 chačke ürečne koncepte elektrajne postavljali,別 na radečnjih neutronikv, vzvečaj ne však mi sega ima, pri antronega svojo izvene in zšlišnje reprevenosti. Vzvečo privatizem izvoje tez na nem�. Ono nekaj naredu, načo privod s riportovom newspaperu vzvečimo na Monty Karlo. na svetu do vrstej reaktorji. OK, smo počučili. Nelj smo na počuče izvestil in drugaj uvijas, ali nekaj, da se vidimo o generaciju 4, zato izvenilo, da je izvenilo generaciju 1, neko je pred vrstej prototajp. I nekaj je generacija 2, pomembno jazelje, in však celj nuklej poplans drugih groups je genučna vsega. In určitava Modena so bolj jazni. Vse je genučen 3v in 3v. Genučen 4 je neko inovativ, nekaj 3v, nekaj povedli jezni. Pripovrimo z nas za z �oč. S genučem 4 reakcija, na genučenom svoj polo. Maritava English, short relay, was created as a co-operative international endeavor, it was organized to carry out the research and development needed to establish the feasibility and performance of the next generation nuclear energy systems so the number of countries listed here, so that Argentina, Brazil, Canada, Frans, Japan, Korea, South Africa, UK and the US. zelo se vsečenje v 2001. V svače svetlje. V svače se je vsečenje in v 2002. V svače se je uratim, tako je to izvah, neko vsečenje, neko vsečenje, ko je ne vsečenje, neko vsečenje, je uratim, neko vsečenje, 2003 in 2006 čečne in raja. Zato se je vsega prišla Australia. V 2001 se prišli vsi expert vsega za to, za to, za to, In se vse reaktor vzupi vstveno, in sečno vodnje inhleti. Pridem tudi, da imamo tudi koncept in nabijem tudi, povedinem je tudi djih, ljubi se vložilo, da imamo logično svega reaktore in nekaj. Vse je koncepti vseh. Zelo zrednega vsega, zelo sem izvahval vsega vsega spektrum in vsega vsega vsega vsega. Vsega po tega systema se zelo, nekaj je vsega vsega vsega vsega. V dobroh vsega sem počustila, So solid line is main, so supercritical water cold reactor. The thermal option is the main and fastest backup. And for molten salt, I would say it's now fast option is main in jif and thermal is optional backup. So the important matrix for the important requirements, which were used in jif from the very beginning, which were applied for development of the system, is this list of four goals. Already mentioned at this school several times. The first one is sustainability, so it's two sites. One site is long term fuel supply, and the second site is minimization of waste and long term stewardship burden. The second goal is safety and reliability. So we would like to develop systems, which has very low likelihood and degree of core damage. And the goal is to practically eliminate the need for offsite emergency response, which is very significant challenge. The third goal is economics. So the life cycle cost should have advantage over other energy sources. And financially risk should be comparable to other energy projects, again very challenging tasks. And final goal is proliferation resistance and physical protection. So it should be the systems, the mass flows should be unattractive, organized to be unattractive material diversion pathways and enhanced physical protection against terrorism. When I present you the six systems, I follow this template. So first I will show you general concept, like the image and main features, and then give you general description, which I called fact sheet, where I present advantages, challenges, designs under developments and reactors under operation. And then for every system I selected one example to be more specific, to give a little bit more details about the design. And it will be main parameters, reactor fuel, core balance of plant. And then the final point for every system will be problems from viewpoint of GIF goals. And then we will consider the possible solution and go to the next system. Okay, I start with generation 3 concept, which I would propose to consider as reference. We also use it in our exercise. So it's classical pressurized water reactor. Everybody knows this design, I hope. So I don't go to the details, but as a specific example I selected EPR with thermal power 4300 megawatt, efficiency 37%, the primary coolant and moderator light water, pressure is 16 megapascals in let-out, let temperature around 300 degrees. Neutron spectrum is thermal and therefore breathing gain is low. And if you look at three goals, so I would like to mention that I'm not going, I'm going to focus on first three goals first of all because I'm not an expert in proliferation resistance. So I will look in this lecture at sustainability, safety, reliability and economics. So from this viewpoint, PWR is good, we would say, good safety, good economics because of the economy of scale. We have a lot of this system. It's already mature technology, but I would qualify a goal one as poor because of low breathing gain and low conversion, low rate of generation of new fissile. So from viewpoint of fuel, assembly and core design, so the fuel is classically enriched uranium dioxide, but it can be also mixed uranium plutonium oxide fuel. It's cylindrical pellet, 1 centimeter height, about 8 millimeter diameter, which is put in the cladding tube made of zircaloi, which is alloy of zirconium isotope. So the length is about three meters. At the top is relatively small, like 20 centimeter fission gas plenum. So then these fuel rods are put in the square assembly. Grit spacers are used to provide the rigidity and make the distance between fuel rods, and this assembly doesn't have the duct or wrapper, so it provides cross flow between assemblies. Then they are put in the core, as you can see here, and the general, I would say, the core, this core is very homogeneous, so it's good from this viewpoint. In particula, even the control rods are inserted in every fuel assembly, and this is an interesting point, because with this design we should be able to remove all control rods from the core during refueling, and we can do it because we have another way to control reactivity, which is dissolving the boron acid in the water. So this allows us to insert control rods in every fuel assembly and obtain very homogeneous core from this viewpoint. So what are the advantages? It's operational experience and established technologies, of course, which is good for economics. It's light water as a coolant. Well, it's common matter. It's transparent, easy to handle. It's boron control I mentioned, and there is more advantages. There are challenges, and the first challenge I would say for safety is high coolant pressure we need, because we have small margin to boiling for water in order to receive this efficiency and this economic output. We have to use high coolant pressure, 16 MPa, and this is a safety issue of depressurization. Loss of coolant accident is design basis accident, which requires a lot of safety systems, analysis, demonstration, and so on. And the second challenge of problem disadvantage is low breeding or low conversion ratio we already discussed. There is many designs under development. EPR is just one example, and there is this number of reactors under operation. Okay, this is the last slide about the PWR, so I repeat here the parameters, so I will do it for every system, and I will add columns in order to have at the end of overall table for comparison. And with this orange color, I showed a kind of problematic, the kind of the parameters which we would like to improve. So in this case we have efficiency of 37, and economics therefore is good, but it can be improved. So if I ask you the question how we can increase efficiency, so we take PWR and we would like to improve the efficiency of our cycle. What we can do, do we have any ideas? Yes, how to go higher? What is the most simple step to do? Yes, I like this moment simply. Let's increase the temperature and we will improve the parameters of the thermal cycle. To increase the temperature we need to increase what? Also we just discussed the margin to boiling. So if you increase the temperature in PW, increase pressure, yes. So increase the water pressure and temperature, and we arrive to supercritical water cooled reactor which operates, which indeed increase the pressure, and even above the thermodynamic critical point of water, which is 374 degrees centigrade and 22 megapascals. So here I remind you the dependence of pressure on temperature. Here is the critical point, and here we have supercritical fluid which is neither liquid nor vapor, but something in between. And so the supercritical water cooled reactor operates both below critical point and above critical point. So why? Why it's good from viewpoint of economics because we can imply existing advanced supercritical water technology used in coal plants. Very well developed. It's working. This is the attempt. Let's combine the PW technology with supercritical water technology. And let's use direct ones through steam cycle. So no steam generator, no steam separators and dryers. This all can potentially make the system better from economical point of view. Okay, advantages. It's based on Gen3 plus reactor technology. It merges this technology with advanced supercritical water technology. It's high efficiency than Gen3. Plus it's possible to have both thermal and fast spectrum. I will show you later the density and we will see that at these conditions the density can go very low. And this we have steam. And this in principle allows us intermediate fast, even fast spectrum option. And I mentioned that there are two options considered for supercritical water cold reactor. Challenges, of course, high pressure, high temperature, materials, water chemistry and radiolysis. Then some hydraulics because for this high pressure there are gaps in our knowledge of heat transfer and critical flow databases. Safety demonstration. So in case of fast spectrum we can have positive void effect as in any fast spectrum. But also high pressure assumes potentially more violent probably loss of coolant accident and things like this. And fuel qualification, high pressure, high temperature. So we cannot use circular anymore. Designs under development, the example I will show you is high performance light water reactor developed in frame of European project. There are no reactors under operation as far as I know. So here I put the first column which is now new. The first generation for systems, specific design HP LWR 2300 megawatt thermal efficiency 44. Ok, increase. We reached the goal. We improved efficiency. We improved the economics. So I put here the green arrow up. It means improved compared to PWR. Primary coolant remains water and you can see how much the delta temperature is increased. So it's now instead of 31 degree around 30 delta T in PWR we have 220 degrees in this. And it goes up to 500 degrees. And the pressure is 25. We still have breathing gain law. We didn't improve because this is the option of thermal spectrum. And I highlighted and marked in red the problem. So water at this pressure and at this temperature definitely is very corrosive, very aggressive against structural materials. Specific design, ok. I started to say that we have delta T which is 220 degrees. And if you take into account the uncertainties, not uncertainties but the power distribution and local peaking factors that then for this high delta T the local peaking temperature can go too high, unacceptably high. And the target is now 630 degrees. So we need, so people looked for design solution to solve this problem, to limit the peaking temperature. And possible solution as far as I know also used in coal plants is organized heating in three steps. So and it's illustrated here. It's a bit complicated design. It was fun for me to learn it. So I will try to explain it quickly as far as I can. So the idea is that the inlet feed water in enters the circuit and divide it in two parts. One half goes down, one half goes up. So down goes along the down camera, low, planum and then enters the core. And the core circulation is organized not in a usual way when everything goes up. But for the part of the core the water, supercritical water goes up and heated up in evaporator, then mixed it up a mixing chamber, then goes down through super heat one, mixed in the lower mixing chamber and then go up through superheated two, superheated two in order to go out through core outlet chamber. So the idea is that we organize very good mixing after each step. After evaporator, everything is mixed. And so we remove the local overheating because of the power non-uniformity. And we do it two times in upper mixing chamber and lower mixing chamber. This allows according to calculation to keep the peak cladding temperature at 630. But of course we significantly deteriorate the potential for natural circulation. Power also reducing at each step. I mean at evaporator it's higher than at super heat one and super heat two. I will show you how it is organized. So there is also dedicated water boxes. You can see here the design of the assembly. Sorry, design of the assembly. So it's square assembly. And there is a water box in the middle which is independent circuit. And we have, it's called water boxes. And we have there the relatively cool cold water which serves as moderator. Okay, complicated. Reactor vessel even more complicated. Okay, I put here some interesting design solutions. So there are four lines to enter for feed water and then it goes down and up. So down it's a core inlet. And here we have upper plenum from where relatively cold water enters water boxes. So the three examples of channels shown as evaporator super heat one, super heat two. What else? We have here interesting device which is back flow limiter which is using the swirl in order to have much higher hydraulic resistance in backward flow compared to direct flow. And we are considering this device now for European sodium fast reactor for similar purposes. And also the important design feature is that the vessel is contacting only cold water, only feed water temperature. And the wall thickness is 45 centimeters here which is huge. Okay, so for the core design I already showed the assembly. It uses wire wrap like in sodium fast reactor to keep fuel rods together. It's closed channels with a wrapper wall. And the evaporator super heat and super heat two is organized as shown here. So it's the same number of clusters, 52 clusters for every channel and one cluster is four assemblies. And then evaporator in the center that means higher power and then lower power. This is a balance of plant concept. So I don't go into details because I don't understand it. I just copy it. And it's very complicated as you can see. And I guess very optimized because it's real balance of plant used in coal plants. And the efficiency is like 44%. Okay, this is a summary for supercritical water reactors which emphasizes, so I don't repeat, but I emphasize the problem. It's water at high temperature and decrease of safety and reliability, I would say, compared to PWR because we increase the pressure and temperature. It creates the problem, both for safety and reliability. So now the question for this system, so how to keep high efficiency, I mean improve economics, still we would like to keep it, but at the same time avoid problems related to water at high pressure and temperature. So improve safety and reliability. Yes, which coolant? Yes, another coolant because it's not what we have here. White gas, inert gas. So, okay, we have active, from viewpoint of corrosion, we have water at high temperature, but if we replace the water with inert gas, then we don't have the problem of corrosion anymore. And we arrive at very high temperature reactor, which uses graphite as moderator and helium as a coolant. So, and we consider both graphite, prismatic and pebble bed as reference configurations. And one of the most important feature of high temperature reactor is very low power density. It's like factor of few tens, like 30 times lower than in PWR. And this is a basis of very good safety of this reactor, of this concept. So advantages, high temperature enables non-electric applications and high efficiency. But I already mentioned the safety. And this reactor is designed so safe that they call it walk away safety. So you just don't do anything and walk away or run away. And the reactor shutdown itself, in fact, even in case when helium is completely lost because of reactivity feedbacks, it shutdown itself and it removes decay heat through the vessel by radiation and natural convection of atmospheric air. Impressive. And advantages in inert gas coolant we already discussed. Challenges, one challenge is in the first world, which is very high temperature reactor. And it means that we need to reach temperature of 1,000 degrees for hydrogen production. I mean, non-electric application. One of the non-electric applications is hydrogen production. And in fact, this gray plant has depicted the hydrogen production. But also coupling with process heat applications. And the important challenge we should remember is graphite as waste. So the big amount of graphite means we irradiated at the end we will have a big pile of irradiated graphite which is a red waste. Designs under development, Chinese, HDR PM and the reactor sander operation Japanese, HTTR. And I selected this Chinese design as an example because I have nice animation. So I put now V in the brackets. It means that it's not necessarily very high temperature. It's still generation 4 system, but it's not 1,750 degrees, which is huge and which gives us efficiency of 45%, which is comparable to or even slightly better than supercritical water reactor. Helium, 7-megapascal pressure moderator graphite, neutronspectral thermal, means breathing gain, slow sustainability. I put question mark because it's probably worse than for PWR because we produce this additional large amount of activated graphite. But it's question mark, I don't insist. So, otherwise, it's, I would say, one of the perfect systems. Except sustainability. So, considering fuel, it uses, this design uses fuel pebbles, which have inside trisokaltered particles, which consist of the U2 kernel and then several layers of porous carbon, paralytic carbon, silicon carbide, and so on. So, very high inertia of this, very low density. So, this 6 centimeter diameter pebble contains about 7 gram heavy metal. So, very diluted. And it contains about 12,000 coated particle, this pebble. Fuel loading scheme is multipass. Every pebble goes through reactor six times. And this animation shows how it is mixed. So, it's first just shown for illustration, these lines, the position. And then when it goes second time back, then it's somehow more uniformly distributed. We try, as a master student, try to simulate this explicitly. And with serpent also this kind of operation. And average discharge burn-up is 90 Mg per kilogram uranium, which is relatively high compared to PWR. Okay, this is a reactor. It's relatively classical gas cooled reactor with reactor vessel and power conversion system, which holds steam generator. So, the fuel pebbles inserted from above and discharged from below. Yes, there is graphite reflektor and there is a containment circulation here. They also consider two reactors connected to a single steam turbine and power density 3.3 Mg per cubic meter, which is factor of 30, as I already mentioned, lower compared to PWR. High thermal inertia, huge thermal inertia, makes this reactor walkway safe. Okay, so here is the summary. And the only, as I mentioned, we have breathing gain below zero and sustainability. And this is the weakness of PWR, supercritical, VHTR, all thermal system. So, it's difficult to fulfill goal number one, sustainability. And the question here, how to reach this and in particular improved fuel utilization, probably trivial. Yeah, develop the design, change the design to obtain the fast neutron spectrum and we arrive here to gas cooled fast reactor. So, we still gas cooled, but now we remove moderator. No moderator. Keep helium cool and we keep pressure, 7 MPa. And both direct and indirect cycle were considered. This is direct cycle with Brighton machine. But later, GIF project decided to focus on indirect cycle. So, what is the advantages? Potential for new fissile breathing due to fast neutron spectrum and better red waste treatment. It's transparent and inert coolant. It's high efficiency. And the challenges, the first and most important challenges is safety demonstration. Safety issues exist. In particular, decay heat removal in case of loss of flow and depressurization accidents. And the difference between HDR, very safe, and GFR, which is not so safe, is that there is no moderator. There is no this huge amount of material which gives thermal inertia. And now we have like bare core, which is fuel with some cladium, but it has very low thermal inertia compared to HDR. This is the issue. And then high temperature materials and fuel qualification. Because we could not use these three particles, so things like this. We need some new materials like probably silicon carbide, which is more acceptable to provide fast spectrum. Design sound development, it's Allegro 75. Originally now they go down. I don't know exactly to what 50 probably. And more large power design is GCFR of 2400 megawatt thermal. There is no reactor sender operation. So I summarize here. No, I present here the specific design, which is GCFR, the big reactor 2400, the efficiency of 45. Very good. Helium, so inlet-outlet temperature is 40780, 7 megapascals, no moderator, fast spectrum. Breeding gain is close to zero, which means isobreeder and sustainability now. We have good, but safety, we definitely deteriorate compared to PWR, and with economics we could not say much. Most likely it will be very poor from your point of economics. So I put here the red code because of depressurization accident, and this is low thermal inertia because there is no moderator. So the fuel of this design, one of the options. So developed at CEA is carbide fuel, mixed carbide fuel in sandwich cladding, so-called sandwich cladding, because they started with silicon carbide cladding, they call it SIG-SIG because there is some reinforced fibers inside the SIG matrix in order to improve the stability or robustness of this cladding because SIG is relatively fragile. There is no plastic limits for this material. Moreover, in CEA they propose some metallic liner in the middle of this cladding because during operation they expect that SIG-SIG becomes relatively porous because of microcracking and the fission products will migrate through the cladding, and to avoid this they consider the very thin metallic liner from refractory metal like tungsten. And the problem here is that all refractory metals are very good neutron absorbers, so it will impact significantly neutronics. Moreover, they consider buffer bone between carbide fuel and cladding which is a kind of carbon-based braid, this kind of stuff, very exotic. I think the reason was that the carbide has very high swelling rate under irradiation, and this makes dangerous the contact and pellet cladding mechanical interaction. So to facilitate these regimes, they consider buffer bone. The core, probably nothing special here, two zones of plutonium content, control assemblies, I discuss it a little bit later. The only interesting feature you can notice is that there are two fission gas planes above and below, and the reason is that it's nearly impossible to make a cladding of SIG, of silicon carbide as long as we need, like, I don't know, two meters or three meters, and they designed this core with kind of two fuel rods on top of each other. So this fission, one rod has fission planum, gas planum above and second below. It's just exotic stuff for this core. So the reactor looks like this. Again, it's relatively classic configuration with reactor vessel, but now we have not one, but three main power conversion loop which hosts the intermediate heat exchanger and also three decay heat removal loop dedicated to decay heat removal in case of accidents. And, well, this creates also the potential danger of mistakes with closure and opening of the valves because this will require reconfiguration of the circulation in case of accidents. In other feature which can make this design very expensive is spherical guard vessel. I will show you later also some, but the idea is to put additional vessel in order to guarantee the backup pressure in case of depressurization events. Okay, this is big balance of plan concept. You see the reactor vessel, the heat exchanger, so circulator, main blower, the temperatures. Then we have decay heat loop which includes the water, some water pool and circulation of water for decay heat removal. It should work fine if we shut down the reactor, then we can remove decay heat. But the problem is when we have the break or any of the pipes, then we have depressurization. And that's why this guard vessel is introduced in order to guarantee the backup pressure to still be able to remove decay heat in depressurization event. Moreover, there is a kind of emergency cooling system like in PWR, but in this case it's heavy gas which is injected when needed. And this heavy gas was selected to be nitrogen. So there is three reservoirs inside guard vessel with nitrogen at 14 bars which is also not something very good. So it's a lot of potential energy inside guard vessel which can kind of explode. Behave somehow, not good for safety. Okay, then there is a power conversion system here with turbines. What water circuit? Water circuit here. Yes, there is DHR blower, so the DHR system is not fully passive. It uses the blower. Okay, and inside guard vessel also there is not nitrogen at atmospheric pressure. So there are several ideas how to improve the safety of gas fast reactor. So one idea is it's all around decay heat removal under depressurized condition. This is a key safety issue for gas fast reactor. One idea is we don't have coolant or moderator thermal inertia. Let's think how to replace this with mechanical inertia. And this one idea is let's put the blower on the same shaft as a compressor and turbine. So then we have a very big momentum from turbine and the blower will have very slow course down. Okay. Nice idea, but I expect that it could create some bad feedback during normal operation. Another idea is to improve the passivity and the replace or complement the decay heat removal loop with DHR blower with another design of DHR loop which is in the Brighton machine which practically will use decay heat to remove decay heat. So there is no active components. There is still the need to run the machine to start up it. Separate question. Two examples of the directions of safety improvement for gas fast reactor. Okay, this is a summary for gas fast reactor where I emphasize the problem so it's high pressure, relatively seven megapascal, snow moderator, low thermal inertia and therefore the deterioration of goal two, which is safety and reliability. So we have low thermal inertia repeating, requiring special safety measures against core meltdown in case of depressurization events. So the question is how to improve what we can do to improve the safety. What is the next step? You can do. Yes, very high thermal inertia. So very high thermal inertia of graphite moderator make transient slow. It's removed from the surface of the vessel by radiation and natural convection of atmospheric air. But the second point is very low power density of HTR compared to GFR. In GFR we have compact core with very high power density. HTR is very big, it's very low power density. Both can operate with natural convection, yes. So what we can do to improve the situation? Yes? Yes. Let's try. Use liquid metal instead of gas. We write that sodium cool fast reactor and this is a concept. So it's a pool type reactor which is traditional for Europe where all components of primary system is immersed in the big pool of sodium. Very big inertia now because of the coolant. We didn't have in case of helium good potential for natural convection. Here we can see that it has intermediate circuit and it uses in this case steam water cycle. So the advantages again. It's potential for new fissile breeding due to fast neutron spectrum and better treatment of red wastes. It's excellent thermal conductivity of sodium. This is very efficient cooling. That's why it was selected as a coolant in the first fast reactors because sodium is the best from viewpoint of thermal conductivity from all available materials. Large margin to boiling in sodium cooled fast reactors it means no pressurization required. Very important improvement compared to all previous considered reactors. I mean JFA, HDR and supercritical load reactors. Significant operational experience. It's more than 300 reactor years. At the same time challenges chemical activity of sodium when in contact with water or air and this requires intermediate circuit which has impact on economy. Makes systems more expensive. Significant scattering cross-section of sodium it means that when we remove sodium then the spectrum will become harder. And this means positive reactivity effect. It's simple if you remember the eta dependence in high energy region for plutonium for example plutonium 9 then it's quite steeply increasing. It means when we shift in the fast region and shift spectrum becomes harder then the ratio of production and absorption becomes better and it means positive reactivity effect. And it means we need special safety measures to protect our reactor for this case. For the case of sodium disappearance one of the most probably possible event is sodium boiling but it's not the only one. The gas entrainment is another example. So design standard development India, PFBR, BN 1200, Russia, France, Astrid and European sodium fast reactor in Europe. Reactor standard operation is three reactors in Russia and CEFR in China. That's it, as far as I know. I forgot something. Oh, small one, yes. Thank you. So now this is our table with last column for SFR where I emphasize the problem which is sodium itself and which is reactive in interaction with water and air. So safety and reliability compared to PWR, I could not say. So something is better, something is worse. And economics most likely is still not competitive. It's still with SFR in general probably because SFR is more expensive as PWR. So for fuel rot and fuel subassembly it's mixed uranium plutonium dioxide as a fuel and stainless steel as cladding. It's classically hexagonal lattice of rot fixed with helicoil wire spacers, closed assembly. So no cross flows between subassemblies but important interassembly flow which is quite challenging for simulation. Absorbers are inserted in the dedicated assemblies which creates heterogeneity of the core. You remember I emphasize that PWR is quite homogeneous and control elements are inserted in every assembly. This could not be done in sodium fast reactor because during refuelings absorbers should remain in the core because we don't have boron regulation. And that means that we need special channels for absorber to allow the refueling, the extraction of fuel subassemblies. That's why we have dedicated channels, dedicated assemblies for absorber. And we need also the special design at the inlet of every assembly in order to redistribute properly the sodium flow rate between very hot assemblies and relatively cold assemblies like fuel and absorber assemblies. So it requires more complicated design of the core compared to pressurized water reactor. We also have fuel stack of about one meter with helium inside, the fuel rod and large about one meter fission gas plenum below the fuel. Anybody knows why it's below the fuel? Why it's not above? Yes, classically it's below because we'd like to gas pressure inside the fuel rod to be low. We don't want to heat up the gas inside and the big gas plenum is heated by sodium. So we would like to contact gas plenum with colder sodium, not with hotter. So if we put it above, then the gas pressure will be significantly higher by definition because it's hotter. So I use European Sodium Fast Reactor which is developed now. It's a long story from SPX-2, then EFR, then CPEFR. Now we have a project where we developed the design of European Sodium Fast Reactor. So here you can see the radial core layout. It's quite nice, I like it. It's perfectly symmetric. It has six batches, six-year fuel cycle. It uses mixed scheme. It means there is no reshuffling. And every year we remove the fuel assemblies of one color and put the new ones. And then it's kind of changing every year. There is internal storage here for 50% of the core. And there are also new feature which is Corium Discharge Tubes. We will talk later on Friday in more details about this. Why do we need Corium Discharge Tubes? And also all DSD rods, which is a scram system, the all drive lines equipped with passively activated QD point locks, which release the absorber in case of temperature increase because of this QD effect. And it inserted by gravity. So the axial core layout, yeah, there is inner zone, the feature here, that they have the same height, but the different bottom height. So we use the same plutonium content, but different height. In the center, in the inner zone, it's shorter, it's outer zone, the fisile is higher. There is also layer of blanket below. And there is a steel blanket, and this is a fission gas plenum. This is a control rod assemblies and Corium Discharge Tubes. Yes, plutonium content is about 18% currently. Then this shows the global view from above. You can see the six loops. So intermediate and secondary loops. So six intermediate heat exchangers in yellow, three primary pumps. Yes, and in every box there are six modular steam generators. That's quickly the overall design. We have three decay heat removal systems shown here, but again, I will present it in more details on Friday. So the primary system looks like this. We propose here to eliminate the second vessel because we can improve in this way significantly economics and replace the safety vessel with metallic liner on the surface of the insulator. So that's one of the proposals, which can be interesting. There is a core catcher inside vessel, which we analyze, make thermal calculations now. The goal is to design it to host 100% of the site, but I think it's not possible. But it's under development. So this is the vessel fuel handling system. I put it here, but there is nothing special. It just illustrates that with two rotating plugs we can reach every fuel assemblies and we can move it into the internal fuel storage and then it can be removed from internal fuel storage and put outside of the reactor. Pit cooling, so reactor pit is cooled by two systems, oil system and water system, and it should be also under force convection. This is auxiliary decay heat removal system, which can be used in case if needed, but normally it is used for cooling down the concrete. This is secondary system, which shows one decay heat removal dedicated. It's connected to eye check, so it doesn't have separate heat exchanger. This is also the new measure we propose. So it should remove decay heat, in the case when we completely lose the secondary system. And we also consider to remove decay heat from the surface of steam generator. That's why we put this six-modular steam generator in a box in the casing, and when you open windows and atmospheric air circulates here and removes some decay heat from the surface of steam generators. Thermal pump is a nice concept, which is used in thermal electricity in order to provide some additional pump head to contribute to natural convection. We will also discuss it on Friday. This is a balance of plan concept, which shows decay heat removal system in the first, second, and the third. Some parameters of the inlet-outlet, which is very classical, like in Super Phoenix. And the tertiary water is at 185 bar. Okay, this is a summary of the SFR concept, where I put a kind of problematic points, issues is sodium itself and safety and economics. And now the question is, although SFR is definitely the most mature concept among generation for fast reactors, however we have the problems, the weakness is the risk of sodium water and sodium air reaction and corresponding design complication, for example, intermediate loop. So, how to improve the safety and reliability and economics and keep at the same time sustainability. So, what is the next step you can propose? Yes, alternate. Yes. Well, it's... Yeah, you know how to do it. How to find out. But yes, so people are proposing, expert proposing, let's consider another liquid metal instead of sodium, either lead bismus or lead. And in generation for international forum, the reference system is lead cooled fast reactor and this shows the concept. So, as you can see, there is no intermediate circuit anymore, so the steam generator is inside the primary pool. In this case, it uses Brighton cycle, but it's probably not the reference, it's just concept. And the features we can mention simplicity, no intermediate circuit. And complication is that oxygen control should be provided for materials protection. So, what are the advantages of lead cooled fast reactor? Potential, the fast spectrum is breathing, there are other fast reactors, high density. So, this is a really very big thermal inertia, which makes all transient smooth, so in a way it's similar to what we have in HDR, but now we have a fast reactor, we have here the high power density. High thermal conductivity, not as high as in the case of sodium, but still it's liquid metal and the expansion coefficient makes very efficient heat removal at low velocity and high natural circulation level. So, lead is relatively passive, is water and air, I mean the quick, the fast interaction, so it allows to eliminate intermediate circuit and it has large margin to boiling. The boiling is 1740 degrees, which is well above the cladent melting point. In any case, this big margin means that no pressurization required, of course. It can operate at atmospheric pressure above the free level. Challenges, there is a number of challenges. Lead has very high density, it means problem with erosion, seismic issues and refueling issues, because when we need to insert something in this huge pool of lead, it requires a technology to do it. At high temperature structural materials such as iron or nickel are slowly dissolving in lead flow. So sometimes this is called corrosion and this is the problem number one of lead cooled fast reactor which requires protection, which requires special technology. And one of the technology I mentioned is oxygen control developed in Russia, in IPP, in particular for lead bismuth reactor for submarines. It was efficient, it works, but it's quite complicated because you should control the oxygen content in relatively narrow corridor and this oxygen allows to create on the surface of cladent very thin and strong layer of oxide, which protects the dissolution of stainless steel components in the liquid lead. There are other solutions or attempts to use dedicated layers, liners on the surface to protect this effect. We still have high void reactivity effect which exists in all fast reactors, but now we don't have the boiling of lead as a potential danger. Ok, we have it, but it will be quite late. Serious severe accident when we have already melting of the cladent and so on, but we have potential of gas entry for example, which gas can enter in the core then we can have big positive reactivity insertion. And another challenge is low margin to freezing which is 327 degrees. Ok, it's exactly 600 Kelvin, easy to remember. And this is relatively low, so the special measures are needed in order to avoid the freezing and in order to mitigate the freezing in case if it happens. So it should be some very powerful electrical heaters, things like this. Designs under development quite a lot. European led fast reactor, which is big option. There is Alfred, which is small demonstration reactor. There is Russian designed Brest of the 300. There is American S star, and the list is not complete. There is no reactors under operation. Very small operational experience. I mentioned military applications. So this shows the parameters of Alfred, which I selected as example. Alfred is European led fast reactor demonstration project of 300 MW thermal power, high efficiency, led as a coolant with these temperatures 400-480 degrees. So the problem I already mentioned. And pressure I put a little bit higher because we have gravitational head, so it's not insignificant in the core, but there is no pressurization. And limited operational experience we can mention as a problem, as a deficiency of this design compared to sodium fast reactor. So fuel sub-assembly, it's hexagonal lattice with wire spacers in closed wrapper. And the feature is that there is no refueling mechanism. So the fuel sub-assembly looks like this. This is like traditional sub-assemblies. This is the bottom, this is the top. But then we have the upper shroud and ballast, which allows us to have access from the top to the sub-assembly. In a way we have like refueling, driveline refueling mechanism connected to every sub-assembly during normal operation. And this ballast, which is some very heavy material, tungsten or something like this, allows to avoid the flowing up of the sub-assembly due to buoyancy. Okay, some details. This is the core. Well, here we don't have anything special. So it's inner zone, outer zone with different plutonium content, control road safety roads. Primary system. So no rotational plugs in reactor roof because we don't have refueling machine. So we can take every sub-assembly and remove it. Reactivity control by two diverse and redundant systems. Primary system configuration is pull type, enhanced natural convection in accident conditions because of the good properties of lead, but also this very simple design, very simple configuration. Mechanical primary pumps at hot lag, which is minus of the design, I would say, put here. Again, to simplify the circulation, just very simple it goes up and then down and that's it. Decay heat removal, for decay heat removal, the designed isolation condenser connected to deep coolers with straight double volt tubes. Two vessels, reactor vessel and safety vessel. Yes. Balance of plan concept, shows main temperatures and eight steam generators. So we have water, 180 bar, precious water inside the primary vessel which requires some measures and demonstration of safety. So DHA condenser, that's main features. And finally, this is the conclusion for Alfred. And here the question, more general probably I would like to ask. So in all considered systems, accidents with core meltdown has extremely low probability, but they are still possible and do we have the idea how to practically eliminate the core meltdown? Melted before, yes. Increased safety margin. No, it's not practical elimination. So the only way to practically eliminate something is to do it before. A bit for me, I consider reactor pool, sodium fast, reactor of pool type, because inside we have still the pipes. But when we look at this pool, we can say, okay, we already realized the pipe break. We can imagine that the sodium goes out and fill this big pool. In a way we eliminated the pipe break accident in this way. And here is something similar to eliminate meltdown of solid fuel. Let's design the reactor with liquid fuel. And here we already mentioned during this lecture several times and later we will have dedicated lecture about molten salt. So I will be very quick here. So the picture of the official picture of generation 4 is thermal concept shown here. And you can see one of the interesting feature immediately that there is a freeze plug and then some emergency dump tanks. So it means that in a passive way so freeze plug is probably the frozen salt, another salt which will melt down at increased temperature and then there will be the pass for molten salt, fuel molten salt to go down in the safe configuration properly cooled and so on. So it's kind of protection against accidents which is peculiar for molten salt reactor. But here I modified the thermal concept by putting this big yellow rectangle in the middle which illustrates the idea of the fast molten salt reactor which is just big empty space filled with molten salt with fuel dissolved which allows us to have critical configuration, critical reactor with fast intermediate fast spectrum. Ok, it's a very long discussion of advantages and challenges that probably go quickly through. We have fast spectrum. This is advantage. We have large margin to boiling. We can operate at atmospheric pressure. Important, very important for safety. Strongly negative fuel, salt density, reactivity effect or void effect. So of course when we reduce the density of salt we reduce the density of fuel and it's strong negative effect. So this is probably the only reactor only fast reactor which has intrinsically negative void effect or cooling density effect. High efficiency because the temperature is high, no structural material so it's apart from the vessel, if you look at the core there is no structural material it's homogeneous core. It means there is no radiation damage and associated problems. So there is a possibility to add low fuel salt and simpler reprocessing which is big topic. What are the advantages of molten salt reactor from viewpoint of reprocessing which I don't touch here. Also natural feature is possibility to continuously remove insoluble fission products and particular gazios fission products which is quite significant part of the absorber which can be removed and stored separately from the core which is probably good news for molten salt reactor challenges. First of all strong corrosiveness of molten salt fuels then lack of usual barriers like fuel cladding. It means that the new safety approach should be developed in order to show for example as I mentioned the fission gases are removed from the core and this is some give some new safety philosophy because we separate isotopes in all other reactors in traditional solid fuel reactors, the fission gases are stored inside the fuel rods and sometimes for many years so they store together with the spent fuel and in case of molten salt give us possibility to separate and probably store different isotopes in different places separated. This is also big topic for discussion how to create this new safety approach new safety architecture so, of course high fluence on vessel the problem part of fuel is always outside the core because it circulates through heat exchanger and it means that we need larger fuel inventory for criticality and we have reduced fraction of delayed neutrons which is issue for safety requires safety demonstration low margin to freezing similarly to lead reactor should be addressed low or unknown solubility of compounds formed during operation so it's a big issue from your point of chemistry solubility of even very exotic probably isotopes we don't have database for this designs under development a very long list one of the last slide I will show you 3, we try to classify different designs and I will show you one proposal there is no reactors under operation so MSRE in Oak Ridge is the only database for operational with operational experience so, example I show you here is molten solfast reactor developing European project evolve and then some of are ongoing now so here you can see the core which is empty space it's open volume is shape optimized for fluid dynamics so around the core there is 16 recirculation loops each includes the pipes bubbles separator, bubble injection pump and heat exchanger and globally like there are 3 circuits of fuel circuit intermediate circuit which is still another salt without fuel and then energy conversion system based on steam water cycle and draining tanks this is a balance of plant concept basically very simplified to show you in particular the level of temperatures it's 700, 800 so it's very high temperature reactor finally that's what I promised you it's just to show that it's kind of jungle there is huge number currently a lot of interest in molten salt reactor, a lot of ideas a lot of students and young engineers working on different aspects we try to put it in some matrix this is the attempt this is the summary finally we have the whole table with 6 GIF systems and PWR so we briefly considered them I would like to emphasize that the goal was to discuss some advantages and challenges and not to rank the designs but nevertheless I put here the examples it's examples selected by me there are other systems but here I put some specific parameters and emphasize where I see the problems of these reactors where R&D is currently focused and where is the direction of improvement last slide I just as a bonus I put here the plot of density as a function of temperature and I put here 5 no, 6 systems in fact 6 coolants like lead, molten salt, sodium water at 2 pressures and I showed the operational ranges for every examples of GIF systems and you can see the level of temperature, margins to boiling margins to freezing the changes of density in latent outlet for example for supercritical you can see that the changes is very big in water density it reminds a little bit boiling water reactor but it is not, it's a supercritical water reactor so this chart can be instructive and contains a lot of information ok, these are references and that's it thank you for your attention