The influence of calm conditions on the atmospheric dispersion analyses at KAERI site, which is located at a complex inland basin, was investigated. The U. S. NRCs computer programs XOQDOQ and PAVAN were used to estimate dispersion factors for routine and postulated accidental releases from nuclear facilities, respectively. The joint frequency distribution was obtained from the annual meteorological data measured in 1997 and used as input data of the computer programs. When the definition of calm is changed from 0.5 m to 0.21 m , the maximum sector dispersion factor becomes 1.62 and 2.16 times higher for routine and postulated accidental releases, respectively.