Why Climate Change requires the use of Safe Nuclear Power

Nuclear power has received a somewhat justified bad rap. We've had commercial nuclear power for about eighty years and have already experienced three major nuclear accidents. The worst accident on record is, of course, Chernobyl which exposed thousands of people to radiation.

However, we literally have no choice but to turn to nuclear energy to arrest the cataclysmic damage of climate change. Why do I say that? The only way to minimize the already staggering effects of climate change is to stop burning fossil fuels as soon as possible. Oil, coal, and natural gas must all be left in the ground and by far the biggest consumers of these fuels are power plants.

So why nuclear energy then? Why not rely on renewable energy sources such as solar, wind, and hydroelectric?

Well there's two main problems that explain why renewable energy sources alone can't power our civilization. Number one, renewable energy sources are very site specific. If you build a solar power plant in Seattle, you won't generate very much energy (and that's assuming you ever see the sun there at all). Hydroelectric power requires a river. Wind turbines require windy areas.

The point I'm trying to make here is that you can't put a solar power plant or a hydroelectric damn anywhere you want. They require preexisting resources for us to leverage and if that resource isn't present, you can't build an effective power source there. Reason number two is that all renewable energy is variable in its power generation. The sun only shines during day and clouds can cover the sun during the day. Rivers can get low, and the wind only blows when it wants to blow. Renewable energy sources are great for generating power but they generate variable power because there is no guarantee that they can generate power at any given time. Short of a major revolution in battery technology we can not rely solely on power sources that can not generate a constant amount of power. Mind you, this situation may improve. We get better and better at generating energy from small amounts of wind and water every year. Deploying solar panels into space and beaming their energy down to Earth is a project in development. However all of these improvements are likely decades away from being viable. We only have one mature power source that is zero carbon, can be built anywhere, and generates a consistent amount of energy and this is nuclear power.

On top of all that, pound for pound Nuclear energy is the most efficient source of power on the planet. The energy released by nuclear fission is, on average, three million times greater than any form of chemical energy. In addition, nuclear fission produces the LEAST waste pound per pound of any fuel source we have.

So the reality is that we really do have no choice but to embrace nuclear energy if we hope to mitigate the cataclysmic damages of climate change.

I'm sure there are a lot of people out there shaking their heads right now. Even if nuclear energy could save us from climate change, is it really worth the trade? Nuclear accidents happen all the time and even when nuclear planets are run properly they produce tons and tons of highly dangerous radioactive waste. We have no idea how to store this waste safely and we know that the waste will be dangerous for hundreds of thousands of years.

Well the reality is we don't need to have accidents and we do know how to manage the waste. Nuclear submarines for example have never had an nuclear accident. However to explain why this is true, we need to get into a few particulars about how nuclear energy works and why these accidents happen.

In principal a nuclear reactor isn't that hard to understand. Fissile material (i.e. any element that can be broken into smaller elements when struck by a neutron) is placed into a tank. Because fissile material is unstable, it is firing off neutrons at a steady rate. When a freed neutron hits an atom, three things can happen. The neutron can bounce off, the neutron can be absorbed by the atom, transmuting this atom into another element (i.e. from Thorium to Uranium), or the neutron can shatter the atom into two smaller elements which releases a ton of energy and many more freed neutrons to continue the cycle.

In the diagram above we see this demonstrated. First a neutron strikes an atom of uranium-235 and is absorbed (briefly producing uranium-236) then the atom shatters into two smaller atoms, freed neutrons, and an enormous amount of energy.

So why do nuclear accidents happen? Well usually they're the product of human stupidity in one form or another. However, every nuclear accident we've ever experienced has had one key thing in common: water.

Most nuclear reactors in service today are a type called LWR: Light Water Reactors. This means that they use water as both a coolant and to concentrate the nuclear reaction within the reactor.

However, water is an extremely dangerous coolant to use for a nuclear reactor because water is only a liquid at an extremely narrow range of temperatures (Zero degrees Celsius to 100 degrees Celsius). Beyond that temperature water turns into steam and the water's volume increases by a factor of 1700. Remember that a nuclear reactor usually operates at temperatures of around 300 degrees Celsius or even higher. So why does the water not constantly boil? Well, normally water boils at 100 degrees Celsius, however, you can change water's boiling point by putting the water under pressure. Water in a nuclear reactor is usually kept at 148 atmospheres of pressure (roughly equal to the pressure a deep sea vehicle would experience 5017 feet under water) resulting in the pressurized water's boiling point being approximately 342 degrees Celsius.

Please take a moment and notice the extremely narrow temperature gap (roughly 40 degrees Celsius) between where a reactor normally operates and the point at which the water coolant boils. This, in a nutshell, is the whole problem with current nuclear reactors. Every nuclear accident we have ever encountered has been a steam explosion in one way or another. If the coolant water doesn't circulate properly it transforms into steam. This increases the water's volume by a factor of 1700 which the reactor must struggle to contain. Worse yet, steam is much worse at cooling the reactor than water so the reactor temperature just shoots higher and higher. In some cases, steam can even cause the nuclear reaction to accelerate, leading to a run away chain reaction. This is what happened at Chernobyl and Fukushima. Although the steps taken to cause the steam explosion were different for each accident, in both cases the coolant water boiled to steam and the reactor was unable to contain the sudden rise in pressure and this led to an explosion. Imagine a giant kettle tightly sealed, filled with far too much water and the stove it sits on is cranked up well past a boil. This is the typical nuclear reactor. A vat attempting to contain almost unimaginable temperatures and pressures. After understanding all these issues you may find yourself feeling less surprised that we've had major accidents at nuclear power plants and feeling more shocked that we don't have them all the time. So having explained the delicate balance that the LWRs are constantly threading just to avoid disaster, why on Earth would I ever suggest making even one more nuclear reactor?

Well the fact is, these disasters are easy to avoid. Just take out the water.

I know that we routinely think of water as the best coolant but at the temperatures a nuclear reactor works at, water is a terrible terrible coolant. It not only can boil but it needs to be kept under pressure to drive a turbine. These issues lead us to the Molten Salt Reactor or MSR. Rather than using water as the coolant, MSRs use molten salts, usually Lithium Flouride, as the coolant. Flouride absorbs heat just as well as water, even better than water in some cases.

Lithium Flouride melts at 360 degrees Celsius and remains in its liquid phase up until it hits its boiling point at 1430 degrees Celsius. This gives an MSR a safe operating range of over one thousand degrees Celsius without risk of the coolant boiling.

Better yet unlike water, salt doesn't need to be kept under pressure. That means if the reactor wall is breached for any reason, there's no explosion. Coolant and fuel just drips out onto the floor, cools off, and can be cleaned up later. MSRs usually operate at about 700 degrees Celsius which gives them plenty of padding for safety. Consequentially the temperature of an MSR would need to double before there was any risk of an explosion. For comparison sake, steel usually melts at about 1350 degrees Celsius so before the reactor exploded, the power plant would have already melted around it, and very likely melted into the Earth. In case you were still worried, this is not a realistic scenario.

In addition MSRs can be designed to be passively safe. This means that regardless of what humans do or fail to do, the reactor can NOT melt down. As the reactor heats up, the fission reaction becomes less efficient and slows down, automatically cooling the reactor. There's no way to have a run away chain reaction in an MSR because the nuclear reaction loses energy as it heats up beyond it's optimal temperature.

MSRs usually are constructed with a "drain tank." Basically the reactor's bottom is sealed with a metal plug that melts at lower temperatures; usually a little over one thousand degrees Celsius. This means that if the reactor ever exceeds that temperature, the metal plug melts and the fuel evacuates the reactor, falling into a special shielded tank where fission is impossible. This means the fission reaction stops instantly.

Even if you crashed a plane into the reactor core, the fuel just spills out and stops reacting. The fuel can not maintain a fission reaction outside of the core. Because nothing in the core is under pressure, even if there is a massive breach in the reactor no fuel is jettisoned into the atmosphere. Nor is the fuel water soluble so it can't contaminate the water table. A major reactor breach in an MSR would just be a lot of hot rocks and salts spilling across the floor that will rapidly cool and need to be cleaned up. In summary, MSRs can be designed to be impossible to melt down. So that's one major concern about nuclear energy dealt with. Maybe with an MSR there isn't a risk of any more serious accidents but that's only half the problem. What about nuclear waste? Nuclear waste is highly dangerous and it will be highly dangerous for far longer than our civilization has existed. What can we possibly do to contain it and ensure it's properly isolated from the environment?

Well, to answer that question we need to explain what nuclear waste is. Nuclear waste is a collection of fission byproducts. Because these byproducts are unstable, their atoms periodically emit radiation as a means to become stable. Emitting radiation allows one element to transform into another element until it stabilizes and stops radiating. That's what a "half life" is: How long an element takes for half of it to transform into another element. Some of these fission byproducts are less radioactive (and thus less dangerous) than coal ash and their disposal is pretty simple. However, some types of nuclear waste emit dangerous kinds of radiation.

Normally we create nuclear waste as a byproduct of splitting very heavy elements of either uranium or plutonium. These are some of the heaviest elements in the Periodic Table. I won't bore you with the details but in simplest terms it is because the elements are so heavy that they produce a lot of very dangerous long term waste.

So that's the problem, how do we solve it? The solution for nuclear waste is two fold.

Number one, stop using uranium and plutonium to generate power. Uranium is what most people think of when it comes to nuclear power but it's far from the best option when it comes to commercial power generation.

The element thorium, two elements to the left of uranium on the Periodic Table, can also be used in a nuclear reactor. We can seed an MSR with a small amount of enriched uranium and then just keep tossing in raw thorium. The uranium transforms the raw thorium in the reactor into fissile thorium that can generate energy. Then the transformed thorium can transform still more raw thorium. Thorium is abundant and cheap, often thrown away by mining companies as not worth anything. It requires no complicated enrichment or refining to use. Best of all, nuclear energy based on Thorium produces barely any waste. The only substantial nuclear waste product produced by the Thorium fuel cycle is an isotope called Protactinium-231. The physics suggests that, in practice, not a lot of Protactinium-231 will actually be produced by a commercial reactor. Creating Protactinium-231 requires a fairly unlikely series of events (called a double neutron emission) to occur in order to create it from thorium but some amount of Protactinium-231 will certainly be generated.

Unfortunately Protactinium-231 is a nasty piece of waste. It has a half life of nearly fifty thousand years and during that half life it emits extremely dangerous Alpha particles. Ok, so what did switching to thorium fuel accomplish? Sure we've created less waste but we are still creating nuclear waste and this type of waste is not only very dangerous but it will be very dangerous for a longer period of time than humans have been practicing agriculture. So what can we possibly do about this? Well here's the thing. We talked way back in the beginning of this article about what can happen when a neutron strikes an atom. Mostly we've been talking about what happens when a neutron shatters an atom into smaller pieces, but a neutron can also be absorbed by an atom, transmuting that atom into another substance. Remember how alchemists claimed you could turn lead into gold? Well it turns out with nuclear energy you can really do that! It's a process called Nuclear Transmutation which allows one element to be changed into another. However, God has a really warped sense of humor and it turns out that, in reality, it's actually a lot easier to turn gold into lead than the other way around.

197Au + n → 198Au (half-life 2.7 days) → 198Hg + n → 199Hg + n → 200Hg + n → 201Hg + n → 202Hg + n → 203Hg (halflife 47 days) → 203Tl + n → 204Tl (halflife 3.8 years) → 204Pb

Above you'll see the general series of steps needed to change an atom of gold into an atom of lead. Put briefly, a neutron (n) strikes a gold atom (Au) which usually weighs 197, turning it into a gold isotope that weighs 198. A few days later this isotope radioactively decays into mercury (Hg) with a weight of 198 which is stable and non radioactive.

The diagram above goes on to illustrate the other transmutations that can be achieved by bombarding that mercury with more neutrons until it eventually turns into lead (Pb).

Don't worry about the specific steps too much, just try to get the general idea. Basically, given the right environment, atoms of one element can be transformed into other elements. Best of all, this applies to nuclear waste as well.

In the right kind of reactor we can transform long term nuclear waste into either short term nuclear waste, or better still, transform the waste into new fuel for commercial reactors. This isn't new technology, it's very well understood science. We just haven't been doing it because it's not cost effective. It's much cheaper to bury the waste than it is to clean it up.

Transmutation of nuclear waste usually can't happen in a commercial reactors but it can be done in specialized reactors designed to transmute waste. These reactors require highly enriched, weapons grade nuclear fuel and so are not viable for commercial reactors due to concerns of the proliferation of nuclear weapons. However, the military runs these types of reactors routinely. Nuclear submarines all operate using highly enriched fuel capable of consuming and transforming nuclear waste.

After a commercial power plant produces toxic byproducts like Protactinium-231, it can all be gathered up and given to the US military. The military already runs nuclear reactors capable of processing Protactinium-231. These reactors can either transform Protactinium into a short lived, less dangerous forms of waste or transform the waste into new fuel.

Cleaning up Protactinium-231 takes one neutron. If Protactinium-231 absorbs one neutron it transforms into Protactinium-232. Protactinium-232 has a half life of one day ( compared to Protactinium-231's fifty thousand year half life) and Protactinium-232 only radiates low risk Beta particles. Better yet, after decaying Protactinium-232 becomes Uranium-232 which can be used as fuel by commercial power plants. One more neutron absorbed changes Uranium-232 to Uranium-233 which is the best commercial nuclear fuel known. These produced Uranium isotopes can then be used to start up new thorium power plants and are extremely difficult to use in nuclear weapons. Long story short, nuclear energy can absolutely be done safely and with a minimal ecological footprint. I can very easily argue that, when done correctly, it provides fewer human health risks and far less pollution than coal or oil.

Moreover the high operating temperatures nuclear energy offers has enormous implications for industry. Nuclear energy's immense heat makes desalination plants trivial to run and we will desperately need lots of desalination plants in a world of increased water scarcity. The reactor's heat can produce hydrogen cells from water, another extremely energy intensive operation necessary to create for more fuel efficient cars. Nuclear fuel is literally the only viable option for any type of space exploration or colonization. I hope I've given you some new ideas to think about and persuaded you to give an old ecological villain a second look. The climate situation on planet earth is desperate. Nuclear energy is our only possible route to escape a civilization ending disaster.