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When the definition of calm in atmospheric diffusion analyses is changed from 0.5 m s-1 to 0.1 m s-1, actual and more accurate low wind speeds and wind directions can be used to calculate the average air concentrations due to continuous releases of radionuclides at 10-m stack height more realistically and accurately. However, this modified calm condition has little affect on the calculated adult thyroid exposure for a postulated accident.

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.

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