The interaction between HLW glass and boom clay host rock

The interaction between the high level waste glasses of interest to Belgium (DWK PAMELA glasses SM513 and SM527, and Cogema AVH glass SON68) and the candidate Boom clay repository host rock has been investigated. Experiments of up to five years' duration have been finished. Basically static conditions, high surface area to solution volume ratio and negative Eh were applied in the tests to simulate the anticipated disposal situation. The roles of the clay concentration, container corrosion products, temperature and test duration were investigated parametrically. Either inactive or Pu and Am doped glasses were used. The presence of Fe2O3 corrosion products in a concentrated slurry strongly reduces glass dissolution; at 40 deg. C, dissolution kinetics are slower by about a factor of 10 than at 90 deg. C; leaching of Pu and Am is characterized by their very large sorption on clay; a minor fraction is leached in a mobile form (<105 molecular weight units), corresponding with average concentrations of 10-9 mol/L (239Pu) and 10-11 mol/L (241Am). These concentrations decrease further when Fe2O3 corrosion products are present in the clay. As a result of this five year programme, there are arguments to conclude that glass will certainly act as a first barrier against radionuclide dissipation. Other observations from this work are as follows: the basic mechanism of corrosion of the glasses in clay media is diffusion controlled leaching rather than congruent dissolution; the longer term results reveal leaching resumption processes related with secondary phase formation, the influence of which on the glass dissolution is not very clear yet; both glass composition and the presence of clay determine the glass dissolution kinetics. (author). 13 refs, 7 figs, 1 tab