Assessment of the compatibility of vitrified high-level waste with geological disposal in a boom clay formation: remaining uncertainties

At SCK.CEN, the compatibility of vitrified high-level waste with the candidate geological disposal in Boom Clay is assessed in an experimental programme. This paper discusses the contribution of this programme to performance assessment, the uncertainties associated with the extrapolation of the experimental data to longer timescales, and other uncertainties affecting the compatibility of the HLW glasses with the geological disposal. The experimental programme has provided estimations for the long-term glass dissolution rate and mobile radionuclide concentrations in media representative for the geological disposal conditions. Long-term glass dissolution rates in Boom Clay slurries are between 10 and 100 times smaller than the initial dissolution rate in pure water, and depend on the glass composition. Very small mobile radionuclide concentrations are observed in reducing conditions at the lowest temperature considered (40 C) - ∝5 x 10-9 M for Np-237 and Tc-99. (orig.)