Pyroprocessing and Electrochemical Reprocessing for Advanced Reactor Fuel Cycles: Optimizing Electrochemical Separation and Waste Form Performance

The global imperative to achieve net-zero carbon emissions by mid-century has renewed interest in nuclear energy as a firm, dispatchable, low-carbon power source, yet the expansion of the world's reactor fleet intensifies the long-standing challenge of managing spent nuclear fuel. With global inventories exceeding 400,000 metric tons of heavy metal and no permanent disposal pathway operational in the United States, the nuclear enterprise confronts a paradox: spent fuel is simultaneously one of civilization's most hazardous waste streams and one of its most concentrated energy resources. Pyroprocessing, an electrochemical reprocessing technology conducted in molten LiCl-KCl eutectic salt at approximately 500°C, offers a pathway to closed fuel cycles for sodium-cooled fast reactors by recovering actinides as a group product with inherent proliferation resistance. However, advancing pyroprocessing from laboratory demonstration to commercial deployment requires answers to interconnected technical, economic, and safeguards questions that cannot be addressed by experiments alone. This dissertation develops, validates, and applies an integrated multiscale computational framework coupling five domains: neutronics and depletion analysis (MCNP6, Serpent 2, ORIGEN), molecular dynamics simulation of molten salt transport properties (LAMMPS), continuum-scale electrochemical process modeling (MOOSE framework), reactive transport modeling of waste form degradation (PHREEQC), and fuel cycle systems analysis (Cyclus). Depletion benchmarking against SFCOMPO post-irradiation examination data yields calculated-to-experimental ratios within ±5% for major actinides, with a systematic U-235 underprediction bias of approximately 4.5%. Molecular dynamics simulations produce actinide diffusion coefficients on the order of 10⁻⁵ cm²/s, validated against experimental electrochemical measurements. Electrorefiner modeling confirms a 0.310 V uranium-plutonium separation window sufficient for selective uranium recovery at greater than 99% purity and greater than 95% recovery, consistent with demonstrated Mark-IV and Mark-V electrorefiner performance. Waste form assessment reveals the ceramic waste form to be 15.2 times more durable than the Environmental Assessment glass benchmark, while the metal waste form demonstrates exceptional technetium retention. Fuel cycle economic analysis indicates a 4.5-fold cost premium for pyroprocessing relative to aqueous reprocessing at current technology readiness levels. Most critically, safeguards analysis identifies a 10-50-fold gap between current nondestructive assay measurement uncertainties and International Atomic Energy Agency detection goals, establishing safeguards technology as the primary barrier to commercial deployment. These findings demonstrate that pyroprocessing is technically feasible but that safeguards measurement capability and economic competitiveness constitute the decisive barriers; integrated computational frameworks of the type developed herein can accelerate technology maturation by enabling virtual prototyping, informing regulatory assessment, and prioritizing experimental investment.