Impact of supersonic versus propeller wind data on dispersion estimates for nuclear plants

Statistical analyses and comparisons of the wind data obtained by the propeller and supersonic anemometers at the Japan Atomic Energy Research Institute (JAERI) were performed. For wind speeds less than 1 ms-1, the propeller readings are inaccurate and are generally 0.5 ms-1 less than the supersonic readings. Thus, the number of calms recorded differs. These differences affect the sum of the inverse of wind speed, frequency distribution of wind direction, and the annual percentage frequency distribution of stability categories. The resultant average air concentrations and ground-level gamma exposure rates due to the normal operational releases from a nuclear plant are overestimated when calculated using the propeller wind data.