20158

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

20159

Seismic Risk
• Pilot plant: A unit at a site with a second unit next toit
• Interactions will be explored• SSHAC (Senior Seismic Hazard Assessment
Committee) process for hazard assessment• Fragility Assessment:
 NRRC/Electric utilities have been conducting various
experiments and numerical simulations in order toevaluate realistic response and capacity.
 NRRC has been conducting the fragility evaluation basedon the earthquake experience
data.
2015
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The SSHAC Process• The utility is the project sponsor. NRRC supports• Expert panels
 Expert panels will be selected for SSC and GMC.
 Number of experts in each panel is 3-4.

• Technical Integrator
 Highly experienced of seismic hazard assessment andSSHAC implementation.

• Objective: To produce the community probability
distribution of seismic risk
• Experts act as proponents and evaluators• Four workshops will be held Mechanism for avoiding weights
2015

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Seismic PRA/Shaking table test
- CRIEPI/NRRC has been conducting shaking table
tests up to 20g for various important equipment.

table size :2m/2m
Max Load:10t
Max Acc.: 20g
Max Vel.: 3.14m/s
Max Disp.: 0.05m
Freq.:10Hz/sine curve

201512

Tsunami effects on NPP
Theme of Hazard
Assessment• Validation of Tsunami
Hazard assessment• Establishment of survey
method of paleo tsunami
deposit•Hydrodynamic force•Scouring•Debris impact•Submersion•Suspended sand•Hydrodynamic force•Clogging due to debris

Reactor building•Hydrodynamic force•Debris impact
Turbine building

Sea wallComponents Tanks
・Pumps•Hydrodynamicforce•Scouring•Debris impact•Lowering of water level•Sand deposition•Hydrodynamic force•Debris impact•Blockage due to debris
Break water deposition

Water tightdoorPipes

Water tight sealIntake•Hydrodynamic force

Category

2015： Water level： Hydrodynamic load： Debris： Sediment (sand)
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・Flooding into buildings

Tsunami PRA/Key Challenges
1.Hazard Assessment:- SSHAC implementation (similar to Seismic PRA)
2. Fragility Assessment:- Pre-Fukushima accident; tsunami evaluation
focused mainly on water level change.
- Hydrodynamic load, Debris impact, Debris
deposition and so on should be considered.
- There are no practical procedures for fragility
evaluation regarding these impacts.
- NRRC has started to establish the methodology fortsunami fragility evaluation.
2015

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Experiments (2014)
Relationship between the debris impact (collision)
force and speed was investigated. A real car wasdrifted in the tsunami-inundation flow, and impacted
on a wall. The impact force was measured.
 Experimental condition Tsunami velocity : 2.6m/s – 6.0m/s
 Depth : 0.2m – 0.8m
 Measurements
 Impact force on the wall
 Impact speed of the car Water depth Velocity
201515Other External Natural Hazards• Seismic Fault Displacement• Tornado/Typhoon• Volcanic Activity• Combination of hazards

201518