Fuel performance of hollow pellets for fast breeder reactors

高速炉における中空ペレットの燃料挙動

石見 明洋 ; 勝山 幸三 ; 木原 義之; 古屋 廣高*

Ishimi, Akihiro; Katsuyama, Kozo; Kihara, Yoshiyuki; not registered

常陽MK-II炉心にて照射された中空ペレットについて、X線CT検査等の照射後試験を実施した。X線CT検査の結果、燃料スタック中央部付近において中空径が製造時よりも小さくなることを確認した。また、X線CT検査結果より中空ペレットのスエリング率を評価し、金相写真より評価した結果とほぼ一致していることを確認した。さらに、中実ペレットに比べ高い線出力で照射された中空ペレットのスエリング率及びFPガス放出率は、中実ペレットと同等であることを確認した。

Three fuel rods containing hollow MOX pellets of uranium and plutonium oxides were fabricated and irradiated at a high linear heat rate to burn-up of nearly 30,000 MWd/t in the experimental fast reactor, JOYO MK-II. After irradiation, one of the fuel rods pellets was examined by X-ray CT and conventional nondestructive and destructive methods. Swelling rate was evaluated by both dimensional change and radial density distribution. There were no differences between both types of results and it was concluded that swelling rate can be examined in detail by the X-ray CT technique by dismantling the assembly. In addition, the swelling rate of hollow pellets was nearly the same as values reported for the fuel rods containing solid pellets. LHR was higher in the examined fuel rod containing hollow pellets than in the conventional fuel rod containing solid pellets, but fission gas release rates for both fuel rods were nearly the same. Since it is possible to decrease the maximum temperature in the radial center of the hollow fuel pellets, they can be effectively utilized in reactor operation at higher LHR.