Investigation of bituminized waste products swelling behavior due to water uptake under free leaching conditions: Experiments and modeling

Abstract

AbstractBituminized waste products (BWPs) were produced by conditioning in bitumen the co‐precipitation sludge resulting from industrial reprocessing of spent nuclear fuel. Underground geological disposal is a solution for the long‐term disposal of some intermediate level long‐lived (ILW‐LL) categorized BWPs in France. After one or several hundred thousand years, the water from the host rock will fully saturate the disposal cells. By an osmotic phenomenon enabled by the semi‐permeable capacity of the bituminous matrix, water in direct contact with BWPs could cause them to swell, which would lead to pressure on the host rock and may damage the disposal facility. Therefore, the BWPs’ swelling behavior has to be taken into account in safety studies for disposal facilities. This paper presents an experimental and numerical investigation of BWPs’ swelling behavior due to water uptake. Experimentally, water uptake, swelling and released salts were monitored for about 4 years during free leaching tests of simplified BWPs. The numerical model presented is extended from an existing one that incorporates transport mechanisms (diffusion, permeation, osmosis) with mechanics via Maxwell's viscoelastic model. An original coupled homogenization of transport terms is proposed to better capture the role of the semi‐permeable membrane played by the bitumen and the porosity dependency of coupled transport coefficients during water uptake. The presented numerical model is able to reproduce the experimental results of free leaching tests and shows its validity for the entire leaching process.