The Oak Ridge National Laboratory is a world leader in molten salt reactor technology development, with researchers also focusing on fundamental science necessary to improve the efficiency of nuclear energy. In a recent study published in the Journal of the American Chemical Society, researchers documented the unique chemistry dynamics and structure of high-temperature liquid uranium trichloride salt, which could be a potential nuclear fuel source for next-generation reactors. This research is instrumental in creating predictive models that are critical for designing future reactors, enabling a better understanding of microscopic behaviors to develop better models.
Molten salt reactors have the potential to produce safe and affordable nuclear energy, with prototype experiments dating back to the 1960s demonstrating the technology’s viability. As countries worldwide prioritize decarbonization, efforts to make these nuclear reactors more widely available have been re-energized. Understanding the behavior of liquid fuel salts unique to these reactors is key for ideal system design, as they differ from conventional reactors that use solid uranium dioxide pellets. Research on these salts at the atomic level is challenging due to their high melting points, complex ion-ion coordination chemistry, and involvement of radioactive elements like the actinide series, to which uranium belongs.
A collaborative study involving Oak Ridge National Laboratory, Argonne National Laboratory, and the University of South Carolina utilized computational approaches and the Spallation Neutron Source (SNS) to investigate the chemical bonding and atomic dynamics of molten UCl3. The SNS is a bright neutron source that enables scientists to conduct state-of-the-art neutron scattering studies and reveal details about materials’ properties. By aiming a beam of neutrons at a sample and measuring their interactions with atomic nuclei, scientists can gain insights into a wide range of materials, from liquid crystals to superconducting ceramics.
Despite the demanding conditions, researchers conducted experiments with molten UCl3 at 900 degrees Celsius, measuring chemical bond lengths and observing surprising behavior as the substance transitioned to a liquid state. Bonds holding uranium and chlorine atoms together were found to shrink on average as the substance became liquid, contrary to expectations based on typical chemistry. The study also revealed complex dynamics that occurred at ultra-fast speeds within the liquid, with bonds oscillating in size and occasionally appearing more covalent instead of ionic. These findings shed light on the fundamental atomic structure of actinides under extreme conditions, offering new insights into the behavior of molten UCl3.
The research conducted at Oak Ridge National Laboratory contributes to improving both experimental and computational approaches to designing future reactors, potentially enhancing the efficiency and safety of nuclear energy production. In addition to advancing molten salt reactor technology, the study improves fundamental understanding of actinide salts, which could have applications in addressing challenges related to nuclear waste and pyroprocessing. The study was part of the DOE’s Molten Salts in Extreme Environments Energy Frontier Research Center, involving collaboration with several national laboratories and utilizing state-of-the-art facilities. The results have the potential to shape future developments in nuclear energy and materials science.