Reactors and Fuels & Nuclear Reactors

good morning folks my name's Groff my way over National Lab for 30 years at which time they made me an offer I couldn't refuse so I retired I it miserably so here I am so with that I have to have some boilerplate what I'm going to talk about is first Neutron interactions with matter and reactor control as a backdrop for then talking about nuclear reactors and then go on and talk about nuclear fuels fresh and spent a couple of overview points I'm going to be largely descriptive because there's a lot of territory to cover and so I'm not gonna I'm going to try to avoid theory and try to make it a little bit more intuitive and see if that works secondly you'll see in some of the material I'm going to present this afternoon I'll go through a bunch of slides and then there's backup material and this is basically I had to put fit 10 gallons in a 5-gallon bucket and so these are basically other reactor concepts some of the more obscure ones that just didn't fit I'll leave the material for you to look at and if there's a point of interest maybe we can do something offline here in the next couple of days first interactions and neutrons with matter first need to talk about the concept of a cross-section which is the probability that a neutron will interact with a nucleus it's measured in square centimeters denoted by a lowercase Sigma most cross-sections are on the order of 10 to the minus 24 square centimeters very small range plus of minus 102 early researchers despite that magnitude it was unexpectedly large and as big as a barn and so that name is stuck the unit of 10 to the minus 24 square centimeters is a barn the cross-section is not the measurement of the physical physical cross section of a nucleus it's more the a measure of how stable the nucleus is relative to a nucleus that interacted with the neutron with a neutron and and so it's it's more of a I can't call it thermodynamic but back that kind of a concept how stable is one situation versus another then a reaction rate a macroscopic cross-section is a microscopic cross-section for a particular nucleus multiplied by the number density of that nucleus denoted by a capital Sigma Sigma and when you multiply that by a neutron flux which is what we're talking about here neutrons you get an interaction rate and interactions might be fission's or captures or something like this and I'll talk about that a little bit more here in just a second Neutron flux is the total path length covered by all neutrons going in all directions in a unit volume usually a cubic centimetre and it's a little bit different than I'd call it the engineering definition of flux whereas for example the the flux of water going through a pipe is just the gallons of water going through a surface area in this case the neutrons are going in all sorts of different directions with all sorts of different velocities and so you have to take all that into account irrespective of what the direction is some other definitions many of you may know fissile means a nuclide that can support a self-sustaining nuclear reaction and there are some really obscure ones but the four you see here are the most common and as has been said u-235 is the only one that occurs naturally others in small amounts of curium isotopes and this kind of thing do exist fissionable or feasible the latter is not used very common which is a nuclei that can fission but it can support a self-sustaining nuclear reaction uranium 238 by far the most common example and but it's virtually any actinide given a high enough energy Neutron fertile is a nuclide that can be converted into a fissile material and the ones most often thought about are u-238 which leads to plutonium plutonium-240 leading to plutonium-240 one in thorium 232 which is the sort of alternate fuel cycle not really being pursued very seriously that leads to u-233 is the fissile material now the concept of a chain reaction we start a start up here with a u-235 and a neutron magically appears it's the u-235 nucleus and at fissions and you get a couple of fission products and you get about three neutrons the number is more like 2.7 but you get three neutrons and some different things can happen to these neutrons there's a possibility that a neutron can hit another u-235 atom and costs another fission there's a possibility the neutron over here just goes on out to oblivion doesn't hit much of anything do anything useful or the neutron can be captured by u-238 or other materials for that matter and lead to other Radio isotopes if you get everything balanced properly this this reaction becomes self-sustaining meaning you're produced just enough the right number of neutrons leading hitting another u-235 and so on so you're you're in level flight in terms of a chain reaction it's not ramping up its not ramping down called a self-sustaining nuclear reaction which is of course the kind of thing you want in a nuclear reactor to elaborate on the fission process a bit the neutron comes in all sorts of radiation comes flying out of here you get to fission fission fission fragments easy for me to say and you get in these fission fragments start off normally with a very short-lived isotope of a certain mass number and here the mass numbers are 90 and 143 and they decay down typically to longer and longer and longer lived isotopes eventually you get to something that's stable over here and the mat the the mass number of these doesn't change but the atomic number does change typically through a series of beta decays decaying by kicking out an electron and usually gamma rays a company that also and this is the fission product yield curve and each fission will produce generally one fission product from underneath this hump someplace and one from underneath here and of course the mass for u-235 fission must total 236 the 235 plus the neutron you added to it but you can you can get them on both sides of the hump and with the maximum probabilities being roughly 90 and 143 as you saw in the previous one there is a small amount of so-called ternary fission that occurs and that's when a fission produces three fission products the third fission product will generally be very very light it will be hydrogen tritium helium nucleus something like this the the amount of such visions is very low it's it's it's down in in in this level and probably wouldn't be noticed at all except the tritium is a little bit of a nuisance and it's a not insignificant source of tritium in spent fuel so that's why we've paid a little bit of attention to it in years past now binding energy the mass of the nucleus is composed of a mass of protons and neutrons depending on which you're talking about and the mass of the nucleus is less then the sum of the masses of the free particles and the difference is the energy that holds the nucleus together it's called the binding energy fission products fission produces fission products and neutrons that have less total binding energy meaning energy is released and what you get is this is basically Einstein's equation you get this change in mass gets converted to energy and that's the energy from fission that's what you're after in a nuclear reactor but it results from the change in the in the binding energy and this is a listening of the energy per fission and it comes out most of it as fission product kinetic energy efficient products are very massive they're charged particles so they go just about nowhere you know far less than a centimeter and the energy comes out as heat but then you see other you've got neutrons and instantaneous gammas and all sorts of other things and the net is about 200 roughly MeV per fission is what it's released it varies a little bit depending on the actinide the heavier they act tonight visioning it goes up a little bit maybe approaching 210 but it's it's in that range for anything that's important now I want to start a call I talked about the fission reaction a little bit want to start talking a little bit about some other Neutron reactions first Neutron capture which is the addition of one Neutron to the target nucleus without fission and it can be parasitic or productive here in the lower left is a parasitic a neutron goes into some nuclide you know cesium 137 and you get a compound nucleus which is sort of excited and it stabilizes and you get a beta particle which is a negative electron given off as radiation and then maybe some gamma rays and you end up with cesium 138 in this case a more productive one is the neutron into you 238 which after a couple of beta decays through relatively short-lived materials you end up with plutonium 239 which is a useful fissile material in the inner reactor we can also have other kinds of neutron captures other than just kicking out a gamma ray you can put a neutron in and you can get two or three or in theory even four neutrons come back out you can get charged particles out you can put a neutron in and get a proton out neutron alpha these are lower normally lower probability than n gamma reactions but they're not inconsequential by a long shot most of these reactions tend to require higher energy neutrons and have relatively small cross-sections and there's an exception when capped the capture project is magic and I'll explain about magic a little bit later on I have I have a diagram and a notational thing an absorption cross-section is the sum of all the neutron capture and fission reactions question is the high-energy neutrons same as a fast Neutron yes and we'll get that to that also all right this big diagram up here is the so-called chart of the nuclides the number of nuclear neutrons in a nucleus horizontal the number of protons go vertical in nuclear reactors and what we deal with well one other point you see these sort of light-colored things sort of going up on the diagonal those are stable isotopes and in the nuclear reactor business we deal with the stuff stable and below stable essentially nothing up here which are Neutron deficient nuclides and there when you're dealing in a neutron system you just can't get up there you make those in in accelerators this if you look at the whole thing it's like a three by four chart on the wall it's useful for freaking out what makes what and down here in the lower left you see a little key for various kinds of radioactive decay if you have a parent in an alpha emission you end up down here Neutron emission Negatron decay or beta decay goes to the upper left up in here these are particle reactions in other words assuming the nucleus is hit by a particular kind of a particle whether it be a neutron alpha particle proton gives you the direction and where you end up and you'll see a couple of other incarnations of this as we go on I want to talk about neutrons and neutrons speed and energy and temperature and because neutrons and and people who deal with all rats I pull the wrong trailer back one people who deal with reactors use these sometimes interchangeably but in the in the first bullet up here I've assumed we have a neutron going at 2,200 meters per second and I picked that with malice aforethought and with just a simple conversion you end up with the energy of the neutron in terms of joules now you can take that and just do another conversion and you get it in terms of electron volts and then you can take the jewels and use something called the Boltzmann constant and you can get the equivalent temperature of of the neutron and neutrons are this confuses people I think a lot of the time but we often refer to their neutrons in terms of their temperature normally with paradoxical we don't have hot neutrons but we have cold neutrons and we have you see your thermal neutrons and we'll talk quite a bit about neutrons as we go in but the thermal Neutron means essentially the the neutron energy is in equilibrium at the temperature its surrounding temperature is a simple way to think of it know with the concept of energy Neutron energy this is sort of a typical Neutron spectrum in in a reactor and if I spectrum it's the number of neutrons on the vertical axis as a function of a neutron energy on the horizontal axis now I like this diagram because it well it gets fairly clear and illustrates a number of concepts but the funny thing you've got to note about it is the energy scale is reversed high energy is here and low energy is down here and I'm not sure what point the originator was trying to make but it's sort of backwards so what you've got here is basically this ragged-looking peak is the fission spectrum when u-235 or plutonium 239 fission it gives off a distribution of neutrons that look something like this and then it's the neutrons sort of interact with matter they rattle around a little bit and they start losing energy in their surrounding environment and then you end up with this peak down here and this peak is roughly equivalent to room temperature equivalent to 0.25 electron volts and this is sort of a maxwellian distribution of distribution a statistical distribution around the the existing temperature and the maximum energy up here is on the order of 10 or 15 million electron volts those are the see there's a huge range of Neutron energies now to turn to cross-sections which is where the neutrons are interacting this diagram is done right with hydrant energy on the right and these are the fission cross sections for plutonium 239 and u-235 and you see a number of features here first the cross-sections are essentially at a maximum at very low Neutron energies and drop down if you ignore all the the clutter here it's it's about a 1 over v1 over the Neutron velocity kind of a shape and this is generically the case for most cross-sections and there is a different well for most cross-sections in the middle area here you see a a resonance region where you see all these bumps at certain energies there's a much higher probability that the neutron will interact with the nucleus so you get this spike in in the cross-section value and this is again very typical of most nuclides and then up in the fast area it it just high energy area just tends to sort of tail off like the roughly 1 over V now I said most have this shape you see an exception over here this is uranium 238 fission cross-section remember it's not it's not fissile but it will fission if you get a sufficiently high high-energy Neutron and it looks like it takes off what's that about 1 MeV over there you start to be getting visions in u-238 and a little bit more on the resonances is a resonance is is a big spike in cross-section but if you imagine sort of a uniform energy distribution of neutrons at the energy of the resonance the resonance is so big it just sucks up all the neutrons at that energy and could suck up more if there were neutrons at that energy what that has the effect of doing is it reduces the size of the resonance that's dip in the flux which is the dashed line the the effective size of the resonance is lower not its actual measured value but you have to treat it like that and that can occur either because the resonance is fairly large or you can just have a lot of a particular nuclide in a reactor and the one case you might imagine is uranium-238 where 95% of your fuel or something like that is u-238 so even though it's resonances may not be monstrous you tend to get this kind of an effect the second thing is Doppler broadening resonance data is 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 begins to get shorter and wider and it's sort of like the what is the Hubble redshift kind of a thing the it's um something's moving the the wavelength of light gets gets longer and these things get broader and so the net effect of this is to increase the size of the resonance and I'll make that a little bit more relevant here in a bit not only one to talk about a neutron interaction that doesn't result in any kind of a capture scattering and there are two kinds of scattering there's elastic scattering this is the billiard ball model where you've got a neutron coming in with some some energy it hits a target nucleus and the target nucleus goes one way and the neutron goes another but the energy of the all rats take me back again trying to use this pointer is proving to be a challenge the incident energy of the neutron is conserved over here in other words the sum of these two energies is this incident Neutron energy whereas in inelastic scattering the neutron interacts with the nucleus and the nucleus moves off with with some energy and the neutron does with some energy but it gets the nucleus a little bit excited and it kicks out it says it's a quantum it's it's it's a gamma ray it's a photon and so you end up with these captured gammas being emitted and both processes go on in nuclear reactors and those processes are important because of neutron moderation in a reactor you know there's a 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 go the issue is neutrons are born with energies of many MeV and you want to slow them down to energies of Av and the process of doing so is called Neutron moderation and it occurs by scattering off moderator nuclei through elastic and inelastic processes the criteria for a good moderator is it maximizes neutron scattering and minimizes non-productive neutron capture and probably should list should have a significant density and be able to get a lot of it in one space the maximum Neutron energy loss per collision is proportional to this little term I've written up here which is at a maximum when the atomic number is 1 which is hydrogen and that thing is zero and then it drops I'm sorry it's 1 and then drops to 0.28 412 which is carbon and that pretty much spans width between those two elements you see all the moderators that have been considered and these are the those that well people who have have taken halfway seriously water very popular heavy water is used good moderating ratio and I should say this moderating ratio is not that little term on the previous slide this moderating ratio takes into account the capture cross-sections and the bad stuff also so water has a significant capture cross section even though it has great moderation so it's a little bit low heavy water not quite as good but its cross-section is above zip so it has a very high number helium is very low and the problem there is its density at one atmosphere there's just not enough atoms in any volume so you can do yourself any good even if you took it to a hundred atmospheres or something like that it's still a very low number so helium even though it's used in reactors doesn't moderate much of anything beryllium has been used in some test reactors and graphite has been used in in a number of reactors and may see more use in in the future now I sort of want to take all this and talk about reactor criticality and then reactor control a thermal reactor you've heard them talked about here already it's a reactor in which the neutrons are moderated down to thermal energies down to the EEV range and most visions are caused by these thermal neutrons not by higher energy neutrons and the definition here again Neutron and thermal equilibrium which is the maxwellian distribution at the temperature of their environment now I want to talk a little bit about this this is sort of the the life of a thousand neutrons in a thermal reactor that's what this chart gets to with I could not push avoid pushing the wrong button and so we're going to start up here with a thousand neutrons well the first thing in this reactor is we there's there's some probability u-238 scan efficient for from the fast neutrons and that's that's about four percent or something so you gain yourself forty four neutrons but then the fast neutrons they're whizzing all around and your reactor it is it has a finite size I mean it's got tops inside and some of the neutrons go out and they just keep on going and don't interact inside the reactor again so you just lose them so you lose a hundred and forty-five there and then when you get into this resonance which is also called epithermal range you lose some more there about 43 and the resonance rate in the residence neutron captures in you 32:38 starts to become important and while that will eventually produce plutonium that becomes part of your fuel for the purpose of keeping the reactor going they're just lost to the sits to the system so you lose another hundred and fifty-seven there and Epsom epithermal neutrons get lost in non fuel material like the cladding in there or get captured in water so if you lose a few more but then you gain something because there are some epithermal fission's in u-235 and then coming down to the thermal neutrons some thermal neutrons can leak out of the reactor and some thermal neutrons are absorbed in the fuel but not productively you know they were due to 35 captures neutrons to make you 236 not deficient and so you lose some there and I mentioned the the the temperature effect and there's a little bit less absorption in there because of the fuel temperature is a bit elevated and you get expansion of the core and so it's dimensions change just a tad but then u-235 eventually it comes down to it captures the neutron and you get the roughly 2.7 neutrons well 1.79 net 2.79 come out but you've captured one to make it fission and so you get 441 back so here at a thousand again and that's your chain reaction and that's sort of where you I mean neutrons are going and coming and this kind of thing you'll see over on the far right a lot of obscure greek letters and other letters and this kind of thing back in the old days before when we used slide rules and this kind of stuff it didn't have computers if you multiply all of these various factors together you'll find that it equals 1 and and each one of these factors is associated with a this notation and they used this equation and then went out and measured these various parameters to predict what they needed to do to get a reactor to build critical and have a self-sustaining reaction it's and in the the product of all these is called a key effective the case of effective and it's just the and it's the multiplication factor back in the old days but uh it helps I hope given intuitive feel for what's going on inside this reactor now getting the critical you want to build yourself a reactor well what do you do to make sure it goes critical it's it's not a real easy thing to do first you can increase the concentration of fissile material within limits but you can do that secondly you can decrease parasitic Neutron absorption we select materials with low cross sections and you just simply put less material in the reactor you know you keep the materials as thin as possible and keep the so well you don't you don't lose the neutrons and non-productive captures and you reduce Neutron leakage neutrons leaked from reactor surfaces the bigger a reactor core gets the lower the surface to volume ratio and the lower the fraction neutrons leaked so those are the basic principles used used in in design to getting to critical and I note this this is just a simple conversion to get the power in watts starting with a fission cross-section the mass of fissile material and the neutron flux you just multiply that out because I wanted to use that here in a couple of seconds now I want to move on to reactor control I'll describe reactors later on but at this point I sort of want to talk about okay how do we how do we keep this beast in in control and not have it go crazy on us each fission releases two and a half to three fast neutrons within a very short time a fission is a very quick event the time from one generation of prawn neutrons to the next in a thermal reactor that is the time it takes the neutron to rattle through that number chart that I showed you is on the order of 10 milliseconds now a concept a stable period is the time it takes to increase the Neutron flux and according to that equation you saw in the previous slide the reactor power by a factor of e which is a factor of 2.7 for prompt neutrons which are the neutrons released immediately did it again mmm released immediately in fission the stable period is a fraction of a second very short amount of time with that kind of a power increase in in a fraction of a second that the reactor is uncontrollable the control rods or other control mechanisms you had can't move fast enough to control something and that's it can move left or right in a fraction of a second so you got a real problem here however there are these things called delayed neutrons a fraction of fission products and the fission products resulting from fusion of u-235 or plutonium 239 decayed by omitting neutrons it's instead of beta particles these neutrons are emitted at a somewhat lower energy than the fission spectrum but they are emitted with a with a defined half-life in other words it's just a fission event it's like the decay of cesium or strontium or whatever it has a measurable and defined half-life that is on the order that there's different ones but on the order of seconds to tens of seconds normally and they're there 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 you average it all out takes the stable period up into the range of seconds and basically that's what allows the reactor to be controlled if it weren't for those delayed neutrons we wouldn't have nuclear reactors all we would have is nuclear weapons now we're back to our chart again and this is the neutron drip line up here fission products are being produced and you saw the I showed you the chains before like the the 90 chain and the 143 and they're decaying up in this direction when you get beyond this ragged red line lower than that that's where these neutrons these Neutron emitters delayed Neutron emitters occur and basically some of the fission's produce fission products that have so many neutrons you know the neutrons just sort of fall out of them it doesn't get a chance to go through the beta decay process the one other thing I wanted to point out here is we get to magic and you see these green bars of course and of course this is the number of protons going up this way and this is the number of neutrons at certain what numbers of protons or neutrons the nucleus is much more stable than to the left and to the right of it and it's it's much like in in chemistry you've got your chemical elements and then you know in one place you've got hydrogen you get just a little bit of it put a match in and poof it chemically reacts it burns next over is helium which is right here man and it's totally stable you can't well you can get it to react with something but under such extreme conditions it doesn't make any sense and and that's because that you have a closed in this case shell of electrons in a chemical sense the magic numbers are the same thing in the nuclear sense you have nucleons your protons and neutrons and certain numbers of them make a very stable configuration and so those nuclides tend to be stable and nuclides near them tend to undergo Neutron reacts that make them because it goes to the more stable product and so in some funny places down here you'll see some very high cross sections for n P reactions because it happens to make something that's that has a magic number alright no nuclear reactor control the way you control a reactor is a neutron poison it's a non you know which undergoes non-productive Neutron captures it just sucks up a neutron and doesn't lead to anything beneficial may have probably better call the fission poison but the term used it is a neutron poison and basically you you know you design your reactor so as you lower the amount of Neutron poison in there at some point it becomes critical you lower it that much more and the reactor starts to increase power and you lower it just enough so it's increasing power based on the delayed neutrons that they weren't there thing would just not increase power and so you start increasing the power and you keep going up and up until you're at whatever power level you want out of the reactor then you put just a little bit more poison back and you get into this level flight where you've got a self-sustaining chain reaction at some power level and so that's that's the the overlying concept the neutron poisons that are often used boron silver cadmium indium samarium europium and get a lynnium these let's see these rate in here are used in material let me call engineered materials but they're also produced as fission products and so you need to take that into account but when you're controlling a reactor you put these in some kind of an engineered form and when we get into the reactors I'll talk a little bit more about what those forms are there are also some inherent control mechanism mechanisms increased temperature normally decreases Neutron interaction and can take you subcritical because of Doppler broadening meaning you suck up more neutrons and non-productive neutron captures in u-238 normally which is the big gorilla in a reactor as you might imagine and as I said before the reactor core expands a bit more surface area and you're dealing with with narrow margins here also in in reactors where it's relevant if the coolant boils you have less moderator in there the neutrons are then at higher energy and the cross-sections are smaller so that tends to decrease it so there are some useful feedback effects to keep reactors from you know sort of going crazy on you at least thermal reactors now reactor physics calculations reactor physics science interaction of elementary particles and radiations characteristic of nuclear reactors and what nuclear reactor physics basically basically does is take some of what I've just talked about and actually being able to calculate how a reactor will behave and to design a reactor and like I said in the old days the reactor physics was basically the infinite or and and the effective multiplication factor I mean it was done using those things and little you know tables and numbers and measurements these days everything of course is computers and calculations like that what do we need to know and I'm gonna focus mostly on the neutrons here since that's what makes a reactor go you need to know the neutron flux in and around a reactor core and the reactions of the neutrons and in the fuel and the structural materials to some extent other radiation but most of the other radiation isn't very important it's mostly the neutrons but as a function of space energy direction and time and fellow named Boltzmann developed an equation that does just that it describes the transport from neutral particles meaning it won't work for protons or alpha particles or anything like that but gamma rays and neutrons that's what the equation is for and this is the Boltzmann equation it's it's hairy and there's some explanation of it for for anybody that's a fan and I just wanted to put it up there will not be a test there there is a problem with the Boltzmann equation other than it's complicated but the the problem is it can't be solved in closed form in other words you can't do all those integrals and stuff and get an equation you can just plug some numbers into and calculate the flux as a function of all these things it's just there are just equations like that you can't do it the closed form so what you do is you approximate and the first thing you do is you take your cross-sections and this is what if I got you to 30 you to 35 pays you know total I guess it is but the cross-section itself is a smooth curve and you can see a couple of resonances and you do what's called discretize this code I said meaning instead of having a continuous function you break it into a cross-section at this energy and another value with this energy so you can imagine the table with those number pairs okay I didn't even know I hit a button that time but anyway you do you know you you do this with all of your cross-sections that's that's sort of the beginning of this process then you're faced with with another wouldn't even touching it thank oh okay thanks oh then there's another complication presents itself you know nuclear reactor I think enough you know enough about nuclear reactors at this point is there not a homogeneous medium they've got like rots and they got water over here and they got edges to them and the rods have cladding and fuel and tops and bottoms and so there's a heterogeneity heterogeneity in there that causes a lot of problems in solving the equation and when you couple that with needing to know where the flux is at all these points and as a and in that all those energies get that you saw on the Moldy group cross-section and over as time goes through you end up with the number of points in the billions which is still way beyond current computing power just there's just too many data points so you do you sort of bite it off you know how do you eat an elephant one plate of the time you start with a single fuel rod indicated up here which is and it's in its it's in a little cell and it's a little round rod there's cladding on the outside and some fuel material in there and then there's water and you use numerical methods either with so-called transport methods or Monte Carlo methods along with the multi groups cross sections for the various radionuclides to calculate what's called a many group Neutron flux and many group might be 50 75 energy groups something like that you saw the u-235 and all the little groups in it it's on the order of that number and there's no universally used number it varies and you calculate the Neutron flux in this little cell as a function of energy for those groups it's a static calculation meaning you're not trying to go through time and see what changes happen you're doing it in two dimensions you don't account for the length of the rod and you have only key radio nuclides your u-235 238 some of the cladding things and maybe a few what are called lumped fission products in other words they'll create some artificial radionuclide that has a cross-section representative of a class of real fission products and so you'll have maybe five or ten or something of those and you run these calculations for a number of fuel compositions so now you've got a flux for this little this little cell and you start to build on it these days there it is possible that you may be able to simulate some some subsection of a fuel assembly this is meant to represent a bunch of rods with symmetry boundaries here and we're getting to the point where you may be able to do those transport or Monte Carlo calculations for something on this order where these different pins might not have the same composition and then calculate a flux representative of this chunk but it's still mostly done using the one in the previous the simpler one it which is called a pin so then you start to grow from there you start to put the pin cells in arrays and these each of these may have a different well they will have a different fluxes associated with them a different flux on Neutron spectrum and what you do is you use the Neutron spectrum on each of these to weight the cross-sections and go from 75 or 50 energy groups down to two to five group energy groups for each of these but in the in this calculation again using transporter Monte Carlo methods you represent this this entire assembly that this would be a fuel assembly with up with all these rods and then you go from there and once you calculate a Neutron spectrum from that you go and you you homogenized the entire assembly so you end up with a neutron spectrum in cross-sections relevant to a homogenized assembly that does not have the the rods represented and all the time what you're doing is on one hand your your your dimensions are going up but on the other hand your number of energy groups are going down so you can so the problem remains tractable and then the next thing is you take those cross-section sets for various assemblies at various you know various places in a reactor core and the assemblies would have different compositions and you do a three-dimensional model of the entire core and this now becomes time-dependent you look at how the composition and the flux and everything changes over time as a as a reactor would be operating operating relatively few energy groups no more than five and sometimes less relatively coarse grid because you're representing it on an assembly by assembly basis and you go through its stepwise with with depletion you count for the changes in radionuclide composition and what effect they have on the flux but in this situation you've sufficiently homogenized it so you don't need to use transporter Monte Carlo which are very computer intensive things especially Monte Carlo and there's another approach simplification called diffusion theory and when it's this homogenized you don't have all that all the spatial heterogeneity you can use it and it sort of treats neutrons basically as if they were they were flowing and it's it's it's mathematically much simpler and and it's these 3d codes that are run many times to optimize fuel composition and fuel movement because when you refuel a reactor you'll take some of this fuel out and you'll put fresh fuel in and you may take some of the existing fuel in there and move it around so you get the the power level remains relatively flat and you don't get into safety problems there's a lot of details in that but that's sort of how you go about the the reactor physics thing and get to being able to calculate the composition and figure out what fuel to put in and what you're getting back out I mentioned depletion the depletion calculation uses a uses few group fluxes you weight the cross-sections for many radionuclides to yield the total flux which which is a single value it's not a function of energy and one energy group cross-sections again they are not a function of energy then you put these in a in a you know another computer code to predict the build-up and decay of many radionuclides as a function of time and so what should we be doing here is you would ping-pong back and forth between the 3d calculation and maybe you'd run that three months or something like that and recalculate the the cross-sections and the flux level then go to your depletion and figure out what the new one you know the new composition is then you start with that and you do the next flux moly group cross section then the depletion and you keep going back that and marching through it over time let's see and once you get this kind of information which is the radionuclide concentration you can convert it to all sorts of others that you can calculate gamma ray intensities you can calculate decay heat all of this stuff if you know all of the radionuclides you have in there and their half-lives you're off to the races you don't need the Boltzmann equation for this you sell the so-called Bateman equations and just describes the build-up and decay of radionuclides one energy group it can be solved in closed form for many cases but it's it's a bit tedious to do so in any but the most simple cases so again computer codes are used there and in a closed-form can't be used in all cases because mathematically you can get into positions where a radionuclide produces itself and this example though I want to use I guess you could start out with say neptunium 237 which you can make plutonium 238 239 240 241 which decays to americium-241 which alpha decays to neptunium 237 this happens in it not in the fission products but in the actinides this can happen and mathematically it blows up so you usually use numerical solutions here to the thing in the bottom is the bateman equation and computer codes exists to do this calculation they have four years in calculation for a thousand radionuclides and oh you know fifty time points might take a second or two it's it's just nothing anymore it used to take overnight like we used to do this okay I want to talk a little bit about fast reactor physics and I think the first point we need to get to is this is 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 isn't quite so pronounced and then you see the the fast fast reactor spectrum a fact reactor has no moderator redditor essentially no moderator and so what you've got here is you don't get all these lower energy neutrons you get your your fission peak and then there is some you know elastic and inelastic collisions so the energies do go down somewhat but not nearly as much it's when there's a moderator in there because you're deliberately avoiding materials that moderate well that's the definition of this reactor ramifications of a fast spectrum critical criticality calculations are somewhat simpler because you don't have the thermal reason region and resonances aren't as important the the neutron spectrum even though it gets into the resonance region is sort of tailing off quite a bit by then but on the other hand visions in fissionable nuclides especially uranium 238 of which there is a lot in the reactor are a lot more important second remembering back to the cross section diagram in the 1 over V shape cross-sections at high Neutron energies are quite a bit smaller than the cross sections at low Neutron energies the physical reason is the the neutron doesn't spend as much time around the nucleus because it's going too fast so it's that that's a physical explanation for it what that means because the cross sections lower is you need higher concentrations of fissile materials in these reactors to make them go to get the criticality and the neutron flux is tend to be higher too to compensate for the small cross section if you remember the the reaction equation before the macroscopic cross section and the flux another ramification is there is a higher ratio of fission neutral Neutron induce fission to Neutron absorption for the actinides in this reactor which means on one hand there's fewer losses of neutrons to unproductive captures because they were but because the neutrons tend to cause more efficiency secondly you can convert fertile nuclides like u-238 the fissile nuclides faster than the fissile nuclides are consumed what that means in practice is you have a breeder reactor where if you put in thousand kilograms of plutonium you might get out 1,100 now that's there's no law of physics violated because what you've done is you've converted a whole bunch of u-238 to the plutonium and of course the u-238 isn't there anymore you've just you've just improved the quality of the u-238 quite a bit let's say like with the fast reactor and there's less production of minor actinides which are conventionally neptunium americium and curium now if you'll notice down in here the the red bar is a pressurized water reactor or a thermal reactor and this is the fission to capture ratio and the can I call it purple violet is is in a fast reactor this is a sodium cool fast reactors what the acronym stands for you know it's for u-235 it's about the same u-238 significantly better in the fast reactor but if you look at the neptunium plutonium 240 especially plutonium 242 and in the americium x' which are normally not fissionable in a thermal spectrum are very very little of it in this reactor you get significant visions in it and that's why they've been considered in many cases for the for the transmutation thing can we get rid of all these ACTA Knights and help the repository and this kind of stuff and they invariably look at fast reactors and this is why they're their fissionable remember the definition of fissile is that it can sustain of sustain a chain reaction these things can't sustain a chain reaction a lot like like u-235 can in particular now can I find a set of minor actinides a very specific set of minor actinides that might be able to sustain a chain reaction maybe I can I might be you know if I could get enough here iam in a pile I might be able to do something with it but as a practical matter it's it helps to reactor efficiency but it running a reactor on it is not in the cards I think at this point it's too early for lunch so let's keep on going with the next first I'm going to talk and a little bit in some generalities and then we'll go on and get into some specific reactors sort of what do you need in a nuclear reactor well basically the primary components first you need fuel you need the amount 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 for a number of years and and to get your money's worth out of it so to speak in the form of energy for the second I'm gonna treat fuel is sort of a black box and subsequently I'm going to go into the fuels in more detail then you got to put the fuel into a core that's a tightly packed array of fuel you take a bunch of this stuff and put it into the general what's I mean in math it's like a it's called a right circular cylinder meaning like a can of soup you know it's got flat top and bottom and more or less around its heterogeneous for the most part and you've got fuel in fuel rods that's separated by a coolant and or moderator you know sort of elaborate on either or both there are some reactors Ray mentioned this morning homogeneous reactors where the fuel is dissolved in the coolant and or the moderator they've been looked at in the past some some Amala development done but they're not being seriously pursued at this point but they do exist or have existed an inexistent concept alright no coolant you've got this reactor it's generating a lot of power 3,000 megawatts thermal and you've got to cool the thing and you need a good cooler first no coolant is ideal the kind of things you want is you want a low melting point in other words you don't want to have to worry about keeping your reactor warm to keep the coolant from freezing up on you and then have to reheat it and usually you'd like a relatively high boiling point and that says pointed out this morning if the boiling point isn't high enough then as you go to heat it up the pressure increases which means you just I mean the higher pressure everything's got to be thicker more massive and more more risky to some extent now there are cases if you if you're in a reactor where you want your coolant to boil well that's a little bit different but for the most part I think a high boiling point is good you want a non corrosive so it doesn't eat away all your components want it to have a low Neutron absorption cross-section just like the moderator you want it to be stable at elevated temperatures and radiation in other words not to disintegrate into other things or played out or generally crap up your reactor you'd like it to have low induced reactivity in other words when a neutron hits it makes a capture product you'd like it to not have a lot of gamma rays because eventually you've got to get near this stuff to refuel the reactor well you may have to get in there let me put it that way no reaction with turbine working fluid and what I mean there is if you got a coolant interactor very often the turbine working fluid is usually water and you wouldn't not like to have the coolant in the reactor have a bad reaction with water because even though there in theory you keep them separate there's leaks I mean things happen so high heat capacity and heat transfer coefficient just helps get the heat out to to the turbines low pumping power low costs and ready availability it's a great wish list but the problem is as I said no coolant meets them all favorably the A's and DS are advantages and disadvantages and the EM is sort of medium or Midland if you will these are the the coolants that have been considered some of them we've talked about before in terms being moderators others are coolants we mentioned just a little bit and down here this last line these numbers are a little bit dated but this is the percent of world reactors that use these various coolants and of course the by far winner and this whole thing is light water reactors whether that choice would be made if we were starting from scratch and didn't have the start in like the nuclear Navy that that led us down the path of PWRs and this kind of stuff whether they all make the same choices I again I don't know but that's where we are and I don't see it changing a lot the heavy water is a reactor I'm not going to talk about hardly at all this it's called a a can-do reactor it's it's a water reactor obviously using heavy water and can use natural uranium if you want and there's a number in the world various countries canada's design there are a few carbon dioxide reactors left in the united kingdom these are legacy designs and they're on their way out the some of the contenders here helium mentioned this morning we'll talk about some more about the high-temperature gas-cooled reactor where helium is the coolant there there's a lot of advantages to it I mean in terms of being a nerd the the problem is it's it's not the greatest heat transfer medium in the world and because it's a gas even though the reactor is operates under substantial pressure it takes a lot more energy to move to moving gas around and circulate it and get the heat out than it does a liquid that's just the way engineering is because because it isn't dense enough a another contender in many people's mind is the alkali metals sodium potassium have been used in the past but pretty much the focus is on sodium potassium just doesn't seem to offer very many advantages it's more expensive and has some downsides and so the focus is on fast reactors using sodium as coolants these are some other metal coolants led in business that have been considered the u.s. is as much a fan of them but the russians like them and they do have some of their nuclear Navy and other ships use reactors that are cooled by LED or bismuth or mixtures of the two middle and in-between molten salts we talked a little bit about that they have a lot of attractive properties I should say the sodium-potassium a couple of downs well I'll talk about that a little later let me just keep going okay these others I'm sorry well the question is what's why does a molten salt have it's a molten salt coolant would typically be composed of a mixture of something like lithium and beryllium fluoride and that was it's a chemical compound assault where as the sodium potassium LED bismuth are all metals 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 get into stability problems the organic just isn't sufficiently stable at high temperatures and in a high radiation field so it would break apart in the stuff that would just crap up all the fuel and it just that duck didn't fly so I'm not gonna remember that it's not a simple one well yes but what organics were used yeah and there's an ortho and a para and something else and they use just one of them the question is why is disposal of the coolant you know at shutdown not an issue in the waste issue a number of them these going across the left up through carbon dioxide I mean well basically become a low-level waste and in in the we well helium does it you can probably clean that up and reuse it it's valuable enough in dental the carbon dioxide the two water reactors make tritium and so the water and you're not going to do an isotopic separation on it so you end up having to treat that as a as a low-level waste Meagan's do remove the true some and sodium disposal can and has been a problem and can be a problem I'm just not I'm trying to think of whether any reactor designer has ever had the foresight to look that far ahead and and and I don't think so they I I don't think anybody's ever looked at far ahead and from the standpoint of just simple common sense some of those you could never use I mean not and not in the DMV if where you were ever thinking you might have the envy that bars and well the follow-up here was what are you going to do with a bunch of lead if you couldn't find another reactor operating on lead you're gonna you're gonna make a bunch of lead bars that are contaminated with some other radioactive isotopes and have to manage it as a radioactive waste and make a mixed radioactive waste is you might might imagine and fortunately we won't have to face that I don't think over here and I don't want to think about what the Russians do No No well there are no power reactors operating now I think there's a couple of alcohol test reactors you know the developmental reactors that are you know that are going to lead up to the commercial ones I thought the Japanese had an HDTV Germans but there's no commercial reactors at this point there there was one that operated some years ago the fort st. Vrain reactor in Colorado it was built it was 300 megawatts electric I would call that a demonstration plant didn't operate particularly well I'm not sure whether they did they had aspirations but I'm not sure that they did anyway moving on now moderator for thermal reactors only obviously I've talked about the moderators here already for water-cooled reactors the coolant is the moderator pretty much at least for our water-cooled reactors the can dues Canadian reactors that's not that's not the case they they have sort of a well the Canadians you can't separate the two they've got sort of a static moderator and then a bunch of flowing coolant and you get some moderating from both of them I guess it's the fairest way to say it only other moderator uses expected to be used as graphite at this point looking at helium coolant a future perhaps a molten salt cool and although nobody's chasing that very seriously the density that this is the density of the graphite there's a theoretical density but it's the reactor graphite isn't quite that dense as in dense it's theoretical and the the annealing business maybe a problem if although I think they'll probably be at sufficient temperatures let me elaborate that a bit ray mentioned this morning the the Vigenere energy that builds up through dislocations of the graphite to cover into carbon bonds and can build up rather substantially he mentioned but sort of sort of the dimensional problem but there's another problem and that is that energy can build up and build up is sort of latent or potential energy and if you all of a sudden heat the graphite up somewhat and not a huge amount not like a reactor accident that energy can release all at once and then the graphite can get you know can can start the burn and you can release radionuclides and this kind of thing and that has happened once in one of the reactors in the United Kingdom the Windscale reactor which operated at a fairly low temperature they went through some kind of a temperature excuse there's an the Wegener energy was released and they had a fire and they put some radionuclides up the stack and this kind of thing it's not particularly difficult to avoid in a low temperature situation you just periodically run the reactor temperature up to get the bonds back together without having so much your get in trouble and for the reactors we're talking about they operate at such a high temperature it's not going to build back up they'll just stay in alignment okay major components of a reactor plan you need a pressure vessel for water and gas cooled reactors and I differentiate that and leave out some of the other reactors because for example a sodium cooled reactor the sodium is operating it basically atmospheric pressure so you don't need a pressure vessel you just need a you know basically a closed vessel or or a tank or something like that you need cooler pumps or compressors depending on what you're going to move around you need heat exchangers for some for some reactor types you need your turbine generator that turbine spins when the working fluid hits it and then spins the generator which makes your electricity no you need a condenser or cooler and in cooling towers you have to remove the low-grade heat to complete the thermodynamic cycle all interconnected piping you've got to have waste processing in the plant you need some kind of a water pool to store spent fuel let's just come out of the reactor and you need all sorts of labs and shops and other things to handle mildly radioactive items talk a little bit about some of these cooling towers these this shows two cooling cooling tower concepts on the left's the so-called wet or evaporative where basically that the hot water comes in and it gets sprayed and has direct contact with the air and sort of evaporative cooling it's the way that works and your cool water comes out and this tower design is its natural circulation and the other one is a closed system where the hot water comes in the cool comes out and there's no direct contact between the cooling air and the water it's all conduction through pipes and fins and radiators and that kind of stuff generally these have to have fans in them to get enough air velocity and cooling without the evaporation effect both cool types of cooling towers exist in general in commerce for the for the most part in in in reactors they use the one on the left evaporative now one other point the these are shown as the hyperbolic designs and I suspect most of you have at least seen pictures if not in fact you're driving down the road and you see simply huge hyperbolic towers a couple of hundred feet tall or or more a hyperbolic Tyler doesn't equal the presence of a nuclear plant in a nuclear plant cooling tower doesn't necessarily have to be hyperbolic a number of the plants of course are there on a river there on an ocean they don't need a tower at all they just have a have a direct cooling loop but cooling tower designs especially the dry type well I guess both types also can be in the form of sort of a bank of cooling I don't want to call them towers but cooling modules that might be 30 feet tall and in the whole raft of it might be a hundred 150 200 feet long and it can be fairly close to the ground and given how close you can get to a nuclear plant for example you might not even be able to see them because they have a low enough profile so there's yeah I know down where I lived there's a you know there's some gas plants down there that that use hyperbolic towers neither just found three pictures of it the one on the left lower left is from someplace in Europe somebody it's somebody did a lot of work there okay we got to have some waste processing in this plant when you're dealing with radioactive materials even though the you know the fuels in the in the pressure vessel you still got some waste processing issues first liquid waste processing invariably you lose some water out of this system there can be leaks and other things and your half you need make-up water in addition corrosion control is a major issue and so you have to control the water chemistry very carefully and that means not only the like the pH and this kind of stuff but inevitably you know some of the rods are going to leak a little bit of something you've got all these neutrons in the core some make activation products and in metals and the metals corrode so they dissolve so you get radioactivity moving around in your cooling water and it gets in odd places and piping and pumps and can make maintenance a headache so you try to keep the water fairly clean use processes like ion exchange or reverse osmosis to purify the water and concentrate the the stuff you don't want maybe evaporate it further to concentrate the dissolved species the water of course gets recycled back into the reactor but eventually the concentrate would be stabilized by grouting it or in some kind of an absorptive medium and you put it in the barrel and it becomes a low-level waste for disposal and all the plants have to do this kind of thing they have various you know various approaches in different plants there's no one standard way to do it gaseous effluent there there is a gaseous effluent nuclear facilities operate on a negative pressure kind of a thing in other words the the higher the radiation level the more negative the pressure and the pressure continues to drop and drop and you do that of course by drawing a vacuum at them from the most the most radioactive part of it and that can contain there's some short-lived isotopes of various gases that that get produced and get released out of the out of the coolant and what you do is you run that through something like a charcoal bed these isotopes tend to be quite short-lived and in the charcoal bed just sort of holds them up for long enough so they decay away and then the resulting gas stream keeps on going through a high efficiency filter and then it goes goes out of stack but eventually the charcoal beds and filters become solid wastes and again they get put in barrels and treated like a low-level waste solid wastes come from the foregoing also there's all sorts of other solid stuff you got lab equipment where you're doing analytical work on your coolant or whatever protective gears all these little funny white sea suits where where they're out there during refueling and doing maintenance failed equipment that's been in contact with radioactive water and eventually you know there's a sort of a steady stream of this stuff it's not a it's not a huge volume but again you you send it to a low-level waste disposal facility in most of the waste forget setting aside spent fuel but most of the waste from reactors is low love a waste that's acceptable for going to one of the operating level of waste disposal facilities now there is a small volume of it that is not it is usually some reactor internals and it's so highly irradiated that it exceeds the limit for these places and so the reactors reactor operators are just holding on to that pending identification of a place to dispose of it and the Department of Energy is working along those lines radiation protection it's primarily I mean accidents inside radiation protection routinely is primarily an issue from the workers because they're the ones that get up close to this equipment where you've got your corrosion products and this kind of stuff the public's just too far away and kept too far away your radiation sources I mean the reactor itself is emits a lot of radiation during operation but it's sealed up in in a containment building and people don't go in there during operation you've got the trace contamination in the cooling water and like I said places where radionuclides accumulate and in these plants theme they manage worker dose very carefully it's they all have to carry personal meters it's tracked the you know they've got records on all this as to who gets what there's limits on it and if they start getting near them they don't get to go back in radiation zones anymore and the industry has a pretty good record over last couple of decades of continuously reducing worker occupational dopes they've done a good job of it radiation shielding most shielding is concrete or water in these plants sometimes you'll use metals like steel or whatever a space is tight but generally water is pretty cheap and concrete isn't all that bad and they carefully planned maintenance and they limit time increased distance it's the as low as reasonably achievable approach for worker DOS that they plan work activities carefully and you know you don't go in there and have a conversation in one of those zones it's it's planned you know you do the business you get out and a lot of pre-planning terms of you got the right tools you know what you're doing kind of stuff public safety talked about the effluence like the gas stream I'll talk about accidents more later let's see what we've got here this is getting close to the reactor design business and when reactor development it will reactor deployment and reactor development sort of deployment hit a bottom for the late 80s and all through the 90s but talk started in the early 2000s in the Department of Energy started development work on more advanced reactors about that time and came up with this sort of evolution of a nuclear power kind of a chart where you started up with some of these very early designs these were relatively small reactors and had to be viewed as prototypes they didn't operate all that well but you know you got to learn by doing to some extent Magnox is a graphite moderated reactor built by the United Kingdom there are none in this country and they're being shut down in the UK Dresden and a shipping port is an early PWR and Dresden I believe was a BW are small BW are then you got into commercial power where there was enough confidence they started building plans of a number of plans of substantial size of PWRs and bdub yours in this country can do reactors in Canada in a few other countries and then but they had their difficulties there and operating experience I guess I call it mixed but as they went on they learned in some of the later plants of that were built before all building ceased so called generation three were more advanced in that they learned what what the problems were and things started operating a lot better here in terms of the reliability and the online factors and the industry has also had in the last 10-15 years a pretty good record of increasing online availability so these things are I think that fleet average is up at the 90% or low 90% at this point of you know 90 year let's say 90 percent of the year these things are online generating power usually full power in the case of a nuclear plant so there's been a lot of success here and with global climate and whatever there's been a move afoot over the last several years to begin deploying what is the so called generation three plus which are evolutionary designs they're not radically different than these that that are built and operating but they've sharpen their pencil a little bit and they have improved safety features claimed to have improved economics and I'll elaborate on some of the whys and wherefores here probably after lunch but and all of these the AP 681 thousand r pw ours this is a european PWR this is a japanese BWR this is sort of a US beat up you are sort of and then there's the so called generation four which was a lot of the this evolution here was done by industry not so much by the government could because this this was all we weren't really pretty commercial over here you've got generation for what some really advanced designs that are by and large they aren't ready for primetime right now they're still subject of R&D which means they're in Department of Energy's demand domain do e and E and it's supposed to be oh this is all the attributes they think they want to have and some of these are you know in my view let me call it reasonable have some potential the the sodium-cooled fast reactor has has some issues but it's potential and the the high-temperature gas-cooled reactor does some of the other reactor design and I'm going to talk more about a little bit about those this afternoon some of the other reactor designs are well I'm skeptical to say the least there's a reactor it's a gas cooled fast reactor and I think they're gonna have problems getting that reactor safe enough there's just so little in the core if they get a little bit of a transient there's not tons of water or tons of sodium or tons of graphite to to help moderate that's the wrong I don't want to use moderate here to help control and any any excursions it's just basically a bunch of metal clad fuel rods and a bunch of helium and that just isn't a recipe for stability and there's a supercritical water reactor which ought to operates it's extremely high pressures it is a water reactor but a supercritical fluid it's it's not liquid and it's not gas but it's both it's it's it's strange stuff and it's hard to explain and it has very different behavior and it's been proposed because you can operate it at very high temperatures but it's got a lot of issues in terms of controllability and corrosion that matter really high temperature water is sort of corrosive but there's a number of those and I think I think all of them I think I have little cartoons maybe in the backup slides this afternoon question was on small modular reactors I'll talk some about those this afternoon - okay well the molten salt reactor that is is being bandied about is a molten salt cooled graphite moderated system and one of those well it has a number of advantages the the the online refueling a number of safety advantages if you're in that kind of a system you don't have any cladding to disrupt and one of those reactors was built a small demonstration plant at Oak Ridge and and the safety system is basically does everybody remember what a freeze plug is used to have them in your radiator blocks so when it froze in the winter it pop out instead of crack in the block but in the bottom of the reactor there's a couple of plugs and molten salts that are kept frozen by active cooling if the reactor starts to go out of control we get to cut the power or the heat supersedes it the plugs melt and they drain in the critically safe naturally convective convectively cooled drain tanks and it operates at a very high temperature so you get your you get you get your thermal efficiency advantages now the the downsides of it at the time the demonstration plant was built there was a program wanting to go to bigger scale but what you've got is this molten salt which is fairly benign in terms of corrosion but you got every fission product in the universe in there and as you might expect one of those fission products started causing a little bit of of cracking in the in the reactor vessel and at the time there was an intense competition between various reactor types - as to who was going to go big-time and who was going to get left behind and that corrosion issue was enough to get the molten salt reactor left behind in favour of the sodium coal fast reactor which is the which gained the most traction at the time now the corrosion problem at least that corrosion problem they had enough enough momentum left to look into it and it turns out fission product tellurium of all things does that and by tweaking the alloy composition they can they can fix that so I've always intellectually sort of liked the reactor but it's just in the u.s. it just doesn't have any traction at this point with hardly anybody I mean it has a few proponents but on the scale of government and whatever that isn't where do is putting its money I had somebody else that I suspect refers to be no no those that was a worldwide you're talking about the worldwide chart no and we in this country we operated the firming plan up near Detroit but that's been long since shot down I got to believe that probably refers at this point to the BN 350 what Russia and and like I say that those numbers are a little bit dated the the Japanese keep trying to start back up the mangia plan but those are sort of those are demonstration level plans possibly you know the question was what's TVA thinking about putting it the old although you see uh Clinch River breeder site TBA is sort of dancing around some kind of a small modular reactor that will be a the one they're looking at it's basically a small pressurized water reactor and I've got I've got a cartoon of that design we'll get into you're in the afternoon I think what's next this is a great place to stop high noon and see you one o'clock now moving on I'm trying to talk a little bit about nuclear power plant thermal cycles or on thermal cycles the most the most common one is the Rankine or steam cycle or basically you've got a heat source no nuclear reactors don't have flames but I sort of like the rest of the diagrams that that heats up water and makes steam and drives a turbine that spins a generator then you have to go on down to the condenser and remove the low-grade heat and you pump it around in a circle this is the Brayton cycle which operates it's for not necessarily gas cooled reactors but it's a gas reactor not steam doesn't condense the working fluid and they'll start over here you got a heat source which is your reactor and you've got pressurized gas you heated up in the reactor and it goes through a gas turbine not unlike what natural gas-fired plants have and spins it and there's a generator in the middle that makes your electricity the gas comes out and we're essentially talking helium here it's the only real game in town for nuclear goes through a recuperator I'll talk it talk about that for a second and the somewhat cooled gas goes to low-grade heat rejection goes back in and on the same axis as your your your turbine is a gas compressor to get the pressure back up to reactor pressures and then it goes through the recuperator and uses the leftover heat that comes out of the turbine and then goes back into the reactor and just keeps going around and this radiator thing is basically your your cooling tower or whatever you have to do reject heat so that's sort of the hope of the future for the helium cooled reactors and then it's it's not a power cycle I guess but some of the reactors are seriously looking at using the reactor heat for processing in other words there's there's no turbine no gas turbine or steam turbine basically the working fluid or the reactor coolant goes out and in a secondary loop you heat up something like maybe a molten salt or whatever just to transfer heat and it goes into a pipeline over to the plant next door that might be petroleum refinery chemical manufacturing somebody that Lee needs a lot of heat and maybe a fair amount of high-grade heat and when I talk about HTG ours I'll elaborate on that just a little bit now reactor designs finally as a framework for this first I'll talk about frame it with the type of moderator or it doesn't have a moderator and then the coolant water moderated reactors I'm gonna essentially focus on light water reactors at this point and not the can do and then graphite moderated reactors gas cooled because I shouldn't have left those in there when I hit I put some of this in backup slides and then I'm moderated which is sodium cooled mainly a little bit on some legacy reactors a couple of those of interest and then a little bit on small modular reactors so that's it's the program here for a while this is the world's most popular reactor type pressurized water reactor and to give you the flow of things this is your reactor vessel some cool pumps I'll say a little bit more about those but the important feature here is the reactor heats up the water which is circulated to a steam generator and then there's a second loop where the steam goes out to the turbine and the generator and gets condensed and and then just comes back in and keeps going out and round in a circle the rest of this I think it's pretty ordinary and we've talked about it but it has this secondary loop is one of the hallmarks of a pressurized water reactor of a cartoon this is the reactor vessel itself you've got coolant pumps you can't see all of them but there's two of them showing back here the the steam generator wants their steam generator and then a pressurizer and to explain that the the water in this primary loop is all liquid water and I think you might have experienced in your home where if the plumbing isn't quite right and somebody slams off a faucet you get the the pipe pipes rattling and it's sort of aggravating and the cure for that is basically you get a plumber in and they in one of the horizontal pipes they put a vertical pipe with a cap that becomes an air pocket and of course the air is compressible and you get rid of that water hammer well that's exactly what this pressurized pressurizer is it's it's got air or a gas space up at the top it's got heaters and by heating it up they make steam and they bring the system up to pressure which is around a couple of thousand psi and and they don't have water hammer problems which can be a real problem with this much power going on a little bit more inside to think the pressure vessel ten to twenty feet in diameter forty to sixty feet tall ten inches thick it's it's carbon steel lined with stainless steel some of the key elements here within the pressure vessel you have a bottom plate that supports the spent fuel with little slots for fuel assemblies you know roughly cylindrical array around the outside it's what is what's called what I used to call a core barrel or a shroud some call the shroud now but that'll get you confused later on and what that does I may have a hard time read know we're here which ones Inlet but the water comes i guess that's in that comes in runs down the outside between the pressure vessel and the core barrel and then turns and moves up through the fuel assemblies and then to the outlet nozzle there's one right there and there's a plate on the top to hold everything down and the control rods that are used in this come in from the top and of course there's there's a lid on it that is it's closed tight when it's operating and for refueling you take that lid off to get your fuel assemblies off and the no one's in this is the inside of a pressure vessel with the lid removed there's an assembly going in or out and number of them in here and you can see some open slots and this is the core barrel going around there cool pumps don't have a horsepower rating on these but they're very large relative to two people and other than that it's a pretty straightforward pump for moving water around except for its size now this is a steam generator it's a so-called u-tube steam generator you see the reactor schematic and the hot water comes up and it goes through tubes up here and then makes a turn and comes back down the other side goes back into the reactor and this is the primary coolant circulation pump and it just goes around and around and up in here on the outside of the tubes water boils and these little gizmos up here are water steam steam separators because the boiling will in train water droplets and you want to knock those out and have a half pure steam without any water droplets going out to your turbine and this is a photograph of one in life they're pretty good size but reasonably straightforward no PWR control the rods are inserted from the top they in general have three kinds of rods shut down rods which are only used when the reactor criticality wise is it's already shut down but to assure the criticality has ceased and stays east while they're working with it full-length rods that are usually withdrawn but are used to initially shut it down under if you want to do it a little bit more quickly and then there's some part length rods that are not nearly as long as the fuel assembly and that's used to shape the power actually if you're getting the power sort of in a core this large can sometimes begin to oscillate a little bit and you use part length rods to control it in a localized region typically made of an alloy of silver indium and cadmium in just in in a long rod about the size of a fuel rod now for routine control in this reactor you don't use control rods you vary the concentration of dissolved boric acid in the coolant remember boron was one of our Neutron poisons in some earlier table and you vary the concentration of it - initially it's it's pretty high because you've got some fresh fuel in there so you got a lot of u-235 so you'll have fairly concentrated you know maybe 500,000 ppm and then as the reactor operates you use an ion exchanger to slowly remove the boric acid and as the ability of the fuel to support fission's goes down you take the poison out so you maintain your criticality and it's you know it's it's very uniform it's very stable and is his work well in the Peet of yours word of nomenclature called a scram which is an emergency emergency shutdown of a reactor if any one of a number of events happen either it happens automatically or it can be done manually by the operators and basically that means driving the rods in within a one or two second period into the reactor and shutting it down immediately even though there's boric acid in there it's and any number of things can can cause this kind of thing there can be in plant or safety issues and it can be something as simple as a thunderstorm knocked out some big switchyard down there and all of a sudden there's no place for the electricity to go and you can't keep running the reactor with nothing without a place for it to go so it shuts itself down pretty quickly so they're they're not they're not daily events but they're certainly not uncommon events either oh and a story associated with that the the source or of the word scram has has been widely debated and never decided there's a couple of theories one is those of you you might remember the first nuclear reactor was the the graphite pile of the Chicago pile under Stagg field in Chicago where they put some natural uranium in it and withdrew some rods and they got a very low-level criticality that was the first nuclear reactor well at the time the physicists there Fermi and others they I mean this was uncharted territory and they didn't know what the thing was going to do so they had poison rods and elegantly enough they withdrew some of these emergency rods and tied them in the out position with a rope and it's it's alleged that they put some guy up on the top with an axe and said if we give you the signal you chop the rope and drop the rod in to shut it down and that's the safety control rod Axman that's that's one story the other story is if if you go back to that same time period which is the you know the early to mid 40s scram was a pretty common word you know in in conversation you know scram get out of here and that kind of stuff so and and then it then it meant you know if we have an emergency scram get out of Dodge so the truth is not known these reactors unknown I didn't actually tumble into this too a year year-and-a-half ago but over the last number of years for the existing reactor fleet there's been with what's called power up rating which is they take an existing nuclear plant and by making various changes in it they they get more power out of the same reactor now these activities they have to conceive of them they got to go to the NRC and get a change in their license conditions so they're looked at but what they've got is just because we know cross-sections better we have better computation improved reactor physics and heat transfer predictions over just the old correlations they got about a 2% in increase in power and then improved instrumentation in other words being able to monitor more accurately what is actually happening in the reactor which lets them run closer to the margin on the fuel two to seven percent and then during during outages and whatever they've gone back in and installed better major equipments more efficient pumps more efficient steam generators and and gotten anywhere from seven to twenty percent depending on the plant and net across the the fleet and the u.s. fleet is 104 power reactors now they've gotten the equivalent of five new reactors without building a reactor which I found sort of astounding but nevertheless oh well I'm here I want to talk about a Russian version on a pressurized water reactor there is not much different I'm not a lot different about it call it V BER and I'm not even gonna try to go where what what the Russian is but it's their pressurized water reactor the assemblies are sort of a little different configuration but conceptually the same for reasons I never figured out it has a horizontal steam generator and why you would you want to generate steam and something that's a long vessel and not real high as eluded me but nevertheless that's what they do this is a relatively current design it does have a full containment you know around the outside and and in meets more or less international standards for these kind of reactors and we'll get the one that sort of doesn't here in a little bit now I've sort of talked about generation 3 our existing fleet a little bit you remember the generation 3 plus which is are the ones that are being marketed and and and billed at this point an AP 1000 is being built down at a volatile plant in South Carolina I think it is Georgia you're right and there's a Westinghouse design which is their ap 601 thousand and that's the roughly the electric output of them AP is supposed to stand for advanced passive and a little bit more about that in a second areevo which is the French vendor has a what they call a u.s. European pressurized water reactor that they're working to get licensed and Mitsubishi has a pressurized water reactor design and I think various US utilities are considering all of these but you can sort of debate how serious it is and within cases some of them the one that's going ahead like it said is in heat P 1000 now one of the things they've done in generation 3 plus is basically they've been able to sort of redesign the thing so they don't have as many so much equipment in it fewer bowels fewer pumps it's less to go wrong it doesn't cost you as much at the outset and the less equipment allows building-sized to be shrunk which means you don't have to pour as much concrete and this is the ap1000 sort of the change in the footprint from there generation 3 to the generation 3 plus and of course always comes down to trying to save save capital dollars and increases in in thermal efficiency and this is sort of due to a lot of the same effects that they've tried to do in the generation 3 plus except I'm sorry generation 3 except in generation 3 they had to do it buyback fit whereas here they can do it by design and put it in at the start which usually works a little bit better Oh rats take me back one and enabling the three plus improvements design standardization across these reactors the generation three plants every one of them just about it's a little bit different you know there's there were three PW our vendors at the time in the country multiple architect engineers which do the balance of plant I mean the turbines and generators and all this so there's enormous variation between them and if you standardize then you tend to learn a lot about improvements share improvements and the whole system seems to go better and they seem to have learned black collection modular construction of components in the factory and then assembly in the field as opposed to all field construction in terms of welding and some big big concrete pieces and a lot of that in and there been efficiency improvements also and for many of the same reasons I listed before in the generation three and the computer aided design has also enabled this now with computers you can do three-dimensional lists and have a whole 3d mock-up of your plan in the computer to make sure it will fit and no exact dimensions of all the components you need what's years ago that just wasn't around I'll talk more about safety approach and the fuels later a little bit about refueling you do some pretty obvious Ling's like you shut down the reactor let it cool off some and then get it below boiling and then lower the pressure to atmospheric you put high concentrations of boron in the water to make sure you don't have a critical criticality issue you remove the head bolts and then the pressure vessel head and the control rods this is a pressure vessel head up here and the the control rods are dangling down here as as they draw them all then you have you removed the upper internals there's plate setting on top of the fuel and so you can access the fuel assemblies themselves then you flood the refueling pool I think I have a picture of that so I'll hold that in abeyance and then you begin removing spent fuel and inserting fresh fuel and that's basically done with more or less a a crane with it with a hook on it and the fuel has little handles on the top and you just lift it up and move it out and while the refueling is going on and over on the right you see the looking down into the core and the refueling pool it's not just refueling you use the opportunity for shutdown to do all sorts of maintenance it's it's a just a frantic scramble to get all this done because every day 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 a little bit more about how this goes on you see the reactor here and the head and control rod drives have been removed and and normally this entire area up up in here is dry it's just a big pit and they usually put some kind of a lid here so if things don't go into it but during refueling after you get the lid off you you flood this entire area here up to essentially floor level and it provides more radiation shielding but then what you do is you take an assembly out and you move it over here and set it down and then this little gizmo turns the assembly on its side lays it from vertical to horizontal and it goes through a little tunnel out into the spent fuel pool which is you know just a big swimming pool where you're gonna store it and let the decay heat go away and then you get it by the handle and drag it up right and just put it in iraq and there it says you'll see later the BW RS are a little bit different than that and maybe in some in some important ways but that's how refuelling basically proceeds with these things Oh after refueling basically you just reverse the process of putting it back together the average refueling outage is on the neighborhood what I found was 38 to 42 days the generation 3 plus reactors are shooting for half of this trying to get another a couple of weeks of operation and in each refuelling 22 to 33 percent of the core is replaced during each refueling outage 33 is probably more of a historical number and now more and more the reactors going to be more at the 20% because they're leaving the fuel in longer and burning it up more so less has to come home ok talk a little bit about some nuclear accidents here a nuclear reactor is very concentrated and in a in a leader which is like a court you're generating 50 to 100 kilowatts of thermal power that's a fairly fair amount of energy in a local place so you got to keep removing the heat even if you shut down the reactor just scram it instantaneous you're still generating heat at about a 6% rate which is a couple hundred megawatts for a large reactor that ramps away at about ten percent per day in the short term which is in an accident scenario you're talking about the short term this is sort of a let me call it a prototypical kind of a reactor accident that that is considered it's basically someplace the primary coolant loop is breached and coolant water escapes you know with it depressurizes it flashes to steam the reactor is presumed to be scrammed immediately so you get down to your six percent but it's still a lot of power and at that point the fuel surface can dry out and begin to heat the surface of the fuel cladding at about 2,200 degrees Fahrenheit you ever take a little bit the cladding begins to fail and I in in Zircaloy cladding Zircaloy is pyrophoric so you get it to a certain temperature it begins to not so much burn with oxygen but more react with water and certain sarcone IAM goes to zirconium oxide with the other product being our delightful friend hydrogen now which I suspect you've heard more you want about in the last couple of months but then if that starts to happen you've breached the cladding so fission products can get out you've got a fire kind of a situation going on which provides a driving force to volatilize and move them around and even though these are in containment secondary containment sand this kind of thing if you over pressurize it radionuclides can essentially escape now that's sort of a rough you know the typical concept of a reactor accident now you know sort of what do you do about it well the first obvious thing is keep the core wet I've got a colleague named Lake Verret who's been active in the Fukushima situation and he says a wet core is a happy core and if you if you keep it wet and maybe as a corollary you can get the heat out of the you know the water that's in there not real bad things will happen at least safety or health impact wise you know you might mess up your reactor real good but that's a economic issue if not those things I mentioned a cladding breach cladding fire fuel melt and steam explosions of steam / hygienic hydrogen explosions rule number two see rule number one and what I mean by there is you want to have defense and depth to make sure you can keep the core covered not just you know one mechanism but two or three or four and rule number three is if you can't do those you deal with the consequences now believe it or not this slide is at least half a year old if not a year so it predates our recent events over in Japan which I astounds me but no preventing an accident first you want to eliminate features that facilitate coolant release you'd like not to have pressure of penetrations in the pressure vessel low below the core because if one of those breaches no matter how much water you keep pouring in the top if you got a hole in the bottom of your bucket your your your your in your in difficulty already and make sure you have I have provisions for active cooling in an accident situation secondly you want to detect solutions you want to be able to understand that problems are happening before they can lead to a coolant loss and prevent them and there have been instances you may have read in the papers of like corrosion that haven't gotten to an accident situation but there's been corrosion in some pressure vessels that has gotten way too far along without being detected and the other is if an accident is you need to be able to detect coolant loss early and accurately and in Three Mile Island you might remember some years ago and in some of the Japanese reactors in both cases they were having a lot of difficulty figuring out exactly what is the water level is the quart uncovered or is it not it's just that kind of information and that's that detection which is more instrumentation needs to be coupled with training solutions which is understand the reactor in both normal and off normal situations and when to intervene or not in the Three Mile Island situation they had some instrument readings and they thought they knew what it meant but it meant something else so the actions they took were actually counterproductive for a while until they figured it out because actually they had an insta you know something what you really want to know which is like the water level you know they had indirect or inferential measurements and and so those are all fairly important now controlling an accident going a little bit more into how to do that you need to supply coolant and sustain it cooling and power or essential to doing that you can have all the water in the world if you can't pump it it's not going to work very well power sources of course you've got external which is the the grid that the reactors are connected up to the power grid and they've got emergency diesel generators with diesel supplies and those are tested regularly and they also have some amount of batteries in there but that isn't going to last you for a long time it can help you with some instrumentation but running a reactor coolant pump on batteries is not a winning proposition and what you'll see here is it's sort of a schematic of a of a PWR and they have multiple reactor injection systems these are bori ated water and if you get into trouble and they scram the reactor the first you've got is a high-pressure injection system which you can inject water at you know 1,500 or 2,000 psi right away while the reactor is is depressurizing but I can't get much volume in then as it gets lower down in the hundreds you've got an intermediate pressure and then a low pressure and as you go down each they can move more water in and the the water is in any water that gets out of the reactor is collected in a sump which goes back to these to these pumps so you can keep circulating the water and you try you try to get you have a coolant feature and a cool heat removal feature in there to try to help get the heat out and this is a generalization each each you know different reactor designs have variations on this but this is a very typical kind of a thing containing the release you want to keep releases from the pressure vessel within the bead building what you've got here is you've got your pressure Peschel 10 inches thick made to contain 2200 psi and presumably we've got a problem that it's it's it's leaking water someplace somehow okay and for pressurized water reactors then there is a is the containment building and that's our containment dome they're not all domes reinforced concrete enough volume to handle pressure and design features to reduce pressure and I've listed a few here and they're not standardized but what you want to do is basically if you're if you're venting outside of the pressure vessel in the primary loop you want to try to keep it in this big concrete building so it doesn't get hold into the environment and that kind of thing and and so I'll say a little bit more about these containment buildings and the last resort if your containment building can't hold it can't hold what's going into it which which means it's in danger of being over pressurized there are there is a filtered venting outside in other words you open a valve and it goes to an off gas processing system to like remove iodine on this kind of thing and then you vent the gas to the outside to alleviate the pressure now for a PWR these are some examples of of containment buildings they're the the current designs are passive this one is basically you've got a you've got the reactor vessel down here you've got up around here is a steel that's the that's the containment and then there's more and the the and you get a lot of steam in here you try to condense the steam by natural circulation air will come in outside of it and then circulate up sort of like a flue so that's one design this is another design inside up in the top you put spray heads and you have a water source in a pipe and if Steen gets in there you said you spray cool water to help condense the steam again the object is to keep the pressure within the limits of the containment and this one is an ice they maintained at all times sort of around the walls big blocks of ice and if steam release comes it's circulated up past these blocks of ice again the condensation one other thing I point out here is you you'll notice this is sort of cartoonish but in all these cases the containment is is large ice a relative to the size of the reactor and I'll come back to that point a little bit later in the BW RS but it's it's a it's 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 are dome shape reinforced concrete pretty standard and expensive big construction oh okay I thought you were going a different hydrogen direction okay the question is about hydrogen recombine errs and some of the reactors recognizing that hydrogen can be produced you can catalytically recombine it you don't need to need a flame but it's I mean I suppose platinum I don't know what metals they use but you've got oxygen in the air you got hydrogen you're running by each other you can get rid of the hydrogen and put it back into water is it okay I'll take your word for it maybe not in Japan what do you think I don't know the generation 3 plus these are the more advanced ones that they're just coming on for the PWRs in an accident the wells surrounding the pressure vessel is flooded whereas during normal operation it is not but there's the capability to flood that there's the capability they designed it so so as to get passive cooling in the core they don't need to actively circulate it with pumps although you know they they and they do need special provisions for heat removal there of course because even if it circulates itself it's it's still warming up and you saw the containments I think they're continuing the approach of passive operations the the natural convection and this kind of thing and I suspect moving away from the spray systems the arriva design I don't have as much information on it but they decided to include a core catcher for melded debris and the general idea of the areas if worse comes to worse and your fuel is melting they put a little device down at the bottom to sort of spread the fuel out and not let it concentrate in one place and us designs don't have that Frenchy seem to think it's a good idea I I can't parse all that but their design doesn't have passive cooling 'he's that's about what I know about their design no I think that summarize the question is well what will Fukushima have in effect on instrumentation and monitoring in the gen 3 plus which are the ones that are being built and I'll extend that a little bit to the to the gen 3 I think the the NRC last week came out with their initial digest of what should be done at u.s. reactors in response to Japan and for the existing reactors monitoring and instrumentation is squarely on the table now what the Commission will decide to do at what pace actually there's a meeting today on 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 amongst themselves which of all those recommendations they will undertake on what kind of a schedule and you know at this point industry sort of you know let's make sure we understand what we're doing before we charge off and at least the chairman of the NRC seems to be maybe a little bit more inclined to charge off so we'll see how it turns out he's got to get votes to do something now in in the with respect to the three plus the ones that are going in now I'm oh I don't know enough detail on those know how much instrumentation they have as a compared to the generation 3 I think it's I'll talk about Fukushima a little bit more specifically here when I when I get through BW ARS in general but it's pretty clear that the reactor operators were really struggling to figure out what the heck was going on in there so they didn't have enough now whether what they have is what we have now and and what's in new designs whether we have more to start with that's still in the unknown pile they haven't gotten far enough down the road well certainly they haven't done it yet and I'm not aware that the Japanese regulator has said that they have to do it yet but they're certainly looking at that and I mean right now they're there they're struggling they got some reactors that are more stable every day but still a mess and maybe more importantly they've got the aftermath of an earthquake which nationwide had had the much greater impact and so they're working through it about sort of a step at a time you know we're going on for a long time a boiling water reactor in and I'm do a little bit approach this by difference with a PWR because there's a lot of similar features but basically what you've got is again your pressure vessel and the water comes in and in the circulation to the bottom goes up through and the difference here is the reactor is operated at a pressure on the order of 1,200 psi give or take a little bit and if that pressure when you get half two-thirds of the way up the water boils and so you're making steam inside the reactor vessel and there's other things up here I'll talk about in a little bit later when I got some better exhibits but the water circulates out and it goes through your turbine and whatever in condense there and then comes back in and what what that means is you're taking reactor from the core and running it through your turbine systems so there's some degree of radioactivity out there from the corrosion products and all this other junk where as in the PWR that's fairly clean water that goes through the turbine which is sort of a downside you take a bit of a temperature hit because of the lower pressure but on the other hand you don't have the inefficiencies of the secondary loop so on balance you know they they end up about with about the same thermal efficiency and our u.s. fleets about two-thirds PWR and one-third BWR let's see talked about the first one now what's probably obvious when you think about it is if you're boiling in there you can't have any boric acid because if you boil the boric acid is a solid powder and it's gonna played out over everything and you wouldn't operate for a day so this reactor is controlled with control rods and and to some extent you can control it a little bit with pumping it's not the control rods a boron carbide which is a solid material by controlling it by pumping what I mean by that is if you slow down the pumping and moving the coolant through you're still generating heat you get more steam which means more void space less moderation so power tends to drop back down and conversely if you pump it faster you tend to get a little bit less void space and a little bit more moderation so you can maneuver within that but the control rods are it in contrast to PWRs the BWR had one vendor for many many years which was General Electric General Electric's now I don't know whether they're owned by Associated by I don't understand all the corporate stuff but Mitsubishi and Toshiba let's see but the designs we have right now in terms of what's deployed are fairly standard and they and they went through sort of a steady steady evolution of reactor designs from BW r126 and containment vessels containment designs from Mark one to mark three and the the reactor is pretty much you've got your core the control rods come in the bottom on this and they have to do well let me start the other way around up at the top of the mixture of steam and water droplets comes off and you've got a steam separator and a steam dryer and then the steam is taken off and it goes to the turbine of course and the water drops back down and there's a sort of an internal you see a recirculation pump that that moves the water sort of pulls it on down and circulates it back up in addition to the to the feed water coming back in from the turbine so you've got this external little external loop down here they aren't huge pipes but they are external they are low on the on the pressure vessel and your of course your reactor core and because you got all this junk up here the control rods have to come in from the bottom and that's it's pretty standard well it's absolutely necessary ah steam separator the vessels a bit taller because you got always all this other stuff up here and the pressure is lower I guess I said most of that this is a little bit of a cartoon you see a little bit more of a flavour of it and I don't think I don't think it adds a lot new so we'll keep motoring just some pictures of it this is the core about core basket and each one of those little squares would contain a fuel assembly in the top view of the core and this is the refueling floor which is sort of up at this level and during normal operation you've got this this plate over this big well and you see here that the vessel head being removed in the refuelling pool and it'll be lift up and sort of set aside as you go through refueling now BWR safety systems these are we've got the three marks and in Japan the reactors that have trouble are all mark ones and so you've got your pressure vessel right here and sort of a lid over that and this light bulb shaped gizmo is the primary containment not not the pressure vessel but the primary containment it's made out of reinforced concrete and fun stuff like that and this the mark 2 design is is sort of similar you see the primary containment but this one well let me describe how this one would work if you get into trouble and you know you know you start releasing water from the pressure vessel you start to pressurize this primary containment if that gets too high the the steam air mixture gets I'll call it blown down into this thing which is a torus I'll have a picture of it in a second they'll give you a better idea but it grows from there's a dry well down into the torus that's like a suppression pool there's bubblers and the steam is bubble released underneath the surface of the water and bubbles up to condense it and then well let me leave any more detail these other two are similar to that the steam would come down and you see these from three down to five those are the bubblers there and this one the gases would come over and there's sort of an over-under kind of a thing and be bubbled up through this pool which is an annulus around the pressure vessel well this cartoon shows things up a little bit more clearly that this is a sort of a 3d rendition and you can see those little legs coming down in the torus and it's like a big donut this whole thing looks like a big light bulb wanted to maybe point out a couple of things here one thing is this primary containment is relatively small compared to the size of the pressure vessel you remember I mentioned the P P WR the primary containment is this big thing and in the BWR is this big building is is not a pressure containment building I mean it keeps the weather out and has some degree of integrity but it's not made to handle any degree any substantial degree of overpressure and that's why over in Japan you see those now let me surprise you with them the other thing I want to notice is this is sort of where you do refuelling up up in here and when you review your lift this lid off and you take the head off the pressure vessel you set it aside and you start taking fuel out and putting fuel in but the fuel storage pool is over here it is very close to the reactor and it's fairly high up and and so in well and and there's a gate from this area over here that can be open or closed and normally during refueling you flood it up to the floor level here and then you open the gate and you take assemblies out and put them here and the fresh fuel is stored over here and you move it back in and and then reverse the process so those are what I think are significant differences on the BW RS now this is a Browns Ferry a picture of the tourist the vessel head and the reactor pressure pressure vessel doesn't have the containment built yet now let's talk about Commissioner for Cuomo easy for me to say and I'll send a little bit of background and then what I think we know and I predict you at the end you'll find it unsatisfying but okay initial and there's the kusuma Daiichi which are the six reactors where they had real trouble and then there was another I think it's a 4-pack called da eenie which is a little bit further than the North that did not get in trouble but there were six reactors at Daiichi all but unit four were operating when events transpired unit four had been shut down for repair it had been D fuel meaning all the fuel had been removed from the core and put in the spent fuel pool and apparently this vintage BWR as they were having problems with the what I call the Cora barrel the shroud the big thing around the fuel and they were removing that they were cutting it up in pieces and hauling it out and going to replace it and so that's why they offloaded the whole thing and it was shut down the event on the March 11 mid-afternoon Japan time they had a 9.0 offshore quake and some say nine three whatever it's it's in that ballpark design basis was an eight-point-two but because this is a logarithmic scale that's about a 6x difference it's not as trivial as it looks comparing eight point two to nine and then roughly an hour later a 14 meters tsunami came ashore the design basis was five point seven meters and the reactor and equipment were 10 to 13 above sea level so what does that lead to the first thing that happened is the earthquake itself basically caused the electrical grid to go down I mean all over the country you know wires came down switch stations went away so they lost their external source of electricity and then the second thing is the tidal wave King or the tsunami came in and came up and actually ran in between the turbine buildings in the reactor buildings in most of these the diesel generators number one were at a relatively low elevation so they got inundated by sea water secondly with that it probably didn't make any difference but the tsunami also washed away some of their diesel oil supplies so after the electricity was lost the external the diesel started normally but then they had a limited fuel supply but then they got flooded out so they basically had some batteries left and so you've got this this thing you can't you have no electricity to circulate cooling water and you have no instruments that the batteries don't last an awful long time they did last a day or so and you've got a real mess on your hands so the reactors proceeded to do bad things and with the loss of coolant eventually the core heated up heated up it started to over pressurize and and the reactor operators saw this and so at some point they have to make a decision and and they don't want the pressure vessel to just rupture so they make a deliberate decision to start venting it out here into the dry well and the Manning gets to at the start at steam but as it if the water level gets down then you get a mixture of hydrogen and steam and the problem you get there is of course hydrogen and any other gases other than steam but most of them most of the other ones are not condensable in other words you can run it through a suppression pool but you're not going to condense hydrogen but anyway they released it out to the primary containment and that continued to pressurize so they eventually started blowing down into the torus now what you know and then the last resort of course is this this vent line that's supposed to be filtered and released outside the building now for let me let me keep on going and this is a little bit more stepwise about the you know the some cladding bursting and then oxidizing hydrogen release partial melting primary overpressure and inventing down this goes through pretty much what I've just talked about and and then the this event to the secondary containment this vent of the secondary containment is part of what I don't understand yet because in theory the venting as you saw in that previous diagram should go through from the torus through what's supposed to be a hardened vent system hardened meaning should withstand this kind of stuff through the filters and outside it's pretty clear that the venting occurred into the secondary containment you know this this big building releasing steam hydrogen fission products at some point now you know was the vent system not hardened and failed was the vent system okay but that'll didn't get opened to operator and they couldn't open at them another possibility is the earthquake cracked the primary containment vessel and all the seals around it and so the overpressure in here and just kept leaking up into the secondary but they lead to enough hydrogen some ignition source so eventually after that units one two and three all had what they were fairly firmly believed to be hydrogen explosions there's and the course of trying to keep these reactors cool the the Japanese and operators started circulating seawater through them which means the I mean the reactors are shot even if they weren't before but they made a deliberate decision to take the do that but I've seen some anecdotal accounts that maybe they waited a bit too long to do that but again they were having troubles with instrumentation and figuring out where the water level was or not is the core uncovered or not so that was the situation in units 1 2 & 3 they blew up and and you can see here you know the the secondary containment blowing up but it's not a real strong structure you know it's you can see don't wash steel steel kind of a framework and then you know there's there's metal paneling on it but it's not like it's a reinforced concrete anything so not if not in the sense you mean it it's not it's not meant to contain pressure it's more meant to you know protect everything from the outside and and so those three blew up and we're melting and they've got fission products very radioactive inside in in many places oh no I want to talk a little bit about you unit 4 I guess maybe I should say units 5 & 6 came through relatively unscathed they were high enough off the ground high enough up that they did they didn't get their local supply the generators Dinka compromised so they did okay now unit 4 remember that's D fueled it wasn't operating so they got a whole different problem at this point the refueling pool was was flooded and they were working in there this says the gate status is unknown I learned last week and in a report the Japanese sent to the IAEA they say that the gate was open and and they were moving things back and forth and trying to get the the core shroud and whatever and explosions occurred in the secondary containment and blew the top inside out of unit four happened fairly soon on that leads to the question of if it's not operating what the heck blew up what exploded exactly the first supposition very let me move on here okay the first thought was that it was due low water levels in the pool that the spent fuel storage pool was leaking someplace the fuel had come uncovered the fuel pool was crammed handsome I mean a whole Corps of very not very old fuel that the water level gone out down start to oxidize fuel and cladding burst the same thing that happened in the Corps the others just a bit more slowly and that the hydrogen had been evolved didn't when went in and went bang okay and that persisted for some number of weeks but then they got they did a couple of things first they got a submersible device remotely controlled and they sent it tooling around the the fuel pool there's a lot I have a little two minute video someplace and I saw that and first we immediate reaction was no there's no melting here you can see the top of the assemblies it looked very good in the pool the pool was fairly clear you could see 30 40 50 feet and what you could see on top of the fuel assemblies there was some debris but of course the building exploded above it so junk dropped down and then they got a water sample out of it that showed much lower concentrations of fission products than you would expect if there'd been any fuel rupture so that's gotten us to scratching our heads and I say me but you know everybody around there was one theory that maybe up in that refueling cavity which is very high up that they might have stored some spent fuel in there which had less water above it and maybe that came down and melted and hydrogen exploded also this coral barrel there taking out is is physically very large it's got a lot hollow space so they had a little een cylinders around to cut it up isn't using in torches and maybe acetylene cylinders went off the most recent theory from the Japanese is that the hydrogen explosion that it was a hydrogen explosion but the hydrogen came from unit 3 because the ventilation duct port excuse me ductwork from secondary containment unit comes for unit 3 and 4 comes together and you know they're you know sort of comes in and do a why and heads on out and goes to the site stack and that is their current theory which I don't know of anything to refute it so far but they don't know that for sure either but that's where they are on this right now other than that on the site we we believe there has been problems or have been problems in the units 1 through 3 spent fuel pools with losing some water and coming uncovered in overheating but that's not certain because inside of those reactors it's it's very radioactive and they named they just haven't been able to get there yet and do the inspections they've had some remote pictures of it but you look at a pool that looks like a junkyard or something you just can't see anything so exactly what happened there remains a remains unknown they did have both a common spent fuel pool and dry storage on the site both of which came through essentially unscathed I certainly would have expected it for dry and the pool didn't have any problems either they've had the shore up the unit for pool from beneath a little bit because of some cracking provide support but and so they're managing the situation is basically they poured water into reactor buildings you saw the long reach fire hoses and a lot of that was at the first just sea water and eventually they were able to switch over to buried in fresh water but they poured a lot of it in there which led then to a water management problem if you keep pouring the water in of course the water dissolves fission products and you got contaminated water and some of it leaked out into the ocean but eventually they ended up with a water management problem the sumps and the basements just kept filling up they didn't want to release it because of the radioactivity but they had no other place to put it so eventually they took some of the lowest concentrations and did release that to the ocean and with time they got some portable tankage and now they're putting in water processing where you run it through high an exchange and get mainly the cesium is the problem gets the cesium out they did after a bit they were able to inert the primary containment to stop the cladding oxidation issue and then they got site power restored and they restored the power inside the reactors for instrumentation and other things and they're about at the point they've contained a restored closed-loop cooling every place but they still got a this timeline now starts to really stretch out they've got to contain the gaseous releases and with cracks or whatever that will be a challenge they've hired I think it's the Arriva somebody to come in and process all the contaminated water in the sump and then D&D is going to take years and exactly what D&D means in this case is not clear are they going to term down and tune them a sacrifice zone for forever I it's it's just not known still much more unknown than is known about about the extent of damage exactly what was done inside each of the reactors and was that a good thing or was that a bad thing firm knowledge is likely to take a couple of years and this this long time frame is is he's unsatisfying to a lot of people in in Washington and elsewhere who'd like more more immediate answers but uh I mentioned Lake Barrett this before who was a manager in the TMI recovery and is now finding yeoman service and advising on Fukushima and he he calls this the accident fog it's just there you know the Japanese are too busy just trying to stabilize the thing and to make sure you know it doesn't come back to bite them and they're not in the mold of investigations and exactly what's in there as long as it doesn't come back to bite them for the time being and it took two years to get into Three Mile Island and over there we've got three to four reactors that that are compromised and of course we've got a language and a culture barrier over there so it's gonna be a while before we know all this there's still fairly high radiation levels inside the units and at the site boundary water processing should help this because the in most places the problem is is cesium and in which is fairly soluble but they're they're working at that and they're making inroads to get inside you see occasional videos and they have little robotic gizmos going around inside the reactor but they're not terribly instructive it's just sort of rolled by a bunch of you know pipes and pumps and instruments and that kind of thing sir the reactors the reactors shut down immediately I don't remember whether they were manually shut down or automatically shut down I'm gonna guess probably automatic because they lost their electricity outlet and you know that that happens real quick and and I'm going to guess that they did get shut down so there was no ongoing criticality but I guess I never the seismometer okay okay so it was very immediate thing that's all I had on our folks in Japan and it's just going to be a story it's gonna one step at a time and we'll have to see what the implications are in the u.s. here oh it's been a couple of months now I had a chance to I and some others sit down with a senior technical person from General Electric u.s. General Electric and at this point they do not have and I think people in the u.s. do not have as built drawings for those reactors so in the case of the u.s. for the mark one containments and that vintage over the years there were a series of improvements made in them in terms of the downcomers into the torus and the fence system and in other emergency features you know by in an NRC direction and those were been done over here for a long time we don't know whether the Japanese did those or not we don't know how well they did them it's just that's all in the fog and to be determined oh you know if they did a lot of that and then got to where they are it maybe will put more pressure in the US if they hadn't done all these maybe less we'll we'll see Indian what would be the difference from in this accident scenario and these bent feet of yard London behavior I don't know this but I would like to think that the larger volume of the PWRs primary containment that big concrete building with its larger volume would have been better able to absorb the pressure and secondly if you would have had some releases instead of being released to a secondary containment that isn't much containment it would be released to a pressure canal you know the primary containment which is a real containment and contain you know some degree of not only pressure but radionuclides so I don't know that I'm not that far into the analysis but I would hope that would have been the case but I don't know generation 3 plus there's the - now GE kind of companies with and as far as I can tell the the Japanese outfits are the the dominant part of these relationships they've again going on the three plus a lot the same as the PWR so efficiency increases they've tried to internalize these recirculation pumps that I mentioned hung off the outside of the generation 3 and and they they claim no penetrations on the lower part of the vessel no in the next slide or so well maybe quibble with that and then find motion control rods remember these guys Peter BWR starts up and shuts down using control rods and in the earlier designs it's sort of a ratchet kind of a thing and the ratchet was too coarse so they would move it you know want one click and all of a sudden they get a bump and reactivity in their reactor and it go a little bit more than they wanted so they maybe click smaller finer gears I guess it's the best way to say it and the extremely safe BW are again the thermal efficiency a noble feature here is they have natural circulation during operation most of these have natural circulation during accidents and in pump cooling in the primary this is designed to have natural circulation gravity flooding in an accident and passive containment most of the rest of the improvements I mean in terms of less equipment and margins and all this other stuff I mentioned for PW ours they're doing the same thing it's and this is the a BW R and this is what I mean that these are the 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 slightly skeptical that but all the rest of it is is fairly much the same and es BW are of course they don't need the recirculation pumps because it's natural I'm sort of amazed this reactor works but it's far enough along and design and whatever that I gotta believe it does so what have we got here I'm not going to go through these at least not at this point and I'd like to bring up the next presentation whatever

Channel: Vanderbilt University

Views: 530,571

Rating: 4.356688 out of 5

Keywords: vanderbilt university, Nuclear Chemistry

Id: 2Hpq-rU92kw

Length: 166min 50sec (10010 seconds)

Published: Wed Aug 14 2013