Hydro-chemical modelling of in situ behaviour of bituminized radioactive waste in Boom Clay

The current reference solution of the Belgian Agency for the Management of Radioactive Waste and Fissile Materials (ONDRAF/NIRAS) envisages underground disposal of Eurobitum Bituminised radioactive Waste (BW) in a geologically stable clay formation such as the Boom Clay. The osmosis-induced uptake of water by the dehydrated hygroscopic salts embedded in the BW might induce a geo-mechanical perturbation of the host formation, caused by the swelling and the increase of the pressure in and around the waste. The interaction between the swelling BW and the host clay formation is a very complicated chemo-hydro-mechanical process and depends not only on the hydro-mechanical behaviour of the Boom Clay, but also on that of the BW. The objectives of the Chemo-Hydro-Chemical (CHM) analysis presented in this work are (i) to get insights on the kinetics of water uptake by BW, dissolution of the embedded NaNO3 crystals, solute leaching, and maximum generated pressure under disposal conditions, and (ii) to study the stress redistribution due to the recompression of the clay around a gallery caused by the swelling pressure of the bitumen and the admissible swelling pressure for Boom Clay.