I have read about various nuclear fuels for power plants being a danger in that they have the potential to emit deadly radiation for hundreds or thousands of years after being buried or stored–wherever. I know Cecil discussed the matter of reprocessing in the original Straight Dope book, but I hope this isn’t the same: Can these materials be treated so as to give them half-lives that are much shorter (some have half-lives of seconds, not millenia) so that they would pose little or no danger?
The best way to reduce the half-life of nuclear waste would be to process it though advanced reactor technologies, which would also be able to use existing nuclear waste as fuel (over 99% of the energy is still available; existing waste and uranium and thorium reserves would last for tens of thousands of years supplying the entire current global energy consumption, making this the most viable long-term energy source, acting as a baseload to renewables), although you are still talking about centuries, but far less than traditional waste.
There are experimental processes termed “transmutation” which aim to do exactly that. I think they’ve been demonstrated in small proof-of-concept experiments, using research reactors, but not on a large scale. In principle, you can basically bombard spent fuel with neutrons to induce fission of the long-lived radioactive isotopes. I think these processes can’t completely eliminate radioactive waste, but they can go a long way towards reducing the overall half life and radiation in spent fuel. You can at least reduce the amount of materials with hundred-thousand-year half lives.
You can read more here. Given the slow pace of nuclear reactor research, I wouldn’t bet on commercial-scale transmutation any time in the next 50 years.
The drawback to reducing their radioactive period is that it also increases their radioactive output for that duration.
A kilogram of material has a predefined amount of protons, neutrons, and electrons; those can be released very slowly over thousands of years or fairly quickly over only a few years. The cancer risk from super long term waste is extremely low, but still non-zero. And since we don’t know how to treat the sort of systemic damage that could occur, people are extremely paranoid about how it’s handled.
The method that I mention would reduce the amount of waste by a hundredfold, making it easier to deal with what is left; it is easier to dispose of 1 kilogram of waste than it is to deal with 100 kilograms, plus I have read that the byproducts aren’t supposed to be as “hot” (given that the goal is to extract as much fission energy as possible, current reactors use less than 1% of the potential energy).
I’m missing something. The Law of Conservation of Mass means you can’t just “reduce the amount” of mass. If you start with 100kg of hot waste, you can’t reduce it to 1 kg of anything, unless you’ve done something else with the other 99kg. Maybe you’ve separated it out so only the hottest 1% of the mass has to be handled with lead-lined kid gloves, but that 99kg is still someplace, and it’s almost certain to be at least low-level nuclear waste, which still has to be handled and stored with great care (mostly to allay the fears of the “OMG RADIOACTIVE!” public).
That’s the “reprocessing” mentioned upthread. As far as i know, once a primary fuel assembly has been “burned”, it still has fissionable fuel which was transmuted (“bred”) from the original reaction. But my recollection is that this bred fuel is diffused throughout the waste, even if it’s in adequate quantities, and has to be extracted and processed into the physical geometry (pellets, rods, etc.) that supports the controlled reaction in the reactor mechanism design. I guess there are some proposed designs for reactors that can breed and burn in the same step, and maybe this is where we need to take this problem: burn the fuel all the way down to the minimum non-fissionable radioactive ash and then dispose of that.
From my understanding, spent fuel rods consist almost entirely of the original fuel, with some heavier transuranics which are produced when the original fuel atoms absorb a neutron but don’t split, and fission products, some of which are very short-lived and highly radioactive. Fuel rods aren’t removed because they don’t contain enough fuel anymore, but because some of the fission products are reaction poisons - they absorb too many neutrons to permit the chain reaction to continue.
Fuel reprocessing mostly consists of removing the fission byproduct isotopes from the still-usable fuel and recycling that fuel back into new fuel rods. The waste isotopes are still highly radioactive, but not for terribly long. Some of the transuranics generated by neutron capture are very long-lived, but those can generally be put back into the reactor as fuel.
Some reactor designs such as the molten-salt reactor perform this processing step continuously, keeping the fuel in a liquid state and constantly skimming out the fission byproducts. This is where the claim of reduction of waste by a hundredfold comes from - instead of removing and storing the entire used fuel rod as is done in conventional reactors, you’re just removing the small fraction of waste elements.
Those Gen IV reactors are theoretical and still being researched.
The Union of Concerned Scientists has this to say about reprocessing:
People should understand when talking about nuclear reactors, the words “reprocessing” and “recycling” don’t mean what they sound like. You end up with even more waste to deal with than before.
Again: When you say “more”, you mean by volume, because you can’t create mass.
It’s too bad we don’t have any technological means to reduce the volume of matter… hmm…
But yeah. Reprocessing and breed-burn reactors get more energy out of the same mass of fuel, but the end products are still wicked hot, even if they’re not usable for fuel. That’s kind of unavoidable in an environment in which matter is being continually transmuted into radioisotopes, either as direct fission products or by neutron-capture activation. But I still think that fissioning all the fissionable mass out of a fuel rod is better than leaving the plutonium laying around for hundreds of thousands of years, as well as having to guard it against being re-purposed for less productive uses.
Read here: Traveling wave reactor - Wikipedia about traveling wave reactors. Without active reprocessing, they manage to “burn” about 90% of the nuclear fuel including the plutonium that uranium reactors produce. The result is much efficient use of uranium and much much less long-lived waste. The short-lived waste has half-lives measured in the tens or years or less and so long-term storage is not nearly as much a problem.
Why hasn’t it been adopted? Two reasons I am aware of. In the early days of reactors, the military wanted a source of plutonium for bombs. AFAIK, there never was much processing of fuels to extract plutonium, so this was actually not a good reason. Now there is simply too much momentum for the older style reactors. It would require a minimum of a decade to research, build, test, certify a radically new reactor design and no one is willing to finance this. Although I did read in one place that China may be the place where it happens.
Why don’t you put in some actual facts:
Is Nuclear Waste Really Waste?
http://www.youtube.com/watch?v=rv-mFSoZOkE