Materials interactions during high temperature transients: Discussion about the use of the kinetic rate constants in Zircaloy oxidation

The codes that simulate materials interactions in nuclear core degradation or core meltdown generally use the kinetic rate constants obtained from isothermal diffusion experiments. They calculate the interphase boundaries (IB) movements during temperature transients as a succession of isothermal steps at different temperatures. An alternative procedure based on a diffusion model is presented here, which we consider more appropriate for studying materials interactions during high temperature transients. As a system to be simulated we have chosen the transient oxidation of Zry at high temperatures (1000-1300 C). It is shown that the evolution of the oxidized Zry when described by both methods throws different results. The same could happen in other materials interacting at high temperature transients. In these cases diffusion codes should be used; otherwise kinetic parameters obtained from isothermal measurements have to be validated in each case. In this work we have developed the DISOL code to simulate the high temperature oxidation of Zr in the region where three phases ar formed: ZrO2, α-Zr and β-Zr. (orig.)