Development of a Real-Time Environmental Radiation Dose Evaluation System for the Vicinity of a Nuclear Facility

A computer code system has been developed to evaluate the environmental radiological impact of accidental releases of radionuclides from a nuclear facility in real time. The system is based on a three-dimensional mass-conserving wind field model and a particle dispersion model with a nesting function in order to calculate the atmospheric dispersion of radionuclides with high spatial resolution in the vicinity of the facility. Input includes on-line local meteorological and effluent data at 10-min intervals, as observed and monitored at the site of the facility, and hourly local meteorological data as predicted by an atmospheric dynamic model. Contour maps and tables of internal and external doses are the output. The performance of the system was validated using environmental monitoring data for the air absorbed dose rate as observed at monitoring stations and monitoring posts around the Tokai Reprocessing Plant when 85Kr was discharged during its operation, based on the safety regulations. The observed increase of the dose rate was simulated well. The agreement of calculated and observed dose rate was within a factor of 2 for 42% of observations, and within a factor of 5 for 74%.