A Comparison of Borosilicate Glass and Synthetic Minerals as Media for the Immobilization of High-Level Radioactive Waste

High-level liquid radioactive waste contains ∼40 different elements and, in time, many of these elements are transformed by radioactive decay into different-sized atoms with new chemical properties. Accommodation of this range of elements in a solid form can be achieved by vitrification because of the geometrical flexibility afforded by unordered glass structures. Crystalline minerals, on the other hand, can only accommodate atoms of specific size and valency and a complex mineral mixture is required to accommodate all the waste elements initially. The detrimental effects of transmutation on a fully crystalline solid raises doubts about the ability of synthetic minerals to immobilize waste elements in a stable structure for a safe period of time. While the vitrification process exploits the metastable (glassy) state, devitrification, if it occurs, introduces an ordering similar to that encountered in crystalline minerals.