Off-shore Nuclear-waste disposal.

dx/dy=?

With the growing human population and its need for energy, and the dwindling supplies of fossil fuels, nuclear energy seems to be the 'wave of the future' for most, but disposal of waste is a key issue.

Disposal of radioactive waste into off-shore subduction zones in the Earths crust have been brought up a few times. The obvious hazards of this proccess being massive amonts of energy released by the waste as it enters the mantle, causing silliping and collapsing of faults in the subducting crust.

This method 'supposedly' reinserts the nuclear-material back into mantle convection cycles where it returns to a form composite of that of the liquid mantle.

What are your thoughs on this method of disposal, and its pro's and hazards?

Also, where do you think the best zones for this proccess of disposal would be?
San-Andreas fault is obviously out

Cheers for your time.

matthyaouw

It probably wouldn't subduct. Chances are, it would just become part of the accretionary prism of sediment that fringes the island arc or mountain range. if it were buried incredibly deep in the sea floor sediment, perhaps it would enter the subduction zone and mantle, but think of the logistics of burying it so deep in sediment when under a few km of water already.
Assuming it could be buried deep enough to subduct along with the crust, it would take so long to decend into the subduction zone that in the forseeable future, it would be no more advantageous than burying it in any other deep water. Let's not forget of course earthquake hazards. Placing something in such a tectonically volatile area is tricky if you'd rather it didn't escape from its container.

Astronuc

One would still want to dilute, isolate and otherwise immobilize the radionuclides in some chemically inert matrix - vitrification or Synroc.

As for subduction, that could take decades or centuries depending on the subduction zone.

Grogs

I haven't heard anything about using subduction zones for disposal. As the others have said, it sounds risky. It would probably be near impossible to design a cask that would survive all the possible stresses in such a zone.

What I have heard about is subseabed disposal though. Essentially, you'd want a nice stable area several thousand meters deep that's got a nice thick layer of silt (compressed into clay) on top. The waste could then be dropped from the surface in a specially designed cask that would penetrate 30m or so into the clay and bury itself. The thick layer of clay around the cask would then serve as a shield against the radioactivity when the cask breaks down in a few centuries or millenia. One of the biggest (technical) challeneges would be minimizing the impact on deep ocean life. radioactive decay in spent fuel produces a good deal of heat and warming the seabed even a few degrees could be detrimental to life there.

Realistically though subseabed disposal is not a likely option. The ocean is international territory and if one nation took it upon themselves, the rest of the world as well as environmental groups would probably complain very, very loudly.

matthyaouw

I'd say millenia at the very least.

LURCH

The main advantage would be permenence. Once buried in a subduction zone, the waste will only continue to get burried deeper as the millenia roll by. Re-absorption into the mantle may take thousands or likely millions of years, but once a canister embedded in one tectonic plate slides under the edge of another plate, it is very secure.

Phobos

Any regulatory agency is going to want to monitor the effectiveness of a nuclear waste disposal program. How the heck would you monitor an off-shore subduction zone?

hitssquad

Here is a simpler method.

Step 1: Weld fins to one end of individual fuel rods.

Step 2: Drop fuel rods in deep, silty-bottomed area of ocean.


It isn't necessary to bury the fuel rods, of course. They might simply be ocean-dropped or perhaps cut open so the fuel pellets can be ocean-sprinkled.

hitssquad

If a given regulatory agency has no political power, then what it might want is irrelevant.

oldunion

how much waste is there?

Has anyone read anything about the possibility of using electromagnetic mass drivers to shoot a payload into space? This would be along the lines of Gauss guns (coil guns).

wonderingingatineau

Forgive me if my reply does not address your question directly but is directed at your assumptions. You initial statement, to wit:

With the growing human population and its need for energy, and the dwindling supplies of fossil fuels, nuclear energy seems to be the 'wave of the future' for most, but disposal of waste is a key issue.

seems to claim that fissionable materials on the planet are NOT fossil fuels. I do not think you were referring to fusion, were you? The supply of fissionable materials on earth is certainly a non-renewable resource, in the same way that stocks of coal and petroleum are non-renewable.

We cannot power a sustainable world economy based on stocks of capital assets such as non-renewable minerals, just as you would not set fire to your home in order to heat it.

I am certain you understand the implications of what I am saying. The only sources of energy that should be considered "long term" are renewable, sustainable sources: solar radiation (in its several manifestations, wind, biomass, climatic variations, etc.), geothermal and gravitation. These energy funds will exist for the lifetime of the planet. Any energy use in excess of that provided by these sources (funds) will deplete our natural "capital" (stocks) irreversibly and should be avoided, even without considering the additional energy costs of disposing of the wastes thereby produced.

Please forgive my intrusion if you feel it was inappropriate....

Andre

Hi and most welcome here, Wonderingingatineau(?). I don't think your statements are very appropriate and indeed very valid.

A little bit semantics her, considerng that fossil is defined:

As a side remark, there is an ongoing discussion if natural oil is indeed "fossil" or if it has an anorganic abiotic origine.

So the use of "fossil" is not the most accurate when "non-renewable" is intended. As far as the threat goes, if we want to re-establish a natural balance between mankind and resources eventually, nuclear fission may or may not be a feasible temporary solution. I should depend on basic economic laws, what are the cost? What is the sustainability and durability? What are the problems (waste) and can those be solved in a feasible way? Decisions should be based on technical, objective considerations about the manageability of risks.

However with our natural human nature of creating devils and dragons to feed our fears, the discussions tend to get rather subjective.

Mattjrat

I think we're getting a little off-topic here. I think the one major setback to subduction disposal is that it is so far outside the normal way of thinking about waste disposal. We are so used to the idea that we need a lang-term stable zone where the waste can sit an decay over thousands of years, and this idea us just the opposite; calling for an extremely active zone that will slowly move the material into the mantle.
When I think of subduction disposal, I imagine a ship that would drill a hole about the size of the Tru-pact container, drop in a canister, cover it over, and move on about 50 miles or so to the next spot along the fault (granted several miles from the actual fault, but you get the idea).
The problem with any sub-seabed disposal is the fact that we have no idea what lives on the ocean floor. Every time we go for a look, we discover somthing new!
To answer oldunion's question, the Nuclear Waste Database is maintained by the IAEA is an excellent authoritative source that relatively available to the public. The simple answer is: Way, way, too much. The programs at WIPP and Yucca Mountain are barely enough to scratch the surface of the existing build-up and do not even remotely address the continued need for burial space.

Just my 2c.

Astronuc

WIPP is primarily for defense waste (US DOE) and Yucca Mountain is for commerical spent fuel. YM is sized for current lifetime discharges for currently operating plants, but prior to life extension from 40 to 60 years, although it might be able to handle some of that. That is why the option to reprocess is back on the table.

DOE is supposed to pick another repository, but this one would have to be sited 'EAST' of the Mississippi River. Not too many Congresspersons would be thrilled about that possibility.