Assessment Model of Atmospheric Diffusion and Radiation Dose for the Stack Gas from Nuclear Power Plants under Calm Conditions.

An assessment model on atmospheric diffusion and radiation dose for stack gas from nuclear power plants under calm conditions with wind velocity less than 0.5m/s is proposed. Annual meteorological observation data were obtained at a nuclear fuel cycle facility in Aomori Prefecture, and were used for condition set up of water tank experiments and dose calculations. Water tank experiments were conducted to investigate plume rise and diffusion processes under calm conditions with stable thermal stratification.Plume rise and diffusion processes are divided into the jet region and the diffusion region in the model, and the concentration of plume in each region is given by a simple formula. The absorbed dose rate in air was calculated using the proposed model and the safety analysis model. The comparison of the calculation results shows that the safety analysis model gives much higher estimates than the proposed model.