[en] This paper describes an evaluation model on atmospheric diffusion and radiation dose for the stack gas from nuclear power plants under calm condition, using the meteorological observation data and the water tank experiments. Meteorological observation was conducted at Shimokita fuel deprocessing facility and meteorological data was obtained under calm condition. Water tank experiments was conducted to investigate plume rise and diffusion under calm conditions with stable thermal stratification. Some simple formulations was proposed as empirical model for atmospheric diffusion and radiation dose evaluation of the stack gas from nuclear power plants under calm conditions. (author)

[en] 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. (author)

[en] The unstable stratified boundary layer that was analogous to unstable atmospheric boundary layer was created in CRIEPI wind tunnel. The overall Richardson number was equall to -4.0 in the unstable flow condition in the wind tunnel and under this condition velocity and temperature fluctuation was measured. Auto-correlation coefficient and power spectram of velocity and temperature fluctuation were calculated and compared with those, of field experiments. Fothermore tracer gas diffusion experiment was mad in the wind tunnel and it's apparant that vertical plume spread in unstable condition was nearly equall to that of atmospheric stability B in Pasquill-Fifford chart. (author)

[en] Water tank experiments were conducted to investigate plume rise and diffusion of gases discharged from stacks under calm conditions with field wind velocity less than 0.4 m/s with stable thermal stratification. The plume rise phenomenon was illuminated LASER light sheet, and recorded video camera. The brightness of an image was transformed into concentration of a tracer liquid, by the equipment of digital image analysis. Plume rise height and plume lengths were measured from the concentration distribution of plume. (author)

[en] Studies were made on the general techniques employed in the wind tunnel investigation of nuclear power stations and examples are described of recently performed studies. The following results were obtained. 1. The influence of terrain and building configuration on gas diffusion. 1) The influence of a reactor building was investigated by using models of BWR and PWR with one or two units. 2) A multi-regression formula was developed to estimate the terrain effect on gas diffusion. 3) An empirical formula was developed to estimate the ''equivalent source height'' in a potential accident. 2. Fundamental examination of the wind tunnel simulation of diffusion phenomena found in the field. 1) A scale model stack with ''orifice'' was developed to simulate plume rise phenomena found in the field at small values of Reynolds number. 2) Two kinds of experimental methods were developed to simulate lateral plume spread in the field, such as σy of the Pasquill chart. 3) It was confirmed that the results of the wind tunnel experiment agreed well with that of a field experiment at the EOCR site in Idaho Falls, U.S.A. (author)