Development of a precise drilling machine for a nuclear fuel pellet

When a new nuclear fuel is developed, an irradiation test needs to be carried out in the research reactor to analyze the performance of the new nuclear fuel. In addition, to check the performance of a nuclear fuel during the burn up test in the test loop, it is necessary to attach sensors near the fuel rod and connect them with instrumentation cables to the measuring device located outside of the reactor pool. In particular, to check the temperature fluctuation of a nuclear fuel during an irradiation test, a C-type thermocouple should be instrumented at the center of the nuclear fuel. Therefore, a hole needs to be made at the center of the fuel pellet to put in the thermocouple. However, because the hardness and density of a sintered UO2 pellet are very high, it is difficult to make a small fine hole on a sintered UO2 pellet using a simple drilling machine. The author developed an automated drilling machine which makes a fine hole in a fuel pellet without changing tools or breakage of the workpiece. Its performance is then verified by primary experiments using sintered Alumina, which has a similar hardness and density with a sintered UO2 pellet