NPRE researchers to examine molten salt properties for MSR development

Molten salt reactors (MSRs) offer an exciting advancement in nuclear energy technologies and at least a half dozen startup firms are pursuing the development. But questions remain about how the material’s properties affect performance in a nuclear reactor. Yang Zhang and Brent Heuser, professors of Nuclear, Plasma, and Radiological Engineering in The Grainger College of Engineering, hope to gain understanding. Recently, they were awarded a three-year, $800,000 contract from

the Department of Energy’s Nuclear Energy University Program to conduct a study. Zhang and Heuser will collaborate with Melissa Rose, a nuclear engineer at Argonne National Laboratory, whose current focus is measuring molten salt properties for reactor applications.

At least six companies – Terrestrial Energy, Moltex Energy, ThorCon Power, TerraPower, Flibe Energy, and Transatomic Power Corp. – have proposed MSR designs. However, current science cannot accurately predict molten salt’s varying melting points, heat capacity, free energy for potential corrosion reactions, solubility of fission and corrosion products, or effect of tritium, a fuel used in the reactors. This knowledge gap poses a major roadblock in the development and commercialization of MSRs.

Zhang, Heuser and Rose will examine the thermodynamic, structural and dynamic properties of molten salts at the atomic and electronic scale. To achieve understanding, the scientists will use molecular dynamics simulations driven by machine-learned, high-dimensional neural network potentials, combined with neutron/X-ray scattering and thermodynamic experimental validations.

At this point, no MSRs operate commercially. In the late 60s in the US, development of MSR and fast reactor technology was put aside in favor of developing light water reactors (LWRs).

According to the World Nuclear Association, MSRs hold some advantages over LWRs:

• Using molten fluoride salts as a primary coolant, MSRs operate at low, atmospheric pressure. Conversely, operating under high pressure, LWRs are more susceptible to releasing radioactive material should an accident occur.
• MSRs operate in a liquid form with molten salts, and cannot melt down. A rupture in a pipe or containment vessel would result in the salts solidifying, with radioactive elements remaining inert.
• If an MSR creates too much heat, the molten salts expand into the surrounding pipes. In such a case, the chain reactions are reduced and the heat levels fall.
• MSRs can run on thorium, making it unsuitable for weapons use and therefore possessing non-proliferation characteristics. 

Another advantage that MSRs could have over LWRs is a greater potential for load-following capability, or the ability to lower the nuclear reactors’ output during times of reduced electricity demand. Heuser is working on that issue with NPRE faculty Kathryn Huff, Tomasz Kozlowski, Caleb Brooks and Jim Stubbins in a study the DOE Advanced Research Projects Agency-Energy (ARPA-E) has funded (see previous story).

 

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