Experimental Investigation and Numerical Modeling of a Joule-Heated Ceramic Melter for Vitrification of Radioactive Waste

Abstract

Radioactive liquid waste generated in the closed nuclear fuel cycle is immobilized by fixing the radionuclides in glass by a process known as vitrification. Vitrification is carried out in a joule-heated ceramic melter (JHCM) by passing alternate current in glass melt using electrodes. Silicon carbide resistance heaters are employed to bring the temperature of the glass to the conducting zone. Experiments were carried out on an industrial scale JHCM. Processing capacities were determined for glass melt having a composition of SiO2 (48%), B2O3 (26.3%), Na2O (11.7%), TiO2 (9.5%), and Fe2O3 (4.5%) for simulated waste with different salt concentrations. The product formed from these trials is qualified for long-term durability based on the study. The energy distribution in an industrial scale JHCM for different salt concentrations, namely, 28 and 56 g/L of simulated waste is calculated based on the experiments conducted. This study also focuses on mathematical modeling of an all-electric glass furnace used for conditioning of hazardous radioactive waste. In this work, a numerical model of the glass furnace was developed and heat flow patterns in a JHCM were studied using finite element analysis. The numerical model is then used to predict the temperature profiles for different stages of the JHCM operation. The temperature profiles predicted by the model are validated using experimental results. The developed model is used for size reduction of the JHCM by decreasing the plenum heating section, thereby facilitating easier decommissioning. A novel method for estimating the effective thermal conductivity of the glass melt based on the experiments and simulations is discussed.