High temperature oxidation of Nb-containing Zr alloy cladding in LOCA conditions

Nb含有Zr合金被覆管のLOCA時高温酸化

中頭 利則; 永瀬 文久 ; 更田 豊志

Chuto, Toshinori; Nagase, Fumihisa; Fuketa, Toyoshi

燃料被覆管のLOCA時高温酸化挙動を調べるために、79MWd/kgまで照射された高燃焼度PWR燃料被覆管を用いて水蒸気雰囲気における等温酸化試験を行った。原子炉照射中に形成された腐食酸化膜が水蒸気中の高温酸化を抑制する効果が示された。一方、高温酸化に及ぼす水素吸収の影響はほとんど見られなかった。M5被覆管は1273Kにおいて有意に小さい酸化速度を示したが、より高い温度においては酸化速度に及ぼす合金組成の影響は小さく、従来のジルカロイ4とほぼ同等の酸化速度を示した。

In order to evaluate high-temperature oxidation behavior of the advanced alloy cladding under LOCA conditions, isothermal oxidation tests in steam were performed with cladding specimens prepared from high burnup PWR fuel rods (79 MWd/kg). Cladding materials were M5 and ZIRLO which are Nb-containing alloys. Ring-shaped specimens were isothermally oxidized in flowing steam at temperatures from 1173 to 1473 K for the duration between 120 and 4000 s. Protective effect of the pre-formed corrosion layer is seen for the shorter time range at the lower temperatures. Influence of pre-hydriding is not significant for the examined range. Alloy composition change generally has small influence on the oxidation in the examined temperature range, though M5 shows obviously smaller oxidation constant at 1273 K. Consequently, the oxidation rates of the high burnup M5 and ZIRLO cladding are comparable or lower than that of unirradiated Zircaloy-4 cladding.