Data acquisition for radionuclide sorption on barrier materials for performance assessment of geological disposal of TRU wastes
Tachi, Yukio ; Suyama, Tadahiro*; Mihara, Morihiro
Sorption of radionuclides in cement and bentonite as engineered barrier materials, and rocks as natural barrier is the one of key processes in the performance assessment of geological disposal of TRU and high-level waste. The magnitude of sorption, expressed normally by a distribution coefficient (K), needs to be measured and determined taking into account the properties of barrier materials and geochemical conditions and associated uncertainty in the performance assessment. The basic concept for TRU waste disposal contains cementitious materials as an engineered barrier materials, in addition to bentonite and rock. It is therefore needed to consider the effects of the cement degradation and co-existing substances such as nitrates on radionuclide sorption. This report focused on data acquisition of distribution coefficient (K) by batch sorption experiments for the systems coupling barrier material-chemical condition-radionuclides that are needed to consider for the performance assessment of geological disposal of TRU waste. The barrier materials considered are ordinary Portland cement (OPC), degraded OPC and tuff rock. The chemical conditions are distilled water and synthetic seawater equilibrated with OPC and those containing nitrates and ammonium salts, etc. The radionuclides considered are organic carbon, inorganic carbon, Cl, I, Cs, Ni, Se, Sr, Sn, Nb, Am and Th. Although K values have been partly reported previously as RAMDA (Radionuclide Migration Datasets) for the performance assessment in the TRU-2 report, these results and addition K data are reported with the details of experimental methods and conditions.