Cementitious Natural Analogues : Safety Assessment Implications of the Unique Systems in (original) (raw)

Cement and concrete are extensively used to condition and isolate the waste in repositories for L/ILW (low and intermediate level wastes) and for construction in many HLW/SF/MOX (high level waste/spent fuel/mixed-oxide fuel) repositories. Consequently, in many repository designs, cementbased materials are expected to dominate the repository, ensuring long-term maintenance of hyperalkaline conditions which are predicted to suppress the solubility of key radionuclides in the waste and enhance their sorption on the cement. Models of cement evolution predict that leaching of the cementitious material in the repository by groundwater will produce an initial stage of hyperalkaline (pH~13.3) leachates, dominated by alkali hydroxides, followed by a longer period of portlandite and CSH buffered (pH~12.5) leachates. It has also been predicted that, as the hyperalkaline porewater leaches out of the near-field, significant interaction with the repository host rock (and, where applicable, benton...