The modeling of interaction between fuel element cladding and steam

Abstract

This work simulates a close to emergency case in the reactor core - the material of fuel element cladding is subjected to steam flow. The presented model takes into account several processes occurring together - the admittance of oxygen and hydrogen, the propagation of heat, diffusion and mechanical disturbances, chemical reaction. The transfer mechanism of oxygen and hydrogen under the action of the stress gradient is taken into account. The model is suitable to describe the processes at very small times, corresponding to short thermal impulses and initial stages of surface interrelation with steam flow. The all short-time accompanying processes (10-9 −10-12 s) affect the changes in the material exposed to steam contact, but they are not easily accessible for direct observation. The problem was solved numerically. The temperature in our numerical experiment is not too high, but it is already sufficient for introduction of hydrogen and oxygen into the Zr-1%Nb surface, as well as for oxidation of zirconium. Examples of calculations are presented. It shows how different-scale processes interact with each other and to what distortions in the distributions of all interacting quantities this leads. Examples of calculations for different durations of vapor interaction with cladding surface are presented. It is shown that the concentration of oxygen and hydrogen in Zr alloy increases when the vapor action is too long-term.