Introduction and overview

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Introduction and overview
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Nuclear Reactor Safety
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You are free to use, adapt and copy, distribute and transmit the work or content in adapted or unchanged form for any legal and non-commercial purpose as long as the work is attributed to the author in the manner specified by the author or licensor and the work or content is shared also in adapted form only under the conditions of this license.
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2011
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English

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Problems in nuclear engineering often involve applying knowledge from many disciplines simultaneously in achieving satisfactory solutions. The course will focus on understanding the complete nuclear reactor system including the balance of plant, support systems and resulting interdependencies affecting the overall safety of the plant and regulatory oversight. Both the Seabrook and Pilgrim nuclear plant simulators will be used as part of the educational experience to provide as realistic as possible understanding of nuclear power systems short of being at the reactor.

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the following content is provided under a Creative Commons license your support will help MIT OpenCourseWare continue to offer high quality educational resources for free to make a donation or view additional materials from hundreds of MIT courses visit MIT opencourseware at ocw.mit.edu hello my name is Professor Andrew Keita I am a professor of the practice here at the Massachusetts Institute of Technology in the nuclear science and engineering department what you're about to see is a summary of a course that we are presenting here at MIT on operational reactor safety this course was prepared with a funding grant from the Nuclear Regulatory Commission in the hopes that this material could be used by other universities in teaching more advanced nuclear power engineering but we're going to try to cover in this course the fundamentals and basically review it fundamentals of reactor physics core design heat transfer thermal hydraulics power conversion systems safety but the implications are in the design for safety as well as probabilistic risk assessments one of the key parts of this course once you establish the fundamentals will be a visit to a simulator both pilgrim simulator which is a boiling water reactor and the Seabrook simulator or you'll be able to test your knowledge and learning to see how reactors actually perform we also will also look at some of the more common accidents that nuclear power plants of experience including 3-mile at home that you're and we'll address some key current regulatory questions that are hot topics for the Nuclear Regulatory Commission and the industry we hope that you'll be able to use this material into classrooms or iself study programs and we look forward to presenting this to you thank you good morning and welcome to the new course on operational reactor safety this course was developed with the support Regulatory Commission and the hopes that could be used for other classes and others city's help you better appreciate when nuclear power plants are really like what I'm going to do this morning is go over what we have as a overall agenda and course objectives we're going to try to focus on understanding the complete nuclear reactor system which basically means the core the balance of plant all the support systems that are required for nuclear and the interdependencies of vote of all the systems in terms of how they affect the safety of the plant we'll also touch a little bit on the regulatory oversight and how that functions if you're running a good plant versus what you're running is a bad way the topics that we will specifically cover are listed below now this course is intended for people who already had fundamentals of reactor physics heat transfer thermal hydraulics and can understand many of the many of the important aspects of the technology and what this course is intended to do is bring all those together in the empower plant to be able to appreciate how we related to performance of the system now specifically we're going to be doing reviews pretty fast lectured by lecture a certain fundamentals to make sure that we're all on the same page the topics we'll be covering are reacting physics physics we're going to be reviewing how we made power using the power conversion
systems we'll look at the basic safety systems and functions that are required a nuclear power plant to keep it safe will introduce the concept assessment in terms of not only in terms of design but also in operations and I think the highlight of the course will be simulator exercise we've arranged for you to suffice to go to the secret nuclear power station which is a fertilizer add to the pilgrim nuclear power station which is important happily there within about an hour's drive of MIT and in those exercises and we'll be going to them after to get some of these models under our belts to actually test your knowledge had to gain an appreciation of what goes the controller will also talk about technical specifications which is who may know are the social sort of the rules of the road in terms nuclear power plant operation they
describe specifically what you are allowed and not allowed to do and what your commit to doing in terms of tests and inspections during an operation unless they're going to talk about a very important system what I call a system and that's the safety culture of the plant which in fact determines whether you're on a state like for a nice safe part clearly there are many reactors are all built in the same title in the same technology but some are not better than others and safety culture isn't clear this is a slide that summarizes the overall course objectives and listen by lecture by lecture as as topical areas today we're going to review the overall reactor types that are presently in existence the next lecture we'll be talking about react to physics and then review of reactor kinetics and control will then study feedback effects and completion then we're going to go to the MIT research reactor to do a reactor physics exercises we'll be doing some changes of control rod position to assess feedbacks ref period and you'll get a chance to actually maneuver the reactor which is just down the street then we'll talk about how we remove heat or energy from the reactor in terms of being able to convert the fission process into his then we'll discuss specifically two types of power conversion systems one is the steam cycle which we call great cycle which is a gas line then we'll address safety systems and functions what kinds of safety systems are incorporated in these plants and what their basic functions are we will then look at the safety analysis reports that are typically prepared for reactors and we'll review certain types of accident and transients will have several lectures on the safety of the plant using the safety analysis report as a basis we'll then touch on the probabilistic safety assessment as a tool we're not going to make you PRA experts but we will help you appreciate this tool that is the veil and design and also operations now this lecture which is thirteen which is the integration of safety analysis into operational requirements but I will try to do in this particular lecture mistake all the safety analysis all of our fundamental understandings of the core and how we're going to eat we're going to translate that into what turns out to be operational requirements which are specified in all technical specification which as they said allow you to do certain things to the reactor that allows it to stay within a design basis which then leads us to do interesting questions what is the licensing basis of the nuclear power station versus the design basis the licensing basis is different than the design base we then we'll go to Seabrook and then pilgrim and we'll do various accident scenarios in their plant simulators which are as you know a replica each of those plants and will do loss of coolant accidents with possibly steam line breaks other types of transients for both they me and a beam of your own these exercises will hopefully give you a good appreciation of how operators really respond to accidents as opposed to simple textbook assessment then we're going to look at some significant accidents ours being the Three Mile Island accident we'll talk about what the causes and what were the consequences of what the industry has done to change and also the Chernobyl accident seas are the two dominant publicly recognisable event really cost me somewhat question in terms of the doctor will also study the davis-besse event the most recent being the reactor vessel that degradation which occurred in 2002 quite many many years later after the generality of iodine well then discuss safety culture then we'll talk about what I listed there its new safety challenges basically this is what the Nuclear Regulatory Commission has on their hot list issues that one needs to be able to resolve as please include terrorists is going to spend fuel the pump some question but those those will be very interested because there are current everyday issues with the NRC destruction and then we'll conclude with a summary discussion of what the industry has develop in terms of advanced reactor designs for the near term and a longer term so hopefully this will be an interesting course view and cover a lot of ground a lot of it's going to go pretty fast but I think once you're done with this course you will be well-versed in operational reactor safety now the way this course is going to work is obviously you have to get grades and the grade structure is homework will be 50/50 percent of the grade and I'm scheduling three quizzes but there might only be two and then the final exam if we only have two quizzes we'll just a portion to 60% of most the truth and of course late Homer will receive so now with that as an introduction to the overview of the course I'd like to now spend some time going over what we have in terms of present technology nuclear reactors an objective objective here is to gain a broader understanding of what we have relatively pressurized water reactors more than water reactors and high-temperature gas reactors which are now coming back in terms of interest because of the next generation plan being a high-temperature helium cool dance reactor now to appreciate nuclear you have to understand the nuclear fuel cycle where reactors fit into this mix and going over the nuclear fuel cycle we have several steps now this this slide comes from the NEPA textbook which will be the textbook for the course and you will see homework assignments based on the NIMH technical textbook and at the end of each lecture you'll see some homework assignments posted on the web now typically we're going to be focused on the reactor but there's so many other important steps that need to understand it's broken up into what we classify the front end which is the steps taken from mining of the or exploring and mining of the ore to ultimately making the fuel that goes into the reactor we also have this back end which after the spent fuel is used up in the reactor it is stored possibly reprocessed which we used to do and recycle back into the reactor as you know the French do this the Russians do this and the Japanese are not doing this we from the reprocessing plant comes to high level waste will be disposed as many of you know the current strategy in the United States is a once-through fuel cycle in which the fuel goes right from the reactor to storage and then as spent fuel assemblies to be disposed to cut the current policy is being reconsidered now where we might affect completely new here close to a psychic
all the mining milling and enrichment enrichment issue an important step for light water reactors we have to take 3.7% Romania through 35 war and enrich it to approximately four to five percent for fuel to be used through thermal yeah so this is sort of a big picture view of the nuclear fuel cycle now to to give you some graphics about what each one of these steps are this is the binding obviously some of these mines are deep mines many of them were Sparsit are not necessarily strip lines but open lines where uranium ore is mined it is then milled and ultimately then enriched as a gas that is converted into fuel pallets and pallets go into fuel pins where the fuel tanks are assembled into fuel assemblies which is right here and then the fuel assemblies will play to the reactor and the floor is operated a year 18 months before it has to be refueled and fresh fuel has to be put in typically in these reactors about 1/3 the fuel is taken out replace with fresh Electronics purposes so they've been wrong now this is a picture of some reactors these are called generation to two reactors were built in probably the 70s and 80s and you'll note that Yamaha Canyon is from California Minnesota New York South Carolina Virginia and you'll know here that these are mostly pressurized water reactors and they also note that what's missing in these photographs by the typical cooling towers which are have been used as a symbol for nuclear power I deliberately chose not doing with those because I wanted you to to show you that nuclear plants have containment and reactor power conversion systems which are typically steam turbines these are 20 plants most of these plants are twin on the site necessary has to and these are the locations if nuclear-power starts we start building more nuclear power plants that they'll be building additional plants at existing sites at least and in the intro now one of the key objectives obviously is to make electricity all the safety stuff all this understanding how these plants work is very important but the objective is to make electricity and in order to do that we have to make heat we've got to remove the heat using some kind of a fluid whether it be water or gas we've got to pass this fluid through a turbine that turbine and turning a generator making electricity that's the whole goal of using nuclear power we do it because we don't lose co2 noxious gases and the environment dust particulates it's essentially a clean energy source people are now recognizing now in terms of the removal of the heat lead back to not only take that fluid as possibly you can see here liquid metal didn't mention this but breeders are another doctor that convenience to pay electricity but we want to take this and without a pump this through the core capture the heat of the Division II and then take it into a system that has circulated that coin and whether it's transferred directly to turbines as boiling steam steam from a like a VW R or the steam generators in a PWM pressurized water reactor now we then have to condense the steam and recirculated back either to a steam trailer to go back to the poor now the next slide gives you up with us a simple version of a boiling water reactor schematic now if you look at the reactor core you see that we're going to be allowing boiling to take place in the core we're going to have certain types of systems like steve dryers and separators that will make the steam driver the water that's remaining in the steam since there isn't work and we're going to send that directly to the turbine which is outside containment structure now this react this part of the nuclear plant essentially replaces a fossil namely instead of boiling water by burning gas on two pressure tubes housing this water we're using this reactor to boil the water and send steam directly you notice the turbine is connected to the generator which which determines spins making electricity now once it comes out of the turbine it's a mixture of steam and water which has to be condensed in what we call the condenser it's basically a whole series of tubes that takes water from the environment now whether it's a river lake or ocean and condenses the steam makes it back into the water we come back into the core now this is the simplest type of nuclear power plant and exactly replicates what is done in the fossil time so if you look at this part of the curve this chart everything to the right is in fact what you might see in a conventional fossil pressurized water reactors a little different and we have and I'll get to that a moment but there are many reactor types that we could talk about I just done the boiling water the pressurized water radish we'll get to but we also have a heavy natural uranium penny Waterloo reactors which are developer today we have Russian RBMK reactors which are wood water reactors but they have instead of water as a moderator to use graphite we have fast reactors which which use Olympic medal in the form of sodium or perhaps land and then we have gas-cooled reactors which could use supercritical carbon dioxide or helium and then the last category which after about recently this organic water of almost all reactors so all of these are choices that the engineers and the utilities can make in terms of what they dress the two types that are common in the United States are the pressurized water and the boiling water and we used to have alien pool with gas reactors but they were shut down pretty much in the seventies now when you want to make some heat what we want to do is use the fissioning of uranium atoms or plutonium which is a fissile material to release some approximately 200 million electron volts of energy per fission now as I mentioned earlier we also need to enrich this material from 0.7% found in nature to three four percent maybe up to five percent yes reactors require the richness of the order of up to 20 percent so we need to fabricate the arrangement to pellets which are planets or chromium tubes which are placed into the reactor core
now the process of fission is relatively simple quite well where where you take a neutron it and a certain proper energy uranium-235 pattern and you create several fission fragments and hopefully at least two and a half or so neutrons that can be used to create more efficient and release of these extra excess neutrons allows one to maintain what we call a critical reactor which is self-sustaining with chocolate now the energy that we try to capture this kinetic energy of these fission products the Neutron energies are relatively small contribution to the energy that we can capture from provision problems so this as these things release 70 and on our main release on achievements were trying to capture as heat now again one fission
releases 200 billions of electron bulbs if you want to calculate how much if you vision one gram of uranium 235 he can when you convert it to electricity make 24 thousand kilowatt hours of electricity which is a lot and one gram can essentially like a small city order now to do that same amount make that same amount of power we need 3.2 tons of coal and roughly 13 barrels per board which is obviously so for doing and the energy density of the Iranian Jew in terms of energy divided by mass it's about 28,000 times the energy density of coal this is an important metric because we can using uranium-235 in fact a small amount produce the equivalent of 28,000 times the amount of energy produced at same mass of coal that's why we are so so desirable now you saw some of these slides where pellets go into ends which are then made into a semblance now when you look at this you see these people handling the uranium pellets now uranium in this form is very low in activity because it's rhenium 235 has a very very long half-life so the activity of this uranium 235 is extremely low which can be handled obviously when you put this back into the reactor it's another story because then you fission products produced so when you create this reactor core what you want to do is take the fuel assemblies and configure them into the core in such a way as to allow the number of neutrons created to be sufficient to contain visioning process which is a critical reactor most and what reactive physicists do is figure out how to arrange the fuel in this reactor such that it maintains criticality for 18 so in order to do this you have to understand what's in the reactor physically so we need the Model T radium fuel the reactor internals which are typically metal they have sword neutrons you have to figure out how the flow will affect the reaction rates because remember water becomes a moderator for us and that moderator allows the thermalization they would be slowing down of neutrons to be able to fission in a thermal reactor we then have to then use react to physics tools and develop what we would basically calculate to be the flux distribution that flux is a flux of neutrons that then will be able to create visions that will then we call power distribution and as you might imagine their power distribution is not flat but is it sort of like cosine shaped in the court because we have neutrons that can leak out of the reactor and also at all but this power distribution creates what we would call the heat source that we then have to now to give you a sense of what's in this reactor vessel the water comes in goes down the sides of your reactor and up through the core and as it's heated up and this is for a PWR it will then go to a steam generator above the core we'll see control robots control rods are used in a PWR typically to change power level and also to shut down the reactor these control rods on top so head and a HOD a signal that the back you should shut down they drop into the core by gravity and essentially shut down reaction now this is a picture of a reactor being the fuel you can see there this is under about 40 feet of water and you can see the fuel elements being placed into the reactor or the there's lot of pictures and you can see the blue clothes of the Trenton truck of radiation that fresh fuel assemblies coming out of the reactor would commit now one of the things I think that we need to appreciate in terms of factors in the design or how and what considerations we have to incorporate in the design of this assure safety oh you know these factors are are part of what an analyst would have to go through and think about in terms of is the design that he's constructed a safe design obviously the first thing is the court is done and in the more design you have to really understand their type five you have to be able to as I said a really model of physics of it for and to be able to understand more power distribution because it's so important to have any flatter for power distribution such that the limits are typically based on the peak the highest power distribution anymore which if you can lower the peaks to make a flat power distribution actually enhancing the efficiency of this reactor the drop then you have to figure out once you design with the basic power distribution you have to make sure you have what is called reactivity control and reactivity control affects the rate of the nuclear reaction and be able to assure that you can shut down the plant under all circumstances and the other important part of the reactor core design is safety analysis the objective is having no fuel failures if there are fluids and two you don't have a melon and the requirements and regulatory requirements are such that you have to make sure to demonstrate under wide variety of circumstances and transients including a complete loss and pull an accident that the plan has emergency systems or keeping the poor in a condition cool theses are limited and minor if pendulum and that's why they said certain temperature lives energy the other part is how you want to remove the heat from which opposite is related to the safety analysis now in in this area the most important thing is understanding the heat transfer from the fuel assemblies to the cooler whatever that word is and clearly many different types of fuel assemblies at best as you will see a VW r VW assemblies are different and all the heats have generated that one need to be removed and obviously in the
safety systems you have to decide what kind of an emergency or pulley systems you need to put into the plan to be able to keep the plan within the condition no fuel failure such that you do not have to charge you can find a radioactive if you have an accident that releases radioactivity into which is this permitted you need to be sure that that radioactivity is not released and they can finally really reactivity the function that's performed is the containment and of course we can never forget all of this is done to produce electricity and this is a graphic of a typical reality now I'm going to go over some of the fundamental systems just to commute again an appreciation of what we're talking about and how interrelated the systems are and how important understanding that interrelationship is an overall reactor design we've already talked about the core fuel the reactor vessel control rules this course it's in the middle of the containment now you see a lot of stuff around them you'll see steam generators which are listed here this is the vessel this is the steam generator this is a PWR that makes team that takes team and they send it to the turbine generating this is called over here what we call a balance of plant or secondary side of the plant the primary side which is the reactor to the steam generator let's see a lot of other systems around the plant these other systems are what we call support systems they are aimed at either cleaning the water in the primary system providing separate shutdown cooling functions water chemistry charging and volume control to make up water so the plant is much more complicated than simply the reactor and the steam it's a lot of things that you need in this plan that you need to completely appreciate to be able to stay long running from the side of a safe nuclear power station now this is a schematic of that particular complaint and again why what I hope you will be able to do after this course is over is be able to look at this diet I know it's like an eye chart but look at this diagram and understand how the reactor is linked to the steam generators link to the pressurizer is linked to the main coolant pumps and all of the other support systems that may affect the safety of this particular planet these are basically entered in in interdependent systems that one needs to appreciate such that if there's a failure say in this area the ability safe condition so this a chart you will be familiar with when you finish this course because you'll be able to find the stand a where the water goes the lose that what happens to temperature and what happens to attainment in the event of certain types of accidents everything is controlled in a nuclear power plant under control now I'm just showing you a relatively modern advanced boiling water reactor control where you can see operators the chef supervisor control room operators and a more modern control board that is used to control all of systems that we talked about in this briefing slot now this is the heart of the plant this is where everything is is monitored and actions taken to shut down systems turn on systems and they're all done and these operators the training of each operator and their party my view of a key safety system for this and when we get to the simulation you'll see an older version of this both the Seabrook and built my receiver was started construction in the 70s as and he'll bring came online and believed in that and also in 1972 so you'll see generational issues compared to the now looking over boiling water reactors and then pressurize schematic here we have the artist on scene a simple diagram you've seen the core and what we have is a direct cycle which is steam coming the reactor going to a high pressure turbine the low pressure turbine going to the condenser then they have three heaters and B water heaters then that water is condensed ultimately and sent back in speed water that's how he VW RS have recirculation pumps which take a stream of water from the reactor and pumping through a jet pump to pain and the core flow through the reactor but bottom line this chart at this point in time we'd like you to focus in is it's a direct cycle where the water is a lot of oil in the core steam is dry and separated and then sent to the turbine to follow or a BWR this is a more detailed view of a reactor for pointing out several other functions the feed water from the condenser coming down the vessel and all three or these jet pumps recirculating water and essentially provide an augmented velocity stream that will send a word to report they have steam separators dryers and then at the end of this one the scheme will be fairly dry we'll look at some analysis as we get late now bwr fuel assembly is unique in the sense that because we have oiling going on before the there is needs to be some assurance that every fuel assembly is getting cooling and getting water so the way the welding water reactor designs fuel the fuel heads which are shown here which contain uranium pellets with a spraying the whole pellets in place or down and what we call a gas planet this gas plenum is used to capture the fission products which are gases such that the fuel in does not over pressurize this fuel pin is placed in this array of bundles called the fuel assembly and the bundles are putting
what we call a fuel tank now this fuel can has has is designed such that the water coming through there has another fuel assembly which allows one to be sure sure that water coming in which is water and water as it's boiling here will stay in this regime this is a very important design difference between a PWR and BWR so VW our fuel assemblies are essentially can to make sure that we have an adequate supply we also have different types of control arms if you look at the fuel assembly these are for fuel assemblies but they have our cruciform controller blades which are put in the or in between the fuel assemblies and they have various water rods and tie rods that are meant to assist in the controller back these cruciform rods in a BW are our place in the core during operation BW ours do not have or on in the water such as a PW the boron is used to control the reactivity of the core activity meaning the extent to which the or will go critical instead the BW our fuel assemblies have vertical poisons which are specific with poisons put into the fuel poison in the sense of Neutron absorbers that will be depleted over time are consumed allowing the reactor to maintain certain levels of criticality now these burnable poisons are designed to deal with what we call the excess reactivity which is we're putting in more uranium than we need to allow the reactor drunk and that excess reactivity needs to be balanced by these horrible poisons in addition we put in control blades during operation to control the power distribution in a PWR now this is a relatively bad picture of the pilgrim nuclear power station on Cape Cod Bay or you can see in the inlet and this is now the discharge and this is the reactor this is the power conversion system these pictures are hard to come by these days because of 9/11 now pressurized water reactors excuse me are are are different and this is a schematic of PW and what we notice are the differences are that the water in the reactor vessel is not allowed to board pressure in a BWR is about a thousand pounds which allows the boiling to take place in the court in a PWR the pressure 2,000 pounds which prevents or they to the core now the water again from the main coolant pump des circulated into the core post along with an opportunity or if needed and not allowed to pour into the PWR we also have what is called a pressurized this is sort of a pressure regulating device it maintains the pressure in their system at about 2200 pounds if the pressure is too low they have eaters here that are used to increase the pressure the pressure gets too high that sprays that will condense the bubble and pressure lines so this water then goes into what we call the steam generator and this is the YouTube steam generator where the tune will progress and his transfers its heat like a radiator to a second okay the steam generator basically takes water from four which is again a two twenty two hundred pounds and sensit routes through tubes and transfers the heat from the tube to the other side into which which has the water that is you to make steam so imagine a tool over which water is flowing which is the blue cloth and that water is allowed in the steam generator and then create steam which is then also dry and then to determine and then ultimately to the we pop in you'll also know in the Miss Baker rehab your debts are taking the water or river lake or an ocean or a cooling tower for that matter that would condense the steam work all together if we were to draw this line to the right here this is the secondary part of the plant which every plant with a new fossil or nuclear has to steep what you see also here is a containment wall these steam generators are inside of you and you'll also know in a PWR we have three different cooling systems in the primary the secondary the third system which is the system that actually goes into the so he had one two batteries best compared to a single man beat on you our system again we never forget the generator making electricity so reviewing again primary system low boiling goes into a steam pattern which is thousands and thousands of tubes to which the primary water passes giving its he up to secondary water system boil the steam is paid now in a PWR we have essentially boron to control activity obviously we need to increase the enrichment of the core such that it can run for say 18 months to two years now that enrichment that extra the activity margin is balanced by the inclusion of boron which is a neutron absorber into the port so the as the reactor is consuming the uranium the boron concentration is reduced and these reactors are typically brought on broadly no control so again you look at the schematic we have the containment we have two reactor core cooling pumps going to the steam generator the steam generator pumping steam to the maybe the electricity came back together I'm sorry cooling down then you have various feed water heaters and we'll send the motor back to the and got back to the steam generator and the primary political support in the container is water so the line is the primary side and typically a trickle PWR and this is typically configuration for for Lupita PWR we have about 200 fuel assemblies arrangement in a roughly cylindrical
pattern we have what is called thermal shield and that thermal shield is meant to protect for the after vessel from fast neutrons to keep the embrittlement of the vessel down and the arrangement of the fuel in this in this reactor is the responsibility of the reactor physicists typically it will put a fresh fuel on the outside because that's the most reactive moles to keep the power Peaks down and recycle fuel in sort of the middle way to level eyes the power distribution these are some parameters for roughly a thousand megawatt electric plant talking anywhere between thirty two to thirty megawatts the amount of heat generated in a few about 97% there's some dominating nominal system pressure is 2200 the SI the flooring is 138 lead pounds for power which is a lot of water the inlet temperature is typically 550 or so degrees the outlet the vessel this battery the outlet from the vessel is 620 roughly and the temperature rise average over six degrees the diameter of the core is 11 feet and more height is about 12 feet as a typical standard people and it's about 86,000 pounds or kilograms so the the design of these PWRs is Pal quotes for the Steve science about similar to the reactive or so if you look at a PWR assembly what you'll see is an open grid with the same fuel pins types of little pins and you'll also see that you'll have to introduce in a picture of a control rod run right into the fuel assembly not in between fuel assemblies and these control rods again falling by gravity and to use only really to shut down the reactor in order to make gross power level changes and if you look at a typical grid you can see here typical control control rod locations that are needed now this is a picture of a PWR fire two reactors one big steam turbine wall and cooling towers for each reactors megawatts and these two came and serviced and he twenty-five days that most of the nuclear fleet came in sir the next reactive like to talk about is a gas cooled reactor this is an example of a Ford same brain plant which is a high-temperature gas reactor to operate I guess late eighties early nineties call off this one but it makes their 330 megawatts of power unfortunately it's operating record was very poor and they converted the plant to a gas turbine now the gas turbine gas reactors use what is called a Brayton cycle which is a gas line and it's probably one of the more simple cycles that we have we're alien gas is is blown into the core and the gas coming out or in this case I think it was around 700 degree centigrade much hotter the librarian goes to a high-pressure turbine low pressure turbines add to the power turbine which is then Meg Turney gender so it's a gas turbine reactor core the core gas goes to exactly a gas power turbine which is then needs to be compressed effort has expanded in the German and sent back into the reactor after it's properly so it's a simple cycle or the gastrin and this is helium gas now this circulated through the reactor most right to yester prismatic astronauts danger and helium is the cooler and it is because they go to high temperatures thing they're much higher efficiencies for they 50% range and this is the technology the future now the fuel is also dramatically different than we might see we are it's a ceramic fuel made of tiny microspheres called tri so common fuel particles that were the uranium is an either part urea oxide or carbide surrounded by a forest buffer layer to capture the fission products and then a pyro carbon layer our oolitic carbonate which is hard surrounded by silicon carbide and another and these are the little tiny field particles that go into it are pressed into in the general atomic space a prismatic reactor which is a fuel compact which are then inserted into graphite blocks these graphite blocks are in fact the fuel assemblies about ten of these are stacked high in the core and there's I don't recall exactly how many but these become the fuel assembles refueled in three dimensions which is another interesting challenge another type of high-temperature gas reactors who recall yeah this this technology has been also used in the past originally I think invented in the United States but developed in Germany the Research Institute bro they had helped and operated for over 22 years what a pebble bed reactor is is in fact the same coated particle and there are about 10,000 of these particles graphite pedal and this graphite pedal is about the size of a billiard room and 10,000 coated particles in a graphite pebble that is literally dropped into the center of this reactor and is allowed to drain out slowly as the reactor operates and then is recirculated and put back into the top of the reactor now the pebble bed reactor has the same basic safety features as a high temperature the prismatic reactor the sensitive as a meltdown three core the power density is about and lower than the white water reactor and the fact that graphite is there is a very high heat capacity medium that can absorb a lot of heat and this technology is as I said has been used and is now being developed at China and they have an operating double bed reactor now there's no research reactor and it's being proposed in South Africa and this is one of the two today's the next generation nuclear plant what the technology again this is an online refueling system which basically avoids the need to shut down the reactor but that was a continuously recirculated
the temperatures are quite high again three centigrade the thermal power however is small it's only 200 200 250 megawatts the South African design 400 and the power output electrical power house I'm looking at 40 to 45 percent internal efficiencies ranges from 100 60 megawatts of light and that's one of the disadvantage of teacher reactors are not designed to be bidding but are suitable for very highly efficient electric production the vessel hot the core high this could be 10 meters 8 to 10 meters of core diameters about three and a half meters and you'll see in this picture there's a center column of graphite pellets this being the fuel zone of this baby this is done because the control rods are not in the penalty the controller odds were in fact outside which also see in this design is that there is graphite a lot of graphite which is the graphite reflected for this core so inside the graph line the pebbles are literally place and discharge through the bottom and then recycle the way these elevator reactors worked as the helium comes in up the side and down through the elevator it's not a fluidized bed and the hot helium comes out here that goes either to a direct cycle direct Brayton cycle or an indirect cycle which can be also scheme so the 60 millimeter diameter pebble babbles in about a 1 the court is in fact helium now this chart which is one of the file charts provides a summary of the major reactor types and I want to focus in on the boiling water reactor and the pressurized water here you can look at the high temperature gas reactor but now this is more or less dated information to a different technology than what has been proposed here but in terms of the different types of reactors the fuel form this the same radium dioxide the enrichment is the same the fertile material meaning the non-fishermen and we're also putting the fuel ends in the same circle like latitudes now what you know it is in a boiling water reactor the typical design is an 8 by 8 which means a fuel pins they by a mule pens again teenage PWR we're talking about a 16 by 16 17 by 17 arrays of people pin and you'll notice the number of tool you are resolved around 750 compared to around 200 to 240 fuel assemblies in the PW so the design differences are really driven by the mechanism of Hever it's awkward if you want to just take a quick look at a breeder or lease a breeder reactor we have either mixed oxide or Newtonian oxide there's a blanket region in which you can make utonium and the fuel pigs are very very very tiny in the sense of diameters so this is sort of gives you an overview summary of the reactor types of we're going to be talking about the safety systems that will be discussed and hopefully as I said at the end of the this this course will gain a much better appreciation of how all the stuff fits together this is the reading list on reading and homework assignments from Neath chapters 1 and chapter 2 and we'd like you to be just chapter 4 next lecture if you have any questions now's a good time to pass them but I this material has been overview nature and it sets the framework for our future discussion recall our next lecture will be on reactor physics now in that one lecture we are going to try to cover everything you need to know you took a whole semester on in an hour half so it's going to be fast if you comfortable with the material let's try to get some help to bring you up to speed because we're going to assume that you understand reactor physics and this is basically refresher course
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