h a l f b a k e r yCeci n'est pas une idée.
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Nuclear waste is usually regarded as an intractable problem, generating heat and radiation for thousands of years into the future. In fact, Yucca Mtn is undergoing a reassessment as to its ability to withstand the prolonged effects of radioactive decay of the waste stored there. The mountain is mostly
tuff, which is showing signs of radiation-induced morphology already.
So, to the idea.
Sinter the waste into glass, making it as concentrated as is possible, then immerse it in water in a small isolated (discrete) artesian basin or a large, purpose-built water reservoir. In fact, I think I'd just go with a manmade reservoir. Much less chance of widespread contamination.
Use the waste heat it generates and imparts to the water to generate geothermal power. The heat radiated is less than that given off by newer fuel but it is still substantial enough to be a problem requiring immersion and sequestration of waste at the moment.
Take advantage of it, making virtue of a necessity.
Yucca Mountain
http://en.wikipedia...wiki/Yucca_Mountain
Anything that requires dangerous waste to be stored safely for up to a million years gets a big thumbs down from me! [DrBob, Jan 05 2009]
SynRoc
http://www.world-nu...org/info/inf58.html
[UnaBubba, Jan 05 2009]
Nanomaterial turns radiation directly into electricity (at newscientist.com)
http://www.newscien...com/article/dn13545
Two birds with one stone. [phoenix, Jan 05 2009]
Link for [david scothern]
http://www.ocrwm.do...ts/doeymp0010.shtml
[cromagnon, Jan 06 2009]
[link]
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There are similarish designs for nuclear reactors that use loose arrangements of fuel (Pebble Bed Reactors) in such a way that the need for complicated core/cooling rod systems is done away with (the earlier designs suffering from problems where a runaway reaction warps the core so much that the control rods no longer fit - resulting in catastrophic meltdown - oops) |
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I'm not sure what grades of waste would provide the qualities we require - low level waste is just clothing and other consumables that have been exposed to radiation, while spent fuel might exhibit the long-term warm properties required. |
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I was thinking of spent fuel materials, spent medical isotopes and decommissioned nuclear weapons. Low level waste is just not "hot" enough. |
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Can't you just dilute the stuff, mix it with cement and put it back where it came from ? |
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Gotta admit I'm not a big fan of putting this stuff into any water table... |
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Why not simply let life imitate art and ship it to a holding area on the dark side of the moon ? |
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(I actually think that's a good idea... furthermore you could take the opportunity to rid the world of horrible 1970's fashions.) |
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bigsleep raises an interesting point: Nuclear fuel has been extracted and refined. We've then extracted energy from it, leaving it (as a whole, including all of the ore we took it from) less radioactive. |
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In principle if not in practice, why can't it be diluted and put back where it came from? |
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Probably because most people are dumb. You see, the stuff
you dig out is Natural, and produces Natural radiation; in
fact, it's probably organic. The stuff you put in, of course, is
not Natural, and is therefore More Dangerous and Manmade -
we have no natural resistance to Manmade radiation,
whereas clearly our bodies have adapted to cope with
Natural, organic radiation. |
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The SynRoc (Synthetic Rock) program is about just that. It is a technology that uses a titanium oxide or aluminium oxide ceramic matrix to hold high level waste in a safe state for a very long time. Lower level wastes are currently sequestered in borosilicate glass. Weapons grade plutonium is the most difficult to deal with and is the waste SynRoc is being used to hold. |
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As to [zen]'s comments above on pebble bed reactors, I advise everyone to have a good read up on them. It's been awhile since I did any real research on PB type fission reactors, but I recall they're one of the most elegant system designs I've come across. What they do is rely on the coolant water being, well, cool, to ensure fission occors. IIrc it's got to do with the water density slowing neutrons enough so the flux is right to maintain the fissions. As the coolant heats up, coolant density goes down (especally when bubbles form) and thus neutrons are able to escape the core in more numbers, slowing the reaction. In this way the reactor is inherently safe, ie a coolant loss, leak, error, etc results in a reactor shutdown rather than a runaway event. |
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Someone should get a medal or at least a few beers down the pub for that. |
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As to the idea here [sorry bubs] sounds good... Are we sure we can [safely] get the energy density high enough for it to be worth trying to extract energy? I couldn't imagine a system able to extract useful energy from a water source under say 80 degrees [c] or so. Unless we're talking about pressurised underground reservoirs here, where you can go over 100 degrees. |
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The elegantly simple pebble-bed reactor is likely to be the first of the Generation IV nuclear reactors to come online - although I've only heard of helium-as-coolant versions. 900 degree centigrade water - (the temperature where effecient thermo-cracking of water into hydrogen becomes feasible) - is inherently corrosive. |
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But, the next Generation IV reactor (after PB) to come online is supposed to be the holy grail of reactors: the molten salt reactor. This reactor will literally use (almost all) of the waste nuclear fuels sitting around as part of it's reactants (even the ultra long-lived trans-uranic elements); making long-term storage less of an issue. [=] |
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To the best of my understanding, pebble bed designs are
already low waste. Since the fuel is
divided into many smaller portions, rather than a few larger
ones (i.e. fuel rods), each pebble can be allowed to (nearly)
fully decay before being replaced. This results in a much
lower volume of high level waste in the form of incompletely
decayed fuel. It also produces lower levels of low level
waste, as less total handling is required for the volume of
radioactive material used. |
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Thanks for the input, [WP] and [MechE]. I was aware of few of the details of pebble bed reactors. I recall seeing a fuel pellet about the size of a grapfruit. It was a pellet of fuel about as big as a golf ball, wrapped in an inch of carbon. |
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I must also admit to having thought about a PBR style of design when I proposed this idea. |
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Geothermal energy is accessible at far lower temperatures than boiling point. |
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One thing I found interesting while reading up on Nuclear Reactors (the 'bakery is like a guided reading programme sometimes) is the suggestion that in the geologic past, natural fission is thought to have taken place wherever suitably radioactive uranium isotopes has gathered in large enough concentrations in the earth's crust - not so likely these days (half-lives and all that) but interesting considering our encringement from what are generally deemed unearthly processes (I remember reading a children's story once that suggested that Satan, or at least some of his wizards, lived in nuclear reactors) - the fact that it is a natural process seems to escape the general consciousness - probably due to its association with the bomb I guess. |
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The thing that does remain worrysome is in the design of legacy reactors (as mentioned previously) where the control system relies on the reactor behaving itself. |
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I believe there is some evidence of spontaneous, self-sustaining nuclear fission at a site in Gabon. I'm a little hazy on the details, as it's a long time since I read about it... maybe 30-35 years ago but the incidents apparently occurred over a billion years ago, from what I remember. |
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...and is the only natural reactor to have been discovered so far, if I remember correctly. Anyone have a link? |
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[zen tom] I completely agree on how this place guides my reading. It reminds me of Dennis Miller's short lived TV show which closed the show with a recommended reading list so you'd understand the following nights jokes. |
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I just found the link posted by [cromagnon], independently. Damn, I love having a photographic memory! |
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