Applicability of meteorological statistics over a 5-year period to evaluation of annual average of radionuclide concentration in surface air; Based on meteorological statistics for 20 years at Oarai Research and Development Center, JAEA

Seya, Natsumi ; Hashimoto, Makoto  ; Nemoto, Koji*; Shimizu, Takehiko; Takasaki, Koji  

Evaluation of annual average of radionuclide concentration in surface air obtained from atmospheric dispersion factor is intended to determine a public dose as a primary source for the safety analysis of nuclear facilities in normal operation. Oarai Research and Development Center (ORDC) of the JAEA have used fixed 5-year meteorological statistics for derivation of atmospheric dispersion factors as average conditions. To show that the meteorological statistics for any 5-year period could be used as representative data for evaluation of average conditions, annual average (1-year average) and 5-year average of evaluated radionuclide concentrations derived from the meteorological data observed from 1991 to 2010 at ORDC were analyzed. The fluctuations of evaluated radionuclide concentrations of any 5-year averages were smaller than those of 1-year averages during 20 years, and any 5-year averages contained no rejections by the F-test (5% significance level). It means that any 5-year averages of radionuclide concentration evaluations are well representative for the safety analysis under normal condition in ORDC.