Chemo-Hydro-Mechanical analysis of Bituminized Waste swelling due to water uptake: Experimental and model comparisons

Abstract : This paper presents a numerical model developed to reproduce the behaviour of French simplified Bituminized Waste Products (BWP) during a leaching test. The model is calibrated on experimental data sets. BWP were mainly produced during industrial reprocessing of nuclear spent fuel and are classified as low or intermediate activity long lived radioactive waste. Geological disposal is the reference solution for intermediate level long-lived BWP. Under geological disposal facility conditions, and after a long period of time, BWP will undergo water re-saturation from the host rock. A chemo-hydro-mechanical numerical model has been implemented with a finite element scheme to model BWP behaviour under such conditions. The constitutive model takes into account the impact of dissolution, permeation, diffusion and osmosis. Original evolution laws of diffusion coefficient and permeability as a function of the porosity are proposed. Specific mechanical model is proposed including Mori-Tanaka homogenization law. To simulate the hydration of the material, an original and simple method is proposed, avoiding costly two-phase flow resolution and complex calibration of the related parameters. This model was mainly used to reproduce the evolution of the amount of both water absorbed and salt leached by the sample during unconfined water up-taking tests. The calibration is based on experimental data obtained on French simplified BWP containing one highly soluble salt. Water uptake could generate swelling mainly due to osmosis.