A new radionuclide sorption database for benchmark cement accounting for geochemical evolution of cement

Abstract

This chapter presents the data selection strategy and the selected sorption values on cement for 25 elements (Ag, Am, Be, C, Ca, Cl, Cs, H, I, Mo, Nb, Ni, Np, Pa, Pb, Pd, Pu, Ra, Sr, Se, Sn, Tc, Th, U, Zr) that need to be considered in safety assessment calculations for the future near-surface disposal facility at Dessel, Belgium. Mainly on the basis of literature data, best estimate sorption values in addition to upper and lower bound values were determined for a so-called benchmark cement" the unperturbed cement without effects of organics, high chloride content or other chemical components that might adversely impact radionuclide sorption. Effects of perturbing components are discussed separately. The geochemical evolution of the cementitious engineered barriers was also addressed to clarify the conditions under which sorption values are applicable. A substantial part of the scientific basis supporting the data selection was established at several meetings of an international panel of experts who reviewed and endorsed the data selection. To this end, the sorption data were checked for reliability, appropriateness for the conditions expected for the Dessel disposal facility, data quality, time frames (i.e. states of cement dégradation), heterogeneity (presence of components in conditioned wastes that could affect sorption), and completeness (in terms of mechanisms explaining the sorption processes).