Oxidation Kinetics of Low-Sn Zircaloy-4 at the Temperature Range from 773 to 1,573K

Abstract

Isothermal oxidation tests in flowing steam were performed on low-Sn Zircaloy-4 cladding tubes over the wide temperature range from 773 to 1,573 K in order to obtain oxidation kinetics applicable to various loss-of-coolant accident conditions of LWRs. The oxidation generally obeys a parabolic rate law for the examined time range up to 3,600 s at temperatures from 1,273 to 1,573 K, and for a limited time range up to 900 s from 773 to 1,253 K. A cubic rate law is preferable for evaluating the longer-term oxidation at 1,253 K and below. The parabolic rate law constant and the cubic rate law constant for measured weight gain were evaluated at every examined temperature, and Arrhenius-type equations were determined in order to describe the temperature dependence of the rate constants. It was indicated that the change of the oxidation kinetics from the cubic to the parabolic rate and the discontinuities in the temperature dependence of the rate constants are caused by the monoclinic/tetragonal phase structure change of ZrO2.