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 st ack gas from nuclear power plants under calm conditions with wind velo city less than 0.5m/s is proposed. Annual meteorological observation d ata were obtained at a nuclear fuel cycle facility in Aomori Prefectur e, and were used for condition set up of water tank experiments and do se calculations. Water tank experiments were conducted to investigate plume rise and diffusion processes under calm conditions with stable t hermal stratification. Plume rise and diffusion processes are divided into the jet region and the diffusion region in the model, and the con centration of plume in each region is given by a simple formula. The a bsorbed dose rate in air was calculated using the proposed model and t he safety analysis model. The comparison of the calculation results sh ows that the safety analysis model gives much higher estimates than th e proposed model.