Visualization experiment for internal structure estimation of reactor using cosmic ray muons

Suzuki, Keiichi*; Onuma, Hiroshi*; Takegami, Hiroaki ; Takamatsu, Kuniyoshi  ; Hino, Ryutaro; Okumura, Tadahiko*

In the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, the nuclear fuel had melted down due to loss of coolant and had already become debris. The debris would fall to the bottom of the CV. To remove the debris for future decommission is necessary; however the area and the size are unclear. On the other hand, cosmic ray muons are absorbed extremely in the debris because of the high density of uranium and plutonium. The inner structure of the nuclear reactor may be visualized with muons penetrating easily throught such the high-density material, as a non-contact or -destructive inspection. In this study, the muons through the HTTR were measured and visualizing the internal structure was attempted. As a result, high density areas were recognized at the same position as that of the reactor pressure vessel (RPV); therefore, the technical possibility with muons could be demonstrated. In the near future, new R&Ds will be promoted toward the practical use.