5 ms·

Let's reverse the logic. Instead of talking about how much radioactive material we're pulling from the ocean, how much could we put in? Am I mistaken in saying

Let's reverse the logic. Instead of talking about how much radioactive material we're pulling from the ocean, how much could we put in? Am I mistaken in saying that we could put back in every bit of radioactive material we'd use until 5000AD and only double the natural background radiation amount? I know the math isn't exact -- it's not a symmetry -- but on a rough-order-of-magnitude basis, is that a reasonable conclusion?

dexen 14y ago
Probably makes sense, but you'd have hard time to pull this one off given the state of modern-day press and other media. Suppose scientists calculate seawater contains, on average, N parts per million of Uranium and aim at inceasing it to just N+1 (assuming N >> 1). Armchair `ecologists' -- think Greenpeace -- would go thermonuclear on you -- and mass media would give those `ecologists' much more print space and air time than to the scientists. Public opinion would be skewed from the get-go.
ScotterC 14y ago
Essentially yes. The ocean is a fantastic dump for radioactive material. Also, it only takes 10 ft of water to block all radiation, alpha, beta and gamma. However. Radioactive 'waste' is actually really useful. We can recycle it and use it. It's just a matter of regulations and cost. I'd much rather make our radioactive by products readily accessible for when we can use it as either fuel (only need a higher neutron flux) or extract elements for various uses.
comicjk 14y ago
No; the waste is far more radioactive than the fuel. Nuclear fuel rods are perfectly safe to touch when they're first made; they rapidly become more dangerous as they fission in the reactor. By the time they come out they are lethal. Then their lethality slowly dies off as the short-lived fission products decay. It would be a very bad idea to mix raw nuclear waste into the sea.
ars 14y ago
> but on a rough-order-of-magnitude basis, is that a reasonable conclusion? No. Uranium is barely radioactive. In contrast the waste from a power plant is very radioactive. Radioactivity is directly related to half life: The longer the half life, the less radioactive, and the reverse as well. Uranium 235 has a half life of close to a billion years, and 238 (the much more common kind) of nearly 5 billion years. So it's barely radioactive. Once you "cook" it in a reactor you generate all sorts of isotopes with much shorter half lives (so none exist naturally in any quantity). Those isotopes are also much more radioactive. The good thing is that the very powerful ones don't last long. The "worst" isotopes are the medium lived ones. Short enough to be radioactive, long enough to last for centuries. Of those Strontium-90 and Caesium-137 are the main ones. Now you also know why nuclear fuel reprocessing is a great idea. The uranium left behind after a pass through a reactor has not been changed (it's not any more radioactive than it was before it started) - you can isolate it chemically and use it again (only a small amount actually burns each time). You still need to deal with the dangerous stuff, but the quantity is massively reduced. (Technically you can burn that as well in a reactor to other shorter lived isotopes, and essentially destroy any hazard, but I don't believe anyone does that.) Just to respond to your actual idea, there are proposals to bury waste in subduction zones. You can find more about it via google https://www.google.com/search?q=nuclear+subduction+zone https://www.google.com/search?q=nuclear+subduction+zone
- ChuckMcM 14y ago
  The DoE actually did extensive research into subduction encapsulation and while expensive (you are working at depths that crush most stuff we build up here) was technically quite acceptable (their design ended up essentially drilling what amounted to bore holes 5000' below the surface and dropping in waste from the top until its half full then covering it up and moving on. The advantage was that containment was expected to be lost but the material would diffuse into the mantle. In terms of cost though is was a couple of decimal orders of magnitude higher than Yucca Mt. Why folks wont let engineers reprocess it and use a fast breeder to incinerate it is simply fear. (well and the fast that a fast breeder can also make stuff you don't want made)
  - ericd 14y ago
InclinedPlane 14y ago
Not at all. Uranium-238 has a half-life of billions of years, and Uranium-235 has a half-life of about 2/3 of a billion years. This means that the natural decay rate, and thus the rate of generation of radioactivity is very low. However, if you pull that out of the ocean and put back things like Radium, I-131, Sr-90, etc. you will vastly increase that rate because such isotopes have a much lower half-life.

dexen 14y ago

Probably makes sense, but you'd have hard time to pull this one off given the state of modern-day press and other media. Suppose scientists calculate seawater contains, on average, N parts per million of Uranium and aim at inceasing it to just N+1 (assuming N >> 1). Armchair `ecologists' -- think Greenpeace -- would go thermonuclear on you -- and mass media would give those `ecologists' much more print space and air time than to the scientists. Public opinion would be skewed from the get-go.

ScotterC 14y ago

Essentially yes. The ocean is a fantastic dump for radioactive material. Also, it only takes 10 ft of water to block all radiation, alpha, beta and gamma. However. Radioactive 'waste' is actually really useful. We can recycle it and use it. It's just a matter of regulations and cost. I'd much rather make our radioactive by products readily accessible for when we can use it as either fuel (only need a higher neutron flux) or extract elements for various uses.

comicjk 14y ago

No; the waste is far more radioactive than the fuel. Nuclear fuel rods are perfectly safe to touch when they're first made; they rapidly become more dangerous as they fission in the reactor. By the time they come out they are lethal. Then their lethality slowly dies off as the short-lived fission products decay. It would be a very bad idea to mix raw nuclear waste into the sea.

ars 14y ago

> but on a rough-order-of-magnitude basis, is that a reasonable conclusion? No. Uranium is barely radioactive. In contrast the waste from a power plant is very radioactive. Radioactivity is directly related to half life: The longer the half life, the less radioactive, and the reverse as well. Uranium 235 has a half life of close to a billion years, and 238 (the much more common kind) of nearly 5 billion years. So it's barely radioactive. Once you "cook" it in a reactor you generate all sorts of isotopes with much shorter half lives (so none exist naturally in any quantity). Those isotopes are also much more radioactive. The good thing is that the very powerful ones don't last long. The "worst" isotopes are the medium lived ones. Short enough to be radioactive, long enough to last for centuries. Of those Strontium-90 and Caesium-137 are the main ones. Now you also know why nuclear fuel reprocessing is a great idea. The uranium left behind after a pass through a reactor has not been changed (it's not any more radioactive than it was before it started) - you can isolate it chemically and use it again (only a small amount actually burns each time). You still need to deal with the dangerous stuff, but the quantity is massively reduced. (Technically you can burn that as well in a reactor to other shorter lived isotopes, and essentially destroy any hazard, but I don't believe anyone does that.) Just to respond to your actual idea, there are proposals to bury waste in subduction zones. You can find more about it via google https://www.google.com/search?q=nuclear+subduction+zone https://www.google.com/search?q=nuclear+subduction+zone

ChuckMcM 14y ago
The DoE actually did extensive research into subduction encapsulation and while expensive (you are working at depths that crush most stuff we build up here) was technically quite acceptable (their design ended up essentially drilling what amounted to bore holes 5000' below the surface and dropping in waste from the top until its half full then covering it up and moving on. The advantage was that containment was expected to be lost but the material would diffuse into the mantle. In terms of cost though is was a couple of decimal orders of magnitude higher than Yucca Mt. Why folks wont let engineers reprocess it and use a fast breeder to incinerate it is simply fear. (well and the fast that a fast breeder can also make stuff you don't want made)
- ericd 14y ago

InclinedPlane 14y ago

Not at all. Uranium-238 has a half-life of billions of years, and Uranium-235 has a half-life of about 2/3 of a billion years. This means that the natural decay rate, and thus the rate of generation of radioactivity is very low. However, if you pull that out of the ocean and put back things like Radium, I-131, Sr-90, etc. you will vastly increase that rate because such isotopes have a much lower half-life.