Optical Emission Spectroscopy Measurements and Simulation of Radioelement Volatility During Radioactive Waste Treatment by Plasma

An optical emission spectroscopy (OES) method has been used to measure the concentration above the melt of some radioelements, ¹³⁷Cs, ⁶⁰Co and ¹⁰⁶Ru during the vitrification of radioactive wastes by thermal plasma. This method allows the study of non homogeneous optically thin plasmas exhibiting a symmetry plane without sophisticated tomographic systems. Local plasma temperatures above the melt have been evaluated using measured relative intensities of spectral lines of the plasma-forming gas. Radioelement concentrations in the plasma are deduced from the intensity ratio of the radioelement–gas spectral lines. A computer model is used to simulate the volatility of ¹³⁷Cs, ⁶⁰Co and ¹⁰⁶Ru, during the treatment of radioactive wastes by thermal plasma. This model is based on the calculation of system composition using the free enthalpy minimization method, coupled with the equation of mass transfer at the reactional interface. In this study, the OES measurements and the computer model allowed the determination of this radioelement volatility depending on the parameters like plasma current, and the nature of atmosphere furnace. The results of the model are compared to those obtained by OES measurements.