Molten salt reactors and electrochemical reprocessing: synthesis and chemical durability of potential waste forms for metal and salt waste streams

Abstract

The molten salt reactor (MSR) is one of the leading advanced nuclear reactor candidates to replace current nuclear reactor technologies in the U.S. Besides having more economical and reliable designs, MSRs are amenable to a closed fuel cycle, in which electrochemical reprocessing can be performed to recycle the used nuclear fuel. This review intends to provide information about potential waste forms for metal and salt waste streams from these salt-based nuclear processes. Metal waste streams arise from reactor components and structural materials. Salt waste streams are generated during reactor operations as fission products build up in salt-fuelled systems. Waste forms that have the highest waste loading and/or have shown the most commercial promise are discussed with an emphasis on the current state of efforts to understand the synthesis and chemical durability of metal and ceramic waste forms.

Thermodynamic and Transport Properties of LiF and FLiBe Molten Salts with Deep Learning Potentials

“…1−3 The design of MSRs centralizes molten salts as fuels and heat carriers in the primary loop, providing inherent advantages over commercial technologies such as meltdown mitigation through passive cooling, negative temperature coefficients of reactivity, low operating pressures, increased operating temperatures for efficiency, and improved waste management. 4,5 However, as molten salts are required to satisfy a diverse number of nuclear, physical, and chemical criteria to operate effectively, knowledge on salt properties is essential for MSR design. 6,7 So far, thermodynamic and thermophysical databases for molten salts are limited by the difficulty of high temperature, toxicity, and corrosive experiments.…”

“…Molten salt reactors (MSRs) first appeared in the mid-20th century and have recently been accepted as candidate Gen IV reactors competing with the existing light water and boiling water reactors. − The design of MSRs centralizes molten salts as fuels and heat carriers in the primary loop, providing inherent advantages over commercial technologies such as meltdown mitigation through passive cooling, negative temperature coefficients of reactivity, low operating pressures, increased operating temperatures for efficiency, and improved waste management. , However, as molten salts are required to satisfy a diverse number of nuclear, physical, and chemical criteria to operate effectively, knowledge on salt properties is essential for MSR design. , So far, thermodynamic and thermophysical databases for molten salts are limited by the difficulty of high temperature, toxicity, and corrosive experiments. , Furthermore, the possible number of salt configurations, including single, binary, ternary, and more complex mixtures of compounds, with the consideration of impurities from chromium alloys and other particulates, further increases the design space of MSRs. This huge design space calls for the development of theoretical and/or computational methods to speed up the present bottlenecks in experimental methods.…”

Integrating the Safety Evaluation for a Molten Salt Reactor Operation and Fuel Cycle Facility Application

“…Known glasses with characteristics suitable for serving as waste forms cannot incorporate high loadings of halide atoms. Because waste volumes are the primary cost driver for geological repositories, multiple strategies have been proposed to provide higher used fuel salt loading into the waste form [84], [85]. Overall, the two general approaches for incorporating higher halogen loading in an adequately stable and durable waste form are to (1) encapsulate halogen salts as a crystalline phase within a robust matrix (e.g., waste glass or metal) or (2) strip the halogen atoms from the used fuel salt and replace them with O before creating the waste form.…”

Review—Fundamental Uranium Electrochemistry and Spectroscopy in Molten Salt Systems

“…4 MSRs can be split into two main categories: salt-cooled or salt-fueled/cooled reactors. 5 For salt-cooled MSRs, a solid TRISO (TRi-structural ISOtropic) fuel is cooled by a molten fluoride salt. 5 Salt-fueled/cooled MSRs have fuel and coolant salt, fluoride or chloride, in the same compartment, typically referred to as the "melting pot."…”

“…5 For salt-cooled MSRs, a solid TRISO (TRi-structural ISOtropic) fuel is cooled by a molten fluoride salt. 5 Salt-fueled/cooled MSRs have fuel and coolant salt, fluoride or chloride, in the same compartment, typically referred to as the "melting pot." For fluoride-based coolants, the FLiBe mixture is used, consisting of 2LiF-1BeF 2 .…”