RECONSTRUCTION OF AIRBORNE ACTIVITY CONCENTRATIONS FROM RADIATION EXPOSURE RECORDS

摘要

Releases of radioactive material from the Fukushima Daiichi reactors were tracked across the Japanese countryside by a network of radiation monitoring stations. However, the measurement of ambient dose rate by these detectors does not account for the dose contribution due to inhalation of airborne radioactive materials, which can be much greater than the submersion dose. The Radioactive Air Inhalation Dose EstimatoR (RAIDER) code is developed to provide an estimate of the committed inhalation dose based upon ambient dose measurement and core inventory and fractional release assumptions. The energy response of the radiation monitoring station detector is used to determine the total activity concentration in the surrounding air, which in turn is coupled with the release assumptions to estimate the activity of the major radionuclides present. Inhalation dose conversion factors then permit the committed effective dose to be calculated. Sample scenarios demonstrate the functionality of RAIDER, indicating that the committed inhalation dose is 58.9 times higher than the accumulated ambient dose in the plume for a measurement occurring five days after reactor shutdown. Future improvements to RAIDER may include the addition of physical removal mechanisms and coupling with other accident analysis codes.