| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 4720982 | Physics and Chemistry of the Earth, Parts A/B/C | 2014 | 7 Pages |
•Corrosion of 200 L sized cemented radioactive waste simulates analyzed for >20 years.•Combination of thermodynamic calculations, solution and space-resolved surface analytics.•Close-to-equilibrium conditions achieved after 14 years duration of leaching experiments.•Uranophane and an amorphous diuranate-type solid identified in solid samples.•Concentration of uranium in solution controlled by solubility of diuranate-type solid.
Retention or release of radionuclides in a deep geological repository for radioactive wastes strongly depends on the geochemical environment and on the interaction with near-field components, e.g. waste packages and backfill materials. Deep geological disposal in rock salt is one of the concepts considered for cemented low- and intermediate-level wastes. Long-term experiments were performed to observe the evolution of full-scale cemented waste simulates (doped with (NH4)2U2O7) upon reaction with relevant salt brines, e.g. MgCl2-rich and saturated NaCl solutions, and to examine the binding mechanisms of uranium. Throughout the experiments, concentrations of major solution components, uranium and pH values were monitored regularly and compared to thermodynamic equilibrium calculations, which indicate that close-to-equilibrium conditions have been achieved after 13–14 years duration of the leaching experiments. Two of the full-scale cemented waste simulates were recovered from the solutions after 17–18 years and studied by different analytical methods to characterize the solids, especially with respect to uranium incorporation. In drill core fragments of various lateral and horizontal positions of the corroded monoliths, U-rich aggregates were detected and analyzed by means of space-resolved techniques. Raman, μ-XANES and μ-XRD analyses of several aggregates demonstrate that they consist of an amorphous diuranate-type solid. Within error, calculated U solubilities controlled by Na-diuranate (Na2U2O7·H2O) are consistent with measured U concentrations in both, the NaCl and the MgCl2-system. Since uranophane occurs also in the corroded monoliths, it is proposed that a transition towards the thermodynamic equilibrium U(VI) phase is kinetically hindered.
