The Genius of Thorium Breeder Reactors

Added: 2026-05-12

[00:00:01]Thorium is a kind of miraculous element.

[00:00:03]Thorium found in nature isn't file. The atom's nucleus won't split when it absorbs a neutron. And yet, if you put a chunk of this same thorium in a special nuclear reactor, after a while, most of the thorium will be gone. A whole bunch of energy will have been generated, and you'll be left with typical byproducts of fision. It's as if thorium is file, even though it's not. This is the genius of thorium breeder reactors. Oh, and I should disclose here that this video is sponsored by Copenhagen Atomics, who are working to make thorium power a reality, but they didn't get any say in the video and didn't get to review it before posting. The standard oversimplified picture of a fision reactor is a uranium nucleus splits apart, or fisions, releasing heat energy and two or three neutrons, and those neutrons go on to be captured by more uranium nuclei and cause them to fision, releasing more heat energy and more neutrons, and so on. The heat is used to generate electricity, the neutrons, to maintain the fision chain reaction. However, the actual story is more complicated. When a nucleus splits, there are actually four things that can happen to the neutrons it emits. One, like we've already mentioned, they can be captured by a file atom like uranium 235, causing it to fision and release more neutrons. And this part has to happen on average at least once per fision to sustain the chain reaction. Two, neutrons can be captured by the nuclei of other atoms in the reactor without causing fision, like maybe the metal case or the moderator or the control rods or whatever. Three, neutrons can escape and leave the reactor entirely. or four, a neutron can be captured by an atom that's not file and transmute it into an atom that is file. Because remember, these are atomic nuclei we're dealing with. Absorption of a neutron will turn uranium 238 into uranium 239. The number is just the total number of protons and neutrons.

[00:01:31]And uranium 239 can then radioactively decay into neptunium 239, which can then decay into plutonium 239, which is file.

[00:01:38]If the capture of a neutron transforms a non-file element into a file one, it's called a fertile capture. And fertile capture is what makes thorium useful. In fact, even in a normal uranium reactor, fertile capture accounts for over a third of the energy generated by the reactor. A normal nuclear reactor uses uranium 235, which is file. But naturally occurring uranium ore contains only.7% uranium 235. Almost all the rest is uranium 238, which is essentially non-file, but it is fertile. Even when using fuels with enriched levels of uranium 235 undergoing fision, there's so much non-file U238 around that some of the chain reaction neutrons instead transform U238 into plutonium 239, which can then fision. But U235 doesn't make enough neutrons and U238 doesn't turn into plutonium easily enough that you can both sustain a fision chain reaction and continue to transform new file fuel.

[00:02:27]So at the end, you're left with a big chunk of unfisioned but still full of radioactive waste, uranium 238. There's a different kind of reactor called a fastreeder reactor that uses plutonium as the primary file fuel and uranium 238 as a fertile secondary source. This combination can both sustain the fision chain reaction and transform new fuel in a self-sustaining way. But fast breeder reactors are less researched, more expensive, and harder to run effectively for now. This is where thorium comes in.

[00:02:51]The same route used in the transformation of uranium 238 to plutonium 239 can be replicated down here. Starting instead with thorium 232 by adding a neutron we get thorium 233 which decays to protectinium 233 which decays to uranium 233 which is file and can be used to generate energy. So if you load your reactor with thorium 232 which remember is not file and you throw in some starter file fuel then for each fision reaction the number of new file atoms created is more than one on average and the number of new atoms split is more than one on average and remember those atoms give you more neutrons. So the transformation of thorium and the fision of uranium can keep going and going and going until in principle all of the thorium is gone.

[00:03:30]And crucially, thorium transformation can happen in a reactor that doesn't have the same challenges as a fast breeder reactor. And it gets rid of most of the long-lived radioactive waste. And thorium is more abundant than uranium and doesn't need the expensive refining process to concentrate the file uranium 235. And so you can see why people get excited about thorium. There are, of course, challenges and downsides to making thorium reactors, which is why we don't have and so far have never had commercial energy generation from thorium. But that's fertile material for another time.

[00:03:58]Making commercial power from thorium may soon be possible thanks to the work of organizations such as this video sponsor, Copenhagen Atomics. Copenhagen Atomics is building compact modular thorium reactors to produce cheap energy. Unlike traditional nuclear power stations, which are giant infrastructure projects, Copenhagen Atomics are designing a self-contained reactor unit that can fit inside a shipping container. The reactors are based on a design pioneered over 50 years ago that uses molten salt to carry the fuel, resulting in fewer lost neutrons and more complete combustion, so you get more energy for less waste. These reactors can also use plutonium waste from classic nuclear reactors as fuel, extracting 10 times more energy out of spent nuclear fuel than the initial reactor did in the first place, and in doing so, converting longived radioactive waste into shortlived radioactive waste. In theory, these reactors could run anything from grids to ships to moon bases. Check out Copenhagen Atomics website to learn more about their work.