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Research Assistant Professor of Nuclear Engineering Ondrej Chvala studies molten salt reactors (MSRs) with an eye for the future and also through the lens of history.

Oak Ridge National Laboratory pioneered MSR technology in the 1950s, and in late 1960s ran the first MSR with significant power generation in the world—the Molten Salt Reactor Experiment—which proved that MSR is feasible.

The Joint Committee on Atomic Energy, a US congressional committee that operated from 1946 to 1977, had the sole responsibility for overseeing legislation on nuclear power in the country. As a result of their decisions, the lightwater reactor design has prevailed over other nuclear reactor designs, including MSRs.

Now, with aging and decommissioning of lightwater reactors, MSRs are poised to make a comeback.

Ondrej Chvala
Ondrej Chvala

Chvala says that the effort to decarbonize energy production means that nuclear production needs to increase globally by roughly a factor of 100 to meet rising energy needs. Over the past five years, about 11,000 additional people a week have been connected to electricity.

This new clean energy needs to be competitive with fossil fuels without subsidies, since the developing world cannot afford to overpay for energy. Chvala believes that MSRs should play a role in providing this much-needed power.

MSRs, which use molten salt as liquid fuel and coolant, could be a major contributor to the nuclear energy sector with benefits including safety, efficiency, and flexibility in fuels and applications. However, Chvala says, there are still problems to solve and barriers to overcome.

“One of the barriers is the lack of knowledge of these systems because they are not taught in curriculum,” said Chvala. “The most powerful MSR that operated for the longest was quite a while ago, and one issue that nuclear power has, especially in the Western markets, is it is not competitive with fossil fuels. People have reasons to think that MSRs will be cheaper and more effective than coal; however, we do not know until we can build not just one but a whole fleet of reactors. Long-term experience will be necessary to judge economic competitiveness of any new reactor technology.”

The chemical stability of molten salts results in a large range of liquid temperature, between 700 and 1700 K (800–2600 F) at atmospheric pressure. This allows for thinner walls of pipes and other components of the reactor loops, improving operational safety and reducing cost.

Chvala says the liquid nature of the fuel presents advantages for safeguards.

“In MSRs, the fuel is homogenized as it is pumped around the primary circuit,” he said. “So if you take a tiny sample of the fuel, it is representative of the entire core; this is impossible in solid fuel systems.”

MSRs can be fueled with comparative ease using nuclear waste from weapons and other reactors due to liquid nature of the fuel, which simplifies fuel manufacturing and burning the fuel up over time. And with higher operating temperatures, MSRs can utilize air cooling efficiently, so reactors do not need to be located near a large body of water like coal plants or lightwater reactors.

Overall, the relative simplicity of their design and operation makes MSRs a potentially cost-effective resource for meeting the world’s growing energy demand.


David Goddard, (865-974-0683​, david.goddard@utk.edu)