INTERMEDIATE LEVEL BURNABLE WASTE VITRIFICATION IN A REFRACTORY FREE FURNACE USING OXYGEN PLASMA

A new and simplified equipment, using thermal oxygen plasma with water cooled walls, is actually being developed at the Valrho-Marcoule nuclear center (France). The reactor mainly consists of a cylinder, a roof and a crucible, all made of stainless steel with a water jacket system. A transferred arc plasma system has been preferred to a non-transferred one due to several reasons: the thermal transfer from the arc to the melt is better, the flowrate of plasma forming gas is lower and consequently, the size of the off-gas treatment equipment is smaller. To avoid classical problems induced by a bottom electrode, an oxygen plasma system design with the arc striked between two electrodes has been developped. The DC arc is transferred between two plasma torches above the glass melt which trap the mineral elements. The waste to vitrify is fed between the two electrodes, inside the arc zone so that temperature and turbulence between the two arc column s are higher than near a non-transferred plasma jet and the chemical reactions are enhanced by arc UV radiation. The plasma gas is oxygen, in order to achieve a perfect combustion on the surface. As it will be shown, control in situ and in real time of the volatility of elements during plasma treatment is feasible. For this purpose, a new Optical Emission Spectroscopy method to probe metallic vapors above the melt has been experimented. It allows the measurement of the volatility of some elements according to the running parameters. The evolution of cesium leaving the melt is presented for exemple versus time and as a function of several treatment atmospheres