Charlie Cole [00:00:58] Hello, my name is Charlie Cole. Welcome back to another episode of Titans of Nuclear. Today, we're talking to Igor Pioro, a professor at Ontario Technical University. Igor, thanks for coming on today.

Igor Pioro [00:01:10] Yes, thank you very much. Good morning.

Charlie Cole [00:01:13] Good morning. So, I think before we dive into some of these slides and conversations of your time as a professor, I'd like to hear a little bit of just about you. Where did you grow up? Did you have an interest in science from an early age? Tell me about your upbringing.

Igor Pioro [00:01:31] Yes, thank you. First of all, I am Kiev, from Ukraine. I graduated from Kiev Polytechnic Institute; nowadays, it's National Technical University Igor Sikorsky. That's because he was our student who moved to the United States and started the company on the helicopters, yes? I graduated in 1979, and my specialty was thermal physics, however, our thermal physics already included nuclear power plants and nuclear power. It is basic education; I already got something about that.

Igor Pioro [00:02:12] I first started to work at the Institute of Engineering Thermal Physics, National Academy of Sciences of Ukraine from '79; half a year engineer. After that, I entered to the postgraduate courses. And in 1983 I possessed a Ph.D; in Ukraine that will be Candidate of Technical Sciences. From '86 to '92, I was the Scientific Secretary of this relatively large institute we had. In total, the complex was around maybe 3,600 employees. And I possessed another degree. It's like a Doctor of Doctor of Technical Sciences there.

Charlie Cole [00:02:56] Oh, my God.

Igor Pioro [00:02:57] Started to work during this... Yes, mainly related to boiling, critical heat flux and boiling. And due to this, I already published a couple of books related to that. In 1992, I was invited to join University of Waterloo for research there. I have spent at the Mechanical Engineering Department from '92 to 2000. And in 2000 I was invited to join the Chalk River laboratories. At that time, it belonged to Atomic Energy Canada Limited, the Canadian nuclear vendor. Canada, deuterium-uranium reactors. And I worked there from 2000 to 2006, and after that I have joined the newly established university and newly established faculty of Nuclear Science and Engineering. Within this university, from 2006... almost 17 years.

Igor Pioro [00:04:12] Within university, I started as an associate professor. I was Director of Graduate Studies for five years, a couple of times Associate Dean. But now, I'm a professor, mainly doing research and other things. Well, what I have done in my lifetime? I have published 13 books in total, 535 publications. Papers in journals, 300 papers at the conferences, 26 inventions, and around 15 major technical reports, including two from the International Atomic Energy Agency. I gave lectures all around the world at different universities. One of the most exciting was the Massachusetts Institute of Technology, University of Cambridge, headquarters of the Westinghouse company, and many reputed universities in North America and Canadian universities also.

Igor Pioro [00:05:09] Because I strongly believe in nuclear; due to this, everyone working in nuclear should promote nuclear. Of course, we have very significant advantages, but also, we cannot say that we have no challenges, yes? This should be an open discussion, what we can do, how we can overcome these challenges and how we can move forward.

Igor Pioro [00:05:39] Possibly, the latest one that I would like to mention... We have published recently, this year, a relatively large handbook of generation for reactors or next generation reactors, our second edition. In total, it's around 1,300 pages. And in this handbook we have 64 experts from almost all nuclear power countries of the world. Due to this, I hope that readers and listeners possibly can find this to buy elsewhere, the official handbook of generation for nuclear reactors.

Charlie Cole [00:06:18] Wow. Wow, that's quite the career. A lot of work in a lot of different places. It's really exciting. What originally got you excited about nuclear energy and why did you want to join the field back in the '80s.

Igor Pioro [00:06:30] I think that may have been too early to say that I was really keen to be in nuclear. I would have liked to be an engineer. I went and studied thermal physics, but within thermal physics in fourth year or fifth year we studied nuclear power reactors, or better to say, nuclear power plants. Unfortunately, which is very well known from that site, like Chernobyl Nuclear Power Plant was monitored from Kiev. Actually, I had visited in 1979. It was a technical tour of the... I think it was Unit #1 of RBMK reactor...

Charlie Cole [00:07:21] At Chernobyl?

Igor Pioro [00:07:23] Yeah. I was absolutely astonished to see like a nuclear power plant of the future. Of course, no one could even think that something might happen, especially such terrible things. It was clean inside, video cameras and all. In '79, there was not too much you could see, right? We were allowed to stand right on top of the nuclear power reactor. Now of course, it's protected; you can work all day with full power in. It's approximately 1,000 megawatts electrical or, I think it's 300 megawatts thermal. As I said, it was very, very impressive.

Charlie Cole [00:08:11] Yeah, my God, wow. Were you in the Ukraine when Chernobyl melted down?

Igor Pioro [00:08:16] Yes. Then I came to Canada in 1992. Yes, it was... First of all, this happened on the 26th of April through the night. No, of course, government would like to cover up. And rumors on Monday appeared in our institute that guys who knew said, "Chernobyl Nuclear Power Plant Reactor #4 under fire." They said, "No, it is impossible. It cannot be. It's anchored in concrete, how could it be?" And after that, a crease appeared and everybody started to understand that this is something very, very unusual that happened. Eventually from three nuclear power plants near accidents. The first one was Three Mile Island. From my opinion, minor from all these three.

Charlie Cole [00:09:20] Right, right, right. Yeah, no significant...

Igor Pioro [00:09:24] Yeah, Fukushima, It's also quite substantial. But as I remember, two people have been killed by falling debris, but I think that...

Charlie Cole [00:09:34] None from radiation...

Igor Pioro [00:09:36] But Chernobyl, we don't know how many. Tens of thousands of people died eventually with... More than 100,000 people died because it was very, very difficult. And after two weeks, the panic more or less started because everybody understood that this is real, severe, strung out of all of the radioactive particles, yes? I remember because services were prohibited by KGB. They're not allowed to measure radiation levels. They measure by themselves, but do not disclose that. Illegal, I found a digital meter for that and went through the park near my building, and we roentgen per hour. And our regular level is only maybe around 15 to 20 microroentgens per hour. It was quite substantial in this particular place. But closer to the plant and... From the beginning, because I remember 55 or 56 firefighters and employees, they died through the very high level of radiation.

Charlie Cole [00:10:54] Right, right. Radiation poisoning right off the bat.

Igor Pioro [00:10:57] Yeah. It was a disaster. It's in my memory forever. And you cannot protect yourself.

Charlie Cole [00:11:05] Yeah. How do you feel like that experience shaped you and your career after Chernobyl? Do you think it sort of shifted your approach to safety or made you more invested in nuclear? How did it impact you, do you think?

Igor Pioro [00:11:20] Well, I trust, of course... Currently, I have already prepared some statistics of these things. What we have to understand is that the most dangerous thing in our regular life... It doesn't matter where we are, it's to drive a car. I know approximately 1.3 million people die every year in car accidents. In this case, no one's saying, "Guys, let's go back to horses," or, "Let's only walk." We reach a certain level of civilization, and with so many people, we cannot go back. We have to move forward. Of course, we have to do everything possible to decrease these things.

Igor Pioro [00:12:02] The risk officially, and based on all data actually... Nuclear energy is considered to be one of the safest. In spite of those three major accidents and more, of course, smaller ones. The worst one will be the coal industry where we're talking about full cycle, like building from coal, it will be number one by so many people dying every year. It continues. Because I believe in a bright future, and I believe that without nuclear, we cannot survive. We need electricity into every house. If you have no electricity, you cannot do air.

Charlie Cole [00:12:48] Right, right. So, here's another question. I know you mentioned you've worked on this Gen IV advanced reactor... You called it a booklet or a pamphlet, with the researchers from every country. I'm interested in your thoughts on... As you said, electricity is really important as this graphic in front of us can show us. And I don't know if everyone will be able to see it, but pressurized water reactors and boiling water reactors make up an overwhelming majority of reactors. Where do you see in the future, in the decarbonization effort, advanced reactors having a point, having a play versus pressurized water and boiling water? What's the balance? Where do you think should be pursued? I mean, I guess the answer's both, but I'm interested in your perspective on the future of new builds in nuclear.

Igor Pioro [00:13:33] Yes. First of all, I would like to say that my view is based purely on statistics. It's not like I'm tampering with data or I would like to represent better one company compared to another one. No, this slide, which I can provide to you later... The case is... And this is more or less as a rule... If a severe accident happened with one type of reactor, usually no one would like to build such a reactor in the future. And this is clearly shown by what we have.

Igor Pioro [00:14:10] Currently, we have 141 nuclear powered reactors... I'm talking about nuclear power reactors connected to electrical grids. Of course, of these 141 it's not that all of them are currently in operation, it's like an optimistic approach. The major problem globally was Japan, because Japan after the Fukushima Daiichi Nuclear Power Plant disaster, they were in third place after the United States, more than 100 reactors. France, 58 reactors in 2011. And Japan has 54 reactors. After Fukushima, they dropped down to 33 reactors. Within the last 12 years from March of 2011, from 2 to 9 reactors were in operation. I could check... I think a couple of weeks ago, I think nine reactors in operation. However, as I know, all of the pressurized water reactors have been put into operation. And they have approximately 50/50 from this 33 amount.

Igor Pioro [00:15:17] If you look at the other data, of course the number one reactors will be pressurized water reactors. Currently, we have 309, which is significantly higher than what we had before the Fukushima Daiichi Nuclear Power Plant, 268. And this site was the most built as of today; 38 definitely, and 36 possibly, which in total is 74 reactors. Number two, it will be boiling water reactors by number. However, before Fukushima it was 92. Right now, it's dropped to only 60. And only two small modular reactors, PWRX...

Charlie Cole [00:16:02] Right, right. The GE Hitachi.

Igor Pioro [00:16:05] And it looks like what I can see, eventually all new projects with boiling water reactors have been canceled all around the world.

Charlie Cole [00:16:15] Yeah. So from your perspective, what are the benefits of the boiling water versus the pressurized water? Why do you think that pressurized water has been the predominant design for the last...

Igor Pioro [00:16:25] Interesting, you say, like two different sides. From a technical point of view, if you have no steam generator or heat exchanger, you're not losing temperature. Yes, eventually it should be higher temperature which more or less controls the efficiency of the power plant. With boiling water reactors, actually the same as RBMK reactors, which exploded at Chernobyl, it was the pressure channel but they both... The reactor, they had drums separating saturated steam and steam going directly from containment building to power hull... And this appeared to not be a good idea from a safety point of view, that reactor coolant transported too far away from containment building. Especially for the Fukushima Daiichi nuclear power plant, it was one of the significant problems there.

Igor Pioro [00:17:23] Due to the pressurized water reactors, they kept steam generators usually forward inside the steam containment building due to reactor coolant not going out of the containment building. If something's wrong, you still have reactor coolant, but in the reactor. It's considered to be an enhanced safety. Of course, I don't want to say that the boiling water reactors are safe, but with steam generator, you have slightly better or enhanced safety for this thing.

Igor Pioro [00:18:00] And what is interesting to build is that in spite of... From a thermodynamic point of view, that it will be an extra couple percent of thermal efficiency. Currently, pressurized water reactors... Better to say, plants with pressurized water reactors, because we're talking about efficiency of the plant, superseded the boiling water reactor plants. The maximum working... They have the steam at 7.2 megapascals and correspond to that situation temperature. The pressurized water reactors, they reached steam 7.8 megapascals, situated steam. Boiling water reactors, approximately 34% max gross. Current pressurized water reactors, they go at 36 and Generation III plants go up to 38%.

Charlie Cole [00:18:53] Wow.

Igor Pioro [00:18:56] Due to this, this advantage was considered to be from purely thermal, originally, was lost. That is why all countries, more or less, are building pressurized water reactors. And possible open to pressure heavy-water reactors, mainly CANDU reactors, Canada, deuterium-uranium or heavy-water cooled, heavy-water moderated reactors, pressure channel reactors. Now, it's only 48 left, but the decrease is not very significant; within the last 12 years, only 2. And new reactors are planned to be built, at least in India.

Charlie Cole [00:19:37] Oh, they're building CANDUs? Or, they're building heavy-water reactors in India? I didn't know that.

Igor Pioro [00:19:42] Heavy-water reactors, because they have been proud to develop their own heavy-water, pressurized water reactor. It's not CANDU. There are some small developments there, but on the positive side. The number IV type will be carbon dioxide cooled. Actually, what is interesting that plants with AGRs in UK, only their reactors left are the most efficient ones. Because they have reactor coolant carbon dioxide, 650 degrees, the second highest temperature in all nuclear power outlets in the world. They connected this reactor to subcritical pressure. Coal-fired power plants can cycle. Due to this, the coolant up to 42 to 43%. It's 4 or 5% higher than the most advanced pressurized water reactor plant, CANDU.

Igor Pioro [00:20:49] For more than 39 years, no developments in carbon dioxide cooled reactors because all of them will be shut down. And currently, UK will build two EPR, Evolutionary Power Reactors by Areva and currently through EDF, Électricité de France. Because unfortunately, these type of reactors, carbon dioxide cooled, they will disappear within, I don't know, maybe five, seven years.

Charlie Cole [00:21:19] Yeah, why is that?

Igor Pioro [00:21:23] Because for 40 years, no development. Due to this, less carbon dioxide is very low heat transfer coefficients. Due to this, helium is much better in this case. And for this, it usually depends on the thermal conductivity of the gas. Of course, the best will be hydrogen. Hydrogen cannot be used in the reactors. But by the average in use inside electrical generators to cool down thermals. But second to hydrogen will be helium. It's normal gas, still high thermal conductivity.

Igor Pioro [00:22:04] Due to this, it will be, actually, a prime generation for concepts that will be very high temperature reactors. And it is called gas-cooled reactors, GCRs, helium cooled. These reactors, there are only two. They are small modular reactors, 100 megawatts, approximately, each. They are connected also to an old style of subcritical pressure cycle from coal-fired power plants with superheated primary steam and secondary steam. Gives you around 42% but the temperature or heating is the highest in... And reactors are 750 degrees. They have quite good potential with time to improve.

Igor Pioro [00:22:45] And also, I would like to mention here that these are unique reactors; they have spherical fuel. It's not fuel pellets in bundles, it's completely different. And helium comes from the top going through, I think 400,000 spheres with fuel. Last year, March... Of course, it's very difficult to say how long it can go. I hold that as regular reactors for many years, but currently it's in China and China is looking how this new technology can be implemented. Because higher temperature of reactor coolant, more possibilities to use heat or to have higher thermal efficiencies for generation of electricity.

Igor Pioro [00:23:38] Number six will be official light-water, graphite moderated reactors or Russian RBMKs. RBMKs means reactor of large capacity, general type. Now, one exploded in Chernobyl, of course. After that, no one developed there. And still in Russia, they have large ones, 1,000 megawatts electrical and three small ones AGPs, it's the smallest reactor in the world, around 10-12 megawatts electrical. Also, I assume that within 5 to 10 years all of them will be shut down and never built again.

Igor Pioro [00:24:15] And the last one will be liquid metal fast breeder reactors, in particular fast reactors around Generation IV. It's a fast sodium reactor, in Russian, abbreviation 600 megawatts. BN-800, newer one, put under pressure in 2016. And in China, a small one, only 20 megawatts electrical, but China possibly within this year or next year will also close to the BN-600 reactor.

Igor Pioro [00:24:52] It's unique... because it's absolutely a unique reactor coolant, it's liquid metal. But it's very, very tricky because it's melting around 98 degrees. It's boiling around... degrees Celsius. And the efficiency of this plant's approximately 40%... And these reactors, they have triple. They have sodium circulating inside of the reactor, heat exchanger sodium to clean sodium in loop. They come out far away from the reactor because within water and sodium it will be hydrogen.

Charlie Cole [00:25:45] Right, you do not want water and sodium together.

Igor Pioro [00:25:49] Sodium... I have seen different sources, but what I have seen right in front of our eyes, it will be heated in air... Around 300 degrees, it will auto-ignite in air. It's very unusual that metal will auto-ignite and you will have some sort of a yellowish flame there. It is very tricky to operate. And I think that in many cases, in many other countries reactors ended with some fires. Not disasters, but eventually when it's leaking there will be fire. Possibly, it will be more or less like liquid metal.

Igor Pioro [00:26:29] Our future, in terms of where we can go to bring creation... nuclear, which is very difficult to believe, can move and be a renewable energy. Of course, it's not like today. I know that currently, Russians built a lead-cooled fast reactor, 600 megawatts electrical. Also, a small modular reactor, and they would like to put this reactor to be a breeder. With plutonium, plutonium after that will be used in MOX fuel and other things. It's really exciting because eventually, the sources of uranium is not infinite. It's substantial, but it depends on how many reactors will use them. This is what we have as of today in the industry.

Charlie Cole [00:27:28] Here's another question for you. I know that you've been teaching a lot of courses recently on small modular reactors. I think I understand a little bit why there's sort of a preference for PWRs, but moving forward, what do you see is the role of the small reactors versus the large ones? Do you think there's going to be some mixture of both? Why do you think the strategy of using all large reactors need to pivot to have SMRs? So yeah, where's the big versus small for you?

Igor Pioro [00:28:02] First of all, the match only started. With my master's degree students, we have calculated around 108 concepts. But I would like to say that the vast majority of concepts have not yet been designed or developed. From 108 concepts, we have only two types of reactors in operation. It will be the Russian KLT-40s, it's more or less propulsion reactors from icebreakers. Before that, from submarines because they are more or less modular reactors in any case. But they're still like a small nuclear power plant inside submarines or inside aircraft carriers or icebreakers. And they pick up two reactors from icebreakers, put on a barge. And this is very important, I think, based on my knowledge that many different experts say, "It's already done. Let's stay put." They spent a significant amount of time and a significant amount of funding to move, because it's not real civil engineering even as an icebreaker. It's still the type of the reactor. They added basic safety systems and so on, and it took much longer than was expected. Now, it's department was electrical each. They put it on a barge in December of 2019...

Igor Pioro [00:29:52] And I strongly believe that of course, small modular reactors definitely have their niche, but some experts say that small modular reactors will replace large ones. I really don't believe that. Still, a small modular reactor is still a reactor. You have to guard it. You have to service it. You have to care about it. You have to have certain conditions, yes? How to handle these things. If you will have hundreds of such reactors all around the country, no, it's also not so simple. Plus... is why you need small modular reactors.

Igor Pioro [00:30:40] Here, I would like to say... old from Chernobyl time. Before that, we said that peaceful atom in home. Then Chernobyl happened, and people started to say, "This is what we got. A peaceful atom in every home and you have to worry about it." Due to this, I believe that the niche can be on a ship. Yes, you bring, for example, to Africa, to Middle East and you put another ship, destination unit. You provide electricity and fresh water. It's a great idea. You will go like... it's a very small city and this very nice land because it provides hot water and electricity at the same time. Military bases, some miles where you need maybe 6-10 megawatts electrical to operate. This is a good idea. But to put near large cities where you have everywhere power lines connected, like in Europe for example, I really don't believe that it will be necessary.

Igor Pioro [00:31:49] I also believe, not to forget, based on Russian experience that they took slightly enriched uranium; they used 18.6% when in pressurized water reactors, the maximum is around 5. This is another specifics of this case. Just as I believe that it's greater here. As you can see here, we have the top 6 different types, it will be water cooled SMRs, land based. Water-cooled SMRs, marine based means on submarines and aircraft carriers. High temperature, gas-cooled reactor is helium cooled, 21 concepts. Lead cooled, sodium cooled, lead bismuth cooled, SMRs 36 concepts. Molten salt SMRs, 17, and other very small. SMRs around 4.

Igor Pioro [00:32:45] It's a lot of talks about that; it's a lot of news. But in reality, only... high temperature modules from China. They are in operation. The rest, very close, or they started to build but are not yet in operation. And of course, I still absolutely cannot believe they won't have it... will be designed and will be put into operation. So, not trivial things.

Igor Pioro [00:33:22] Based on history, you know that even very large nuclear reactors, they disappear from the surface, correct? Atomic energy, you cannot the limit the scale, being split it and sold to... CANDU energy, Chalk River Laboratories currently and can have nuclear laboratories in the hands of the government. Areva also, the correct nuclear part have been given, I think, to EDF, Électricité de France. Some other companies went through bankruptcies. Areva, actually, as I remember, 75,000 employees. It's a huge nuclear company. And they have failed to put into operation their first EPR, the largest nuclear power... In 2006, they put into operation more or less of this much.

Charlie Cole [00:34:22] Yeah, they just did it.

Igor Pioro [00:34:23] This is actually a problem for all nuclear power industry. They promise one date, and after that they usually have delays and delays. We have to fix it.

Charlie Cole [00:34:34] Obviously, reactors used to get built on time very frequently. What do you see as the reason why construction delays and cost overruns have really plagued the industry?

Igor Pioro [00:34:45] I think that it's very complicated, the designs in general. Because it's not only reactors, it's coal plant, it's power cycling. A lot of drawings, you have to be absolutely sure that one corresponds to another one. When you're dealing... you have to possibly introduce some changes into that, and eventually it's delay and delay. As I remember, CANDU reactors, I think in China, they have been built on time and second round, possibly even slightly ahead. It was quite... but not everywhere. And of course, this Finland... However, now it is in operation.

Charlie Cole [00:35:40] Yeah, I had a professor in undergrad who worked on Olkiluoto, I think, in 2008. And at the time that I was studying with him, he was fully convinced it was never going to come online. This was a couple of years ago. Obviously, it did come online, which is great.

Igor Pioro [00:35:55] Yes, finally. Actually, it was connected to grid one year ago, but there were some problems with pumps and other things and I think they reached the real output... Actually, it's the third largest reactor in the world. Two plants built before in China. And China now is country number one in terms putting money into nuclear.

Charlie Cole [00:36:24] Have you personally worked on either the design of the construction of any nuclear power plants or more from the research, academic side?

Igor Pioro [00:36:34] When I worked at Chalk River Laboratories, we have performed... Eventually, I'm more from the experimental part. At Chalk River Laboratories, we had a large thermal hydraulic loop, but instead of water we used a modulant fluid as... But we had a formal test and full scale bundle test. Twelve short bundles, 500 millimeters each, cooled with... We have developed scaling... And nearby at... It's another site at Toronto... Laboratories, very famous in the world, and they perform experiments in full scale bundle tests. It's like one fuel chain completely in water.

Igor Pioro [00:37:21] In this combination of two, with refrigerants you can go for higher heat fluxes without any problems, but of course you cannot design the reactor based on... You must do experiments in the actual reactor coolant. But you can do all experiments to see certain boundaries wider with water. This was where I had this experience, and this was a great experience. We analyzed data from laboratories in water, we compared what we have in refrigerant, and this is how we have moved also at Chalk River Laboratories. I have started experiments with supercritical carbon dioxide and modulant fluid instead of supercritical water. Also, it was a quite interesting approach.

Igor Pioro [00:38:10] I have participated in two coordinated research projects by the International Atomic Energy Agency on supercritical water reactors, and currently we started with the first year of the third one. One of six generation for control of supercritical water reactor, also a quite legitimate one and an interesting one, but possibly not the right choice for many researchers and designers. Primary will be very high temperature reactor with 1,000 degrees... Of course... fast reactor because it's proven in the industry, especially like Russia it's... already in operation. BN-600 and before it was BN-350. Due to this... we have to be very proper and justified. We cannot jump, "Let's try this, and let's try that." We cannot afford any an extra serious accidents. Otherwise the most reliable and the most powerful with minimum CO2 emissions source of energy will go. And it will be a complete disaster for the world, not even for a particular country.

Charlie Cole [00:39:33] Yeah, wow. I know one of your research areas in particular was supercritical water. Is that right? You've worked with supercritical water?

Igor Pioro [00:39:44] Yes.

Charlie Cole [00:39:45] What are the benefits of supercritical water? And do you think there will be supercritical reactors built? Is it an efficiency thing, or what do you see as the key battle?

Igor Pioro [00:39:57] In front of nuclear power, we have thermal power. We use a power cycles coming from the thermal power which... Thermal power started with subcritical pressures that reached around 17, I think maybe 18 megapascals. Usually it's around 17... 16, 17 megapascals of pressure. Superheated steam, maybe 535 degrees primary and... you reached around 43%. From the thermodynamic point of view, you have to go to higher temperatures and for water, it would be pressures. But closer to critical point, the critical... limit, the heat locks in the side reactor when... boiling... For this, it's not the case, but for a liquid, for water, it is eventually going to zero.

Igor Pioro [00:41:11] That is why subcritical pressure... coal-fired power plants, they're not operating higher than 17, 18 megapascals. Because critical point is 22.064 megapascals. And then over that... And eventually... we have advanced coal-fired power plants from 60s with thermal efficiencies up to 55%. It will be a from 23 megapascals to 38 megapascals. But the vast majority of them are range of 23, 26, 27 megapascals. The range of 25 megapascals, 625 degrees.

Igor Pioro [00:41:57] Thermal efficiency for thermal power plants was the major driving force starting from the beginning. Nuclear power plants stuck at more or less for military applications, but with time and eventually, who cares about efficiency? If you will get 30%, 32%, it will be really, really great. But because nuclear power has to compete with other sources of energy, hydro, wind, coal-fired power plants, gas-fired, combined cycle power plants which going up to 62.5%... This is the highest thermal efficiency. You cannot ignore that. The thermal efficiency for nuclear power plants is also the driving force, but you cannot compromise safety. The emphasis still... safety should be enhanced, not slightly dropping down.

Igor Pioro [00:42:58] We know from the thermal power industry, that if you would like to move pressurized water reactors, boiling water reactors to higher thermal efficiency as plants, we need to move from subcritical pressure in cycle to supercritical. And this is more or less the current supercritical water reactors. Also, we have to understand that supercritical reactor cycle for six years in the industry. We cannot expect anything unknown.

Charlie Cole [00:43:34] You're talking about supercritical water, right? Not supercritical CO2? And then, second question, supercritical... Is this for a pressurized water reactor, I assume? And so, is it just the primary loop that is supercritical, or is there supercritical water going into a turbine?

Igor Pioro [00:43:51] You have to have supercritical as reactor coolant, and...

Charlie Cole [00:43:59] And as a... That makes sense.

Igor Pioro [00:44:00] The direct cycle like we have in boiling water reactors, but more or less like... I'm sure with Fukushima Daiichi Nuclear Power Plant disaster, no one will go with supercritical pressure direct cycle. It will be in steam.

Charlie Cole [00:44:17] Right, right. You need to be...

Igor Pioro [00:44:20] Because it's not steam. It's supercritical water. There is no difference between liquid and... But supercritical 25 megapascal reactor coolant water inside the reactor... Steam generator... And after that, supercritical pressure can cycle taken from industry. Eventually, we need to replace gas-fired or coal-fired things with nuclear energy. This is...

Igor Pioro [00:44:50] But many problem are in materials. It's not thermodynamics, it's not more or less heat transfer, these things can be fixed. But we know materials for supercritical pressure... Cycle there, but they have no neutron flux. And neutron flux, it's not enhancement... It's actually quite detrimental back on materials. Due to this, currently to the narrowest place to move to supercritical reactors. And of course, 25 megapascals, it's not fun.

Igor Pioro [00:45:27] I remember from some estimations if... And we're talking about pressure vessels, yes? In pressure vessels, if you have you 15.5, 16 megapascal pressure, you can't pressurize water reactors. The wall thickness can be up to 22 centimeters... If you move this same pressure vessel to supercritical pressures, estimations show that it should be 50 centimeters.

Charlie Cole [00:45:59] Oh, wow.

Igor Pioro [00:46:02] Even to manufacture that pressure vessel, it's also challenging.

Charlie Cole [00:46:06] Yeah, that's going to be...

Igor Pioro [00:46:08] I'm not saying that it's impossible but... First of all, you can say impossible, but you will manufacture and test and you will prove that it will operate. I know that some companies, I think in Japan, they said that they can do that, but still it should be proven in the industry. It's very important. This is... We're talking about supercritical water reactors as one of the...

Igor Pioro [00:46:34] Eventually, all Generation IV or next generation reactors, they should be more efficient, thermally efficient compared to current ones. Sodium cooled fast reactors, it will be around 40%. I'm sure that they will go above 550 degrees because they are afraid to get boiling inside the reactor and the boiling temperature of atmospheric pressure is 883 degrees. Possibly maybe 42, 43% can be liquid lead or molten lead. Reactors, of course, supercritical water reactors, it would possibly be exactly as if you have coal-fired power plants, 55%.

Igor Pioro [00:47:19] Helium, we definitely can go maybe 55, 60, something like that. Depends on the cycle. Of course, the original was helium turbine, but somehow they found that there is ingress of helium in the gas turbine bearings and now this... cycle is now going slow. And of course, just one turbine is not very high efficiency. This is should be considered also like a thermal power industry combined cycle. Some sort of turbine, maybe nitrogen gas in there, or 80% nitrogen, 20% helium. And after that, possible then can cycle at the lower values.

Charlie Cole [00:48:07] Awesome. Very interesting stuff. I think the supercritical world is really cool. Obviously, as you say, efficiency is really important, and it's important that nuclear keeps up with other energy sources.

Igor Pioro [00:48:18] Yes. Thank you very much. Goodbye.