Abstract
The Nuclear and Industrial Safety Agency, Ministry of Economy, Trade and Industry revised the “Guideline for environmental impact assessment of power plants” in 2007. The guideline added prediction of air quality under unique meteorological conditions as a reference method. In this study, the calculation conditions used to carry out dispersion prediction for environmental impact assessment are examined in cases where an inversion layer is formed and where plume fumigation is generated along with the development of a thermal internal boundary layer.
In the former and latter cases, the height from the ground surface to the bottom of the inversion layer and the proportional coefficient that determines the thickness of the thermal internal boundary layer, respectively, are the important parameters used in the calculation. In some cases, these parameters are determined by carrying out upper observation; however, in general, conditions producing overestimates are used without carrying out upper observation. Under conditions producing overestimates, very high concentrations of air pollutants, which are unrealistic when compared with observations at ambient air monitoring stations, are obtained by calculation. By analyzing both air monitoring data obtained in the vicinity of power plants and the sensitivity of the dispersion calculation, rational parameter values used in the environmental impact assessment are estimated.
It was found that effective stack height can be used as the height from ground surface to the bottom of the inversion layer and that 6 is an appropriate value for the proportional coefficient that determines the thickness of the thermal internal boundary layer.
