The Department of Energy has made several awards under their solicitation DE-FOA-0003364 and one of them was to Flibe Energy. The total funding was originally described as $10M but ended up being $19M in the final selection, divided among five awardees.

DOE’s Office of Nuclear Energy Awards $19 Million to Advance Recycling of Used Nuclear Fuel

Flibe Energy’s partners on this proposal include Savannah River National Laboratory (SRNL), the University of Michigan, Virginia Tech, Alabama A&M University, the Tennessee Valley Authority (TVA), and the Electric Power Research Institute (EPRI).

We at Flibe Energy have been pursuing the opportunity to address the challenge of spent nuclear fuel for many years. We proposed to the Industry Opportunities for Advanced Nuclear Technology Development (“IFOA”) program within the DOE in 2019. We always knew that SNF work was an indirect fit to the overall objectives of that program, but it was one of the only solicitations available. Our reasoning was that we could create the fuel needed for a molten-salt reactor from the transuranic residuals of existing spent nuclear fuel inventories. But that was not successful. We updated the proposal and tried again in 2020, but also did not succeed. We applied to the ARPA-E CURIE program in 2022 but were not selected, much to our disappointment.

We yearned for a direct solicitation around work on spent nuclear fuel, and that hope was answered in late 2024 with their request for proposals. We were very grateful for a chance to show how molten-salt chemical processing technology could be used to prepare spent nuclear fuel for recycle and partitioning.

This heavily-stylized video shows the overall concept of what we would like to do for spent nuclear fuel. We chose to depict the process around a CANDU fuel bundle because it is a lot shorter than the assemblies used in American LWRs, but the overall idea is the same.

The fuel bundle is immersed in a liquid-fluoride medium and the metallic zirconium cladding is removed electrolytically. The remaining uranium dioxide fuel pellets are fluorinated to first dissolve them into the salt and then to remove the uranium as gaseous uranium hexafluoride, suitable for reuse and recycle. UF6 is precisely the chemical form of uranium that the industry relies on, so having a fluoride-based process makes perfect sense. Fission product and transuranic residuals are then intended to be processed into fuel for lithium-fluoride reactors.

One might wonder, why does a thorium reactor effort care about spent nuclear fuel? I mean, we intend to design a reactor that doesn’t produce long-lived, transuranic, hazardous waste. Why should we worry about the waste that has already been made in a previous generation of nuclear reactors that were based on uranium and have operated at a tiny fraction of the efficiency that we plan to operate?

The reason we care so much and why we must care so much is that any thorium reactor we wish to build needs to have fissile material to start it up. That is simply avoidable. We can have all the thorium in the world and no nuclear reactions will begin without fissile material to initiate the reaction. Thorium is potential fuel, but that potential will go forever unrealized without fissile material to get things going.

The ideal fissile fuel for a thorium reactor is, of course, uranium-233. Uranium-233 is produced from neutron absorption on thorium, and uranium-233 is by far the best starting material. It’s easy to call it a “super-fuel” because it has so many impressive qualities. It produces more neutrons in thermal fission per absorption than any other fuel. It decays, albeit at an incredibly slow rate, into thorium-229, an incredibly valuable precursor to the medical isotopes actinium-225 and bismuth-213. U-233 is incredible stuff, but we just don’t have very much of it. It’s heartbreaking that we have so little and even more heartbreaking when one considers that the DOE is actively destroying what little we have.

But even in the ideal scenario where we preserve all the uranium-233 that we currently possess, it is only enough to start about 400 megawatts worth of lithium-fluoride thorium reactors (LFTRs). We want to power the planet with thorium. The LFTR uses thorium and U-233 at nearly ideal levels of efficiency, but we have to start those LFTRs, and we just don’t have enough U-233 to start very many of those, even if we immediately reverse course and preserve the U-233 we have and commit it to use in LFTRs.

This is where plutonium and spent nuclear fuel comes into the picture. The reactors that we have been operating on natural and enriched uranium for the last 70 years or so have produced plutonium in their fuel. This happened when the fissile uranium-235 split, released neutrons, and some of those were captured in uranium-238, and this led to the formation of plutonium-239. Pu-239 is fissile as well. It’s not a “super-fuel” in the environment of a thermal-spectrum reactor. It only undergoes fission about two out of three times it absorbs a neutron. So it’s not the best stuff but there’s a lot of it.

We made plutonium on purpose for weapons in the United States and other countries, and the US produced about 100 tonnes of so-called “weapons-grade” plutonium for military purposes. Some of that is now being made available for use in advanced reactors. That’s a tremendous step forward. But even all of that inventory would only get us to about 100 gigawatts of LFTR generation capability in the United States, roughly equivalent to our entire nuclear generation fleet currently. Now that would be a remarkable accomplishment, but we’re aiming even higher than that. We’re looking at how we could repower the whole United States with thorium.

That’s where we have to look intently at spent nuclear fuel. There is far more plutonium in our inventories of spent nuclear fuel than was produced for weapons purposes. There is probably 600-800 tonnes of plutonium in spent nuclear fuel inventories in the United States. That’s material that, right now, is considered a tremendous liability, but we see it as a tremendous potential asset, if it is used correctly.

The key to the whole effort is to use plutonium to start the thorium fuel cycle. We have had many ideas around how this is to be done. There are fast-spectrum options that would use liquid-chloride salt, and there are thermal-spectrum approaches that would use liquid-fluoride salt. But in every approach we consider, the core of the reactor is jacketed by a “blanket” that contains as much thorium as possible. The purpose of this blanket is to capture the neutrons from the fission in the core into thorium and to begin its transformation into useful uranium-233. In our most compelling versions of this plan, we would have a dedicated reactor that would consume plutonium and it would generate the uranium-233 from its thorium blanket that would start other thorium reactors. We attempt to depict this idea in this short animation.

This strategy is very special and makes maximum use of the value of the residual transuranic material (mostly plutonium) in the spent nuclear fuel. Unlike uranium-based strategies, which might consume plutonium while still making more from uranium-238, this approach truly consumes plutonium (through fission) and avoids the production of more plutonium. Thus it will consume plutonium much faster than uranium-based approaches. The fissile value of that plutonium is not lost, however, it is transformed into the fissile value of uranium-233, the “super-fuel” that unlocks a thorium-powered future for the world.

I hope that helps you understand why we are so excited about this announcement and this opportunity.