Breakthrough: US finds key salt-based fuel chemistry for next-gen nuclear reactors

Oak Ridge National Laboratory (ORNL) scientists seem to have cracked the code of a potential fuel source for the next generation of nuclear reactors by documenting the unique chemical dynamics and structure of high-temperature liquid uranium trichloride (UCl3) salt.

This is the first time in the world that such research has been conducted on UCl3, a potential fuel source for advanced molten salt reactors. This breakthrough aims to detail how atoms move in the molten salt.

“This is a first critical step in enabling good predictive models for the design of future reactors,” said Santanu Roy, who co-led the study at ORNL. “A better ability to predict and calculate the microscopic behaviors is critical to design, and reliable data help develop better models.”

Notably, molten salt reactors, which have been under research since the 1960s, offer numerous advantages over traditional nuclear reactors. They are considered inherently safer and more efficient and produce less radioactive waste.

As the world grapples with the challenges of climate change and the need for clean energy sources, molten salt reactors are gaining renewed attention as a potential solution.

Unexpected findings

Contrary to the typical expectation that heat causes expansion, the uranium-chlorine bonds within the molten UCl3 actually contract. This unexpected behavior challenges conventional notions and underscores the unique properties of actinide elements, such as uranium, at high temperatures.

“Ideal system design for these future reactors relies on an understanding of the behavior of the liquid fuel salts that distinguish them from typical nuclear reactors that use solid uranium dioxide pellets,” underscored the scientists in a press release .

Furthermore, the bonds within the liquid salt exhibit a dynamic oscillation, fluctuating between remarkably short and surprisingly long lengths.

“After rigorous safety precautions and special containment developed in coordination with SNS beamline scientists, the team was able to do something no one has done before: measure the chemical bond lengths of molten UCl3 and witness its surprising behavior as it reached the molten state,” explained the press release.

This atomic-level choreography provides crucial insights into the complex interactions occurring within the molten fuel.

The scientists discovered the brief appearance of covalent bonding within the UCl3. At its tightest bond length, the typically ionic bond transforms into a covalent one, albeit fleetingly. This cyclical behavior offers an explanation for certain inconsistencies observed in previous studies.

Neutron scattering studies

To delve into the atomic mysteries of molten UCl3, the research team employed a combination of cutting-edge computational approaches and the Spallation Neutron Source (SNS) at ORNL.

“The SNS is one of the brightest neutron sources in the world, and it allows scientists to perform state-of-the-art neutron scattering studies, which reveal details about the positions, motions and magnetic properties of materials,” highlighted the press release.

By bombarding a sample with a neutron beam and analyzing the scattered neutrons, scientists can glean detailed information about the material’s atomic structure and dynamics.

For reference, this technique, known as neutron scattering, has revolutionized materials research across various fields, from pharmaceuticals to superconductors.

Beyond nuclear energy

The knowledge gained from this research has far-reaching implications for the future of nuclear energy.

With a deeper understanding of the behavior of nuclear fuel salts, scientists can now develop more accurate predictive models and designs for advanced reactors.

The implications of this research extend beyond nuclear energy. The insights into the fundamental behavior of actinide salts could also aid in tackling challenges in nuclear waste management and pyroprocessing, a technique used to recycle spent nuclear fuel.