Reactors and Fuels & Nuclear Reactors

range of neutron energies. Now to move on to the cross sections, which is where the neutrons interact, this diagram is. it's done well with the Hyer energy on the right and these are the fission cross sections for plutonium 239 and u235 and you'll see a number of features here first the cross sections essentially add up at most to very low neutron energies and fall down if you ignore all the mess here, it's a form of one over V one over the speed of the neutron and this is generically the case for most cross sections and there's a different well for most cross sections uh in In the central area here you see a resonance region where you see all these bumps.uh, at certain energies, uh, there is a much higher probability that the neutron will interact with the nucleus, so you get this peak in the value of the cross section and this is again very typical of most nuclides and then increases in the fast area. only the high energy area tends to decrease like the previous one.

Now I said that most have this shape. You see an exception here. This is the cross section of uranium 238 Vision. Remember it's not, it's not a file, but it will work if you do it. you get a high enough energy neutron and it seems to take off, what's that about one of me? You start getting fions at u238 and a little bit more at the resonances, it's a resonance, it's a big peak on the cross. section, but if you imagine a kind of uniform distribution of neutron energy in the energy of the resonance, the resonance is so large that it simply absorbs all the neutrons with that energy and it could absorb more if there were neutrons with that energy, what is it about that ?

The effect of doing this is that it reduces the size of the resonance, this drop in flux, which is the dashed line, the effective size of the resonance is smaller, it is not its actual measured value, but you have to treat it like that, and that can occur. either because the resonance is quite large or you can simply have a large amount of a particular nuclide in a reactor and the only case I could imagine is uranium 238 where 95% of your fuel or so is u238, although its residences Don't be monstrous, you tend to get this kind of effect.

The second thing is Doppler broadening, uh, residents are measured at room temperature. Conventionally,

reactors

operate at a higher temperature depending on what you're doing and as you get to the higher temperature the resonance starts to shorten and broaden and it's kind of like the Hubble redshift, sort of. of thing, uh, if something moves, the wavelength of light gets longer and these things get wider, so the net effect of this is Increase the size of the residence and I'll make it a little bit more relevant. Here in a moment I want to talk about a neutron interaction that does not result in any type of capture scattering.

And there are two. types of scattering there is elastic scattering this is the billiard ball model where you have a neutron coming in with some energy, it hits a target nucleus and the target nucleus goes in one direction and the neutron goes in another but the energy of the uh oh The rats They lead me back to trying to use these tips which prove to be a challenge. The incident energy of the neutron is conserved here. In other words, the sum of these two energies is this incident neutron energy, while in inelastic scattering the neutron interacts with the nucleus. and the nucleus moves with some energy and the neutron moves with some energy, but it excites the nucleus a little bit and kicks it, it says it's a quantum, it's a gamma ray, it's a photon, and so you end up with these gammas capture are emitted and both processes continue in

nuclear

reactors

and those processes are important because of neutron moderation.

In a reactor, you know there is a complication for many reactors. You want the cross section to be as large as possible if you remember from the cross section graph that occurs when neutron energies are low and you want it that way because if the cross section is large you don't need as much

nuclear

material in the reactor to make it work. The problem is neutrons. They are born with many-I energies and you want to reduce them to EV energies and the process to do this is called neutron moderation and it occurs by scattering the moderator nuclei through elastic and inelastic processes.

The criteria for a good moderator is Maximizes neutron scattering and minimizes non-productive neutron capture and should probably have a significant density and be able to get a lot of it in a space. The maximum neutron energy loss per collision is proportional to this small term. I've written here that it's maximum when the atomic number is one, which is hydrogen, and that thing is zero, and then it drops, sorry, it's one, and then it drops to 0.28 for 12, which is carbon, and that extends quite a bit. between those two elements, you see all the moderators that have been considered um uh and these are the ones that well, people have taken water half seriously, heavy water is used very popular uh good moderation ratio and I should say This ratio moderation is not that little term on the previous slide.

This moderation ratio takes into account the trapping cross sections and the bad stuff as well, so the water has a significant trapping cross section even though it has a lot of moderation, so it's a bit under heavy. water is not as good, but its cross section is about zip, so it has a very high number. Helium is very low and the problem is its density in an atmosphere, there are simply not enough atoms in any volume so it can do you any good. Even if you take it to 100 atmospheres or something, it's still a very low number, so helium, although used in reactors, doesn't moderate much of anything.

Burum has been used in some test reactors and graphite has been used in several reactors and may be used more in the future. Now I want to take all of this and talk about the criticality of the reactor and then the control of the reactor, a thermal reactor, you've already heard about them here, is a reactor in which the neutrons are moderated to thermal energies up to the EV range and most fions are caused by these thermal neutrons, not higher energy neutrons, and the definition here again is thermal and neutron balance, which is the maximum volume distribution at the temperature of your environment.

To talk a little about this, this is something like the lifetime of a thousand neutrons in a thermal reactor. That's what this graph comes to. If I can't press, avoid pressing the wrong button, so let's start here with a Well, the first thing that happens in this reactor is that there is some probability that u238 will fission from the fast neutrons and that's about 4 % or something like that, so you get 44 neutrons, but then the fast neutrons are whizzing around and your reactor is a finite size, I mean it has a top and a side and some of the neutrons go off and they just keep going and they don't interact inside the reactor again, so you just lose them, so you lose 145 there and then when you get into this resonance, which is also called the epithermal range, you lose a little bit more around 43 and the R resonance in the captured resonance range per neutrons in U2 238 starts to become important and while that will eventually produce plutonium which becomes part of your fuel for the purpose of keeping the reactor running, they are simply lost in the SI of the system, so another 157 are lost there and EP, some epithermal neutrons are lost in non-combustible material, like the cladding there, or they get captured in water, so you lose some more, but then you gain some because there are some epithermal fions in u235 and then they go down the neutrons thermal.

Some thermal neutrons may escape from the reactor and some thermal neutrons are absorbed into the fuel, but not productively. in other words the u235 captures neutrons to make the u236 not vision defining so you lose some there and I mentioned the temperature effect and there is a little less absorption there because the fuel temperature is a little elevated and you get The expansion of the nucleus and its dimensions changed just a little, but ultimately u235 ultimately boils down to it captures the neutron and you get about 2.7 neutrons, well, 1.79 net, 2.79 out, but you've captured one to do it. vision and then you get 441 back, so you're at th000 again and that's your chain reaction and that's where I mean the neutrons come and go and this kind of stuff, you'll see a lot on the far right. of obscure Greek letters and other letters and this kind of thing in the old days, when we used slide rules and this kind of thing didn't have computers, if you multiply all these various factors together, you will find that it equals one and each of these factors is associated with this notation and they used this equation and then went out and measured these various parameters to predict what they needed to do for a reactor to become critical and have a self-sustaining capability.

The reaction is uh and and the product of all of this is called uh K effective K sub effective and it's just the uh and and it's the uh multiplication factor uh in the past, but it helps. I hope to give an intuitive idea of ​​what is happening. inside this reactor, now we are reaching a critical point, you want to build a reactor yourself, what do you do to make sure it goes critical? It's not really an easy thing to do, first you can increase the concentration of fist material within certain limits. but you can do that, secondly, you can decrease the parasitic neutron absorption, you select materials with low cross sections and you just put less material in the reactor, you know, you keep the materials as thin as possible and you keep them so that you don't. no neutrons or non-productive captures are lost and neutron leakage is reduced.

Neutrons escape from the reactor surfaces. The larger the reactor core becomes, the lower the surface-to-volume ratio and the lower the fraction of neutrons that escape, so those are the basic principles you've used. uh used in uh in design to get the critical point uh and I notice this uh this is just a simple conversion uh to get the power in Watts starting with a fission cross section, the mass of the fist material and the neutron flux, just multiply that um because I wanted to use that uh here in a couple of seconds now I want to move on to the reactor control uh I'll describe the reactors later, but at this point I want to talk about well how do we do?

We keep this beast under control and don't make it go crazy on us. Each fion releases two and a half to three fast neutrons in a very short time. A vision is a very quick event. The time from one PR neutron generation to the next in a thermal reactor and that's the time it takes for the neutron to make noise through that numerical table that I showed you is on the order of 10 milliseconds now a concept that a stable period is the time it takes to increase the neutron flux and according to the equation that you saw on the previous slide, the power of the reactor is calculated by a factor of e, which is a factor of 2.7 uh for fast neutrons, which are the neutrons released immediately, released again immediately in fission, the stable period is a fraction of In a very short second period of time with that kind of power increase in a fraction of a second, the reactor is uncontrollable, the rods control or other control mechanisms you had can't move fast enough to control something that can move to the left. or just in a fraction of a second, so you have a real problem here, however, there are these things called delayed neutrons, a fraction of the fission products, the fission products resulting from the fission of u235 or plutonium 239.

They are It decays by emitting neutrons instead of beta particles. These neutrons are emitted at an energy somewhat lower than the fission spectrum, but are emitted with a defined half-life; In other words, it's not just a fission event, it's like cesium decay or strumming or whatever has a measurable value. and and the defined half-life is of the order, there are different ones, but of the order of seconds to tens of seconds typically uh and they are uh these neutrons are emitted along the so-called neutron drip line and I'll talk about that in just a second the existence of these decay neutrons with their much longer life when everything is averaged brings the stable period to the range of seconds and basically that is what allows us to control the reactor if it were not for those uh delayed neutrons we would not have nuclear reactors as much as we would have like nuclear weapons now we go back to our graph again uh and this is the neutron drip line here uh fission products are being produced and you saw, I showed you the previous chains, like chain 90 and chain 143, they are decaying in this direction when you get beyond this jagged red line, lower than that, that's where these neutrons, these delayed neutron emitters, and basically some of the fions are produced. produce fission products that have so many neutrons, you know, the neutrons just fall out of them, if they don't have a chance to go throughthe beta decay process, the other thing I wanted to point out here is that you get to Magic and you see these green Bo, of course, and of course, this is the number of protons that go up this way and this is the number of neutrons in certain numbers of protons or neutrons, the nucleus is much more stable than to the left. and on the right and it's a lot like chemistry, you have your chemical elements and then you know in one place you have hydrogen, you get just a little bit, you put a match in it and it reacts chemically.

The next thing that burns is helium, which is right here M and is totally stable. You can't make it react to anything, but in such extreme conditions it doesn't make any sense and that's because you have a closed loop. In this case, the electron shell in a chemical sense, the magic numbers are the same in the nuclear sense, you have nucleons, protons and neutrons, and certain numbers of them form a very stable configuration, so those nuclides tend to be stable and nuclides near them tend to be stable. undergo neutron reactions that produce them because it goes to the most stable product and in some fun places down here you'll see some very high cross sections for NP reactions because it happens to produce something that has a magic number okay uh now nuclear reactor control , uh, the way you control a reactor is neutron poison, you don't know which one becomes unproductive.

The neutron captures, it simply absorbs a neutron and does not lead to anything beneficial. It's probably better to call it fission poison, but the term used is neutron poison and basically you know you design your reactor so that as you lower the amount of neutron poison in there, at some point it becomes critical, you lower it much more and the reactor starts to increase power and you turn it down enough so that the power increases based on the delayed neutrons, if they weren't there the thing just wouldn't increase power, so you start increasing power and keep going up and going up until you're at the power level you want to get out of the reactor, then you put a little more poison back in and you get into this level of flight where you have a self-sustaining chain reaction at some power level and that's it. the underlying concept the neutron poisons that are often used Boron silver cadmium indium samarium europium and galenium uh these uh let's see that these here are used in materials, let me call near-engine materials, but they are also produced as fission products and so you have to keep that in mind, but when you control a reactor, you put them into some kind of designed shape and when we get into the reactors, I'll talk a little more about what those shapes are.

Also some inherent control mechanisms, increasing temperature normally decreases the neutron interaction and can bring it to subcritical levels, due to broadening, which means more neutron absorbing and non-productive neutron captures in u238, which is normally the large gorilla in a reactor. Imagine and as I said before, the reactor core expands a little bit more on the surface and you are dealing with tight margins here also in the reactors where it is relevant, if the coolant boils, you have less moderator there, the neutrons. so they have higher energy and the cross section is smaller so it tends to decrease it so there are some useful feedback effects to keep reactors from going crazy, at least thermal reactors uh now physics calculations reactor, science of reactor physics. interaction of elementary particles and radiations characteristic of nuclear reactors and what nuclear reactor physics basically does is take some of what I just talked about and be able to calculate how a reactor will behave and design a reactor and uh, like I said In the old days, reactor physics was basically the uh infinity or and the effective multiplication factor, I mean, it was done using those things in little you know, tables of numbers and measurements, these days, everything, of course, is computers and calculations like that, what do we need to know?

I'm going to focus primarily on neutrons, since that's what makes a reactor work. You need to know the neutron flux in and around the reactor core and the reactions of neutrons and in the fuel and structural materials, to some extent, other radiation, but most of the other radiation is not very important, they are mainly neutrons, but as a function of spatial energy, direction and time, and a colleague named Boltzman developed an equation that does precisely what it describes. neutral particle transport, which means it won't work for protons or alpha particles or anything like that except gamma rays and neutrons, that's what the equation is for and this is the Boltzman equation, it's hairy and is there some explanation for it .

Someone who is a fan and just wanted to post it there, there won't be a test. There is a problem with the Boltzman equation other than that it is complicated, but the problem is that it cannot be solved in closed form. In other words, you can't do all these integrals and stuff and get an equation that you can just plug some numbers into and calculate the flow based on all this stuff, there are just equations like that that you can't do. in closed form uh so what you do is you approximate and the first thing you do is you take your cross sections uh and this is what I have U23 u235 Vision not total I guess it is, but the cross section itself is this smooth curve and you can see a couple of resonances and you do what is called discretize it, discretize it, that is, instead of having a continuous function, you divide it into a cross section with this energy and another value with this energy, so you can imagine a table with those pairs of numbers, okay, I didn't even know I pressed a button that time, but anyway, you know, you do this with all your cross sections, that's the beginning of this process and then you face another one.

I wasn't even touching it, I think, okay, thank you, then another complication occurs, in a nuclear reactor. I think you already know enough about nuclear reactors at this point. They are not a homogeneous medium. they have rods and water here and they have edges and the rods have coating and fuel and tops and bottoms, so there is a heterogeneous heterogeneity there that causes a lot of problems when solving the equation and when you combine that with the need to know where the flow is at all these points and how and that all those energies that you saw in the multigroup cross section and as time goes by you end up with the number of points in the billions, which is still far beyond the current computing power, just there are too many data points, so you bite into it, you know, how you eat an elephant, one bite at a time, you start with one fuel. here, which is and it is inside, it is in a small cell and it is a small round rod and there is a coating on the outside and combustible material there and then there is water and numerical methods are used, whether they are called transport methods or Monte Carlo. along with the cross sections of the moldy groups for the various radionuclides, uh, to calculate what is called a many group neutron flux and many groups could be 5075 energy groups, something like you saw the u235 and all the little groups that it contains are of the order of that number and there is no universally used number, it varies and you calculate the neutron flux in this small cell, as a function of the energy for those groups, it is a static calculation, which means that you do not try spend time and see what changes happen uh you're doing it in two dimensions you don't take into account the length of the rod and you only have one key rad that nuclear your u235 238 some of the liner stuff and maybe some of the which are called chunky fission products in other words.

They will create some artificial radio cores that have a cross section representative of a class of real fishing products, so you will have maybe five or 10 or something and you will run these calculations for various fuel compositions, so now you have a flow for this little, this little cell and you start building on it. These days, you may be able to simulate some subsection of a fuel assembly that should represent a group of rods. with symmetry limits here and we're getting to the point where you might be able to do those mon Carlo protractor calculations for something in this order where these different pins might not have the same composition and then calculate a representative flux of this fragment, huh , but it's still mainly done using the previous one, the simplest one which is called pin cell, then you start growing from there, you start putting the pin cells into arrays and each of them can have a different well, they will have a different uh flux associated with them a different flux neutron spectrum and what you do is you use the neutron spectrum in each of these to weight the cross sections and go from 75 or 50 energy groups to two to five energy groups for each of these, but in this calculation again using the Monte Carla protractor methods, you represent this entire assembly that would be a fuel assembly with all these rods and then you go from there and once you calculate a neutron spectrum from that, you go and You homogenize the entire assembly to end up with a neutron spectrum in relevant cross sections for a homogenized assembly that does not have the rods represented and all the time what you are doing is on one side. your dimensions are increasing but on the other hand your number of energy groups is decreasing so the problem is still tractable and then the next thing is to take those sets of cross sections for various assemblies in various places that you know. the core of a reactor, uh, and the assemblies would have different compositions and a three-dimensional model is made of the entire core and this is now time dependent.

You can see how the composition and flow and everything changes over time, like a reactor would. It operates by operating relatively few energy groups, no more than five and sometimes a relatively thick network because you're representing it assembly by assembly, uh, and you do it step by step with the depletion, accounts for the changes in uh, composition of the radio cores and what effect they have on the flow, but in this situation you've homogenized it enough that you don't need to use protractor Monte Carlo, which are computer-intensive things, especially Monte Carlo, and there's another approach, uh, simplification called Diffusion Theory and when it is this homogenized you don't have all the spatial heterogeneity.

You can use it and it treats the neutrons basically like they're flowing and it's mathematically much simpler and it's these 3D. codes that are run many times to optimize the composition and movement of fuel because when you refuel a reactor, you take some of this fuel out and put new fuel into it and you can take some of the existing fuel in there and move it so that the power level remains relatively flat and you won't get into safety problems. There's a lot of detail in that, but that's how you approach the physics of the reactor and get to being able to calculate the composition and determine what fuel to put in and what you're going to get out of it.

I mentioned exhaustion. The depletion calculation uses some group fluxes, measuring the cross sections of many radionuclides to produce the total flux, which is a single value is not a function of energy and the cross sections of an energy group again are not a function of energy, then you put them into another computer code to predict the accumulation and K of many radionuclides is a function. of time, so what you would be doing here is going back and forth between the 3D calculation and maybe running what you know 3 months or something and recalculating the cross sections and flow level, then going to your exhaustion and calculating you find out what the new one is, you know it's the new composition, then you start with that and you do the next flow multigroup cross section, then the exhaustion and you keep going back and forth through time, um, let's see and once you get this guy . of information, which is the concentration of radioactive nuclei, you can convert it into all kinds of others, you can calculate the intensities of gamma rays, you can calculate the heat dek, all this if you know all the radionuclides that you have there and they give you half a life. re Off to the Races uh, you don't need the Boltzman equation for this, you solve the so-called Baitman equations, um, and it just describes the accumulation and decay of the radionuclide One Energy Group, uh, it can be solved in closed form for many. cases, but it's a bit tedious to do except in the simplest cases, so again computer codes are used there, in closed form, they can't be used in all cases because, mathematically, you can get to positions where radionuclei are they produce alone and what example do I want to use?

I suppose you could start with, say, neptunium 237, which you can convert to plutonium 238 to 239 240 241, which decays to amorium 241, which alpha decays to neptunium 237. This happens not in the fission products, but in Acton this can happen and mathematically it explodes, so you usually use numerical solutions herealso. This at the bottom is the Baitman equation and there are computer codes to do this calculation that they have had for years. calculation for a thousand radionuclides and all you know, 50 time points can take a second or two, it's just that it didn't take anything overnight anymore that it used to do this, okay, I want to talk a little bit about the physics of the fast reactor and I think The first point we need to get to is that again the neutron spectrum is a function of energy.

You see the thermal spectrum with the thermal peak on the left and the fission peak on the right. This is not as pronounced and then Look at the spectrum of the fast, fast reactor, a fast reactor has no moderator or essentially no moderator, so what you have here is you don't get all these lower energy neutrons, you get your fission peak. and then there are some elastic and inelastic collisions, so the energies decrease a little bit, but not as much as when there is a moderator there because you are deliberately avoiding materials that moderate well, that is the definition of this reactor, ramifications of the calculations of critical criticality of the fast spectrum are somewhat simpler because you don't have the thermal registration region and the resonances are not as important.

The neutron spectrum, although it enters the resonance region, is a tail of sorts. They have died down quite a bit by then, but on the other hand, fusions in the visible nuclide F, especially uranium 238, of which there is a lot in the reactor, are much more important. Secondly, let us remember the cross section diagram in the general form. cross sections with high neutron energies are significantly smaller than cross sections with low neutron energies. The physical reason is that the neutron doesn't spend as much time around the nucleus because it goes too fast, so that's a physical explanation for it.

What that means, because the cross sections are lower, higher concentrations of FAL materials are needed in these reactors for them to reach criticality and the neutron fluxes tend to be higher to compensate for the small cross section, if you remember. The reaction equation before the macroscopic ma cross section and the flow, another branch, there is a higher proportion of neutron fission, neutron-induced fission and neutron absorption, for actin in this reactor, which means, on the one hand , that there is less neutron loss for unproductive captures because, uh, because neutrons tend to cause more fission, secondly, you can convert fertile nuclides like u238, the fle nuclide faster than fle nuclides are consumed, which what that means in practice is that you have a breeder reactor where if you put th000 kilograms of plutonium, you could get 1100 now that no laws of physics have been violated because what you've done is converted a bunch of u238 into plutonium and of course , u238 is no longer there.

I have just improved the quality of u238 quite a bit, let's say with the fast reactor, and there is less production of minor actinides which are conventionally neptunium, amorium and curium. Now, if you look down here, the red bar is an is. a pressurized water reactor, a thermore reactor and this is the fission-capture relationship and uh, can I call it violet violet? It's in a fast reactor, this is a cold sodium fast reactor, that's what the acronym means, notice it's u235. the same uh u238 significantly better than the fast reactor, but if you look at the neptunium uh plutonium 240, especially the uh uh plutonium 242 and amorium, which are normally not visible in a thermal spectrum or very, very little in this reactor, you get a significant amount.

Visions in it, uh, and that's why they have been considered in many cases for transmutation. Can we get rid of all these actinides and help the repository and this kind of thing? And they invar look at fast reactors and this. it's why, okay, why fion if they're not, they're, they're, they're, they're viewable, remember the definition of file? uh is that it can sustain uh uh sustain a chain reaction these things cannot sustain a chain reaction like u235, in particular, now I can find a set of minor actinides, a very specific set of minor actinides that could sustain a chain reaction , maybe I can, it could be, you know, if I could get enough curium in a stack, I could I could do something with it, but as a practical matter it helps reactor efficiency, but running a reactor is not in the cards.

I think it's too early for lunch at this point, so let's move on. Next up, first I'm going to talk a little bit about some generalities and then we'll go ahead and get into some specific reactors, kind of like what's needed in a nuclear reactor, basically, the primary components. first you need fuel, you need the quantity and composition to support a chain reaction for years, you want this to be. I'm talking about power reactors, now you want it to be in the reactor, uh, for several years and to get your money. It is worth it, so to speak, in the form of energy.

Right now I'm going to treat fuel as a kind of black box and later I'm going to address

fuels

in more detail. So you have to put the fuel in a core which is a lot of fuel, you take a bunch of these things and you put them in general, what I mean in math, it's like a right circular cylinder, which means like a can of soup, you know it has a plan. up and down and more or less round uh it's heterogeneous for the most part and you have fuel and fuel rods that are separated by a moderator Andor coolant and somehow I'll go into more detail on one or both uh there are some reactors uh Ray mentioned The reactors homogeneous this morning where the fuel dissolves in the coolant or moderator.

They have been examined in the past. There has been a certain amount of development done, but they are not seriously taking place at the moment, but they do exist. or or have existed and an existing concept uh now coolant you have this reactor that is generating a lot of thermal energy of 3000 megawatts uh and you have something cooler and you need a good coolant first of all no coolant is ideal uh the The kind of thing you want is a low melting point, in other words, you don't want to have to worry about keeping your reactor hot, to prevent the coolant from freezing and then having to reheat it, and generally I'd like a relatively high boiling point. , uh, and that's as pointed out this morning, if the boiling point is not high enough, as you heat it, the pressure increases, which means that at higher pressure everything has to be thicker. massive and more risky to some extent now there are cases if you are in a reactor where you want the coolant to boil well that's a little different but for the most part I think a high boiling point is good, what you want is not corrosive , so it doesn't corrode, all of its components want it to have a low neutron absorption cross section, just like the moderator, they want it to be stable at elevated temperatures and radiation, in other words, not to disintegrate into other things or plating or generally ruining your reactor. uh, you would like it to have low induced reactivity;

In other words, when a neutron hits it and produces a capture product, you'd like it not to have a lot of gamma rays because eventually you have to get close to these things to refuel the reactor. Well, you might have to get closer. Let me put it that way. There is no reaction with the working fluid of the turbine and what I mean is that there is cooling in the reactor. Very often the working fluid of the turbine is usually water and you wouldn't want the cooling in the reactor to have a bad reaction with the water because even though they are theoretically separated, there are leaks.

I mean, things happen very hotly. capacity heat transfer coefficient simply helps get the heat to the turbines, low pumping power, low cost and ready availability, it's a great wish list, but the problem is, like I said, no one refrigerant satisfies them all favorably, the A. and the D are advantages and disadvantages and the m is kind of a mean or mean if you will uh and these are the uh the refrigerants that have been considered some of them that we've talked about before in terms of being uh moderators uh others are coolants, we mentioned just a little bit uh and uh down here in this last line, these numbers are a little bit dated, but this is the percentage of world reactors that use these various coolants and of course winter in everything this issue.

It's about light water reactors, whether that choice would be made if we started from scratch and didn't have the star like the Nuclear Navy, that led us down the path of pwrs and this kind of thing, whether we all make the same decisions . Again, I don't know, but that's where we are and I don't see it changing much. Heavy water is a reactor that I am not going to talk about almost at all. It's called can A. The reactor is a water reactor, obviously, that uses heavy water and you can use natural uranium if you want, and there are several in the world, several countries, Canada design, there are some carbon oxide reactors left in the UK, these are Legacy. designs and they're on their way out, some of the contenders here, helium, they mentioned this morning, we'll talk a little bit more about the high temperature gas cooled reactor, where where helium is the coolant, it has a lot. of advantages, I mean in terms of being inert, the problem is that it is not the best heat transfer medium in the world and because it is a gas, although the reactor operates under substantial pressure, it takes a lot more energy to move . gas around and circulates it and removes heat than a liquid, that's how the engineering is because it's not dense enough.

Another contender in many people's minds is the uh. The alkali metals, sodium and potassium, have been used in the past, but the focus is mainly on sodium and potassium, it just doesn't seem to offer many advantages, is more expensive and has some disadvantages, so attention focuses on fast reactors using sodium coolants, these are other metallic coolants. uh uh lead and bisas that have been considered uh the US is not a big fan of them, but the Russians like them um and they have uh some of their Nuclear Navies and other ships use reactors that are cooled by lead or bismuth or mixtures of the two, uh, what's the Midland chart in the middle?, oh, uh, molten salts, uh, we talked a little bit about that, uh, they have a lot of attractive properties, uh, I should say the couple of disadvantages of sodium and potassium, well, I'll talk about that. that a little bit later let me continue what is the difference between that own M Sals okay, these others I'm sorry, the question is why does a mole salt have it?

An example of a salt coolant would normally be made up of a mixture of something. like lithium and shine fluoride, in other words, it is a chemical compound like salt, while sodium, potassium and lead are all metals and not a compound and organics were considered in the early days of reactor development , a couple of small reactors were actually built using organic coolants. but there you run into stability problems: the organic just isn't stable enough at high temperatures and in a high radiation field, so it would break down into something that would just ruin all the fuel and that conduit wouldn't fly, so what? ?

Where were Organics used? What Organics were used? Oh, I won't remember, it's not simple, yes, what Organics were used together, yes, and there is an ortho and a Pear and something else, and they use only one of them, and oh, why? It is one of the criteria that does not allow the final removal of the coolant because some of these coolants present significant problems when the reactor is shut down or dismantled. Yeah, the question is why the removal of the refrigerant that you know at shutdown is not a problem in the waste problem, uh, several of them cross the left up through the carbon dioxide, I mean, they basically become low level waste, uh and and, well, helium does it, you can probably clean it up and reuse it, it's valuable. enough uh and for the carbon dioxide, the two water reactors produce trio and therefore water and you're not going to do an isotopic separation on it, so you're going to end up having to treat it as a low level waste.

Canadians eliminate treatment. some, yeah, not all, uh, and I mean sodium removal is a problem. Sodium elimination can and has been a problem and may be a problem. I'm just not. I'm trying to think if any reactor designer ever is. I had the foresight to look that far and I don't think, oh, I don't think anyone has looked that far. I mean, from a simple common sense point of view, some of those you could never use. I mean, no. Not in a DND where you ever thought you might have to DN that facility carries, we are in the name of God, you have to get rid of it, you will have a lot of lead rods and well, the follow up here was What what are you going to What to do with a lot of lead if you can't find another reactor that runs on lead?

You are going to make a lot of lead bars thatThey are contaminated with other radioactive isotopes and they have to manage it as a radioactive waste, a mixed radioactive waste, as you can imagine, uh and uh, fortunately we have to face that. I don't think here and I don't want to think about what the Russians do, no, uh no. Well, there are no power reactors operating now. I think there are a couple of what I'll call U test reactors, you know, the development reactors that are, you know, U, that will lead to the commercial ones. I thought the Japanese had an HTTR and maybe the Germans U, but there are no commercial reactors at this time, there is one that operated a few years ago, the Fort St Vine reactor in Colorado, it was built, it was 300 megaw electrical, I I would call it a demonstration plant uh it didn't work particularly Wella uh not sure if they did they had aspirations but I'm not sure they did uh anyway moving on uh now moderator uh for thermoreactors just obviously I've talked about moderators here already uh for the water cooled reactors the coolant is the moderator at least for our water cooled reactors the canas the canadian reactors that is not the case uh they have a kind of well the canadians you can't separate the two, they have a kind of well static moderator and then a bunch of flowing coolant and you get some moderation from both.

I guess that's the fairest way to put it. Just another moderator we were hoping would be used as graphite. At this point, looking at the helium coolant, a future perhaps molten salt cooling and although no one is pursuing that very seriously, the density, this is the density of graphite, there is a theoretical density, but it is that the reactor graphite it's not that dense as the density is theoretical and the analysis business can be a problem if, although I think they'll probably be at sufficient temperatures, let me explain a little. Ry mentioned this. In the morning, the Vigner energy that builds up through graphite dislocations, carbon to carbon bonds and can build up quite substantially, you mentioned the kind of dimensional problem, uh, but there's another problem and that is that the energy can accumulate and The accumulation is a kind of latent or potential energy and if you suddenly heat the graphite a little bit and not in a large amount, not like in a reactor accident, that energy can be released all at once and then the graphite can acquire it. it starts to burn and you can release radionuclides and this sort of thing and that happened once in one of the reactors in the UK, the wind scale reactor which was operating at quite a low temperature, they went through a sort of temperature Excursion Wier Se It released energy and they had a fire and they put some radionuclide in the pile and this sort of thing is not particularly difficult to avoid in a low temperature situation, just periodically increase the temperature of the reactor to get the bonds. again together uh without having that much you get into trouble and for the reactors we're talking about they operate at such a high temperature that it's not going to build up again they'll just stay aligned um well, main components uh of a reactor plant, it needs a vessel. pressure for water and gas cooled reactors, and I differentiate it and leave out some of the other reactors because, for example, in a sodium cooled reactor, the sodium basically operates at atmospheric pressure, so it doesn't need pressure. container, you just need a container, you know, basically, a closed container or a tank or something like that, you need coolant pumps or compressors, depending on what you're going to move, you need heat exchangers for some, for some types of reactors, you need your turbine. generator, the turbine rotates when the working fluid hits it and then spins the generator, which generates electricity, it needs a condenser or chiller and cooling towers, it must remove low quality heat to complete the thermodynamic cycle, all interconnected pipes, you need to have waste processing in the plant, you need some kind of water pool to store the spent fuel that just came out of the reactor and you need all kinds of labs, shops and other things to handle moderately radioactive items, uh talk a little over some of these cooling towers, this shows two cooling cooling towers.

The concepts on the left are so-called wet or evaporative, where basically hot water comes in, it is sprayed and has direct contact with the air and a kind of evaporative cooling is the way it works and the cold water comes out and this tower design is natural circulation uh and the other one is a closed system where the hot water goes in and the cold water comes out and there is no direct entry the contact between the cooling air and the water is all conduction through pipes and fins and radiators and that kind of thing These generally have to have fans to get enough air velocity and cooling without the evaporation effect.

Both types of cooling towers generally exist in commerce, mostly in reactors, they use the evaporator on the left, now another point, these are shown as hyperbolic designs and I suspect most of you have at least seen pictures , If that is not the case. As you drive down the road you see some of these huge hyperbolic towers about two hundred feet tall or more. A hyperbolic tower is not equivalent to the presence of a nuclear plant and a nuclear plant cooling tower does not necessarily have to be hyperbolic. number of plants, of course, they're on a river, they're on an ocean, they don't need a tower at all, they just have a direct cooling loop, uh, but the cooling tower designs, especially the dry well type, I guess that both types can also be in the form of a kind of cooling bench.

I don't want to call them towers, but cooling modules that could be 30 feet high and the entire raft could be 100, 150, 200 feet long. um and they can be pretty close to the ground and given how close you can get to a nuclear plan, for example, you might not even be able to see them because they're low enough profile, so it really falsifies the news industry, TRUE? because they always think that's yeah, I know, where I live there is one, you know, there are some gas plants there that use hyperbolic towers, these were just found, three photos of them, the one in the lower left corner is from somewhere in Europe, uh.

Someone, someone did a lot of work there, okay, we have to have some waste processing in this plant when it comes to radioactive materials, although you know the

fuels

in the pressure vessel, you still have some problems with waste processing. uh, first processing of liquid waste, invariably some water is lost out of this system, there may be leaks and whatnot, and you need make-up water, also, corrosion control is a major issue, so you need to control the water. chemistry very carefully and that means not only things like ph and this kind of thing, but inevitably you know that some of the rods are going to lose a little bit of something.

You have all these neutrons in the core, some create activation products and in the metals and the metals corrode and dissolve, so the radioactivity moves in the cooling water and gets to strange places in the pipes and pumps and can make maintenance a pain, so try to keep the water fairly clean. like iron exchange or reverse osmosis, to purify the water and concentrate the stuff you don't want, maybe evaporate it further to concentrate the dissolved species, the water of course is recycled back to the reactor, but eventually the concentrate would stabilize. for example, slurrying it or in some type of absorbent medium and you put it in the barrel and it becomes a low level waste for disposal uh and all plants have to do this type of thing, they have various knowledge, various approaches in different plants there is no standard way to do it uh gaseous effluent uh there is a gaseous effluent nuclear facilities uh operate with a kind of negative pressure in other words, the higher the radiation level, the more negative the pressure and the pressure continues to fall and fall and that, of course, is done by creating a vacuum in the most radioactive part of it and that it can contain, there are some short-lived isotopes of various gases that are produced and released from the refrigerant and what is done is passed to through something like a coal bed.

These isotopes tend to be pretty short lived and in the carbon bed they just hold them for long enough for them to decay, uh and uh, then the resulting gas stream continues to pass through a high efficiency filter and then out. from the pile, but eventually the carbon beds and filters become solid waste and are again placed in barrels and treated as if they were of low quality. Level waste, uh, solid waste comes from the above. There's all kinds of other solid stuff too. You have lab equipment where you are doing analytical work on your coolant or any protective equipment.

All these fun little white seats that are out there during refueling. and when doing maintenance the equipment failed, uh, that has been in contact with radioactive water and, finally, you know that there is a kind of constant flow of these things, uh, it is not a huge volume, but again you send it to a container of low level waste. disposal facility uh and most of the waste uh to set aside the spent fuel, but most of the reactor waste is low level waste that is acceptable to go to one of the operational low level waste disposal facilities l Now there is a small volume of them that isn't, it's usually internal parts of a reactor and it's so highly radiated that it exceeds the limit for these places, so reactor operators are hanging on to that in hopes of identifying a place to get rid of it and the energy department.

This is working along those lines, radiation protection, uh, it's primarily, I mean accidents, in addition to radiation protection on a routine basis, it's primarily a worker issue because they're the ones that get close to this equipment where They have their corrosion products and this type. of things, the public is too far away and kept too far away, uh, its radiation sources, I mean, the reactor itself gives off a lot of radiation during operation, but it's sealed in a containment building and people don't go in there during the operation, uh. you have traces of contamination in the cooling water and, as I said, places where radionuclides accumulate and in these plants they administer the doses of the workers very carefully, everyone has to carry personal meters, it is an act of monitoring, you know, they have I have records on all of this, as to who gets what, there are limits and if they start getting close to them, they won't be able to go back into the radiation zones anymore, and the industry has a pretty good track record in the last two. from Decades of continuous reduction of the occupational dose of workers, they have done a good job, the radiation shielding, most of the shielding is concrete or water in these plants, sometimes you will use metals like steel or whatever, a space is tight, but generally water is pretty cheap and concrete isn't that bad uh and uh they carefully plan the maintenance uh and limit the time they increase the distance is the lowest approach that is reasonably achievable for the workers dose uh that they plan the work activities carefully and you know don't go in there and have a conversation in one of those areas, it's planned, you know, you do the business, you go out and there's a lot of pre-planning in terms of you have the right tools, you know what you do.

We're doing those kinds of things um Public Safety talked about wealth like gas flow. I'll talk about accidents later. Let's see what we have here. This is getting closer to the business of reactor design and when the reactor is developed. Well, the reactor deployment. and the type of deployment of reactor development bottomed out in the late 1980s and throughout the 1990s, but talks began in the early 2000s and the energy department began work on developing more advanced reactors at that time and came up with this kind of The evolution of nuclear energy is kind of a chart or you started with some of these early designs, these were relatively small reactors and they had to be seen as prototypes, they didn't work very well, but you know you have to learn doing.

To some extent, Magnox is a graphite-moderated reactor built by the United Kingdom. There are none in this country and they are being closed in the UK. Dresden and the port of embarkation is one of the first sources and Dresden, I believe, was a small bwr. bwr uh, then you got into commercial power where there was enough confidence, they started building plants a substantial number of pwrs and bwrs plants in this country, they can make reactors in Canada and in some other countries, and then, but they had their difficulties there and their operational experience, I guess I call it mixed, but as they progressed they learned in some of the later plants that were built before it ceasedAll the construction, the so-called generation three was more advanced in the sense that they learned what the problems were and things started to work much better here in terms of reliability and online factors, and the industry has also had in recent 10 to 15 years a pretty good track record of increasing online availability, so these things are, I think, the fleet average is up to 90% or is it a low 90% right now, you know, the 90 or let's say 90% of the year, these things are online generating power, usually at full power in the case of a nuclear plant, so there have been a lot of uh. success here and with the global climate and any movement that there has been in recent years to start implementing what is called Generation 3 plus, which are evolutionary designs, they are not radically different from these that are built and running uh but they have sharpened a little bit your pencil and they have improved the safety features they claim to have improved the economy and I will explain some of the wise and words uh here uh probably after lunch, but uh and all of these uh the ap600 and ap1000 are pwrs, this is a European pwr , uh, this is a Japanese bwr, this is an American type of bwr, and then there's the so-called Generation 4, which was, uh, a lot of this evolution here was done by the industry. not so much by the government because this was all already quite commercial here you have Generation 4 which are some really advanced designs that are not very big, they are not ready for prime time right now, they are still the subject of R&D , which means they're in the demand domain of the Department of Energy, NE and uh, it's supposed to be uh, oh, these are all the attributes that they think they want to have and some of these, you know?

In my opinion, let me call. It's reasonable, it has some potential, the sodium cooled fast reaction has some problems, but its potential and the high temperature gas cooled reactor is part of the other reactor design and I'm going to talk more about a little bit about those this afternoon uh some of the other reactor designs are okay, I'm skeptical to say the least uh there is a reactor uh it's a gas cooled fast reactor uh and uh I think they're going to have trouble making that reactor safe enough uh there's so little in the core if they get a little bit of a transient for which there aren't tons of water or tons of sodium or tons of graphite to help moderate, that's bad.

I don't want to use moderate here to help control any excursion, it's basically a bunch of armored fuel. rods and a bunch of helium and that's just not a recipe for stability um and uh there's a super critical water reactor that operates it at extremely high pressures. It is a water reactor but a super critical fluid, it is neither liquid nor gas. but it is both something strange and it is difficult to explain and it has a very different behavior and it has been proposed because you can operate it at very high temperatures but it has a lot of problems in terms of controllability and corrosion.

Water at really high temperatures is somewhat corrosive, but there are several of those and, I think, I think all of them. I think I have little cartoons maybe in the backup slides this afternoon. What about the small modulars? Oh, the question was about small modular reactors. I'll talk a little bit about that this afternoon as well, okay, at the blue ribbon commission in several of the blue ribbon commission meetings there was a very vocal contingent to promote M react mentioned that a couple of times obviously there are some advantages , there must be some disadvantages. and it turned out to be one of the wells, the molten salt reactor that is being talked about is a graphite moderated system cooled by molten salts, and one of those wells has a number of advantages, online refueling, a number of safety advantages if you're in that type of system, you don't have any linings to mess with and one of those reactors was built in a small demonstration scheme in Oakridge and the safety system is basically, does everyone remember what a plug is? freezing?

It is used to have them in the radiator block, so when it freezes in the winter, it pops instead of cracking into the block, but at the bottom of the reactor there are a couple of plugs of molten salt that are kept frozen by active cooling If the reactor starts to go out of control, you cut the power or heat takes over, the plugs melt and drain into critically safe, naturally convective, convection-cooled drain tanks, uh, and it runs at a very high temperature, so that you get your thermal efficiency. pros now cons at the time the demonstration plant was built there was a program that wanted to go to a larger scale, but what you have is this molten salt that is pretty benign in terms of corrosion, but you have all the fission products. in the universe there and, as expected, one of those fission products started to cause a little bit of cracking in the reactor vessel and at that time there was an intense competition between various types of reactors to see who was going to go to how big and who was going to be left behind and that corrosion problem was enough to leave the molten salt reactor behind in favor of the sodium-cooled fast reactor, which is the one that gained the most traction at that time. the corrosion problem, at least that corrosion problem, they had enough momentum left to investigate it and it turns out that the fission product, thorium of all things, does that and by adjusting the composition of the alloy, they can fix it, so which I have always done.

Intellectually I liked the reactor, but it's only in the US, it just doesn't have any traction right now, with almost none, but I mean, it has some defenders, but on the scale of government and whatever it's not , where? You are putting your money. He had someone else. Yes, your graph on slide five had a sodium-cooled reactor. Where is? How old are you? I suspect he means he was close too. you're talking about the world chart no and uh we we in this country operate the fway plant near Detroit but it closed a long time ago uh I have to believe you're probably referring at this point to the Russian BN 350 Russia and uh and like I said, those numbers they are a bit dated, the Japanese are still trying to restart the mangu plant, but those are demonstration level plants, uh, possibly, yes, what is TVA proposing to put in the old molten salt reactor?

Sodium reactor, the question was what was TVA thinking about putting on the old site there, oh oh, the Clinch River breeding site, the Clinch River, uh, TBA is dancing around some sort of small modular reactor that will be the that they are looking for. It's basically a small pressure IED water reactor and I have a cartoon of that design that we'll cover here in the afternoon. I think what's next. This is a great place to stop at midday and see you around. :00 Watch it again here 1:00 Now let's talk a little about the thermal or non-thermal cycles of nuclear power plants, the most common is the ranking or steam cycle, where basically I have a heat source, there is no Nuclear reactors, they don't have flames, but I like the rest of the diagram, since it heats water and produces steam and drives a turbine that turns the generator.

Then you have to go to the uh, condenser and it removes the low heat from the grill and you pump it in a circle. This is the braon cycle that operates. It is not necessarily for gas-cooled reactors, but it is a gas reactor, not steam. It does not condense the working fluid and I will. It starts again here, you have a heat sorus which is your reactor and you have pressurized gas, you heat it in the reactor and it goes through a gas turbine, not unlike what natural gas fueled plants have, it spins it and there is a generator. in the middle that generates your electricity, uh, the gas comes out and we're essentially talking about helium here, it's the only real game in town because nuclear energy goes through a recuperator.

I'll talk about that for a second and a bit. The cooled gas goes to a low grade heat rejection and returns to the same shaft as its turbine is a gas compressor to recover the pressure up to the reactor pressures and then passes through the recuperator and uses the left superheat that leaves the turbine and then it goes back to the reactor and it keeps going around and this radiator is basically your cooling tower or whatever you have to reject heat from, so that's kind of the future hope for helium cooling. reactors um and then uh third, I guess it's not a power cycle, but some of the reactors are seriously considering using the reactor heat for process heat in other words, no turbine, no gas turbine and no steam turbine , basically the working fluid. or the reactor coolant is turned off and something like maybe molten soot or whatever is heated in a secondary circuit just to transfer heat and it goes into a pipe to the plant next door which could be an oil refinery that makes products chemists, someone who needs a lot of heat and maybe a good amount of high grade heat and when I talk about htgrs, I'll explain it a little bit more now, reactor designs finally, as a framework for this, first I'll talk about uh, frame it. with one type of moderator or no moderator and then the coolant, the water-moderated reactors.

At this point, I'm going to focus essentially on light water reactors and not the ones I can make, and then graphite moderated, gas cooled reactors I guess. I shouldn't have left them there when I put them on backup slides and then unmoderated, which is sodium cooled mainly a little bit in some Legacy reactors, a couple of the ones of interest and then a little bit in small modules. reactors, so that's the program here for a while, this is the world's most popular reactor type pressure IED water reactor, uh, and to give you the flow of things, this is their reactor vessel, uh, some coolant pumps, I will say a little more about them.

But the important feature here is that the reactor heats the water that circulates to a steam generator and then there is a second circuit where the steam goes out to the turbine and the generator and is condensed and then comes back and is maintained. going around in a circle uh the rest of this I think is pretty common and we've talked about it but it has this secondary loop uh it's one of the hallmarks of a pressurized water reactor uh a little more like a cartoon this is the vessel of the reactor itself, you have coolant pumps, you can't see all of them, but there are two shown back here, the steam generator, once through the steam generator and then a pressurizer, and to explain that the water in this circuit primary is all liquid water and I think you may have experienced in your house where, if the plumbing is not quite right and someone slams a faucet, the pipes rattle, it's kind of irritating and The cure for this is basically you hire to a plumber and they, in one of the horizontal pipes, put a vertical pipe with a cap that becomes an air pocket and of course the air is compressible and you get rid of water hammer, that's exactly it.

What this pressurizer is is, it has room for air or gas at the top, it has heaters, and when you heat it up, they produce steam and raise the system to a pressure that's around a couple thousand PSI, and I don't have any problems. of water hammer, which can be a real problem with so much power going, a little further into the thing, the 10 to 20 foot diameter, 40 to 60 foot high, 10 inch thick pressure vessel, is carbon steel clad with stainless steel, some of the key elements here, inside the pressure vessel, it has a bottom plate that supports the spent fuel with small slots for fuel assemblies in a roughly cylindrical array around the outside, is what I It used to be called COR Barrel or a shroud, some call it a Nile shroud, but that will confuse you later and what it means.

I'm having a hard time reading here what the entrance is, but the water comes, I guess it is and that enters. it runs on the outside between the pressure vessel and the core barrel and then it turns and goes up through the fuel assemblies and then to the outlet nozzle there's one right there uh and there's a plate on the top to hold everything down and the control rods that are used on this come from the top and of course there is a cover that is closed tightly when it is running and to refuel, you remove that cover to take out the fuel assemblies and the new one is on this It is the interior. of a pressure vessel with the lid off, there's a set going in or out and several of them here and you can see some open slots and this is the core of the barrel running through there, there's not much else to those coolant pumps, uh They don't have a horsepower rating, but they are very large relative to people and other than that, it's a pretty simple pump for moving water, except for its size.

Now, this is a steam generator, it's the so-called YouTube steam. generator, you see the schematic of the reactor and the hot water goes up and goes through tubes up here and then it goes around and comes back down, the other side goes back to the reactor and this is C's primary circulation pump and it just goes around and around and up here on the outside of the tubes the water boils and these little gadgets up here are uh uh water vapor separatorsbecause boiling will drag water droplets and you will want to eliminate them and have pure steam. without drops of water coming out of your turbine U and this is a photograph of one uh in life they have a fairly good size but now they are reasonably simple power control uh the rods are inserted from the top, in general they have three types of rods closed rods that are only used when the criticality of the reactor is already turned off, but to ensure that the criticality has ceased and remains that way while they work with it, full length rods that are usually removed but are used to turn it off initially, uh low if you want make it a little faster and then there are some partial length rods that are not as long as the fuel assembly and that are used to shape the power ax if you get the power in such a big core.

Sometimes it can start to warp a little and partial length rods are used to control it in a localized region which is usually made of an alloy of silver, indium and cadmium in a long rod about the size of a fuel rod. Now, for routine control in this reactor, no control rods are used. The concentration of boric acid dissolved in the refrigerant is determined. Remember that boron was one of our neutron poisons in some previous table and VAR its concentration a initially is. it's pretty high because you've got some fresh fuel in there so you've got a lot of u235 so you'll be pretty concentrated you know maybe 500,00,000 PPM and then while the reactor is running you use an ion exchanger to slowly remove the boric acid and as the fuel's ability to support fions decreases, the poison is removed to maintain its criticality um and you know it's very uniform, it's very stable and it's worked well in the pwrs uh a word of nomenclature Se called scram, which is an emergency shutdown of a reactor if one of several events occurs, it either happens automatically or the operators can do it manually and basically that means inserting the rods in a period of one or two seconds. into the reactor and shutting it down immediately even though there is boric acid there, and any number of things can cause this type of thing, there can be implementation issues or safety issues and it can be something as simple as a lightning storm. a big switchyard down there and suddenly there's nowhere for the electricity to go and you can't keep running the reactor with nothing to go to, so it shuts down pretty quickly, so they're not daily events, but they are certainly not uncommon events either, and a story associated with the U Source or the word get out has been widely debated and never decided, there are a couple of theories, one is, those of you who may remember the first nuclear bomb.

The reactor was the uh uh, the graphite pile, the Chicago pile under Stag Field in Chicago, where they put some natural uranium in and took out some rods and got a very low criticality level, that was the first nuclear reactor in At that time, the physicists there made fairies. and others, I mean, this was Unexplored Territory and they didn't know what that thing was going to do, so they had poison sticks and they quite elegantly took out some of these emergency sticks and tied them in the outside position with a rope and it's alleged that they put a guy on top with an ax and said if we give you the signal you cut the rope and pull the rod to put it out and that's the ax from the safety control bar, that's one story, the other history is.

If you go back to the same time period, which is you know, early to mid-40s, get out, it was a pretty common word that you know in conversation, you know, get out, get out of here and that kind of thing, so on and so forth. then. so it meant you know if we have an emergency like getting out of Dodge, then the truth is unknown, these reactors, unknown, I actually didn't get into this until a year and a half ago, but in the last issue. For many years for the existing reactor fleet there has been what is called ramp-up, that is, they take an existing nuclear plant and by making various changes to it, they get more power from the same reactor.

Now you have to conceive these activities. of them have to go to the NRC and get a change in their license status to get them looked at, but what they have is, simply because we know the cross sections better, we have better calculations, improved reactor physics and heat. They transferred predictions only on the old correlations, got about a 2% increase in power and then improved the instrumentation - in other words, they were able to more accurately monitor what is really happening in the reactor, allowing them to operate closer to the fuel margin. 2 to 7% and then during blackouts and whatever they went back and installed better major equipment, more efficient pumps, more efficient steam generators and they got 7 to 20% depending on the plant and the network across the uh the U.S. fleet and fleet now has 104 power reactors.

They've gotten the equivalent of five new reactors without building a reactor, which I thought was kind of surprising, but never. Les uh oh, while I'm here I wanted to talk about a Russian version in a pressurized water reactor uh, there's not much difference, it's not much different, it's called vve and I'm not even going to try to go to where the Russian one is, but it's your pressurized water reactor, uh, the assemblies are kind of a little bit different configuration but conceptually the same for reasons I never found out that it has a horizontal steam generator and why you would want to generate steam in something that is a long vessel and not very high has escaped me, but nevertheless that is what they do, uh this is a relatively current design, it has complete containment, you know, on the outside and it more or less meets the international standards for this type of reactors and we will get there one that does not comply here in a little um now I have talked about generation three of our existing fleet a little uh do you remember the Generation 3 plus, which are the ones that are being marketed and uh and and built at this point uh an ap1000 is being built at the uh botal plant in South Carolina I think it's Georgia Georgia, you're right uh and uh uh there's a Westing house design that's their AP 600 1,000 and that's about the electrical output of them uh it's supposed to be AP for advanced passive and a little more on that in a second ariva, which is the French supplier has what they call a US European pressurized water reactor that they are working on getting a license and Mitsubishi has a reactor design of pressurized water and I think we American utilities are considering all of this, but how serious it is for some of them can be debated.

The one in front, as I said, is an AP1000, one of the things they have done in Generation. 3 Plus, basically, they've been able to redesign the thing so that they don't have as much equipment, fewer valves, fewer pumps, it's less likely to go wrong, it doesn't cost as much. a lot at the beginning, and the smaller amount of equipment allows the building to be reduced in size, which means you don't need to pour as much concrete and this is the type of change ap1000 in the footprint from its Generation 3 to Generation 3. Also, and Of course, this all comes down to trying to save capital dollars.

Increases in thermal efficiency and this is largely due to the same effects that they have tried to achieve in Generation 3 plus. except sorry Gen 3 except in Gen 3 they had to do it via snapback whereas here they can do it via Layout and put it at the beginning which usually works a little better oh rats take me back a uh and enabling. the standardization of the 3 plus design and improvements in these reactors the three generation plants, each one of them is a little different, you know, there were three energy suppliers at that time in the country, several architect engineers who do the balance of plant.

I mean turbines and generators and all this, so there is a huge variation between them and if you standardize, you tend to learn a lot about improvements, share improvements and the whole system seems to go better and they seem to have learned that lesson, uh, modular construction of uh. components in the factory and then assembly in the field as opposed to all construction in the field in terms of welding and some big, big concrete pieces, and a lot of that, and there have also been improvements in efficiency and for many of the same reasons. I listed it before in Generation 3 and computer DEA design has also allowed this, now with computers you can make a three dimensional list and have a full 3D simulation of your plan on the computer to make sure it will fit and know the exact dimensions of all the components you need, that years ago simply didn't exist, I'll talk more about the safety approach, and fuels later, a little bit about refueling, you do some pretty obvious things, like shut down the reactor, leave it. cool slightly and then bring to a boil and then lower the pressure to atmospheric.

Put high concentrations of boron in the water to ensure you don't have a CR criticality problem. Remove the head bolts and then the pressure vessel head. and the control rods, this is a pressure vessel head up here and the control rods are hanging here as they take them out, then you have to remove the top internal parts, there is a plate on top of the fuel and so you can access the fuel assemblies, then you flood the refueling pool, I think I have a photo of that so I'll hold it up on the risers and then you start removing the spent fuel and inserting new fuel and that's basically done.

More or less a crane with a hook and the fuel has some little handles on the top and you just lift it up and move it out, and as the refueling continues to the right, you see the uh looking looking towards the center and the pool of refueling, uh, it's not just about refueling, you take the opportunity of shutdown to do all kinds of maintenance, it's a frantic scramble, uh, to do all this because every day that you're not operating is You know, another million or two of electricity you're not generating, so they've gotten very good at this, a little bit more about how this happens.

You see the reactor here and the head and the control rod. The units have been removed and normally this whole area up here is dry, it's just a big hole and they usually put some kind of cover in here to keep things out, but during refueling after removing the cover. You flood this whole area here essentially down to the floor level and it provides more radiation shielding, but then what you do is you take out an L assembly and you move it here and you place it and then this little Gizmo rotates the assembly. The side puts it from vertical to horizontal and it goes through a little T-tunnel into the spent fuel pool, which is just a big pool where you'll store it and let the decay heat go away and then you'll get it. by the handle and drag it upright and simply place it on a rack and it fixes there.

You'll see later, bwrs are a little different than that and maybe in some important ways, but that's how refueling is basically done. these things, uh, after you refuel, you basically just reverse the process of putting it back together, uh, the average refueling outage is in the neighborhood, uh, what I found was 38 to 42 days. Generation 3+ reactors are firing at half of this, uh, trying to get another couple. of weeks of operation um and in each ref fuing 20 to 33% of the cores replaced during uh each refueling outage uh 33 is probably more of a historical number and now more and more the reactor will be at 20% because they leave the fuel for longer and they burn it more, so it has to go out less.

Okay, let's talk a little bit about some nuclear accidents here. A nuclear reactor is very concentrated in a liter, which is like. with a quarter you're generating 50 to 100 kilowatts of thermal energy, uh, that's a pretty good amount of energy at a local location, so you have to keep removing the heat even if you turn off the reactor, just turn it off instantly, you're still generating heat at a rate of about 6%, which is equivalent to a couple hundred megawatts for a large reactor ramping up at about 10% per day in the short term, which is in an accident scenario, you're talking about the short term. uh, this is kind of a let me call it a prototypical type of reactor accident which is considered to be basically somewhere where the primary coolant circuit breaks and coolant water escapes, you know, it depressurizes, it turns into steam, uh, the reactor is supposed to be throttled immediately to get down to its 6% but there's still plenty of power and at that point the fuel surface can dry out and start heating the fuel cladding surface to about 2200 degrees Fahrenheit or so. .

It takes a little bit, the coating starts to fail and I on the zeroy zeroy coating is pyrophoric so you bring it to a certain temperature and it starts to not burn as much withoxygen or else react more with water and zirconium Z becomes zirconium oxide with the other product being our lovely friend hydrogen, which I suspect you've heard more than you want to in recent months, but if that starts to happen, you have broken the coating so that the fishing products can come out. We have a kind of fire situation that provides a driving force to volatilize them and move them and although these are in containment, secondary containments and this type of thing, if it becomes overpressurized, the radionuclei can and do essentially escape.

That's a little difficult, you know the typical concept of a reactor accident, now you know what to do about it. Well, the first obvious thing is to keep the core moist. I have a colleague named Lake Barrett who has been active in the Fukushima situation and he says that a wet core is a happy core and if you keep it wet and maybe like a coral it can take heat out of the water that is there, things won't happen. really bad. happens at least, uh, uh, safety or health impact, you know you could mess up your reactor, fine, but that's an economic problem, uh, if not, those things.

I mentioned liner rupture, liner fire, fuel melting and steam explosions, hydrogen explosions, steam, hydrogen, rule number. two, see rule number one and what I mean by that is you want to have defense and depth to make sure you can keep the core covered, you don't just know one mechanism, but two, three or four, and rule number three is yes you can. Don't do that, deal with the consequences now, believe it or not, this slide is at least half a year old, if not a year old, so it predates our recent events in Japan, which surprises me, but now it prevents an accident , you first.

If you want to eliminate features that facilitate coolant release, you would like to have no pressure penetrations in the pressure vessel under the core because if one of those breaks, it doesn't matter how much water you keep pouring into the top, if you have a hole in the bottom of your bucket you're you're you're in you're in difficulties already uh and um make sure you have uh I have Provisions for active cooling in an accident situation secondly you want to uh detect solutions you want to be able to understand that problems occur before they can cause a loss of refrigerant and prevent them, and there have been cases that you may have read in the newspapers about corrosion that have not reached an accident situation, but there has been corrosion in some pressure vessels, it has advanced too far without being detected, and the other is that if an accident occurs, you need to be able to detect coolant loss early and accurately, and on Three Mile Island you may remember a few years ago. and in some of the Japanese reactors in both cases they were having a lot of difficulty determining exactly what the water level is, the core is discovered or not, it's just that type of information and that's detection, which requires more instrumentation and training.

Solutions that include the reactor in both normal and abnormal situations. and when to intervene or not to intervene in the Three Mile Island situation, they had some instrument readings and thought they knew what it meant, but it meant something else, so the actions they took were actually counterproductive for a while until they realized , because they hadn't really instrumented, you know, what you really want to know, which is like the water level, they had indirect or inferential measurements, and those are all pretty important, now controlling an accident, going a little deeper into how to do it. . uh you need to supply coolant and keep it coolant and power are essential to do that uh you can have all the water in the world if you can't pump it it won't work very well uh power sources of course you have external which is the grid that the Reactors are connected to the electrical grid and have emergency diesel generators with diesel supplies and are tested periodically and also have a certain number of batteries, but that is not going to work.

It can last a long time, it can help you with some instruments, but running a reactor coolant pump on batteries is not a winning proposition and what you will see here is some kind of schematic of a power supply and they have multiple Rea. The water injection systems are borated water and if you have problems and they shut down the reactor, the first thing you have is a high pressure injection system that can inject water at, you know, 1500 or 2000 PSI immediately while the reactor is shutting down. depressurizing. but you can't get much volume as it goes down in hundreds, you have a medium pressure and then a low pressure and as you go down each one they can move more water and the water is any The water that comes out of the reactor is collected in a sump that go back to these pumps so you can continue to circulate the water and try to achieve that.

You have a coolant function in a CO heat removal function there. to try to help remove the heat and this is a generalization, everyone knows that different reactor designs have variations on this, but this is a very typical thing that contains the release. You want to keep the pressure vessel releases inside the you're building now, what you have here is you have your Vel 10 thick pressure made to hold 2200 PSI and presumably we have the problem that it's leaking water somewhere somehow well and for pressurized water reactors, then there is the containment building and that is the containment dome.

Not all are reinforced concrete domes with enough volume to handle the pressure and design features to reduce the pressure. I've listed a few here and they are not standardized. but what you want to do is, basically, if you're selling out of the pressure vessel in the primary circuit, you want to try to keep it in this big concrete building so it doesn't come out. the environment and that kind of stuff uh and then I'll say a little bit more about these containment buildings and the last resort if your containment building can't contain what's going into it, which means it's in danger of being overpressurized, there's a filtered vent outside in other words you open a valve and it goes through a gas processing system to remove the iodine and this type of stuff and then you vent the gas to the outside to relieve the pressure uh now for a pwr these are some examples of containment buildings uh are the The current designs are passive this is basically you have a reactor vessel down here you have over here is a steel that is the containment and then there is more or less a shell built around that and this steel thing is that it has no penetrations and if something were to happen, uh and you get a lot of steam here try to condense the steam through natural circulation, the air will come in from the outside and then it will circulate upwards like a flute, so that is one design, this is another design of inside up, at the top, you put sprinkler heads and have a water fountain. in a pipe and if steam gets in, you spray cold water to help condense the steam again, the goal is to keep the pressure within the containment limits and this is ice that they keep around the walls at all times.

Blocks of ice and if steam is released, it circulates past these blocks of ice again, condensation. Another thing I point out here is that you will notice that this is a bit cartoonish, but in all these cases the restraint is great, let's say. relative to the size of the reactor and I will come back to that point a little later in the bwrs, but it is a large volume relative to the size of the reactor, this is a picture of a containment, some of them are cylindrical, some of them They are made of reinforced concrete in the shape of a dome, a large, fairly standard and expensive construction.

Sorry, you haven't mentioned at all the fact that there are hydrogen reactors, you know, that prevent Loca from getting rid of the hydrogen Rec combiners, oh there are no, okay, I thought you were going in a different direction from hydrogen, okay the question is about hydrogen recombiners and some of the reactors recognize that hydrogen can be produced, you can recombine it catalytically, you don't need a flame, but I mean, let's say platinum, I don't know what metals they use, but you have oxygen in the air, you have hydrogen, you connect them together, you can get rid of the hydrogen and put it back into the water which is required in all reactors, unless re inerted I think it's a requirement for the license, yes, okay, I'll take your Word, sure maybe it's not in Japan, what do you think maybe not?

I don't know, uh, Generation 3 and these are the most advanced. that they simply come to get power in an accident, the well surrounding the pressure vessel is flooded, whereas during normal operation it is not, but there is the ability to flood, there is the ability that they designed it to get Passive cooling in the core, they don't need to actively circulate it with pumps, although you know they need special provisions for heat removal there, of course, because even if it circulates on its own, it's still heating up, and you saw the containments I think they continue with the passive operations approach , the natural convention and in this type of thing and I suspect they are moving away from spray systems, the ARA design.

I don't have that much information on it, but uh, they decided to include a Coreal Molten Debris Catcher and the general idea is that if things get worse and the fuel is melting, they put a small device on the bottom to spread the fuel and not let him focus on one. place uh and American designs don't have that The French seem to think that's a good idea. I can't go into all that uh but their design doesn't have passive cooling so that's what I know about their design now Advent advanc I think fuka. EV will have an effect on how facilities are built because thinking back I know it would be nice to have actual measurements of these things when they happen, also for POR analysis of what happened throughout the process, not just to find out what is happening . in real time, but being able to measure things when you can't access them.

Know? Do you think it will have an effect on them? I think what I'll summarize the question is, well, we'll focus on do they have an effect on instrumentation and monitoring on the Gen 3 plus, which are the ones that are being built and I'll extend it a little bit to the Gen 3. I think the NRC last week published its initial summary of What Should Be Done About US Reactors in Response to Japan and for existing reactors, monitoring and instrumentation is squarely on the table, now what will the commission decide to do and at what pace. In fact, there is a meeting today about that.

I think that. what we heard last week was the staff recommendation to the commission and today the commission is holding a public meeting to discuss among themselves which of all those recommendations they will undertake and on what kind of timeline and, you know, at this point the industry is you know, let's make sure we understand what we're doing before we attack and, um, at least the NRC president seems to be a little more inclined to attack, so we'll see how that turns out. to get votes to do something now in the uh regarding the three plus the ones that are coming in now.

I don't know enough details about them to know how much instrumentation they have compared to generation three uh, I think I'll talk about uh kushima a little more specifically here when I'm done with bwrs in general, but it's pretty clear that the reactor operators were really struggling to find out what the hell was going on. there, uh, so they didn't have enough now, if what they have is what we have now and what's in New Designs, if we have more to start with, that's still in the unknown pile, uh, you know one thing with that that no I don't know that the Japanese had to do it, but after three years on my island we had all this red type 197 new red 0737 where they had to put a lot more instrumentation, so we knew it well.

I don't know if the Japanese had to do it. I had to do that with the G design. They haven't gone far enough down the road. Well, they certainly haven't yet. And I'm not aware that the Japanese regulator has said that they have to do it yet, but they are certainly looking at that and I mean, right now they are struggling, they have some reactors that are more stable every day but they are still a disaster and maybe they will More importantly, they have the consequences of a terrestrial earthquake. Which Nationwide had had much bigger impacts, so they are working on it step by step and it will run for a long time like a boiling water reactor and I'm getting a little bit closer to this. by difference with a pwr uh because there are many similar characteristics, but basically what you have is again your pressure vessel and the water enters and circulates to the bottom and rises and the difference here is the The reactor has operated at a pressure of the order of 12200 PSI give or take a little bit and at that pressure, when you get halfway 2/3 of the way, the water boils and then you are generating steam inside the reactor vessel and there is I'll talk about other things up here a little later, when it has better displays, but the water circulates and passes through the turbine andwhatever and the capacitor and then it comes back and what that means is uh.

You're taking the core reactor and running it through your turbine system, so there's a certain degree of radioactivity coming from corrosion products and all this other junk, like in energy, which is pretty clean water that goes through. through the turbine. which is kind of a disadvantage, you get a little bit of a temperature hit due to the lower pressure, but on the other hand you don't have the inefficiencies of the secondary circuit, so overall you know they end up with about the same thermal efficiency and our American fleets about 2/3 pwr and 1/3 bwr oh there's something El, let's see, I talked about the first one now, what's probably obvious when you think about it is that if you're boiling there you can't have boric acid because if you boil the acid boric is a solid powder and it will spread on everything and it won't work for a day so this reactor is controlled with control rods and to some extent you can control it a little bit with pumping, now the control rods are boron carbide, which is a solid material when controlled by pumping.

What I mean by this is that if you slow down the pumping and move the refrigerant around, you are still generating heat. you get more vapor which means more empty space, less moderation, so the power tends to go down and conversely if you pump it faster you tend to get a little less empty space and a little more moderation for that you can maneuver within that, but the control rods are, in contrast to the pwrs, the bwr had one supplier for many years, which was General Electric, now General Electric. I don't know if they are owned by Associated by.

I don't understand all the corporate stuff. but Mitsubishi and uh TBA uh, let's see, but the designs that we have now in terms of what's implemented are pretty standard and they and they went through kind of a constant evolution of the reactor designs from bwr 1 to 6 and the vessels. containment, uh, containment designs from Mark 1 to Mark 3i and the reactor is pretty much you have your core. The control bars come at the bottom and have to work well. Let me start the other way around, at the top, the mixture of steam and water droplets comes out and you have a steam separator and a steam dryer and then the steam is removed and goes to the turbine, of course, and the water goes back to fall and there is a kind of interior. a recirculation pump that moves the water, sort of pulls it down and circulates it back up, plus the feed water coming back from the turbine, so you have this little external loop down here, which are No They are huge pipes but they are external.

They have little level in the pressure vessel and of course the reactor core and because you have all this junk up here the control rods have to go in from below and that is pretty standard, well, it's absolutely necessary, steam. separator the bowl is a little bit higher because you have all this other stuff up here uh and the pressure is lower I guess I said most of that uh this is a little bit like a cartoon uh it gives you a little more flavor of and I don't think that adds a lot of new things, so we'll keep driving.

Just some photos. This is the center basket and each of those little squares would contain a fuel assembly. and the top view of the core, it screams, uh, and this is the refueling floor which is sort of up on this level and during normal operation you have this plate over this big well and you see here the head of the canister that is retire in the uh refueling pool and it will rise and move away as you go through the refueling now uh bwr Safety systems these are uh uh We have the three brands and in Japan the reactors that had problems are all Mark and so you have your pressure vessel right here uh and uh kind of a lid over that and this light bulb shaped Gizmo is the main containment, no not the pressure vessel but the main containment, it's made of reinforced concrete and fun things like that, uh and this, the Mark I design, is somewhat similar.

You see primary containment, but this one, well, let me describe how it would work if you get into trouble and you know you start releasing water from the pressure vessel and you start pressurizing. This primary containment, if it gets too high, the vapor and air mixture increases, I'll call it blow down on this thing that's a Taurus. I'll have a photo in a second that will give you a better idea, but grow up. from this dry well to the Taurus which is like a suppression pool, there are bubblers and the steam is released below the surface of the water and it bubbles to condense it and then well, let me leave more details, these other two are similar to that uh, the steam would go down and and you'll see these three through five, those are the bubblers there and in this one the gases would go down and there's some kind of thing above and below and they would bubble through this pool that There's a ring around the pressure vessel .

Now this cartoon shows things a little more clearly. This is kind of a 3D rendering and you can see those little legs coming down on the Taurus and it's like a big donut. All this is seen. like a big light bulb, maybe I wanted to point out a couple of things here, one thing is that this primary containment is relatively small compared to the size of the pressure vessel, remember I mentioned the p uh pwr, primary containment is kind of big and In the BWRs, this big building is not a pressure containment building, I mean, it keeps the weather out and has some degree of integrity, but it is not made to handle any substantial degree of overpressure and that is why in Japan it is go.

Those, oh, let me surprise you with them. The other thing I want to note is that this is where you're refueling here and when you refuel, you lift this cap and take the head off. pressure vessel you put it aside and you start taking fuel in and out, but the fuel storage pool is over here, it's very close to the reactor and it's pretty high up and and uh uh and like that and well and and there's a door to this area from here it can be open or closed and normally during refueling you flood it to the floor level here and then you open the door and you take out the assemblies and you put them here and the fresh fuel is stored here and you move.

Go back in and then reverse the process so those are signs that I think are significant differences in the bwrs, now this is Brown's fairy, a picture of the bull. The reactor head and pressure vessel have no pressure vessel. containment was built yet uh now let's talk about fum fua it's easy for me to say uh and I'll set a little context and then what I think we know uh and I predict that in the end you'll find it unsatisfactory, but Well, initial S and there's the Bakushima Daichi, which are the six reactors where they had real problems and then there was another one, I think it's a four pack called Diini, which is a little further north and which had no problems, but there were six reactors in daichi uh all but the unit four were operating when the events occurred unit four had been shut down for repair uh had been defueled meaning all the fuel had been removed from the core and put into the spent fuel pool and apparently this old bwrs were having problems with what I call the barrel, the Shroud, the biggest thing around the fuel, and they were removing it, they were cutting it into pieces, they took it out and they were going to replace it, so they unloaded everything. thing and it was closed uh event uh on March 11th mid afternoon Japan time, they had a 9.0 earthquake offshore that some say 93, whatever it is, on that stadium design basis it was an 8.2, but because because this is a logarithmic scale which is about a 6X The difference, uh, is not as trivial as it seems, comparing 8.2 with 9, and then, about an hour later, a 14 m tsunami hit the coast, the The design base was 5.7 M and the reactor and equipment were between 10 and 13 above sea level.

What led to that to the F? The first thing that happened is that the earthquake itself basically caused the power grid to go out, I mean across the country, you know, the cables went down, the switching stations disappeared, so they lost their external source of electricity. uh and then the second thing is that the tidal wave came or the tsunami came uh and it came up and it actually ran between the turbine buildings and the reactor buildings in most of these, the number one diesel generators were at a relatively low elevation, so they got flooded by seawater, secondly, it probably made no difference, but the tsunami also wiped out some of their diesel supplies, so after the power was lost, the external diesels started normally, but then they had limited fuel. supply, but then they flooded, so basically they were left with some batteries, so you have this thing, you can't, you have no electricity to circulate the cooling water and you have no instruments, the batteries don't last a long time, they lasted about a day, uh, and you have a real disaster on your hand, so the reactors proceeded to do bad things, uh and W with the loss of coolant, eventually the core got hot, started to overpressurize. and the reactor operators saw this and then at some point they have to make a decision and they don't want the pressure vessel to just burst so they make a deliberate decision to start venting it here to the dry and venting uh At first it comes to the steam, but if the water level goes down, you get a mixture of hydrogen and steam and the problem that arises is, of course, hydrogen and any other gas that is not steam, but most of them, most of the others. the ones that are not condensable and in other words you can run it through a suppression pool but you're not going to condense hydrogen but they still release it into primary containment and that continued to pressurize so they eventually started blowing into the Taurus, now what you know and then the last resort, of course, is this vent line that's supposed to be filtered and released out of the building now, let me, let me go ahead and this is a little bit more step by step about the ya you know, the CL, some liner bursts and then oxidizes, releases hydrogen, partially melts, primary overpressure and vents down, this happens, uh, pretty much what I just talked about, and then this containment vent secondary, this secondary vent containment is part of what I still don't understand because in theory the ventilation, as you saw in the diagram above, should pass from the Taurus through what is supposed to be a hardened ventilation system.

The hardened meaning should withstand this sort of thing through the filters and Outside it's pretty clear that the venting occurred in secondary containment. You know, this big building released steam from hydrogen fission products at some point. Now you know that the ventilation system was not hardened and failed. The ventilation system was fine, but a valve did not open? to the operational operator and they could not open a possibility that the earthquake cracked the primary containment vessel or the seals around it, so the overpressure here continued to leak into the secondary, but they leaked enough hydrogen to some extent.

So finally after that, units 1, two and three had what are strongly believed to be EXP ITIONS of hydrogen. There is an attempt to keep these reactors cool and the Japanese operators started circulating seawater through them, which means that I want to say the reactors are fired even if they weren't before, but they made a deliberate decision to do so, but I've seen some anecdotal accounts that maybe they waited too long to do that, but again, they were having problems with the instrumentation and determining where the water level was or not, whether the core was exposed or not, that was the situation in the units one, two and three, they exploded and as you can see here, you know that the secondary containments exploded, but they don't. a really strong structure, you know, you can see, you know, steel, U type, steel frame type, and then you know there are metal panels, but it's not like it's reinforced concrete, so is it even a containment, no no no? in the sense that you would mean it outside of a container, it's not that it's not meant to hold pressure, it's more to protect everything from the outside, right, uh, and then, those three exploded and they were merging and they were They have very radioactive fission products in many places.

Now I want to talk a little bit about unit four. I guess maybe I should say that units five and six came out relatively unscathed. They were high enough off the ground. they didn't get their local supply the generators weren't compromised so they did fine uh now unit 4 remembers it ran out of fuel it wasn't running so they had a completely different problem uh at this point the refueling pool was flooded and they were working there, this says that the state of the door is unknown. I found out last week in a report that the Japanese sent to the IAEA.

They say the door was open and they were movingthings from one place to another and trying to get there. the cor scream and whatever came out uh and the explosions occurred in secondary containment and blew off the top and side of unit four uh it happened pretty soon that begs the question of is it not working what the hell did it explode what did it explode? exactly the The first assumption is very, let me continue here. Well, the first thought was that due to the low water levels in the pool, the spent fuel storage pool was leaking somewhere, the fuel had been discovered, and the fuel pool was overcrowded. a complete core of very not very old fuel, but the water level dropped and it began to rust.

The fuel and the cladding exploded the same thing that happened in the core of the others, only a little more slowly, uh, and the hydrogen had broken off and and and it sounded good, uh, and that persisted for a few weeks, but then they made a couple of things first, they got a remote controlled submersible device and they sent it with tools around the fuel pool, uh, there's a I have a little two minute video somewhere uh and uh I saw that and the first immediate reaction was no, no melting here you could see the top of the assemblies looked very good in the pool the pool was pretty clear you could see 30 40 50 ft um and what you could see on the top of the fuel assemblies there were some debris, but of course the building exploded on top of it, so the garbage fell out and then they took a water sample that showed much lower concentrations of fission products than you would see.

I guess if there was some fuel rupture, that made us scratch our heads, uh, I say it, but you know everyone around, uh, there was a theory that maybe in that refueling cavity, which It's too high up, they could have stored something worn out. fuel there that had less water on it and maybe fell and melted and the hydrogen exploded. Also this central barrel that they are taking out is physically very, very large, but it has a lot of hollow space, so they had acetylene cylinders around it. to cut it using blowtorches and perhaps sedimentation cylinders were fired.

The most recent theory from the Japanese is that the hydrogen explosion was a hydrogen explosion, but the hydrogen came from unit 3 because the vents, excuse me, the secondary containment ducts come together for units three and four. and you know, there you know it comes in and does a y and comes out and goes to the site stack, uh, and that's their current theory, which I don't know of anything to disprove. So far, but they don't know for sure either, but that's where they are right now. Other than that on site. We believe there have been problems or there have been problems in spent fuel units one through three. pools that lose some water and become uncovered from overheating, but that's not safe because inside those reactors it's very radioactive and they and they just haven't been able to get there yet and do the inspections, they've had some remote photographs of it.

But if you look at a swimming pool, it looks like a junkyard or something, you just can't see anything. Exactly what happened there remains unknown. They had a common spent fuel pool and dry storage on site, both of which emerged essentially unscathed. I certainly would have expected it to be dry and the pool didn't have any issues, uh, they've had to prop up the pool unit a bit from below due to some cracks. They provide support, but uh, but and uh, so they're handling the situation, they basically poured water into the reactor buildings, you saw the Long.

I reached for the fire hoses and a lot of it was, in the first sea trough, and they were finally able to switch to borated fresh water, but they poured a lot of it in there, which created a water management problem if you keep pouring the water. Of course, water dissolves fission products, so the water was contaminated and some of it leaked into the ocean, but they ended up with a water management problem, the sumps and basements kept filling up and they didn't want to release them. This was due to radioactivity, but they had no other place to put it.

So eventually they took some of the lower concentrations of uh and released them into the ocean and over time they got some portable tanks and now they're processing water. where you pass it through the iron exchange and you get mainly the cesium is the problem, getting the cesium out, they did it after a while, they were able to inert the primary containment to stop the coating oxidation problem and then they got the energy back from view . and power was restored inside the reactors for instrumentation and other things, uh, and they're at the point where they've contained closed-loop cooling restored everywhere, but they still got to this timeline, now it begins to really spread.

They have to contain gas emissions and with cracks or whatever, that will be a challenge. They have hired, I think it is the ARA, someone to come and process all the contaminated water in the sinks. And then D and D will take over. uh years and exactly what d and d mean in this case it's not clear if they will be torn down and buried in a sacrifice zone forever. It's just not known, much more is still unknown than is known about the extent of damaging exactly what was done inside each of the reactors and was it a good thing or a bad thing.

Firm knowledge is likely to take a couple of years, and this long period of time is unsatisfactory for many. people in Washington and elsewhere who would like more immediate answers, but uh, I mentioned earlier Lake Barus, who was a manager in the TMI recovery and is now finding service and advice from uh yman on Fukushima and he calls this the fog of the accident, it's just There you know, the Japanese are too busy trying to stabilize the thing and make sure you know it won't come back to bite them and they're not in Investigations and EXA mode, what's there in the meantime. since it's not coming back to bite them for the moment, and it took two years to get to Three Mile Island and there we have three to four reactors that are compromised, and of course, we have There is a language and culture barrier there, so it will be a while before we know all this.

There are still quite high radiation levels within the units and at the site boundaries. Water processing should help because in most places the problem. This is cesium and it is quite soluble, but they are working on it and they are making progress to get into it. You watch the occasional video and they have little robotic contraptions inside the reactor, but no. terribly instructive, it's a kind of Rolls by Bunches of, you know, pipes and pumps and instruments and, uh, that kind of thing, sir, I don't know if you mentioned it or I missed it, when after the earthquake happened, did they what they did?

The reactors shut themselves down. Did they turn them off? The reactors were immediately shut down. I don't remember if they were turned off manually or automatically. I guess it was probably automatic because they lost their power outlet and you know that happens very quickly, and I'm going to assume that they shut down, so there was no ongoing criticality, but I guess the report never states that they shut down automatically based on the seismometers. . Well, so it was very immediate, so, that's all I had about our people in J Japan and, uh, it's just going to be a story, it's going to go step by step and we'll have to see what the implications are in the U.S. uh here. uh it's been a couple of months.

I had the opportunity to uh myself and a few others sit down with a senior technician from General Electric US general electric and right now they don't have them and I think people in the US do. I don't have construction plans for those reactors, so in the case of the US for the Mark1 containments and that time over the years there were a number of improvements made to them in terms of the downpipes to the Taurus and the ventilation system and uh and other emergency functions, you know, by the direction of the NRC and they have been done here for a long time, we don't know if the Japanese did them or not, we don't know how well they did them, it's just that's all. in the fog and to be determined, you know, if they did a lot of that and then got to where they are, maybe it would put more pressure on the US if they hadn't done all this, maybe less.

I'll see, in your opinion, what the difference would be from this accident scenario if these had been pwrs instead of bwr. I don't know, but I would like to think that the greater volume of the pwr primary containment, that large concrete building with its greater volume would have been better able to absorb the pressure and secondly, if it had had some releases in place of being released to secondary containment which is not much containment, it would be released to a pressure, you know primary containment, which is real containment and contains, you know, a certain degree of not only pressure but also radio nuclei, so which I don't know if I'm not that advanced in the analysis, uh, but I hope that would have been the case, but I don't know. uh Generation 3 plus uh, now there are the two GE companies with uh and as far as I can tell, the Japanese companies are the dominant party in these relationships, uh, again they have gone to three more, same as pwrs efficiency. increases uh have tried to uh uh internalize these recirculation pumps that I mentioned hanging from the outside of the Generation 3 uh and uh and they claim that there are no penetrations into the bottom of the vessel now on the next slide more or less maybe argue with that and then thin motion control rods, remember these guys, uh P bwr turns on and off using control rods and in the previous designs it's some kind of ratchet and the ratchet was too thick for them to move.

You know, one click and all of a sudden they get an increase in reactivity in their reactor and it will go a little further than they wanted, so they made the clicks with smaller, finer gears. I guess that's the best way to put it. the extremely safe bwr uh again the thermal efficiency a noble feature here is that they have natural circulation during operation most of these have natural circulation during accidents and uh cooling pump uh in the primary this is designed to have natural circulation uh gravity flooding in a passive and accident containment, most of the rest of the improvements, I mean in terms of less equipment and margins and all these other things that I mentioned for pwrs, they are doing the same thing, it's uh and this is the uh abwr and uh , this is what I mean, these are the recirculation pumps and well, it's not a pipe, but it still looks like a penetration and a pressure vessel to me, so I'm a little skeptical about that, but the rest is.

Pretty much the same and uh eswr, of course, they don't need the recirculation pumps because it's natural. uh, I'm kind of surprised that this reactor works, but it's far enough along in design and everything that I have to do. I think so, so what do we have here? I'm not going to go over this, at least not right now, and I'd like to mention the next presentation, whatever it is.