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 degrada tion or core meltdown generally use the kinetic rate constants obtaine d from isothermal diffusion experiments. They calculate the interphase boundaries (IB) movements during temperature transients as a successi on of isothermal steps at different temperatures. An alternative proce dure based on a diffusion model is presented here, which we consider m ore appropriate for studying materials interactions during high temper ature transients. As a system to be simulated we have chosen the trans ient oxidation of Zry at high temperatures (1000-1300-degrees-C). It i s shown that the evolution of the oxidized Zry when described by both methods throws different results. The same could happen in other mater ials interacting at high temperature transients. In these cases diffus ion codes should be used; otherwise kinetic parameters obtained from i sothermal measurements have to be validated in each case.