Designing the Aalo-1 Reactor Core | Critical Thinking Ep. 3

追加: 2026-05-12

[00:00:00]Earlier this year, the president signed an executive order calling for three nuclear reactors to [music] go critical by July 4th, 2026.

[00:00:08]With a single signature, an impossible clock started ticking. Most of the industry looked at it and decided it couldn't be done. We decided to try.

[00:00:17]This is our story. The hard decisions, the long hours, the relentless push, and the small winds that keep us moving forward. This isn't a highlight reel.

[00:00:28]It's our unfiltered diary.

[00:00:31]Instead of polished press releases, we're going to show you the messy middle, the decisions we agonize over, the days when nothing seems to work, and the breakthroughs that [music] make it all worth it. The second atomic age starts here. And you've got a front [music] row seat.

[00:00:51][music] In this episode, we're going deep into the heart of nuclear reactors. We're going to look into the physics of what actually happens inside the core when a neutron splits an atom. Why are some of the neutrons fast and others are slow?

[00:01:14]and how that distinction really affects the overall reactor design. You'll hear from our nuclear engineers about why we chose U2 lowenriched uranium fuel instead of halo. Why did we put graphite in the core as a moderator and what does a moderator really mean and some [music] of the tricks that we had to pull together to make sodium work with all these materials around as a coolant.

[00:01:39]We'll talk about the engineering tradeoffs that makes reactor design so hard and how [music] some of the designs that were done in the 50s and 60s still affect some of our design [music] decisions today. This is critical thinking episode number three. Let's go.

[00:01:56]You kind of joined us not from the very early start but you know the history right? So originally when we started Alo we were inspired by the fuel that we use in the Marvel program which is the uranium zirconium hydride but you know about the physics of that fuel type right so what do you think are the benefits of why that's an attractive fuel again that's an old fuel but what do you think are the pros of that >> yeah so I know a little bit about the lore from that time and I would assume that what aid that fuel particularly um an in an a design choice was it's very strong temperature feedback. It has a very strong negative temperature feedback.

[00:02:45]>> Why don't you explain to the audience uh what uh feedback means?

[00:02:50]>> Yeah. So the basically the negative temperature feedback is um whenever you have your fuel temperature rise your reactivity decreases. So your overall neutron population starts to decrease and that's basically inherently safe. If you have a neutron population that starts rising with increasing temperature then you're going to have a runoff of your reactivity and your your power just going to continue to rise. So having that negative temperature feedback is what makes the reactor inherently safe.

[00:03:26]>> Now when we looked at this fuel, it was was probably the only fuel form that had such a strong negative feedback. Is there any other fuel type that had that feature? It it's it's it's unique to the user hydride because um the the moderating effect in the in the zer hydronone that's chemic the hydrogen that's chemically bound um its scattering effect becomes less predominant at those higher temperature.

[00:03:57]So it's very unique to that fuel. But I would say that um although user hydride was attractive in that sense of the physics um generally you it has a very small uranium density. So you need >> basic you need a lot a large high enrichment to maintain uh a reactor with user hydride and you know that that that's problems for burnup for commercial burnup reactors. Um and also the temperature problem. Um you typically don't want to uh you can do power pulses because of the negative temperature feedbacks effect that we talked about but at high temperatures you you you get the hydrogen migration and the fuel doesn't retain the hydrogen good enough. So you might have uh hydrogen migrating to certain places and you have skewed fluxes >> and I would imagine it'll be super hard to model that.

[00:05:07]>> Yeah, it's yeah very hard to model. Uh you'd need a lot of testing to to figure out um for your exact system how the hydrogen migrates. So yeah, it is very um attractive in that sense. Um uh obviously every fuel type will have advantages and disadvantages for sure.

[00:05:28]>> So a lot of our audience may not know what happens inside a nuclear reactor core. We understand you know maybe we've heard of chain reaction and neutrons but but walk us through the quantum level like what's happening >> when a neutron is born and you know we we we nerds we talk about fast spectrum and thermal reactor and fast reactors.

[00:05:53]What does that really mean? Let's explain and talk to the audience about it.

[00:05:57]>> Yeah. So basically what's happening in the reactor is you have millions to billions of neutrons bouncing around your your uh core and in that core you have your fuel and uh when a neutron basically is absorbed by um a uranium atom it basically splits into fision products and it generates neutrons and gamma ton of heat.

[00:06:25]>> Yeah. And these neutrons are usually fast neutrons. Now fast Yeah. when they're born.

[00:06:32]>> Okay.

[00:06:33]>> After a fision event.

[00:06:34]>> Now fast neutrons, you know, they're they're high energy neutrons and they react with other elements less than a thermal uh neutron. So basically when that neutron is born um you can keep it as a fast system. So most of your population of neutrons remains mo mostly in the fast spectrum or high energy or you can slow it down with the moderator.

[00:07:04]So your moderator is those um lower atomic number elements like hydrogen and carbon and they scatter the neutrons, slow them down and those neutrons are easier to to react with your uranium to cause fision. Correct. This is precisely the reason why you know we were adamant about always keeping the reactor in a thermal range because we don't need Halo which has a lot of you know uh you know supply chain challenges right uh yes there's a lot of investments going into producing Halo in this country uh but it does not exist at large quantities so we wanted to make sure we stay away from Halo and so we were adamant about using thermal spectrum and it causes higher probability of vision uh without you know raising cranking up the enrichment too too much. So that's a big benefit for us. Right.

[00:08:06]>> Yeah.

[00:08:06]>> Okay. Now let's talk about shielding.

[00:08:08]Right. Um compared to a thermal reactor core and a fast reactor core relatively which one requires more shielding?

[00:08:17]Typically you you'll need require more shielding in a fast reactor uh predominantly because you you're not slowing down your neutrons. They they remain fast. So you need to slow them down and capture them and you already start with a higher flux. So so the shielding requirements for a fast reactor is more >> compared to a thermal.

[00:08:42]>> Yeah. We we want less material inside the reactor or outside the reactor, right? Yeah.

[00:08:46]>> Um so that's great. All right. So um so okay so let's recap. Uh we shifted off from user hydride and then we are using uranium oxide fuel which is typically used in light water reactor and we figured out a way how to use it in our liquid metal cool reactor. And we said okay you know what we can't stay in a in a fast spectrum. Let's slow it down. So we use graphite as the moderator to do that piece. Um but that seems like a new configuration. I'm setting you up here, right? Um ha do we have any practical experience of a graphite moderated uh you know >> sodium cooled reactor that we uh have data on.

[00:09:30]>> Yeah.

[00:09:31]>> Uh this is definitely not a new configuration. Um there interestingly there's SR and Hallum uh two reactors that operated here in the United States.

[00:09:44]SR in California and Halum in Nebraska I believe. Um they were both sodium cooled graphite moderated reactors >> almost in the 50s60s >> in the ' 50s and60s 50s and 70s. Yep.

[00:09:58]And um yeah, we we interestingly enough came to the same conclusion they did even though they designed it 50 years ago that this is the system that we're confident works best for uh for us. Yeah. Isn't that crazy like how you know people in the past they didn't even have like advanced computers they had slide rules and they did all these uh calculations and analysis they ended up with the same conclusion as as what we are uh finding out today with modern sophisticated tools right I mean that goes to show you like physics is physics but speaking of um the SR reactor the reactor run great but they actually had an accident that was not even related to uh uh uh graphite or sodium. Uh they had a a sodium uh primary pump uh and they use a liquid organic fluid to cool the pump and that leaked through into the primary coolant where they had sodium very hot sodium and it carborized and all that carbon solids got trapped in the bottom of the core and once you don't have fluid from the core it got overheated and the fuel melted too. And so what they did, they like opened up the reactor, uh, pulled up the fuel assemblies and it half of it remained in the in the bottom of the core and half to came out. So they cleaned it up, you know, purified everything and then put a fresh new core in and restart it again.

[00:11:26]>> Yeah. And they they restarted it again.

[00:11:28]They put fuel new fuel in and they continued operating for some time.

[00:11:33]>> Pretty awesome. And and I think the challenges with the sodium graphite reactors can it they're not major in a sense they can be overcome with engineering and design and that's um something like the the challenges of these reactors we're aware of and we're tackling right now as a team. Yeah. So, okay, let's come back to um you know our our sodium cooled graphite moderated UO2 fuel. Now, we also use U2 fuel in in water cooled reactors and obviously water is such an amazing uh moderator uh from a physics perspective. How does this two compare um you know if you compare the uh the neutronic performance?

[00:12:23]Yeah. So water for other reactors can act as like a moderator and a coolant which is um very effective. Uh it's a very effective moderator. Um and typically it's you would need lots of hydrogen to or or water to to slow down your neutrons compared to graphite.

[00:12:52]It takes up less space than graphite. Um but it doesn't operate you can't operate at very high temperatures. So a very good um or attractive thing about our design is we don't need a pressurized system. We can operate at very low pressures and high temperatures and that opens the door for other um industrial users to operate at these high temperatures.

[00:13:18]>> Yeah. And for for those of us uh you know uh who have not seen the previous episode, we covered the advantages of why we use sodium. Um and that a primary reason is the fact that unlike water uh which gives a you know high pressurized system sodium does not which is a huge plus everything can be thinwalled. Um so that's the major benefit right and again I really like uh the fact that you mentioned and I totally forgot about this is you know water cannot operate at super high temperature uh cuz you need them you know significantly higher pressure to keep it in the liquid form.

[00:13:55]Uh but with graphite moderator you can go pretty high to high temperature operation.

[00:13:59]>> High temperature operation no pre without a pressurized system that's already a win especially going to this smaller more compact designs. Yeah, >> I think that is a very significant advantage >> and that's a winning design if you ask me because you can operate uh high temperature which is what we like for efficiencies, low pressure so your system is thinwalled and compact >> and it's moderated so you don't need halo. I mean >> I mean >> that's a winner combo. I >> I feel like we we ended up here for a reason. It's >> I don't know why more people are not doing what we're doing essentially, you know. I think I think once we start up and running, who knows? We we'll be ahead of the game, but there will definitely be some copy out there.

[00:14:45]>> Yeah. Again, there's, you know, talking about conservation of pain, we'll find our pain points and we'll deal with it along the way, but at least the benefits would outweigh some of those challenges.

[00:14:55]Now let's talk about okay today we don't have supply chain for Halo but let's say the world you know put enough money and time and effort into it and Halo does become available tomorrow and all of a sudden it makes economic sense to use Halo. What benefits would it provide in our core in our configuration? Oh wow.

[00:15:18]Uh so the number one benefit and I think the number one driver is obviously efficiency. How well we utilize our neutron economy and >> and what do you mean efficiency when you convert that is it power. So basically um how much fuel can you per kilogram can you convert to power >> and the efficiency term that we use is burnup.

[00:15:47]>> Okay. And basically that is megawatt days. So how much uh megawatt days you operate and per kilogram >> per kilogram of uranium that you use and and and using halo fuel will jump it will will improve the efficiency by a large degree and it doesn't take away from or still a thermal spectrum even with a higher enriched field. Um, and there's really only benefits to to that change. And I think um, it won't only help us obviously having that supply chain.

[00:16:23]>> And I'm glad you mentioned burnup because if you think about it, if the megawatt stays the same, same same power level and the kg of uranium remains the same.

[00:16:34]So with higher enrichment, you can get longer duration out of that same material. Uh so you can get a longer cycle length. So our refueling interval is going to go down essentially.

[00:16:46]>> Exactly. And that's a main uh caveat to these power reactors is that we have to the refueling cycle. Um it takes uh some time and that's downtime and that's less uh that that can hurt your fuel economy.

[00:17:08]So, um, the longer time that we run without refueling, the better for the economy of our fuel.

[00:17:16]>> Yeah. No. Fantastic. So, obviously, like, you know, this is just the beginning. We've done a lot of iterations. How many iterations have you done for this core?

[00:17:25]>> Oh, um, two I can't count like there has to be like more than I can count. There has to be like at least 100 iterations of this core. And it it's it you have to um balance the safety aspect of it.

[00:17:42]Obviously that's the the most important thing that you look into your um temperature feedbacks, your inherent safety feedback, your um uh transi analysis, accident scenarios and you also have to balance it with your fuel economy. So uh when you interface with a lot of the manufacturing engineers who are going to build this core you know do they provide a lot of feedback as to like what you can do what you cannot do in practice? Of course I mean I I would love to you know uh limit the use of certain materials like stainless steel or um make things a certain thickness or you know [clears throat] improve neutron economy in in that type of aspect. So basically reduce the amount of materials that absorb neutrons and add uh no contribution to the fuel economy and that's not how things work, right? You have to work with your manufacturing engineers to >> basically see what the limitations are.

[00:18:48]>> Yeah. The reality is like the fuel is not going to float on its own. It needs structural materials to hold it and one of the common material is steel. But steel eats neutrons and lowers your overall economy. So there's always this like dynamic I would say a tugof warar between nuclear engineers like for us who's like okay give me less steel lower thickness and the mechanical engineers like no because I need to have mechanical integrity and then the manufacturing is like no you can't do that I need to be able to make this uh in a practical way. So it's always a tugof-war between the different engineering disciplines and that's why all these iterations come into place like you know where do you converge as to like okay can we get to a configuration where you know nuclear engineer is happy with the performance we're getting out of the fuel the finance guy is happy with the economic performance the mechanical engineer is happy because it's going to last you know for 3 or 5 year fuel cycle and the manufacturing engineer is like okay I can actually build this thing not like Somebody did a analysis paralysis, right?

[00:19:53]>> Um, so yeah, that's it's an interesting journey we all go through on a day-to-day basis.

[00:19:58]>> Yeah, for sure. Very.

[00:20:07]uh just few years ago the conditions uh uh were created that really a lot of startup companies uh came up and trying to pursue nuclear advanced nuclear uh designs uh and that was really one of the two factors uh that that led me to nuclear engineering in general 20 years more than 20 years ago >> you wanted to build reactors >> uh exactly I wanted to build reactors and the time was great in early 2000s uh People talked about nuclear renaissance.

[00:20:38]It was the time of generation 4 advanced reactors. Um and everything looked great. Um and even going through my education all the way to my way to Belgium. Um things were happening uh until obviously Fukushima happened and and so that kind of ended that wave.

[00:20:59]Uh so um the second wave is here. Uh I think uh I think uh Al is surfing on the top. Uh and uh it was an incredible opportunity to actually actively contribute uh to that and to to actually do something that I think most nuclear engineers dream about is to work on a technology on the design and realization of the design uh in reality. Uh so um our um specifically uh as one of the multiple players uh really attracted me by the overall approach. Um it's not a company strictly focused on specific technology. It's not really the technology is not the goal. It it's the means to a goal. And uh and also the fact that we are not only focusing on on the technology itself and specifically the reactor core uh which many other companies do uh but the overall package uh that we are really having manufacturing capability uh uh we are procuring stuff, building stuff, testing stuff.

[00:22:16]>> Uh we have the whole package the whole team is developing the whole power plant together. uh there is no uh stone unturned and so that it really gave me this kind of approach gave me the confidence uh that this company our uh will actually build the reactor.

[00:22:35]>> Very flattering. Thank you for joining us David. Um so let's dive into >> the design. I mean when you came in we were dancing around with multiple types of iterations and and you you drank you came in joined us drank from the fire hose and brought some order to this chaos. Talk about that chaos you know how did that go when you first came in?

[00:22:58]>> Yes. Um so again it was in August uh we have we are at the end of January uh so not that far uh not not that too too long ago. And >> that was a year ago right? Oh no, in August. So half a year ago.

[00:23:13]>> Oh my god. Time. I can't keep track of time.

[00:23:15]>> Yes. Yes. Feels like uh three years ago.

[00:23:19]Um but when I came uh obviously there was a reactor design. Um and uh we have we have our mission, we have our goals um ahead of us in terms of what that design should deliver. Um um and we have our technology, we made some choices. Um but it was you know I I think uh we grew the the the size of our team twice since the time I joined.

[00:23:52]>> Mh.

[00:23:53]>> And so we still have we were relatively few people. Um and uh it was really a very creative environment I would say.

[00:24:04]uh very creative uh very actionable um uh but what what it really needed was some kind of a direction um and and have the capability to communicate and kind of make decisions uh in a controlled manner. So um I hope I help with it a little bit. Uh we have a great team um absolutely amazing team. Um we are lucky to be hiring great people. Um and that's one of your special talents actually. Um so uh I think you know uh the environment is very stimulating creative it still is. Uh but I think we are just uh making decisions more effectively. We are we are all on the on board with with our decisions um design choices and so on. So um I think we are just a little bit you know better uh orchestrated synchronized um and and uh we pull in one direction.

[00:25:04]>> Why is it so hard to nail down a nuclear reactor core design?

[00:25:09]>> Yes.

[00:25:09]>> Uh can you can [laughter] you share maybe a little bit more about the ups and downs of it?

[00:25:14]>> Yes. So nuclear engineering is a is a is a class of engineering.

[00:25:20]There is many engineers and many different disciplines. mechanical engineering, electrical engineering, uh civil engineering, uh and many more. So, nuclear is one of them. And on our team, we have basically all those engineering bases covered. We have people designing building buildings, electric circuits, um uh or the mechanical parts and and we have nuclear engineers. So, you can feel and you hear it from the other engineering disciplines. this exactly these questions. Why is it so difficult? Why does it take so much time? Why cannot you design in two weeks? And it really is because uh the nuclear engineering is very sensitive and intricate uh type of engineering where things are delicate in the sense that you cannot simply go for robust solution uh in one aspect of the design.

[00:26:22]because it negatively will impact the other.

[00:26:25]>> So you can make things very efficient in terms of energy production but then you may uh impact negatively the the safety uh of the of the design.

[00:26:38]So it is really this delicate uh delicate uh balance between all these nuclear engineering subd disciplines that you really have to synchronize and and and and make the right choices. Uh it's the physics a little bit more complicated. Things are not simply linear. Um um and if you want >> nonlinearity that that's what kills us.

[00:27:02]>> Uh exponential behavior that we try to avoid is possible. And so all these things were really delicate balance uh um uncertainties uh all considerations that we had to take into account this this this mutual uh impact of effects neutron economy uh uh thermmohydraulics material properties and performance mechanical design structural evaluation um these are all uh coupled together and impact for they each impact all the other ones and So this delicate balance really makes it complicated.

[00:27:40]>> Yeah. So what are some of these sub nuclear engineering disciplines? So neutronics is one.

[00:27:45]>> Yes. So neutronics I would call maybe because I'm uh biased because of my background primarily in neutronics is I would call really the heart of nuclear engineering. Mhm.

[00:27:56]>> Uh because nuclear engineering um in the sense that it really focuses on let's say the uh the power being generated from nuclear reactors um or design of reactors for other purposes. Uh the neutrons really is the essential particle that makes it all happen and that is really the ultimate source of the heat in the system. Um in other technologies it's come from other sources like gas or coal. Um in our case it's the uh fishision of u the atom uh nucleus. And so neutronics is one discipline that really uh um uh is about the the the the behavior of neutrons in the system. um thermmo hydraulics um uh is equally important part because that really relates to the safety aspect of the design.

[00:28:53]>> Uh with fishision um uh we create energy a lot of energy and we have a lot of neutrons in the system and a lot of uh atoms that actually can split and generate their energy. So that energy has to be evacuated. has to be moved away otherwise things can get heated up and um and can melt and cause other problems. So thermmohydraulics is that discipline uh specifically for uh uh nuclear in nuclear engineering uh that concerns uh is concerned about the uh the heat um transport. Um I would mention another one uh material um uh materials performance materials.

[00:29:40]>> Um that's that's another >> how neutrons interact with materials and and damages and all that.

[00:29:46]>> Exactly. Exactly. So that's exactly that's specifically for nuclear uh domain because we deal with neutrons.

[00:29:53]Those are kind of exotic particles in a way and they cause damage to the materials. Um and because we need to in our technology um uh keep things together uh sustain pressures, stresses, temperatures um we need to take into account the degradation of those metal properties uh caused by those neutrons. And >> we also have shielding.

[00:30:19]>> Yes.

[00:30:20]>> Radiological consequence.

[00:30:22]>> Yes. Yes. the the the um the beautiful but also challenging property of neutrons is they are uh electrically neutral. Uh so they fly through through a substance of material and they are not be really being slow down by um uh electrical forces.

[00:30:41]>> Yeah.

[00:30:41]>> And so they when they are created and they are fast they can fly and they can they can fly through the wall and and so on. Uh and so that's one of the challenges with uh every nuclear reactor design. How are we going to protect the surrounding structures and people being behind those structures uh from any potential um harm uh that could be caused to them by by those flying particles?

[00:31:06]>> Yeah. So the life of a nuclear engineer is is hard because you're not dealing with one kind of physics. You're dealing with multi-physics all working together. And so that's why it's so sensitive. like you change one thing in one area, it it has a trickling butterfly effect to all sorts of different areas and other engineering disciplines like mechanical, chemical, materials engineer.

[00:31:29]>> Um and so it is really you know it's not an understatement to say that nuclear core is that's why it's called the core.

[00:31:38]>> Yes. [laughter] >> Right.

[00:31:40]>> Yes. Exactly.

[00:31:41]>> It's the heart and soul of a nuclear reactor. So maybe a lot of our audience are not familiar with the fundamentals of what happens in a nuclear reactor.

[00:31:50]Maybe David put on your professor hat on. Okay. Explain to us in layman's terms. Uh you know if you want to explain uh how a nuclear reactor works uh you know can you describe the physics of it?

[00:32:03]>> Uh I will give it a try. Uh has been sometime since I left uh college. since you became a prof since you [laughter] were a professor.

[00:32:10]>> Um sure uh in in a principle it's it's not that um complex uh but it is unique.

[00:32:19]Um just for people to understand not even 100 years ago people didn't know about neutrons >> and uh few few years later after the neutrons actually were discovered only then uh they discovered the fish and it was shortly before the second world war. Uh so I just want to put in perspective how still you know new the field is. Um and the I already talked about neutron. I mentioned neutron multiple times but it really is the essential um uh you know particle that that that makes this field uh come up and and and exist. And so what happens in nuclear reactor specifically in the nuclear fuel nuclear reactor is actually a complex structure with multiple parts in it that have dedicated roles and uh and specific designs. But the nuclear fuel is uh the part where the action is happening where the energy is being created generated.

[00:33:28]How it happens? Um we have different materials. Uh some of them have the property that when they absorb a neutron neutron that flies through the nuc nuclei of that material.

[00:33:44]uh some of those neutrons actually can be absorbed by those nuclei and under right conditions they can actually cause a fishision of the nuclei uh nucleus um into multiple fragments typically two sometimes three and that reaction itself uh also releases a lot of energy um a lot of energy in terms of uh how small the scale is >> way more than this >> no no no [laughter] you you will have you will need few billions of neutrons to get there.

[00:34:17]But >> uh but we have many neutrons. Uh everyone knows atoms are small. No matter what material it is and uh every nucleus has neutrons in it, it's one of the three particles uh that constitute atom, right? And so that's how the fish energy is being released effectively by splitting the uh atom's nucleus. Obviously it has to happen under certain conditions. That's why we have all those different uh designs of reactors that actually um uh enable that reaction or its efficiency um uh the speed of the neutron um the the property of the material to be able to capture the neutron and actually cause vision. Um and then not only uh we release the energy, we create fragments um um what we called uh fishing products. Uh but we also produce more neutrons.

[00:35:19]>> Mhm.

[00:35:20]>> So that that that's the trick. Uh you put one in and you get more out.

[00:35:26]And if those neutrons are conditioned in a way that they can cause another fish in each of them, then you can imagine how that reaction propagates.

[00:35:38]>> Chain reaction.

[00:35:39]>> Chain reaction. There we go. And uh obviously it's not that simple. um uh neutrons not only go and cause fishision, they can leak, they can um get absorbed, bounce around, >> they can be absorbed without any um fishing reaction. Um so uh you know in order to actually make a chain reaction that can sustain itself um uh in in a controlled manner and in the process create enough heat that we can actually use it >> that that is another delicate problem that we have to solve and the way we do it is really by smart design choices material used geometry and so on >> and so we have um software tools yes that can model and simulate down to this part particle level. Right? So, uh c can you maybe give a little bit more explanation on what are some of these modern modeling simulation tools that are available at our disposal today that weren't available back in the 50s and 60s.

[00:36:45]>> Yes. Yes. So, uh absolutely. Uh however the the process that I described may seem complex and and people can guess that there are a lot of um a lot of uh complex uh physics involved. We are talking about fundamental particles. We are talking about interaction between them and we are talking really about uh physics at a uh nucleus level. You still can approximate those reactions by simplified methods uh that are actually accurate enough for us to have the predictive power to >> simulate and analyze those systems um >> uh with the tools that we have and models that we can create uh effectively. Uh so uh for many many years um basically from the time that we really started to design reactors uh computers were involved uh not the computers we have today but simpler systems. Um and we we talk really the first reactor obviously uh became operational in 1942.

[00:37:53]Uh so um computers have evolved a long way since then.

[00:37:59]>> Uh the tools that we use is uh historically the first tools that we had were really deterministic meaning they would predict the behavior of the system in a deterministic fashion. So really just following equations that describe the behavior of the system and solving them in then manner numerically. Um so all the reactions I talked about they would be described basically mathematically experimentally verified as a as a physically described system. Uh so those would be one types of tools that we have been using for decades and we are still using them for for uh with our computers even today. uh the the advantage of those tools is that they are extremely quick. With our modern computers, we can really execute uh these calculations extremely extremely well. However, with the growing computing power, we were able to utilize uh uh uh models based on a statistical modeling of our systems.

[00:39:00]So in that case we are really modeling basically uh uh we are tracking the particles how they would behave um essentially in a real environment uh tracking them um tracking their behavior reactions involved um and then we do it for many particles.

[00:39:20]uh we can we can afford it with modern modeling uh tools and then we stochastically uh in the sense of uh big numbers uh having having described a behavior of of a very very large number of particles we can actually um uh uh extract information that has a very very high predictive uh u predictive um power for for the systems that we are modeling.

[00:39:48]>> Right? So complex physics, complex models, complex uh equations and then we use all of that to come up with a design uh that is you know after many iterations we come up to the right configuration that satisfies all this multi-ysics phenomenon. So um kind of jumping the gun into you know at the end of that journey um what is our reactor design right now? If you were to explain to the audience what our core design looks like, how >> Sure. Um, so obviously Alo X we want to make power, right? We we want to generate um we want to generate power that can um generate electricity um or maybe have some other applications um but for that we need to create a lot of heat.

[00:40:40]>> I already mentioned different sources of heat. uh our job is to to get it from nuclear reactions. The reactor that we have designed and that we will be building very soon um uh is uh a reactor that has multiple advantages. Um and I will just go quickly over them uh just to uh explain why we decided for this technology. Our reactor uh is a reactor that we can build now.

[00:41:18]Uh all components and materials are available.

[00:41:23]Uh our reactor is relatively uh um easy on all the materials involved. We don't need high pressures.

[00:41:33]we can operate at atmospheric pressure um which um makes things easy in in in the sense of uh manufacturing and and structural requirements uh weights weight loads on on different structures and so on. Um also our system um has some inherent safety characteristics that are important from the safety standpoint. Um and uh is effective in terms of the the way we can uh utilize the heat generated.

[00:42:05]>> Mhm.

[00:42:06]>> Operating at higher temperatures than uh what most people know from from from our um conventional power plants uh based on lightwater designs. Uh so what the design is um the fuel that is available as I already mentioned is conventional uh uranium dioxide um uh ceramic fuel that is used basically by all power plants here in the United States and many many more most of them internationally >> um the advantage of that fuel is as I said it's available there is multiple vendors just within the United States uh that um sell that fuel um to their customers. So we don't have to develop any new fuel fabrication capacity. We can go and work with the vendors and get it from the existing market. Um so that's really uh our basis for our design. uh our coolant which is the medium that moves the heat away uh from its source to keep things cool and sustain and actually propel uh you know the systems that that create the the energy form that we want in our case electricity. Uh that coolant that medium is liquid sodium uh so uh it's different than water uh mostly used in in applications today. uh but there is a lot of experience with liquid sodium from the past from many countries from many different reactors. Uh the United States states has been the pioneer and and um the leader in in the sodium technology um for many decades. Uh so it is proven um coolant that uh performs very well and has very favorable heat transfer properties.

[00:44:00]>> Mhm. Um so I would say uh that's the coolant that's the fuel and the third part uh that plays very important role and and makes us little different than many other designs is the moderator. Uh >> what's a moderator?

[00:44:16]>> What is the moderator? Uh the role of the moderator in the reactor core in that environment is to condition those neutrons uh in a way that they will become efficient uh um efficient for causing the fishision reaction.

[00:44:33]>> Mhm.

[00:44:34]>> Um >> yeah maybe to add to that for our audience when a neutron is born as part of a fision chain reaction it is very energetic. It's uh it's a fast neutron and so when it's too fast it can cause fision but it's not super efficient at it. So uh what you have to do is kind of slow it down uh which increases its probability of causing fision which is exactly what we want >> and that's why we need this moderated material uh and typically you know it's hydrogenous material like water. Um there's other moderator like berillium or carbon which is graphite. Um so this essentially like slows down the neutron so it can be uh you know cause more fision essentially.

[00:45:18]>> Exactly. Exactly.

[00:45:20]>> So what do we use for uh for our moderator? Uh >> uh the how did we choose that?

[00:45:26]>> Yes. Yes. Uh the the moderator of our choice is is graphite. Um so it is a solid material that uh we we put into the core. And the core I I talk about the core a lot but the core really is a system where we have the fuel uh located there and then the coolant as well and in our case additionally as well the moderator. Uh so I will mention one more advantage of this setup where we have um the uranium dioxide ceramic fuel uh and then we have the sodium coolant um and then we have our moderator. The advantage here of that setup that we are working with thermal reactors. So exactly uh uh uh exactly what you were talking about that we actually slow down thermalize those neutrons from those high energies to low energies. Um what is the advantage of that design? Well uh it enables us to use that fuel that I talked about. Um if we didn't have the moderator there are designs that can do that but um then they would require different different fuel. So >> how different is it? Is it more fuel?

[00:46:39]>> Exactly. Exactly. Uh you you will need um basically higher concentration of of those types of uh nuclear nuclear that you can fish and [snorts] um what we are talking here is uranium. I forgot to mention uh that is really I I said uranium dioxide but uh it is really the uranium that that is the material that causes fishision and uh in nature uh uh the uranium that we have in nature only a very small portion of that uh material uh cause is is very efficient in uh in that fish being able to u be fish by the neutron >> it's an isotope of uranium >> exactly exactly so so it's a it's an atom of a uranium that chemically is as behaves as any other atom of uranium but the number of neutrons in the nucleus of that specific atom is different than u uh than other bulk.

[00:47:38]>> Yeah. Yeah. So, so the just the amount of uh that fishable u isotope that that specific atom or nucleus configuration uh in the nature is around uh.7 uh%.

[00:47:55]>> Uh our fuel 5%. So we need to bring that portion of of of those specific atoms that we want that that fishision up from 7 to 5%. Uh but if we were not to use the moderator uh that would have to really go up to something like 20% or we would have to actually use a different type of fuel. Do we get uh oh well for the audience a 20% enrichment is called generally generally called halo high essay lowenrich uranium and what's the challenge of uh halo why can't use that >> sure uh the the process of bringing up that fraction of that useful type of uranium and I'm really using loose uh terms here u for our audience uh so that process of bringing up that portion uh uh to to the levels we talked about where it's 5% 20%. Uh it's difficult and requires a lot of energy and it's expensive um and is not being typically done for uh our power industry. Uh that kind of fuel is heavily in use for specific applications like for instance in research reactors that have totally different mission than is power production. uh but is not used uh in the existing fleet uh that we have that >> so we don't have a common supply chain for that.

[00:49:24]>> Exactly. Exactly. So that um that is the challenge that if we were to uh have a technology that relies on that type of fuel and we would like to expand and deployed at the rate that um we are aiming for that would be a really big challenge and there yeah >> so you know we don't use Halo we use uh you know the low 5% enrichment fuel which is more available supply chain wise and it's it's lower cost compared to Halo which does not have a mature supply chain and is generally more expensive. Uh so great. So >> I will add one I will add one point um the halo is very attractive type of fuel that many companies are interested in.

[00:50:10]>> Our design can use it when it becomes available bring it on and we will just make it better.

[00:50:18]>> Uh but we don't need it right.

[00:50:20]>> So >> amazing. Okay David let's talk about July 4th. what are we doing? What are we building? So July 4th, 2026 will be a day uh will be the day where uh we actually will go critical and what that means um what we have to do to make it happen is to build a reactor, make it operational and the chain reaction that I talked about that is controlled and sustained >> that's something we have to achieve. So that's our goal for July 4th, 2026 and we are on the way to get there.

[00:51:00]>> And that core and our actual commercial reactor uh what's the commonality or differences between the two? Yeah, I should point out that the criticality that we will we will reach uh will be done with a simplified system >> uh that resembles at least the core uh resembles to a high degree uh the core of the power producing uh design.

[00:51:27]>> Um so so that that really is um the relation between the two. So the simplified system that we we call critical assembly uh that is our goal for July. Um and that will be our step to get to uh a system that will actually produce energy at a substantial level by the end of the year.

[00:51:54]>> Okay. Amazing. Good stuff. Movers and shakers. Well, thank you so much, David.

[00:52:00]Uh thanks for joining us today. Um for the next episode we're going to dive a little bit deeper into the other subtopic of nuclear engineering which is thermal hydraulics. Uh great we can create the chain reaction but how do we design a reactor that is safe? What role does it play? Um and on what kind of learning that we have to have to make this technology work and then we're going to talk a little bit uh after that how we control a chain reaction. We'll bring in our friends that design these reactivity control systems uh and and they've got all sorts of gizmos to make sure they can reliably control the reactor. So with that, thanks for watching. Uh until next time. Thanks, David.

[00:52:44]>> Thank you. My pleasure.

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