CHEMICAL ASPECTS ASSOCIATED WITH THE ASSESSMENT OF RADIONUCLIDE MIGRATION THROUGH NATURAL GEOCHEMICAL BARRIERS

摘要

The migration and subsequent release of radionuclides from a repository to the accessible environment is an important part of the assessment of natural barrier systems. The speciation of key radionuclides in natural waters as well as the solubility limits for the principal solid phases are prime problems for physico-chemical modelling. A simple and effective method for calculating equilibrium actinide concentrations at the interface between solid phases and solution was achieved using the dissolution of PuO_2 as an example. Complex formation processes were taken into account using the Froneaus function, which reflects the extent of complexing and depends on ligand concentrations. Possible increases in Pu concentrations of 6 to 8 orders of magnitude were predicted for groundwaters of Bottstein granites and Hanford basalts, respectively, owing to plutonium-fluoride complexing. The increasing influence of oxalate complexes on the dissolution of Pu-containing solid phases can be expected at oxalate concentrations > 10~6 M.