- Nuclear power, exactly what is it? What is happening inside of that reactor aside from making superheros? (upbeat music) - We learned in the 19th century that there's certain elements
that we dig out of the ground that are warm when there's no
other source of heat going on. So we said hmm, what's going on there? And through the works of Marie Curie and other sort of early, Henri Becquerel, and there's some physicists way back then who were the leaders
in trying to figure out what these properties are. And then ended up
calling it radioactivity. - Radioactivity?
- Right. And so when something's radioactive, ooh, what it means is there
are unstable elements in that substance. If it's unstable, it means they're actively
becoming something else. If you have a heavy element and it naturally then becomes
a slightly lighter element, it will give off energy. - Energy.
- Yeah. And it'll manifest as heat in that object. - Okay. - Turn of the century,
like 1800s to 1900s, people started wondering,
well, how much energy is it? Then Einstein writes
down E equals MC squared, equating mass and energy. So if you're getting
energy out of the atom, where's it coming from? It must be losing mass. We were pretty sure you can
get energy out of the atom, but we had to sort of
develop the physics of that. And quantum physics had to come forward. That was in the 1920s. Quantum physics is the
physics of the small, atoms, molecules, that sort of thing. Once that was put into place, oh my gosh. - We got something.
- We got something here. - Got something.
- We got something here. And what do you find out? For example, uranium. - Okay.
- Okay? You can send a neutron, what's
the charge on a neutron? - Should be nothing, right? - Nothing.
- Right. - Where'd you get the bar joke, okay? - What's the bar joke? - Neutron goes up to
the bar, orders a drink. Neutron says how much? And the bartender says for you, no charge. (laughs) You didn't know? (laughs) What we were deducing
through our equations and through experiments was that there's this uranium nucleus. If you hit it with a neutron, and how can you just
send a neutron in there? It's got no charge. Neutrons go right through
the front door of anything. There's no electrical
repulsion or attraction to it. It'll just, I want to go here? I'll go there. I want to go here, I'll go there. It marches through the front door of the nucleus of the atom. - All access pass, baby. - All access backstage!
- I'm a neutron! - I come in the front,
back, side, top, or bottom. - Any door you want. - Okay, so it comes in. If it has enough energy, it can break the uranium
atom nucleus into two pieces. And we're pretty sure we knew at the time what two pieces it would be. It would be two other elements, and it would release two neutrons. - [Chuck] Oh, it would have the ability to go through any other door they want. - And if you have a--
- And then they tell two friends--
- And then they tell-- - [Chuck] And then they tell two friends. - Yes, yes. Then you have a runaway process. - Man, we got ourselves a reaction! - A reaction! Okay, a chain reaction.
- A chain! - Remember, we haven't heart
that expression in a while. A chain reaction.
- Yeah, exactly. - So what you need is
enough sort of critical mass of uranium so that when the neutrons go in and they tell two friends
and they tell two friends, that you get enough neutrons so that every single uranium
atom by the end of that gets broken apart.
- Gets broken apart. - Right. Okay, and this is nuclear
fission, big atoms becoming little atoms.
- Breaking apart. So that must produce a tremendous amount of energy?
- Oh, yes! Because at the end, you have less mass than when you started, and the act of splitting
an atom releases energy and the two pieces have less mass than the one piece that you started with. - So that energy has to go somewhere. - And so now you build a device that concentrates that energy and you put it in a delivery vessel, and you have what the
military would call a bomb. That's how every nuclear power
plant is making energy today, through nuclear fission, okay? - Which is breaking apart, becoming smaller, releasing energy. - Right. - [Narrator] In nuclear power plants, the energy released by fission heats up the water surrounding the reactor. This turns the water into steam which passes through turbines
and spins a generator. But if the reaction's
not closely regulated, it can overheat leading to a meltdown, just like what we saw at Fukushima. So how do the control rods
slow down the reaction? By absorbing some of the neutrons. The rods are composed of elements, like boron, silver, and cadmium, that can absorb the neutrons
without undergoing fission. If the neutrons have an all-access pass that leads to a chain reaction, well, think of the
control rod as a bouncer. Without regulating this chain
reaction with control rods, the temperature would keep increasing. With them, we can keep
the fission reaction at a temperature we can control. - And so this is the fear factor that people have of nuclear power plants. - Not in my backyard! - You don't want to put it on a fault line or where they're think, you want to sort of protect these things. - Gotcha.
- Right, right. You can break atoms apart only so far and expect to get energy out of it. - Okay.
- Okay, now put a pin in that. At the other end, you have
hydrogen, the lightest element. You can fuse hydrogen atoms together and get heavier elements. And that takes heat, so
thermonuclear fusion. - Thermonuclear fusion. - Yes. So you can bring hydrogen
atoms together and make helium. Bring helium together, make carbon. Nitrogen, oxygen, silicon. Each of those releases energy, as well. - [Narrator] The nuclei
of atoms are held together by the strong force which attracts protons and neutrons together strongly but only when they get
really close together. After the width of a few protons, the attraction falls to zero. Without the strong force, all the protons packed
into one small space would repel each other and the
stable nuclei can never form. And as they fuse to form
larger and larger elements with more protons and neutrons, their nuclei are more stable
since they're bound together by more and more of the strong force. Fusing light elements together
makes more stable atoms, releasing leftover energy, but as the elements get heavier, each additional proton
fuels a repulsive force from any of the protons
that aren't super close. And as we get heavier than iron, the nuclei become less stable. And when they get really big, the tap from a neutron is all they need to break apart into two
smaller more stable elements, releasing a whole lot of
energy in the process. - Seems like no matter
what you do with an atom you're going end up with some energy. - Okay, so turns out if you fuse iron, it sucks energy out of you. - So it defeats the purpose. - Defeats the purpose. - Right, gotcha. - Stars undergo fusion, and
if you have enough mass, it'll go hydrogen, helium,
and it'll do that in its core. And it reaches, a star's in
the business of making energy. That's all they know how to
do, and that's all they do. They get to iron in the core, they try to fuse it, it sucks energy. They try to fuse it, it sucks energy. - Before you know it,
that star is just like what's happening to me? All my energy seems to be
going back in on myself. - And then it collapses and it rebounds as a
titanic supernova explosion. - Damn you, iron!
- It is be-- (laughs) - Cool. Cool! - You blew it up!
- You blew it up! You did it! (laughs) - Iron is this magic place on
the periodic table of elements that is the boundary between fission and fusion.
- Fission and fusion. - Yeah.
- Wow! - Yeah, last point. - Go ahead. - Ready?
- Go ahead. - I saw a bumper sticker
that said no nukes. - No nukes. - And the O in the no was the sun. - Oh, no! - (laughs) I said no, you got that wrong! (laughs) The sun is all about nukes! - That's all it is! - That's all it's ever done. - It's just one big giant reactor! - That's what that is! - Yeah, we need that. - We need that. - There you go. - Obviously, they want to, you
know, promote solar energy, but just in the geek analysis says-- - Wrong choice of--
- Right. - Of representation.
- Iconography. - Look at that, turns
out things didn't get as hectic as I thought they would. Maybe instead of blowing up our world, nuclear power can actually save it. After all, Springfield's still around. (laughs) - That's your evidence? - There you go, that's my evidence. Hey, if you're interested in learning more about nuclear energy, fusion, fission, and how our sun works, no nukes, do yourself a favor and spend
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thank you for joining us, and you're here to remind them to what? - To keep looking up. (upbeat music)
One small critique of Tyson. He says "if the neutron has enough energy, it will cause the Uranium to split"
While technically true, the slower a neutron is, the way more likely it is to cause a fission (as a general trend if you start at 2MeV and ignore resonance peaks). That's why a moderator is so essential to certain reactors. It helps slow the neutrons down so they can cause fission before escaping
ARE YOU NOT ENTERTAINED?!?!?!
Okay, seriously now. It is ultimately a good thing that someone with the recognition of NdGT can take 10 minutes to give the lay public an ELI5 version of nuclear technology. Light-heartedness aside, he gave a succinct & accurate explanation of the key science involved. But what does he think/say when not in "teacher" mode? I think it is important to ask because once I had strong respect for Tyson's colleague Bill Nye for both his advocacy on behalf of science education and knowledge on the one end as well as his efforts in the skeptics movement on the other. But then his views on nuclear technology compelled an about-face for me. (The awfulness of his latest Netflix series also played a factor, but I digress.) Does NdGT have similarly backwards perspectives on this topic, in spite of his ability to communicate the ideas effectively? I tried a quick google search to see if Tyson has a public stance on nuclear energy one way or other and so far I've found mostly crickets. The one telling thing that crops up consistently is oddly something that is lacking. Time and time again, I find mentions of the very noticeable absence of any time devoted to nuclear technology in his recent COSMOS series, a show that otherwise covers an incredibly diverse range of science topics. However the case may finally settle, I'm holding the applause.
Isn’t that a graphic for a coal plant and not a nuclear one near the end?
Boron? Aren't most modern reactors moderated with water? It's been my understanding that if the reaction gets the water too hot that water will boil away and the chain reaction would come to a stop. Thus water moderated reactors have their own failsafe unlike the graphite moderated Chernobyl.
And I also thought moderators were needed to sustain the chain reaction.