Consolidated waste forms: glass marbles and ceramic pellets

Abstract

Glass marbles and ceramic pellets have been developed at Pacific Northwest Laboratory as part of the multibarrier concept for immobilizing high-level radioactive waste. These consolidated waste forms served as substrates for the application of various inert coatings and as ideal-sized particles for encapsulation in protective matrices. Marble and pellet formulations were based on existing defense wastes at Savannah River Plant and proposed commercial wastes. To produce marbles, glass is poured from a melter in a continuous stream into a marble-making device. Marbles were produced at PNL on a vibratory marble machine at rates as high as 60 kg/h. Other marble-making concepts were also investigated. The marble process, including a lead-encapsulation step, was judged as one of the more feasible processes for immobilizing high-level wastes. To produce ceramic pellets, a series of processing steps are required, which include: • spray calcining-to dry liquid wastes to a powder; • disc pelletizing-to convert waste powders to spherical pellets; • sintering-to densify pellets and cause desired crystal formation. These processing steps are quite complex, and thereby render the ceramic pellet process as one of the least feasible processes for immobilizing highlevel wastes.

Comparative assessment of TRU waste forms and processes. Volume II. Waste form data, process descriptions, and costs.

“…The marble machine is based on a Corning Glass Works patent (Knapp and Smith 1962). It has also been demonstrated at PNL (Treat and Rusin 1982). Here marbles have been produced at rates and glass compositions very similar to those required for this study .…”

“…This device consists of a continuous moving chain on which marble-forming molds are attached (see Figures 38 and 39). Glass falls into the hemispherically shaped molds, forming globules of glass (Treat and Rusin 1982). The molds are then vibrated, causing the globules of glass to rotate.…”