RESEARCH-SCALE MELTER: AN EXPERIMENTAL PLATFORM FOR EVALUATING CRYSTAL ACCUMULATION IN HIGH-LEVEL WASTE GLASSES

摘要

A crystal-tolerant glass approach is being developed for the Waste Treatment and Immobilization Plant at the Hanford Site in Washington State with a goal to maximize the loading of high-level waste in borosilicate glass without jeopardizing melter operation by crystal accumulation in the melter discharge riser. The research-scale melter (RSM) was employed to validate the crystal accumulation rates obtained at laboratory scale for a high-Ni-Fe glass and to investigate the possibility of removal of the accumulated layer during pouring after periods of idle time. Three 35-h feeding and 7-day idling periods resulted in accumulation of a ～6-mm-thick layer. Crystals accumulated in the layers during double crucible tests were significantly larger (>70 μm) compared with those in the RSM (～20 pm). However, a good agreement was found among the thicknesses of layers accumulated in the double crucible (2.7 mm) and in the discharge outlet of the RSM (1.7-1.9 mm) during 7 days of idling. Glass samples collected right after idling contained an increased concentration of spinel. However, two 35-h periods of glass pouring, each after 7 days of idling, did not remove the accumulated layer, confirming its high stability at temperatures above 1000°C.