Study on monitoring method of atmospheric radioactivity using continuous dust (gross beta) monitor in nuclear emergencies with atmospheric release

Kashimura, Keita; Kawasaki, Masatsugu ; Okura, Takehisa 

In nuclear emergency response involving atmospheric release, the supplementary reference materials of the Nuclear Emergency Response Guideline require dust monitor to monitor radiation situation in the environment to be able to detect facility-induced releases of about 5 Bq/m for detecting unexpected releases earlier, and to determine the spatial distribution of radioactive materials in the air during emergencies, the difference in the gross beta activity concentration measured every 10 minutes is used. In this study, method of monitoring radioactive plume by dust monitor was investigated, and it was confirmed that the method can discriminate facility-induced releases of about 5 Bq/ m against variation of natural radionuclides. Furthermore, capability of the dust monitor corresponding to radioactive plume was confirmed. According to the time series comparison between the gross beta radioactivity concentration measured by the dust monitor and the radioactive concentration analyzed from gamma-ray emitted nuclides in the air following the Fukushima Daiichi Nuclear Power Plant accident (1F accident), a good correlation was observed and it was found that the dust monitor responded accurately to the fluctuation of the concentration in the radioactive plume. And it was confirmed that it was possible to discriminate the incremental difference in gross beta radioactivity caused by the facility of about 5 Bq/ m against the slight increase in concentration caused by the 1F accident.