Radiation Risk Analysis Research Group

Our research objectives

  • Countermeasures in the wake of a nuclear disaster based on lessons learned from the Fukushima Daiichi Nuclear Power Plant accident and assessing radiation doses to inhabitants of the contaminated area.
  • Contributions to safety regulations that are based on risk information and provide a technical foundation for safety goals and methods of evaluating site safety. In addition, contributions to effective technical plans for disaster prevention in areas surrounding nuclear sites.
  • Contributions for devising assessment methodologies and management of individual radiation doses to inhabitants in contaminated areas and for developing the method of comprehensively assessing doses to inhabitants. In addition, optimization of countermeasures that consider social effects.
  • Our research area

     We are focused on analyzing the influence of nuclear accidents using atmospheric dispersion analysis of radioactive materials and dose assessment and considering exposure pathways of radionuclides released in the environment from a nuclear power plant.
     In a nuclear disaster, three transitional staged have been defined in time: The "planning stage," the "corresponding stage," and the "restoration stage." There are different degrees of risk in each stage. We conduct research corresponding to the objectives of each stage.

    (1) Research for pre-accident "planning stage"

     In a nuclear accident, we expect a high radiation-dose rate. Therefore, deploying rapid countermeasures to prevent radiation exposure and devising a rapid decision-making system based on the results of environmental measurements is necessary and important.
     Countermeasures must be designed based on the level of severity of the effects of the potential accidents, covering the accident scenarios technically investigated. We propose the development of a probabilistic risk assessment (PRA) code designated OSCAAR (Off-Site Consequence Analysis code for Atmospheric Release in reactor accident) to comprehensively evaluate the potential risk of release of radioactive materials from a nuclear power plant.
     The OSCAAR code is a series of assessments of atmospheric dispersion and deposition, dose, and countermeasure efficacy based on the radionuclide release information from analyzing a nuclear power plant accident (Source term). OSCCAR can comprehensively evaluate accident effects considering various accident conditions and weather conditions. In an OSCAAR calculation, countermeasures are evacuation, medication with stable iodine tablets, relocation, and restriction of food intake.

      Fig1
  • Application of OSCAAR code
  •  OSCAAR calculates the radiation dose in inhabitants and the dose-reduction effects of countermeasures in light of a validated concept of public safety regarding nuclear power plant location and the effectiveness of countermeasures in severe accidents as required by regulatory criteria for contributing to improving safety regulations based on risk-analysis information.
     OSCCAR can propose appropriate scale and timing of introduction of countermeasures for public safety as part of planning for disaster prevention in the local area.

  • Developing the Operational Intervention Level (OIL)
  •  Specific accident and weather conditions prevailing during pre- and post-accident stages of any event are difficult to predict. Therefore, to ensure the safety of local inhabitants in each stage, practical and rapid actions are necessary.
     We have, thus, developed the concept of the Operational Intervention Level (OIL), which determines whether any specific countermeasure is necessary or not based on measurements of environmental data.

    (2) Research for corresponding and restoration stages

     In these two stages, which assume a stable reactor, radiation dose rates are low and local inhabitants are exposed to such radiation in daily life. Therefore, reasonable countermeasures that consider the economic and social effects of the accident are necessary. Therefore, we are developing the supporting technology for decision-making, such as cost-benefit analysis, using OSCAAR.
     In addition, assessing dose rate to grasp the degree of radiation exposure of the inhabitants is essential. It is important to manage radioactive contamination considering economic and social impacts.
     Therefore, we developed a new dose-assessment method to assess doses to inhabitants in the course of daily living. Doses to inhabitants in daily life vary according to the degree of contamination and the lifestyles of individuals. We evaluated these uncertainties in dose assessment and developed a probabilistic dose assessment taking uncertainty into account.

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