Research Overview
The center for Molten Salts in Extreme Environments (MSEE) is building a fundamental and predictive understanding of molten salt bulk and interfacial chemistry, including the effects of solutes and impurities, inspired by the need to strengthen molten salt science underlying the development of molten salt reactors (MSRs) for next generation nuclear power. MSEE is also investigating the effects of ionizing radiation on molten salt chemistry since MSR materials will encounter significant radiation exposure in operation. MSEE brings to bear a wide array of advanced experimental and computational tools and methods that enable unprecedented understanding of fluids and interfaces on the atomic scale.
MSEE coordinates the efforts of three national labs (Brookhaven National Laboratory, Oak Ridge National Laboratory and Idaho National Laboratory) having unique expertise and capabilities in experimental and theoretical research on molten salts, interfacial structure and corrosion, radiation chemistry, and interactions with actinide fuels, with principal investigators at six universities: University of Iowa, University of Michigan, University of Notre Dame, Stony Brook University, The University of Tennessee at Knoxville, and the University of Wisconsin at Madison. The university investigators bring key expertise in molecular and phase field modeling, radiation chemistry, synchrotron imaging methods, and electrochemistry applied to molten salts. Central to the efforts, MSEE benefits from unique capabilities at DOE synchrotron, neutron, nanoscience and nuclear facilities, with the overarching goal to transform our understanding of the fundamental basis of molten salt behavior and interactions using 21st century tools.
Science Challenges for Molten Salt Applications in Molten Salt Reactors
MSEE research is guided by objectives to advance the fundamental understanding of complex molten salt systems that will be a scientific foundation to guide the design and application of molten salt reactors (MSRs).
- Molten salt structural heterogeneity is important, and it is critical to understand its role in the speciation, solvation and transport properties, which are relevant to behavior in MSRs, especially for salts containing actinides and lanthanides.
- The solubilities and oxidation states of species dissolved in molten salt must be managed, to ensure stable MSR operation over wide ranges of composition, temperature and radiation flux, including speciation, solubilities and chemical reactivities of actinides and fission and corrosion products in molten salts.
- Interfacial behavior of molten salts with MSR reactor materials must be understood to limit corrosion and inhibit processes that compromise material integrity. Understanding the fundamental chemical and physical processes that occur at interfaces is critical to better understand and mitigate corrosion and materials failure.
- Ionizing radiation in an MSR environment affects each of these issues, including solute speciation, particle nucleation, and material corrosion.
MSEE Research Objectives
To address these scientific challenges underlying the application of molten salts in MSR environments, MSEE is pursuing the following objectives with broad impact:
- Understand the behavior of corrosion and fission products in molten salts. MSEE is elucidating the structure, dynamics and thermodynamic properties for metal ion solvation and their impact on speciation, heat capacity, basicity, and redox potential. MSEE is developing an atomistic view of the multiple coexisting coordination states of metals, the role of multivalent metal networks and the lower-charge spacer solvent salt. The objective includes the properties of actinide and lanthanide containing salts.
- Build a multiscale mechanistic understanding of salt-material interfaces. MSEE scientists are revealing the structural dynamics of the salt ions at interfaces on the atomic scale as well as the kinetics governing the chemical reaction and morphological evolution at interfaces from mesoscale to continuum level. The multimodal research framework is integrating synchrotron and electron characterization with multiscale simulation methods to understand complex interfacial phenomena.
- Understand the impacts of ionizing radiation. MSEE is advancing the understanding of ionizing radiation effects on the physical and chemical properties of molten salts and developing multiscale models to predict ionizing-radiation-induced processes in solution and at interfaces over multiple time and length scales. MSEE is leveraging this understanding to investigate reactivity in molten salts such as radiation-driven chemistry and corrosion.
Research Funding Progress
Research Progress in Current Funding Period, 2022-2026
Guided by these objectives, during its second funded cycle since 2022, MSEE has advanced experimental, computational, and artificial intelligence (AI)-driven capabilities to probe the fundamental nature of molten salt mixtures and metal-salt interfaces. These efforts have led to major advances in our understanding of molten salt behavior, particularly:
- Bulk molten salts: how molten salt composition determines structure and physical properties, including the speciation and redox behavior of solute metal ions and radiation-induced transient species;
- Molten salt interfaces: the mechanisms driving metal-salt interfacial evolution, including impurity- and redox-controlled corrosion pathways and coupled transport-reaction processes that govern chemical and microstructural transformations in molten salt environments.
- Studies of actinides in molten salts: While expanding its existing computational efforts in actinide molten salt chemistry, MSEE is establishing research capabilities in radiation chemistry and synchrotron science for the direct study of nuclear fuel materials and fission products in molten salts, which is important for MSR designs with fuel dissolved in molten salts to enable novel, efficient fuel cycles that can reduce the amount and hazard of spent nuclear fuel handling.
Read our science highlights to learn more about recent research progress in bulk and interfacial molten salt chemistry.
Research Progress in First Funding Period, 2018-2022
In its initial research period (2018-2022), MSEE set objectives to understand the structure and dynamics of molten salts and solutes on the atomic scale by developing state-of-the-art experimental methods and advancing theory and computation for accurate prediction of key model systems, both in bulk solutions and at interfaces.
Molten salt solutions: MSEE combined expertise in synchrotron and neutron scattering experiments, Raman spectroscopy, computational simulations, machine learning and thermodynamic predictions to probe both bulk structure and local solute-induced structure and chemistry and link atomic level structure and chemistry to bulk properties and behavior, and to advance atomic-level descriptions of characterization methods such as X-ray and Raman spectra. Broadly, MSEE illustrated that molten salts are dynamic, with low barriers to interconversion of local structures, and that multiple coordination states contribute to X-ray absorption spectra, X-ray and neutron scattering patterns and to UV-Vis and Raman spectra. This contrasted with prior interpretations of a dominant metal ion coordination structure and revealed a complex reality of salt and solute structure, local dynamics, thermodynamics and transport.
Molten salt interfaces: MSEE also advanced understanding of molten salts at materials interfaces to predict the kinetics of interfacial reactions and corrosion processes. Scientists visualized the morphological evolution of metal-salt interfaces in real time via operando synchrotron X-ray nano-tomography and quasi-in situ TEM analysis. Scientists also revealed chemical distribution at interfaces and elucidated interfacial processes and radiolysis leading to corrosion.
Molten salts scientific tools: To enable the scientific advances, MSEE developed high-temperature in situ experimental capabilities to apply modern synchrotron X-ray scattering and spectroscopy, neutron scattering, electron microscopy, and radiation chemistry techniques to molten salts studies. Scientists developed multiscale microscopy combining X-ray and electron modalities to study interfaces and designed and implemented containment cells for advanced measurements on high-temperature molten salts, both for bulk and interfacial studies, including at X-ray and neutron beamlines. MSEE also advanced theoretical descriptions of molten salt structure and dynamics and validated computational results against extensive experimental results.
The research in the first funding period, including development of experimental methods for in situ studies of molten salts and validated methods for numerical simulations of molten salts properties from atomic-level descriptions, established a critical foundation for current research studies (2022-2026) of complex molten salt systems.
