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Zircaloy-steam reaction rate in flowing steam was measured in the temperature range of 900-1,33O"C. T h e reaction rate measured from the weight gain followed a parabolic law above l,OOO"C, but it deviated from the law a t 900 and 950°C. Growth rates of ZrO, layer and Zr02+stabilized a-phase were also parabolic above 1,OOO"C. T h e parabolic rate law constants a r e represented a s follows : Weight gain k,=0.468 e x p (-40,71O/RT) (gZ/cm4 .set) ZrO, k3=0.0215 exp(-35,860/RT) (cm2/sec) ZrO,+stabilized a kc=0.306 exp(-38,970/RT) (cm2/sec). The ductility of zircaloy tubings oxidized in the temperature range of 950-1,33O0C was measured by a ring compression test a t 100°C. It tends to decrease with increasing the amount of oxidation and the oxidation temperature except the case of 9.iO°C, where the specimens become brittle even a t 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 cons e r va ti ve.

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