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Armando Nava Dominguez

Technical Lead, SCWR Gen IV Project

Canadian Nuclear Laboratories

August 14, 2023

Ep 416: Armando Nava-Dominguez - Technical Lead, SCWR Gen IV Project, Canadian Nuclear Laboratories
00:00 / 01:04
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Bret Kugelmass [00:02:15] We are here today on Titans of Nuclear with Armando Nava-Dominguez, who is the Technical Lead on the Supercritical Water-cooled Reactor Gen IV Project at Canadian Nuclear Laboratories. Armando, thanks for joining me today.

Armando Nava-Dominguez [00:02:28] Thank you very much. It is my pleasure to join this interview. I'm very excited and, yeah, let's do it.

Bret Kugelmass [00:02:37] Yeah. Okay, so why don't you start off by reading this important paragraph, and then after we do that, we're going to get back into your background and story. But this will be a great way to kick off the episode.

Armando Nava-Dominguez [00:02:47] Sure. And the reason I want to read this paragraph is because I noticed that a lot of people do not know exactly what it means, supercritical. And unfortunately, the word critical is so universally used in different camps in neutronics. A critical reactor is mostly related to criticality. We have critical heat flux that is related to thermohydraulics. There are some multiple uses for this word, but here what I want to explain is really what is critical about supercritical.

Armando Nava-Dominguez [00:03:20] And I found a very interesting paper from the '90s that explains that in a very short paragraph and it says, "There is nothing critical about supercritical. Supercritical is a thermodynamic expression describing the state of our systems where there is no clear distinction between the liquid and the gaseous space. That means they're homogeneous fluid. Water which is at a state of pressure above 20.1 megapascals." What it says, there is nothing fancy about supercritical conditions. And actually, supercritical fossil-fired plants, they have been operating at supercritical conditions since the 1960s. This technology is mature. It is available and is nothing that we cannot achieve. It is a proven technology.

Bret Kugelmass [00:04:09] I honestly could not agree more. And this is why I have been trying to drive to find someone like you to explain to me why this wasn't the natural progression of PWR and BWR technology, as opposed to why everyone feels like they need to advance the nuclear technology development roadmap by throwing water out the window and switching to a different coolant when the coal industry has already proven that you can get your higher temperatures and higher efficiencies with water.

Armando Nava-Dominguez [00:04:43] That's right. And I have to be honest, I have been fighting this battle for some years. And you are right. In my end, this is my vision and I will share it with everybody. In my image, we can replace all fossil supercritical fossil-fired plants with a supercritical reactor. Like, we have the best of the two technologies.

Bret Kugelmass [00:05:08] Or just even normal coal plants that operate at, say, like 500 C with a supercritical 500 C PWR or something.

Armando Nava-Dominguez [00:05:16] That's right. And that will help a lot because then you can use what is already there. The equipment that is already there, the expertise from the utilities that not only operate water reactors, but also that operate also fossil-fired plants. There is for me, there is a no-brainer. An excellent transition to help with the greenhouse gas emissions.

Armando Nava-Dominguez [00:05:44] This is one for me, and this is the reason I like this supercritical water reactor because there is actually a transition plan here. We can evolve as the supercritical fossil-fired plants evolved. And fossil-fired plants evolved from subcritical to supercritical, and now they're talking ultra-supercritical. If we can do that in a nuclear reactor, I believe it will be a game changer because we can use what is already there. But most importantly is experience.

Bret Kugelmass [00:06:26] It drives me crazy when everyone wants to just launch towards the unknown when there's a known way to solve a problem.

Armando Nava-Dominguez [00:06:34] That's right. There is a quote that I love from Albert Einstein, I believe. He says that, "Knowledge is experience. Everything else is just information." And here, we have 70 plus years of experience with water-cooled reactors, 70 plus years with supercritical fossil-fired plants. If we combine them, we can have an excellent platform to really help the planet, and we can replace those old fossil-fired plants. We maintain some jobs. We extend these capabilities. We have the codes. We have, basically, the majority of things that we need to make this happen. Why would we want to change to another technology?

Bret Kugelmass [00:07:20] I know. Okay, well, let's come back to that because I actually do want to pull apart and analyze what your interactions are with other people and what those debates look like when you have these discussions. But before we get too far ahead of ourselves, we'd love to learn about you as an individual. Can you start off by telling us where did you grow up and how did you get into the nuclear industry?

Armando Nava-Dominguez [00:07:39] Yes, definitely. Well, I'm Mexican. I was born and raised in Mexico City. That was in 1975. Since I was a little boy, I was passionate about energy, the universe, time. I remember going to the high school and asking my professors, "What is time? We live in the present. What is time and the present?" And they would tell me, "You know, these kinds of questions are very difficult to answer." And actually, they may not have an answer. They said, "Focus on something else, something that you can manage concretely."

Armando Nava-Dominguez [00:08:17] Then little by little, I started studying more energy. By the end of high school, we had to choose what we majored in. And somehow, I found a very interesting program at the only university at that time in Mexico that gave the program on energy engineering. I applied and I was accepted. But I had to make a lot of sacrifices because my friends, my best friends, they were going to different universities and I decided to go to this one alone. I always studied in private schools and this was a public university. I decided that I would give it a try and actually it was an eye opening experience.

Armando Nava-Dominguez [00:09:03] I started studying energy and was amazed. I loved thermodynamics. I took all the courses that I could in thermodynamics of systems. And by the end of the program, I had to focus on very specific parts of the degree. We had renewables, energy management, thermodynamic of systems, and there was also nuclear but I was not really interested in that. It was more like I wanted to continue studying thermodynamics.

Armando Nava-Dominguez [00:09:38] But one professor came from Laguna Verde, the power plant in Mexico. He said, "Well, I can help you. I know you love heat transfer, thermohydraulics, fluid mechanics. Why don't you give a try to this technology?" I said, "Well, why not?" And yes, I decided to start my path in nuclear. I love it. I learned a lot. At that time, I had to do it by myself. I had to learn to program in Fortran and use also LabBack and all of these things. I really enjoyed it. It was heavy, but I really enjoyed it.

Armando Nava-Dominguez [00:10:15] And then somehow, I had the opportunity to come to Canada. And I went to Polytechnique Montreal, a French university. And by chance, I met a professor in thermohydraulics and he told me, "Armando, you want to study here?" And I said, "Yeah, why not?" And he said, "Bring me your notes and let's see." And I went back again to the university the next day. He looked at my notes and he says, "Let's go and talk to the lawyer," because I was still studying only languages in Montreal. And he told me, "You sure you want to study here in Canada?" I said, "Yeah, that will be my dream. I would love to do that." And the lawyer says, "Okay, I'm submitting your papers and you are officially now a student. And here we go."

Armando Nava-Dominguez [00:11:02] And the professor told me, "Well, you start tomorrow." And I say, "What?" He said, "Yeah, you start tomorrow because the classes started two weeks ago, and you start tomorrow." I said, "But I don't even speak French." He said, "You start tomorrow." I had to learn French on the way which was not that easy.

Armando Nava-Dominguez [00:11:23] And after that, a few months later, Hydro-Quebec in Quebec, the province of Quebec, called because they needed some people. I went there; they interviewed me. And after a few months they told me, "Well, come here" and I started the program with them. And it was exceptional, a beautiful team. I had the opportunity to work in the Safety and Reliability section of the Gentilly-2 Nuclear Power Plant in Montreal. And beautiful, I had the best hands-on experience in nuclear power plants, especially CANDU reactors, the Canadian reactor.

Armando Nava-Dominguez [00:12:06] And finally, when I finished my my master's, they asked me to apply for the Chalk River Laboratory, so the Canadian Laboratory. I submitted my application and probably a month later, they called me for an interview and they also accepted me. And what was interesting is that they asked me to continue doing what I was doing in my master's, which was an analysis of thermohydraulics of fuel assemblies. And I decided to say, "Yeah, why not?" And I'm here since then.

Bret Kugelmass [00:12:40] Cool, that's great. And how did you decide to focus your studies? Or your research, I should say.

Armando Nava-Dominguez [00:12:50] Well, life has been giving me that path. And I don't know how, but I remember when I started in Mexico, I studied heat transfer and hydraulics. The last class I had, it was about subchannel analysis. And the professor said, "Well, this is the last lesson. Today we finish the program with this. This is more advanced topic, but I will give you some ideas of what is a subchannel analysis." And it finished there.

Armando Nava-Dominguez [00:13:20] When I went to Montreal, it happened that the professor who accepted me worked in that field. He gave me that to continue as a project. But on top of that, he asked me to start studying genetic algorithms. And those algorithms are based on mimicking nature. It's an optimized process. It was beautiful because then you just combine not just the science, but also you understand a little bit more about the evolution of the planet, of the species, and why we change, how to find the optimum point. Very interesting.

Armando Nava-Dominguez [00:14:02] And that really helped me to have a better view of, I will say, our planet. How energy is the element that is needed to evolve our society. Each individual... Energy for me is basically everything. And we need it, but we need to be very careful with the type of energy that we use to manage it, because the byproducts can also be very harmful to the planet and for ourselves. But basically that's it.

Bret Kugelmass [00:14:40] Cool. So the subchannel analysis, this became your first focus area? Or the biomimicry stuff?

Armando Nava-Dominguez [00:14:47] My first focus was subchannel analysis.

Bret Kugelmass [00:14:50] What is subchannel analysis? Can you just quickly describe it to our audience, what that study is?

Armando Nava-Dominguez [00:14:53] Yeah, I will show you something; I have it with me. This is a CANDU bundle.

Bret Kugelmass [00:15:02] I love it. I love it.

Armando Nava-Dominguez [00:15:03] And what I tried to study with the subchannel analysis is how the fluid behaves inside of this fuel bundle with the elements. We discretize the dissection into small subchannels, like small passages, and we try to predict the thermohydraulic behavior of the fuel assembly.

Bret Kugelmass [00:15:27] And when you say thermohydraulic, do you primarily mean heat transfer or does it include everything like turbulent flow and other things as well?

Armando Nava-Dominguez [00:15:37] That's right. Yeah. What we try is to predict the distribution, that means somehow to compare to a distribution, we want to make sure that it's not getting hot on one side and the other, not that much. We want to have a balanced distribution. We want also to predict the void fraction. That means the volume of space that occupies the void. We want to predict how it's distributed, the power in the bundle. All these kinds of things, we do it with subchannel analysis. This is more detailed analysis.

Armando Nava-Dominguez [00:16:10] System codes are one-dimensional. They predict average. They take the average of that section and they give you the values. Subchannel analysis will give you more detailed analysis. If you want even more detail, then you go to CFD, computation of fluid dynamics, and you will have much greater details about that. But I stay in subchannel analysis. It's good enough for the nuclear industry.

Bret Kugelmass [00:16:38] So subchannel analysis is actually pretty comprehensive, is what you're saying. It actually includes multiple subfields within it.

Armando Nava-Dominguez [00:16:44] I will say, yes, it's quite a specific tool, the analysis of the fuel assembly when you remove the heat of the core.

Bret Kugelmass [00:16:54] I see. But is that term, subchannel analysis, is that also used on like the boiler side? Like the shell and tube heat exchangers, do they also use a field of subchannel analysis to describe heat transfer, or this really just for nuclear fuel?

Armando Nava-Dominguez [00:17:07] It's basically just for nuclear. Also, mainly for water-cooled reactors because other types of reactors, they don't have the same geometry.

Bret Kugelmass [00:17:18] Got it. Okay, great. And then, how has your research progressed over the years to today? What was your evolution in terms of your research focus that got us to the topic of supercritical water-cooled reactors?

Armando Nava-Dominguez [00:17:36] Excellent question, and I love it. It was about 2011 when Dr. Lawrence Leung approached me and said, "Do you want to work in a supercritical water reactor?" And I said, "Yeah, definitely. That would be quite interesting."

Bret Kugelmass [00:17:51] Who was this who approached you? What was his position?

Armando Nava-Dominguez [00:17:53] Dr. Lawrence Leung. He was the previous project lead of the SCWR Project. I told him, "Here's the thing, I would love to work on it," but I didn't know exactly what was a supercritical water reactor. And he gave me my first task. To design the fuel assembly with subchannel analysis of the Canadian SCWR, supercritical water reactor.

Armando Nava-Dominguez [00:18:20] It was a beautiful exercise. I used everything that I knew from my degree in Mexico, my master's, all my knowledge I put in there, optimization of systems, subchannel analysis. And finally, about six to eight months later, we completed that task. It was a very multi-disciplinary exercise. I had to be in constant communications with the guidance of fuel, neutronics, making sure that we met all the requirements. But by the end, we managed to get all the requirements and we had a fuel bundle. It was amazing.

Bret Kugelmass [00:19:00] Amazing. Let me ask one quick question then one long question. The quick question is, given that it's a Canada project, does this mean that heavy water is the coolant?

Armando Nava-Dominguez [00:19:09] No. We have light-water as a coolant, but it's moderated with heavy water.

Bret Kugelmass [00:19:18] Okay. So similar to CANDUs where they have the two different volumes of water.

Armando Nava-Dominguez [00:19:24] That's right.

Bret Kugelmass [00:19:25] But you're just replacing the flow water with normal water. Is there a specific reason why you don't just use heavy water for the coolant as well?

Armando Nava-Dominguez [00:19:33] Well, heavy weight is quite expensive.

Bret Kugelmass [00:19:38] Is it? But is it relative to your fuel, like your neutronics savings cost? Yeah, it might be expensive, but so is enriched fuel. And if you can cut down on your... Like, how do those economics work?

Armando Nava-Dominguez [00:19:54] To be honest, I don't have the specific numbers, but I know heavy water is extremely expensive. I know when I worked in the CANDU nuclear power plant, there is a system just to collect the drops. Literally all the leaks, they collect the heavy water. It is very expensive.

Bret Kugelmass [00:20:12] And is there a reason... If you're simply going to be using the heavy water as a moderator, why not just replace it with graphite or something like that, like an RBMK would or something? Is there a reason that you still want to keep the heavy water in as a moderator?

Armando Nava-Dominguez [00:20:28] One of the reasons is we have the experience with heavy water. That's something.

Bret Kugelmass [00:20:33] Okay. So save a little bit of money but still stick with heavy water.

Armando Nava-Dominguez [00:20:39] That's right. Because the project in the end, it has multiple goals. It was R&D to develop the Canadian SCWR, but also to maintain capabilities. You can see we're leading a generational gap, and we want also to have some capabilities. That's the reason we also continue with the pressure tube design and heavy water moderator, and that is also a way to maintain some of the capabilities here. And actually, I love the fact that we use heavy water. Yes, there are disadvantages, but also there are multiple advantages.

Bret Kugelmass [00:21:17] No, I like heavy water, too. That's why I was curious as to why replace the coolant? But I guess that makes sense. It's more prone to leak if it's being used as a coolant and therefore it's going to be more expensive, operationally. I get it. I get it.

Bret Kugelmass [00:21:30] Okay, it's now my longer question. That was my short question. My longer question is, when you came into this project in 2011, what had been the state of the prior work on this topic? When you did your background research to see what everyone else had done, how many labs had worked on it previously, how extensive was the research in Canada on this topic? The world that you walked into when you started your research, how full of information was it?

Armando Nava-Dominguez [00:21:58] Well, actually, I was surprised. There was already a big chunk of information. In Canada, we call it Generation X Project. There was already, what we called it, the Canadian Supercritical Water, but it was really a CANDU type. It was a steel horizontal core, and it was basically just a pressurized CANDU. But there were already some projects and materials, some documents or knowledge gaps on how to understand the thermohydraulics under these conditions. There was already, I will say, a large body of knowledge, but it was still under development.

Armando Nava-Dominguez [00:22:40] And also, because supercritical water was considered in different fields. I found some documents from General Electric from the 1960s where they also proposed a supercritical water reactor. And they had the program, and I found some universities in the US that also performed supercritical experiments in materials on thermohydraulics.

Bret Kugelmass [00:23:05] In the US, was that recent research or was that long prior research?

Armando Nava-Dominguez [00:23:09] No, that was long ago. Long ago. And I remember, they also participated in the SCWR Project for some time, the United States. But then, little by little, they are not more active in this area. Right now, Canada, I will say, is one that remains active. Our colleagues from China and the European Union... We have a very interesting program with the European Union called ECC Smart. And ECC stands for European, Canadian, and Chinese contributions. The three continents work together to establish the requirements for supercritical SMRs.

Bret Kugelmass [00:23:53] Other than you, who is the most vocal advocate for this technology out there in the world right now?

Armando Nava-Dominguez [00:24:00] I will say, from the IAEA there is a person called Tatjana Jevremovic. She has been really helping us with that. Right now, we are working on the third coordinated research project on SCWRs. She has been supporting this technology, I will say, for several years, and she knows quite well this technology as well.

Bret Kugelmass [00:24:27] So that's the IAEA. Any other labs like university labs or research labs that do...

Armando Nava-Dominguez [00:24:32] Well, in the US there's one that is amazing, the University of Wisconsin-Madison. They are doing an amazing job on SCWRs.

Bret Kugelmass [00:24:41] They are. Okay, I didn't realize that. Okay, great.

Armando Nava-Dominguez [00:24:42] Yeah, they're still working on that, and it's quite interesting. They have amazing facilities. We have in Europe, the University of Pisa doing thermohydraulic analysis. In the Czech Republic, the laboratories there. They're doing materials analysis. TAT, they're doing thermohydraulics in Germany. University of Sheffield, they're doing CFD and DNS analysis in England. University of Notthingham, Romania... We have a few countries contributing and doing research on SCWRs.

Bret Kugelmass [00:25:18] Okay, great. That was actually a pretty good list of labs. Now, I'm going to ask you to give me the other side of the argument. That's a good number of labs, but I who study this field of nuclear energy as a profession have only recently come across this as a viable pathway forward. I think it should probably be the pathway forward. What do people say is wrong with it? What do people say is the downside of pursuing this?

Armando Nava-Dominguez [00:25:58] Well, I think one of the biggest fears is what happened with Fukushima. That we know was a very unfortunate accident.

Bret Kugelmass [00:26:08] Okay, but let's rewind even before that. I want to know why people weren't more seriously pursuing it, let's say, in 2010 or 2005. Then we can get to the Fukushima stuff. But I want to first understand why this wasn't like the main area of EPRI research in terms of...

Armando Nava-Dominguez [00:26:28] I may not have the answer. I can give you my opinion, but for me, what I can see is because nuclear reactors... They last for several decades. And you cannot, basically, touch them because the licensing process is very stringent.

Bret Kugelmass [00:26:45] Of course.

Armando Nava-Dominguez [00:26:46] The evolution of the reactors is very slow.

Bret Kugelmass [00:26:51] Okay, so that's a good answer for the macro picture of why we don't advanced technologies. But I'm actually still quite curious as to why this hasn't been the leading candidate among advanced reactor technologies. Because there are a lot of people putting a lot of money into lead, molten salt, high-temperature graphite, pebble-bed, TRISO, but I just never hear about this pathway.

Armando Nava-Dominguez [00:27:16] I get it and I follow you. And I have been discussing that with a lot of colleagues, especially one colleague in economy, Alberto. We have very good discussions, and we still do not understand. But what we know is that we live in an age of distraction. And actually, he published some notes about that in a book. Because what happens is we believe we're getting tons of information constantly with different types of reactors. We get these thousand voices calling us and we just get distracted and all of our energy is diffusing.

Armando Nava-Dominguez [00:27:57] What's interesting about this book, what it's saying about the age of distraction is if someone comes and says, "Okay, I will give you something that is better, that is safer and is cheaper," somehow people will start looking to that. The problem is, unfortunately the nuclear industry has been promising cheap and safe reactors for decades.

Bret Kugelmass [00:28:24] I actually think that most nuclear... Let's say, nuclear entrepreneurs, new people who are trying to pioneer new paths to nuclear actually don't ever want to build anything. They just always want to be chasing after a shiny object. That's my theory. But before we philosophize too much, I actually do want to get to the technical substance. There must be some downsides, and these are the areas of research that people are trying to de-risk with this technology. Materials, I get it. Okay, you've got some more corrosion issues at higher temperatures. What else? What are some other technical areas?

Armando Nava-Dominguez [00:28:59] The technical area, one... And I agree that there's a challenge, but it's proving to be feasible. It operates at high pressure. 22 megapascals is the supercritical pressure of water. The core design operates at 25 megapascals.

Bret Kugelmass [00:29:14] Okay, but coal plants operate at high pressures. Like, we get it.

Armando Nava-Dominguez [00:29:17] Now the fashion is saying, for example, molten salt operates at, basically, a very low pressure. That's the same argument that there is pressure...

Bret Kugelmass [00:29:27] Okay, I personally am not worried about the high pressures. Thicken up the wall vessel. If you're operating at anything above standard atmosphere, just make a thicker wall vessel and call it a day. So, I'm not worried about that. What else should I be worried about, though? Anything to do with pumps? How are you going to move the coolant? Do pumps cavitate when you pass supercritical water through them? What's going on there?

Armando Nava-Dominguez [00:29:48] No, because we have the supercritical fossil-fired plants operating with that and it has been proven a very safe technology. To be honest, I think it's just about marketing. And relative to technology, when we started this, yes, we had some challenges with materials. That's well-known. But especially, the biggest challenge in the materials needs to be to find the cladding. That's the big, big challenge.

Bret Kugelmass [00:30:14] Let's talk about that for a second. Why is Zircaloy-4 for not good enough to operate at, let's say, 500 C water? I'm not saying we have to go all the way up to 700, 800. Let's just say 500 for the moment. Why is it not good enough?

Armando Nava-Dominguez [00:30:29] Well, the challenge with that is that Zircaloy deteriorates at those temperatures and conditions. It just simply... We put it, and...

Bret Kugelmass [00:30:37] I thought that Zircaloy's oxidation potential really only kicks into gear after 700 C and doesn't really oxidize until 1,100 C. What's happening at 500?

Armando Nava-Dominguez [00:30:47] Well, we did some experiments and we put it under supercritical conditions and they didn't last long. Not enough to be feasible for a supercritical water reactor.

Bret Kugelmass [00:30:56] Interesting. Okay, so cladding is the issue.

Armando Nava-Dominguez [00:31:00] That's the big issue, and we have been working on that for several years. We have two international tests with different institutions.

Bret Kugelmass [00:31:11] What's wrong with stainless steel? Because reactors, I get that you lose... There's like a parasitic neutron effect with stainless steel. They used to make reactors out of stainless steel before Zircaloy. So what's wrong with just going back to stainless steel?

Armando Nava-Dominguez [00:31:26] Well, actually that's one of the candidates that we have, stainless steel 310.

Bret Kugelmass [00:31:33] What else? Inconel? Is Inconel any good?

Armando Nava-Dominguez [00:31:37] We're trying another, Alloy 800H. We also tried Alloy 625. We have a list of different cladding candidates. The challenge is they have to meet so many requirements. They have to withstand the harsh conditions of the supercritical water. But also, they are subject to neutronics. Then the material can be gradated to the neutron flux. It can brittle, it can age, you can have a different corrosion mechanism. Then when you finally think, "Oh, I have one that makes sense," you put it in another test and it fails. It's like, "Oh no, here we go."

Bret Kugelmass [00:32:21] Okay, so materials seem to be the big issue right now.

Armando Nava-Dominguez [00:32:25] Identifying the correct cladding.

Bret Kugelmass [00:32:28] And why clad at all? Why not just allow your fuel pellets to just kind of sit in a giant pool?

Armando Nava-Dominguez [00:32:37] Well, the cladding... We need it to keep the fission product inside. We don't want to...

Bret Kugelmass [00:32:41] Why not just keep them inside? Why do you need so many barriers? Why not just keep the fission products inside the reactor vessel and say, "Those are enough barriers. We don't also need cladding?"

Armando Nava-Dominguez [00:32:51] Well, I'm not sure that it would be very safe. I think we need that.

Bret Kugelmass [00:32:57] But okay, can I push back on that, though? Because in most postulated accident scenarios where you experience a depressurization of your primary loop, you have to assume a fuel clad gap release. You have to assume that you lose your fuel cladding integrity anyway, and those fission products are going to get out of your system. And so, why do we focus on cladding? A large majority of the fission products are trapped inside the ceramic matrix. Like, that technically is your first barrier.

Armando Nava-Dominguez [00:33:27] That's right. That's the first... I have to be honest, I may not have the complete answer for that. But we have to maintain, also, the integrity of the fuel, like if there is any vibration, to keep it in place. Otherwise, there is nothing that will contain it. It will just simply, probably...

Bret Kugelmass [00:33:46] Okay, what do we think about graphite tubes, then? There are graphite heat exchangers that exist out there that you pass coolant through. What about just instead of a cladding tube that's metal, why not just a graphite cladding tube?

Armando Nava-Dominguez [00:33:58] I'm not sure graphite will make it with supercritical water.

Bret Kugelmass [00:34:02] Oh, you think it would eat it up?

Armando Nava-Dominguez [00:34:03] Yeah. I'm not sure, but I know that there are some materials that... Supercritical water, one of the challenges is that it's a solvent. It is a challenge, yes, but we have chemical processes to reduce that. But I'm not sure if graphite will be an option for that. I don't know how it will interact with water.

Bret Kugelmass [00:34:27] Okay. So can you just actually describe to me the chemical and mechanical processes by which supercritical water corrodes the material? What is it actually doing? Is it oxygen is just more prone to... What's actually happening?

Armando Nava-Dominguez [00:34:47] I have to be honest, I am not the materials guy at all. I'm in thermohydraulics. I don't know exactly what happens. I know it's extremely interesting. I saw some of their pictures that they took of the cluster of molecules under supercritical conditions to see what is the effect. I have to be honest, I will have to ask somebody from Chemistry to explain exactly what happened.

Bret Kugelmass [00:35:15] No problem, no problem. Okay, so let's talk about the heat transfer potential then, and why there's such an advantage in moving to a supercritical region. Let me ask the question a little bit differently. Is this a direct cycle? Do you go straight from your reactor to your turbine?

Armando Nava-Dominguez [00:35:33] That's right.

Bret Kugelmass [00:35:33] Okay. And then, so what is the ideal pressure and temperature that you've modeled getting up to that you feed into the turbine inlet.

Armando Nava-Dominguez [00:35:44] For the Canadian Supercritical Water Reactor, the conventional size reactor is 25 megapascals with an outlet of 625 Celsius.

Bret Kugelmass [00:35:54] 625, 25 megapascals. And then, is there anything unique about your steam turbine? Because you get so much higher on the pressure, do you not have to go as high on the low side? What's the tradeoff there?

Armando Nava-Dominguez [00:36:10] Well, in this case, we really didn't touch much on the balance of plan of the turbine. We're trying to use what is available in the supercritical turbines.

Bret Kugelmass [00:36:22] Okay. And then, does this necessitate, like in a boiling water reactor, a feed water pump? Is there some sort of natural circulation that you're able to do?

Armando Nava-Dominguez [00:36:35] No, it will make some feed water pump. Yeah, it will need it.

Bret Kugelmass [00:36:38] And why not switch to a natural circulation system like an integral style PWR but with supercritical water? Because by actually going to this weird phase change territory, you'd be able to induce natural flow a lot better, I think. So why not have an integral PWR that is supercritical?

Armando Nava-Dominguez [00:37:01] Yeah, and actually that's a very good question. And at some point, we want to study that with more detail. But there are some effects that happen under supercritical conditions with the heat transfer and the effect of the buoyancy. At some point, we can have a heat transfer deterioration, depending on the orientation. Because it's so hot, basically you have very little flow and time to cool and that will have an impact on the reactor. It is a very good question. Working on the natural circulation under supercritical conditions, that will require a little bit more research in that area because the buoyancy forces are much more stronger than in water.

Bret Kugelmass [00:37:46] Which is great. Like, you want more buoyancy forces to drive pumping power in a natural circulation system.

Armando Nava-Dominguez [00:37:51] That's right. But the issue is when you are close to a wall that is hot. That may create hotspots because maybe the fluid will not move that much.

Bret Kugelmass [00:38:04] Is this because you don't have laminar flow issues, or what is the...

Armando Nava-Dominguez [00:38:08] That right. That's what we call it, laminization of the flow.

Bret Kugelmass [00:38:11] And why not then just like create a torturous path to deal with that or something?

Armando Nava-Dominguez [00:38:17] That's something that we tried. Yes, actually, we used a concept in the fuel bundles that promotes turbulence, but we noticed it may not be enough. It will create some turbulence, but it might not be enough to really help to decrease the margin and to avoid the heat transfer deterioration.

Bret Kugelmass [00:38:40] Interesting, interesting. Interesting.

Armando Nava-Dominguez [00:38:43] That is quite interesting. It's very, very interesting. And there is still some work to do. And we're trying to use the experience that we have already with force flow. Yes, what we tried to do is also to study the possibility of natural circulation in case of an accident and see how it behaves. But that's still an open gap that we're working on. And this next fiscal year, we'll start to study natural circulation under supercritical conditions.

Bret Kugelmass [00:39:14] Great. Let's talk about the neutronics side for a minute, if we can. I'd love to also understand... Does it have a better transient response when it operates in the supercritical region? How does the void fraction coefficient, the temperature coefficient, and the Doppler effect come into play when you're operating in the supercritical region?

Armando Nava-Dominguez [00:39:36] Well, right now, basically we're using the same as we have with a water-cooled reactor, because we don't have more information about that. There is no information in nuclear at supercritical conditions. There are no nuclear libraries about that. But we hopefully, this year, will measure neutronics scattering at supercritical conditions. That will give us a very good idea of what's going on at high-pressure in the reactors.

Bret Kugelmass [00:40:07] And what's your hypothesis going in?

Armando Nava-Dominguez [00:40:10] Well, we hope that they would behave similar to what we know. Hopefully, we will not get any surprises. I mean, in terms of R&D, we get one surprise, it will be great because we're hoping it's something new that we didn't know. That would be great. But this will be something that we have to do. And we're planning, hopefully, this year to start some experiments to irradiate and to measure neutronic scattering under supercritical conditions.

Bret Kugelmass [00:40:44] And how do you measure neutron scattering? So you're saying we don't have a good cross-section library for the thermalization of neutrons at like 600 C, right now?

Armando Nava-Dominguez [00:40:55] Maybe, I'm not sure what is the limit. But I know that the high pressures compared to this, there is not enough information for that. And for that, we need to perform experiments. One of my colleagues here at CNL, she managed to get some neutron beam time in Australia. We constructed a cell, and hopefully we'll be able to send it there and perform some experiments there. That will give us much more confidence in the neutronic calculations.

Bret Kugelmass [00:41:27] And what about historical experimental data? I feel like they did so much cool stuff in the '50s and the '60s before everyone got uptight about research for nuclear reactors. Is there like a treasure trove of information that you've identified but haven't been able to access or declassify yet but you know is out there?

Armando Nava-Dominguez [00:41:49] Not really. I think most of the information is already declassified. I was able to get it through a few websites. No problem, because it was from the 1960s. There is no issue anymore.

Bret Kugelmass [00:42:04] Yeah. Okay, interesting. When you get together with this international forum... You rattled off the various labs. When you guys get together, do you decide, "In order to advance us forward, here are the topics that we need to explore. So you guys take this one. I take this one." Is that how it works? Or, is it that everyone just does what they want and then comes back with what they've learned?

Armando Nava-Dominguez [00:42:29] Actually, you made a very good point. I'm very fortunate to be the Chairman of the System and Steering Committee of the SCWR under the chief program. And one of my goals is really coordinating the whole program, internationally, of the partners. It is not an easy task. It is quite complicated.

Bret Kugelmass [00:42:49] Why? Why? Because everyone wants to do what they want to do and they just don't want to listen?

Armando Nava-Dominguez [00:42:54] Well, you have different nationalities, you have different ideologies, you have different budgets, different languages, different objectives. Sometimes you have to navigate different things and make sure that we all understand the same thing, that we're on the same page. And also, understand that we may not have the same resources. Some countries, they may have more than others, and some they may decide just to join in the group. Trying to put that together in a document, it takes time.

Armando Nava-Dominguez [00:43:27] What we do, for example, on the Generation IV International Forum, we have what we call a PMB, Project Management Boards. We draft a plan, like a five year plan. We have meetings together all day. The participants, we discuss the areas that we want to advance and we say, "Who wants to participate in that area?" We have a plan, we stick to a plan with deadlines, deliverables. Once we reach a consensus that is approved, we sign it. That is, for example, for Generation IV.

Armando Nava-Dominguez [00:44:03] We have also, under ECC Smart. We prepare the proposal, we prepare the plan. We submit it to the European Union EURATOM. And if they like it, that's okay, then we can continue. But yeah, it is the work of several people brainstorming what we can do based on the facilities and capabilities.

Bret Kugelmass [00:44:29] What are the open debates... Let's say, within the supercritical water-cooled community, the people who have bought into it. What are the open debates on which direction it should take? Are people arguing about the max temperature? Are people argument about the materials? What are the debates?

Armando Nava-Dominguez [00:44:49] We have multiple. Actually, any nuclear reactor is a multi-disciplinary exercise. You have to have all on board. And for example, right now one of the big challenges is to set up the maximum temperature. Of course, my theory as I will tell, "No we want this one because it's quite comfortable," but thermohydraulics will tell you, "You know what? We cannot reach that compared to, well, will we pass it? Always." And that is always the debate. Even just to propose the right operating conditions can take some time.

Armando Nava-Dominguez [00:45:21] But once you have this, you can really start the process. It's a very, very tricky process. And you have to be in constant communication. And to have a good general view of the nuclear power plant and how the disciplines are interrelated. Because sometimes you forget one variable, and it may be quite important. You advance sometimes, you advance and advance, then you realize that you forgot something, that it was very important. Then you have to go back. And this kind of thing, it will slow down the research.

Bret Kugelmass [00:45:57] Yeah. Let me ask another question. Is there a big difference in behavior? Let's say I were to look at a PWR that is operating close to the supercritical point. So, normal PWR operating conditions, 2,250 PSI, 315 C max, or something. If I were to just bring that up... If I were to just take those conditions and just bring it up another 40, 50 degrees so I'm just barely in the supercritical region, would you see a lot of the same problems emerge, like material problems? Or, do the problems grow linearly with temperature? Is there something really distinct about once you cross that triple point?

Armando Nava-Dominguez [00:46:42] Yeah, there is actually. Things change drastically. The properties of water change dramatically from passing from the subcritical to supercritical. And the closer you get to the supercritical point, you get a lot of instabilities there because you are changing to a different state. It's not that straightforward. There are actually books where they call it "thermohydraulics near the critical point." Because when you start getting close to that point, the properties start changing a lot.

Bret Kugelmass [00:47:21] Can you help me develop a physical intuition for this? How do I think about the molecules as they approach the critical point and go past the critical point?

Armando Nava-Dominguez [00:47:29] That's something, to be honest, I also have been wondering. And it's difficult, because to really visualize that at that pressure is not that easy. But what I can see is that the pressure is high enough that there is no surface tension, then there is no physical distinction between the gas and the liquid. They are just like molecules with different densities. It's like if you had gases at different densities.

Bret Kugelmass [00:48:01] How intermixed are these different densities? Do they form pockets and clusters? Like, if I were to look at it like a color chart, would I see things that look like water everywhere, but then little pockets that look like gas? Or, would it be evenly distributed?

Armando Nava-Dominguez [00:48:19] To be honest, I just saw a few pictures of what's going on. That's something that even the scientists are trying to see how they're distributed. But there are a few pictures out there, especially, I believe, one of my colleagues from China. He specialized in that, and he took a few pictures. And you can see some clusters of molecules just close to the wall. They are gas-like and they are liquid-like that. I have the feeling... This is my personal feeling, that they will mix very fast. That they will not remain like separate entities. But because we have localized heat, then you will also have localized effects.

Bret Kugelmass [00:49:03] Yeah. Are there other fluids that are supercritical near room temperature that we can use as proxies to analyze that and then guess what the behavior of water might be?

Armando Nava-Dominguez [00:49:16] Well, actually, that's another very good point. Supercritical conditions, it depends on the fluid. And there are some fluids that can be at supercritical conditions to demonstrate pressure. But the challenge here is... The reason we're operating at supercritical conditions is to take advantage of the heat capacity of the fluid to absorb that. And that is happening only with water. If we go with another fluid, we will not have the same effect. Probably, the heat capacity will be very different. We may not be able to remove all that heat. For example, some fluids, especially some of their mixtures, they start deteriorating. Water, the beautiful thing is that it's universal and it's proven to be very stable.

Bret Kugelmass [00:50:18] Yeah. I know, water is an amazing coolant.

Armando Nava-Dominguez [00:50:24] It's basically neutral; it's easy to work with. And that's the reason we have... A lot of plants in the world, they use water as a solvent. Everything, yeah.

Bret Kugelmass [00:50:39] I know, I know. I just never understood this idea of moving to other coolants when it's like... I always say that if it was a good idea to use a different coolant, the coal industry would have used a different coolant. Like, they really care about efficiencies. They really care about improving the engineering of these plants. If it was a good idea, they would have done it.

Armando Nava-Dominguez [00:51:04] I'm very lucky to have had hands-on experience in practical work and also in R&D. And I have to be honest, R&D problems, they are not as difficult as the engineering problems. These guys, they have to really make it work. As a scientist, we always estimate, we make things... "Oh, it's almost a circle," things like that. In the engineering world, you have to make it work. And there are tolerances. The pipes corrode. They deform. And that is a challenge. And if you find a fluid that is friendly to use, that is neutral, that is not toxic, work with that.

Bret Kugelmass [00:51:54] I know, I know. And then, just remind me. You might have already said this, but has anyone ever built a research reactor that operated in the supercritical region in all of history?

Armando Nava-Dominguez [00:52:07] Not exactly that I'm aware, but there were a few rectors that did operate at what we call superheated temperatures. Actually, it's the wrong name, but they called it that at the time, under supercritical temperature. And one was in Russia. I don't remember... I cannot pronounce, exactly, the Russian name, but it was functional for several years.

Bret Kugelmass [00:52:33] And this is just where they had separate compartments or channels and then passed steam through those channels or something?

Armando Nava-Dominguez [00:52:40] That's right.

Bret Kugelmass [00:52:41] Yeah. That makes sense to me.

Armando Nava-Dominguez [00:52:44] I mean, at some point the nuclear industry, I guess, in the beginning, in the '60s, they tried all different concepts. They tried everything and they tried to use nuclear reactors everywhere. I saw that they would trying to put them in airplanes, in cars. Like, wow. It was a boom, and they tried different options, different technologies. And in the end, the water-cooled reactor was the selected technology.

Bret Kugelmass [00:53:14] Yeah, yeah, I know. It's funny, I feel like a lot of people say... A lot of people who try to advance alternate coolant technologies say, "Oh, the only reason that we have water is because the Navy forced us to. Rickover forced us to use water." And I'm like, "That's so crazy that you would say that. Like, that's the only reason? Not all power plant operating experience ever?"

Armando Nava-Dominguez [00:53:42] And I know what you mean. That is the reason I started the conversation about what is critical about supercritical, because I was at the same comments about, "Oh no, we'll never operate supercritical water. That will never happen." And when I tell them, "You know that supercritical fossil-fueled power plants existed since the 1960s?" They're like, "Oh, really? Wow." Yeah, they exist, and they have been operating safely for years and decades. It's not a new technology. It's new in the nuclear reactor, but in the power system it's quite old.

Armando Nava-Dominguez [00:54:16] Yeah, you are right. There are still a lot of things that we have to clarify. For me, if I put on my engineer hat, I'd say, "Keep it simple."

Bret Kugelmass [00:54:34] Yeah, keep it simple. Oh, that's exactly what I say. And all the best engineers say that too.

Armando Nava-Dominguez [00:54:38] Yes, keep it simple. Don't try to come up with very crazy ideas because in the long run, it's difficult to control and sometimes you cannot even build it.

Bret Kugelmass [00:54:50] Yeah. Okay, well, as we wrap up here, I'll ask maybe two questions for you to wrap up with. One is, is there a realistic plan where you think you might get one of these built someday, and when? And then, the other question would be what's your vision for the future of nuclear, more broadly?

Armando Nava-Dominguez [00:55:09] Well, I really hope so. And that's one of my challenges. Alongside some of my colleagues, we really wanted to have discussions with what I call the nuclear reactor industry to really help us to try to clear a path for this technology, because we believe it has several advantages. In my mind, we can replace the old fossil boilers, supercritical boilers with nuclear reactors, supercritical reactors. It will be a win-win situation. I mean, it's not that it's straightforward, but it is feasible, and we want to really see if that works. But for that, we need to build a prototype and see if that is actually a feasible idea, and if it's also an economical idea. But for that, we need support from the industry as well. And that's one of the things.

Armando Nava-Dominguez [00:56:08] When it may happen, we don't know. Right now, as you can see, the new advanced water-cooled reactors basically are still a downscaled version of the Generation II reactors. They just made them smaller and with enhanced safety systems. But in terms of efficiency, gain of increasing the temperature and all these kinds of things, very little.

Armando Nava-Dominguez [00:56:35] And I believe, right now we're leading that generation in transition. And I think this is the right time if we want to implement new technology in the nuclear industry. The nuclear industry is a slow machine because it takes years to build the reactor. You cannot touch it. You have very few opportunities to really bring innovation to that. And I believe right now we have that opportunity. I think we have to take advantage of it.

Bret Kugelmass [00:57:14] Yeah, absolutely. Well, thank you so much, Armando. This has been just a great episode, a great educational experience for me. So, thank you for sharing this with us.

Armando Nava-Dominguez [00:57:23] No problem. Thank you very much for the opportunity. Have a wonderful day. Thank you.

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