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Olothreutes posted:Reprocessing is illegal in the US right now, and was banned in the 1977 by Jimmy Carter, who I have a great respect for as a president and diplomat and also some disdain for as he stopped or prevented a great deal of work in the nuclear industry. Why is reprocessing illegal? I'm assuming it has something to do with bombs?
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May 17, 2016 00:51
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SouthLAnd posted:Why is reprocessing illegal? I'm assuming it has something to do with bombs? Exactly. It's illegal because there is a law that says so. I'm not really sure of the motivation for it in detail (bombs), but a reprocessing program is essential to a weapons program, you (very nearly*) can't have weapons without reprocessing. On the civilian side right now there isn't an impetus to have reprocessing because uranium is abundant enough that we don't need it. There are a few nations that have poor natural reserves of uranium that are pursuing civilian reprocessing, Japan and South Korea, but it is fraught with troubles and complications and there is a lot of international oversight because of the weapons program potential those facilities present. *The US is the only nuclear armed state in the world that does not have an active reprocessing program. We found the only way to get around it, which was to reprocess so much material that we just don't need to make any more at this time. We could start it back up, but our stockpile of nuclear material is vast and substantial.
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May 17, 2016 00:59
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Does anyone know why the early Manhattan Project experiments were so colossally stupid? This screwdriver I'm holding wedging two half-shells apart is the only thing keeping me from death, SEEMS LEGIT. I mean, the theoretical physics was all worked out by then, did they just not really understand the medical implications of said theoretical physics?
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May 17, 2016 01:02
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You've never met anyone who actually works with radiation in a lab, have you?
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May 17, 2016 01:13
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slap me silly posted:You've never met anyone who actually works with radiation in a lab, have you? No, I have not. Glad you took this opportunity to be condescending, friend.
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May 17, 2016 01:17
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AugmentedVision posted:Does anyone know why the early Manhattan Project experiments were so colossally stupid? This screwdriver I'm holding wedging two half-shells apart is the only thing keeping me from death, SEEMS LEGIT. I mean, the theoretical physics was all worked out by then, did they just not really understand the medical implications of said theoretical physics? Maybe people didn't fully understand the risks? I was reading a PDF of a book called "dangerous trades" from the late 1800s early 1900s. That was when the hazards of electricity weren't fully understood. One worker was lecturing others, and stated that "a pressure of 500 dc volts was harmless". To demonstrate, he took each hands and grabbed across the aforementioned 500Vdc bus, and he slumped over dead as the current fried his heart.
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May 17, 2016 01:17
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Three-Phase posted:Maybe people didn't fully understand the risks? This is my thought exactly, but at the same time the screwdriver incident in particular is so freaking stupid. It was after there was already one fatality and one close call from things incidentally reflecting neutrons back into the core and causing it to go supercritical. So the dude was holding apart two half-shells designed for making the core go supercritical with only his screwdriver. Perhaps they didn't have a physical understanding of what specifically had caused the injuries in the previous incidents, and the straighforward explanations that you now find everywhere were written much later? AugmentedVision fucked around with this message at 01:32 on May 17, 2016 |
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May 17, 2016 01:27
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Olothreutes posted:
So...gently caress You, Got (my nuclear weapons already)?
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May 17, 2016 01:29
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AugmentedVision posted:No, I have not. Glad you took this opportunity to be condescending, friend. Heh, sorry, the feeling was really directed at my grad school buddies who were complete loving morons about radiation, to the point of not wearing their dosimeters and idiotic crap like that. Fifty years after the incident you referred to that should have taught everybody in the loving world to have a little respect for what they were doing.
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May 17, 2016 01:49
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SouthLAnd posted:So...gently caress You, Got (my nuclear weapons already)? Exactly. We manufactured tens of thousands of warheads during the cold war. We've reduced that number under various treaties, but we still have thousands of warheads and unmachined material to make thousands more. AugmentedVision posted:Does anyone know why the early Manhattan Project experiments were so colossally stupid? This screwdriver I'm holding wedging two half-shells apart is the only thing keeping me from death, SEEMS LEGIT. I mean, the theoretical physics was all worked out by then, did they just not really understand the medical implications of said theoretical physics? It's been pretty well covered, but the risks associated with that stuff weren't well understood. We still made mistakes with things and, perhaps more importantly, we were at war and needed results yesterday. The combination of a lack of understanding, enormous pressure to produce results, and more than a little hubris will often result in stuff like this. Hubris in particular has stuck around and is a basic human trait that we have to engineer around in basically every field. People STILL think they are right and go to great lengths to defeat interlocks and bypass safety systems that were engineered in because they obviously know better than the designers, right?
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May 17, 2016 01:51
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Olothreutes posted:It's been pretty well covered, but the risks associated with that stuff weren't well understood. The deaths of Harry Daghlian and Louis Slotin, combined with field studies of victims of the bombings of Hiroshima and Nagasaki were literally the first time modern medicine had encountered radiation exposure of that magnitude. Prior to those cases, it was simply not known exactly how the human body would react to high doses of radiation. This is part of why so many nuclear weapons tests included animal testing.
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May 17, 2016 02:03
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/\/\/\/\ Thanks, that makes sense.slap me silly posted:Heh, sorry, the feeling was really directed at my grad school buddies who were complete loving morons about radiation, to the point of not wearing their dosimeters and idiotic crap like that. Fifty years after the incident you referred to that should have taught everybody in the loving world to have a little respect for what they were doing. No problem sir, the only lab experience I have is machine shop and engine lab, and everyone stuck pretty closely to the safety procedures as far as I remember. I guess the fact that it's invisible probably makes people forget how dangerous it is, even if they know the dangers academically. Olothreutes posted:It's been pretty well covered, but the risks associated with that stuff weren't well understood. We still made mistakes with things and, perhaps more importantly, we were at war and needed results yesterday. The combination of a lack of understanding, enormous pressure to produce results, and more than a little hubris will often result in stuff like this. Hubris in particular has stuck around and is a basic human trait that we have to engineer around in basically every field. People STILL think they are right and go to great lengths to defeat interlocks and bypass safety systems that were engineered in because they obviously know better than the designers, right? Slotin's death in particular is still so colossally stupid, though. Daghlian? OK, I get it, you had to do things by hand because there was a time crunch. You dropped a thing and you died. What the hell was Slotin doing with his screwdriver though? There had to be an ignorance of the medical risks, I just can't accept that the guy KNEW that if his screwdriver slipped, he was guaranteed an agonizing death, and went with this plan anyway.
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May 17, 2016 02:04
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After letting myself get 200+ posts behind I've finally caught up. Had to take some time away to properly insure I graduated. I now hold my bachelors in nuclear engineering, horay  Olothreutes posted:Exactly. It's illegal because there is a law that says so.
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May 17, 2016 02:32
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AugmentedVision posted:Slotin's death in particular is still so colossally stupid, though. Daghlian? OK, I get it, you had to do things by hand because there was a time crunch. You dropped a thing and you died. What the hell was Slotin doing with his screwdriver though? There had to be an ignorance of the medical risks, I just can't accept that the guy KNEW that if his screwdriver slipped, he was guaranteed an agonizing death, and went with this plan anyway. From a purely physical perspective why would you not ask the machine shop to make something that can do the same job without trusting your inherently shaky and error prone hand? E ^ Grats! And fake edit, Android tried to autocorrect that to Grays 
goatsestretchgoals fucked around with this message at 02:42 on May 17, 2016 |
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May 17, 2016 02:38
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bitcoin bastard posted:From a purely physical perspective why would you not ask the machine shop to make something that can do the same job without trusting your inherently shaky and error prone hand? Apparently they already had shims precisely for this purpose but Slotin just preferred to use the screwdriver 
AugmentedVision fucked around with this message at 02:51 on May 17, 2016 |
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May 17, 2016 02:45
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AugmentedVision posted:Apparently they already had shims precisely for this purpose but Slotin just preferred to use the screwdriver This! This is the thing. loving radiation cowboys, it's some kind of irrepressible genetic defect.
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May 17, 2016 03:18
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AugmentedVision posted:Apparently they already had shims precisely for this purpose but Slotin just preferred to use the screwdriver Hubris, man. Hubris. The Protagonist posted:After letting myself get 200+ posts behind I've finally caught up. Had to take some time away to properly insure I graduated. I now hold my bachelors in nuclear engineering, horay Congrats! Welcome to the club. Where are you headed?
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May 17, 2016 05:28
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AugmentedVision posted:
No, dude knew just how dangerous what he was doing was. He was, in fact, pretty proud of doing the procedure successfully several times. It was known as 'tickling the dragon's tail'. E: gently caress, beaten. Sooo, any of you nuke fellas work in Y-12 or K-25? Or some of the other stuff Oakridge has going on? I'm a gross radiation baby from the nearby areas and grew up with tales of deer with too many limbs and two headed frogs. 
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May 17, 2016 05:41
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This time on Spent Nuclear Fuel chat: Technical challenges! We’ve covered the first part of spent fuel life, the cooling pool. We’ve talked about dry storage casks. Now, we’ll talk about final disposition. There are only so many places you can put spent fuel, and really any nuclear waste. In the ground, in the sea, on the surface, or in space. That’s about it. In space seems like a great idea until you remember what happened to those SpaceX rockets when they exploded on the launch pad. Imagine if a rocket full of nuclear stuffs blows up a few tens of thousands of feet into the atmosphere. Nuclear fuel is also VERY heavy and therefore VERY expensive to get into orbit. So let’s dismiss space out of hand, leaving us with our more terrestrial options. Surface storage is basically what we are doing now. It works ok, but the canisters are exposed to the atmosphere and weather and all that stuff. It’s a challenge to keep them going, and I’m pretty sure that we’re going to find that we need to repack the bundles into new canisters over time. This might be true even underground, but on the surface things are a lot more variable and exposed. It’s a real possibility that we just end up keeping them above ground forever, as it stands they might need to be here for a long while anyway. In the ocean. There was an old project a while back, project seabed. It looked at the feasibility of making casks with slightly missile shaped cones and fins on them and then dropping them into the ocean. The idea was that the casks are so heavy they would build up plenty of momentum and bury themselves really deep into the sludge at the bottom of the ocean, which would then cover them back up. I’m not entirely sure why it got canned, but it did. I’ve heard some people talk about it recently though, so there might be a resurgence in the works. Probably not. One guy I know talked about dropping them into the subduction zones at tectonic plate intersections, where one plate slides under another. The idea is that you drop them in there and the tectonic action pulls them into the mantle, never to be seen again. Most of these are pretty easy to dismiss and the prevailing wisdom is that we should put it underground in a deep geologic repository. We even went so far as to build one here in the US, yucca mountain, but we aren’t using it for reasons we discussed last post  . So you dig a very big hole and put these canisters in it. Doesn’t seem that hard, right? Well, there are a lot of technical challenges that need to be met. All these challenges are around keeping the casks intact, as a leaky cask is a bad cask. The regulations say we need to keep this stuff underground basically forever. At first we said 10,000 years, for sure, but some clowns somewhere said a million years and then Nevada sued the DOE because yucca mountain didn’t meet the million year standard (Hint: nothing can, it’s impossible) and it looks like we’re stuck with it for the moment. The Blue Ribbon Commission was put together in 2008 by president Obama to look at this and they basically deferred any decisions until 2048, a convenient 10 presidential election cycles down the road when no one they know will be involved and therefore no toes were stepped on. Business as usual.So these casks are hot, which is the major issue. Very hot, in fact, a few hundred degrees isn’t out of the question. On the surface we can cool them via moving air but that’s a lot harder underground, doubly so if they are sealed into whatever media they are in. So one of the things you need to look at when considering where to put a repository is what sort of material you would be digging out. Granite, shale, and salt are the big contenders. Each of them has certain characteristics and advantages and disadvantages. Granite: Very hard rock. This is good because it isn’t likely to go anywhere for a long time, assuming the region is seismically stable. It’s very hard to mine, though. It’s relatively impermeable to water. Another issue that people worry about is waste leaking and hitting the water supply. So water by the casks is doubly bad because it promotes corrosion and also provides transport to released waste. The rate at which the waste moves in water is a function of soil/media porosity, chemistry, and what the waste is. In general the stuff moves very slowly, but it does move, so we’d like to avoid that if possible. Granite has poor thermal performance, though. Granite can’t hold very much heat and it doesn’t transmit heat very well, so the area around the cask will heat up very fast and then that heat has nowhere to go and could begin to degrade the cask. This has the effect of having to put a LOT of granite around each cask to make sure that nothing overheats. Like 100 feet apart in some models, depending on other factors. That could mean a very, very large facility. Shale: This is basically very compact mud. Shale has better thermal properties than granite does (not hard to do, granite is bad) but is more permeable to water. This is a tradeoff that you would need to carefully consider. Shale also isn’t quite as stable as granite is. Salt: This one is interesting. Salt has, comparably, fantastic thermal properties. Salt can handle very large amounts of heat and the heat moves quickly through the salt, meaning you can pack more casks in the same footprint. This could make a huge difference. But salt dissolves in water. That might be a problem, depending on your location. There are, however, deep salt deposits that have been in place for hundreds of millions of years. And a little water isn’t so big a deal because it can only dissolve so much salt before it becomes saturated and is done. Salt also has a unique behavior in that it closes up on itself. If you don’t constantly maintain a tunnel in a salt deposit it will creep itself closed over a period of a few decades at most. So it’s self healing, which is awesome. A lot of people, myself included, think salt is the way to go. Other people are not convinced. So heat needs to be managed. Based on the material characteristics of your repository you can determine a maximum safe surface temperature. Usually the number I see is 120 °F for shale and granite, and 200 °F for salt. Based on these numbers you can determine how long a set of assemblies will need to sit around above ground before you can store them underground in your repository. This is also a function of how many assemblies you want to put in each container. With only four assemblies in a container you can get away with only a few years of above ground cooling for salt and about 10 years or so of cooling for shale/granite. Four assemblies isn’t very many, though, so you might want to put more in there. The largest number than anyone has considered for long term storage is 24 assemblies. This configuration needs to sit around for several decades to be cool enough to store in salt, but could take over 100 years to be cool enough for shale or granite. This is why they might be sitting above ground for a long while, since the current casks have 37 assemblies in them. So these things sit around for a bit and now you’re ready to put them underground. How do you get them there? Current storage casks, mostly, aren’t licensed for transport, just for sitting on a concrete pad. So you’ll probably have to open the casks and repack them for transport. Do you intend to use the same cask for transport and storage so you don’t have to open it again, or will you use a third cask for storing them? This stuff gets complicated really fast, and it isn’t made better by the byzantine regulatory system around it. Currently the casks are held at private sites, and they are the responsibility of private companies and governed by the NRC regulations for those companies. But once you put them on a truck you have to play by EPA rules. Is the trucking handled by the DOE, or a private entity? What about trains? And once you get them to the storage site they become property of the DOE and the rules revert to a combination of the DOE and the NRC. None of these are similar and even the NRC rules that govern them at the different sites are different. It’s really a mess there too. Still, the biggest issue is getting things cool enough to transport and store safely. Nextly, how do you select a site? So you chose your media (salt, right?) and you go looking for places with this material. It needs to be deep, but not so deep that you are close to the water table. It should be seismically stable. It shouldn't have lots of people near it. And hopefully there will be nothing else nearby than anyone wants, because you are going to need a large exclusion zone around this place to keep people from accidentally digging into it. This is a big issue for shale right now because fracking companies are suddenly drilling into shale deposits willy nilly and incursions into waste repositories would be a thing if we had any repositories to dig into. It's not an easy process and you definitely need the support of the local populace. I was at a really crunchy panel discussion recently where someone told me that volunteerism wasn't the way to select locations for storage. I think this is insane, because if the answer isn't volunteerism what should it be? He did not have a good answer, but this is part of the issue. I asked him, and another guy on the panel, what we should actually do about the issues they had talked about. Mostly they didn't have an answer. Lots to complain about, but little help to offer when finding a solution. It's a pet peeve of mine to complain loudly and publicly about something but not offer solutions. Anyway, there we have it. Olothreutes fucked around with this message at 09:14 on May 18, 2016 |
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May 18, 2016 09:05
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Does the US even have a suitable subduction zone in our territory? How would you be certain that these spent fuel pods are correctly penetrating the muck and getting sucked down the inch per year until they hit mantle? Would the muck eat the pod over time, because having that poo poo exposed to actual ocean water would mean it spreads all over the loving place, right? Not to mention the risk of godzillas Oceanic disposal might be a good plan but I guess like any other one you're absolutely hosed if it goes wrong. What about the mud worm ecosystem 
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May 18, 2016 16:16
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I wonder how difficult it would be to separate short lived and long lived isotopes. If they were separate we could store the long lived stuff above ground because it isn't dangerous and we could store the short lived stuff above ground because it would only need to be stored a few hundred years.
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May 18, 2016 16:30
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DreadLlama posted:I've heard people say, "You can't give Candu reactors to middle-eastern countries because you can just refuel them whenever and nonproliferation treaties will be violated!" CANDUs burn up a lot of the plutonium they make and the stuff that's left will reside in some very dirty fuel that still needs to undergo heavy chemical processing to get the goodies out of. Just having a CANDU isn't any more of a turnkey-solution for making nuclear weapons than any other reactor will be. In fact, with modifications to any thermal neutron reactor (i.e. most models) you can get better results by exposing depleted uranium to a thermal neutron flux. It would still need to be processed, but it would be cleaner. Not to speak for him, but Refuelling CANDUs is such a routine part of operation (8-12 bundles replaced every day) that at the very least we don't hire contractors for the job and instead have permanent staff per power plant to do it. So his job would differ in that he'd probably be a full-time employee. edit: fuel bundles aren't very big and can be handled by hand when fresh, but can only be handled by machines when discharged. Because the bundles are small and only a small number of them are replaced at a time, the actual refuelling process doesn't take very much of the workday. However, monitoring the fuel in the reactor, inspecting both fresh fuel and spent fuel for defects, planning which channels get replaced each day, etc. takes up a lot of the time of a fuel worker for a CANDU BattleMaster fucked around with this message at 16:50 on May 18, 2016 |
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May 18, 2016 16:45
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So okay, I say this as someone who is as layman as it can possibly get regarding nuclear energy - If the waste is so hot, IE hundreds of degrees, what about using it for heating homes, like how geothermal works? Or is this a problem of "oh my god you want to heat my home with nuclear waste? My children!" and licensing/regulation? Because if this is feasable, hell yeah I'd keep waste containers on my property to drop my heating/power bills, in a heartbeat. Let 'em spend their above ground time cutting my bills, cycle them out when they cool off, works for me.
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May 18, 2016 22:37
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Probably either the actual heat level is so low there's not a good way to efficiently get usable energy out of the waste, or it's too radioactive to be safe at all? There is some kind of almost totally passive power source they use for space probes and Russian unmanned lighthouses and stuff, but I think the lower the temperature gradient the less work you can get out of the thing. Like 100° is nowhere near the 1000° or whatever is in a running reactor core. Also some random guys were out hunting and it was balls cold out, so they busted into one of those lighthouse power supplies, curled up for the night, and accidentally killed themselves with the deadly atoms.
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May 19, 2016 01:36
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Or it's not worth chunking in the up front cash to make it work, when you're only going to get a fraction of that money's value in sellable kilowatt hours Or the regulations is dumb Or nobody cares? I'm curious about this now, you might as well wring out the most from the whole process
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May 19, 2016 01:38
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SniperWoreConverse posted:Probably either the actual heat level is so low there's not a good way to efficiently get usable energy out of the waste, or it's too radioactive to be safe at all? yep
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May 19, 2016 01:38
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drat, so no fusion cores I can plug into my cell and get a reasonable battery life I guess
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May 19, 2016 01:39
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Code Jockey posted:So okay, I say this as someone who is as layman as it can possibly get regarding nuclear energy - You could, in theory, set one of these in your basement and use the hot air that comes off it to heat your home, yes. Other people have covered the issues with just how much heat they do or do not make. Also they weigh 150 tons, which isn't easy to move, especially up or down stairs. The big issue is the regulatory environment around this. Your basement, and by extension home, would need to satisfy the regulations set forth for the storage of spent fuel. This will be super dry reading material, but here you go: 10 CFR PART 20—STANDARDS FOR PROTECTION AGAINST RADIATION 10 CFR PART 50—DOMESTIC LICENSING OF PRODUCTION AND UTILIZATION FACILITIES 10 CFR PART 51—ENVIRONMENTAL PROTECTION REGULATIONS FOR DOMESTIC LICENSING AND RELATED REGULATORY FUNCTIONS 10 CFR PART 72—LICENSING REQUIREMENTS FOR THE INDEPENDENT STORAGE OF SPENT NUCLEAR FUEL, HIGH-LEVEL RADIOACTIVE WASTE, AND REACTOR-RELATED GREATER THAN CLASS C WASTE 10 CFR PART 73—PHYSICAL PROTECTION OF PLANTS AND MATERIALS Those are the relevant sections of title ten of the code of federal regulations (10 CFR) when it comes to putting spent fuel anywhere, including your basement. Among the things you would need: An approved radiation protection plan that meets 10 CFR 20 requirements for members of the public. You could probably get away with worker protection levels for any adults in your home, but children and visitors would almost certainly be members of the public. This means keeping your basement off limits and properly posted (administrative controls) and locked with alarms (engineered controls). You would need to submit to NRC inspections to ensure everything is going as planned and would be subject to huge fines if things weren't kept up to standard. Maintaining things to standard and keeping up with the paperwork is a full time job, btw. Stay at home spouse, perhaps? You would probably have to post a guard at your home 24/7. Anyway, it gets more complicated and requires so much work that it would be the absolute worst furnace you have ever had. It would be easier to just take the same volume of paperwork and burn it in a fireplace to heat your home instead of filling it out to keep the waste. SniperWoreConverse posted:Probably either the actual heat level is so low there's not a good way to efficiently get usable energy out of the waste, or it's too radioactive to be safe at all? There is some kind of almost totally passive power source they use for space probes and Russian unmanned lighthouses and stuff, but I think the lower the temperature gradient the less work you can get out of the thing. Like 100° is nowhere near the 1000° or whatever is in a running reactor core. Those lighthouses and space probes are powered by Radioactive Thermoelectric Generators, RTGs. These are basically a very hot rock, probably highly radioactive in addition, that you stick some thermocouples on and generate electricity. You get a few watts from them and they can be quite dangerous for what is ultimately a small amount of power. They do last a very long time and require zero external influence, though, so if you have low power applications that need long lifetimes and little external involvement they are quite good. The usual materials are Pu-238 or Sr-90. SniperWoreConverse posted:Does the US even have a suitable subduction zone in our territory? How would you be certain that these spent fuel pods are correctly penetrating the muck and getting sucked down the inch per year until they hit mantle? Would the muck eat the pod over time, because having that poo poo exposed to actual ocean water would mean it spreads all over the loving place, right? Not to mention the risk of godzillas Yes, actually! The Pacific plate subducts under both the Alaskan plate in the Aleutian Islands, and under the Americas where the Cascade Mountains are. Both of these zones are probably within US waters. As for being certain of the cask behavior after you drop them, you really can't be 100% sure. This is probably part of why project seabed got canned. I don't know enough to say if the muck is corrosive or not, but I imagine not any more so than seawater is. I don't think the fuel would really go anywhere if the canister was breached, the muck is probably good at immobilizing any solid or liquid that is released. Gasses not so much, but most of the gasses are short lived in terms of radioactivity. I mentioned this to someone I met at a party who knows more about subduction zones than I do, a geophysicist. She thought the idea was insane because we have basically zero idea what actually happens in those subduction zones. So there would need to be a lot of science done to support this sort of an idea. Germstore posted:I wonder how difficult it would be to separate short lived and long lived isotopes. If they were separate we could store the long lived stuff above ground because it isn't dangerous and we could store the short lived stuff above ground because it would only need to be stored a few hundred years. Technically not very hard. You could separate them using chemical processes that would be able to distinguish and separate the various elements with different chemical properties. You would need to either dissolve the fuel into an acid bath, nitric acid probably, and then use chemistry from there, or you could melt it down in a molten salt and use some electrochemical process from there. Both are things we know how to do, and both are technically reprocessing and therefore illegal in the US. You would also need equipment that could handle the highly radioactive spent fuel while doing this, and ultimately you separating equipment would be radioactive as well. Another option is to put the fuel into a fast spectrum reactor which is capable of fissioning transuranic elements, leaving you with fuel that is only the lighter and shorter lived stuff. Again, this is technically possible but no one does it. Nuclear reactors come in lots of different shapes and sizes and designs, much like cars do. When you are building one you need to decide what you want the reactor to do and build one that does those things. If you want to move lots of heavy material you buy a truck, if you want to zip around a track you buy a racecar. Similarly if you want to burn transuranics you build a fast reactor, if you want to breed weapons material you build a thermal reactor with a breeding blanket, and if you want to power homes you build a light water reactor, for example. Olothreutes fucked around with this message at 03:16 on May 19, 2016 |
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May 19, 2016 02:49
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Olothreutes posted:Congrats! Welcome to the club. Where are you headed? Thank you! I managed to snag a fellowship with my alma mater soooo I figure a paid ride to a PhD is the way to go for me. There's a lot I need to touch on, like the whole LFTR thing which was the focus of my senior design project over my whole senior year, two concurrent semesters, but whoever said that the thorium breeder solution got a bunch of mindshare from that one viral TED talk is dead right. I'm right from the heart of that mini little fart of a renaissance but rather than go out and parrot a bunch of poorly communicated and misunderstood half-truths I actually got to introduce the very concept of liquid-fuel nuclear reactors to our department's curriculum and garner a much, much deeper understanding of just how deep the technical challenge that still remains behind such a system is. Olothreutes you covered it pretty well in that demonstrated material lifetimes is one of many, many major R&D challenges that exist between the experimental setups they did at ORNL back in the 70's and an actual, functioning commercial Liquid Fluoride Thorium Breeder reactor. Here, have a fluid flow scheme from one of the more well though out hypothetical breeder designs from that era of giants and understand at once both A) how loving brilliant it is and B) what loving investor poison it looks to be on the face of it.  This is from a '69 paper by Whatley and co. from ORNL (which I'll be happy to link in its entirety if you're interested), where basically all the solid gold research and development that actually exists on this type of system is from. Worth mentioning is the counter-current immiscible-fluid extractor which we adopted for our senior design project. This relates directly back to that whole issue with the Pa-233 isolation necessity and the simplicity that Sorenson projects. I think he's probably aware that he's describing a (grossly) simplified model but it is may be disingenuous enough to actually have harmed thorium fuel precursor advocacy as a movement.
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May 19, 2016 04:27
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CANDU fuel bundles and refueling: https://www.youtube.com/watch?v=-YhHNjjFqb0
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May 19, 2016 04:56
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By the way, you don’t know how right Olo is about the sheer range of ways there are to create a reactor. Fission is this fascinating physical process, in that it is essentially a catastrophic decay which can be induced by the very material which undergoes it; this is a little pedestrian and I think most people understand that part, but there are some subtleties I think are rarely appreciated. First, going back to load-following. This sounds more or less like a pleasant perk, “Reactivity follows power demand” goes the mantra over and over again, before you can really appreciate just how loving amazing that is. But think about it a moment more. Commercial reactors, as mentioned, can comfortably load follow around ~10%. The highly enriched, tuned up sports-cars of the propulsion fleet on the other hand… Well, the way they are operated is they move the fuel rods once, to start up to criticality to some low power. Every power change following that is handled by throttling the turbines. Pause a moment and dwell on that. Changing the rate of steam entering the secondary system turbines… readily and quickly adjusts the rate of fission in the reactor core. This is such a phenomenally amazing fact it needs to be savored…the order of change in primary fluid density, compared to the change in reactor power output is nothing short of extraordinary. It should deepen your appreciation for just how on the cusp of radical dynamics this otherwise stable ‘criticality’ state is. But it gets even better. Most people think of an atom fissioning and spitting off two or so neutrons and then those neutrons causing further fissions, perpetuating the process. But if that were the case in a power reactor… well, it’d be a bomb. It’s a state referred to as ‘prompt critical’, that is the fission chain reaction is sustained by ‘prompt’ neutrons alone, those occurring from the original nucleus fissioning. But the reality is, to make them controllable, reactors rely on more than that family of neutrons to actually get critical. We keep the reaction so on the cusp of dying that it relies upon the additional neutrons that get emitted by the recently born fission products undergoing decay. But yet again, the order of magnitude of difference between the number of prompt neutrons and the so-called delayed neutrons is so great it is an incredible fact that not only are they the crème-de-la-crème that sustain the whole chain reaction, they are born on a timescale slow enough to actually make reactors a thing that is possible at all. The reason why this is true actually makes very good physical sense, which I’ll (or Olo I’m sure) will be happy to go into if wanted. Oh yeah, tomorrow the DoE is doing a webcast about the Gateway for Accelerated Innovation in Nuclear (GAIN) at 12:30EST for those interested. MisterOblivious posted:CANDU fuel bundles and refueling: CANDUS are rad. Even then, I recently encountered a refuel worker from up north that viewed the online refueler system as a finicky downside of using unenriched fuel, really surprised me. The Protagonist fucked around with this message at 05:19 on May 19, 2016 |
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May 19, 2016 05:09
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I watched that Candu video, but in the side bar it linked to a documentary on Molten Salt Reactors. It was pretty cool. https://www.youtube.com/watch?v=xIDytUCRtTA
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May 19, 2016 05:55
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Goodpancakes posted:I watched that Candu video, but in the side bar it linked to a documentary on Molten Salt Reactors. It was pretty cool.
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May 20, 2016 04:41
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Goodpancakes posted:I watched that Candu video, but in the side bar it linked to a documentary on Molten Salt Reactors. It was pretty cool. I skimmed through this video last night and it was really interesting, but it sounds like the earlier work was scrapped for a combination of political/financial reasons, and because we found enough enrichable uranium that the regular PWR/BWR reactors that we already had going ended up being easier to use? A couple questions (for, like, whoever wants to answer them): 1) They sounded like they were conflating Thorium reactors with salt reactors, but is that just because the guys in the documentary found Thorium fuel and also molten salt to be useful technologies, or are the two somehow actually related (can't have an MSR without Thorium or something)? 2) A couple people had mentioned earlier in the thread, various problems with Thorium and with molten salt. Things like the generation of neutron poisons or undesirable elements in the case of Thorium fuel, and things like corrosion by the liquified salt in the case of the latter, but I never quite understood why. Is thorium a valid fuel source and is an MSR a valid reactor design, or is it some kind of tech that sounds good to the layman but is actually untenable?
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May 20, 2016 07:20
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st1LL_51ngl3 posted:I skimmed through this video last night and it was really interesting, but it sounds like the earlier work was scrapped for a combination of political/financial reasons, and because we found enough enrichable uranium that the regular PWR/BWR reactors that we already had going ended up being easier to use? You can most definitely have thorium based reactors without salt, I had to design one for my senior project. It was a nightmare to work with the additional poison that Th-232 is and we didn't get much in terms of extra life out of the fuel, but when the Pharaoh says design me a pyramid... MSRs also come in many designs that use a bunch of different fuel types and forms. I suspect that the thorium people focus on molten salts because of the issues that have been brought up regarding protactinium separation. The objective is to turn Th-232 into U-233. This is a several step process and it can go wrong in a few places. The first step is to get Th-232 to absorb a neutron and become Th-233. That's easy. Th-233 has a 21 minute half life and turns into Pa-233. Here's where it gets tricky, Pa-233 has a 27 day half life, so it's going to take a month or so to get the uranium you are really looking for. In the mean time any of those intermediate elements can absorb another neutron, giving you Th-234 or Pa-234, neither of which do what you want them to do. In particular Th-233 has an enormous cross section to become Th-234. So to get to the U-233 that you really want you need to get that first neutron in there and then get that stuff out of the core for a while so you can let it decay as needed. This isn't impossible, but it's far easier to do with liquid fuels than with solid fuels. Thorium is indeed a valid fuel source, it would work and there are several groups/nations in the world that are pursuing it. It really comes down to a question of availability and need. If a country has very little uranium but lots of thorium they will probably be more likely to look at a thorium based reactor system just because they have those resources available to them. MSRs are similarly a valid design, they have both benefits and drawbacks when compared to conventional light water reactors, but right now the inertia and the majority of the experience are in light water so that's largely what people are willing to build. Each reactor represents a massive investment so people want to be 100% sure that they know they are going to get their money back on that investment. Experimental technologies aren't likely to be the sort of thing that people want to bet the company on, you know? The question then is, who does prove it? Probably the government, or a startup company that needs to break ground to prove their concept. I expect that China will be the big player in the near term, they're building reactors like crazy and are more than willing to try new things over there. They have a much more... commanding regulatory system, and a need for power that is second to none in the world right now. Look to China for the next 10 years or so and see what comes out of there as a doable concept, then you might see someone try to build one here in the states. Longer term, India and some other places might also take the innovation baton and run with it, but sadly I don't think the US is really in the innovation game anymore.
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May 20, 2016 10:58
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Olothreutes posted:sadly I don't think the US is really in the innovation game anymore. Is that because we've got plenty of uranium, or nimbyism, or the fact that we're pretty comfortable with building and maintaining light water reactors, or a combination of all three? e: Thanks for the detailed responses itt, btw. Murray Mantoinette fucked around with this message at 15:10 on May 20, 2016 |
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May 20, 2016 15:01
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st1LL_51ngl3 posted:Is that because we've got plenty of uranium, or nimbyism, or the fact that we're pretty comfortable with building and maintaining light water reactors, or a combination of all three? It's really all these things. LFTRs are just so outside the realm of regulatory experience there doesn't really exist a framework for evaluating their safety in the US. Simple basic differences from what we've always taken to be a rule like "nuclear fuel should be solid and stay that way" is actually a huge detriment compared to the potential safety and lifetime of a fluid fuel system. It's a something I've repeated a lot, fluid fuel is the future. But the potential cost of the extractor in a breeding system is huge, both to construct and safely operate, all in addition to the normal difficulties of every commercial NPP. That, coupled with the fact that there just isn't a great incentive to push for new fissile fuel channels any time soon puts the breeder on the back burner  for a while.The US isn't totally out of the game yet though. The ORNL has been quietly doing research on the FHR, or Fluoride-Salt-Cooled High-Temperature Reactor in a mock setup that would still use solid fuel, but with a mixture (called a eutectic) of lithium fluoride and beryllium fluoride, colloquially called flibe as a coolant. These salts, when contained properly with super alloys, make for a great low pressure heat transfer medium, they're just so ideal for a heat engine cycle it's enough to offset the whole corrosion/chemistry-related concerns. But if the guys with the FHR are really brilliant, they could potentially design two reactors in one. Now this is just my little conspiracy and I doubt they're doing this, but one could maybe potentially design the FHR to run with solid fuel in one state, or swap out the solid fuel rods for fuel directly in liquid solution and replace the fuel rods with moderating/controlling elements.
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May 20, 2016 17:46
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The Protagonist posted:The US isn't totally out of the game yet though. The ORNL has been quietly doing research on the FHR, or Fluoride-Salt-Cooled High-Temperature Reactor in a mock setup that would still use solid fuel, but with a mixture (called a eutectic) of lithium fluoride and beryllium fluoride, colloquially called flibe as a coolant. Fun story, I've actually seen real flibe (solid). My university is part of the IRP that works on the FHR, along with UC Berkeley, MIT, UW Madison, and some others. There are a lot of challenges that are being worked on right now in that arena. For the FHR designs that use pebbles there are some questions about how the pebbles interact with one another and if carbon particulates that come off of them will ruin the salt, and how do you clean the salt if that is the case. I'm of the opinion that the FHR is neat, but seeing they work that is going on and the challenges they are working with, it's mostly an academic exercise that will probably be built in China if at all. It is very easy to swap the FHR to liquid fuel, though. The usual design is a pool type reactor with solid fuel in it and that's basically a stone's throw from a pool with liquid fuel in it. Protagonist: This one is for you. For liquid fuel reactors, consider that the criticality equation has a convection term now. Think about how fun that is to solve in multigroup. Olothreutes fucked around with this message at 23:56 on May 20, 2016 |
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May 20, 2016 23:54
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So assuming it's lacquered, is DU safe?
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May 21, 2016 05:10
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| # ? Jun 7, 2024 07:32 |
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would probably be fairly safe even without a coating as long as you washed your hands after handling it and didn't let it get damaged
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May 21, 2016 05:13
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