Investigation of actual condition of contaminated soil in regulation pond conducted by underwater radiation measuring instrument installed in remotely-operated vehicle (2nd field test i Fukushima)

Ishiyama, Shintaro; Yamaguchi, Katsuhiko*

Prototype remotely operated vehicle equipped with high resolution TV monitor and underwater radiation measuring instrument was developed and actual condition of contaminated soil in the regulation pond in Fukushima was investigated. Remarkable contaminated point was observed beneath rainwater outfall of impounding reservoir (Length Width Depth, 112m 30m 3.5m) in the order of 3.3 to 5.24 Sv/h. It is found that contaminated small particles in the order of 1 to 3mm are deposited in the polluted mud at the bottom of the reservoir and suspended by disturbance of water flow and the contaminated zones in the order of 0.75 to 3.5 Sv/h are distributed in a patchy fashion caused by confluent of outfall in the demarcated region (10m 10m 10m).