SIERRA-II; Simulation system (II) for emergency dose by released radioactive substances

Takeyasu, Masanori ; Takeishi, Minoru* 

A computer code system (SIERRA-II) has been developed to estimate the environmental radiological impact of accidental releases of radionuclides from a nuclear facility in real time. The SIERRA-II is based on a three-dimensional mass-conserving wind field model and a particle dispersion model with a nesting function to calculate with high spatial resolution in the vicinity of the facility. Input includes on-line local meteorological and effluent data observed and monitored at the site of the facility, and local meteorological data as predicted by an atmospheric dynamic model. The SIERRA-II was validated using environmental monitoring data for ambient dose rate as observed at monitoring posts around the Tokai Reprocessing Plant when Kr-85 was discharged during its operation. The observed increase of the dose rate was simulated well. The agreement of calculated and observed dose rate was within a factor of 5 for 74 % of observations.