How should we get rid of Nuclear Waste?

[cantab]

Basaltic rocks melt from 1000 to 1200 °C or so. Most steels are solid at that temperature. If the fuel inside melts, so what?

Presumably you would bury the sphere initially so that it won't waste its heat. It could also help to have a sphere made of something with a higher melting point that's then placed in a mass of molten iron. The iron does most of the "work" of getting down through the rock.

[Nuke]

i still think drilling into bedrock is the better solution. that pretty much guarantees subduction will consume the waste, and isolates it better from the ocean environment.

[theend3r]

If it's radioactive then use it, why would you discard a power source? (For example depleted uranium can be used in thorium reactor fuel cycle.)

[Beowolf]

If it's radioactive then use it, why would you discard a power source? (For example depleted uranium can be used in thorium reactor fuel cycle.)

Exactly! Nuclear waste is "waste" the same way gasoline was waste in early oil refining. There wasn't anything to do with gasoline at the time, so it was waste...but that situation didn't last long.

The goal should be safe storage of this material, but with the idea firmly included that it's likely to be recovered and used someday.

[Brotoro]

...The goal should be safe storage of this material, but with the idea firmly included that it's likely to be recovered and used someday.

I agree. Put the dry casks into Yucca Mountain. The stuff will be useful later. But keeping it all over around the country is stoooopid.

[Seret]

Basaltic rocks melt from 1000 to 1200 °C or so. Most steels are solid at that temperature.

Solid maybe, but too soft to function as a pressure vessel. Even titanium will creep under those temperatures and pressures. It's not a practical idea.

[Nuke]

If it's radioactive then use it, why would you discard a power source? (For example depleted uranium can be used in thorium reactor fuel cycle.)

i made it clear earlier that i would prefer it be burned. but even then we will end up with wastes that you cant use as fuel. use the good stuff, dump the crap in the subduction zone.

[peadar1987]

Basaltic rocks melt from 1000 to 1200 °C or so. Most steels are solid at that temperature. If the fuel inside melts, so what?

Presumably you would bury the sphere initially so that it won't waste its heat. It could also help to have a sphere made of something with a higher melting point that's then placed in a mass of molten iron. The iron does most of the "work" of getting down through the rock.

Depending on the composition, it's going to melt between 1100 and 1500°C

So you're right, the steel won't be liquid at that temperature. However, metals start to creep at about 1/3 of their melting temperature in Kelvin, so at around 320°C. The effect isn't too bad at first, but at the temperatures we're talking about, the steel is going to behave like chewing gum. Even if you do manage to get something hot enough without ruining its mechanical properties, it's going to sink unbelievably slowly. Lava is incredibly viscous. Even the least viscous lava is about as thick as motor oil, and that's very specific compositions at very high temperatures. We're probably looking at something more like room temperature honey or thicker.

If you're going to bury it anyway, you're probably better off just putting it in a subduction zone to be honest.

[lajoswinkler]

It's not waste, and its volumetric amount is pathetic. My country's power plant has been working for more than 30 years and its spent fuel rod pool still has plenty of space left.

You know why are politicians trying to bury it? Because of the "green" idiots (unfortunately, lots of greens are like that - "green"). It's not waste. It's precious material waiting to be reprocessed.

[hugix]

Toss it in the ocean. Water is a great insulator and it's a hell of a job to get it back to the surface so it's safe from terrorists.

[lajoswinkler]

Toss it in the ocean. Water is a great insulator and it's a hell of a job to get it back to the surface so it's safe from terrorists.

You know, rays are the least serious problem with this waste. 5 km below the surface of the ocean and 5 km in the middle of a desert is the same thing. What you don't want is contamination, and that is likely to happen if you toss it in the ocean.

[FREEFALL1984]

Just dig a deep enough hole and bury it, failing that bury it in an existing empty oil well, that should be more than sufficiently deep and isolated.

[Beowolf]

i made it clear earlier that i would prefer it be burned. but even then we will end up with wastes that you cant use as fuel. use the good stuff, dump the crap in the subduction zone.

Objection. Those are "wastes" solely because we can't use them today. That in no way means some of those isotopes won't be worth $1,000/gram a century from now. Heavy elements are one resource we can't count on finding in space. Don't throw them away, at least until we learn otherwise.

[78stonewobble]

You know, rays are the least serious problem with this waste. 5 km below the surface of the ocean and 5 km in the middle of a desert is the same thing. What you don't want is contamination, and that is likely to happen if you toss it in the ocean.

Terrorist wise theres a big difference between having to go 5-11 km. into a desert versus going 5-11 km. to the ocean floor (or trench floor).

Also, stuff gets blown from deserts hundreds, if not thousands of kilometers away all the time. Stuff rarely leaves the ocean (or trench floor), travels to the surface and then gets blown by wind hundreds or thousands of kilometers away.

[78stonewobble]

Objection. Those are "wastes" solely because we can't use them today. That in no way means some of those isotopes won't be worth $1,000/gram a century from now. Heavy elements are one resource we can't count on finding in space. Don't throw them away, at least until we learn otherwise.

And here I thought that heavy elements came from space, since they were made in, you know, stars and supernovas.

[andrewas]

Many of the isotopes found in nuclear waste have half-lives too short to be found in nature, any that were produced in stars decayed long ago. If any of them are useful, it may be easier to separate them from nuclear waste where they were formed as a byproduct, rather than synthesizing them in a lab.

[xcorps]

Just dig a deep enough hole and bury it, failing that bury it in an existing empty oil well, that should be more than sufficiently deep and isolated.

Empty oil wells do not lead to huge chambers or pockets of air. They are generally less than 3ft in diameter and include cement formatives and drilling pipe of various diameters, so they aren't even empty. They rarely go straight down. The average Td of a dry well in the United States is about 5000ft.

LLW is about 90% of our current production of waste. Most of it isn't actually nuclear material, but stuff exposed to nuclear material. Like chains, gloves, tools, containers, etc etc. So you'd have to convert it into pills with proper size and shape to fit into an empty well that was completely decommissioned and deconstructed (which is about 5x the cost of drilling the hole in the first place) to have an empty tube. Then you'd have to figure out a way to line it with a material that is permanently waterproof and radiation proof, which is probably an engineering task 25x more difficult than just drilling a hole. I suppose somebody could come up with a liquid injection through a mold, but again your looking at extreme costs just to manage to line the dry hole. Let's assume that you have left a 5000 ft hole with a foot diameter interior space. That's about 15,000 cu ft, which is 0.11 percent of the total yield of LLW per year.

Unless you don't mind poisoning the strata. In which case you should just dump it in old coal mines. It'd be cheaper by far.

Toss it in the ocean. Water is a great insulator and it's a hell of a job to get it back to the surface so it's safe from terrorists

You can go to prison for a year for causing 1 teaspoon of oil to be discharged into the navigable waters of the United States.

[lajoswinkler]

Terrorist wise theres a big difference between having to go 5-11 km. into a desert versus going 5-11 km. to the ocean floor (or trench floor).

Also, stuff gets blown from deserts hundreds, if not thousands of kilometers away all the time. Stuff rarely leaves the ocean (or trench floor), travels to the surface and then gets blown by wind hundreds or thousands of kilometers away.

I was just commenting on the rays. Dispersion is another thing.

Vertical mixing does happen even at the deepest parts of the ocean, and it isn't that slow. Otherwise, there'd be no animals breathing oxygen down there.

[Nuke]

Objection. Those are "wastes" solely because we can't use them today. That in no way means some of those isotopes won't be worth $1,000/gram a century from now. Heavy elements are one resource we can't count on finding in space. Don't throw them away, at least until we learn otherwise.

as said elsewhere in the thread, not all nuclear waste is spent fuel.

[Floppster]

I don't know if anyone has said it before, but beside being horribly inefficient and stupid, flinging heavy elements into the sun isn't a very good idea. Anything heavier than iron takes more energy to fuse than it gives away and by tossing tons of nuclear waste into it, the lifetime of our sun would drastically change.

[Seret]

as said elsewhere in the thread, not all nuclear waste is spent fuel.

Low and medium level wastes aren't a problem for disposal, we do it routinely. The OPs question implies the currently unsolved problem of high level waste.

[Brotoro]

...tossing tons of nuclear waste into it, the lifetime of our sun would drastically change.

No. The Sun would laugh at any amount of material we could drop on it with our puny technology. The Sun is huge.

[lajoswinkler]

I don't know if anyone has said it before, but beside being horribly inefficient and stupid, flinging heavy elements into the sun isn't a very good idea. Anything heavier than iron takes more energy to fuse than it gives away and by tossing tons of nuclear waste into it, the lifetime of our sun would drastically change.

Just... no. Total volume of the high level waste today (waster after reprocessing and spent fuel combined) would fit in a few large swimming pools. Earth is much larger than such volume, and Sun...

So... no.

[peadar1987]

And here I thought that heavy elements came from space, since they were made in, you know, stars and supernovas.

As andrewas has said, some of these elements aren't found in nature because of their short half-lives (short in a cosmological sense). Also, even other elements will be found in different concentrations in different places in the universe. Far out in the solar system, hydrogen and helium are plentiful, but heavy metals are relatively rare. The opposite is true further in (very broadly speaking, of course)

[Beowolf]

And here I thought that heavy elements came from space, since they were made in, you know, stars and supernovas.

Well, sure. But because they're so dense, the overwhelming majority end up in the cores of the star and planets. Earth seems to have formed in a particularly rich part of the primordial solar system. Not only is Earth the densest planet in the system, but because of all those lovely radioactives it still has a molten core, and therefore the magnetic field that makes our lives possible.

From what I've read, the deposits of uranium and such in Earth's crust are part of its original formation rather than from later bombardment. They are (probably) upwellings from deep below caused by turbulence during the asteriod bombardment period. The crust hardened before they sank again.

I didn't mean to imply there isn't any uranium off Earth. We already know it can be found on the Moon and on Mars in a concentration of around 1 ppm, but you can't mine that! The only other data point we have (that I'm aware of) is there are definitely not any large asteroids made of uranium ore like golden-age science fiction frequently predicted. It doesn't take that much radioactive ore to cause an asteroid to get a few degrees warmer than it should be, and IR telescopes would notice.

All I'm saying is we really don't know if there are non-terrestrial deposits of uranium and thorium which are both accessible and profitably dense. And until we actually do know of more, I'm opposed to throwing any transuranics away. Even the dangerous ones.