Naked Science Forum
General Science => General Science => Topic started by: albert on 14/02/2007 22:02:41
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There are a million reasons why this couldn't work - but I'll throw it into the pot anyway....
Caskets of nuclear waste are dropped into a post-eruption volcano - where the pressure has been released and before the lava has started to set. The caskets (oh how stupid this sounds) sink down to the fluid core where even if they break open, the radioactive material is dispersed within the core.
Or maybe, where the earth's crust is thin enough, we could bore a hole through and 'inject' the caskets into the core.
Go on - debunk me!
Albert Titan
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...or the volcano re-erupts creating its very own mega-Chernobyl. Remember that the decay time of the plutonium in radioactive waste is about 250,000 years (10 half-lives).
That means you'd be relying on the volcano you dumped the waste into not to re-erupt for another quarter of a million years. A fairly significant gamble I'd say!
Chris
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Ah - I was assuming 'the core' had a flow and like a post-apocalyptical game of nuclear pooh sticks, the caskets would be drawn away under the mantle never to re-emerge!
I guess it's a little like weeing in your own bathwater though - I'll put my drill away and cancel the meeting with BNFL!
Albert
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If you leave radioactive waste for a geologically fairly short period of time it becomes no more unpleasent than lots of metal ores. So what you want from a disposal site is something that is very likely to be geologically boring for a few hundred thousand years, and ideally that is waterproof, and liable to stay that way.
A volcano as Chris says is a bad place to put it because something interesting may happen, an erruption through the depository, an earthquake breaking it open, hot corrosive fluids dissolving it and moving it into the water table.
Putting it in the mantle would probably be safe, as if you get it deep enough getting stuff up would take a long time, although we don't really understand what is going on down there, and we haven't managed to drill that deep yet, so it would be inordinately expensive.
You are much better putting it somewhere in the middle of a continent where there is nothing tectonic happening anywhere near, ideally in clay so that if there are any deformations the local rock will bend not break, and it is waterproof. You probably also want to put it somewhere where either it is very flat so there is little errosion, or somewhere there is going to be a little deposition. Geology should be good enough now to be able to predict which places on the earth are going to be absolutely fine barring a major meteorite hit, at which point a little radioactivity is going to be the least of our problems.
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More madness....
I think DARFA or NASA has awarded a grant to a team proposing to build a humungous mag-lev rail gun satellite launching device.
If that could reliably and cheaply launch small capsules at escape velocity then there's no risk of launch pad failure, crashes or re-entry and we can launch the pellets into the sun.
Or we could just bury it....
My worry is that even in 100 years we could see some catastrophic decline in present day civilsation due to war, disease, environmental degradation, biological/nanotechnological contamination, the emergence of a new AI driven species that we're predicted to initialiate in 2020 - or most likely a religious fundamentalist fuelled, post-industrial dark age.
So who be around to tell folk to keep away from the derelict nuclear stations and radioactive waste stockpiles if we entered a post-industrial decline?
I don't think we should be so smug as to believe that things will always be this way (like I bet the Egyptians, Greeks, Romans did) and for this reason I think that we either need to avoid more nuclear developments or to be able to put this stuff far out-of-reach for the sake of whoever (or whatever) follows us.
Albert
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If you bury the stuff, you ought to be able to make it difficult enough to get at that you will need at least early 20th century technology to get into it, and therefore you ought to have enough knowledge to either read the warning signs or to detect the radiation. And even if someone did get inside, and spread the stuff around only a relatively few people would die compared to what must have happened to cause civilsation to go back so far. Not many people died in chernobyl and that was a reactor melting down in a nasty way, so probably comparable to a catastrophic release of a depostiory.
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I have always wondered what would be the implications of dropping spent nuclear fuel in the tectonic subduction zones like the deep trenches. That would eliminate the fear of the volcano spewing the nuclear material back out. Plus the tremendous pressure of that depth should prevent the material from spreading right?
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Firstly, in radioactive terms, I am not at all sure that plutonium is that dangerous. It may be chemically dangerous, but as you say, it has a half life of between 24,000 tears (Pu239) and 80 million years (Pu244); but with such long half lives, you wont actually get that much radioactivity.
The other problem with plutonium is ofcourse a security issue - you don't want the bad guys digging it up again.
Subduction zones are definitely not a good idea because there is a significant risk of the crust that gets pushed down in a subduction zone getting pushed up again in a volcano (which often happen in the lee of a subduction zone).
Aside from burying the stuff, I would have thought that dumping it in the middle of the ocean in containers that have a controlled rate of leaching would be preferable. The oceans anyway contain pretty much ever element that can exist, and most of the substances we are trying to dump are not dangerous in very dilute form - it is only above a certain concentration that they get dangerous. That having been said, given the political problem that arose with the attempted sinking of the Brent Spar platform, despite the fact that a good environmental impact assessment had been made; it would probably be a non starter to dump nuclear waste in the deep ocean, no matter how sensible it might be proven to be.
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They are actually thinking of putting the nuclear waste into outer space, just let it floating around. But many people are arguing against this, because eventually, repeated process of this means that we're damaging and polluting our Space.
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They are actually thinking of putting the nuclear waste into outer space, just let it floating around. But many people are arguing against this, because eventually, repeated process of this means that we're damaging and polluting our Space.
I think people can get obsessed about this notion of 'pollution'.
In terms of the impact on space itself, all the communication satellites we put into orbit cause every bit as much pollution, within the context of space itself, as putting a chunk of plutonium up there.
The biggest problem is not with having nuclear waste up in space, as the risk that it may not stay in space, but may fall back to Earth (as has happened to at least one Russian nuclear powered satellite).
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Ermm, George. There's no comment on yours. [;D]
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Ermm, George. There's no comment on yours. [;D]
There is now - sorry - I hit the post button instead of the preview, so had to go back and modify the post.
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Oh OK [;D]
How did it fall back to Earth? Failed to launch? Or went out.. Span all the way round space, then came here again? [:P]
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This is fun...
Plutonium does have a reasonably long half-life. Unfortunately it is an alpha emitter and so, if ingested/inhaled (e.g. as dust) Pu presents a particularly high risk of tissue damage and/or later cancers. So, you have to decide to either (a) leave it well-wrapped up with the rest of the waste or (b) separate it out (carefully!) and use it as fuel. Pu-239 is a better fuel than U-235 as it produces more neutrons per fission at higher energies.
The UK sea-dumped low level waste in deliberately leaky containers just as is suggested here up until the mid-1980s. (Un?)fortunately this is now illegal under international treaty.
Putting waste into space is NOT being considered seriously by anyone within the industry. The risk at launch is too great as rockets aren't anywhere near as relaible as nuclear reactors! One day, when we have a Space Elevator perhaps this would be a more sensible idea.
Space Junk: It's not the size or really the amount that matters, its's the relative velocities... If you are in orbit at 27,000 km/h the last thing you want to do is meet something (say, a spanner) coming in the other direction! This is why so much trouble is taken to track very small items of 'space junk'.
Things falling back to earth are rarely a problem as it is only the very largest items that survive re-entry. A lot of interest was shown in the re-entry paths for Mir and Skylab (have a look with Google) but nothing much smaller reaches teh ground.
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How did it fall back to Earth? Failed to launch? Or went out.. Span all the way round space, then came here again? [:P]
It was a low orbit satellite (not a communication satellite, so it was not in geostationary orbit, but a spy satellite, so it wanted to stay low to have a good view of the Earth).
Satellites that are in low orbit are still effected by the drag of the Earth's atmosphere (there is very little atmosphere at that altitude, but still enough that every once in a while a satellites need to to be given a little kick to recover the speed they lost through drag, otherwise they lose speed, and fall to Earth.
Cannot remember exactly what happened, whether the satellite ran out of fuel, or lost communication with Earth, but whatever it was, I think they were unable to continue instructing the satellite to give itself that kick to stay in orbit, so it began to slow down. As it slowed down, it began to fall, but as it fell it encountered ever thicker atmosphere, and so the drag increased, and so it slowed down even more, until it tumbled into the main atmosphere, broke up in the upper atmosphere, some of it burning up in the upper atmosphere, while the larger chunks fell to Earth.
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Personally I prefer isolation of nuclear waste in inland salt basins, such as the Paradox Basin in the US. It needs be deep! very deep. 4+ miles deep. Tectonism will most likely expose it to the surface before it is totally safe, but that is going to happen, even if buried deep under a mountain. Before the PU244 isotope is 90% lead is a LONGGGGGG time. The mountains will be gone and another species will dominate the earth.
In Europe, there are such salt deposits in Poland and Russia.
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It depends on the isoptopes in the waste. short lived isotopes may be stored in a reasonably dense and secure underground location and the low grade heat used for agricultural purposes. longer lived isotopes may benefit from further irradiation near a nuclear reactor or possibly with high energy electrons to convert them into shorter lived byproducts