Modelling Long-term Chemical Degradation of a Concrete Container under Near Surface Disposal Conditions

The paper presents an application of a simplified 2D model of chemical degradation for a cracked concrete container termed monolith under near surface disposal conditions. The objective is to gain an improved understanding of the rate of degradation of the cracked monolith and its impact on transport of radionuclides under saturated conditions. Chemical degradation of concrete affects physical and mechanical properties and consequently accelerates migration of radionuclides from the cementitious engineered barriers. The abstracted large scale 2D model of chemical concrete degradation is based on a more detailed model who consider Ca leaching from concrete and consequent evolution of the physical properties such as porosity, bulk density, hydraulic conductivity, and tortuosity. Due to the uncertainty associated with the long term evolution of cracks in concrete, different crack networks have been postulated for different periods of time. The paper examines the effect of different crack densities, water boundary condition and magnitude of hydraulic conductivity on the degradation evolution of the monolith and release of radionuclides from conditioned waste grouted in the monolith.