INL Opens First US Facility for Measuring Molten Salt Reactor Fuel Properties
Molten salt reactors have been under development in various configurations for decades, and several companies are now pursuing commercial versions. The appeal is real: liquid fuel salts can operate at high temperatures without pressurization, enabling more efficient power conversion; they allow continuous fuel processing that reduces long-lived waste; and some designs can consume existing nuclear waste as fuel. The technical barriers are equally real, and one of the most fundamental is simply data. Before you can design, license, or operate a reactor cooled and fueled by molten salt, you need to know precisely how that salt behaves under the conditions it will actually experience - its heat capacity, density, thermal conductivity, and viscosity at high temperatures, and how irradiation from the reactor core changes those properties over time.
That data is difficult to generate. Molten fuel salts contain radioactive actinide elements, they operate at temperatures of several hundred degrees Celsius, and they react aggressively with moisture and oxygen. Standard laboratory equipment is not built for these conditions. The Molten Salt Thermophysical Examination Capability, or MSTEC, unveiled at Idaho National Laboratory in February 2026, is specifically designed for them.
What MSTEC Actually Is
MSTEC is a shielded argon glove box - a sealed enclosure filled with inert argon gas to exclude moisture and oxygen, with radiation shielding integrated into its construction. Inside this controlled environment, researchers can handle both irradiated and non-irradiated actinide materials in liquid form at the high temperatures relevant to reactor operation. The facility includes specialized measurement instruments for characterizing thermophysical properties, along with flexible laboratory space for small-scale experiments.
The shielding is not incidental. Working with irradiated materials - salts that have been exposed to reactor neutron flux and therefore contain fission products and activated isotopes - requires protection that standard chemistry laboratories do not provide. MSTEC allows these measurements to be made safely and systematically, generating the kind of reliable, reproducible data that reactor designers and licensing bodies need.
Brad Tomer, director of the National Reactor Innovation Center, described the capability as providing essential experimental infrastructure and expertise to industry partners who lack the facilities to perform this work themselves. For companies developing molten salt reactor concepts, access to MSTEC addresses a genuine bottleneck in the path from design concept to licensed plant.
Where MSTEC Fits in the Nuclear Development Chain
Reactor licensing in the United States requires demonstrating that the proposed design operates safely across its full range of operating conditions, including off-normal events and accidents. For molten salt reactors, this means understanding how the fuel salt's properties change with temperature, with irradiation dose, and with composition changes that occur as the reactor operates and fission products accumulate.
Without measured data on these properties, reactor models rest on extrapolation and assumption - which regulators cannot accept for safety analysis. MSTEC's role is to fill that data gap: providing measured thermophysical properties for specific salt compositions under conditions representative of actual reactor environments.
The location at INL is strategic. The laboratory operates the Neutron Radiography Reactor and the Advanced Test Reactor, which can irradiate salt samples to simulate the neutron environment inside a reactor. The Analytical Research Laboratories at INL provide isotopic and elemental analysis capabilities for characterizing what happens to the salt after irradiation. MSTEC connects these capabilities into a coherent experimental pipeline: irradiate the salt, then measure what changed.
Training the Next Generation
INL senior molten salt researcher Toni Karlsson identified another function of the facility beyond immediate research use: providing a training environment for the next generation of actinide scientists and fuel cycle researchers. The specialized skills required to work safely with high-temperature radioactive liquids are not taught in standard university programs, and the existing pool of researchers with hands-on molten salt experience is small. MSTEC creates a place where that expertise can be developed systematically, alongside the data generation it is primarily designed to support.
This workforce development dimension matters for the longer term. If commercial molten salt reactors reach deployment scale, the industry will need engineers and scientists who can operate, maintain, and continue developing these systems. Building that human capital now, as the technology matures, is considerably easier than trying to assemble it after the first commercial plants come online.
The facility is now accepting users from the Department of Energy, industry, and academia. Information is available at nric.inl.gov.