SRNL Tests Technologies to Fuel Molten Salt Reactors and Reduce Existing Spent Nuclear Fuel Inventories
With plans to increase the number of research and commercial nuclear reactors across the next decade, dealing with spent nuclear fuel (SNF) will continue to be a challenge facing our nation. While SNF can be reprocessed, numerous separation steps are required to convert this material into a usable product. Scientists at the Savannah River National Laboratory (SRNL) have a project underway to test a new technology for processing existing commercial SNF for use in a different type of reactor known as a molten salt reactor (MSR). MSRs are gaining attention for their increased efficiency and reduced waste volumes compared to conventional reactors. SRNL Scientist Bryan Foley said, “SRNL is focused not only on advancing technologies related to MSR fuel fabrication, but also on how to remediate the waste that comes out of proposed MSR systems.”
The project seeks to chlorinate SNF from conventional light water reactors, thereby converting the SNF into a fuel that could be directly fed to an MSR without further purification or separation. The resulting chloride-based fuel would be less corrosive than alternative fluoride fuels, less costly than bromide-based fuels and the process does not separate elements that could pose a nuclear proliferation threat. In theory, SNF from any existing reactor could be converted into fuel for MSRs using a molten salt-based chlorination technique patented by Metatomic, Inc. SRNL is currently working with Metatomic, Inc. to perform proof-of-concept experiments assessing the viability of this molten salt- technique.
The Department of Energy (DOE) Gateway for Accelerated Innovation in Nuclear (GAIN) awarded a voucher for the research collaboration in 2023 and the project was divided into two phases. The primary goal of Phase 1 was to determine the feasibility of the Metatomic hydrochlorination process, assess the impact of various temperatures on the reaction and evaluate the applicability of existing analytical techniques for this process.
Prior to transfer into reaction crucibles, a mixture of the starting materials is pre-blended. Photo by Bryan Foley.
Observations made during Phase 1 experiments have shown the successful hydrochlorination of uranium dioxide within the furnace. Testing was conducted on a matrix salt, which is typically white in color. After reactions at various temperatures, the salt exhibited a distinct yellow color at lower test temperatures and green coloration at elevated temperatures. The change in color indicates a successful reaction of the uranium with hydrogen chloride.
Loaded crucibles in a process tube prior to insertion into the tube furnace. Photo by Bryan Foley.
Phase 2 will continue the collaboration to test a scaled-up version of the experiment in a custom-built, lab-scale reaction vessel . These proof-of-concept experiments could lead to a scalable technology that could broaden the options for processing the large mass of existing commercial SNF. If successful, both the emerging molten salt reactor community and the existing commercial nuclear industry sector could benefit from this new pathway for SNF processing, while supporting new sources of reliable and secure energy and the reduction of the existing SNF inventory around the US.
Solidified reaction mixtures after removal from the alumina crucibles. Photo by Bryan Foley.