The swelling of Eurobitum by water uptake and its geo-mechanical consequences - Status 2010

ONDRAF/NIRAS proposes the direct underground disposal of Eurobitum bituminized radioactive waste in a geologically stable clay formation as the preferred long-term solution for this waste. Compatibility studies are ongoing at the SCK•CEN to investigate the geo-mechanical and geo-chemical perturbation of the Boom Clay as a consequence of the osmosis-induced uptake by the large amounts of dehydrated and hygroscopic salts that are embedded in an efficient semi-permeable bitumen membrane. In this report we discuss the results of (i) theoretical calculations, (ii) laboratory water uptake experiments, and (iii) the development of a chemo-hydro-mechanical (CHM) formulation for Eurobitum to evaluate the geo-mechanical perturbation of the Boom Clay by swelling Eurobitum. The theoretical calculations demonstrated that from a mechanical point of view the 'direct' geological disposal of Eurobitum seems to be possible as long as the number of drums per gallery cross section is limited. The water uptake experiments yielded a comprehensive understanding of the phenomenology of the water uptake by Eurobitum in restricted swelling conditions. The CHM formulation for Eurobitum can reproduce successfully the key features of the results of the water uptake tests with inactive 'reference' Eurobitum, at least for a period in which the samples are only partially hydrated.