Distribution estimation of radioactivity concentration by compact polarization lidar in Fukushima

摘要

Hydrogen explosion on Fukushima No. 1 nuclear power plant caused huge damage in real life. Especially its radiation damage caused widespread. Field works on intermediate storages and reuses of decontaminated soils has been started in earnest under government promotion since 2017. This study put a compact polarization lidar at the intermediate storage site, where was only 3 kilometers away from Fukushima No.1 plant. There was a difficult-to-return zone. The lidar system was remotely controlled at Chiba univ. Its observation range was 300m. It covered almost the whole of working field. The lidar monitoring was conducted at one month during Nov. and Dec. in 2017. The lidar scanned horizontally by crossing the dropping port of the decontaminated soils and capturing the suspended dusts on the soil preparation. The lidar monitoring was synchronized with 3 dust-samplers, and we obtained spatial distributions of dust density and estimated the distribution of the radioactivity concentration. The lidar counting rate for dust and the radioactivity concentration was estimated 0.001 mg/m~3/count and 10~(-9) -10~(-10) Bq/cm~3, respectively. This estimation was much lower than the working rule of safety assessment of 10~(-5) Bq/cm~3. The expressions of these distributions are helpful as communication tool to civilians' safe and workers' secure.