A multi-region transient erosion model for concrete with time-dependent surface heat flux

Abstract

A multi-region, transient concrete ablation and decomposition model is developed. The model consists of four regions of concrete containing a thermally affected region, a dry (evaporated and chemically dehydrated) region, and a gas-free (decarboxylated) region with ablated concrete at the melt/concrete interface. Each region has an interface where the latent heat of local decomposition reactions is taken into account as heat sinks due to endothermic characteristics of the reactions. The time dependent temperature profiles, and depth and growth rate of the regions are evaluated by use of the heat balance integral method. Solutions are obtained for surface heat fluxes in forms of constant, e ⁻(λ)ᵗ, t⁻(λ) and -At to analyze various melt cooldown schemes. The erosion front progresses with a constant rate proportional to the surface heat flux in case of constant heat flux, and terminates at a finite erosion depth that is logarithmically proportional to the cooldown rate for surface heat flux in forms of ⁻(λ)ᵗ and t⁻(λ). Sensitivity analyses are performed to investigate the effects of important thermophysical parameters. Larger erosion depth and rate is observed for higher thermal conductivity. Decomposition temperatures are found to be significant in ablation. Model results were compared with previous experiments and models, and determined to be valid and accurate for different types of melt/concrete interaction. The model presented in this study is simple yet very detailed and accurate in simulating the actual molten core/concrete interaction (MCCI) phenomena, and in investigating the concrete reaction to the molten core. It not only can be embodied into the MCCI codes currently being developed, but also can be used to determine the containment integrity, and fission products released into the environment and to the public as a stand alone code.