Joint Vitrification of Various Mixed Wastes

Abstract

Mixed wastes involve radioactive constituents and hazardous components and must be conditioned to be disposed. Joint vitrification of low and intermediate level radioactive wastes (LILW) from nuclear power plants, together with spent catalysts, sorbents, and cathode ray tube (CRT) glass is proposed as a suitable means to condition these wastes. Preliminary experiments on vitrification in crucibles in a laboratory-scale resistive furnace were carried out that demonstrate possibility of 40 wt.% LILW salt loading in a batch. Homogeneous silicate- and borosilicatebased glasses have been obtained and characterized. A phase separation problem at high sulfate and chloride content caused a “yellow phase” to be formed. To prevent this, sulfates and chlorides must be separated from the LILW. The most promising method of mixed waste vitrification is inductive melting in a cold crucible (IMCC) because of its high throughput rate, high achievable temperatures, and long lifetime of the apparatus. Bench-scale tests have been carried out. Preliminary testing of IMCC of spent CRT glass and a combined batch of this glass and LILW salt surrogate was also conducted. LILW salt loading in the batch reached 30 wt.%. The starting melt was formed by heating electrically conductive silicon carbide rods in a high frequency electromagnetic field. The CRT glass melt has low electric conductivity and high viscosity at temperatures of about 1200°C, which does not allow the required IMCC starting melt to be formed. Addition of up to 30 wt.% of surrogate RW salts to the batch increases the electric conductivity and reduces the viscosity of the melt to values that support IMCC. The batch is preferably fed as a calcine.