Crystallization during processing of nuclear waste glass

In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: a b s t r a c t a r t i c l e i n f o Under typical glass-processing conditions, crystals nucleate, grow, and dissolve in a nonuniform temperature field in a melt subjected to deformation and flow. Using examples of the results obtained on nuclear waste glasses, this paper describes various phenomena associated with crystallization under non-static conditions, such as crystal formation during batch melting, crystal settling at the melter bottom, and crystal precipitation during glass cooling, including its impact on glass corrosion resistance. Almost all commercial glasses, all waste glasses and geological glasses, and many specialty glasses are multicomponent. Crystals that grow or dissolve in such glasses have a different composition from the matrix glass, and they often grow and dissolve at a changing temperature in a moving melt, or while moving through the melt by buoyancy. Nuclear waste glasses are outstanding examples of multicompo-nent glasses. They contain a majority of the chemical elements of the periodic table, and their design and processing provide a plentiful opportunity for crystallization, which is allowed as long as it does not impair the chemical durability, the sole measure of waste glass quality. For the processing and storage economy, the waste fraction in the glass is typically as high as the processing and product quality constraints allow. Because the waste components are usually prone to crystallization and the final product is formed into large bodies in which the internal portion of the glass cools slowly, nuclear waste glasses may contain a variety of crystalline forms. Though this paper is based on studies undertaken with glasses designed for the vitrification of nuclear wastes stored at Hanford, the features covered are typical, in many aspects, also for glasses industrially processed or made by nature. Section 2 briefly describes the batch-to-glass conversion process, in which initially crystalline materials turn amorphous. Sections 3 and 4 review the role of the phase equilibria and crystal nucleation in multicomponent glasses. Section 5 focuses on the nonisothermal kinetics of crystal growth and dissolution when solid and liquid phases are in mutual motion. Section 6 informs about the effects of crystallization on glass processing and on the …