STUDY OF THE THERMAL BEHAVIOR OF HIGH-LEVEL WASTES USING THE LASER DRIVEN THERMAL REACTOR

High-level wastes (HLW) consist of multiphase and multicompound substances of which there is a dearth of information on their thermal behavior in a dynamic environment. A prime candidate technology for HLW treatment is thermal waste destruction, and vitrification for its disposal. The focus of this work was to study the thermal behavior, and develop an empirical model, of the thermal decomposition of an organic simulant HLW substance. Measurements were carried out using a laser driven thermal reactor (LDTR) at conditions representative of actual thermal treatment processes. The device provides reliable thermophysical and chemical kinetic data over a wide range of temperatures, heating rates, gas pressures, and environments. Unlike conventional thermal analysis techniques, which are designed to measure a selected thermal or chemical property in a nominally near-constant, equilibrium temperature environment, the LDTR measures an integrated thermal response. This integrated response represents the effects of multiple thermal and chemical properties in an environment characteristic of real-world reactors, where the temperatures are high, and rapidly changing. The LDTR was used as an off-line analytical device to characterize the thermal behavior of the organic high-level simulant waste PAS 94, under different thermal and physical conditions. The results showed a strong exothermic contribution of 2.9 kJ/g between 720 K and 870 K, which was virtually undetected in measurements obtained with a conventional differential scanning calorimeter. The thermal behavior of this waste was then used to develop a two-stage empirical model of the reaction kinetics. These data demonstrate the importance of heating rate and temperature on detection and characterization of HLW reactive behavior