What is the future of nuclear power?

Daniel and Kelly talk about how nuclear reactors work and explore the new techologies that try to limit the risks. See omnystudio.com/listener https://omnystudio.com/listener for privacy information.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Daniel Whiteson?

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• 2:11Daniel Whiteson?

  Nuclear power is kind of a hallmark of the modern age. Finally, all that nerding out to understand the nature of matter and how the atom was put together led to some real applications. And wow, did things get real. Nuclear physics gave us nuclear weapons and the omnipresent threat of total annihilation. But it also gave us nuclear energy, an incredible way to generate emission-free energy from weird little rocks. Later this week, we'll dig into the policies and politics of all that, whether nuclear power is a net good or bad for the environment, and talk to a journalist who explored the new pro-nuclear environmental movement.

• 2:52Daniel Whiteson?

  But today, we're going to dig into the science and make sure our next conversation is well-informed by the science. How does it all work? What about salt reactors and pebble fuels? What is the future of nuclear technology? Welcome to Daniel and Kelly's extraordinary, powerful universe.

• 3:25Kelly Weinersmith?

  Hello, this is Kelly Weiner-Smith. I'm a parasitologist who also studies space, and we are recording this episode on Pi Day.

• 3:33Daniel Whiteson?

  Hi, I'm Daniel. I'm a particle physicist, and I will judge anyone who says nuclear instead of nuclear.

• 3:39Kelly Weinersmith?

  Oh, I mean, that's fair. Yeah, or nuclear. Yeah, yeah. Judge away, man, judge away.

• 3:47Daniel Whiteson?

  I heard a lot of that in Texas when I lived there. Nuclear power.

• 3:50Kelly Weinersmith?

  Oh, man. How long were you in Texas?

• 3:52Daniel Whiteson?

  I went to Rice in Houston. Yeah. And that's where, you know, one of our presidents came from, and he said nuclear every single time.

• 4:00Kelly Weinersmith?

  Bush went to Rice?

• 4:02Daniel Whiteson?

  No, but he's from Texas.

• 4:03Kelly Weinersmith?

  Oh, yeah, got it. Okay, right.

• 4:05Daniel Whiteson?

  But one of the Bushes went to Rice with me, I think with George P. Bush, son of Jeb Bush, was at Rice with me, yeah.

• 4:11Kelly Weinersmith?

  Oh, were you two BFFs?

• 4:13Daniel Whiteson?

  No, definitely not.

• 4:14Kelly Weinersmith?

  Oh, all right.

• 4:16Daniel Whiteson?

  I mean, just that he was very political, and I very much wasn't. I don't know the guy at all.

• 4:20Kelly Weinersmith?

  Yeah, got it, got it. What is the most that you've ever leaned in to celebrating a particularly nerdy holiday?

• 4:32Daniel Whiteson?

  I don't know if it counts as celebrating a holiday, but during the pandemic, some of our friends and neighbors challenged us to a bake off competition who could make the most interesting cake with movable parts, which was a big engineering challenge. And when we showed up at their house, we had to measure the width of their door to see if our cake would fit because I made this enormous landscape with a boat that would go down a river and a windmill with pieces that turned. I think I took like a week off of work and I bought all the marshmallows and all the Rice Krispies at the grocery store to make this ridiculous landscape. Yeah.

• 5:11Kelly Weinersmith?

  Did you win?

• 5:12Daniel Whiteson?

  Oh, yes. We absolutely destroyed them just by sheer size, you know? I was going for like, this thing has got to pop. So yeah, it was pretty impressive. I gotta say.

• 5:21Kelly Weinersmith?

  I mean, that's a good way to pass the pandemic. Did you take a picture?

• 5:25Daniel Whiteson?

  We have a picture somewhere. Absolutely. And then it had other weird downstream consequences because nobody could eat that much Rice Krispies. And so we ended up throwing a lot of it away, which led to a huge explosion in the neighborhood rat population. And then we ended up discovering a rat's nest, literally like a mom and 10 little rat babies near our garbage can. And when you discover a rat's nest, the mom will just abandon the babies. So then we had like 10 cute little rat babies and they starved to death because the mom wouldn't come back and you can't feed rat babies. I don't know if you know much about rats, but like they have to be nursed and also they can't poop on their own. Like rat babies are a whole

• 6:07Daniel Whiteson?

  thing. And so then we felt really bad about that. And that's why we ended up adopting rats.

• 6:12Kelly Weinersmith?

  That story was a roller coaster ride, Daniel. There were some real highs and real lows there.

• 6:17Daniel Whiteson?

  I know. And because we had such a good experience with having pet rats, the kids were able to convince me to get a dog. So the reason we now have a dog who is an integral part of our family is because I went all out celebrating this crazy engineering challenge bakeathon.

• 6:34Kelly Weinersmith?

  Oh my goodness. It is kind of incredible. The way small things in life can lead you down completely different paths. Well, your story is way more wholesome than mine.

• 6:43Daniel Whiteson?

  Yeah. What's yours?

• 6:44Kelly Weinersmith?

  I was born on mole day. So Avogadro's number is what 6.23 times 10 to the 23rd or something like that, but October 23rd. And so for my junior and senior year of undergrad. I had chemistry themed birthday parties and it would be like,

• 7:01Daniel Whiteson?

  That sounds really fun. Why didn't I get invited?

• 7:03Kelly Weinersmith?

  If I had known you, man, you would have been invited, but it was, you know, like how many electrons are in beryllium? Wrong. Drink. And it was,

• 7:14Kelly Weinersmith?

  because, you know, no one knows that.

• 7:15Daniel Whiteson?

  Nobody knows that because it's chemistry. It's all exceptions.

• 7:18Kelly Weinersmith?

  That's right. That's right. And, you know, my friends didn't know chemistry very well either. So it was a, we had a really great time.

• 7:25Daniel Whiteson?

  But this is high school. So you're what? Drinking soda or punch or something?

• 7:28Kelly Weinersmith?

  Undergrad, undergrad.

• 7:29Daniel Whiteson?

  Undergrad. Oh, so these were fun parties.

• 7:32Kelly Weinersmith?

  These were fun parties. We were all of legal drinking age and we were careful. We watched out for each other, but way less wholesome than a cake with a waterfall.

• 7:43Daniel Whiteson?

  Well, it does sound like your parties are maybe the only way to make chemistry fun.

• 7:48Kelly Weinersmith?

  We did have a good time. The benzene ring and I, me and my five friends, six of us total, because there's six carbons in a benzene ring.

• 7:56Daniel Whiteson?

  And today on the podcast, we're going to be exploring how small decisions can lead to big consequences that also involve chemistry. Nuclear power is incredible because these tiny little weird rocks can lead to incredible influence on our economy.

• 8:10Kelly Weinersmith?

  I am always impressed by the way you bring our tangents back to the topic.

• 8:15Daniel Whiteson?

  I don't know if it's easy, but I'm like, wow, we could do a whole episode on Kelly's weird college parties.

• 8:21Kelly Weinersmith?

  I think our listenership would go down pretty fast at that point, but okay. So today we're talking about nuclear power and I'm really excited to be talking about the sort of advances in nuclear power technology now. Cause when Zach and I wrote Soonish, which came out in like 2017, we did some research on advanced nuclear fission reactors. And I always have to pause before I say fission infusion because I memorized it in the opposite way initially. And so now I will always pause and have to think through it. But anyway.

• 8:51Daniel Whiteson?

  Well, you got nuclear, right? At least you didn't say nuclear fusion.

• 8:55Kelly Weinersmith?

  There you go. That's right. Now I'm going to avoid saying that word too out of a concern for messing it up. But we had a chapter on fission and a chapter on fusion. But I haven't thought about this in about the decade since we researched the topic. And so I'm looking forward to your coverage of what the new and exciting things are in the world of advanced nuclear reactors.

• 9:13Daniel Whiteson?

  Yeah, if we're going to talk about nuclear power, we need to understand how it works and how it's changing because it's not a stagnant field, right? Nuclear reactors today are not the same nuclear technology your grandparents grew up with. And so there's lots of promising directions, some with more waste, some with less waste, some with greater risks, some with smaller risks. And so it's crucial to understand the whole spectrum of possibilities in order to have an informed conversation about nuclear politics, which we're going to have in the next episode. So I was curious what listeners thought about the future of nuclear technology. What have they heard about in terms of advanced nuclear reactors? So I went out there and I asked our group of volunteers, what is the most promising advancement in nuclear power technology? Here's what they had to say. If you'd like

• 9:58Daniel Whiteson?

  to play for a future episode of the podcast, we really, really, really, really want to hear your voice on the pod. Write to us to questions at danielandkelly.org. So think about it for a minute before you hear these answers. What do you think is the most promising advancement in nuclear technology? Here's what our listeners had to say.

• 10:18Speaker 06

  Just for Kelly, I've heard of biologists working on microbes to solve our nuclear waste problem. Somehow they eat the nuclear waste. No idea how it works, but hey, yo, biology.

• 10:27Speaker 07

  There are a few promising advances, but the most promising comes in the form of superpowers from what used to be just ordinary bug bites.

• 10:34Kelly Weinersmith?

  But where I would like to see more study is in medical applications such as radiation treatment for cancer. Not running redundant systems through the same conduit. I think the most promising advance is the potential to use what used to be waste as fuel for a whole new set of nuclear reactors.

• 10:56Speaker 01

  Reusing or repurposing fuel that has been expensed. Reusing the nuclear waste as opposed to storing it. Without a doubt, fusion. Decreasing the waste. People have probably paid a lot of money in PR to make me think of thorium, so I'm going to say thorium.

• 11:14Speaker 03

  SMRs, which are those small modular reactors. Micronuclear energy, where they're able to build much smaller nuclear power stations, I guess. To me, what seems most interesting is the liquid thorium salt reactors, which can use up the material really well, from what I understand, or have beneficial byproducts and are also seem a lot safer.

• 11:41Kelly Weinersmith?

  The very teeny tiny amount of nuclear material that's necessary now to create vast amounts of energy, which means it's not as big of a risk of a meltdown and things like that. Perhaps the reactors are more efficient, more manageable, less likely to melt down in the case of an earthquake or tsunami or other natural disaster. As usual, a lot of fantastic answers. We're not going to be talking too much about fusion today, but if you want to hear more about fusion, a little while back, we recorded an episode on whether or not there would be enough fuel available to run fusion plants. And we go through the science of fusion reactors there as well.

• 12:23Daniel Whiteson?

  And throw cold water on that whole industry.

• 12:26Kelly Weinersmith?

  Well, I remember we were optimistic at the end that, you know, once we got fusion going, maybe we'd get the technologies needed to make like deuterium and trinium more available, but

• 12:36Daniel Whiteson?

  Maybe.

• 12:38Kelly Weinersmith?

  Maybe. But all right. But now today, we're talking about fission reactors in particular.

• 12:43Daniel Whiteson?

  Yes, exactly. And so let's dig in first and make sure we and Kelly and everybody understands the difference between fission and fusion.

• 12:52Kelly Weinersmith?

  Ouch. Okay.

• 12:52Daniel Whiteson?

  Because they're closely related, but very, very different, right? So fusion is what powers the universe. It's what makes stars bright. It's where all the energy on Earth comes from. It's really almost ubiquitous in the universe. Fusion is much, much more rare. A fusion is basically when you take light elements, hydrogen, helium, things lighter than iron, and turn them into heavier elements. So you stick them together and energy is released. So for example, if you take hydrogen and you stick it together to make helium, energy is released and the mass of that helium is less than the mass of the hydrogens combined. So energy is released there in fusion. So that's fusion is you take light elements, you stick them together and energy is released.

• 13:36Kelly Weinersmith?

  Which sounds easy, but requires super extreme conditions to make happen, which is why it's been so hard to make a fusion plant.

• 13:42Daniel Whiteson?

  Exactly. Those nuclei do not want to stick together. They have coulombic repulsion. You need high density, high pressure, all sorts of stuff to make that happen. If you make it happen, it releases energy and that helps it happen. So it's this cool ignition process where the energy released from fusion helps make the next round of fusion happen. And you have a sort of similar chain reaction going on in fission, but fission is the other direction. Fission says, take a heavy element, break it open to make it a lighter element and energy is released. In that case, you might wonder a whole lot of second, didn't Daniel just tell us that when you squeeze light elements together to make them heavy, energy is released? Now he's saying if you break elements apart to make them lighter, energy is released? And yeah, those do sound contradictory and the difference is whether you're starting with

• 14:27Daniel Whiteson?

  light or heavy elements. So if your elements are light, like below iron specifically, fusing them together releases energy, making them heavier towards iron. If your elements are heavy, like uranium, something heavier than iron, breaking them apart, bringing them again towards iron releases energy. So basically anytime you're taking a step towards iron, which is like the middle of the periodic table, you are releasing energy.

• 14:52Kelly Weinersmith?

  Can you remind me, inside of stars, is that where we get iron and everything up from that? What is the break off there?

• 14:59Daniel Whiteson?

  Yeah, it's about iron. So inside stars, you mostly have hydrogen. Hydrogen fuses to make helium and then that fuses to make neon and carbon and oxygen and heavier stuff, silicon, nickel, all the way up to iron. And that whole process keeps the star hot because every step along the way releases energy. What happens when you start fusing iron if a star is really big and really hot? And has the high enough temperature to fuse iron that cools the star? It takes some energy because it costs energy to fuse iron together into heavier stuff. That cools the star and kills it. So that's the end of a star's life. When it has enough iron in it that that iron starts to fuse and cools the star. So you can't really make stuff heavier than iron in any substantial quantities inside a star.

• 15:43Daniel Whiteson?

  To make this stuff heavier than iron, uranium, platinum, gold, all that good sparkly stuff. You need other kinds of events, collisions of neutron stars and supernova, for example. Very briefly have the conditions to make those. It costs a lot of energy to make those very heavy stuff.

• 16:00Kelly Weinersmith?

  Okay, interesting. All right. So fusion, really hard to do unless you're in the sun. Fission, much easier to do using big stuff.

• 16:07Daniel Whiteson?

  Yeah, exactly. So find some uranium, shoot it with a neutron, for example, the uranium will break apart. And it will release more neutrons and those neutrons can hit more uranium atoms, which can release more neutrons. So if you have it set up correctly, like your fuel is dense enough. So there's a high enough chance for that neutron to hit another uranium nucleus. And the neutrons are at the right speed to make that happen, like really fast neutrons or slow neutrons. Might be more or less likely to make the uranium nucleus break up. We'll dig into that in a minute. Then you can get a chain reaction. If it's a runaway reaction, like the fuel is very, very dense and things are growing exponentially, you get a bomb. That's a nuclear bomb. Don't do that, folks.

• 16:48Kelly Weinersmith?

  Not in your basement.

• 16:49Daniel Whiteson?

  If you manage it so that the rates at which one nucleus is spurring the fission of another nucleus. You regulate it to be steady, then that's a reactor. It's releasing energy. But it's not growing exponentially out of control.

• 17:03Kelly Weinersmith?

  And why is uranium the sweet spot on the periodic table for stuff you want for your fission reactor?

• 17:10Daniel Whiteson?

  It's not really that sweet. It's just something that's around and for a while was pretty cheap to mine. As we'll hear about, there are lots of things that are fizzle. It's just a question of what's present in the earth's crust, what's cheap to mine, what's not already being used by other industries. And so uranium is actually not a great source for fuel because most of the uranium we find in the earth's crust is an isotope that's not great for fission. It's uranium 238. Uranium 235 is pretty good for fission, but most of what we find in the ground is uranium 238. Less than 1% of natural uranium is the kind we want. So as we'll talk about, there are other options like thorium that are maybe even better for nuclear fuel.

• 17:54Kelly Weinersmith?

  Let's dig in then to uranium a bit more. So you said we mostly find uranium 238, but we need 235. How do you get it from 238 to 235?

• 18:05Daniel Whiteson?

  So what you do is just enrich it. Like remember chemistry lab, when you have like a pile of goo and you need to separate it out into the elements of the goo, you can like boil it and one will boil off, or you can, you know, try to make them settle or something. There's lots of different tricks in chemistry. And what they typically do, because one of them is heavier than the others, they use a centrifuge. So if you remember, like hearing about Iranian centrifuges as they're trying to purify uranium, that's a typical strategy because they have different masses is use a centrifuge. And so you can enrich your uranium, run the centrifuges more and more and filter out the 238, you get a higher and higher fraction of 235.

• 18:42Kelly Weinersmith?

  I've always been unreasonably concerned about USB sticks after hearing the story about how the virus that messed up the Iranian centrifuges was brought in by somebody who just had a USB stick that had the virus. And then when they stuck it into one of the computers, it spread, which is like amazing. And I'm sure there's a lot of other things I should be way more worried about. And of course, like, nobody really cares about what I've got going on in my office. But, but I remember thinking that was just like such a cool story. And now every time I see a USB stick, I think, oh, what's on you?

• 19:11Daniel Whiteson?

  It's a pretty cool story about engineering, like cyber espionage, pretty cool stuff. But are you running a uranium centrifuge and your science farm?

• 19:19Kelly Weinersmith?

  Well, I mean, why would I admit something like that to you, Daniel? On air, that's ridiculous, but you wouldn't be a good spy at all. But yeah, I mean, the story there is that like this virus messed up their centrifuges because there was concern that Iran was turning 238 into 235 so that they could start making weapons. And by messing up that process, by messing up all of their super expensive centrifuges, we at least managed to slow them down.

• 19:42Daniel Whiteson?

  And so you need to enrich uranium because you need dense enough source of the good stuff, uranium-235. If you don't have it dense enough, then it makes neutrons when it splits, but then those neutrons don't find other 235 nuclei and it just peters out. So you need it to be dense enough. You need to enrich it up to like 2 or 5%. Doesn't have to be pure uranium-235 at all, just up to like 2 to 5%. But this is still kind of a problem because you end up mostly just burning the U-235 and the U-238 is just sitting there and it sits there and makes heavy elements which are bad. So this is like really not a great mixture. A lot of the waste comes from U-238 being in the reaction, not being part of it, and

• 20:25Daniel Whiteson?

  then getting converted to toxic stuff. So it's not like a great situation. But what you need to do to make uranium fission happen is to enrich your fuel so you have like 2 to 5%. Then you also have to engineer the speed of those neutrons to make things work.

• 20:41Kelly Weinersmith?

  So if you want the neutrons to be going quickly so that they're bumping into the 235, why would you want to slow them down? It seems like more neutrons is, you know, that's better, that's more energy.

• 20:51Daniel Whiteson?

  Yeah, it seems like fast neutrons are good, right? The whole point is to get energy out. Well, the thing is that U-235 is a little persnickety. Like if you shoot fast neutrons at it, sometimes they will just go right through. They will not make it fizz. What is the verb anyway? Fission? They will not make it fission? Can one atom fission? That seems weird.

• 21:10Kelly Weinersmith?

  They will not fission it. I don't know.

• 21:13Daniel Whiteson?

  I will not stand for that. Anyway, U-235 likes slower neutrons. U-238 likes faster neutrons, but uranium fission doesn't make enough fast neutrons to sustain fusion with 238. So you gotta use the 235 and you gotta slow down the neutrons till they're in the sweet Spot for making other uranium nuclei go. So you've got to moderate the temperature. So you hear a lot about neutron moderation. And so the way they do this is they use water. So you have like these fuel rods and then you have water around them, which is also good for cooling them and extracting the energy. But it slows down the neutrons to keep the reaction going. It's a little counterintuitive, but this stuff is a little bit sensitive.

• 21:53Kelly Weinersmith?

  I thought the answer, because my memory is great. I know I wrote about this about a decade ago, but I thought the answer was going to be you don't want the neutrons to go too fast because you don't want the reaction to go too fast and overheat. But that's not the answer. I was misremembering. Okay, so you've got the water, the water is heating up. How does this create energy? Does the water turn into steam and turn a turbine? Or is the energy being collected in some other way?

• 22:17Daniel Whiteson?

  Yeah, so not directly. The most popular technology is called a pressurized water reactor. You have uranium rods surrounded by water. The water moderates the speed of the neutrons, also keeps the core from overheating. And then you've got to extract the energy from that water. So that it heats up the water. How do you get the energy out of the water? Typically a turbine, right? Also, that water becomes radioactive. So you want to buffer yourself from that. So typically there's like a heat exchanger with that water. Well, then heat up other water. You have like these two corkscrews that interwove with each other, sort of like electrical inductance, but with heat. Or just basically a radiator. You have this water pass near other water and the hot nasty radioactive water heats up the clean cold water,

• 23:02Daniel Whiteson?

  which then boils into steam and then turns a turbine. So that's the most common steps. And this is called a light water thermal reactor, sometimes known as a pressurized water reactor.

• 23:14Kelly Weinersmith?

  If I'm remembering correctly, the reason that light water thermal reactors are the most common kind of reactor out there isn't because we were super careful and we looked at all the possible reactor designs and there was definitely none that could be better than this. But because we sort of happened upon one design because it fit really well in our submarines that we wanted to have nuclear powered. Is that story correct?

• 23:35Daniel Whiteson?

  Yeah, that story is correct. In the 50s, they were exploring lots of different technologies. Some of which we're going to talk about thorium and other technologies. But this was a good fit for the military because one of the waste products of this reactor is plutonium, which the military wanted to produce anyway for their weapons. Also, if you're on a ship or a submarine, places that the military wanted to put nuclear power, water is plentiful. It's not so hard to find water. And so these light water thermal reactors were explored for the military. And the government basically stopped funding all these other directions. The government's decisions early on determined like what was explored and what was made economically feasible. No private industry was like involved in developing nuclear technology.

• 24:19Daniel Whiteson?

  This is definitely like a public investment by the government.

• 24:22Kelly Weinersmith?

  All right, well, let's take a break and when we get back, we'll talk about some of the risks of this particular kind of reactor.

• 24:38Speaker 01

  That sound? That's pro squash. Some of the fastest rallies in sport played inches from the crowd. The National Squash League is back in full swing for season four. The sport is heading to the 2028 Olympics for the first time, and you can see it up close right now in a city near you. Watch every match for free on YouTube. Search National Squash League and hit subscribe or follow live updates on Instagram at NSL.Sport.

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• 25:48Kelly Weinersmith?

  Like Daniel. People would always think I was lactose intolerant. So I just kind of shortened my explanation to I'm deathly allergic in a big way that defined a lot of my childhood. And while there are challenges, there are moments that remind you you're not alone. One of the best guys that I dated, he made a point to memorize all my food allergies. So join us and hear their stories and more because living with food allergies isn't just about what you can't eat. It's about still having your seat at the table. Brought to you by Genentech and Novartis. Listen to At The Table, the food allergy podcast on America's number one podcast network, iHeart. Follow At The Table and start listening on the free iHeart Radio app today.

• 26:40Kelly Weinersmith?

  All right, we just finished talking about how light water thermal reactors work. Let's talk about some of the risks of this particular kind of reactor. Go for it, Daniel. Your turn to be the negative Nellie.

• 26:53Daniel Whiteson?

  I don't know how to order them, but you know, it's called a pressurized water reactor. So let's start with the pressurized water. You've got this water that you want to keep liquid because you want to keep it flowing. It's easiest to control if it's liquid. It's a more efficient heat transfer if it's liquid. You've got other things like control rods, graphite, you want to dip in the liquid. So basically you want to keep this stuff liquid, but it's also really hot. So how do you keep something liquid if it's really hot? Chemistry tells us you need to keep it at high pressure, right? Basically build a really strong vessel and force the water to have high pressure. So it doesn't turn into steam. We're talking like 100 to 150 atmospheres of pressure. So really high pressure stuff. This is kind of dangerous because very high pressure, right?

• 27:36Daniel Whiteson?

  If you lose containment, you know, you can imagine like a rivet pops and steam shoots out, right? It's super hot, it's super high pressure, it's going to burn somebody. Also, as soon as you lose pressure, you're losing your coolant, right? This water is crucial to keeping the core from overheating, right? We don't want the core to turn into a bomb. We don't want the energy from that thing to like melt the Reactor itself. So you've got to keep the temperature at a certain level so it doesn't melt down. That's literally what melting down happens. But as soon as you lose containment of your water, then you're losing your coolant and boom, you have overheating and a meltdown. This is what happened to Three Mile Island, like one of the water hatches jammed. At Fukushima, one of the water pumps was knocked out.

• 28:20Daniel Whiteson?

  And in Chernobyl, the water boiled off. And so this is really important to keeping this whole thing going is keeping this very high water pressure. And that's not easy to do. And if it fails in any way, boom, you have a disaster.

• 28:33Kelly Weinersmith?

  So one, you have to worry about the boom, but you also have to worry about when the water gets out, it's a steam. Can that steam travel great distances or does that tend to settle near the plant?

• 28:43Daniel Whiteson?

  If you have any loss of containment, then the clouds can travel great distances. Like what happened at Chernobyl is these clouds of radioactive dust and steam and all sorts of stuff drifted over Europe and like caused cancers all over Europe. It was really bad. Yes, it's terrible.

• 28:59Kelly Weinersmith?

  This pressurized containment problem, is that only a problem for light water thermal reactors? Or is this a problem for some of the other reactor types we're going to talk about as well?

• 29:08Daniel Whiteson?

  It's only a problem for light water thermal reactors, for these pressurized water reactors. And there's lots of designs inspired specifically by avoiding having high pressure liquid. And we'll talk about some of those. But this is by far the most common, like something like 85% of all reactors in the world are pressurized water reactors.

• 29:27Kelly Weinersmith?

  All right. So the pressure part is not great. Let's move on to another risk.

• 29:34Daniel Whiteson?

  Yeah. So the U238, that's mostly what's in your fuel rods, is not burning. It's not undergoing fission, but it does get hit with a lot of neutrons and it breaks down into other stuff. It can make things like plutonium, right? Plutonium 239, for example, or plutonium 238. 238 is short-lived and very, very toxic. It has a half-life of 88 years, but 239 has a half-life of 24,000 years. So you've got sort of two different angles here. One is you're making weapons fuel, right? Plutonium is excellent for making weapons. And you're creating stuff that has like thousands of years or sometimes millions of years, like neptunium 237 has a 2.1 million year half-life.

• 30:18Daniel Whiteson?

  This stuff is toxic for a long, long time.

• 30:21Kelly Weinersmith?

  So how big is the weapons risk? If you run one of these plants for a decade, Does that give you enough plutonium to make a big bomb? Or do you need to run it for 200 years? Or does it depend on a lot of other factors? How much weapons-grade radioactive material is produced?

• 30:37Daniel Whiteson?

  Not a lot, but you don't need a lot to make a few bombs. Right? And in order to have like geopolitical deterrence, you don't need a huge number of bombs. Like North Korea started out with like three, four, five bombs, but that completely changed the politics of dealing with North Korea. Right? One bomb dropped on Seoul is a huge impact. And so, yeah, you can make a weapons significant amount of plutonium without a huge industry. Absolutely.

• 31:04Kelly Weinersmith?

  This is one of the things that's so frustrating to me about nuclear power is it's so clearly a technology that would be, you know, great in this world where we're dealing with climate change. If only humans weren't so human-y.

• 31:19Daniel Whiteson?

  Yeah, exactly. And, you know, there's two sides to this as we'll dig in when we talk to Becca later this week. Like, most of the stuff, when you make it, you just keep it on site at the reactor. You don't drive it all around. But there's this question of like, where is it going to go long term? You know, like, can we just bury it in the ground? Can we put it in Yucca Mountain? Should we launch it into space? Isn't that a terrible idea? And, you know, a lot of people are concerned about that and the environmentalists are very concerned about that. On the other hand, you have to remember that this stuff has a finite lifetime. Right? This stuff will decay away into something non-toxic after hundreds or thousands of years. But if you're making really terrible forever chemicals with fossil fuels, that stuff is poison forever. Like, literally, you come back to Earth in five billion years, it'll still kill you.

• 32:04Daniel Whiteson?

  And so we should remember that a long lifetime is still shorter than an infinite lifetime.

• 32:09Kelly Weinersmith?

  Speaking of sending nuclear materials to space, once there was a piece of, I think it was polonium, that was being sent up and the rocket blew up and the radioactive material sort of scattered over the Soviet Union. And then the Soviet Union also sent up a bunch of tiny nuclear reactors to power some of their satellites. And one of those satellites went rogue and the nuclear material that powered that reactor scattered over northern Canada. So, you know, sending the stuff into space could go wrong and scatter it over a big stretch of land if anything happens to that rocket. These are complicated problems.

• 32:42Daniel Whiteson?

  Basically, each time you do a launch, it's a potential dirty bomb. Right?

• 32:45Kelly Weinersmith?

  Yeah, yeah. You gotta be really careful about this stuff.

• 32:47Daniel Whiteson?

  And nobody wants dirty bombs. I don't want clean bombs or dirty bombs, but I definitely don't want dirty bombs.

• 32:52Kelly Weinersmith?

  Yeah, no, thumbs down to dirty bombs. We both agree.

• 32:55Daniel Whiteson?

  And there's another factor to this waste, which is the waste produced in the actual reactions is not that large. You know, the total amount, the volume of waste produced worldwide in the history of the industry is not huge. It's like a football field size, but that's not all of the waste. Like in order to get uranium out of the ground, you have to mine it. And there's a lot of waste produced in that mining. Some of that is also radioactive and toxic and much, much higher volumes. So when you hear people talk about the waste from nuclear power plants, yes, the actual waste from the reactions is quite small and very toxic, but there's a much larger volume of waste produced in the processing to get the fuel to the plant. That's not always considered in those conversations.

• 33:39Kelly Weinersmith?

  And what do we do with that waste?

• 33:40Daniel Whiteson?

  Yeah, that waste we store on site near the mines and like that's dangerous also when you're polluting water tables. And so, yeah.

• 33:47Kelly Weinersmith?

  Oh, yeah. No easy answers. Okay. All right. So let's move on. We've now talked about the benefits and risks of the light water thermal reactor. Let's move on to some of the alternative designs that have sort of different problems and different benefits. Let's start with the boiling water reactor.

• 34:03Daniel Whiteson?

  So the most obvious thing to do is to focus on the pressure of the water. Can you make a design for a nuclear reactor core that doesn't require high pressure water? So there's a boiling water reactor that says, hey, let's just let the water boil and turn into steam. And that makes the heat transfer less efficient. So you have to build it larger. So you can have like more of this steam and the water, of course, is less dense because now it's steam, but it lets you lower the pressure down to like 75 atmosphere because now you can just have the water turn into steam and then you use that steam directly to generate energy. Basically what you were saying earlier. So instead of having this like weird heat exchange system where the hot water boils other clean water, you just use the dirty water directly to make your steam.

• 34:47Kelly Weinersmith?

  So that seems clearly better than the other method. Is there a downside to this reactor?

• 34:54Daniel Whiteson?

  Downside is now you are using a radiated water and steam to generate your energy. And so it's a little less contained. You have it like now involved in these turbines and stuff like that. So you haven't like decoupled the energy production and the electricity production. So there's some risks there. Also, it has to be larger. And so, for example, we're talking about later, the benefits of small modular reactors. Those require a technology that has very dense fuel and very small reactor core. And you can't do that with a boiling water reactor. You need a large core because the steam isn't as dense and the heat transfer is less efficient.

• 35:28Kelly Weinersmith?

  I think I'm still a little confused about the decoupling thing. Is the point that you're going to at some point also need to replace the turbine? And now you have a radioactive turbine and that's the problem?

• 35:39Daniel Whiteson?

  Yeah, exactly.

• 35:40Kelly Weinersmith?

  Okay, so about what percent of our reactors right now are boiling water reactors?

• 35:45Daniel Whiteson?

  These are like 15%. So a good number of these, and this is proven technology, right? And I mentioned this because some of the stuff we're talking about later is like a little bit more speculative. But these are reactors that are running. We know how they work. We have people out there in the world with experience running these reactors. It's not speculative. It's not experimental technology. This is like, it's been proven. And then the last piece are heavy water reactors. Like 5% of the reactors out there say, well, let's just take the pressurized water and replace it with heavy water. So heavy water is not just like water that feels heavier. It's water where some of the hydrogen has been replaced by an isotope of hydrogen. So instead of just having like a proton as for the hydrogen, you have like a proton and a neutron together.

• 36:27Daniel Whiteson?

  Basically, deuterium, one of the important fuels for fusion, can be used as an alternative moderator in your reaction in a heavy water reactor.

• 36:37Kelly Weinersmith?

  And you had told me in that fusion episode that there's not a lot of deuterium. Is that right? Is getting enough deuterium one of the difficult things of running these reactors?

• 36:47Daniel Whiteson?

  Yeah, exactly. Deuterium is not free and it's not that easy to filter out. I mean, there's a lot of it out there, but it's a little bit rare. And so heavy water is an excellent moderator because it will slow the neutrons down to the speed that U235 needs it, but it never captures them, right? And so it lets them fly through. Basically, it's perfect at converting fast neutrons to slow neutrons without ever gobbling up the neutrons. And so you could actually run a heavy water reactor without using enrichment. You can have a much lower density of U235 in your fuel for a heavy water reactor. So there's pros and cons there.

• 37:22Kelly Weinersmith?

  Okay, so it's good to use more 235?

• 37:26Daniel Whiteson?

  It lets you use less 235. Usually you need more 235 so the neutrons can find other 235 nuclei. But here, heavy water converts all the fast neutrons into exactly the right neutrons that U235 needs so that even if you don't have an enriched fuel, those neutrons will find enough 235 nuclei to get the reaction to keep going.

• 37:48Kelly Weinersmith?

  But 238 is the stuff that turns into the nasty byproducts, right?

• 37:52Daniel Whiteson?

  Yeah, exactly.

• 37:53Kelly Weinersmith?

  So now you've got the same kinds of waste and you have the same confinement issues as the light water reactor?

• 38:01Daniel Whiteson?

  Yeah, you still have to keep it at high pressure here because you have the same issues. You want to keep the water liquid, et cetera. So the heavy water reactor is one variation of the pressurized water reactor. It's not a boiling water reactor.

• 38:13Kelly Weinersmith?

  Okay, so you still have the same problems with waste and the same problems with pressure, but you don't have to start the process by enriching the uranium as much?

• 38:21Daniel Whiteson?

  Yeah, exactly.

• 38:22Kelly Weinersmith?

  Okay. All right, so we've gone through the main kinds of currently existing nuclear fission reactors that are out there. Let's take a break and when we get back, let's talk about some of the more advanced designs that are being researched at the moment.

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• 40:48Kelly Weinersmith?

  And we're back. All right. So we talked about the most common nuclear reactor designs that we've got at the moment. And now we're going to talk about some more advanced designs that are being researched. So Daniel, tell us about gas cooled reactors.

• 40:59Daniel Whiteson?

  Yeah, so these are super cool. Ha, ha, ha. The idea is to use something like helium to cool your reactor. Helium is excellent because it's a noble gas. It hardly ever reacts. It likes to ignore everything. So it's basically inert. It's a very high heat capacity. So it'll absorb a lot of heat. So take your water out and replace it with helium. But the water also was doing two jobs, right? The water was not just keeping your reactor from overheating. It was also moderating the neutron speed. So they were just right for getting the U235 to do its thing. So now you need something else to do that moderation. And so they use graphite, either rods of graphite that you insert between the rods of fuel, or you can

• 41:41Daniel Whiteson?

  take the uranium and coat it in graphite. Graphite is awesome because it will moderate the temperature and it's like almost indestructible. You cannot get a nuclear reactor up to high enough temperatures to melt this graphite. So for example, you coat your uranium in graphite. It does the moderation and it's basically impossible to have a leak or a meltdown or to lose containment because the graphite is really going to wrap it up forever.

• 42:08Kelly Weinersmith?

  For this hot stuff that's happening, do you have a container of water that makes the steam that turns the turbine? Is that where the power part happens?

• 42:16Daniel Whiteson?

  Yeah. So the uranium is wrapped in graphite. That whole thing is surrounded by helium. Then the helium has a heat exchanger to water and then that water turns turbines. We should do a whole episode about like, why we still use steam driven turbines. Like we have this incredible, modern age technology. And in the end, it's basically a steam engine.

• 42:34Kelly Weinersmith?

  Yeah.

• 42:35Daniel Whiteson?

  I think that's super fascinating. But yeah, so uranium surrounded in graphite, covered in helium, and then the helium heats water, which turns a turbine, which generates electricity, which powers your phone.

• 42:47Kelly Weinersmith?

  Okay, so I've got graphite in my pencil. And when I go and I draw something and I Shade it in. I always have to like brush away the graphite because it's all like dusty and stuff. Do you have a similar problem with like the uranium pebbles rubbing up against each other and graphite becomes a powder? Do you have to worry about that powder?

• 43:02Daniel Whiteson?

  Graphite is really complex stuff and there's lots of different forms of it. And so the kind that's in your pencil is like a very, very soft kind of graphite. You can also make a very, very durable, very hard graphite, and that's the kind they use. So nobody is like going to be drawing portraits of people with graphite pebble fuel. But you're right, there is some graphite dust produced and we do have to worry about that. But this is very cool technology. They call it pebble fuel. Basically, there's no meltdown risk here at all. It's really amazing.

• 43:31Kelly Weinersmith?

  So why don't we have these yet then?

• 43:33Daniel Whiteson?

  So we do have some of these. There are seven of them that have been ever made. It's sort of experimental. It's a little tricky because in order for it to work, you have to have very highly enriched fuels. They call these H A L E U, highly enriched fuels. And that's like five to 20% enrichment. And so this is much more enriched than the typical stuff, but it allows for very small, very dense reactor cores. And it allows for small modular reactors. The idea is like, don't build this like huge plant that takes an enormous amount of space and produces energy for like half of California. Shrink the reactors, make them like the size of a shipping container, and then you can produce them at scale. So now they become modular.

• 44:18Daniel Whiteson?

  Every reactor we've ever built is basically a one-off bespoke design, which is one of the reasons why they take like 20 years to build and to regulate and to check and to verify that it's actually going to work, right? If you had a plant that pumped these things out and you knew every single one was the same, you could develop once the technology and then pump them out. And the idea is that you could distribute them to lots of places where otherwise there isn't a market for nuclear energy. Remote places, rural places. So you would have fewer bigger plants and more small plants. And that's enabled for technologies that have a very small core.

• 44:55Kelly Weinersmith?

  Okay, awesome. Alright, so you've got these cheaper modular reactors. You still have to worry about bad byproducts being made with those uranium pebbles eventually, right?

• 45:07Daniel Whiteson?

  You do. The pebble fuel itself is fascinating because you can use it over and over again. It doesn't use up all the fuel immediately. So the pebble remains in the core for like three years and then they circulate it in and out several times to burn it up. So like a single pebble, you can use it for decades. And then in the end, all the fuel is still encased in your graphite, right? So all the bad stuff is also inside the graphite. So basically it comes out already sealed.

• 45:32Kelly Weinersmith?

  That's amazing. Do you not have to worry about the helium because it doesn't get radioactive the same way water does because it doesn't react to stuff?

• 45:37Daniel Whiteson?

  Exactly. It's inert.

• 45:39Kelly Weinersmith?

  Awesome. Okay, so it makes less bad waste that's also easier to clean up while not having this explosion risk.

• 45:46Daniel Whiteson?

  Yeah, exactly. And so this is very promising. And there's a bunch of private industry developing this technology. It's like exploding right now. And I talked to a nuclear chemist here at ECI and asked her like, is this realistic? Or is this just like private industry hype? And she said, no, it's real. The tech has been demonstrated. We know this works. It's really just a question of getting it regulated and getting the economics to work.

• 46:09Kelly Weinersmith?

  All right. So it sounds like it's all upsides for this particular reactor. Are there any downsides?

• 46:15Daniel Whiteson?

  So you know, this is a newish technology. They're still developing it. There's only seven that have ever been made. Two of them are operating now in China. And in some cases, there were issues, like there's a reactor in Germany where they had exactly the problem that you were talking about. The graphite pebbles were rubbing against each other and they made dust. And that dust is radioactive. It has cesium, it has strontium. It's not good. And so there's always risks there. But you know, people are working on this technology. It's new. It's promising. It's definitely not perfect.

• 46:43Kelly Weinersmith?

  Okay, awesome. So let's move on to the last kind of new reactor that we're going to be talking about today, which is liquid metal salt, which is definitely the most awesome sounding of the reactors.

• 46:55Daniel Whiteson?

  I know. It's super cool and it sounds much more dangerous. And the idea is let's avoid again, having very high pressure water. That seems bad. So let's replace the water with something else that doesn't need to be super high pressure in order to stay liquid. So metal, for example. Metal is a very high heat capacity. It can remove heat very quickly. And it doesn't need to be a super high pressure to stay a liquid, right? It's not going to want to turn into gas because its boiling point is much, much higher. And so you can have, for example, liquid metal flowing through your reactor at basically one atmosphere, still super duper hot, but now it's liquid metal instead of liquid water, which you're forcing to stay liquid. It's like very happy to stay a liquid.

• 47:40Kelly Weinersmith?

  Wow. So if the reactor cools off, is it hard to get that metal to be liquid again? Or no, you just get the reaction going and it melts happily?

• 47:49Daniel Whiteson?

  That's actually one of the safety mechanisms, right? Is to have a plug at the bottom made of metal that melts at a slightly higher temperature. And if the core ever overheats past a certain temperature, it melts the plug and all the metal just drips out and then it cools. And now you have the big solid. So it's not like exploding everywhere. It can't melt down anymore, right? Because the fuel also is dissolved into the metal. In the case of the water, you have like the water flowing around the fuel rods. Here you take the uranium directly into your liquid metal. The reaction is happening within the metal. But if it ever overheats, it breaks the containment and just drips out and then cools. And so it's all good. So it's much safer.

• 48:30Kelly Weinersmith?

  That's such a cool passive solution. Like if something catastrophic happens and all the humans need to leave, it sounds like it solves the problem on its own with no humans there to help. That's fantastic.

• 48:39Daniel Whiteson?

  Exactly. So the pressurized water reactor needs active containment. And this one, if it fails, it just basically cools itself down. So no risk of overheating or meltdown. And it's liquid metal or salt because you can do the same thing with what we call salts in the periodic table, you know, whatever. It's just another element which if you heat it enough, turns into a liquid and has all the right chemical properties. You can dissolve uranium into it, has the right boiling and melting points, et cetera, et cetera. So they have these experimental reactors using liquid metal or salt. And this is one of the designs that was explored early on in the history of nuclear power and then ignored because the military wanted to use pressurized water reactors.

• 49:20Kelly Weinersmith?

  Oh boo. Okay, so we've talked about the benefits here. Does it have downsides?

• 49:25Daniel Whiteson?

  I mean, I think it's mostly upsides. The only downside here is that we don't have as much experience, so it's not as proven. Like, we've been using pressurized water reactors for decades. We know how they work. We know how they fail. Liquid metal and salt reactors are just much more experimental. But they have a lot of other potential upsides. For example, you can use other fuels than just uranium. You can use, for example, thorium. Thorium is awesome because it's not fizzle on its own, right? You need to start off with some neutrons to hit the thorium, and then the thorium will convert into uranium-233. Uranium-233 is another isotopic uranium. It's much better for these reactions. And

• 50:06Daniel Whiteson?

  then you don't produce any weapons half-life. You can also use a thorium reactor to burn fuel from other reactors. So you take like the byproducts of a light water reactor, you can put it into your thorium reactor, and it will burn it. It will use up some of that fuel. Remember that we talked about light water reactors mostly burn the uranium-235, the 238, turns into all this other stuff. You can take all that stuff and put it into a thorium reactor, and it will burn it.

• 50:33Kelly Weinersmith?

  But will burn the nasty stuff and turn it into not nasty stuff?

• 50:37Daniel Whiteson?

  Turns it into less nasty stuff, exactly. The waste here has much shorter half-lives. So you can take stuff that starts out with millions or thousands of years of half-life and turn it into stuff with tens or hundreds of years of half-life. So that's really good. And it can't make plutonium, so there's no weapons byproduct. And thorium already is a product of rare earth mining. Like, you're digging for zinc and cadmium and all sorts of other stuff you need for fancy technologies. Thorium is a waste product. We're already producing huge amounts of thorium in our industry. So thorium is really an excellent direction for nuclear technology.

• 51:14Kelly Weinersmith?

  You said it's a waste product, so it's stuff we're currently just throwing out?

• 51:17Daniel Whiteson?

  Yeah, exactly. And there's huge deposits of it. India has massive access to thorium, for example. And so a lot of countries around the world, China, India, are developing these thorium reactors. Again, more experimental, so there could be things we don't understand about them yet, because we just haven't spent 30 years watching them fail. But it's definitely a good direction.

• 51:37Kelly Weinersmith?

  Okay. All right. So we've talked about some new designs. We've talked about the old designs. Let's back out and take a big broader picture. I feel like I'm hearing more about nuclear reactors as the impacts of global climate change are sort of becoming more day to day and bearing down upon us. And so what do you think, Daniel? Do we need advanced nuclear reactors to deal with global climate change?

• 51:57Daniel Whiteson?

  I think it's going to be part of the future. I mean, currently, nuclear power provides like 5 to 10% of the worldwide energy use. It's like 20 ish percent in the United States. Some countries like France, it's a much, much higher fraction. A lot of those reactors are really decades old. Like, the United States has really old reactors, as our rate of turning on new reactors has dropped basically to zero. But nuclear power is also very attractive for lots of reasons. Like, it's very constant. You turn on a nuclear power plant, it's going to pump out energy day and night, rain or shine, wind or no wind, doesn't really matter. And so, on one hand, that's great to supplement things like wind and solar, which do fluctuate, obviously, day to night, and windy to not windy. What

• 52:39Daniel Whiteson?

  you actually want, though, to supplement renewables is not something like nuclear that's hard to turn on and off, but something you can turn on and off very quickly. Because you don't want to be running your nuclear power plant when you already have too much energy on the grid from solar. You want to shut it down then, and then turn it back on during the night. But nuclear power plants are hardest to turn on and hard to turn off, so they're very constant.

• 53:00Kelly Weinersmith?

  One of the things I really loved about Atomic Dreams, and one of the things that we don't end up getting into in our interview with Becca, is that you can take those times when you don't necessarily need the nuclear power, and you can do things like run a desalination plant, which would be very helpful in California, that's having all these issues with fresh water. So there's things that you can do to make up for the fact that nuclear power is not easy to turn on or off to, you know, still make it beneficial.

• 53:24Daniel Whiteson?

  Yeah, exactly. And it seems like definitely part of our portfolio in the future. The UN has all these different pathways to limiting the warming of the planet to 1.5 degrees, and every single one of those pathways includes nuclear power and expanded nuclear power on top of what we already have. So I think it's an important quiver in our arsenal. It's definitely not perfect, and there are definitely issues with it, and boy, do I wish we just had fusion around the corner. That would be awesome. But, you know, we're in an imperfect situation, we have imperfect options, and next time, we'll talk all about the pluses and minuses, and whether nuclear power is good or bad for the environment on the whole.

• 54:01Kelly Weinersmith?

  All right, so in the next episode, we're going to be talking to Becca, and in particular, we're going to be talking about how public perception is impacting the rollout of nuclear power. Things like fear from the reactor meltdowns, what to do with the waste, problems with licensing, et cetera. So we look forward to seeing you on Thursday for that conversation.

• 54:27Kelly Weinersmith?

  Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio. We would love to hear from you.

• 54:33Daniel Whiteson?

  We really would. We want to know what questions you have about this extraordinary universe.

• 54:39Kelly Weinersmith?

  We want to know your thoughts on recent shows, suggestions for future shows. If you contact us, we will get back to you.

• 54:45Daniel Whiteson?

  We really mean it. We answer every message. Email us at [email protected].

• 54:52Kelly Weinersmith?

  You can find us on social media. We have accounts on X, Instagram, Blue Sky, and on all of those platforms, you can find us at D and K Universe.

• 55:01Daniel Whiteson?

  Don't be shy. Write to us.

• 55:07Kelly Weinersmith?

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