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| | Abstract | | In Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, the nuclear fuel has melted without cooling that, and the fuel has become the debris. The debris has estimated existing in the lower part of the containment vessel. For decommissioning the FDNPP, it is required to remove the debris. However the position and size of the debris are unidentified at the present situation. We estimate that the cosmic ray muons are absorbed extremely in the debris because of the high density of uranium and plutonium. It may be able to visualize the structure in the nuclear reactor in non-contact and nondestructive using cosmic ray muons which penetrate easily in such the high-density material. In this study, we attempted visualization internal structure of the test nuclear reactor using cosmic ray muons. We set up five measurement points and five fan-shaped measurement lines of each point at outside of the containment vessel of the test nuclear reactor. As a result of the experiment, high density areas were recognized at the position equivalent to the pressure vessel in the nuclear reactor. We have been able to demonstrate the possibility of visualization in the internal structure of the nuclear reactor. We will promote the theoretical investigation and the consideration of the concrete problem for the practical use at FDNPP site in future. |
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