Reactors of the Future (Generation IV)

you what's in future for nuclear reactors today we have what are called generation 3 Gen 3 and these have the wonderful feature of being passively safe you don't need someone pressing a button you don't need to keep the water on it you can just use the laws of nature convection to be able to take away waste heat in case everything goes wrong and that's great they have greatly improved safety but other than that they still have the same efficiencies they still basically have the same types of design you're still fissioning uranium-235 the future is called generation 4 and this is where you come up with the newer ideas to try to address some of the limitations from nuclear power safety is in pretty good shape but these other limitations are usually the low efficiency now the low efficiency isn't all that low it's about the same as coal plants or gas plants this low efficiency is a result of having low temperatures well order really hot under high pressure that's certainly not low well relative Carnot efficiency sells us that the maximum efficiency you'll ever get is 1 minus the cold temperature over the hot temperature if I want this number to be closer to 1 I want this fraction to be near zero cold I'm kind of stuck with I got the outside world that's about as cold you're gonna get you're not going to spend electricity to refrigerate it but means that I have to make this tea hot bigger this would go to infinity efficiency would be one so a desire in the new generation of reactors is to find ways to do this all at higher temperature if you do it at higher temperature you can do it in better efficiency and if you can solve other problems like downtime reactors have to be refueled it used to be they would be shut for a month or two while you put took out some of the old fuel and put in new fuel modern engineering techniques and attention to detail has improved that and now many reactors are only shut for a couple weeks when they refuel every year but another Gen 4 concept besides going to higher temperatures is to go to higher availability maybe something that's continuously fueled and therefore you never have some type of lack of ability of downtime let's look at some of these generation 4 reactor concepts instead of using water after all it boils at 100 C why don't we use something that's already boiled at gas in the gas cooled reactor the high-temperature gas-cooled reactor you know is water now remember if you're not using water you need a different moderator so in many of these cases they will use carbon or something as another moderator they can still be extremely safe because of their design in the high-temperature gas-cooled reactor you use high temperature gas the fission products heat makes the gas even hotter and you can run it first through some type of of gas turbine the waste heat can then boil more water and go through a combined cycle there's the helium cooled reactor the very high temperature reactor and likewise it uses a gaseous coolant since the gas is already a gas until you get it into its plasma state which is ridiculously high no solid material would even live to see that you can get things so hot that you might be able to just hydrolyze and take water and turn it into hydrogen and not even have to go through a system of making steam to make electricity this would be a wonderful hydrogen generator another scheme instead of using water is still to use a liquid but to use liquid lead solder for instance is often made of tin or lead or things like that and you can melt it a metal that melts at a relatively low temperature but still much much higher temperature than water so you actually move molten lead around and then do the same things you would do in a power plant you could do it with sodium or some type of salt you actually take salt which we all think of as something you just eat heat it up enough and it turns into a liquid and you use it as your cooling fluid or you can take another metal like sodium a molten sodium reactor in fact this type of reactor has been used the Phoenix and super Phoenix commercial nuclear reactors in France were sodium-cooled fast breeder reactors now the things we saw before are still sort of your standard and I've got uranium and rods and I'm now just trying to run it all at a higher temperature but Gen 4 includes a lot more stuff than that some things that are really really clever that's the petal bed concept so we're gonna take these these pebbles you know almost a little less than baseball size and inside you notice that there are a bunch of more smaller pebbles and those smaller pebbles have both the uranium fuel and the moderator mixed in and this larger pellet here will allow visions to take place and it's made of very high temperature stuff so as soon as visions are taking place this thing gets very very warm the pebble bed aims at two aspects one is again a safety type of aspect and the second is a continuous refueling you see there isn't a lot of uranium in one of these pellets and if you design a system where it kind of works it way through a reactor you can introduce new pellets in one spot and take out used ones from the bottom and maybe if some of them get mixed up you have a little testing this uranium is left and then recycle them in the other thing is if all these pellets fell down into a place where you had a neutron absorber a control rod then of course there's no chain reaction it absorbed all the excess neutrons no chain reaction takes place to fluidize the bed to have a fluidized pebble bed reactor you would take this and put your coolant through it it would push all the pellets up into an area where now there is no neutron absorber fact there's an additional moderator of the coolant water and as long as that was there and you haven't boiled all the water away your reactor would operate great if it gets too hot and all the water turns to steam guess what all the pellets fall back down to where the neutron absorber is here's a picture of an actual pellet and you can see it's compared to let notecard but smaller than a baseball and here is one of the reactor concepts that illustrates the continuous fueling you can take the spent fuel pellets out of the bottom you can put new fuel pellets into the top so generation four reactors may allow new fuels the thorium cycle may allow fuels to be utilized more completely wastes to be contained the nice thing about the pebble bed is in the end you got a pebble it's got its fission products in it it's already in a storage state as opposed to France it takes the reprocesses the high level waste and then puts them into glass beads hey you can just take these things and put them in your high-level waste repository directly so generation four is in the research labs and in the National Labs in test facilities and as long as there's an economic imperative into the future maybe the reactors that are powering us in 30 or 40 years that's what you need to know about generation four [Music]

Channel: Illinois EnergyProf

Views: 287,606

Rating: 4.9158964 out of 5

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Id: _mJ3S-VQuHY

Length: 9min 10sec (550 seconds)

Published: Tue May 14 2019

Reddit Comments

[u/NukeRocketScientist]

Really interesting stuff. I'm an AE student in undergrad right now and I'm seriously considering getting a masters in nuclear engineering. My ultimate dream is to work in nuclear space propulsion so I feel mastering in nuclear would help me specialize and get closer to that goal. I could really use some advice on that potentiality if anyone has some.