John Brockman asked:
I have wondered if the geological, tectonic subduction of nuclear waste materials might be a practical way to permanently remove these dangerous substances from the earth's surface and at the same time to feed the Earth's magnetic field. Is anyone working on the development of such notions?
Dave - So, this sounds like a lovely idea, this subduction zone. It’s where stuff is being sucked down deep into the earth and you'd expect then it not to come back out again and it will be a nice comfortable place to put all the nasty stuff we want to get rid of.
Actually, that's not quite how the geology works. Where a subduction plate gets pulled down under earth, it gets a huge amount of friction and that surface layer get very, very hot. That surface layer tends to melt and then come back up to the surface and form a volcano. And so, you get a lot of volcanism related to subduction zones and it’s this top layer heating up, melting and floating up to the surface through the surrounding rock and creating volcanoes. This means that actually, if you put all your nuclear waste on that surface zone, there's a big possibility it would shoot out a volcano, probably in a few hundred thousand million years later. And also, there's an awful lot of water, hot fluids flooding through that so there's a really, really aggressive environment.
Chris - What about John's point about the magnetic field?
Dave - So, magnetic field is all to do with the very, very centre of the earth, right down in the core. In there, there's some complicated system involving liquid metal flowing around because parts of the core is metal and to do with the earth spinning and a convection current in there which to be honest I understand and I think scientists have only recently understood it at all.
Creates this magnetic field and so, doing anything near the surface probably isn’t going to affect that very much. It’s got to go down through the whole mantle which is thousands of kilometres of really thick gooey rock. I think at the moment, the best thing for the nuclear waste is probably just to bury it somewhere where nothing is going to happen. So, a really dull geological place, ideally in some clay because it will sit there for a hundred thousand, few million years. Nothing is going to happen to it and you can just sit there until it calms down and isn’t dangerous anymore.
Chris - A lot of people say, “Well, we’ll just embed it in concrete or glass or something” but then there was this paper which was published by Ian Farnan who’s a researcher at Cambridge University about 7 or 8 years ago. He found that if you look at the ceramics that you put these radioactive chemicals into, because of the radioactive decay, when a uranium atom decays, it fires almost like a recoil as it fires out a radioactive particle. It’s like a gun recoiling into your shoulder when you fire a shotgun for example. This has the effect of knocking all of the other atoms off kilter in the substance. The result of that is that over time, with all these atoms being knocked off kilter, you end up with the material becoming amorphous as it’s called and it’s basically riddled with holes. It’s leaky. So, after just 5,000 years, you'd go from something which was a solid concrete or piece of glass which would be something analogous to a sieve.
Dave - Yeah, this is why you want to put it in some rock which is naturally waterproof and actually doesn’t have cracks in it which is why I think the ideal solution is a big lump of clay. I think East Anglia is meant to be especially good for it. But possibly not popular.
I don't think it's a practical because we can't get political agreement on where to put it.
Deep boreholes (5 km or more) are one suggested solution. One elegant idea for high-level waste is to seal it in half-metre tungsten containers, put it at the bottom of a deep borehole so that the heat it generates will melt the rock below it, and it will sink into the depths, with the rock cooling and setting above it. dlorde, Thu, 14th Nov 2013
Ahh, just love this reply Chris. That's exacly what was being tried in the States, and found failing. There are no known containers that will contain radioactive waste from nuclear over longer time periods, as I know.
Ian Farnan was only about 50 years late in publishing his work. Radiation damage effects in structural ceramics have been extensively studied since about 1950 and indeed form the basis for archaeological dating of ceramic artefacts - though admittedly most of that work was done in Oxford in the 1960's so the news wouldn't have reached Cambridge just yet.
I understand that we have amongst the best, stable old rock, in the world here in Sweden Alan, geologically speaking. and that we were thinking of trying to sink it into deep mines, 500 m down, filled with bentonit clay, radioactive waste clad in a copper and steel encasing. But we're still debating it, although waterfall (Vattenfall) in its infinite wisedom would love the project to go through. That's the same company now getting thrown out of Germany, more or less, as it bought up old nuclear facilities, now planned to getting dismantled, as well as 'brown coal power plants'. I really trust those guys :) and their approach to a greener world. The worst thing about them is that over fifty percent are owned by us all, aka 'the state'. Tells you something about our new political agenda, doesn't it :) A economical 'world power' in the making, well, at least Vattenfall thought so, until recently.
by the way dlorde, check out the waters outside Africa for where some of that stuff gets illegally dumped, as outside Somalia. yor_on, Mon, 18th Nov 2013
Wish I could be as sure as you guys, but I'm not. I know that the copper encasing is expected to leak in the Swedish idea for long term storage, one reason for the long term storage project being halted. Another is microscopic fractures even in this 'perfect old rock', as well as a question about the permeability of the clay surrounding those 'caskets'. The same problem as Yucca.
Dave, it seems to me, a mere layman, that your first 2 paragraphs involve a difference in timescale of at least 5 orders of magnitude - that's a wide-open door that it should not be beyond the wit of man to walk through, especially for low-level bulk waste. A sub-oceanic active area of subduction, with a relatively high angle of flow, near to a relatively sparsely inhabited landmass of the most suitable geology would be ideal. D D Jones, Thu, 22nd May 2014
"...Actually, that's not quite how the geology works. Where a subduction plate gets pulled down under earth, it gets a huge amount of friction and that surface layer get very, very hot. That surface layer tends to melt and then come back up to the surface and form a volcano."