As humanity moved from wood to fossil fuels, it was an order of necessity. Humanity's possible move from fossil fuels to the advanced nuclear world would be an order of magnitude with the environment and efficiency in mind. In attempts to phase out fossil fuels and lean into greener energy, there are many moral, monetary, and ecological discrepancies, especially in the nuclear world. The need for nuclear reactors that are practical, economical, and sustainable to replace fossil fuels is what drives the revolutionary developments in the world of nuclear engineering. Scientists have been attempting to piece together this puzzle since the 1960s beginning at Oak Ridge where, for the first time, a molten salt reactor experiment was performed with salt acting as a fuel and coolant in a self-sustaining reaction. Now, with evolving technologies, interest is pouring into the subject of molten salt reactors. One piece of this puzzle is the SALT Research group at Berkeley.

SALT, or Reactor Safety and Inorganic Chemistry of Light Elements at High Temperature, is one of the many groups concerned with advanced nuclear reactors. One remarkable feature of the SALT research group is their current work with the advanced reactors known as molten salt reactors, or MSRs.

A researcher using a lead cave, wearing the classic blue UC Berkeley lab coat.
Photo by Jayden Chow

One graduate student of the SALT group is Sarah Heagy. Sarah grew up in the Pacific Northwest in places that had environmental concerns front and center, instilling ecocentric values from a young age. Sarah seeks to employ a mindset of “rather than how best can the environment serve me, how can I serve the environment,” which steered her towards her undergraduate studies in environmental engineering. Sarah is now working toward her M.S. in nuclear engineering, achieving environmental efforts by seemingly unconventional means. This environmental identity that Sarah aligns herself with has shifted to the nuclear world through the SALT research group, where she and the SALT group may have a tangible impact on the future.

The SALT lab team. Sarah is in the front row, second to the left.

“I mean it's everything, right? It's my future, it's your future, it's all of our futures at stake… now is as important a time as any to be working towards that goal of net-zero carbon… and trying to figure out a way to continue living as we like to with all our creature comforts… [and] supporting those things in a way that is sustainable for us… The SALT group and my individual research is a much smaller piece of that.”

Sarah’s individual research seeks to identify irradiated samples of salt and graphite, and she hopes to conduct experiments on preparing waste from MSRs to create lower level waste compared to what is produced by traditional reactors.

Sarah and a colleague identifying a sample.
Photo by Raluca Scarlat

The term MSR itself is an umbrella for the multitude of reactor designs that function either as molten salt cooled or powered. Broadly speaking, the more molten salt is used in these reactors, the less high-level waste will be produced. The MSR the SALT group is focusing on is the salt cooled Kairos Power reactor or the KP-FHR (Kairos Power fluoride salt-cooled High-temperature Reactors). The KP-FHR is fueled with TRISO fuel and cooled with “FLiBe.” TRISO fuel is TRi-structural ISOtropic particle fuel “made up of a uranium, carbon and oxygen fuel kernel..the size of a poppy seed.” FLiBe is the salt that cools this MSR (lithium fluoride and beryllium fluoride (2LiF-BeF₂)). This salt is then heated up to about 454°C and at this temperature, the salt behaves similarly to water.

FLiBE compound. Photo by Adam Lau

Molten salts behaving similarly to water in conductivity and viscosity at this temperature allow them to be substituted for water in a reactor core. This is just one of the MSRs advantages over traditional reactors, MSRs are also advantageous in safety, energy production, and in waste production.The increased safety and stability mean a decreased likelihood of a meltdown (Williams). Because the salts remain liquid, they cannot boil away, reducing the risk of a meltdown. These salts also operate at lower pressures, reducing the risk of a break and or a meltdown, and have a safety plug in place composed of frozen salt to drain the reactor in case of an emergency- ensuring a sustained reaction cannot occur.
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The advantage over fossil fuels comes in power production and higher thermal efficiency (Toth and Williams). Thermal efficiency is the amount of energy output with consideration to the amount of heat put in. Combustion reactors achieve 20 percent, conventional water-cooled reactors achieve 32 percent, and an MSR could achieve 45 percent (Toth). Concerning power production, Doctor Raluca Scarlat, a nuclear engineering professor at UC Berkeley spearheading the SALT group’s work, remarked on the KP-FHR’s TRISO fuels efficiency compared to traditional fuels: “the volume comparison would be a poppy seed to the campanile tower where the campanile would be petroleum or gas, the poppy seed would be the mined ore for uranium [in the TRISO fuel].”

Doctor Raluca Scarlet. Photo by Adam Lau

Another key concerns the waste and energy production as it relates to the carbon-free process. Less waste would be produced and this waste may be electrochemically separated. Electrochemical separation means that the non-naturally occurring elements and rare earth metals may be separated and the waste conditioned for geologic disposal (Toth and Williams). This decontamination is something that the SALT group and Sarah are actively working at in their lab.

The big picture benefits of the KP-FHR and MSRs are the shift from older nuclear reactor technology to newer, more advanced technology. This technology may be more practical, economical, safer, and more environmentally friendly when compared to fossil fuels’ efficiency and waste produced.

SALT is backed by large-scale funding from the Department of Energy (DOE) through government funds that are split into sub-tasks at different universities and national labs. The SALT group is one of many organizations under the DOE’s funding working to make molten salt technology a possibility. The SALT group is making leaps in this advancing realm of new-generation nuclear reactors that are a logical step toward more efficient energy in and outside of the United States. Professor Per F. Peterson at UC Berkeley is a co-founder of Kairos Power, the two other co-founders being Berkeley Alumni. Kairos Power and TerraPower are both involved in a multi-research consortium “bridging the gap between experiments and modeling to improve the design of molten salt reactors” among others. Nationally, growing interest from groups such as Bill Gates’s, TerraPower, developments in China, and Kairos Power is pouring in. The overarching goal of these organizations is to achieve a more positive future through what may seem to be unconventional means.

The nuclear conversation is one with a long and layered history. Now, in 2024, the developments and innovation involved in this field highlight the increased push towards a greener future. The possibility that some reactors, in combination with green and renewable energy, may be the practical future for the next generation everywhere is enticing. Nuclear technologies impact daily life, and their development towards a greener future is no binary matter. It’s not a case of nuclear energy being good or bad, but a dynamic situation with various pros and cons that are worth exploring and understanding. As fossil fuels destroy the environment, conversations on how nuclear can benefit or hurt us are as important now as ever. It seems that renewable resources alone can’t power our world, but nuclear meets carbon-free emissions, and molten salts highlight one of many possible methods of doing so without destroying the planet. These multifaceted conversations surrounding the future of energy will determine the future ways of life for generations now and to come. These conversations will determine how we live out our lives and how our children do too–whether it be continuing the irresponsible use of fossil fuels or greener horizons.
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