The Next Nuclear Step, Simplified

All Nuclear energy ultimately comes from atomic nuclei. The largest nuclear reactor we all use – the Sun – harnesses fusion: smashing hydrogen together to form helium and releasing enormous amounts of energy in the process. Fission is the opposite: releasing energy by splitting atoms. When we harness solar power, all of that energy is ultimately nuclear power.

The second largest nuclear reactor we use is beneath our feet, within the outer core. Around half of Earth’s internal heat comes from nuclear fission. So when we harness geothermal energy, half of that energy is nuclear power.

Fusion requires incredible mass and pressure, possible in a lab, but not (at least not yet) useful for net energy gain. Even in the sun, there is more energy being put into the system than what comes out; it’s just at such a massive scale that the output bombards us with plenty for the planet to use. But fission just needs the right material in the right conditions. With just a little bit of energy put into the system, a lot of energy can come back out.

We’ll be looking over the basics of Nuclear technology, and a revolution of how we do it on the horizon.

Uranium and Plutonium
Current nuclear technology relies on Uranium and Plutonium. To understand how this works, we’ll need to understand isotopes.

An isotope is a kind of ‘flavour’ of atom. An atom has a set number of protons and electrons, but the number of neutrons it has can change. U238 and U235 are both isotopes of Uranium: one has 238 neutrons while the other has 235. Chemically, they are the same. But physically, they are hugely different.

U235 is fissile. This means that it can sustain a chain reaction: each time it splits, it spits out at least 2 neutrons that can continue the process. This isotope is what most current Uranium reactors rely on for energy generation since it results in a net gain of energy. U238 is fertile in current Nuclear reactors. ‘Fertile’ means it can be transmuted into another atom that is fissile – in this case, Plutonium (Pu239). It’s fairly ambivalent about you throwing neutrons at it. It would rather just gobble them up. A fission dead-end.

But there are a lot of problems in just that one paragraph.

Splitting atoms produces a wide variety of byproducts. When an atom splits, the new separate atoms it creates have different quantities of protons/electrons (and as we know, that means they’re different atoms altogether). This will be important to remember when we cover Fukushima and Liquid Fuel.

U235, the fissile isotope that ultimately provides us power, is ultra rare. Uranium-the-atom is roughly as abundant on Earth as tin. But only 7/1000 (0.7%) of that Uranium is the isotope we need, making it as rare as Platinum, 10 times rarer than Gold.

And all of this material isn’t separate, it’s locked in amongst U238 isotopes. Most solid fuel rods need to be ‘enriched’, increasing the proportion of U235 so it can sustain fission in a reactor. This is why Nuclear power has a slight reputation of being unreliable for very-long-term use. Because it’s kind of true with current technology.

The U238 isotopes that remain in fuel rods don’t typically provide us energy. Instead, they often absorb a neutron being thrown at it, becoming U239. It then decays into Pu239. This is largely what makes up ‘Nuclear waste’. But Pu239 is still fissile! Which means it can be recycled in some reactors to get energy from it, right? Yes, and it’s messy, inefficient and unfortunately is more expensive than simply getting more Uranium. More importantly, Pu239 is the most common fissile material used for nuclear weaponry.

None of this is to say that Uranium and Plutonium fuel isn’t worth it. They’re powerful materials that have bad PR, but the physics behind them are well understood and immensely useful.

Solid Fuel
All current nuclear reactors rely on solid fuel rods: little pellets of highly processed Uranium. This poses multiple drawbacks. And in many ways is comparable to printer ink.

• Enrichment is a pain. For Uranium to be useful in a reactor, we need to pump it with isotopes we need to a higher concentration, a step that costs a lot of energy and specialised machinery.

• A lot of the energy goes unused. It’s comparable to a barbecue, where most of the charcoal hasn’t actually burned at all, but you throw it all away instead of picking the good bits back out. Or a printer ink cartridge that definitely has a lot of ink still left in it, but none of it can be used. Recycling is such a big challenge that most of it is better off buried and guarded for a few thousand years.

• Byproducts from fission reaction are wasted and interfere with energy production. After the U235 splits and becomes different atoms, it stays in the solid and reduces energy production, and it’s locked in and thrown away.

• Reactor companies rely on the concept. Printers are often not sold for a particularly impressive profit margin – the company gets its profit from the ink cartridges. Reactors are the same: they sell the fuel rods used in their reactors. In essence, they’re financially encouraged to perpetuate wasteful solid fuel.

Liquid Fuel
We’ve looked at what we have, and some of its problems. Let’s start looking at solutions.

Before we get into details, let’s consider this conceptually.

If we just imagine that the fuel was a liquid cycle instead of solid chunks that you plug in, how would those drawbacks be resolved?

• Most of the energy is used. With the barbecue analogy, imagine that all the ash is simply siphoned out the bottom, leave burnable charcoal behind for the next time. In the case of a printer, imagine that printers simply had trays that you just refilled with ink from a jug. New material is introduced steadily while non-fissile material is filtered out

• Byproducts are more easily separated. Instead of being locked into a solid, the byproducts could be taken out during the cycle. For example, gaseous byproducts like Xenon could by siphoned out of the system with basically no chemical treatment. Not only does that mean less interference with energy production, it also means active production of other materials.

• Reactors aren’t beholden to special solid fuel manufacturing. Instead of relying on third parties to make complex, expensive rods, the only thing that really matters is the composition of the liquid which can be done completely independently – again, just like filling up your printer with the right ink.

• It’s naturally safer. Ridiculously safer. PWRs (Pressurised Water Reactors) rely on active cooling to stop the rods from melting down and causing a big mess. MSRs (Molten Salt Reactors) work in reverse. Instead of using liquid (water) to moderate solid fuel down to safe conditions, solid moderators are used to increase liquid fuel into useful conditions. This means that in an emergency shutdown situation, it’s as simple as evacuating the fuel – and most MSR designs contain a kind of physical ‘fuse’: a ‘freeze plug’ that will pop by itself if there’s ever a serious issue.

In general, liquid fuel techniques reduce radioactive waste, sharply decrease meltdown threat and damage, recycle waste product into useable product, and extract far more energy than solid ever can or will.

Thorium
Now we’re really getting into it.

Perhaps the great benefit of a liquid fuel solution is that is makes Thorium a valid fuel candidate.

Most, if not all, criticism surrounding Thorium as a fuel source starts with a false preconception: that Thorium is proposed as solid fuel. As solid fuel, Thorium is categorically not viable and makes absolutely no sense for multiple reasons. The main one being that Th232 is not fissile – it’s fertile. It therefore needs extra levels of processing before being useful as a fuel rod.

Opponents of Thorium as a fuel are right in this regard, but it’s an argument that no serious organisation is making.

The potential of Thorium is in Molten Salt Reactors, first successfully operated over 50 years ago.

Thorium is around 3 times as abundant as Uranium, and we have shed loads of it. It’s actually considered a byproduct in many mining operations. We have a huge surplus of it that people actively get rid of. New mining operations for Thorium simply aren’t necessary.

Th232 is the most abundant isotope of Thorium (making up almost 100% of all natural deposits), and is the isotope we need. Th232 is therefore almost 500 times more common than U235, and is entirely separated from other isotopes.

When bombarded with neutrons, as a fertile material, it absorbs them, becoming Th233 before decaying down to Protactinium-233 (Pa233) over around 20 minutes and finally down to U233 over around a month. U233 is fissile Uranium (so rare it doesn’t occur naturally anywhere on Earth) that has a 91.2% chance of fissioning when hit with thermal neutrons.

In short: Th232 is a common material that can be transmuted into fissile Uranium with tiny amounts of relatively safe waste that can’t be easily weaponised.

If This is so Great, Why Aren’t we Doing It?
An important question, and there are many answers to it.

To grasp the depth of the question, we need to ask a different one first. Why are we using Nuclear at all?

Nuclear power technology is fairly taken for granted now, but the amount of research and money required to make it even half way useful was enormous. Only through military financing can something like this really be achieved, because it was done at a loss.

Upgrading Nuclear fission from theory to practice required motivation. It wasn’t attractive as a financial investment, but it had the most powerful motivation humankind ever bestows on technology: warfare. It was, without any hyperbole, a technological revolution.

The upshot of this was decades worth of development time in just a few years. A nuclear blast of technological advancement. The downside is the direction that development took.

For Nuclear to be viable, it had to provide military might. PWR and solid fuel Uranium in general offered that in spades, which is now its scariest aspect – while the impotence of Thorium as a weapon, one of its greatest selling points today, was its leading downfall in favour amongst key decision makers.

MSR Thorium reactors need a comparable push from theory to practice, but its still an uninvestable technology as current reactors once were. Just as before (although not as severe), investment at this stage is largely at a loss. And with no military application or drive, can’t reap the same benefits as current technology did.

And finally, we actually are doing it, just not yet everywhere. Multiple Chinese research and manufacturing centres have been seriously pursuing this since 2010, and several engineer and humanitarian-focussed companies elsewhere are doing the same.

Thorium MSRs are an improvement on Uranium PWRs in every single metric. The biggest challenge was getting the next Nuclear revolution started, and it’s well underway.