CRYSTALLIZATION IN HIGH-LEVEL WASTE GLASSES U.S. DEPARTMENT OF ENERGY OFFICE OF RIVER PROTECTION WTP ENGINEERING DIVISION

Various circumstances influence crystallization in glassmaking, for example: (1) crystals nucleate and grow before the glass-forming melt occurs; (2) crystals grow or dissolve in flowing melt and during changing temperature; (3) crystals move under the influence of gravity; (4) crystals agglomerate and interact with gas bubbles; (5) high-level wastes (HLW) are mixtures of a large number of components in unusual proportions; (6) melter processing of HLW and the slow cooling of HLW glass in canisters provides an opportunity for a variety of crystalline forms to precipitate; (7) settling of crystals in a HLW glass melter may produce undesirable sludge at the melter bottom; and (8) crystallization of the glass product may increase, but also ruin chemical durability. The conclusions are: (1) crystal growth and dissolution typically proceed in a convective medium at changing temperature; (2) to represent crystallization or dissolution the kinetics must be expressed in the form of rate equations, such as dC/dt = f(C,T) and the temperature dependence of kinetic coefficients and equilibrium concentrations must be accounted for; and (3) non-equilibrium phenomena commonly occur - metastable crystallization, periodic distribution of crystals; and dendritic crystal growth.