Abstract
The Rokkasho Reprocessing Plant includes a vitrification facility for immobilization of the highlevel liquid waste from reprocessing. The generation of a separate salt phase composed mostly of molybdate and sulfate salts was observed during the early part of the active test at Rokkasho. Subsequently, yellow phases were eliminated by adjusting the concentration of components in the waste contributing to their formation. To reduce the amount of vitrified waste, it is desirable to develop higher waste loading glass formulations. However, higher waste loading, without proper glass formulation design, would increase the tendency for yellow phase generation. Laboratory testing was performed to develop higher waste loading glass formulations that can suppress yellow phase formation. The formulation approach assumed that the present glass product and glass bead compositions used at Rokkasho can be modified, and that some of the glass bead components can be redistributed to the liquid waste such that cold cap reactions can be favorably influenced to suppress yellow phase formation. New glass formulations with waste loadings of more than 30 wt%, compared to around 20 wt% for the present glass, were developed. Smallscale melter tests with the new formulation showed that it can accommodate waste loadings as high as 34 wt%. This work was carried out as a part of the research supported by Japan Nuclear Fuel Limited
