Remote Measurement by Robot Arm Equipped With PAUVP and LIBS

Abstract This paper presents a prototype of a system for remotely detecting leaks and determining the shape and elements of the sediment in the primary containment vessels (PCVs) of the Fukushima Daiichi Nuclear Power Plant, which is currently undergoing decommissioning. The accident resulted in breaches of the PCVs, causing the cooling water injected to cool the fuel debris to leak, along with relatively large sediments present in the leakage field in addition to small fuel debris. Up to now, the primary focus of the investigation is the internal structure of the vessel, leakage position, and the distribution of nuclear fuel debris within the reactor. The paper applies the Phased Array Ultrasound Velocity Profile (PAUVP) and Laser-Induced Breakdown Spectroscopy (LIBS) is employed in this study to identify the elements present in the sediment above the water surface part. Additionally, an arm robot capable of carrying both PAUVP and LIBS was developed as a result of the radioactivity. The experiments conducted in this study confirmed that the location of the leakage and the sediment characteristics were estimated from the visualization flow field map and the elements of sediment above water were identified, enhancing the efficiency of the detection process. The results showed that the PAUVP technique could accurately capture the velocity distribution and the leakage location in the simple flow field and that the LIBS technique could effectively determine the elemental composition of the above-water part. The arm robot was able to perform the measurements remotely and safely, avoiding human radiation exposure. This study demonstrates the feasibility and potential of using the PAUVP and LIBS techniques combined with an arm robot for investigating leak locations and sediment properties in the PCVs of the Fukushima Daiichi Nuclear Power Station. The system developed in this paper could provide valuable information for the decommissioning process and contribute to the safety and environmental protection of the nuclear power plant.