Nuclear waste disposal idea

[farmkid]

The other day, I read someone mention this idea for disposal of nuclear waste and thought I would present it here for discussion. The idea is to dump it at a subduction zone to be drawn into the mantle of the planet and sequestered there. What do you think of this idea? Here are the questions I would want answered before deciding whether or not it is a good idea:

• Will it actually be drawn under the surface of the earth, or will it just be scraped off the subducting plate and sit on the surface? Will we have to dig down into the subducting plate to get it to be drawn into the mantle?
• How long will it take to be subducted under the overlying plate?
• What will happen to it once it has entered the mantle? It will surely melt, but then what?
• Will it come out of a nearby volcano? Or, will it be heavier than the material of the mantle and sink? If it will come out of a volcano, how long will that take?

With regard to the last question, I suspect that the density of the high level waste such as spent fuel rods will cause that material to sink deeper into the mantle. The rest would probably take long enough to reach the surface of the earth again that it would not longer pose a hazard. So if it were as simple as dropping stuff at subduction zones in containers that will be secure for as long as it will take to be drawn under the other plate, I think this is a good idea. However, there are a lot of ifs there that really need to be answered.

 

[John Picard]

Two words: Breeder reactor.

 

[PlixTixiplik]

I think it depends on the particular subduction zone (whether it is sediment-full or sediment-starved), but in general the upper levels, perhaps the upper 2/3rds, of the sedimentary cover are stripped off and underplated to form the accretionary prism that is common at convergent margins. So to even get the waste subducted you would have to drill and bury it beneath several hundred meters of sediment.

Also, plate convergence is very slow (typically 5-10 cm per year) and there isn't exactly a knife-sharp edge to the subduction zone. So even if it was dropped in a trench it would sit on the seafloor for thousands of years before being subducted.

I'm not too sure what would be its ultimate fate in the mantle - I'm not convinced that the metal casing would melt, for example. Temperatures in the upper asthenosphere are maybe 1500 degrees C and the pressures are very high, so it's possible that the container would remain intact and would probably sink. If the waste was actually buried in the ocean crust it would probably stay in the subducting slab, which are usually carried down to the boundary between the upper and lower mantle (670 km) or even deeper. Even if the container and its contents did melt, it would be homogenized so there wouldn't be much worry about highly radioactive lava coming out of the nearest volcano.

So all in all it's pretty impractical, and the residence time on the ocean floor or in the shallow subseafloor before subduction would be an issue. Land-based repositories or further processing and use in different reactor types would be much simpler.

-MEC

 

[Anticitizen]

Reprocessing is definitely the only sane answer, IMHO, and it's pretty disgusting that we're burying this valuable resource under the ground to be poisonous and deadly for many thousands of years to come. When reprocessed enough, the ultimate resulting waste is very low-level.

As I understand it, we can thank Gerald Ford and Jimmy Carter to thank for halting nuclear waste reprocessing by way of executive order, as a nonproliferation measure. The ban has since been lifted but the initiative was killed.

 

[Ariadne]

Two words: Breeder reactor.

Breeder reactors can't deal with nuclear waste, they just reduce by production of it by getting more energy out of the same amount of fuel. (IIRC)

Reprocessing is definitely the only sane answer, IMHO, and it's pretty disgusting that we're burying this valuable resource under the ground to be poisonous and deadly for many thousands of years to come. When reprocessed enough, the ultimate resulting waste is very low-level.

As I understand it, we can thank Gerald Ford and Jimmy Carter to thank for halting nuclear waste reprocessing by way of executive order, as a nonproliferation measure. The ban has since been lifted but the initiative was killed.

QFT.

 

[TEH BABA]

Dumb them on a native american reservation just kidding. kinda what we are doing now.

 

[All Seeing Eye]

I don't know why we don't just store it all in heat shielded thick secure spherical containers and slingshot them into space from the ground. Worst case scenario it falls back to Earth and into the sea (because it will be aimed out toward the ocean aswell as space).

 

[SG-17]

Why not just dump it into an active volcano on some remote island where no one lives?

 

[Mr. B]

I don't see anything wrong with the Yucca Mountain site. The project should be good for 10,000 years, but even if it's only good for 500, surely we will have invented a technology to make the waste inert by then anyway.

 

[Neopeius]

I don't see anything wrong with the Yucca Mountain site. The project should be good for 10,000 years, but even if it's only good for 500, surely we will have invented a technology to make the waste inert by then anyway.

Long ago, when I was doing a pro-nuclear power paper, I read that Yucca Mountain was poorly managed and not very sound.

I don't remember my sources or the exact issues involved. I just remember being surprised.

 

[TerriO]

This is an idle thought that's been brewing in the back of my head for a while now. Why not just shoot it into the Sun? We know we can get nuclear cargo off the ground fairly safely. What am I missing here? Cost is mitigated by the risk of hauling through dangerously populated areas. Gives an entire subdivision to the rocket manufacturing industry. The fact that we're not doing this means I have to be missing something.

 

[Captain Intrepid]

Eh, just put it in some shithole not inhabited by anything resembling intelligent life. Ottawa or Washington DC for example.

 

[Jadzia]

It would be unpopular Terri. International relations would suffer. There were accidents in the 60s/70s with nuclear power cells on rockets, that failed to make it into orbit, exploded in the atmosphere and the on board plutonium was vaporised, that we all have to breathe in now.

This is the issue:
(1) The vast majority of the waste is low level waste, like bricks, clothing of core engineers, disassembled machinery, tools, lead shields... which is far too heavy to throw up in rockets. You know they say rocket costs is $100 per 1g of payload or something. It's an expensive way to get rid of slightly radioactive bricks. They're better off being buried in the mountains.

(2) the medium level waste is the magnesium casing around the fuel, and the material from decommissioned reactor cores. The magnesium is recycled and used for new fuel packaging. The rubble from the core is genuine waste. What's best here? Well again it depends on mass and quantity. Decommissioning is expensive as it is. But this is a viable candidate for rocket-into-sun disposal.

(3) High level waste (spent fuel) isn't really waste. It is potentially fissionable material, so it isn't really disposed of -- consider it to be stored for the future generations. So although a rocket into sun is possible, it's too dangerous, and too wasteful of something potentially useful... One day when all the Uranium is burned up, we might be grateful of having the spent fuel there to recycle.

 

[bigdaddy]

Reprocessing is definitely the only sane answer, IMHO, and it's pretty disgusting that we're burying this valuable resource under the ground to be poisonous and deadly for many thousands of years to come. When reprocessed enough, the ultimate resulting waste is very low-level.

That's the one thing the french do correctly. There is also talk of scientists using it as a power source. I don't really understand it, but the plan is to "burn" it and somehow that would create power and not be as huge of a hazard.

 

[John Picard]

Eh, just put it in some shithole not inhabited by anything resembling intelligent life. Ottawa or Washington DC for example.

DC or California would be my first two choices.

 

[Neopeius]

Eh, just put it in some shithole not inhabited by anything resembling intelligent life. Ottawa or Washington DC for example.

DC or California would be my first two choices.

Jealousy doesn't become you.

By the way, it's 70 degrees here in San Diego and I'm wearing shorts.

 

[John Picard]

Eh, just put it in some shithole not inhabited by anything resembling intelligent life. Ottawa or Washington DC for example.

DC or California would be my first two choices.

Jealousy doesn't become you.

By the way, it's 70 degrees here in San Diego and I'm wearing shorts.

That's nice. Your state is plagued with budget problems, while mine has been voted as most likely to weather the recession very well. Our housing market never dropped, either.

 

[Neopeius]

And what state might that be?

 

[Spaceman Spiff]

This is an idle thought that's been brewing in the back of my head for a while now. Why not just shoot it into the Sun? We know we can get nuclear cargo off the ground fairly safely. What am I missing here? Cost is mitigated by the risk of hauling through dangerously populated areas. Gives an entire subdivision to the rocket manufacturing industry. The fact that we're not doing this means I have to be missing something.

Well, it would take a tremendous amount of fuel to do it. You'd first have to have a rocket phase to get it to launch, then a second one to get it out of Earth's gravity.

It took a couple of million pounds of thrust to get New Horizons on its way to Pluto, and it's just about half a ton.

Sending it to the moon would be easier, though I don't know if that option would be all that practical, either.

 

[Brent]

What about The Mariana Trench, just dump it all in there and let it sink.