Impact of High-Temperature Heat Treatment on Pyroprocessing of LWR Spent Nuclear Fuel: A Thermodynamic and Material Flow Analysis

This study presents a systematic thermodynamic evaluation of pre-treatment strategies in the pyroprocessing of light water reactor spent nuclear fuel, with particular emphasis on the selective volatilization of fission products under controlled high-temperature atmospheres. Thermodynamic equilibrium calculations combined with material flow analysis demonstrate that the composition and distribution of fission products can be effectively tailored by adjusting the processing atmosphere, enabling selective removal of volatile species such as Cs, I, Te, Se, and Tc. Under the conditions considered, this selective removal results in significant reductions in radioactivity and decay heat in molten salt during oxide reduction. The resulting changes in molten salt composition also influence Li 2 O solubility and anode behavior. In particular, the absence of Cs in the heat-treated case increases Li 2 O solubility due to Sr and Ba accumulation, while dissolved Te and Se are predicted to react with Pt anodes, indicating thermodynamically favorable compound formation and possible anode degradation, whereas no direct thermodynamically favorable reactions with C anodes are predicted. This study provides the first integrated thermodynamic and material flow-based comparison of pre-treatment strategies, quantitatively linking volatile fission product removal to molten salt chemistry, oxide reduction behavior, and anode stability.