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Author Topic: Could subduction zones be used to bury nuclear waste?  (Read 6292 times)

Offline thedoc

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"matthew_doughty asked the Naked Scientists:
   
Hi

Would it be possible to dispose of nuclear waste safely and permanently by burying it deep in an area where the earth's crust is sliding under another ?

Regards

Matthew

What do you think?
« Last Edit: 15/08/2012 00:30:01 by _system »


 

Offline CliffordK

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Re: Could subduction zones be used to bury nuclear waste?
« Reply #1 on: 15/08/2012 06:54:16 »
Interesting idea, as over thousands of years, the material would be slowly driven deeper into the Earth.  I'm not sure how deep one would have to drill, perhaps out in the deep ocean.

I can envision a few issues. 

Plate boundaries are always tectonically active.  That means one would have to prepare one's systems to deal with earthquakes.  I'm not sure how deep one would have to go to be sure one was in, say the Pacific plate.  Perhaps a mile or so.  Depending on how close one started to the plate boundaries, it still might take thousands of years before it would be driven below the continental plate. 

As the plate plunges down, then it would begin to melt down.  I'm not sure how big the contamination plume would be.  My guess is that it would not be significantly dispersed underground, so a glob of molten radioactive materials might remain.

The risk is then that the nuclear material could contribute to volcanic material, and be delivered back to the surface, potentially contaminating large areas.  This might happen hundreds of thousands of years in the future, but could be devastating for future inhabitants of the planet.

Anyway, if one goes deep enough with offshore drilling, one would get away from water tables, oil, briny water (which may become an important future resource), etc, but the distant future volcanism might make the plan a non-starter.
 

Offline Mazurka

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Re: Could subduction zones be used to bury nuclear waste?
« Reply #2 on: 16/08/2012 09:53:51 »
Notwithstanding legal / political ramifications, there are a couple of issues with this - keeping the material contained until it had been subducted (which will be a period of thousands of years) and preventing it becoming caught up in the accretionary prism.

As Clifford points out subduction zones are tectonically active - so containment would have to be significant, otherwise you might as well just sink it onto abyssal planes where it would probably bury itself and be out of harms way for a long time.


There is the "dilute and disperse" argument to say that it does not matter compare the volumes of high level waste vs the volume of the oceans and concentrating waste in a few locations poses a greater risk environmentally. 

Other oceanic options that have been put forward are dropping containers onto the continental slopes so that they woudl be buried by turbidity currents (a kind of oceanic mud slide) which we know a lot more about following research in the 60's and 70's into the viability as a method of radioactive waste disposal...

I don't think the issue of radioactivity coming back out in volcanos would be a huge issue - due to dillution and mixing within the melt and because not all of the melt comes out as extrusive igneous rocks - much remians underground (in dikes and sills etc.) where the radioactive elements be encapsulated in various minerals. 
 

Offline slush33

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Re: Could subduction zones be used to bury nuclear waste?
« Reply #3 on: 25/09/2012 21:07:18 »
I'm neither scientist nor expert but I'd like to get in my two cents.

We are now capable of drilling to great depths[the Russians have reached 7 miles]. Seems to me we could drill to a couple of miles and fill the bottom 1/2 mile with waste as long as we were clear of volcanism. Much of the waste could be disposed of on site. With the exception of plutonium this stuff is non-toxic in considerably less than a hundred years.

Is that feasible or no?
 

Offline Mazurka

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Re: Could subduction zones be used to bury nuclear waste?
« Reply #4 on: 26/09/2012 11:51:21 »
Drilling to that sort of depth costs a fortune.  Costs increase very quickly the deeper you go.

However, as I understand, there is a facillity in Sweeden are developing a facillity (near Osthammar) , where a "mine" has been dug into very stable rocks. 

Inside the mine,large diameter boreholes will be drilled.  Into the holes high level waste (encapsulated in iron) and placed in copped cylinders  will be disposed of.  To further protect the cyclinders this they will be surrounded by a swelling clay (bentonite) , so if water gets into the hole, it will be firstly absorbed by the clay which then swells up.  Becasue the clay will be confined in the rock, the swelling will result in a practically impermeable barrier, so the copper containers will not corrode. 
 

Offline yor_on

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Re: Could subduction zones be used to bury nuclear waste?
« Reply #5 on: 23/10/2012 11:57:41 »
Nope and nope. We have a suggestion of this Mazurka but it's being contended by other (material) scientists and as I know there is no agreement of doing it yet. And we better know what we're doing there. And as for only plutonium being the only one radioactive over any longer time periods Slush??

"The radioactivity of all nuclear waste diminishes with time. All radioisotopes contained in the waste have a half-life—the time it takes for any radionuclide to lose half of its radioactivity—and eventually all radioactive waste decays into non-radioactive elements (i.e., stable isotopes). Certain radioactive elements (such as plutonium-239) in “spent” fuel will remain hazardous to humans and other creatures for hundreds or thousands of years. Other radioisotopes remain hazardous for millions of years. Thus, these wastes must be shielded for centuries and isolated from the living environment for millennia.[2]

Some elements, such as iodine-131, have a short half-life (around 8 days in this case) and thus they will cease to be a problem much more quickly than other, longer-lived, decay products, but their activity is therefore much greater initially. The two tables show some of the major radioisotopes, their half-lives, and their radiation yield as a proportion of the yield of fission of uranium-235."

Furthermore, talking about a 'half life' of, let's say 8 days, only means the substance losing half its former radioactivity, it doesn't tell you when it is safe for humans.
 

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Re: Could subduction zones be used to bury nuclear waste?
« Reply #5 on: 23/10/2012 11:57:41 »

 

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