Investigation of Bituminized Waste Products Swelling Behavior Due to Water Uptake Under Confined Leaching Conditions: Experiments and Modeling

Bituminized waste products (BWPs) were produced by conditioning in bitumen the co-precipitation sludge resulting from the industrial reprocessing of nuclear spent fuel. For some intermediate level long-lived (ILW-LL) classified BWPs, a long-term disposal solution in France is underground geological disposal. One of the challenges for BWPs in geological disposal conditions is their swelling behavior due to water uptake. This swelling, if sufficiently important, could lead to mechanical coupling with the host rock, resulting in the application of pressure that could damage it. Consequently, the swelling behavior of BWPs must be considered in safety studies for the underground storage facility after site closure. The present work is a continuation of a previous one and focuses on investigating both experimentally and numerically the BWPs’ swelling behavior due to water uptake under confined leaching conditions. The swelling of simplified BWPs was experimentally monitored for about 2.5 years during leaching tests under constant counterpressure. The numerical model is extended from a previous work that incorporates coupled homogenization of transport terms (diffusion, permeation, osmosis) with mechanics via Maxwell's viscoelastic model. An original nonlinear poro-viscoelastic model taking into account large strains is proposed in this paper to better model the BWPs leaching behavior under confined conditions. The experimental results of leaching tests under constant counterpressure are generally well predicted by the resulting numerical model. The role of the poorly soluble salts BaSO₄ within the solid BWP matrix is investigated.