Nuclear Waste: What Do We Do With it?

[This is a transcript with links.]

Nuclear power used to be a conversation stopper. Luckily, we now all agree that it’s the fastest, safest, and most reliable way to get off fossil fuels. If it wasn’t for this little issue with the radioactive waste. Do you get superpowers if you roll around in it? If you came here to answer that question, you’ve got the wrong channel. But we’ll talk about the next best thing to superpowers: numbers. How much nuclear waste is there, how dangerous is it, what can we do with it, and what the heck is a ray cat? That’s what we’ll talk about today.

Almost all existing nuclear power plants run with uranium. The uranium is formed into small pellets which are then sealed into metal tubes called rods. A bundle of such rods forms the core of a reactor. In the reactor, they fuel rods exposed to neutron radiation, which starts a controlled chain reaction. This generates heat which evaporates water which spins turbines which creates electricity. As a theoretical physicist I’d say it kind of works like a water mill, just a little more dangerous.

The fission processes that generate the energy in a nuclear power plant create a lot of new atomic nuclei, many of which are radioactive. In the course of time the number of atomic nuclei in the fuel rods that can still be split declines, and the power generation becomes less and less efficient. Eventually, the fuel rods must be replaced. How often this must be done depends on the reactor, but typically it’s every 3-8 years. Think of fuel rods like world leaders but a bit more reliable.

This process of energy generation at a nuclear power plant leaves behind radioactive waste that must be safely discarded of. It can roughly be distinguished into three categories: lightly contaminated waste, intermediate level, and high-level waste, though there’s no international agreement on the exact classification.

Going by volume, most of the waste is lightly contaminated and won’t radiate for long. This is stuff such as tools, equipment, building material, shielding, clothing and so on. This makes up about 90 percent of all nuclear waste. 7 percent is intermediate and about 3 percent of it is the high-level waste that we’re concerned with here, that’s primarily what’s left from the fuel rods. It’s really very similar to wealth distribution - the highest three percent are the most toxic.

The main components of the high level waste are Strontium-90 and cesium-137, which each have half-lives of about thirty years. And then there’s plutonium-239 that has a half-life of 24 thousand years. It’s the plutonium with its long half-life that is the major problem because it means this high-level waste remains harmful for about a hundred thousand years.

In this figure you see how the radiotoxicity of the high-level waste, that’s the green line, compares to that of naturally occurring uranium, that’s the straight horizontal line. As you see, spent fuel starts out about a ten-thousand times more radiotoxic than uranium in its natural form and takes a few hundred thousand years to decay back to that level. Even Keith Richards won’t be alive at that point.

Just how deadly is this stuff? Well, depends on how much of it you’re exposed to and in which way. The uranium in the unused fuel rods isn’t all that highly radioactive. There’s a handy website here which lets you calculate just how high the radiation dose would be if you’d touch it, inhale it, or eat it.

If you happen to eat 1 gram of an unused nuclear fuel rod, that’d give you about 1 point 3 milli Sievert. This is about the maximum recommended annual dose. The fresh nuclear waste from the used rods is, as we just saw, a ten-thousand times more radioactive. Eating a gram of it would probably kill you in a couple of weeks. So please do not eat used nuclear fuel rods. It’s not healthy and also probably not all that tasty.

How much of this stuff do we have lying around? According to a 2018 report by the International Atomic Energy Agency, we have globally about 400 thousand metric tons of spent nuclear fuel. That’s the *total amount of the nuclear waste ever produced since the first nuclear power plant. The amount increases each year by about 12 thousand tons. Most nuclear waste producers are currently located in Europe and the Americas.

12 thousand metric tons a year sounds like a lot, but let’s put this number into perspective. The total amount of hazardous waste created globally each year by industrial production is a few hundred million tons. That’s about 20 thousand times as much as nuclear waste.

Another useful comparison. A 1 Giga Watt power plant can supply electricity to about a million people in the developed world. If you do this with nuclear power, it produces about three cubic meters of high-level waste per year. If you do it with coal, that produces approximately 300 thousand tons of ash and more than 6 million tons of carbon dioxide every year. Just the ash of one plant in one year is more than the high-level nuclear waste ever produced globally. And the ash of coal plants by the way is also radioactive. Yeah, that’s right, coal ash is radioactive. Not as radioactive as used fuel rods and not as long-lived, but you shouldn’t eat it either.

Why is there so little waste produced by nuclear power plants? It’s because the energy density of uranium is dramatically higher than that of fossil fuels. This is why nuclear fuel rods last years, whereas you constantly have to shovel new coal.

Okay, so for one thing we see that when you put the numbers into context, nuclear power plants produce very little waste. Also, in contrast to other waste that for the most part you don’t even know what it is before they tell you it’s in your drinking water, radioactive waste is easy to detect. Afraid of radioactivity? Buy a Geiger counter. Afraid of chemical pollution? Well, I guess you could move to the moon.

But what happens to the nuclear waste? When the used fuel rods are taken out of the reactor core, they are first stored in a pool of water at the reactor side. They sit there for a few years to cool down and let some of the nucleotides with short half-life decay. It’s the same physical principle that’s also behind twitter suspensions. After a few years, the spent fuel is moved to a dry cask storage container at the power plant site. These are temporary storage solutions. They are canisters made of concrete steel, filled with inert gas such as helium or nitrogen. Each might weigh more than 100 tons.

These encased rods still emit roughly one hundredth of a milli Sievert per hour. So if you sit next to them for 100 hours you’ve got your annual dose. You shouldn’t exactly use them as dining table, but dry cask storage is safe enough if you know what you’re looking at. The problem is keeping an eye on those things for a hundred thousand years.

Of the near 400,000 tons of existing spent fuel, 47 percent are currently in the cooling pools, that’s called “wet storage”. 20 percent are in the canisters, that’s called “dry storage”, and the remaining 33 percent have been reprocessed -- more on that later).

This highly radioactive waste has to be transported sometimes, for which there are special containers and train carriages. In a 1984 test, a train was crashed into one of these containers, filled with non radioactive stuff, at over 100 miles per hour. It was quite a scene. After the crash, the pressure inside the container was almost unchanged from before the collision. If the test containers had actually held nuclear waste, nothing would have happened to it, but everyone on the train would have been dead.

The small nuclear reactors by the way that are currently rather fashionable and that we talked about in this earlier video create more waste per energy. According to a recent study from researchers at Stanford University, the currently planned small modular reactors will increase the total volume of nuclear waste by a factor of two to thirty, depending on design. Most of this is low or intermediate level waste coming from the need of more construction material per fuel. They also found that the high-level waste that those small reactors create is more radiotoxic than that of conventional nuclear power plants because the smaller size leads to somewhat different fission reactions.

Okay, so we can seal the stuff up into concrete and move it around, but what do we do with it eventually? We could shoot it into space, but given that every once in a while a rocket blows up in the atmosphere or fall back down, it may not be such a great idea. It also wouldn’t be fair to aliens. I mean suppose a spaceship comes by *our solar systems and everyone is very excited, but it turns out to be a nuclear waste, that’d be really disappointing. We don’t want to disappoint aliens do we.

So we keep the stuff down here, but where? At the moment, no long-term storage facility exists. It’s a difficult task because it’d have to survive independent of human maintenance for hundreds of thousands of years.

The best storage solution for nuclear waste that engineers have come up with is geological repositories. They’re caves, basically, located inside stable geological formations that are expected to remain stable for at least a few millions of years.

In the 1980’s, the USA tried to create the first such facility at Yucca Mountain in Nevada. It was supposed to open in 1998, but it didn’t work out as planned. To this day nothing’s been stored there. That’s partly due to government hang-ups on safe radiation levels but mostly because it turned out people don’t like having nuclear waste in their vicinity.

Finland is currently building the world’s first deep geological repository. It’s scheduled to be opened next year. The Onkalo spent nuclear fuel repository is located near the Olkiluoto Nuclear Power Plant on the west coast of Finland.

It’s basically a lot of tunnels, about 400 meters under the ground. In them, thousands of corrosion-resistant copper canisters will be buried and the holes will be plugged with bentonite, which is a water-absorbing clay. Each tunnel will then be filled with more bentonite and sealed with concrete.

The Fins have created a computer model of the whole tunnel network to forecast how groundwater will move through cracks and fractures and the effects that this may have on people living on the surface. There’s really a lot of planning and engineering that went into this, it’s not like they just dump the stuff in a cave.

People often ask me, but would you want to live near a nuclear waste site. Guys, I’ve grown up next to chemical industry, I made an internship in the chemical industry, today I live near the largest chemical production site in the world. Every once in a while, something blows up there and we’re all asked to close the windows and pray that the shit dilutes quickly. If I had to pick one of the two, I’d pick nuclear waste storage any time.

But most people don’t like to have plutonium in their backyard, and I have some understanding for that. So how do we keep the stuff locked up safely for 100 thousand years? That’s quite a challenge. Even written language has only existed for about 5 thousand 500 years. God knows what language people will read in a hundred thousand years. If they’re still people and they still read.

This question was studied in 1981 by the Human Interference Task Force, that was commissioned by the US Department of Energy. Their task was to find a way to warn people of the future of the nuclear waste that was planned to be deposited at Yucca Mountain.

It was a team of engineers, anthropologists, nuclear physicists, behavioral scientists, philosophers, and semioticians, that’s folks who study signs.

They came up with some general rules, including that, whatever the warning message, it should be read top to bottom and should repeat the message in several different ways, so basically like a story book for children.

The semiotician Thomas Sebeok had the idea that “if the site can be rendered repulsively malodorous for a lengthy period, that would be, at least provisionally, a deterrent against casual exploration.” He proposed creating a mythology where the actual ‘truth’ would be entrusted exclusively an ‘atomic priesthood’ and other people are told scary stories.

And this weren’t even the craziest ideas. A book from 1984 collected contributions from scientists who suggested, among other things, that the exact location of the waste be forgotten and instead “only information about the existence of nuclear waste repositories and about methods of measuring radiation be preserved”. Others proposed that “animals can be bred that will react with discoloration of the skin when exposed”. They called them “ray cats” and proposed that we creation proverbs and myths that would tell people if your cat changes color, you’re near a dangerous place.

I really love it how they assumed that in a 100 thousand years everyone alive would be a complete idiot.

In 1993, Sandia National Laboratories published a report with ideas to protect another deep repository in New Mexico. They came up with the idea of a “physical language” that maybe would be understandable by future civilizations. Examples of that would be thorns, spikes and other sharp shapes that may induce uneasiness or fear. They also proposed to draw human faces expressing horror though they might think it’s an early Munch.

In the end they mostly concluded that the best thing might be to just make sure that the storage is only accessible with advanced technical equipment. The idea is that a civilization who has the technology necessary to drill into the nuclear waste should also know what radioactivity is.

So, we’ve talked about just hiding our waste underground. But how about… recycling it?

Almost all spent nuclear fuel (97%) actually can be reused. This recycling requires extracting the plutonium and uranium from the used fuel rods, and mixing it with “fresh” uranium.

This is currently done for example in, La Hague in France, and a few other places, like in the UK and in India. In La Hague they’ve been recycling fuel rods since 1976 with a capacity of about 1,700 tons per year.

They extract plutonium, which is then used to create a mixed oxide fuel, MOX for short. This type of fuel can be used in the most common type of reactors, the light-water reactors, like the uranium fuel rods. The French use some part of this MOX fuel themselves and sell some of it to other countries. What this reuse does is basically to allow you to get more energy out of the original uranium. It doesn’t avoid waste, but it reduces the amount of waste per energy produced. However, it currently doesn’t make economic sense to reuse this fuel a second time.

Why isn’t this done in more places? Because it’s expensive. In 1996, the US National Research Council estimated that reprocessing all the existing used nuclear fuel in the US would cost more than 100 billion dollars.

In 2007 the Council declared that research and development of such technology should be halted, because the money could be better spent on next-generation reactors. Since there isn’t much of this waste to begin with, and what there is can be stored underground, this decision makes economic sense.  

However, the question of whether it makes economic sense depends on how much energy one can still get out of the used fuel rods, and there’s been quite some research on that in the past decades. For example, Russia is currently testing a different way of reprocessing spent fuel. It’s called REMIX and they say it can be used up 5 times. It’s still in the testing phase though.

Another way to reduce nuclear waste is to use a pressurized heavy water reactor. That the water is “heavy” doesn’t mean it likes its muffins too much, it means that the hydrogen in the water is replaced with deuterium, so that’s hydrogen with an additional neutron in the nucleus.

Pressurized heavy water reactors are currently the second most common reactors in use and they already have the potential of reusing their own nuclear waste. They can run on natural, un-enriched uranium, on a mix of uranium and plutonium oxides, this includes plutonium from dismantled nuclear weapons, and also on thorium and plutonium. This fuel can be recycled and reused in a number of ways.

Then there are the so-called fast reactors, fast because they use “fast” neutrons. If they produce more plutonium than they consume, they are called fast breeder reactors. The good thing about fast reactors is that they destroy the nuclear waste with the longest half-life. Most of the remaining waste decays to harmless in a few centuries rather than hundreds of millennia. You can feed used fuels from the other reactors into those fast rectors. This isn’t new technology, but it hasn’t been used as much as it could have been. Canada is currently building two of those fast reactors.

There are many ways to reuse, reprocess and cycle around radioactive stuff from one power plant to another. The whole topic gets very confusing very quickly and I know you didn’t come here for a two-hour lecture. Let me therefore just show you a summary figure from a report to which I leave you a link in the info below.

This is the amount of conditioned high-level waste in cubic meters per tera watt hour of created energy. That it’s conditioned means it’s been prepared for disposal. The most common type of running nuclear fission plants is presently scenario 1a. Scenario 1b is with one round of recycling. The scenario 1d is if you take the spent fuel from the most common light water reactors and stuff it into a heavy water reactor. The ones on the right are various advanced nuclear fuel cycles that are possible with current technology but are not presently used.

The bottom line is that we could significantly reduce the amount of nuclear waste if we’d used some of the modern technology, and final deposits sites are under development. Personally, I think that the whole topic of nuclear waste is totally overblown. Burying the stuff underground seems a perfectly fine solution to me. There are good reasons to object to nuclear power, and I went through those in my earlier video. But nuclear waste isn’t one of them.