Microstructure and mechanical property changes in fuel cladding during RIA-type temperature transients

RIAタイプの温度遷移における燃料被覆管ミクロ組織及び機械特性の変化

永瀬 文久 ; 杉山 智之 ; 更田 豊志

Nagase, Fumihisa; Sugiyama, Tomoyuki; Fuketa, Toyoshi

温度遷移における燃料被覆管のミクロ組織及び機械特性の変化を調べ、さまざまなRIA条件下での広範な温度範囲における燃料挙動を評価するために実験を行った。被覆管の延性は温度上昇とともに基本的に増大する。水素化した被覆管の延性は300から473Kの間で明確に増大するが、473から573Kでの増大は小さい。RIAタイプの速い温度遷移では再結晶による延性増大は期待できない。一方、1100K以上で起こる相変態は急激に起こり機械特性に影響を及ぼす。870K以上では水素化物リム中の水素化物が固溶するため、水素化物リムが及ぼす影響はないと考えられる。

Laboratory-scale experiments are performed to examine microstructure and mechanical property changes of the fuel cladding during temperature transients and estimate the fuel behavior for a wide temperature range under various RIA conditions. Ductility of the cladding generally increases with the temperature. The ductility increase of the hydrided cladding is obvious between 300 and 473 K, while it is small between 473 and 573 K. Ductility increase due to recrystallization is not expected during the RIA-type quick transient. On the other hand, phase transitions above 1100 K occur so quickly and affect the mechanical property of the cladding. The influence of the hydride rim at the cladding periphery would not be seen above 870 K since hydrides in the rim are in solid solution for a very short time.