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Behavior of pre-hydrided Zircaloy-4 cladding under simulated LOCA conditions

LOCA模擬条件下における水素添加ジルカロイ-4被覆管の挙動

永瀬 文久; 更田 豊志

Nagase, Fumihisa; Fuketa, Toyoshi

冷却材喪失事故(LOCA)時の高燃焼度燃料棒挙動に関し、未照射ジルカロイ-4被覆管を用い、LOCA模擬試験を行った。水素濃度約100$$sim$$1400ppmを有する被覆管を、水蒸気中にて1220$$sim$$1500Kの温度範囲で等温酸化した後、冠水により急冷した。急冷時に生じる燃料棒の収縮を拘束したが、生じる荷重の最大値を4段階に調節した。主として肉厚に占める酸化割合に依存して、被覆管は急冷時に周方向亀裂を伴って破断した。酸化割合に関する破断/非破断のしきい値は、初期水素濃度と拘束荷重の増大とともに低下した。結局、拘束荷重が535N以下であれば、水素濃度にかかわらず、破断しきい値は酸化割合20%を超え、日本におけるECCS性能評価指針の基準値を上回ることが明らかになった。

Regarding high burn-up fuel behavior under LOCA conditions, LOCA-simulated experiments were performed with unirradiated Zircaloy-4 claddings. Claddings containig 100 to 1450 ppm were isothermally oxidized at at 1220 to 1500 K in steam flow, and quenched by flooding water. Axial shrinkage of the rods during the quench was restrained controlling the maximum restraint load at four different levels. Primarily depending on fraction of the cladding thickness oxidized, the claddings fractured into two pieces during the quench, with circumferential cracking. The fracture/non-fracture threshold as for the oxidized fraction decreases as both initial hydrogen concentration and axial restraint load increase. Consequently, it was shown that the threshold is higher than 20% cladding oxidation, e.g. sufficiently higher than the limit in the Japanese ECCS acceptance criteria, irrespective of hydrogen concentration, when the restraint load is below 535 N.

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パーセンタイル:12.22

分野:Nuclear Science & Technology

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