Long-Reach Compact Robotic Arm with LMPA Joints for Monitoring of Reactor Interior

To reduce the risk of radiation leakages similar to the incident at the Fukushima Daiichi Nuclear Power Station, robots have been employed to remove fuel debris from reactors. To perform this process safely, it is important to monitor the interior of a reactor. A camera and neutron sensors are attached to the end of a robotic arm to monitor the interior of the reactor. The basic design requirement for the monitoring system is that the arm must be highly extendable and rigid. To achieve this, a novel compact long-reach manipulator with a joint structure built using a low-melting-point alloy (LMPA) is proposed. The LMPA enables switching between the free and locked states of the rotational joints of the manipulator. Herein, we first explain the design of the proposed joint structure and verify whether it has adequate mechanical strength. The required maximum torque to be sustained by the structure was calculated using the cantilever model, and the actual breaking torque was measured by the tensile test. Experimental results confirmed that the joint could withstand approximately 1.86 times the required torque. Finally, the effectiveness of induction heating, which is used to switch between the free and locked states of the joints, was evaluated experimentally. The LMPA arm was installed in the coil of the induction heating module, and the time required to melt LMPA was measured. The experimental results confirmed that the induction heating can change the state of the LMPA joint, and the time required for the melting is approximately 30.3 s. Therefore, the findings of this study show that the proposed system is capable of averting nuclear disasters through the prevention of radiation leakages at nuclear plants.