Improved feed compositions for slurry-fed ceramic melters

One method for immobilizing high-level nuclear waste is to convert it into a glass. This is commonly done by fusing together glass frit and waste, which in the case of West Valley Demonstration Project (WVDP) is an alkaline sludge. In work conducted at Battelle Pacific Northwest Laboratories for the WVDP, frit is being evaluated in large-scale, slurry-fed ceramic melter tests. However, the glass frit can give rise to some difficulties, and therefore other ''glass formers'' are being investigated in parallel. Melter feed consisting of frit is abrasive, which results in relatively high wear of pumps, valves, and piping. For example, mechanical seals can fail in a short time. Even pumps designed to avoid seal problems can exhibit significant wear of the impeller and housing, and flowmeters are similarly susceptible. To compound the situation, frit and sludge mixtures tend to separate upon standing unless they are properly agitated or transported above minimum flow velocities. If separation does occur, a ''hard pan'' can form that is difficult to resuspend. This phenomenon seems to be the reason why airlifting of a glass frit--waste suspension is frequently terminated by plugging. West Valley wastes are high in iron and contain nickel and manganese oxides and, as such, are susceptible to spinel formation during vitrification. This tendency would be increased if localized high waste to frit concentrations occurred because of separation of the frit from the waste. For the same reason, a molten sulfate phase that is both corrosive and prone to segregate cesium can form even when the average sulfate level is below the saturation limit in the glass. In contrast, a melter feed based upon a colloidal dispersion of glass formers is nonabrasive, can be easily pumped and airlifted, and is not prone to settling or thixotropic behavior. Furthermore, the glass formers mix more intimately with the waste sludge before melting than can be achieved by using frit