I’ve been exploring different types of clean energy generation and storage in my videos over the past few months, and a topic that has been mentioned a lot in the comments is Thorium reactors. Thorium is often held up as one of the best paths forward for achieving a mix of cheap, clean energy for our grid. Even former presidential candidate Andrew Yang was pushing for Thorium reactors along with wind and solar. So what is it? Why are there so many people excited about it? And is it really the future of clean energy?

In recent years we’ve seen a huge increase in the amount of solar and wind power being added to the grid, which are viewed as the ultimate clean energy power sources. And there’s a growing movement to provide better grid-scale energy storage options to capture that energy generation for use at times when they may not be producing enough energy. But some argue that’s not going to be enough, so nuclear needs to be a part of the clean energy mix.

It’s probably a good idea to quickly go over nuclear energy, but just like I said on my fusion energy video, I’m going to keep this higher level because nuclear physics is clearly a very complex topic that’s out of scope for this video … and it hurts my brain a little bit. As always, I’ll include a link in the description to my research if you’re interested, but here’s how it works at a high level.

All fission based reactors use the same exact process. It’s the result of an extra neutron slamming into a larger nuclide, which splits it into two smaller nuclide. The splitting of the nuclide releases a massive amount of energy and produces more loose neutrons. And those neutrons can start a chain reaction by slamming into more nuclides to continue the process. It’s a nuclear chain reaction, and that reaction generates heat. Nuclear reactors can then capture that heat to turn water into steam, which then turns a turbine to produce electricity … all without producing carbon emissions associated with climate change.

But many today are scared off of nuclear energy because of disasters like The Three Mile Island, Chernobyl, or Fukushima. All of which came down to a failure in the cooling systems. U-235 is the common fuel source used today and an out of control chain reaction can cause a catastrophic meltdown. And it’s this fear around nuclear meltdowns that’s holding back public interest in increasing the number of nuclear power plants. But what if there was a type of nuclear reactor that still had no carbon emissions, produces nuclear waste with a dramatically shorter half-life, a fuel source that’s three times as plentiful, and … oh … wouldn’t have the same risk of a meltdown? Enter Thorium.

What is thorium

So where and why does Thorium come into this? Thorium is one of the 15 heavy metallic radioactive elements in the bottom row of the Periodic Table of Elements and goes back to Swedish chemist Jons Jakob Berzelius who first isolated Thorium in 1828. But it wasn’t until 1898 that Gerhard Schmidt and Marie Curie separately identified Thorium’s radioactive nature.1 Th-232 is the most stable of the 27 Thorium isotopes, which can be found in the minerals thoriate, thorianite, and monazite. For commercial purposes Thorium is most often found from monazite mining2, and is fairly abundant worldwide. The countries with the highest estimated deposits are India, Brazil, Australia, and the United States.3

So what sets it apart from U-235 that’s used in nuclear reactors today? Well, U-235 is used because it’s highly fissile. The neutron speeds can be controlled and slowed by using water as a coolant and regulator, which increases the number of U-235 nuclides that split. Most uranium ore is U-238 and only contains about 3-5% of U-235. When U-238 absorbs an extra neutron it turns into U-239 and then quickly into plutonium … the material we use in nuclear weapons. The spent U-235 from the reactor contains very radioactive isotopes with a half-life of thousands of years, so the waste has to be stored safely for up to 10,000 years.4 And with today’s reactor designs, which in the U.S. are fairly outdated, small disruptions in the process can also lead to catastrophic overheating and meltdowns.

Thorium on the other hand isn’t fissile, which means it’s not a good source for a fission reaction. While it’s not directly usable in a fission reactor, when it absorbs a neutron it decays into P-233 (Protactinium). Then it can be chemically separated into U-233, which in turn can be used in a reactor and is very efficient for fission reactions. Thorium is able to “breed” U-233. It’s the ability to separate the U-233 from the thorium that sets it apart from U-235 and U-238. We end up with a vast amount of waste from today’s reactors that needs to be stored safely. The waste from a thorium reactor is radioactive for about 500 years compared to up to 10,000. All of this is what makes Thorium a unique option for nuclear fuel because it’s more abundant than Uranium, can be turned into usable fuel, and dramatically reduces the amount of nuclear waste.

Myriad types of reactors

There’s no shortage of reactor designs and concepts that can take advantage of Thorium as a fuel source. Some of the reactor types you’ll find are Heavy Water Reactors (PHWRs), High-Temperature Gas-Cool Reactors (HTRs), Boiling Water Reactors (BWRs), Pressure Water Reactors (PWRs), Fast Neutron Reactors (FNRs), and Accelerator Driven Reactors (ADS). And that’s still not all of them. But you can really narrow it down to two major categories of reactor designs leading the way: Water (thermal) Reactors and Molten Salt Reactors (MSRs).

Probably the reactor type that gets the most focus are Molten Salt Reactors, like the Liquid Fluoride Thorium Reactor (LFTR), which uses Thorium fluoride in a salt-mixture that’s melted into a liquid. This is often referred to as a “breeder” reactor design: Thorium goes in, fission products like U-233 come out.5 It’s the liquid nature of the fuel that makes this type of Thorium reactor special. It’s both the coolant and the fuel, so it can self-regulate the process to keep the temperature from getting out of control. The simplest way to describe the how and why is that the liquid fuel is run through a reaction chamber filled with graphite rods. These graphite rods are acting as a fission moderator because they’re slowing down the speed of the neutrons, which increases the probability of a fission reaction. Remove the graphite rods from the equation and the fission chain reaction stops. This is the biggest safety benefit over the traditional nuclear reactors we have in use today. Thorium-based reactors are safer because the reaction can easily be stopped and they don’t operate under extreme pressure.6 In the event of a catastrophic incident in a Liquid Fluoride Thorium Reactor, it will automatically drain the liquid fuel into a tank away from the graphite … stopping the reaction. There’s essentially a walk-away safety factor to thorium reactors like this.

Challenges of thorium

So why aren’t we seeing Thorium reactors everywhere? In fact, why aren’t we seeing ANY Thorium reactors in commercial use at all? There’s varying levels of interest and investment into Thorium reactors around the world. While the principles have been understood for a long time, there are still a lot of technical and practical challenges to overcome, like finding materials that can contain the corrosive molten salts. Lin-Wen Hu, from MIT’s Nuclear Reactor Laboratory said in a Wired interview:

”There is still a lot of work to be done in terms of demonstrating molten-salt reactor technology, even for uranium-based reactors. Molten-salt reactors need to be demonstrated with a uranium fuel cycle before that system can be used for a thorium fuel cycle. Moving toward a thorium fuel cycle has a lot of unknowns.” -Lin-Wen Hu, director of research and irradiation services at MIT’s Nuclear Reactor Laboratory7

Countries like the U.S. haven’t viewed thorium as a leading candidate for nuclear power historically, so there hasn’t been a lot of funding towards the research. And looking at the history of why the U.S. settled on uranium as a fuel source instead of on thorium goes back to the cold war with the Soviet Union. As I mentioned before, uranium-fueled reactors produce plutonium, which can be refined into weapons-grade material, which is used to make nuclear bombs.8 So the path the U.S. ended up going down has been set for a long time, and shifting from a uranium-based infrastructure to a thorium-based one will take time. But countries like China and India, that don’t have a long standing uranium infrastructure, have been investing heavily into thorium. In 2009 China demonstrated the potential of thorium-based fuels and has the first high temperature experimental fluoride salt loop in operation.9 India has one of the largest thorium reserves in the world, and has a 3-stage plan that focuses on reaching thorium reliance by the 3rd stage.10 In both cases, it’s about countries establishing self-reliant forms of clean energy generation to support massive populations. Solar and wind alone won’t be able to support the rapidly growing baseline energy needs, which is why they’re investing so heavily into next-gen nuclear reactors and thorium.

While countries like the U.S. have been lagging behind on thorium research compared to others, there is still interest. During his presidential run, Andrew Yang made the case to invest $50 billion in the development of molten salt nuclear reactors … wanting to get them online by 2027.11 And Bill Gates has been investing heavily into next-gen nuclear. He invested in TerraPower in 2011, which is working on a next-gen nuclear reactor called a traveling-wave reactor (TWR).12 The biggest game changer for this reactor is the ability to use fuel efficiently without uranium enrichment, so it can use depleted uranium and nuclear waste as a fuel source. We’d be able to reuse that waste we’re storing for 10,000 years. And the design could also work for thorium. Sadly, the test facility they were building in China has been put on hold. The Trump administration has put a lock on the potential for the Gates Foundation to keep nurturing China’s nuclear innovations, but Bill Gates remains convinced that nuclear energy is our single greatest weapon to combat climate change in the immediate future and requires significant investment into new designs.13

And while not directly related to thorium, In May 2020, the US Department of Energy just started a new project called the Advanced Reactor Demonstration Program (ARDP)14, which is funding $230 million into next-gen nuclear. There’s worldwide recognition that while solar and wind are great and viable sources of clean energy, by itself they aren’t enough to get us to a 100% clean grid quickly. A mix of solar, wind, energy storage, and nuclear can help the world achieve that goal. There’s a lot of exciting potential around thorium, and it’s going to be interesting to watch how this evolves in the coming years.

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