The Element Thorium

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Podcast Transcript

Located in the 90th place on the periodic table is the element Thorium. 

Thorium, as with every element, has unique properties, making it useful in certain applications. 

However, Thorium’s best days might still be ahead of it and might move it to the front of the list of the world’s most important elements.

Learn more about Thorium, how it was discovered, and its potential uses on this episode of Everything Everywhere Daily.

The story of Thorium begins in 1815 at the Falun copper mine in Sweden. Falun, at the time, was the most productive copper mine in the world, and copper from the mine had been the single biggest export from Sweden over the previous several centuries.

A previously unknown mineral had been discovered, and it was given to the chemist Jöns Jacob Berzelius to determine what it was. Berzelius had previously discovered the elements cerium and selenium.

After analyzing the substance, in 1817, he determined that he had once again discovered a new element. He called the new element Thorium, after the ancient Norse god of thunder, Thor.  

However, Berzelius got it wrong. It wasn’t a new element. It was actually yttrium orthophosphate. 

Fast forward to 1828, an amateur Norwegian mineralogist by the name of Morten Thrane Esmark found an unusual mineral in Telemark, Norway. He sent it to his father, who was a professor of geology. He couldn’t figure out what it was, so he sent it to Berzelius.

Berzelius concluded that this was, in fact, a new element, and this time, the new element was now named Thorium. 

This time he got it right, and the mineral it was found in was dubbed thorite. 

For decades after its discovery, there was no practical use found for thorium. It wasn’t until 1885 that it found its first and biggest use as a mantle for gas lamps. 

For those of you old enough, you might remember seeing mantles in gas camping lanterns. They looked like mesh bags that would shine brightly when heated by a gas flame. 

They were, in fact, mesh cloth bags that were impregnated with thorium oxide, a substance with a very high melting point. When the gas mantles were lit, the cloth part would burn away, leaving a very fragile mesh of thorium oxide which would glow brightly. 

In 1898, probably the most important attribute of thorium was discovered. Both the German chemist Gerhard Carl Schmidt and the Polish-born Marie Curie discovered that thorium was radioactive. 

This was the second element that was discovered to have this property after uranium two years earlier. 

The next year, the New Zealand physicist Ernest Rutherford and the American electrical engineer Robert Bowie Owens were studying thorium and found some very confusing results. It appeared that the radioactivity of thorium could vary dramatically. 

What they found was that one of the elements that thorium decayed into was present. It was a radioactive gas that was dubbed Radon, a new element. 

It was the study of thorium that led to the discovery of half-lives and solidified the theory that radiation was the decay of elements.

Thorium was found to be very weakly radioactive. The half-life of thorium was determined to be 14.05 billion years. To put that into perspective, the age of the universe is believed to only be 13.7 billion years old. 

If you remember back to my previous episode on radiation, the shorter the half-life of something is, the more radioactive it is. It is, to use a metaphor, burning up faster.

When I was in boy scouts, we would use gas lanterns, and we were always told that the mantles were radioactive. Technically, that was true. There was thorium in the mantles, and thorium is radioactive. 

Over the last 30 years, the use of thorium in gas mantles has been phased out because the delicate mesh which is created can easily turn to ash where it can be breathed in. While thorium is usually quite safe, it can be dangerous if ingested or inhaled. They have subsequently been replaced by mantles made of substances like yttrium, which don’t glow as brightly, but also don’t contain thorium. 

With the phase-out of gas mantles, there are almost no other industrial or commercial uses for thorium. 

The end.

Wait. I forgot there is one other potential use for thorium. 

Thorium could possibly provide clean, almost unlimited energy for the entire world. 

Yeah, you heard me right. 

Currently, all the active nuclear power plants in the world use uranium as their power source. If you remember back to my episode on uranium, there are two naturally occurring isotopes of uranium. U-238 and U-235. 

99.3% of all uranium is U-238 and only 0.7% is U-235.

U-235 has the special property of being fissile. A fissile isotope has the ability to sustain a chain reaction of nuclear fission. It emits somewhere between 2.5 to 3 neutrons when it is hit by a neutron, those neutrons hit other fissile isotopes, which release more isotopes, and so on and so on. 

U-238 is what is known as a fertile isotope. When it is hit with a neutron, it can undergo a series of decays to become plutonium-239, which is a fissile material. 

Pu-239 and U-235 are the most common fissile materials used in nuclear reactors and nuclear weapons. 

The process of separating U-235 from U-238 is known as enrichment, and it is an incredibly expensive and slow process. The vast majority of money spent during the Manhattan Project was in separating U-235 or creating Pu-239.

What does thorium have to do with any of this?

Thorium only has one naturally occurring isotope, Th-232. There are no fissile versions of thorium that exist. 

However, Th-232, like U-238, is fertile. Meaning if you hit it with a neutron, it can be turned into something which is fissile. 

In the case of Th-232, when it captures a neutron, it turns into Th-233, which is very unstable. This undergoes beta decay, where a neutron spits out an electron and becomes a proton. This turns Th-233 into Pa-233. 

Pa-233 is likewise unstable and undergoes another beta decay, which creates U-233. 

In my previous episode on Uranium, I never mentioned U-233 because it doesn’t exist in nature. For all practical purposes, it isn’t used for anything. However, U-233 is fissile, just like U-235, and it is part of the thorium cycle. 

So, when thorium captures a neutron, it sets off a series of events resulting in uranium-233, which gives off neutrons, which allows for a chain reaction.  Reactors which use fertile isotopes to create fissile isotopes are known as breeder reactors.

Long story short, you can use thorium for nuclear power. 

Moreover, there are a whole bunch of benefits to using thorium over using uranium for nuclear reactors. 

For starters, thorium is more abundant. There is about three times as much thorium on Earth as there is uranium. 

As I mentioned above, thorium has no real applications or use. Thorium ore is usually just a by-product of mining other rare earth elements. Ore with large amounts of thorium is just left behind in slag heaps. 

Moreover, you don’t need to enrich thorium because there is only one isotope.

Another big benefit a thorium reactor has over a uranium reactor is that it is almost impossible to make nuclear weapons from it. 

Modern reactors create Pu-239, the primary fuel for nuclear weapons. This wasn’t considered a bug in the design of these reactors. It was at the time considered a feature. The ability to create plutonium that could be used in weapons was considered a side benefit during the cold war. 

A thorium reactor doesn’t create Pu-239. 

In theory, it is possible to make a weapon from U-233, but both the Americans and Soviets experimented with this and found it far too difficult to be practical. In terms of nuclear proliferation, it would be easier to build a bomb from scratch than it would be to try and use U-233.

However, it gets better. 

One particular type of reactor that has been suggested not only uses thorium but also uses a liquid salt rather than a solid as the fuel source. This type of reactor is known as a Liquid fluoride thorium reactor, or LFTR, or “lifter” for short. 

The proposed fuel would be a salt made out of lithium fluoride and beryllium fluoride. The mixture is known as FLiBe.  

FLiBe would serve both as a coolant for the reactor but also a solvent for the nuclear material. 

FLiBe has a much high melting and boiling point, which means that you could run a reactor with much lower pressures than with water.  Water in conventional nuclear reactors is one of its most dangerous aspects. 

At the exceptionally high temperatures found in nuclear reactors, water becomes steam with very high pressure. Think of a pressure cooker on steroids. This high pressure is the reason why containment facilities are needed in most nuclear reactors. To prevent the catastrophic release of high-pressure steam.

A LFTR is considered a high-temperature reactor. A solvent like FLiBe would just be a very hot liquid, not a gas under high pressure. 

Moreover, a liquid fuel source can be consumed more completely than a solid fuel source, resulting in less waste. 

Not only would there be less waste, but the waste that comes out of a thorium reactor would be about 1,000x less radioactive than what comes out of a conventional nuclear reactor. 

There is a lot to be said about the subject of nuclear waste, but I will save that for a future episode. 

On top of all these benefits, a molten salt reactor can have built-in, inherent safety mechanisms which would kick in even if all the machinery were turned off and all the humans disappeared. In the event of overheating, plugs made of solid salt would melt, allowing the liquid to drain away into a tank where moderators would stop the chain reaction. 

The only thing required in a thorium reactor is some neutron emitter to kickstart the process. Where can you get that? From current nuclear waste that is sitting around. 

So, if thorium reactors are so great, why weren’t thorium reactors developed?

There have been advocates for thorium reactors as long as there has been nuclear power. There was a period of time when most nuclear scientists assumed that thorium reactors, or at least breeder reactors, were going to be the future. 

The United States went down the path of using uranium-based reactors in the 1950s due to the knowledge gained during the Manhattan Project. More was known about uranium than about thorium. 

There have been experimental thorium reactors that have been built. In 1962, a thorium reactor was built at the Indian Point Energy Center just outside of New York City.

The Oak Ridge National Laboratory built the Molten-Salt Reactor Experiment. It went critical in 1965 and ran until 1969 and used thorium in molten salt as its fuel source.  It ran for over 15,000 hours producing energy.

The development of uranium reactors continued both because of institutional inertia and because plutonium was needed for the production of nuclear weapons.

In 1973, the United States stopped all research into thorium reactors. Alvin Weinberg, head of the Oak Ridge National Labs, which is the largest nuclear research and development center in the US, was fired in 1974 because he championed the development of safer thorium reactors. 

Within a matter of years, it was possible to get a Ph.D. in nuclear engineering and never once encounter the thorium reaction chain. 

There has been a revival of interest in thorium power, given all of its benefits.

Several atomic agencies around the world have conducted experiments with thorium reactors or have recently announced their interest. China has begun tests on thorium reactors. India has probably shown the biggest interest in thorium as they have abundant thorium reserves and very little uranium. 

There has been renewed bipartisan interest in the US Congress to revive thorium reactor research. There are also several start-up companies that are looking to create thorium-based reactors and small modular reactors.

In previous episodes about various elements, I’ve mentioned the role they’ve played in history and how they have contributed to the modern world. 

In the case of thorium, it has played almost no part in the modern world, and it has almost no historical impact. 

But that may be about to change. Thorium may be thrust into the spotlight going from one of the most useless elements to one of the most important for the future of humanity. 

The Executive Producer of Everything Everywhere Daily is Charles Daniel.

The associate producers are Thor Thomsen and Peter Bennett.

Today’s review comes from listener autumnvine101 from Apple Podcasts in South Africa. They write:

Great for old and young

This is a great informative podcast. We as a family with teens learn so much while listening to the short episodes, even on our current road trip through a part of our beautiful country, South Africa. We all love this informal way of getting to know more about the world and far-off places. We differ from you in many aspects in our view of the world and history, but find there is more to learn this way as it opens our minds to different viewpoints and points of view. Our constant companions are atlases, roadmaps, a globe, timelines, and history books.

AutumnVine101 – from the Helderberg basin, South Africa.

Thank you, AutumnVine! I’m glad to hear you are enjoying the show, and your country is indeed beautiful. I’ve had the pleasure of visiting every state in South Africa I’ve enjoyed all of it, from Kimberly to Kruger, Cape Town, Johannesburg, Soweto, Durban, Port Elizabeth, and Bloemfontein. I’ve even taken the Blue Train from Cape Town to Pretoria.  It is a great place for a road trip.

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