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温度遷移による高燃焼度PWR燃料被覆管の機械特性変化

Mechanical properties changes of high burnup PWR fuel cladding by temperature transient

永瀬 文久; 上塚 寛

Nagase, Fumihisa; Uetsuka, Hiroshi

軽水炉の異常過渡や事故時の燃料棒健全性を評価するための基礎データを得ることを目的に高燃焼度PWR燃料被覆管を673~1173Kで0~600s間加熱し、室温においてリング引張試験を実施した。試験の結果から、加熱温度と加熱時間に依存した被覆管強度と延性の変化が明らかになった。温度遷移による機械特性の変化は、主に、照射欠陥の回復,ジルカロイの再結晶,相変態,それらに伴う水素化物析出形態の変化に対応しているものと考えられる。また、未照射被覆管との比較により、高温においても短時間では照射の影響が消失しない可能性が示された。合わせて、高燃焼度PWR被覆管の半径方向水素濃度分布を測定し、被覆管外表面部で約2400wtppmという高濃度の水素を検出した。このような高濃度の水素集積は、高燃焼度PWR燃料被覆管の延性低下や加熱後の延性変化と密接に関連すると考えられる。

To obtain basic data to evaluate fuel rod integrity during abnormal transient and accident of LWRs, high burnup PWR fuel claddings were heated for 0 to 600s at temperatures of 673 through 1173K, and the mechanical property changes were examined by using ring tensile test at room temperature. As a result of the test, it was shown that strength and ductility of the cladding are changed depending on heating temperature and time. The mechanical property changes by temperature transients are considered to be correspondent mainly to recovery of irradiation defect, recovery and recrystallization of the Zircaloy, phase transformations, and associated change of the hydride distribution and morphology. Comparison with unirradiated claddings suggested that irradiation effects are not completely annealed out by the short-term annealing at high temepratures. Radial change of hydrogen concentration was measured for the high burnup PWR fuel cladding and very high hydrogen concentration of about 2400wtppm was detected at the cladding periphery.

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