KAERI의 PRIDE 시설에서 공학규모의 전해환원용 원료물질인 UO2 다공성펠렛 제조를 위해 공정과 장치를 최적화시킨 내 용을 다루었다. UO2 분말과 별도로 attrition 밀링된 대용산화물 분말을 출발분말로, 정밀 칭량을 통해 사용후핵연료 조성을 모사하였다(Simfuel). Simfuel 분말은 각각 tumbling mixer로 혼합하여 균질화 하고, rotary press로 성형하여 furnace를 이 용해 소결하였다. 4% H2-Ar 분위기에서 1450℃ 24시간 고온 열처리하여 제조된 소결펠렛은 6.89 g·cm-3의 벌크밀도를 가 지며 이는 후속 전해환원 공정의 요구에 부합한다. 소결된 다공성펠렛의 미세구조 관찰을 통해 다공성 기지상과 함께 산화/ 금속 석출물이 관찰되어 사용후핵연료의 상이 모사됨을 확인하였다. 본 결과는 향후 공학규모 이상의 파이로 연구를 위한 UO2 다공성펠렛 제조에 중요한 기초자료로 활용 될 것이다.

When a new nuclear fuel is developed, irradiation test needs to be carried out in the research reactor to analyze the performance of the new nuclear fuel. It is necessary to attach sensors in the fuel rod and connect them with instrumentation cables to check the performance of the nuclear fuel during the burn up test in the test loop. A thermocouple is installed at the center of the fuel rod to check the centerline temperature of a fuel rod during the irradiation test. Therefore, A hole needs to be made at the center of a fuel pellet to put the thermocouple. However, it is difficult to make a small fine hole on the sintered UO2 pellet with a simple drilling machine, because the hardness and density of a sintered UO2 pellet are very high. In this study, an instrumented fuel rod mock-up was fabricated using an automated precise drilling machine. Four sintered alumina were drilled off and assembled into the zircaloy tube and a thermocouple was instrumented in the fuel rod mock-up. Sealing of an instrumented fuel rod mock-up was performed in the following two methods. It is sealing of similar metals perform by welding method, and sealing of dissimilar metals perform by swagelok method.

In order to investigate a nitriding process of spent oxide fuel and the subsequent change in thermal properties after nitriding, simulated spent fuel powder was converted into a nitride pellet with simulated fission product elements through a carbothermic reduction process. Nitriding rate of simulated spent fuel was decreased with increasing of the amount of fission products. Contents of Ba and Sr in simulated spent fuel were decreased after the carbothermic reduction process. The thermal conductivity of the nitride pellet was decreased by an addition of fission product element but was higher than that of the oxide fuel containing fission product elements.