Coordination-driven mixing behavior of corrosion and fission products in NaCl-UCl₃ molten salt

Molten salts play a crucial role in Generation IV nuclear energy technology, with chloride salts like NaCl-UCl₃ garnering significant attention due to their distinctive properties and potential applications in fast-spectrum molten salt reactors (MSRs). The corrosive nature of molten salts can cause the dissolution of structural materials, leading to the formation of new species in molten chlorides. In addition, the radioactive decay of nuclear fuels results in the accumulation of fission products in the salts. Understanding the behavior of these corrosion and fission products and their impacts on the properties of molten salts is critical for the design of MSRs. This paper presents a systematic study on the properties of eutectic NaCl-UCl₃ molten salt in the presence of corrosion products (CrCl₂ and CrCl₃) and fission products (CsCl and SrCl₂) utilizing ab initio molecular dynamics (AIMD) simulations. We focus on essential structural and thermophysical properties such as density, mixing energy, coordination numbers (CN), and Radial Distribution Functions (RDF) with varying compositions of these corrosion and fission products from 0 % to 15.8 %. It is found that the mixing behavior of these corrosion and fission products is strongly driven by their coordination chemistry in eutectic NaCl-UCl₃. Both CrCl₂ and SrCl₂ have identical coordination to eutectic NaCl-UCl₃, thus exhibit negative mixing energies at a lower concentration. In contrast, CsCl exhibits significant different coordination compared to NaCl-UCl₃, resulting to positive mixing energies. Our results offer valuable insights into the coordination chemistry and mixing behavior of corrosion and fission products in chloride molten salts and provide essential data that can be used as input to property databases to supplement experimental data.