Oxidation of zircaloy-4 under high temperature steam atmosphere and its effect on ductility of cladding.

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Zircaloy-steam reaction rate in flowing steam was measured in the temperature range of 900-1, 330°C. The reaction rate measured from the weight gain followed a parabolic law above 1, 000°C, but it deviated from the law at 900 and 950°C. Growth rates of ZrO2 layer and ZrOv2+ stabilized a-phase were also parabolic above 1, 000°C. The parabolic rate law constants are represented as follows : Weight gain kw=0.468 exp (-0, 710/R T ) (g2/cm4•sec) ZrO2 kδ=0.0215 exp (-5, 860/RT ) (cm2/sec) ZrO2+ stabilized α kξ= 0.306 exp (-38, 970/RT) (cm2/sec). The ductility of zircaloy tubings oxidized in the temperature range of 9504, 330°C was measured by a ring compression test at 100°C. It tends to decrease with increasing the amount of oxidation and the oxidation temperature except the case of 950°C, where the specimens become brittle even at less amounts of oxidation. From these experimental results, it is concluded that the regulation for the amount of the zircaloy oxidation in the acceptance criteria for LWR's LOCA analyses is con-servative.
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