Interaction Swelling Bitumen – Host Formation: Scoping Calculations

Abstract

The Eurobitum bituminised waste product (BWP) from the former EUROCHEMIC reprocessing plant in Mol-Dessel (Belgium) contains a lot of salts, mainly NaNO 3 and CaSO 4 . In contact with pore water in an underground repository, the dehydrated salts in the BWP will rehydrate, resulting in swelling and, possibly, a swelling pressure build-up. A high swelling pressure might impede the integrity and the safety of the repository by creation of preferential pathways for radionuclide migration. In Belgium, the Boom Clay is studied as a reference host formation.The interaction between the swelling BWP and the host formation is a very complicated hydromechanical process. It depends not only on the hydromechanical behaviour of the Boom Clay, but also on that of the BWP. The hydromechanical constitutive law of Eurobitum is not yet established. We have therefore realised scoping calculations to assess the stress redistribution and deformation due to the recompression of the clay around a disposal gallery caused by a swelling pressure. Sensitivity studies have evidenced some important influencing factors.The scoping calculations showed that the swelling pressure exercised to the Boom Clay should be limited to 7 -8 MPa. Beyond this limit, the Boom Clay host formation will be subject to important deformation, and the risk of preferential paths for radionuclide transport becomes very high. The convergence during the excavation of the disposal galleries is of primary importance for a safe waste disposal system design. Indeed, excess convergence may result in a higher damaged zone before disposal of the bituminised waste.Mat. Res. Soc. Symp. Proc. Vol. 932

Osmosis-induced swelling of Eurobitum bituminized radioactive waste in constant total stress conditions

“…In addition to the dissolution of NaNO 3 , anhydrous calcium sulfate ('natural anhydrite'; solubility $0.015 mol/L (M); density $2.96 g/ml) can recrystallise with 0.5 water molecules to 'Paris Plaster' (solubility $0.21 M; density $2.74 g/ml) or with two water molecules to gypsum (solubility $0.014 M; density $2.32 g/ml), also resulting in a volume and/or pressure increase. High swelling-induced deformation and stresses could thus lead to a mechanical disturbance and possibly damage of the surrounding host formation [17], of which the consequences in terms of barrier performance have to be assessed.…”

Deformation and Flow Driven by Osmotic Processes in Porous Materials: Application to Bituminised Waste Materials

“…The salts contained in the BW are important because they can affect the integrity of the Boom Clay through an osmosis-induced pressure caused by osmotic uptake of water by the waste (Li et al 2006;Valcke et al 2009). When water comes into contact with the BW the salt will dissolve and diffuse away.…”

Osmosis-induced water uptake by Eurobitum bituminized radioactive waste and pressure development in constant volume conditions

“…The results of the nearly constant volume tests demonstrate the importance of a well-reflected disposal design for the BW, to avoid high stresses on the Boom Clay. Preliminary scoping calculations have shown that there will be little or no damage to the clay if the radial stress exerted by swelling BW remains below $6.5 MPa 16 [37,38]. To avoid higher radial stresses, the number of drums per gallery cross-section should be limited.…”