Pollucite and feldspar formation in sintered bentonite for nuclear waste immobilization

Future reprocessing of nuclear fuel may produce a waste stream consisting of alkali and alkaline earth fission products that can be converted into stable aluminosilicate minerals after sintering in bentonite. Precise knowledge of the mineral composition of the host phases is required for ultimate disposal. As determined by several analytical techniques, stable pollucite and celsian phases formed after sintering of bentonite and a simulated waste at 1200 °C. This relatively low temperature was likely a result of several impurities in the bentonite and simulated waste stream. While most of the waste metal ions were enriched in the crystalline phases, trace amounts remained in a silica-rich glassy region with other impurities.