Why don't we bury our radioactive waste in an ocean trench?

I apologize for my poor memory of a science show many, many years ago. I have no details or cites (or sites!) and some comments may be slightly misremembered. This is how I remember the program:

A mini-sub descended into a trench off of the coast of California. There, they showed where the Pacific plate is slowly subducting under the North American plate. Over millions of years, the ocean floor travels deeper underneath the continent until it is melted into magma. Millions of years later, it comes out of volcanos as lava. In another millions of years, the lava is eroded to sand and is carried down to the ocean.

Once in the ocean, the sand joins a flow of sand that begins in the rivers of Alaska. As the sand travels southward, the amount of sand greatly increases. It becomes a virtual river of sand. Eventually the sand reaches the trench where it forms a “waterfall” of sand that is constantly raining into the trench. The sand is accumulating quite rapidly. There was concern that if the sub accidentally drifted under the cascade it could be trapped and buried.

If we dumped our Nuclear waste into that trench, it would be immediately covered by layers of sand, and only resurface after millions of years. No concerns about groundwater contamination, earthquakes, people nearby, monitoring for hundreds of thousands of years, etc.

Dump it, forget it, its gone forever. Even if the containers corrode through in several years, any contamination is buried deeper and deeper every day.

Should’t we be dumping our nuclear waste in this trench?

Well, the process takes a long time, meanwhile the containers would most probably leak and contaminate the seawater, although if a reasonably resistant container could be used then the idea is not too bad.

Never heard of this place… the best current technology I know of involves vitrification - turning radioactive materiels into a relatively inert (but radioactive of course) glass-like materiel. That could fix it for the short time it’s exposed. The earth’s core is already naturally radioactive…

If this place really undergoes that rapid of subduction, it doesn’t sound like that bad of an idea.

This sounds like the perfect solution.

Drop in the damn deep parts.

I don’t think you even need containers. We’re talking seriouslly dense metals, here. Just form the waste into fairly hydrodynamic slugs and let 'em rip. When you drop a one ton tear-drop shape into the water it’s going to have some serious KE when it reaches the bottom, terminal velocity notwithstanding.

There is a real dearth of currents inside the deep ocean trenches. I don’t think I can get this by the California Coastal Commision, though…

More’s the pity.

I think I’ll be visiting my college’s Earth Science department to ask an expert about how this could work.

This is not terribly dissimilar to an idea put forward by SF writer Larry Niven in one of his short pieces - he suggests dropping the waste into a subduction zone, where it will become one with the Earth’s mantle in a short space of geological time (he later dismisses the idea in favour of turning radioactive waste directly into currency, arguing that it would be so unpleasant to handle that it couldn’t fail to circulate fast and this would be good for the economy).

The problem with this excellent idea is that it involves putting the waste in the ocean, which is of course home to those misunderstood superior beings, the whales and dolphins. :rolleyes: This will always freak the ecofreaks out, and they never listen to reason.

Why bother finding a way to get rid of it, when we shouldn’t be making it in the first place? Nuclear energy is the most expensive energy technology there is…

Yes, well thanks for completely pointless post. :rolleyes:

The fact is that it is here and what are we going to do about it.

The UK, France and Belgium processed 1000 tonnes of vitrified radioactive stuff last year. cite That works out to 16.3 cubic meters of material. That could easily be dropped straight down and the mass alone should be enough to punch nice and deep to avoid being disturbed.

I see Greenpeace freaking out though.

I think only a fringe of the ecological groups would be up in arms about it, and most people ignore the fringe of any movement. I think it would be a grand idea, and I’m surprised we haven’t already done it.

Bullshit. See the pretty colored graph about 1/3 the way down the page.

Ok so I took a bigger look at this. I’ll use the 1000 tonne number from my cite above.

Now divide that up in to 100 tonne (100e3 kg) blocks to make it slightly more reasonable. First off we make them into spheres and drop them over the side and they travel 3 km down)

Now with no drag the max speed becomes 865 km/h and it hits the bottom in 24 seconds! :eek: So that’s our maximum.

Drag will significantly slow the sphere down. Cd differs depending on the velocity of the object but let’s say its 0.5. The Vterminal would be 71.7 m/s or 258 km/h. It’s possible that the thing would hit the bottom before that. I don’t have the time right now to figure out travel time.

I should also say that the cost of natural gas, oil and coal does not include the capture and treatment of flue gases and particles so those cost don’t factor into the power equation.

And buoyancy. That’s at least 5% reduction, off the top.

hey, even better idea. drop it in the ocean… AND generate power from the fall. just hang a bunch of ‘wind mills’ from a rope and drop it along side. (actually probobly totally impractical but a sort of cool factor of getting MORE electricity out of it)

Took it into account. :slight_smile: Think it was ~ 2-3% actually.

I find it hard to believe the thing is going to reach almost 300 km/h though. Wow.

owlofcreamcheese, if you look at my no drag numbers the drop only lasts 24 seconds. Probably not worth the effort for the cool factor

If you wanted to avoid the problem of leakage of material, why not just dump them in one of the very active volcanoes? All the nasty stuff gets dissolved into the lava.

Couple things.

  1. The “glass” will melt immediately
  2. The material will remain local to the volcano
  3. Volcanoes tend to go boom from time to time

The trench idea has the advantage of time to be subducted and time to be churned and spread across the mantle/core.

Specific gravity of uranium or plutonium is less than 20, whereas water is 1. That’s greater than 5%.

If that’s OK by you, why not just set it out curbside in the morning?

I would think that the reason for not doing this is simply the problem of transporting waste that far out into the ocean and then safely getting it miles down to the rift zone to right where you want it. Digging a deep hole under a mountain in the desert is much easier (you’ll always know exactly where the waste is).

The main reasons why we don’t bury radioactive waste in an ocean trench, or reprocess high-level waste, or put low-level waste into a safe location undergroung, are primarily political. Any waste disposal plan raises the ire of a number of interest groups. Second, any disposal site far from power plants will necesitate transporting radioactive waste across habited areas, an expensive and dangerous undertaking. Also, what we call “waste” today could be turned into a fuel source tomorrow, so burying it in an ocean trench might not be the best long-range plan.

What I’d like to know is why we aren’t encouraging nuclear plants to reprocess their own spent fuel. Yes, reprocessing fuel rods leaves a supply of plutonium that a terrorist would love to have, but security is already tight at existing plants. Furthermore, new reactors can be designed to be 1:1 breeder reactors. In a 1:1 breeder reactor system, all fuel is totally consumed, leaving no high-level waste to dispose of.