Concrete Degradation Modeling in the Evaluation of Entombment as a Decommission Option

For entombment to be a viable option for the decommissioning of nuclear structures, the effectiveness of available engineered barriers needs to be assured. Barrier performance should be estimated with the aid of computer models that can accurately predict the response of the barrier to foreseeable physical and chemical conditions. For concrete barriers, virtually all degradation mechanisms are controlled by the transport of water and ionic species within the pore space. These, in turn, are controlled by the appropriate transport coefficients. For sound concrete, the transport coefficients are sufficiently small enough that isolation is expected. It is the presence of cracks within the concrete that compromises the barrier by increasing the transport coefficients dramatically. Therefore, additional efforts to characterize the performance of concrete barriers must focus on quantifying the existing cracks and flaws within the concrete. This characterization would include sampling (when possible), nondestructive techniques, and computer modeling. All of these are incorporated into a coherent monitoring plan.