Focusing Down to an Atomic View of Molten Salts in Extreme Environments: Improving Clarity Through Collaboration
With the last eight years having the hottest recorded global temperatures in history, rising global energy consumption has flashed a warning sign that is driving world leaders to invest in developing solutions for sustainable energy generation. Despite some skepticism among members of the public, nuclear energy is a reliable source of clean electricity that advocates say will play a pivotal role in the planet’s transition away from using fossil fuels such as coal or natural gas for electricity generation. While some renewable energies like wind and solar can only generate electricity when the wind is blowing or the sun is shining, nuclear energy can provide continuous reliable electricity. Nuclear energy is typically generated by nuclear fission, where one atom is split into two smaller atoms and some additional neutrons. This process releases massive amounts of heat that can be converted to electricity by boiling water into steam to turn turbine generators, similar to how a steam locomotive train burns wood or coal to create steam that turns its wheels.
Most of the world’s currently running nuclear reactors use water as a coolant, but they consequently have associated risks of coolant loss accidents, like the one the world witnessed at Fukushima, Japan. A new class of alternative nuclear reactor designs, dubbed “Generation IV”, are being designed by commercial and government researchers to have key advancements in safety, environmental sustainability, and efficiency. Some of these designs completely replace water as the coolant, such as the class of molten salt reactors (MSRs). The Molten Salts in Extreme Environments (MSEE) EFRC, a consortium of universities and national laboratories, studies the physical behavior of molten salts on the atomistic level to understand how actinides and fission products are dissolved in molten salt, and how these salt systems corrode metals and metal alloys (like steel) that are commonly used in nuclear reactor construction. Their ambitious fundamental research program aims at understanding how the structure of a corroding interface in the presence of molten salt changes with time. To meet the research challenges, MSEE continues to develop strategic partnerships essential for advancing progress through teamwork, including adding two new university partners to enable multi-scale simulations and high-throughput experiments.
University partnerships have been essential for developing a fundamental understanding of atomic structures found in various molten salts. To help the scientific community get a better overview of molten salts in general, MSEE researchers from Oak Ridge National Laboratory and the University of Iowa worked to develop a “brief guide to molten salt structure.”1 Further investigations have yielded methods for determining not only the structure of the molten salt, but also the dynamics and coordination environments of the metal ions dissolved in the salt (uranium and the fission and corrosion products), which are essential to understand for reliable and durable reactor operation.2 The chemical effects of radiation are also considered. For example, these effects could cause metal particles to form in the molten salt, which also need to be controlled.3
With a focus on multi-institutional projects with interdisciplinary collaboration, MSEE has succeeded in bringing scientists together to form a holistic picture of molten salts that would otherwise be unattainable through individual efforts. For example, researchers from Stony Brook University and the University of Tennessee worked extensively with collaborators at Brookhaven, Oak Ridge, and Idaho National laboratories on new methods for measuring early and late stages of molten salt corrosion, capitalizing on their experience with multiple experimental techniques.4 These developments were recently used to investigate the real-time production of microscopic pores in Ni-Cr metal alloys due to corrosion.5 In addition to a more thorough examination of the data, critical partnerships like these give the scientific community a fundamentally new perspective at the frontiers of molten salt chemistry.
Capitalizing on diverse perspectives from academic researchers and staff scientists across the nation, the MSEE EFRC has been a leader in developing methodologies centered around cross-validation, increasing confidence in scientific results. With some experiments having conflicting design requirements and some salts having melting temperatures upward of 800℃, it is imperative that researchers collaborate to test the validity of customized sample enclosures. For example, Brookhaven and Idaho National Laboratories worked with researchers from the University of Notre Dame to design a multi-purpose sample cell with a built-in furnace, which enabled re-use in several different types of experimental techniques.6 In contrast, cutting-edge techniques that are newly developed can require specialized sample enclosures with an even greater need for cross-validation. MSEE researchers at the University of Tennessee and Oak Ridge National Laboratory demonstrated this by publishing their designs for a customized cell for neutron reflectometry, a technique that can measure the atomic structure of molten salts near a solid interface.7 With new guidance from the U.S. DOE on open-sourcing taxpayer-funded research, key advancements like these will be disseminated to benefit and be validated by the greater scientific community.
The MSEE EFRC’s facilitated collaborations have led to the development of new technologies and innovations that have helped to “unblur” the current understanding of the atomic structure of molten salts in both the bulk and at interfaces. This newfound clarity through collaboration has accelerated the discovery process for the next generation of energy scientists and engineers to follow.
1. Sharma, S.; Ivanov, A. S.; Margulis, C. J., A Brief Guide to the Structure of High-Temperature Molten Salts and Key Aspects Making Them Different from Their Low-Temperature Relatives, the Ionic Liquids. The Journal of Physical Chemistry B 2021, 125 (24), 6359-6372, doi:10.1021/acs.jpcb.1c01065.
2. Roy, S.; Liu, Y.; Topsakal, M.; Dias, E.; Gakhar, R.; Phillips, W. C.; Wishart, J. F.; Leshchev, D.; Halstenberg, P.; Dai, S.; Gill, S. K.; Frenkel, A. I.; Bryantsev, V. S., A Holistic Approach for Elucidating Local Structure, Dynamics, and Speciation in Molten Salts with High Structural Disorder. Journal of the American Chemical Society 2021, 143 (37), 15298-15308, doi:10.1021/jacs.1c06742.
3. Ramos-Ballesteros, A.; Gakhar, R.; Woods, M. E.; Horne, G. P.; Iwamatsu, K.; Wishart, J. F.; Pimblott, S. M.; Laverne, J. A., Radiation-Induced Long-Lived Transients and Metal Particle Formation in Solid KCl–MgCl2 Mixtures. The Journal of Physical Chemistry C 2022, 126 (23), 9820-9830, doi:10.1021/acs.jpcc.2c01725.
4. Bawane, K.; Liu, X.; Gakhar, R.; Woods, M.; Ge, M.; Xiao, X.; Lee, W.-K.; Halstenberg, P.; Dai, S.; Mahurin, S.; Pimblott, S. M.; Wishart, J. F.; Chen-Wiegart, Y.-C. K.; He, L., Visualizing time-dependent microstructural and chemical evolution during molten salt corrosion of Ni-20Cr model alloy using correlative quasi in situ TEM and in situ synchrotron X-ray nano-tomography. Corrosion Science 2022, 195, 109962, doi:10.1016/j.corsci.2021.109962.
5. Yu, L.-C.; Clark, C.; Liu, X.; Ronne, A.; Layne, B.; Halstenberg, P.; Camino, F.; Nykypanchuk, D.; Zhong, H.; Ge, M.; Lee, W.-K.; Ghose, S.; Dai, S.; Xiao, X.; Wishart, J. F.; Chen-Wiegart, Y.-c. K., Evolution of micro-pores in Ni–Cr alloys via molten salt dealloying. Scientific Reports 2022, 12 (1), 20785, doi:10.1038/s41598-022-20286-5.
6. Phillips, W. C.; Gakhar, R.; Horne, G. P.; Layne, B.; Iwamatsu, K.; Ramos-Ballesteros, A.; Shaltry, M. R.; LaVerne, J. A.; Pimblott, S. M.; Wishart, J. F., Design and performance of high-temperature furnace and cell holder for in situ spectroscopic, electrochemical, and radiolytic investigations of molten salts. Rev Sci Instrum 2020, 91 (8), 083105, doi:10.1063/1.5140463.
7. Browning, J. F.; Seo, J.; Wenzel, J. F.; Veith, G. M.; Doucet, M.; Ivanov, A. S.; Halstenberg, P.; Lynn, G.; Dai, S., A high temperature cell for investigating interfacial structure on the molecular scale in molten salt/alloy systems. Review of Scientific Instruments 2021, 92 (12), 123903, doi:10.1063/5.0065860.
The Molten Salts in Extreme Environments (MSEE) Energy Frontier Research Center is funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences).