Oxygen diffusion based modelling of zircaloy steam oxidation during high temperature transients. 4

High temperature steam oxidation of Zircaloy cladding is one of the most important items on the safety analysis for a loss-of-coolant accident(LOCA) in a water cooled reactor. The isothermal oxidation has been found to obey a parabolic oxidation law and the temperature variation of the reaction rate constant can be expressed in an Arrhenius form. But a discontinuity is found in the temperature dependence of the reaction rate. A calculation code based on the oxygen-diffusion controlled process has been developed to explain the discontinuity which derived from the phase transformation of the oxide layer. The predictions from the code show very good agreement with the experimental data obtained for isothermal oxidation over the temperature range of 1000-1800degC. (author)