Revisiting Molten Salt Reactors

Molten-salt reactors could potentially provide carbon-free nuclear power with less radioactive waste and for a more affordable price. But the technology is not without its complications.

One of the starkest drawbacks to nuclear energy is radioactive waste. Molten-salt reactors (MSRs), a class of next-generation nuclear technologies, may offer a route to provide power more sustainably and with less waste than traditional reactors. As it stands, MSRs face considerable development challenges, but there is growing interest from investors to find innovative solutions. Recently, the Department of Energy granted $36 million to various institutions for research in curbing waste specifically from advanced nuclear reactors. Moreover, the past decade has seen a flurry of accelerations, from MSR development by China to the emergence of Bill Gates’ TerraPower corporation.

Physicists suggested that MSRs might be hypothetically feasible soon after the harnessing of nuclear power, with subsequent research undertaken primarily by Oak Ridge National Laboratory. The project ran into technical difficulties and since other reactor designs were successful, research was largely halted after a decade. The technology differs from a traditional, light-water reactor (LWR) by stimulating the nuclear reactions within a pool of molten salt, as the name suggests. This medium, which can be as commonplace as normal table salt, allows for the reaction to take place at very low pressures, unlike LWRs. By operating just over atmospheric pressure, MSRs would substantially reduce the risk of meltdown often caused by breaches in system pressure. With lower demands on pressure control and meltdown mitigation, MSRs are garnering hype as affordable nuclear, unlike conventional nuclear plants with price tags in the billions.

For all the excitement surrounding MSRs, there remain real challenges that need to be addressed. In discussions surrounding nuclear power, a common concern expressed is about the release of contaminants into the environment. While studies have shown that MSRs can be useful in facilitating reactions that produce less overall waste, they also create far higher levels of certain radioisotopes that are much trickier to contain than in an LWR. Xenon-137, in particular, is bred in far greater quantities than in LWRs and because xenon is chemically inert, it is difficult to capture, an undesirable attribute for radioactive material. Furthermore, one of the key fail-safes incorporated into MSR designs are small “freeze-plugs” on the bottom of the reactor pool that are meant to melt should the salt get too hot. The fluid would then fall into a secure chamber where the reaction would be interrupted automatically to prevent infrastructural damage. The catch is that no such plugs that would fully guarantee this result have been demonstrated to be adequately reliable. Without self-regulating freeze-plugs, MSRs may actually be quite dangerous. But with them, MSRs could revolutionize nuclear safety.

Despite those hurdles, the key policy takeaway should not be to shy away from MSRs, but to seriously invest in research and development to surmount challenges under strict safety standards. Oak Ridge concluded its MSR program over fifty years ago but since then, our technological capabilities and need for low-carbon energy have multiplied. Although the implementation of MSR power plants may yet be decades away, as our society undergoes a broad electrification to achieve carbon reduction goals, demands for robust, reliable energy will only increase. Offering to operate with lower costs, commercial MSRs could meaningfully democratize nuclear power, all the while curtailing waste. MSRs are not yet technically viable and may never be if scientists cannot figure out how to resolve such issues as freeze-plug design and xenon capture. These obstacles demand concerted attention and aggressive funding from the public and private sectors to give this reemerging nuclear pathway the chance to prove its worth and supercharge our future.

This insight is a part of our Undergraduate Seminar Fellows’ Student Blog Series. Learn more about the Undergraduate Climate and Energy Seminar.

Eitan Weinstein

Undergraduate Seminar Fellow
Eitan Weinstein is an undergraduate student in the College of Arts and Sciences majoring in physics. Weinstein is also a 2022 Undergraduate Student Fellow.