In nuclear waste repository design bentonite has been included as part of the backfill for its sorbtive capacity and low water permeability. Nevertheless, it cannot keep the waste form dry once intrusion of groundwater has occured [1]. Leach experiments [2], [3] with the radioactive nuclear waste form borosilicate glass JSS-A have been performed with and without bentonite present to provide a database which allows the long term stability of the glass in aqueous environment to be forecasted and the chemical effects of bentonite to be studied.

The results from the JSS phase II static glass leaching experiments are presented. The experiments have been performed in the presence of bentonite, granite and stainless steel corrosion products at 90°C for 28 days. The leaching behaviour of Cs has been analysed using gamma-spectrometry. The surface of the leached glass samples has been analysed by infrared reflection spectrometry.The presence of uncompacted bentonite seems to have a very small, increasing, effect on the leach rate of the glass compared to when no bentonite is present. In the presence of compacted bentonite, a lower leach rate has beep founy than in the prgsencelof uncompacted bentonite. (For Cs 0.3 g × m−2 × d−1 and 0.7 g × m−2 × d−1 respectively.) The addition of stainless steel corrosion products seems to have a slightly increasing effect on the leach rate in the presence of compacted bentonite. The beneficial effect of granite on the leach rate seems to be overshadowed by the presence of uncompacted bentonite.

A joint research project with participation from Japan, Switzerland and Sweden is underway at Studsvik (The JSS-project). The project concerns investigations on the leaching of fully radioactive glass (containing 12 wt% fission product oxides and actinide oxides) manufactured by CEA/Marcoule. So far the glass has been leached in doubly distilled water and in silicate water at 90 C. Some leaching experiments involved the presence of crushed Stripa granite in the same containers as the glass.Due to strong radiation and the presence of plutonium the leaching was carried out in a specially designed lead cave using gilded stainless steel containers.Weight losses, pH and elemental mass losses were determined together with infrared reflection spectral changes. These data are compared to those obtained from a simulated nonradioactive glass of nearly the same composition and to similar alkali borosilicate glasses previously investigated at Studsvik.

The corrosion experiments of crushed, radioactive waste glass at Studsvik within phase V of the JSS Project are described. The experiments were performed with high S/V ratios (1100 and 4000 m−1) which resulted in silica saturation already after the shortest reaction time studied (91 d).Thee long term leach rate of the soluble elements is about 10−3 g.m d−1, both in the presence and absence of bentonite. In the presence of bentonite + magnetite the leach rate is higher, about 0.007 g.m1.d−2. The release rate to the solution of Cs is one order of magnitude lower and that of Pu-238 + Am-241 three orders of magnitude lower than the release rate of the soluble elements Mo and B. Most of the Pu-238 and Am-241 fraction, found in the solution, is present as colloids.

The release of Am-241 during corrosion of the radioactive waste glass, JSS-A, has been studied in the presence of corrosion products and/or uncom-pacted bentonite. The corrosion behaviour of Am-241 has been analyzed using gamma spectrometry. Adsorption of Am-241 on bentonite is observed in all cases. The contents of Am-241 in centrifuged leachates are in most cases less than 1/100 of total values. The normalized elemental mass loss of Am increases initially with corrosion time, and the values in the presence of bentonite and corrosion products are larger than those in the presence of bentonite alone. This tendency is in agreement with results previously found for other elements. The release of Am is low, only about 10–20 % of the corresponding total mass loss.