[en] The purpose of the present study is to develop the computer code for the determination of atmospheric diffusion factors relevant to the gaseous radioactive effluents and to furnish the results readily applicable to the regulatory purposes of nuclear safety. Various meteorological data from the Kori site for the period of Janurary 1975-February 1982 were processed for ready use. For the estimation of diffusion factor in the case of accident, 2.5 percentile of the normal distribution is assumed and it is turned out to correspond to that for the period of 8-24 hours after the occurrence of accident in US NRC Regulatory Guide 1.4 and its suggests a new direction of our own guide for accident which should be established in the near future in Korea. (Author)