Leaching of B-Si-glass by water in the presence of bentonite

Incorporation of high-level radioactive waste (HLW) into borosilicate glass is used on an industrial scale in most countries developed large-scale nuclear power engineering with closed fuel cycle. The vitrified HLW in a steel canister is planned to be disposed of in an underground repository. The bentonite clay serves as an important protective barrier and can significantly influence the durability of the borosilicate glass when groundwater penetrates the canister due to corrosion of its walls or mechanical damage resulting from rock movement caused by rock bursts or increased seismic activity. An experimental study of the leaching of borosilicate glass with simulators of HLW components (U, REEs, corrosion products) by water in the presence of bentonite has been carried out. The effect of the initial mass ratio of water to bentonite on the leaching rate of the glass is analyzed. Colloidal forms of glass leaching products are revealed by filtering the leach solution through membranes of different pore sizes. The elemental content of the filtrates was determined by inductively coupled plasma mass spectroscopy (ICP MS). The surface and cross section of the glass after leaching were studied using scanning electron microscopy (SEM) combined with energy dispersive X-ray analysis (EDX). The influence of the mass ratio of water and bentonite on the leaching of borosilicate glass can be noticeable at the beginning of the process. The presence of bentonite affects the colloidal form of radionuclide simulants in the leach products, in particular, the uranium-bearing colloid in the leach solution decreases radically. The outer surface of the altered glass layer is significantly enriched with aluminum in the presence of bentonite.