00:59:02 · Isaiah Taylor
[00:59:02] S1: I have come to gain massive, massive respect for amazing technology leaders and technologists in this company. It's not that, you know, it's really just like you don't know what it's gonna feel like until you do it. And to stand here and, like, look at the reactor that the team has built and to think about the insane hours and effort and blood, sweat, and tears that have been put into this, and that they just come back every single morning with energy and ambition and ready to completely rethink it when the time comes and to take the next step. Like, I don't know. It just is... I hoped to see that, but actually seeing that in your team is one of the most rewarding feelings on Earth. I had a theory about how the the nuclear industry was structured, but I wasn't sure yet. And now I'm, like, a lot more confident about it, which is that a lot of people in the nuclear industry really do wanna go fast, and they just not have been... They haven't been given the avenue to do that. I meet people in the nuclear industry all the time who, you know, look at what we're doing, you know, with with envy because they're like, I've been working for twenty years in nuclear, and I haven't seen an advanced reactor turn on yet. Right? I worked on this design. I worked on that design. I worked on this study, and you guys are about to turn one on. Right? And so I've learned that, yes, there are deep problems in how the nuclear industry is formatted, but, like, there are a huge amount of people who want to go fast. And so, you know, that's that's a powerful thing that we get to do is is unlock those people and let them run.
01:00:50 · Ty Morse, Isaiah Taylor
[01:00:50] S0: It's important to talk about safety and like why... What makes reactors dangerous and also what makes like this sort of thing very safe. [01:00:59] S1: Yeah. [01:01:00] S0: Can you just talk about the like sizing and how everything works?
01:01:03 · Isaiah Taylor
[01:01:03] S1: Yeah. So there's like, let's break down what nuclear safety is and why. Fundamentally, nuclear safety is about making sure that the public and workers don't get dosed with radiation above acceptable thresholds. Everyone is always dosed with radiation all the time. You and I are currently getting dosed with radiation just because the sky is above us and the ground is beneath us and these, you know, these things are radioactive, so it's about making sure that we don't get dosed with radiation above acceptable levels. And the way that would happen in a nuclear reactor if you were not careful is that when uranium splits, it forms a variety of what we call daughter products. So a uranium atom will break apart and now you have fragments of what used to be uranium atom and is now a bunch of other random atoms. And those atoms are radioactive, they produce gamma rays. And those gamma rays at enough dose are harmful to your body and could kill you. So there's this sort of, okay, gamma rays are coming from the reactor while it's running, and so you need to make sure that you stay a certain distance from it and that you shield those rays. And then there's the issue of, and really this is what nuclear safety comes down to, how do we make sure that those fission products stay inside the reactor where they are controlled? Right? So the ultimate goal of nuclear safety is make sure that those fission products stay in a controlled state inside of the core. What you don't want is for those reactive, you know, those radioactive fission products to, you know, be distributed into the air or into the water or into the next, you know, the field next door. How do you do that? Well, there's sort of two ways that... There's two sort of aspects you have to think about in terms of nuclear safety. The first is, how do you make sure that the fission reaction itself is controlled? Right? So you... Inside of a nuclear core, have uranium, you're trying to create a chain reaction. Right? So one uranium atom splits, it creates roughly two neutrons. Those two can go cost two more fissions. Now you have four neutrons. Those four go create four fissions. Now you have eight neutrons, 16, 32, 64, 128, right? So you have an exponential growth of neutrons. And each time a fission event happens, you have heat production, and that's the principle of nuclear energy, right?
01:03:24 · Isaiah Taylor, Ty Morse
We use that heat for useful things. Now, the danger is that an exponential growth function is exponential, and so you need that curve to taper. Right? You need to get up to a certain rate of fission and then go no further so that you don't have an exponential growth of heat. So that's the first principle of nuclear safety is reactivity control. Now reactivity control has many factors, there are lots of different ways to control the rate of reactivity, but in traditional nuclear power plants, the control rods are the main way to control reactivity. I I hesitate to to talk negatively about the traditional nuclear industry because the fact is, traditional nuclear is the safest form of energy on earth. Even with all of the flaws I'm about to describe, it is still the safest energy on earth. But I think we could do a lot better. [01:04:14] S0: In
01:04:15 · Isaiah Taylor
[01:04:15] S1: traditional nuclear, the control rods are really, really important. Right? If you run, you know, take those rods all the way out, and you're not able to put them back in to shut the reaction down, the plant can get into a very dangerous state where you're producing much more energy than you can safely handle, and that can lead to an explosion. Now we do a lot of engineering and they've done a lot of engineering to make sure that that's not possible, and they use other effects like Doppler broadening in u two thirty eight to moderate that. But it's still, you know, a piece of engineering that you have to treat very carefully and get right. This type of reactor is actually totally different. We do have control rods here, but the control rods are actually not for nuclear safety, they're for plant shutdown. So this is a really interesting thing. The way that we guarantee that this reactor maintains a reactivity level that is not going to result in a runaway reaction or a meltdown is actually through the inherent physics of the plant itself. And how that works is that as uranium two thirty eight heats up, two thirty eight by the way is the non fissile isotope of uranium, so there's two thirty five and two thirty eight, and two thirty eight is the one that doesn't split, And there's always a bunch of two thirty eight in every reactor, this is what uranium enrichment is, you enrich up to a certain percent, but not all of it. And as uranium two thirty eight heats up, it actually captures neutrons more effectively. And so there's actually this natural response curve where the hotter the reactor gets, the less reactive it gets. And so it's a self regulating principle. And specifically in a graphite reactor, graphite has really, really high thermal inertia, and it's really good at spreading that heat out, it's thermally conductive. And so when you have this growth of neutron flux and you have this growth of heat, that heat rapidly gets spread out and you have this moderating effect in the Doppler broadening, and then actually the graphite itself also becomes worse at scattering neutrons back into the core. So what you call this is you have strongly negative thermal feedback of reactivity, and what that means is there's a very strong negative relationship between temperature and reactivity.
01:06:28 · Isaiah Taylor
As the reactor core gets hotter, it gets significantly less reactive, and that's all physics. We don't have to do anything in the plant control to make that true, it just happens because of physics. So, again, we have control rods to make sure that we can shut the reactor down, but if the control rods broke for whatever reason and got frozen and, you know, they're gravity fed, so, you know, if the plant turns off or loses power, they'll just drop it in the core. But let's say for some crazy reason their controllers get stuck up, that is not going to lead to a runaway event. So that's the first aspect of nuclear safety. The second aspect of nuclear safety is meltdown. So most people don't know this, but meltdown is actually something that generally happens after a reactor has been turned off. So it's a post shutdown meltdown, this is what happened in 3 Mile Island in Fukushima. A meltdown is when you've already turned the reactor off, the rods are down, but there's still heat being produced in the core, and that's because after uranium splits, you still have recently split daughter products, back to these fission products, that are unstable isotopes of various atoms, and they are themselves still decaying into other things, and they produce heat when they do that, and so after you turn a reactor off, you still have about 7% of the active heat production still present in decay heat, and it goes down to about a percent and it kind of tapers off over about a twenty four hour period. And so immediately after shutdown, in a traditional nuclear power plant, in order to prevent that heat from just building up to an unacceptable level, you have to keep running the cooling loop. So in a normal nuclear reactor, after shutdown, you actually keep running the pumps, and you keep pulling that heat out for about twenty four hours after shutdown, And that's the condition of failure that leads to what we call nuclear meltdown.