For Unit 1, fuel debris distribution measurements based on penetration muon detection of transmission method were made in the periods from February to May and from May to September 2015. With the measurement results, it is reasonable to assume that no fuel fragment larger than 1 m, which is maximum muon detection capacity by transmission method or no water exists at the original reactor core region.
The results obtained by the evaluation by the comparison between analysis value by muon detection and measured value indicate that the survival rate of the fuel in the core region was (9-36)ﾂｱ51%.*
*Joint research by TOSHIBA and Nagoya University