3 ms·

> The technical answers are simple cough waste management cough We're talking about megayear timescales when it comes to nuclear fission waste. Humans have b

> The technical answers are simple cough waste management cough We're talking about megayear timescales when it comes to nuclear fission waste. Humans have been around for how long? What's the age of the oldest building around? What's the usual timescale for modern age buildings to deteriorate?

odonnellryan 11y ago
Is dumping it in a mountain hoping we'll figure it out in 100,000 years not valid? I'm being completely serious. Our current problems are on the span of hundreds of years. If we have hundreds of thousands we will be able to sort it out. It's barely borrowing on the future.
anigbrowl 11y ago
I am completely OK with burying it inside a mountain or a geologically suitable mine. True, we should be very selective about where we put it given that waste can be hazardous over geological timescales.
DennisP 11y ago
Fast reactors can eliminate almost all the long-term waste, which consists of transuranic isotopes that fast reactors use for fuel. Russia has two fast reactors in commercial operation right now, one since 1980. The U.S. had the Integral Fast Reactor almost complete in the mid-1990s, when the Clinton administration shut down the program. The rest of the waste is fission products. Encase them in glass and bury them, they're back to the radioactivity of the original ore in a couple centuries. That's a human timescale. When I lived in Germany, we had a brewery in town that had been continuously operating for 800 years.
- datenwolf 11y ago
  > Fast reactors can eliminate almost all the long-term waste, which consists of transuranic isotopes that fast reactors use for fuel. Not every transuran is viable fuel. Some of the stuff is actually actively getting in the way of an efficient fission chain reaction. The key benefit of fast breeder reactors is, that you can fuel them with stuff that's more abundant on Earth, so you're not getting into a fuel shortage (our supplies of U235 are quite limited, some 70 years or so, using conventional fission reactors). So you need to either go through a fast U238→Pu239 or a Th232→U233 process if you want to make use of the abundant stuff. Oh, and most of the fission products are not very pleasant either and you can't efficiently burn them in any way whatsoever. Burner Accelerators? I've got a few things for you to look up: Penetration epth, Bragg peak, small volume active zone. > The rest of the waste is fission products. Encase them in glass and bury them, they're back to the radioactivity of the original ore in a couple centuries. Unfortunately not. The generation zero of nuclides will decay in that timeframe. But all the other stuff to follow, less radioactive, but still dangerous, takes much more time to decay; and those daughter generation nuclides is where the headaches start. And it's not just the physics that's a problem, it's also chemistry. Some of the elements that are born are quite aggressive, chemically.
  - DennisP 11y ago
    A large majority of the waste though. Most of the long-term radioactivity is from plutonium isotopes, all of which work in fast reactors just fine. I didn't claim all radioactivity would be gone, just that overall it will be comparable to uranium ore in a reasonable timeframe. If we really want to break up all the transuranics, neutrons from D-T fusion would crack them apart handily. We already have 70% energy return with D-T fusion; a hybrid fission-fusion reactor would probably achieve net power just with that.
    - datenwolf 11y ago
      > I didn't claim all radioactivity would be gone, just that overall it will be comparable to uranium ore in a reasonable timeframe. As you correctly pointed out, radioactivity is inversely proportional to half-life. Or in other words, given the same chemical concentration the net half-life of the remaining nuclear waste would be on the same timescale as the of uranium ore. The most abundant uranium isotope us U238, with a half life of about 703Ma. Here's a list of half-lifes of the most common fission and spallation products: 99Tc 211ka (side note: used as radioactive tracer nuclear medicine) 126Sn 230ka 79Se 327ka 93Zr 1.53Ma 135Cs 2.3Ma 107Pd 6.5Ma 129I 15.7Ma Three things to note here: - Those are all isotopes, which you can't actively "break down" further without making things worse. A couple of those above are very efficient at neutron capture, thereby getting slightly more radioactive, still not enough to significantly shorten the half-life. - Those are still about 1000 to 20000 times more radioactive than U238, so it's a far cry to call that "comparable to uranium in a reasonable timeframe" - We're definitely in the Ma timescale here. Say you want that nuclear waste decay down to 0.1% of the original material. How long does it take? Easy enough to figure out: 0.001 > 2^-n → n = log2(1000) =~= 10. Or in other words, it takes 10 half life periods for the stuff to break down to a concentration, that's still far from being homeopathic. When it comes to technology IMHO a reasonable timeframe to deal with technological aftermath is 50 years (and not more). Anything beyond that and it will become a clusterfuck simply due to "human nature". Heck, today we've even got problem erecting structures that will last longer than 50 years without requiring major maintenance. And if you're honest about it, except for the few outliers of historical significance (the pyramids, port walls built by the Romans with their "super concrete" we still haven't reverse engineered, and such) we humans are quite terrible in building stuff that can go by without maintenance for more than a few decades. And that's the core problem in nuclear waste management. A problem I'd like to point out, we have to solve, because there's already plenty of nuclear waste around. Oh and then there's of course the problem how to treat and prepare the highly radioactive waste for long term storage in the first place. One of the proposed methods (and already employed by some nuclear energy companies) is to melt it into glass. But here's the problem: Glass is a quite complex material and its mechanical properties largely depend on its chemical composition. Radioactivity however means, that the chemistry is changing over time. Not to mention that some stages of the decay chain have a very high vapour pressure or are gaseous at ambient temperature/pressure. Which in turn means: Your once solid and smooth slab of glass will form lots of cracks, may even break down at some spots into fine sand (which could become air or waterborne). I did my graduation thesis at an accelerator facility where also some aspects of nuclear waste treatment were researched. If you see some of the principal investigators in that area doing research on the renewable energy stock market or even having invested in family members green energy startups and advertising for them, that's a very strong signal.
jerf 11y ago
"We're talking about megayear timescales" No, we're not. Anything with megayear halflifes is effectively not radioactive. There's a lot of great answers. None of them are politically feasible because instead of thinking of it as an engineering problem, people think of it with the Sealed Evil In A Can memeset [1] and treat it like it is eternally a baleful evil demon that smites everyone that so much as thinks about it for too long, by magic. It is, literally, a small problem, as in, literally, we're not really talking about very much stuff volumetrically. It's only a problem because paradoxically people treat it with such fear that it stays a problem, because we're so fearful that nobody is even allowed to try to solve the problem because to our fearful brains it would basically be poking the baleful evil spirit with a stick. If it were just legal to stick it in glass bricks and stack them up somewhere, as has been studied, we could be done thinking about it, but instead we have to leave it in a more dangerous form. It is frankly difficult for me not to see this as a problem that people in charge make sure to deliberately make sure stays unsolved because it suits them, not because I'm really prone to conspiracy theories but simply because while not necessarily "trivial", it's just not that hard of a problem. You should fear your local garbage dump a lot more than you fear a pile of glass bricks piled in a mountain in Nevada. [1]: http://tvtropes.org/pmwiki/pmwiki.php/Main/SealedEvilInACan http://tvtropes.org/pmwiki/pmwiki.php/Main/SealedEvilInACan
- datenwolf 11y ago
  > No, we're not. Anything with megayear halflifes is effectively not radioactive. Yes, we are. You've to consider the daughter and grand^n-daughter nuclides as well. Makes for a very nice undergrad tutorial on coupled differential equations. Fun times.
brc 11y ago
What is surprising to me is actually how small the waste is, especially compared to the amount of energy that was extracted. One mountain can be used to bury the waste. That is a tiny footprint compared to other, conventional means. Even a single small hydro dam - itself a great way of making power - covers a far larger area of the earths surface than all the nuclear waste ever made, combined. Compared to coal waste and even the mining waste for rare earths, it is a tiny amount of waste.

odonnellryan 11y ago

Is dumping it in a mountain hoping we'll figure it out in 100,000 years not valid? I'm being completely serious. Our current problems are on the span of hundreds of years. If we have hundreds of thousands we will be able to sort it out. It's barely borrowing on the future.

anigbrowl 11y ago

I am completely OK with burying it inside a mountain or a geologically suitable mine. True, we should be very selective about where we put it given that waste can be hazardous over geological timescales.

DennisP 11y ago

Fast reactors can eliminate almost all the long-term waste, which consists of transuranic isotopes that fast reactors use for fuel. Russia has two fast reactors in commercial operation right now, one since 1980. The U.S. had the Integral Fast Reactor almost complete in the mid-1990s, when the Clinton administration shut down the program. The rest of the waste is fission products. Encase them in glass and bury them, they're back to the radioactivity of the original ore in a couple centuries. That's a human timescale. When I lived in Germany, we had a brewery in town that had been continuously operating for 800 years.

datenwolf 11y ago
> Fast reactors can eliminate almost all the long-term waste, which consists of transuranic isotopes that fast reactors use for fuel. Not every transuran is viable fuel. Some of the stuff is actually actively getting in the way of an efficient fission chain reaction. The key benefit of fast breeder reactors is, that you can fuel them with stuff that's more abundant on Earth, so you're not getting into a fuel shortage (our supplies of U235 are quite limited, some 70 years or so, using conventional fission reactors). So you need to either go through a fast U238→Pu239 or a Th232→U233 process if you want to make use of the abundant stuff. Oh, and most of the fission products are not very pleasant either and you can't efficiently burn them in any way whatsoever. Burner Accelerators? I've got a few things for you to look up: Penetration epth, Bragg peak, small volume active zone. > The rest of the waste is fission products. Encase them in glass and bury them, they're back to the radioactivity of the original ore in a couple centuries. Unfortunately not. The generation zero of nuclides will decay in that timeframe. But all the other stuff to follow, less radioactive, but still dangerous, takes much more time to decay; and those daughter generation nuclides is where the headaches start. And it's not just the physics that's a problem, it's also chemistry. Some of the elements that are born are quite aggressive, chemically.
- DennisP 11y ago
  A large majority of the waste though. Most of the long-term radioactivity is from plutonium isotopes, all of which work in fast reactors just fine. I didn't claim all radioactivity would be gone, just that overall it will be comparable to uranium ore in a reasonable timeframe. If we really want to break up all the transuranics, neutrons from D-T fusion would crack them apart handily. We already have 70% energy return with D-T fusion; a hybrid fission-fusion reactor would probably achieve net power just with that.
  - datenwolf 11y ago
    > I didn't claim all radioactivity would be gone, just that overall it will be comparable to uranium ore in a reasonable timeframe. As you correctly pointed out, radioactivity is inversely proportional to half-life. Or in other words, given the same chemical concentration the net half-life of the remaining nuclear waste would be on the same timescale as the of uranium ore. The most abundant uranium isotope us U238, with a half life of about 703Ma. Here's a list of half-lifes of the most common fission and spallation products: 99Tc 211ka (side note: used as radioactive tracer nuclear medicine) 126Sn 230ka 79Se 327ka 93Zr 1.53Ma 135Cs 2.3Ma 107Pd 6.5Ma 129I 15.7Ma Three things to note here: - Those are all isotopes, which you can't actively "break down" further without making things worse. A couple of those above are very efficient at neutron capture, thereby getting slightly more radioactive, still not enough to significantly shorten the half-life. - Those are still about 1000 to 20000 times more radioactive than U238, so it's a far cry to call that "comparable to uranium in a reasonable timeframe" - We're definitely in the Ma timescale here. Say you want that nuclear waste decay down to 0.1% of the original material. How long does it take? Easy enough to figure out: 0.001 > 2^-n → n = log2(1000) =~= 10. Or in other words, it takes 10 half life periods for the stuff to break down to a concentration, that's still far from being homeopathic. When it comes to technology IMHO a reasonable timeframe to deal with technological aftermath is 50 years (and not more). Anything beyond that and it will become a clusterfuck simply due to "human nature". Heck, today we've even got problem erecting structures that will last longer than 50 years without requiring major maintenance. And if you're honest about it, except for the few outliers of historical significance (the pyramids, port walls built by the Romans with their "super concrete" we still haven't reverse engineered, and such) we humans are quite terrible in building stuff that can go by without maintenance for more than a few decades. And that's the core problem in nuclear waste management. A problem I'd like to point out, we have to solve, because there's already plenty of nuclear waste around. Oh and then there's of course the problem how to treat and prepare the highly radioactive waste for long term storage in the first place. One of the proposed methods (and already employed by some nuclear energy companies) is to melt it into glass. But here's the problem: Glass is a quite complex material and its mechanical properties largely depend on its chemical composition. Radioactivity however means, that the chemistry is changing over time. Not to mention that some stages of the decay chain have a very high vapour pressure or are gaseous at ambient temperature/pressure. Which in turn means: Your once solid and smooth slab of glass will form lots of cracks, may even break down at some spots into fine sand (which could become air or waterborne). I did my graduation thesis at an accelerator facility where also some aspects of nuclear waste treatment were researched. If you see some of the principal investigators in that area doing research on the renewable energy stock market or even having invested in family members green energy startups and advertising for them, that's a very strong signal.

jerf 11y ago

"We're talking about megayear timescales" No, we're not. Anything with megayear halflifes is effectively not radioactive. There's a lot of great answers. None of them are politically feasible because instead of thinking of it as an engineering problem, people think of it with the Sealed Evil In A Can memeset [1] and treat it like it is eternally a baleful evil demon that smites everyone that so much as thinks about it for too long, by magic. It is, literally, a small problem, as in, literally, we're not really talking about very much stuff volumetrically. It's only a problem because paradoxically people treat it with such fear that it stays a problem, because we're so fearful that nobody is even allowed to try to solve the problem because to our fearful brains it would basically be poking the baleful evil spirit with a stick. If it were just legal to stick it in glass bricks and stack them up somewhere, as has been studied, we could be done thinking about it, but instead we have to leave it in a more dangerous form. It is frankly difficult for me not to see this as a problem that people in charge make sure to deliberately make sure stays unsolved because it suits them, not because I'm really prone to conspiracy theories but simply because while not necessarily "trivial", it's just not that hard of a problem. You should fear your local garbage dump a lot more than you fear a pile of glass bricks piled in a mountain in Nevada. [1]: http://tvtropes.org/pmwiki/pmwiki.php/Main/SealedEvilInACan http://tvtropes.org/pmwiki/pmwiki.php/Main/SealedEvilInACan

datenwolf 11y ago
> No, we're not. Anything with megayear halflifes is effectively not radioactive. Yes, we are. You've to consider the daughter and grand^n-daughter nuclides as well. Makes for a very nice undergrad tutorial on coupled differential equations. Fun times.

brc 11y ago

What is surprising to me is actually how small the waste is, especially compared to the amount of energy that was extracted. One mountain can be used to bury the waste. That is a tiny footprint compared to other, conventional means. Even a single small hydro dam - itself a great way of making power - covers a far larger area of the earths surface than all the nuclear waste ever made, combined. Compared to coal waste and even the mining waste for rare earths, it is a tiny amount of waste.