CORALUS-II. An integrated in situ corrosion test on alpha-active HLW glass - phase II. Detailed final report of SCK•CEN for the EC project CORALUS II

Integrated in situ corrosion tests with alpha-doped SON68 glass samples are performed in the HADES underground laboratory in Mol, Belgium. Two test tubes, bringing active glass samples in contact with three clay-based backfill materials at high density, have been dismantled. The glass and clay samples have been extensively analysed. The results on glass corrosion agree well with results from surface laboratory tests and modelling predictions. The glass alteration is two orders of magnitude higher at 90 °C than at 30 °C. The addition of powdered glass frit to a Ca-bentonite backfill reduces the glass alteration by two orders of magnitude in comparison with another backfill, dried Boom Clay. The alpha-doped glass samples had slightly thicker alteration layers. The thickness seems to increase with increasing alpha-beta-gamma activity. All backfill materials proved to be efficient barriers against radionuclide migration. The decreased glass alteration due to the addition of powdered glass frit resulted in a concomitant decrease of the radionuclide leaching. In many cases, the migration profiles showed a contribution of colloidal transport.