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Annealing behavior of (Pu,Cm)O$$_{2}$$ lattice and bulk expanded by self-irradiation damage

自己照射損傷により膨張した(Pu,Cm)O$$_{2}$$結晶格子及び焼結体の焼鈍挙動

高野 公秀 ; 赤堀 光雄; 荒井 康夫

Takano, Masahide; Akabori, Mitsuo; Arai, Yasuo

マイナーアクチノイド含有酸化物燃料ペレットの自己照射損傷とHe蓄積の影響を評価するため、(Pu$$_{0.95}$$Cm$$_{0.05}$$)O$$_{2}$$固溶体試料の結晶格子と焼結体寸法の膨張及び焼鈍挙動を調べた。室温における格子定数と焼結体寸法は、保管時間に対して同様の依存性を示しながら膨張し、60日で0.3%の膨張率に飽和した。2年保管(0.33%壊変)してHeを蓄積させた後、1433Kまでの温度範囲で焼鈍試験を行った結果、格子定数は未損傷の値まで回復したものの、焼結体寸法は1433Kでの加熱時に再び膨張し、未損傷時の値まで回復しなかった。焼結体試料の破面を走査電子顕微鏡で観察した結果、粒界に沿って直径200から300nmの気泡状組織が確認された。結晶粒内に溶存していたHe原子が、1433Kでの加熱中に拡散により粒界に集まり、気泡を形成した結果、Heガススエリングを引き起こしたと考えられる。

To investigate the influence of self-irradiation damage and accumulation of He in oxide fuel pellets containing minor actinides, the expansion and annealing behavior of the crystal lattice and bulk were examined comparatively on a (Pu$$_{0.95}$$Cm$$_{0.05}$$)O$$_{2}$$ specimen. The lattice parameter and pellet dimension at room temperature grew with the similar dependence on storage time, and their linear expansion saturated to 0.3 % within 60 days. After two years storage, the annealing examinations were performed in the temperature range up to 1433 K. The lattice parameter recovered to the undamaged value, whereas the pellet dimension grew again during the heat treatment at 1433 K. The fractured surface of the annealed pellet was then observed by a scanning electron microscope. The gas bubbles with 200-300 nm in diameter were recognized along the grain boundaries like the fission gas bubbles. It was considered the dissolved He atoms moved toward grain boundaries by diffusion and formed gas bubbles, which resulted in the He gas swelling of the pellet specimen.

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