Improvement of the center boring device for the irradiated fuel pellets

燃料ペレット中心孔加工装置の改良

豊川 琢也 ; 宇佐美 浩二; 椎名 秀徳 ; 小野澤 淳 

Toyokawa, Takuya; Usami, Koji; Shiina, Hidenori; Onozawa, Atsushi

The power ramp test will be performed at Japan Materials Testing Reactor (JMTR) in Japan Atomic Energy Agency (JAEA) to study the safety margin of high burnup fuels. The commercial fuel rods irradiated in Europe (approx. 70 GWd/t) 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(dry ice) during its boring process. At the Reactor Fuel Examination Facility (RFEF) in Tokai Research and Development Center, 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 improved boring device was installed into the hot cell in 2010, and the mock-up test was performed with the dummy pellets to confirm the benefit of the improvements.