Risk Assessment Research Team

Personnel

Approximately 45 researchers (Main Research Center: Yokosuka-area)

Research Fileds

Risk Assessment Research Team is composed of five research fileds as follows.

Nuclear Risk Engineering
Specialties of Members	Nuclear reactor system, Heat transfer and thermal hydraulics, Risk engineering, Reliability engineering, Risk communication, etc.
Main Research Topics	Development of PRA methods and their application / Improvement of maintenance with risk information / Development of risk communication method for plant risk management
Internal Hazard PRA
Specialties of Members	Fire engineering, Combustion engineering, Reliability engineering, etc.
Main Research Topics	Enhancement of internal fire and flooding PRA / Development and Demonstration of fire protection measures / Improvement of fire model
Human Reliability
Specialties of Members	Reliability engineering, Nuclear reactor system, Human factors, etc.
Main Research Topics	Development of Human Reliability Analysis Methods / Development of human performance improvement measures
Severe Accident Assessment and Technology
Specialties of Members	Heat transfer and thermal hydraulics, Nuclear fuel, Nuclear reactor engineering, Computational fluid dynamics, Electrochemistry, etc.
Main Research Topics	Elucidation of severe accident-related phenomena, model development and implementation in analysis codes, uncertainty quantification, and application of accident progression analysis to Level 2 PRA
Environmental Assessment
Specialties of Members	Environmental risk evaluation, Atmospheric diffusion, etc.
Main Research Topics	Development of level 3 PRA method / Development of atmospheric diffusion evaluation methods

Main Research Facilities

• Filtered Vent Testing Facility
• Experimental Facility for Simulated Rod Bundle Cooling of a Light Water Reactor
• Simulation of Ocean Diffusion of Radioactive Materials

Filtered Vent Testing Facility

　Installation of Filtered Containment Venting Systems (FCVSs) in the nuclear power plants has been advanced to enhance nuclear safety. The FCVS allows for the containment over-pressure release and reduces the radioactive release through multi-scrubbers. Typical FCVSs adopt venturi scrubber, water (alkaline solution) scrubber, metal-fiber filter and molecular sieve as multi-scrubber. CRIEPI constructed a FCVS performance test facility to acquire a systematic database of FCVS performance and optimize the FCVS operation procedure (February 2014). This test facility has a real scale test vessel (8m in height, 0.5 m in inner diameter), steam boiler, iodine/ aerosol generation system and the latest measurement system. This system can measure the FCVS performance under a variety of conditions (temperature, pressure, gas-flow rate, and water quality).

Experimental Facility for Simulated Rod Bundle Cooling of a Light Water Reactor

　On the bases of the lessons learned from the accident at the Fukushima Daiichi Nuclear Power Station, it is necessary that safety measures should be in place to mitigate the beyond design basis events. Therefore, it has become more important to develop accident management measures considering the process of fuel rod damage as well as serious conditions resulting in a severe accident.

　CRIEPI has designed and constructed an “experimental facility for simulated rod bundle cooling of light water nuclear reactor” to evaluate the cooling characteristics inside reactor fuel assemblies in the accidents. This facility is comprised of a high-temperature and high-pressure thermal hydraulic loop capable of simulating rated operating conditions of a light water reactor and an x-ray CT/real-time radiography system, and allows for three-dimensional visualization of the internal flow and simulated fuel assemblies. The experiments have been conducted since October, 2014.

Simulation of Ocean Diffusion of Radioactive Materials

　The oceanic pollution that resulted from the discharge of radioactive materials following the accident at the Fukushima Daiichi Nuclear Power Station was a concern not only for the coastal population of Fukushima, but also for countries facing the Pacific Ocean. This called for rapid clarification of the actual dispersal situation by oceanic monitoring, but it was hard to gain an adequate understanding because of the difficulty in collecting water samples by ships.

　Therefore, right after the accident at the Fukushima Daiichi Nuclear Power Station, CRIEPI has developed a simulation method to illustrate the oceanic dispersion off the coast of Fukushima and in the North Pacific based on the research of global warming and knowledge from safety evaluations for sea transport of radioactive materials. CRIEPI compared the simulation results with the oceanic monitoring data to clarify the actual situation of oceanic dispersion, and publicized its findings in academic journals. CRIEPI will apply the methodology not only to the coast of Fukushima but also to other ocean areas.