Improvement of the center boring device for the irradiated fuel pellets

Shiina, Hidenori ; Usami, Koji; Sakuraba, Naotoshi; Harada, Akio; Onozawa, Atsushi ; Nakata, Masahito

The power ramp test will be performed at JMTR to study the safety margin of high bumup fuels. The commercial fuel rods irradiated in Europe will be refabricated as the test rods with the several instrumentations to observe the fuel behavior under the transient condition. One of the important parameters to be measured during this test is the center temperature of the fuel pellet. For this measurement, a thermocouple is installed into the hole bored at the pellet center by the center boring device, which can fix the fuel pellet with the frozen CO gas during its boring process. At the Reactor Fuel Examination Facility, several improvements were applied for the previous boring device to upgrade its performance and reliability. The major improvements are the change of the drill bit, modification of the boring process and the optimization of the remote operability. The mock-up test was performed with the dummy pellets to confirm the benefit of the improvements.