 So, as we continue on with our lectures for the rest of the week, we're going to be going into more subsequent detail. As we heard this morning on the information we talked about yesterday, so our next topic up is Reactor Core. What we're going to try to do in this presentation is we're going to go through some more, we're going to try to go through some practical examples of, you know, how to implement the requirements and the associated guides, just to give you an idea of sort of the effect of the safety standards on the finished product, which is again, in this case, the Reactor Core. So, with that, let's go ahead and begin. This is an outline of what we're going to talk about today. We're going to go through some of the general safety considerations in design, and then we're going to go into more specific information from the general. Again, if you recall, the structure of the safety standards, you know, we have the general safety guides that apply to all activities, and then we have specific safety guides that apply to just the activity in question, in this case, the Reactor Core. We'll go over some qualification and testing information, and then end up discussing one of my favorite topics, which is quality assurance. And quality assurance, again, as you'll find in this business, is everywhere. It has to be in everything that we do. Everything needs to be quality assured. You've seen this picture before. This has a little bit of a different twist. You're right, Marco. This is hard to see. These colors are different. This just kind of breaks out as we talked about, you know, we have the generic safety requirements, and then we have the specific safety requirements, and then below those we have the generic safety guides, followed by the specific safety guides, but the principles are the same that we talked about yesterday. This is an example of, well, this is going to be sort of a summary of the guides that will apply, and obviously the requirements documents that will apply when we're talking about the design of the Reactor Core. Obviously, everything starts with the fundamental safety principles. We talked about that document yesterday. Sets a series of high-level guidelines that have to be complied with. Then we go down from there to the specific design safety requirements for nuclear power plants. The current version is SSR 2-slash-1 Rev-1, which actually will be published, by the way. I got the email last week. In the next couple of months, we expect to have the document actually published on our website and obviously available hard copy as well, but it has been approved by the Board of Governors, so it is indeed an actual implementable safety requirements document. Let me go down from there into some specific safety guides. I'm going to have to apologize, bend over here so I can read the screen here. There are some here that you might not actually think about that actually apply, but what's interesting is you find that we have to think about multiple safety guides when we're thinking about a particular component. For example, we have to consider seismic loading on the Reactor Core. It's a very important component. It will be affected by a seismic event. It has to be designed to meet seismic load requirements. So you see on here we have a safety guide for, this is called, seismic design and qualification for nuclear power plants. We have to think about emergency power systems for nuclear power plants. Again, what you find is linkages between these different guides. Obviously, in order to maintain core cooling over the long period of time, even in the short period, we need to have, we have to have emergency power because we have to be able to run systems to be able to pump water into the core. So again, we see the linkage of these guides. There's a linkage between the Reactor Core and the containment, okay? I mean, the containment has multiple hazards that it has to address, both external hazards and also internal hazards. The largest sort, you know, the entire purpose of the containment is, as the name applies, to contain the energy that's within the reactor cooling system. That is the source of what the containment functional design is. So there's a linkage there between those two guides. And you'll see that in the presentation this afternoon. I have some discussions there about how we link the analysis that we do the safety analysis that we do for the reactor cooling system. It becomes a source term basically for the containment design calculations. You know, that is the energy that we have to, that we have to contain. And then finally, we get to the guide that specifically talks about the Reactor Core, which is what I'm going to focus on today. But the purpose I had with this slide was I wanted to show you that it's not just as simple as, you know, one guide applied to a particular component. And there quite frankly might be some guides here that I didn't list, which also could be applicable, you know, to the Reactor Core. I just wanted to give you an idea here that we have to think more than just what's within that one document. Okay. Main safety functions, again, we talked about this, but it's never a bad idea to reinforce these. We think about control of reactivity. And we have, you know, have some information and hear more on this. Obviously, this applies directly to the reactor primarily. And as we talked about yesterday, there are several different ways in which we accomplish this objective. We have to provide cooling at all times for the reactor. Again, there are many different approaches to this, many different systems, many different circumstances to consider. This is just your typical pressurized water reactor configuration. We have to talk about confinement of radioactive materials. Again, I have more on this this afternoon when we talk about the containment system itself. But the key here is all these components are interrelated with one another. And that's kind of the message that I wanted to convey here. And again, this is a typical large, dry pressurized water reactor containment structure that you find around the world. Okay, so as we move down more specifically into thinking about the reactor core itself, on the left-hand side here, we have a picture of a typical pressurized water reactor core. Right-hand side, we have a picture of a vessel prior to its installation in the reactor, just to give you an idea of how some of these components look. So when we think about the reactor core design, we have to have expertise in many disciplines. We have to think about the neutron design. Obviously, this is a nuclear reactor, so that's certainly one of the main areas we have to focus on. We have to think about thermohydrolics. You know, this is the ability to calculate the movement of fluid throughout the system. And that is an extremely complex set of analysis. We have much more on this next week. But it's not just as simple as doing a simple single-phase calculation in a pipe. We have to be able to analyze the, you know, this water, extremely high pressures. We have to be able to analyze that water as it transitions rapidly from those extremely high pressures down to atmospheric pressure. It goes through many different types of physical phenomena. It's extremely complex. The computer codes have the models and capabilities to do it. But when we think about doing the kind of analysis, it really requires a considerable amount of expertise, because as we mentioned yesterday, these codes are not perfect. And you have to be able to apply them correctly. We have to do mechanical design. You know, in the end, we have a reactor fuel assembly. We have the reactor core internals that are made of various materials. In some cases, you know, we're going to find zirconium alloy metals. We're going to find stainless steel. We're going to find, obviously, the fuel itself is a uranium ceramic material. We have to think about how all those materials interact with one another. We have to be able to think about the structural integrity. You'll find later in the presentation here that, you know, the fuel itself, as it's in the core, changes its material properties. And these properties change by a large amount, extremely dramatic changes. You know, the reactor core is a very challenging environment. It has extremely high radiation fields, extremely high temperatures. And as the material changes, as its properties change, we have to be able to continually demonstrate that the material will meet the safety functions and will stay within the analyzer. I had this picture yesterday of this box of the analysis, of the safety analysis. We have to be able to constantly say that the materials will stay within that box throughout the entire lifetime of the reactor. So it's a very challenging materials problem. And actually, even today, we find areas that we're still learning quite a bit about this. As we look at reactors going to higher and higher exposures, or, you know, or somebody will call that burn up of the fuel, you know, higher and higher longer lifetimes of components, it's extremely challenging environment. Okay. And then we talked about safety classification. I'll defer to my colleague's presentation this morning on this area. So these are things that we, you know, this is as a, I think the flavor that was left this morning is safety classification is not an easy task. It is very complex. In some cases, it becomes controversial. I think we should just simply concede that at the beginning. Because ultimately safety classification leads to components that require much more scrutiny, much more quality assurance. In the end, much more expense. So it's a, so as you, as you can imagine, it becomes, when you get multiple stakeholders involved in that discussion about safety classification, it becomes a very challenging problem to resolve. Okay. So, Neutronic Design. Boy, I really cannot read this. Obviously, we want the core to be intrinsically stable. I mean, when you think about a stable core, can anybody tell me what they think a stable reactor is? I mean, what does it mean to be stable? Yeah. Exactly. I mean, that's one example of it. That's what we call negative feedback. In other words, as you said, if the power increases, the reactivity of the core will drop. So it's basically going to take care of itself. It's going to stay within a certain range of operation. There are other things to think about. Stability as well. You know, we have to always keep in mind that it's not just a nuclear system. There is, there are large amounts of high pressure water in reactors. There are, there are many types of thermohydraulic instabilities that can happen in vertical channeled flow. And that's just, that's just basic physics. We cannot, we cannot ignore it. We cannot get around it. We have to address those concerns because you'll find in the safety requirements that there are requirements that the reactor be stable or be able to be brought into a stable configuration rapidly by automatic systems. So I mean, I mean, this is the basic design principle that we find here. All right, we talked about this one. Reactivity with the feedback characteristics of the core rapidly compensate for an increase in reactivity from thermohydraulics and neutronics. The capability of the control and shutdown systems to actuate for all operational states and all design basis accidents. There's been quite a bit of information learned over the years about the importance of, of rapid reactivity control systems and having adequate shutdown margin. I use the word shutdown margin. What does that mean? All right, right, right. Exactly, yeah. It's, it's, it's usually articulated in requirements as, well, as you said, there's usually a Delta K or a Delta PCM is one of the typical parameters you'll find under which the reactor has, we have to have enough negative reactivity in the control rods or the soluble fours and or some combination thereof to ensure that under all conceivable possibilities the reactor can always be shut down quickly and rapidly. Have you heard of the, the one stuck rod out assumption? Okay. Well, that, that, that, that, that, that, that requirement ultimately comes from a hard lesson that was learned back in the, I believe it was the 1960s in the United States at a reactor called SL1. It was a test reactor in the Idaho, at that time what was called the National Reactor Testing Station out of the state of Idaho in the U.S. It was a test reactor and they were doing some work on that reactor during, it was a night shift during a holiday. One of the operators was on top of the reactor, was a very small reactor, actually doing some patrol rod maintenance and they accidentally pulled the control rod out and it caused the reactor to go super critical and all of the operators in that reactor were killed by that accident. So that's a lesson learned by that operating experience was now we require that one control rod out is not enough to lead to some kind of a reactivity excursion. I mean that's one of the, that was one of the issues that led to that thinking. And it's, I think it's a pretty common requirement around the world that also leads to additional reliability and ultimately additional shutdown margin because we have to meet the shutdown margin requirements even with the most reactive rod out of the reactor, okay. These pictures here show some other things we have to think about. As we're in the reactor itself, you know, again, zirconium metal or we use zirconium alloy typically as the cladding in the fuel. Obviously there's very specific designs of that alloy and they vary by fuel vendors. That information is very proprietary to them. Because they spend quite a bit of effort trying to design the zircoly alloy so it will have the best performance in the reactor. But there are some basic physical properties of zirconium that we cannot ignore. And one of them is as we, as we impose fast neutrons on zirconium alloys, they grow axially. We cannot, that's something we cannot eliminate. It's a fact of life, it's physics. So what we have to do, and this is just an example of one of the design considerations that includes really, this includes your nuclear design specialty and it also includes your mechanical design specialty. Because the material will grow, we have to allow for that growth in our design over the expected lifetime of the fuel. Because what will happen, I don't have a pen here, if we don't allow for that growth as the cladding grows and grows and grows, it's going to hit the upper structure and it's going to begin to bend. As it bends, it could impact the flow of our control rods. In other words, it could allow them to not insert because they can actually bend the entire assembly. We can have assemblies come together into contact, which will cause those fuel pellets to fail because you'll have a local hot spot of heat because you cannot cool it. So these are all things that have happened throughout the lifetime of reactor operating experience around the world. So the point is, these are considerations that add to the level of complexity in the design of the reactor core and they require multiple disciplines. And these are all things that we have to consider as we're looking about the design of the reactor core. Okay, so thermal hydraulics. I have more on this later in the presentation, but let me just start here basically here. We use a thermal hydraulic calculation to ultimately, it's one of the major parts of establishing the design and ultimately the operational limits of the reactor. We talked yesterday about the departure from nuclear boiling ratio criterion, which is the typical value, which limits the operations of pressurized water reactors in a modern reactor using modern analytical tools. That wasn't always the case, but with modern tools, that's the way it typically comes out. It's driven mainly by the thermal hydraulic calculation. Some of the other things we have to consider are the maximum heat generation rate. We have to consider the peak fuel temperature and the peak cladding temperature as well. We have to think about the maximum heat generation rate because we want to limit the local hot spot in the core actually. Because again, if we don't do that, we could exceed the capability of the cladding. We could have the cladding melt, for example, if we overheat the cladding. We think about the peak centerline temperature in the fuel pellet. We worry about that because we could actually melt the fuel in the reactor and we don't want it to happen. It's a very high temperature obviously because uranium ceramics melt at a very high temperature, but it has happened and it's something that we have to do our design calculations and we have to operate in order to prevent it. Now the other point here to make is we're thinking about, well, we're thinking about margins. I had that picture yesterday where we have the safety limit and then we have the regulatory limit. And they're not the same value. There's always some margin built in there and that margin accounts for many things. Some of it is the uncertainty and the calculation. Again, when we think about using deterministic safety analysis, it is simply a mathematical representation of reality. It is not perfect. It has error. We have to think about the measurements, you know, the data that we used to derive the limits, as I talked about yesterday. It has uncertainty. It has gotten better over the years, but it's still not perfect. The instrumentation has error. It has to be propagated through the entire process. That's what some of this margin is for. Because ultimately, our intent is to limit field failure during design basis accidents. Now it's important to say limit. You know, most regulatory bodies around the world don't require zero field failure. In fact, I don't know of anybody that does because you really can't meet that requirement. You allow a certain amount of field damage during a design basis accident as they get more extreme. What you're talking about there is what's the radiation at the site boundary because ultimately you're talking about how am I protecting the public and the environment, which is typically measured at the boundary of the site. So again, that's one of the things we're trying to do with these calculations. Instrumentation and control. I know we have a presentation on this tomorrow, but instrumentation and control is extremely important. We have to think about how we're going to design it, how accurate it's going to be, and where we're going to put it. Some of the parameters we want to think about is what's the coolant flow? What's the coolant temperature? What's the neutron flux? There are other parameters that we measure. These are just some of the primary examples. One of the things to think about as well, and I'll have a little more on this later too, we think about instrumentation and control, is the INC system in the reactor also has error. It's not perfect. If I put a venturi meter in my reactor to measure the rate of flow of the coolant, yes, I will go through the proper procedure to calibrate that instrument, but the instrument has error. It's not perfect. The instrument degrades over time. As it's sitting in place, the error will grow sometimes. We have to have the ability to predict how the instrument responds, how the instrument will change through its lifetime, because ultimately it impacts reactor safety limits. We have to account for the instrumentation uncertainty in our ability to monitor the limits. And that's something that's very challenging. I know we'll have some more on that tomorrow. I believe instrumentation issues, but it's something that's very challenging. So it's an area that we have to consider. We cannot ignore it. I think I have this last point here. We have to think about the instrumentation for monitoring. We have to think about accident conditions. One of the many things that we learned during the Fukushima Daiichi accident, I don't know if you've read much about the ability to measure the reactor water level and a boiling water reactor. I can tell you from personal experience that it's one of the most important parameters in boiling water reactor operations. Where is the water level in the vessel? It might not be so important for pressurized water reactors, but it is extremely critical for boiling water reactors. Unfortunately, the instrumentation that's installed in these old BWRs does not perform very well under extreme conditions. And the way the instrumentation is designed when you have elevated pressure and temperature in the containment, the water level instrument will measure in error and it will measure in error high, which is not what you want it to do. It's going to tell you that you may have maybe one or two meters of the reactor water in the core. In reality, the water level is well below the core. It's just the way the instrument is designed. These are considerations that have to be dealt with. So maybe under those circumstances, one could consider installing a different type of instrumentation to use during these kind of severe conditions. Or maybe we train our operators to understand how the instrument performs. So they're aware of it, so they're not using that as a primary decision-making tool. These are just considerations that we have to think about. We're thinking about how we're monitoring our limits in the reactor. Okay, mechanical design. Leak type cladding. All right, we have to think about, let me just see the key points here. We have temperature pressure. We have to think about irradiation, fission products, static and dynamic mechanical loads. We have to talk about seismic loads. Basically, if you can think of an external mechanical load, you've got to think about it when you're thinking about the reactor. I mean, if we look at the fuel itself throughout the lifetime of the fuel, it's in the reactor upwards of maybe one year, two year, three year, four years, depending upon your fuel loading and your fuel cycle strategy. Under those conditions, I have the cladding. I have the fuel pellets inside the cladding. When the fuel is in the reactor, I'm constantly making fission gas inside the cladding itself. So that's going to tend to pressurize that pin. And it can actually go to extremely high pressures, which in some cases will actually exceed the pressure of the primary system. So what I find during operations is I could have a fuel rod which goes from being in compression to an expansive force throughout the lifetime of that fuel. I have to think about these things in terms of my mechanical design. So I don't want the fuel rod to pop like a balloon during operations. That's not acceptable. So these are the kinds of mechanical considerations I have to think about. Plus adding on to that is the cladding is weakening throughout its lifetime. It's losing ductility. It's becoming more brittle as it's in the reactor core due to the effects of irradiation on the cladding, due to the effects of the pickup of hydrogen within the zirconium itself. It's physically changing its material properties. Very challenging to understand how those properties change with the kind of precision that we would like. Again there's been considerable work done in this area over the years by the fuel vendors. They spend quite a bit of time on this because cladding is a very important component to them and they're able to differentiate themselves from the other vendors if they can show they have a better cladding product which will perform better under these kinds of conditions of long-term operations. We see here just some examples of different kinds of fuel assemblies. On the left-hand side is your typical pressurized water reactor assembly. In the middle is a typical boiling water reactor assembly. On the right-hand side is what you'll find as a typical VVR-1000 assembly. Okay, that's what I wanted to say there. So mechanical design. We can't ignore the fact that we have to move the fuel assemblies too, right? As they come into the facility on the truck, we have to unload them. We have to put them into the fresh fuel vault. We have to then move the fuel from the fresh fuel vault and typically into the spent fuel pool. And then from there, I'm going to use the crane on the pool in the various systems depending on the kind of reactor you have to move the fuel from the pool into the reactor. I also have to move the fuel from the reactor into the spent fuel pool and then ultimately to some sort of off-site either dry or wet storage facility or go to reprocessing, you know, whatever the fuel cycle strategy that the various members say adopts. I have to think about, you know, the fuel being in the reactor for four years. I don't want to have a fuel assembly go down. When I go down to pick it up, to lift it up, to just lift up and have the upper type plate come off, then the fuel assembly stay in the reactor. I don't want that to happen. It has happened, but we don't want it to happen. We want to think about the mechanical design. The assembly needs to retain enough structure so I can move it. After it's been in the reactor for four years of operation, for example, if that's the fuel cycle strategy that a particular country adopts. So these are things we have to constantly think about. I mean to think about the ability for the fuel to survive long-term in whatever kind of storage configuration I choose, be it wet or dry or ultimately reprocessing. These are considerations that we have to think about. Okay, okay. I've already talked about this for the most part, but let me make another point here. The picture on the lower left-hand side here is really one of the challenges that we have that's really kind of associated not just, and this kind of talks about the linkages of these guides is the point I want to make here. We think about loose parts. Have we heard about loose parts in reactors? Little bits of metal or somebody up on the refueling deck drops their hard hat in the water or something accidentally. I mean it happens or someone drops a wrench or something into the water. I mean it happens. These are things, these are industrial facilities. These kind of mistakes happen. What we want to avoid is getting things into the reactor. What you see here on the bottom left-hand side is a picture of a small piece of metal which got caught in between several of the fuel rods and a fuel assembly. So what do you think is going to happen if I keep that metal there in the reactor throughout a long operational cycle? What's going to happen with that metal, that little eddy-beddy piece of metal with all these little sharp corners on it? What's it going to do? Well, yeah, it's small, but it's possible. Yeah, it's possible. There's another mechanism to think about too, though. I mean it's possible. I can't say what's going to happen for sure, but that's definitely possible. There's one other mechanism. Yeah, it can. Yeah, actually, and it happens. It has happened. What you find is you have extremely high-velocity water going axially up through the fuel assembly. It's going to get around that little piece of metal and it's just going to sit there and just wiggle along just like the whole time. And that sharp metal is just going to wear away on the cladding and the clad will fail. And it happens. It happens all the time. Well, thankfully not all the time anymore. It used to be pretty common. What fuel vendors are doing now is they're typically putting at the bottom of the assembly filter assemblies. Try to filter out these small pieces of metal. But this happens. It can come from maybe a pump in the system. Part falls off a pump or maybe we have a spacer grid damaged or somebody drops something in the reactor. It's hard to say. These are things we have to try to think about. Again, one of the solutions that designers that come up with are these what they call debris filters at the beginning of the assembly to try to keep these small debris out of the reactor because they tend to go up, get caught in the spacer grids and they just sit there. And they are definitely a failure mechanism. Okay. We have to think about the compatibility of our materials with the radiation, chemical, physical processes. I mean, let's take the reactor pressure vessel itself. I mean, if we think about the lifetime of reactor, there are most components can be replaced in a reactor, ultimately. I can take out the fuel. I can take out the shroud. I can, you know, I can even replace pipes in a reactor. I can't replace the reactor vessel. It's just too big. I can replace team generators. You know, major components can be replaced. But the reactor vessel, no, I cannot replace the reactor vessel. We have to think about the reactor vessel long term. We have to think about its lifetime. We have to think about its ability to survive during an accident. Again, we have the reactor core that's going to be the core barrel typically. Usually there's some shield material and there's going to be the downcomer and there's going to be the reactor vessel itself. Now throughout, from the edge of the reactor core out to the inside of the reactor vessel, there is quite a bit of attenuation of the neutron flux, the fast neutron flux, because the thermal neutrons at that point are all pretty much gone. But it's not zero. So I have to think about fast neutron fluence, which is the accumulation of fast neutron damage on the reactor vessel itself over a long period of time throughout its lifetime of operation. What it does is it changes the material properties of the vessel, causes small little micro damage inside the vessel. And there's several concerns there. One is, what if I have to do a rapid quench or cool down of the vessel? You know, I have my big accident, you know, lost a coolant, I drain the vessel, I turn my big high pressure pumps on, I pump a lot of water into the reactor vessel. Well, that water is going to be really cold, right? It's coming from a tank that's sitting outside the reactor building, just sitting there. So it's going to be whatever the outside temperature is. And that's going to be a heck of a lot colder than the reactor operating temperature. So I've just put a step change of temperature on the inside diameter of that metal. Now when the metal is brand new, we go through our code qualifications. We heard about the ASME boiler and pressure vessel code. There are other national codes, the Russian's half codes, the French half codes. The purpose of that code qualification is to demonstrate that the vessel has a certain number of heat up and cool down cycles in its lifetime that it will survive. But if I have a large amount of fluids, in other words, a radiation damage on the inside of the vessel, you know, that's going to challenge those qualifications. Now there are mechanisms within the code to continue to qualify the vessel. But this is the concern. We have to think about it in our design to make sure that the vessel maintains enough ductility so it can handle a rapid cool down event. Because we don't have a design basis accident for vessel failure. That just cannot happen. If it happens, there's nothing you can do. So that is one of those things that has to be practically eliminated. It can simply not happen. Okay, so that's enough on that. Uncontrolled moving or reactivity control devices has to be prevented. This is also a mechanical question. Again, think about this. We have, let's say we have a control rod which is inserted either fully or partially into the reactor. Have extremely high velocity fluid coming up through the reactor. If that control rod is not properly designed, that the fluid can actually push it out of the reactor because of the velocity of the water is so high. So we have to think about the ability of our control devices to stay where we want them to be under all conditions. Okay, fuel elements and assemblies. Eight effects to be considered in the design. Talked about some of these already, but I want to go into a little bit more detail on some of these. Better picture on this next. Yeah, let me just go to these more detailed descriptions here. I think this is a little bit better the way to go through this. So fuel and burn up effects. We think about the effect on the fuel pellet itself and ultimately the design of the fuel. As we create fission products and other materials in the fuel pellet, you know, again, we think about the fuel pellet. It's, you know, it's about that large in diameter and about that high. It's, you know, that's the individual ceramic. So we're down to that level of detail. As I burn up that fuel, as I use the fuel in the reactor, obviously I'm creating other things. I create fission products. I create other higher actinides, various isotopes of, you know, plutonium, you know, neptunium, ameratium. Now those things are all going to stay in that fuel pellet, except for the fission gases, which will ultimately escape out into the cladding itself. The point is, is that I have a distribution of flux or power in that fuel pellet. It's going to start out generally as some sort of a cosine shape. And what that means is that I'm going to be burning more of the uranium in the middle originally than I burn on the outside. As it, as the burner proceeds, that's going to tend to flatten itself out a little bit, just because of the changes in the material properties and the distribution of the fissile material and the creation of other fissile material. For example, you know, we will create plutonium in the pellet. That will begin to burn as well in the reactor. We have other, we have other poisons we create, various fission products, etc. The point is, is we have to think about how those changes will affect the performance of the pellet, the ability of our, we have to think about our ability to predict the temperature, because again, the limits on the fuel pellet themselves cannot change. You know, I have, I have a centerline temperature that I want to avoid melting. I have to think about, you know, I might think about the mechanical interactions of the fuel pellet on the cladding itself. So these are things that are not going to change as a result of burn-up, but I have to be able to take it into account. So we have very, again, extremely challenging calculations in the changes of the material property. I've already talked about the fuel pellet temperature, but one thing we've got to think about, one other important parameter in fuel is, is what we call thermal conductivity, the basic property of a matter. Do we all know what thermal conductivity is? Basically the, you know, how good is a material at transferring heat from point A to point B? That's the thermal conductivity. If I have higher thermal conductivity, it's better at actually transferring heat. Now, I have a picture on this later, but I want to talk about it now in words, you know, the pellet starts out as an ice-clean ceramic. There's no cracks in it. It's a good solid material. If you look at fuel as it's discharged from the reactor, you take it to, you know, take it to a lab, put it in a hot cell, cut it open, take a look at it, you can get like little bits of gravel, you know, falling out of the, out of the cladding, because the fuel is turned into these little bits of, of ceramic. It's, it's not that it's falling apart, but it has all these little micro cracks in it. That, that affects the thermal conductivity of the material. And that's a very important parameter when we think about safety analysis, because that, again, that, that's one of the governing parameters of how we transfer heat from the fuel to the gap, to the cladding, to the cooling. So it's a parameter that's affected. Again, the point I want to make is these are things we have to think about. These are things we have to measure. You know, you're not going to be able to predict the thermal conductivity of exposed uranium ceramic material with some sort of a theoretical model. It has to be tested in a test facility in a lab, because we have to know that parameter as a function of exposure. Okay, design of fuel. I've talked about this already for the most part, effects of solid and gaseous fission products, fuel design criteria to do that. Okay, yeah, here's a picture that I wanted to show you. On the left-hand side is essentially fresh fuel. It's only been in the reactor for one cycle. So doesn't that have a lot of burn up on it? On the right-hand side is we go to two cycles. On the left-hand side, we go to three cycles. You know, if we keep going to higher cycles, we're going to find more cracks in the fuel. It's unavoidable. It's basic physics. The point is we have to design for it, and we have to account for it in our operations and how we design and run the reactor. We talked about the ability to transfer heat from the fuel into the cooling. Again, if we go back to... You know, I think I might use the chalk board. Look at that. Let me get some chalk here. This will be kind of novel chalk. I've used this in a long time. Let's see if this works. If we go back to, again, pardon my ability as an author. I'm not an author or I'm not an artist. As we go back to the original, as designed, as built configuration, this is our fuel. This is the gas gap. This is our zirconium clad, whatever alloy it may be. So if you can see the original configuration, if I'm going to do a standard basic heat transfer calculation, you know, simple basic conduction calculation that we all learned about in college, I'm going to calculate, you know, I'm going to calculate at various nodal positions along this material, the, you know, temperature here or here, and then I have to calculate the material across the gap into the clad, ultimately into the cooling. Now, you know, this seems pretty simple, but as with most things in a nuclear reactor, it's not that simple. As I burn the fuel up in the reactor, as you can see in this picture, this gap will close, and I will have direct contact between the pellet and the zirconium material. So I have to change the way I do my heat transfer calculations. Plus, I also have to account in the design of the cladding, the fact that I may have the fuel pellet itself actually pushing on it. So it has the ability to retain enough strength so it doesn't break when the fuel as the fuel expands and pushes on it. So these are the things I'm going to think about. And the way most designers address this kind of thing is, you know, they're going to build in enough gap size, you know, to allow for their, to have this growth and this eventual contact so the cladding will not fail. And I'll also be able to do these calculations. I'll know this material. Okay. That's what I wanted to say here. Okay, effects of the linkages of ultimately, you know, reactivity or power on the fuel itself. There was a question about this before the lecture started. I figured what the gentleman was who asked me. All right, there, yes, sir. So, well, let's see. Let me start with the first point here. Effects of irradiation, everybody talked about this. I talked about axial growth. The way fast neutrons will affect or will impact the zirconium alloy, they will also have an effect on the deatility and the strength of the material. These are things that just all have to be accounted for in the design process. Again, the discipline here is going to be, you know, both a combination of the nuclear engineering skills and also mechanical and material designs. Okay, so, but the bottom point is what I want to really, really focus on here. The thing about the reactor core itself, you know, depending upon what kind of reactor it is, how it's operated, I can either have control rods in the reactor during operations. They can all be all out. It all depends on the reactor itself. But one of the things you have to think about is if I have a, let's say I have a fuel rod right here and then right next to it, I have a control rod. In these pellets here, you know, the power is going to be relatively low and this is what the control rod is doing, right? It's going to, you know, it's going to be absorbing all the thermal neutrons, so the power here will be pretty low. The power here will be high. Some of the challenges you find and what we have to design for, and this is where the linkage of reactivity to the fuel itself comes into play. One of the ones I'm familiar with is, as I withdraw this control rod, what can happen is this pellet here, for example, can experience a rapid burst in power because I just moved a control rod. And so now I don't have it next to the pellet so it's going to create more power. What that tends to do is the pellet tends to rapidly expand quickly and it can then impact the cladding, cause the cladding to fail. The, you know, the mechanism is basically what we call PCI, or pellet-clad interaction, so the pellet rapidly expands and it can cause a mechanical failure on the cladding. It has happened. There's been quite a bit of experience with this over the years. For the most part, the phenomena has kind of gone away from my observation of fuel performance around the world. I don't really see too many PCI failures anymore, but for a time period it was a big issue. But this, again, is one of the things to think about in terms of the linkage of reactivity to the mechanical performance of the fuel. All right, stress corrosion cracking. I'm going to go through this here pretty quickly because I want to get to the rest of this material. Fuel cladding design, stress and strain. Yeah, this is, we have to think about, again, ultimately, how the material will be. What kind of stresses the cladding will experience throughout its lifetime? I've talked about many of them already, you know, one particular one being, again, the creation of fission gas within the pellets, oh, oh, oh, within the cladding, which will tend to pressurize the fuel and have to ensure that that fuel pellet's not just going to pop like a balloon during normal operations and during accidents. You know, let's think about, you know, I take a fuel pellet that's been in the reactor for two or three cycles. Let's say it's sitting roughly around, you know, the pressure of the primary system. You know, they're about equal. The inside pressure of the rod and the outside pressure. But then I rapidly reduce the pressure of the primary system because I just had a loss of coolant accident. Well, that cladding needs to be able to retain that inside gas pressure under those conditions. And so because, again, we don't want it to just pop like a balloon under those conditions. So these are the kinds of design considerations that we have to think about as we're going forward. Okay, we haven't talked too much about the effect of exposure or the effect of lifetime on reactivity, but as with many things, it's not easy. We think about the changes in the fuel material itself throughout its lifetime, the changes in the isotopic concentration of fuel. You know, I go from clean uranium dioxide to having various combinations of fission products, higher actinides. That affects the fuel temperature coefficient of reactivity. It's hard to predict exactly how the effect's going to be because it depends a lot on the reactor itself. But these are considerations that have to be taken into account. They're going to affect both the performance of the fuel per transient. They're also going to affect our need, as it says here, to add various types of burnable poisons or maybe soluble poisons into the fuel to compensate for the changes in reactivity. Okay, effects of corrosion and hydriding. I've talked about this already. And thermal hydraulic effects on fuel assemblies. I've already talked a little bit about this, so I'm going to go through this rather quickly. This is a picture that I wanted to show you, which I've already talked about hydriding on zirconium. You know, even when the zirconium is just simply sitting, if I put a piece of zirconium that's fresh and clean on the table here, it's going to start to oxidize. I mean, it's inevitable. It's not a very high rate of reaction because it's not at an elevated temperature, but it will begin to oxidize. And it will also, which will change its material properties. In the reactor, even under normal operations, I will begin to create oxides and hydrides on the external surfaces of the cladding. It's inevitable. We've all heard about the exothermic zirconium oxidation reaction. That's what we try to avoid during our accidents, but even during normal operations, the material properties will change. And so I have to take that into consideration as the fuel is in the reactor, especially if I'm going to be going to extremely high burn-ups. In this case, this goes to 60 gigawatt days per ton on the rod, which is a pretty high burn-up. Okay, I believe I've talked about all of this already. Consideration of mechanical safety of the fuel, Boeing, strain fatigue. Okay, I haven't talked so much about hold-down forces. Let me bring that in here. We talked about the control rod, and we have to design its ability to always stay in place, even when I have extremely high velocity water coming up through the assembly. Well, if I don't hold the fuel assembly down, the water can actually pick the assembly up, too, in some cases. So I have to think about the hold-down forces on the assembly itself to make sure that it stays in place during these conditions. So again, that's another consideration that I have to take into account. I've talked about Boeing in the assembly, which has caused from a radiation-induced changes to the zirconium material itself. In other words, again, the assembly can bow, which can impact the ability to insert control rods. There are other mechanisms which can cause deformations in fuel assemblies. Under certain conditions, under high velocity flow in reactors, sometimes the fuel assembly can get sort of like a torsional spin on it in some cases, which is not caused by radiation. It's caused just by the forces of the water itself that can impact the ability to insert control rods. I don't think I've ever seen an experience where the water itself can actually cause the assembly to bow, but I have heard of situations where it's had a little bit of a twist on it, which again will impact the ability to insert control rods. Coolant and moderator. Okay, so obviously, when I think about the coolant now, I'm going to move from the fuel outside of the cladding into the coolant and or moderator material, depending upon the kind of reactor that you're operating. Many things have to be considered there as well. I want it to be physically and chemically stable. I mean, that statement of the obvious. Water fortunately happens to be one of the best materials in the world because it has that kind of stability throughout the operational lifetime. Some things to think about for safety is I want to be able to make sure the coolant system is free of foreign object and debris. This is particularly important for a fresh startup of a plant. After a major outage or even the first commissioning of the plant, I want to try to take steps to make sure that I don't have any foreign material in the coolant system because it will eventually, you know, it can eventually make its way into the fuel or it can damage other internal components as well. I mean, if you put a big piece of metal through a pump impeller, the pumps not going to survive. So I have to think about these considerations as well. I need to think about the, what kind of radioactivity or activity am I going to have in the coolant? You know, I mean, there will always be some level of radioactivity in the coolant. It's inevitable. There are many sources of that. Sometimes I may have a fuel leak, which I can consider acceptable if I stay below my limits. You know, there are sources of radiation within the coolant itself. Certain, you know, while I try to purify the water as much as I can, there are, there are always certain chemical substances in the water that can be activated in the reactor as they go through the reactor. That's another source. That's another source of activity. But I need to think about how do I want to, you know, what are acceptable limits basically, which I'm going to put into my technical specifications, at which point I will force a mandatory shutdown of the reactor. And I'll go in and find out what's going on. Do I have a fuel leak or something strange with my chemistry control? And I need to figure it out. I have to think about, you know, how am I going to get that radioactivity out of the coolant? I have to have some kind of a system, you know, going to try and purify the water throughout its operation. Obviously, I want to have a sufficient supply of coolant. That really accounts for not just during normal operation, but I need to think about how much water do I need during an accident? Is it going to be in a tank somewhere or maybe in some reservoir or something? I want to be able to access that water when I need it. And I have to have enough of it to make sure that I can always shut the reactor down and always keep it cooled for all the accident sequences I have to think about. And I talked about flow instabilities. I'm not going to get into that in great detail because it's extremely complicated. But the simple factor of the matter is axially moving water under high velocity and pressure under certain conditions can lead to thermohydraulic instabilities. It's a fact of life. We cannot ignore it. We cannot design away from it. We have to deal with it in our designs. Generally speaking, it's more of a boiling water reactor problem. Typically only happens when I have a two-phase flow column on top of a solid column of water. But there are also thermohydraulic instabilities in solid water as well. So I have to think about how to design against those. FSS, fuel, what is this? Physically and chemically stable with effective both high temperature and a nuclear irradiation. I'll have to look that up. I don't remember actually, but I'll look it up after the presentation. Okay. Effects of changes in the coolant, this is really getting at more of how do I calculate the properties of the coolant during a transient? I mean again, it's relatively simple to look at the coolant during normal operations. I can go to a steam table. I can find out what's the density, what's the viscosity. I can just grab those parameters. But I have to have the ability to have an equation of state for water to go from the typical operating pressure of a pressurized water reactor all the way down to atmospheric pressure. And the properties change dramatically throughout those conditions. I have to have the ability to have that information. I think about how the chemical additives impact the coolant. The most typical that I know of is using boric acid in the water. I think about how is it going to change the pH of the water? Is it going to be acidic? Is it going to be basic? And the reason I worry about that is it changes how the coolant affects the surfaces of the material in the reactor. Because I don't want the coolant to damage that material, to cause any changes in the surface material as much as I can control that. Means of controlling corrosion in hydrogen products. Again, this really gets at I have to have a system to remove those products during the operation. And we've heard of like in the CVCS systems, chemical volume control systems, those kind of systems are there to remove corrosion products, from the hydrogen out of the water. Because I want the water to be as pure as I possibly can during operations. Okay, reactor core and associated structures. Possible damage mechanism. These are things that I've talked about for the most part. I think I've actually talked about all of these. High pressure and for distribution. Yeah, so I can go on past this. Okay, designer reactor core and associated structures, factor radiation, heating on the structure, we calculated the proper cooling provided. The one point I think it's valuable to make on this slide here is we talk about adequate safety margins. I mean, I can't even remember how many different types of technical specialties I've talked about in the last hour. I mean, I'm sure it's dozens of different types of processes or physical phenomena or measured parameters or material properties. And unfortunately, life is what it is and reality is what it is. Every one of those parameters has a certain amount of uncertainty. We take for granted, when we're in our engineering school classes, that when I'm told the thermal conductivity of material is 1.6, I take it as 1.6. But the reality of it is that it's 1.6 plus or minus something. Because I don't know, we don't typically talk about that, but that's just reality. And we have to, under certain circumstances, we have to account for that information in our design and our operations by applying adequate safety margins. Again, it's an added level of complexity. In some circumstances, we might be able to argue that we know a parameter with enough precision to not have to worry about it. Some circumstances, maybe not. We have to go through the process of actually thinking about each one of the parameters at the point to make here. I have to be able to think about when I'm designing the ability to inspect components. Most member states around the world have implemented a process called a periodic safety review. Generally involves once every 10 years, the reactor is taken down for an extended outage. There's inspections of components, parts are performed, any necessary upgrades. At that time, typically it's taken into consideration improvements in standards, improvements in science. Well, in order to do that, I have to be able to actually inspect things. I have to think about that in my design. You know, am I going to make a really small channel or I can't physically put a camera down into it? Not a really good idea, because I won't be able to inspect it. I'll have to physically take the entire component out rather than inspect it in situ in the reactor. Obviously, under these circumstances, I'm going to take the fuel out, but there are other components in the reactor that have to be inspected. So we need to think about that in our design to ensure that we have inspectable components. So we can go through and do a PSR. Maybe sometimes we'll have a situation during operations where we have an elevated amount of radioactivity in the coolant. I don't know where it's coming from. So I shut the reactor down. I need to be able to find it. So I have to be able to inspect. These inspections are done remotely under water, typically involving cameras or other types of instrumentation. I have to make room for the instrument is the point. To be able to go down and do that kind of inspection. Okay, I've talked about the vessel. So I'm not going to go through that already anymore. Reactor coolant support structures. But the main issue here in my mind is really more the ability to handle mechanical loads, which are things again induced by the seismic event. I don't want to have the reactor collapse in the vessel because the lower support structure is not strong enough to handle the loading from a seismic event. These are the things that need to be considered here. Operational guide structures, okay. There's a little more focus here on reactivity control devices. I've talked about already again this concept of the fuel assembly bowing can impact the ability to insert the control rods, for example. I have to think about the ability to replace control rods throughout the lifetime of the reactor. They have a finite lifetime. They have to be replaced. So I need to really design in the ability to do that. So these are considerations that have to be taken into account when I'm thinking about the design of the reactor. I think that's the main point to make on that one. We're doing okay here. One of the concepts that we constantly come back to. Oh yeah, please go ahead. These support structures to avoid the vibration of the fuel assembly during the operation. Right. And how this would be for the DPA. How would this be polite? Okay. Well, if you think about the reactor internals, typically what I'm familiar with is reactor. I'm going to have the core barrel here. I'm going to have various fuel assemblies. What will happen typically is there's going to be a nozzle at the bottom of the fuel assembly, which is going to be placed into the lower core support structure, which is typically a metal plate with a bunch of holes in it. And the nozzle is fit into these holes on the top. What I've found is there's typically some sort of, it's like a metal grid structure. The assemblies go down in the middle of that. And there's always some kind of a hold down mechanism on there. What we're talking about here is if I have my reactor, I have my cold leg and hot leg. So I have a fluid flow going like this. And the reactor coming down like this and going out like that, right? And it's basic. This is what happens in normal operation. Okay. Well, let's assume that I break that pipe right there in half. And I put a huge pressure differential on it. What's going to happen to the fluid that's flowing through that area right there? I mean, it's going to rapidly accelerate, right? Okay. So it's going to put a lot of lift forces on that assembly. I don't want the fluid to lift the assemblies actually out of location during the design basis accident. That's what I'm talking about. I want to keep them in place. Okay. So instrumentation. We talked about this already very briefly. And I know we have more on it tomorrow. The point I want to make here is that we have to consider the environment within which the instrumentation is functioning. Yeah. Hard to say. I mean, you have to do the calculation. I mean, that's a design solution that a designer came up with. You know, I can't say whether it's sufficient or not here. I would just argue that it has to be evaluated and considered. But the point is that they're thinking about it. And that was the solution that they came up with. So yeah. Okay. Okay. Well, the point here again, instrumentation but control needs to be available and function during all operational states and all design basis accidents. I think that's having, we've made that point over and over and over again. Well, the instruments themselves are exposed to the conditions in the reactor. If I have a series of nuclear instrumentation inside the reactor, it's going to see, you know, it's going to see the flow of the reactor, depending upon the design of the instrument, it may or may not. It's going to see the radiation fields. It's going to see the neutron flux. It's going to see the gamma flux and the reactor, extremely challenging conditions. I have to think about this in my design of the instrumentation to make sure that it will survive during all these possible configurations, during normal operations, during accidents, so it can give the operators a reliable set of information upon which to make decisions. It's important to consider that the instrument doesn't move. I mean, if I put an instrument in place, I'm going to calibrate it for that location, right? I mean, that's standard instrumentation. Well, if it moves this way, well, the instrumentation calibration is now all wrong, but the instrument is still going to give me a signal. So the operator is not going to know that, but they're not going to know that the instrument moved. So they're going to think that the instrument is telling them something, but it's going to be giving them false information. So the instrumentation needs to be fixed in place. And obviously, you have to think about how can I replace instruments. Instruments wear out. I need to be able to replace them throughout our designs, or throughout the lifetime of the reactor. Okay, other internals talked about this when we move on. Core management. Okay, operational states versus design basis conditions. We've talked about this briefly again, but I want to make this point again. What is most often required for operational states, and this includes normal operations and anticipated operational occurrences is we require no cladding damage. In other words, the plant needs to be brought to a safe condition with no cladding damage. Now, some people approach that from a statistical perspective, which one could argue could allow a small amount of cladding damage, but the general prescription is no cladding damage. Now, when we get into design basis accidents, we will allow, most member states will allow or provide for a certain amount of permissible field failure under these conditions. And then the point is I'm looking at what is the radiation that's released to the environment at that point. That's my concern at that point. What's the source term? So these are the distinctions, but I have to have the ability to monitor, manage, and control all that information, which is where we get into ultimately the control system here, or which we get into core management, which is mainly the design of the core to address these considerations. We'll get to that here in a minute. So in order to achieve the desired outcome, which is to have an understanding that for normal operations or anticipated operational occurrences, again, I will have zero cladding damage. And for DBAs, I will have a predictable amount of cladding damage. I have to design the core with certain limits. And we talked about this already. Again, this gets back to this box concept. I do my safety analysis, and the safety analysis demonstrates either I have no cladding damage or I have a small amount of fuel damage leading to this source term. And that set of analysis establishes limits on the reactor. Limits on, for example, DNBR limits, limits on axial power, limits on radial power, all kinds of limits. Those are just a few of the examples. And the point of the core management is to design the reactor throughout its lifetime. Again, the reactor is constantly changing to design the reactor throughout its lifetime. So all of those limits will be met under all conditions. So I can always say that I'm within the envelope of my analysis because the analysis is what supports the statement about whether I meet the limits or not. So that's the linkage there. Does that make sense? If it makes sense to me, does that make sense? Okay, we want to stay within the analysis is the point. Okay, okay, reactor calculations. This is what I was talking about. Basically, we're talking about a bunch of computer codes here. You know, we have codes for nuclear design, we have codes for thermal hydraulics, we have codes for transient nuclear performance, codes for transient thermal hydraulics, codes for mechanical fuel performance, all kinds of codes. They all have to work together. And in the end, they give us an answer, which is a suite of operational limits that I can then transfer to the control room. And the operators will operate the core against those limits to make sure that they don't exceed those limits. Because again, I need to be able to state that I'm within my safety analysis. That's the whole point. Okay, I have to think about again, I have this analysis has to be conducted over the lifetime of the core. Again, as we talked about, the fuel changes, the materials change, the control rod locations change, everything changes throughout the reactor. So the analysis has to be done to demonstrate that I can meet the limits throughout its lifetime. These are some examples of limits and calculated results. I'm not going to go through these here, they're here for your reference. One of the challenges I have to think about is in how I manage the core, how I design the core, how I calculate the core is throughout the lifetime of a reactor, it's very common to change fuel vendors. Obviously, depending on the technology, you could change the vendor of the fuel. The last thing you want to do is put another, because you're not changing the entire core all at once, you're changing a third or a quarter of it, depending upon your fuel management strategy, which is all part of your core management strategy. Well, I don't want to put in a third of the fuel, which is not hydraulically compatible with the other assemblies. In other words, I don't want to put a fuel assembly into the reactor that's going to have more flow than the one right next to it. That's bad, because it leads to a thermo-hydraulic instabilities. And I want to avoid that. Also, it's going to tend to starve this assembly of coolant, which could tend to overheat it. So again, we think about core management. We think about, as we transition to new fuel vendors, how are we going to ensure that the characteristics of the new fuel are compatible with the old fuel? Okay, these are the kinds of, these are challenges. I have to think about during refueling, you know, it's a very active time on the site, very chaotic, people are moving all over the place. I mean, the last time I heard someone describe to me a fuel reloading plan, they had the plan timed down to two-minute intervals over the course of 30 days. Very, very high precision activity. Thousands of people are on site, running around, doing different things. One of the activities has to be done is I have to reload the core, have to put fuel back into the core locations. Well, how do I ensure that I put the right fuel in the right place? You know, fuel, you know, certain reactor designs, certain core management strategies have different fuel enrichments for a given batch of fuel. Again, that depends on your fuel management strategy. Some reactors do, some reactors don't. If I do, I have to make sure that I put the right assembly in the right spot. Because if I don't, then what happens? I analyze the core that I designed, but I'm not running the core that I designed, right? So I'm not inside my box anymore. I'm now outside of my safety analysis. That's unacceptable. Now there are means to test that during startup, but the last thing you want to do is start the reactor up and find, oh boy, put the fuel in the wrong place, shut it back down, take the head off, take all the parts out and move the fuel around. That's a huge, huge waste of time. You don't want to do that. Okay. So core monitoring system, again, through the core management strategy, we design our core. We design how it operates. We design the long-term perspective of where we're going. Typically, operators or designers will be thinking, you know, two or three cycles ahead because they want to be able to plan how they're going to load their fuel, how they're going to manage the fuel. You know, the purchasing of fuel is a long lead time activity. You need to give people time to manufacture the assemblies. So we're thinking long-term. But now I'm getting down to operations. I have to actually operate the core. And I want to ensure, again, that I'm operating the core consistent with the safety analysis, consistent with the design. So I need to have a series of instrumentation. I need to have a core monitoring system. I'm going to be looking at various parameters. One of the key parameters that I want to monitor, I'm going to go back to this again, is the departure from nuclear boiling ratio, right? It's a parameter that basically tells me how close I am to losing good heat transfer on the fuel, extremely important. Okay, can I measure that? Can I directly measure the DNBR in the reactor? No, I can't. It'd be nice if I could, but I can't. I don't have a DNBR instrument that I can put in the reactor and measure what the DNBR is. So I have to infer that parameter from other parameters. Usually it's done by nuclear instrumentation, where I'm going to get my local power. And then I know the inlet flow and temperature and pressure. From that, I can infer what the DNBR ratio is. Of course, that, as with many things in this business, has uncertainty that I have to account for. But the problem is I have to design my core monitoring system, my concept, so I can get to the parameter that I need. Because unfortunately, I cannot directly measure it. I don't have a probe that measures DNBR. It'd be really nice, but I don't. Okay, so that's really the point that I wanted to make on this slide. Okay, characteristics of instrumentation. We talked about this already, but I don't want to spend too much time on this. The point I want to make again, instrumentation changes throughout its lifetime. I have to think about how the speed of response changes. A certain NI or certain nuclear instrument has a certain response time, several milliseconds or something, to register a signal from measurement to what you see in the control room. Well, that response time can change. It can go longer, it can go shorter, depending upon the instrument. I need to know how the instrument behaves. That's obviously going to take a certain amount of testing and experimentation with the actual instrument, typically done in test reactors or research reactors, so I can have a controlled environment in which I can get that information. The point is I have to translate it into my core monitoring system, so the operators are given good information. Throughout the lifetime of the reactor. I've already talked about the need to consider instrumentation and its performance during accident conditions. Again, we go back to the level instrumentation question that they faced at the Fukushima Daiichi power plant when the level instrumentation was giving them the wrong level. And it was a wrong level high, not low, so that would have been better. But to think about the environment that the instruments are going to be in throughout various accident conditions. Okay. I need to think about shutdown, refueling. Let's take the example of refueling. If I'm doing a shutdown refueling of the reactor, I'm going to be replacing in-core nuclear instrumentation, typically too, because they wear out, right? All right, well, can I replace my nuclear instruments at the same time I'm shuffling fuel? Yes, no? I have a, you know, I have a source range instrument in the reactor. Typically there's three or four of them, radially. I'm moving fuel around over here. Well, I mean, the answer is yes, you can, under certain conditions. You never want to be blind, okay? You never want to pull all your instruments out and then start moving fuel around. You need to think through a strategy of moving fuel, maybe move the fuel over here on this side of the reactor and you replace the source term or and you replace the source range on this side of the reactor. Because you never want to be moving fuel into an area where you don't have an instrument that can see that fuel. Because that can lead to a reactivity excursion if something bad happens. So I want to make sure that I always have instruments covering the reactor. Start up again. I want to have ranges of instruments that are going to be able to cover the entire range of startup. You know, if I think about the neutron flux going from extremely low values up to something on the order of 10 to the 14th, you know, there is no way to design one instrument that can monitor the flux from startup to ops. It's not possible. So I need to think about my source range instrumentation, the intermediate range instrumentation and the power range instrumentation. The key is I want to make sure the key is I want to make sure I have sufficient overlap on those ranges as I'm coming up in power. So I always have instruments covering the reactor at all times under all conditions. It also gives me the ability to cross calibrate instrumentation so I can make sure that the instruments are always giving me a reliable set of information. Okay. Pass on this. Provisions for inspection and testing. Qualification program. I'm going to go through this. Okay. Quality assurance and design. Okay. I think that's it. Yeah. All right. I'm going to stop with quality assurance and design because I want to leave a few minutes for questions here. Look, you're going to hear a lot about quality assurance throughout the course of the next two weeks. And as I said yesterday, it's a very good point for that. I mean, again, I go back to just this simple hour and a half lecture. I mean, how many different processes did I talk about? How many different components did I talk about? I mean, literally dozens, maybe even hundreds of them throughout this one simple hour and a half lecture. All of those activities have to be quality assured because in the end, the operator, the operating organization has to have confidence that what they're operating will do what the designer says it's going to do. That's the bottom line of quality assurance. And I have to ensure that also, when I think about quality assurance of analysis, I want to make sure and I want to be able to say that the reactor is designed and analyzed as the designer said it is. And again, many moving parts, many things have to come together. So QA is extremely important. And again, one thing you remember about QA, QA is not about blame. QA is not about malice. QA is about getting it right. Okay, I've made plenty of mistakes myself. Thankfully they've been found by somebody else. In the end, it doesn't matter. What's important is that they were identified, they were corrected, and then you move on. I think a lot of people think about QA as it's a, you did something wrong. No, QA is not about that. QA is about getting it right. Okay, so with that, any question? We have a few minutes for questions before lunch. I'm sorry for this sort of, well, this is kind of a blitz of information. You'll have this as reference material for you as you go into the future. But there's a lot of material. So any questions? All right, must have done a good job then. Or everyone's hungry. Maybe it's hungry. Okay, well, tell you what. It's basically the lunch time, so why don't we go ahead and go to lunch? And we'll be back here at two o'clock. For our next presentation. So thank you very much.