In my current Earth Science college class, we are debating the long term storage facility in Yucca Mountain. This got me wondering, and i can’t really find the answer.
Why is there so much nuclear waste? The plutonium and uranium is going to be radioactive for thousands more years, isn’t there some use we can get out of this? Maybe put a crapload of this lesser radioactive material into a reactor and get energy out of that?
Nuclear waste adds up because radiation contaminates pretty much everything used in the process of generating power. Coal, as an alternative example, may be dirty and even dangerous in some circumstances, but it doesn’t contaminate the mining equipment used to dig it up or the bins used to store it or the trucks used to haul it.
And the amount of radiation that can contaminate something is far less than the amount that can generate any useful energy. So lots of things are too radioactive to leave lying around but nowhere near radioactive enough to use as fuel.
Recycling reactor waste produces weapons-grade fissile material. It is therefore Not Done in the US.
So the waste store at Yucca isn’t just used-up uranium and plutonium? Interesting.
I recall an article by a nuclear scientist on the web I ran across a few years ago. Something like only a few percent of the fission energy available had been extracted from disposed fuel. His position (and mine) is that in the future (barring cheap alternate energy sources) nuclear waste would be dug back up because it was so valuable.
You can reprocess spent fuel and get a lot less waste out of it. The main problem with this is that you end up creating a lot of plutonium, which you don’t want to risk having some bit of it end up in the hands of terrorists and the like. President Jimmy Carter therefore banned the reprocessing of spent nuclear fuel from commercial reactors just because of the potential security risk. Everyone since then has recognized the potential risk and has left the ban in place.
Here’s Cecil’s article on the subject:
Dammit! :smack: Beat by one minute! :smack: :smack:
I thought this was going to be about why there are so many articles on nuclear waste or radiation themes on the SD front page lately.
Disclaimer: IANANuclear Engineer, just an interested spectator.
The main reason reprocessing isn’t done isn’t because of proliferation, it is because it is much cheaper to use fresh fuel.
This fuel may become economically viable in the future. It (spent fuel anyway, don’t know about decommissioned reactor vessels, etc.) is currently stored on site at nuclear power plants and, since the last time I heard, Yucca Mountain was dead, will remain there for the foreseeable future. We could use hybrid fusion fission reactors to burn the waste (burn as in nuclear burn, i.e. fission, not oxidise). I don’t know if you get lead out of the other end of those things, but as I understand it, the only waste you would be left with was the container at decommissioning time.
FWIW,
Rob
But you know what the half life is for the toxicity of lead is? Forever! How can we store such a toxic substance as lead FOREVER?!
Won’t someone think of the great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-great-great great-great-great-great-great-great-great-great-grandchildren?
Dump into Mariana’s Trench.
Yah, I think this is a fair point. Much of the debate around Yucca Mountain has involved the question of whether it will truly be capable of safely containing waste for tens of thousands of years. Frankly, I have to ask - who cares? The earliest human civilizations certainly didn’t give a damn about those who’d follow thousands of years after then - why do we owe any particular duty to our descendants that far down the line? If they have any level of technological civilization at all, they can work up fixes on an as-needed basis. And if they’ve descended into savagery, then they aren’t really our civilization any more at all - and frankly, who cares what happens to them?
I think if I were them I’d be a bit more pissed there wasn’t any oil than I shouldn’t dig a hole in a few square miles of desert.
This is correct. It is relatively easy to ‘poison’ plutonium to make it totally unsuitable (and incapable of being purified) for weapons use (which requires nearly pure [sup]239[/sup]Pu). In fact, producing plutonium requires constant reprocessing in order to prevent the buildup of neutron-consuming isotopes. On the other hand, the ability to separate uranium by centrifugal methods is becoming more widespread, and the ability to design an enriched uranium implosion device–once limited to only those with access to massive supercomputers that could run the hydrocode simulations necessary–is now the province of a bright nuclear engineering graduate student or physicist with a desktop PC.
The separation of fissile materials from spent nuclear fuel is reason that it isn’t currently economically viable (compared to producing fuel from existing ore deposits). This is not only time-consuming but produces even more waste–especially chemically reactive and highly radioactive shorter-lifetime daughter products. Such elements either consume neutrons, preventing a chain reaction, or can cause unstable cascades, making a reactor unsafe, and thus have to be removed by a series of processing and dilution cycles. This actually produces more waste than processing raw ore. The way fuel elements are packaged can also be an issue; the pebble bed modular reactor (PBMR) offers high thermodynamic efficiency and safer operation than a conventional PBR reactor, but the way the fuel elements are packaged makes it very difficulty to extract usable fuel from them.
Breeder reactors (used in France and in several East Bloc nations) can actually produce more fuel than they consume, but they also require more stabilization and have a more narrow criticality threshold.
Hybrid reactors offer the promise of both extracting most or all of the fission energy and reducing the resulting waste to relatively non-threatening levels of radioactivity by impinging them with high energy neutrons from a neutron source like an electrostatic fusion cell (like a Farnsworth fusor). In this way, you can not only extract energy from fissile isotopes, but also from fissionable ones, or convert fissionable species into fissile ones. The neutron flux can be controlled and shut down on command, making stability almost a non-issue.
Hybrid reactors are still far from being a practical energy source due to an overall lack of development of nuclear fission, but the basic principles are readily demonstrated, and it substantially reduces most of the concerns about nuclear fission power, including possible instability and supercriticality, and storage and transportation of waste and spent fuel.
Stranger
Coal produces oodles more waste than nuclear energy does. Heck, even if you’re just looking at radioactive waste, coal still produces more. It’s just that, for some reason, people don’t care when it comes from coal.
So what’s the trick here? Is it a matter of engineering or are there a lot of problems left to be discovered? Could you just throw any mix of fuel on the pile? Does the core have to be specifically engineered like it does for a conventional reactor (apart from making sure it doesn’t achieve critical mass, of course)? Can you cool it with inert gas and use that as a working fluid in the turbine like you can with PBMRs? Can you get a lot of juice relative to what the fusor or whatever uses? Is anybody actively working on this? Steven Chu never got back to me when I asked him.
Rob
The main problem is that it requires(or would at least be prudent to try) at least one research/test reactor first before building a commercial version. I’ve had way more sexual partners than the number of prototype research reactors that have been built worldwide (and certainly in the US) in a simliar time frame. Or run of the mill fission reactors for that matter. Its a value that ranges between and including 0 and a very small number.
Absolutely. People get wigged out about radioactive waste seeping into the water table or released from atmospheric nuclear testing, but in fact there are tons of radioactive elements released by burning coal, especially potassium and barium found in small but significant concentrations of lignite and the lower grade bituminous coals. Of course, the level of radioactivity escapage is small but constant, whereas radiation released into the environment by an inner loop coolant leak or criticality accident is high but generally more localized and limited. And anyone who smokes tobacco should stop worrying about either the radiation in coal or a Three Mile Island-type excursion; they’re far more likely suffer damage from long term exposure to the low level but intimate exposure to radiation from [sup]210[/sup]Po, [sup]223[/sup]Ra, and [sup]224[/sup]Ra, all of which are potent alpha emitters (normally harmless unless injested or inhales, as alpha particles can’t penetrate the epidermis).
As billfish678 notes, the low level of funding and obstructive levels of bureaucracy and government oversight have placed severe limitations on novel nuclear energy research; witness the fate of the Integral Fast Reactor (though I think the claims of utter fail-safe-itude by its developers were somewhat bombastic). This is disappointing, especially considering the billions spent on the National Ignition Facility, which is less a fusion energy development program and more intended as service for Enduring Stockpile stewardship and to support development of new fusion weapons in the current test ban environment. There is also an entrenched conservatism in the nuclear power industry, which is dominated by a few large players who are highly invested into very conventional technology and have little interest in putting research money into novel methods that can be reproduced by smaller players once the basic technology is developed. It’s not a conspiracy per se, but kind of a tacit cartel against developing more scalable technologies that aren’t as profitable to build and maintain, plus the possibility of accident or design flaw that may come back to haunt the developers.
I’ve seen a number of conceptual schemes for hybrid reactors. They do require a specified fuel cycle, though the ability of the fusor to emit a regulated amount of neutrons does give a fair amount of latitude as to the initial composition of the fuel, and if the user is willing to accept low efficiency, natural uranium (which is <1% [sup]235[/sup]U) or thorium can be used, as these will fission with the energetic neutrons from D-T fusion, but not from natural “thermal” (slow, low energy) neutrons. In contrast, a conventional breeder reactor requires highly enriched uranium (>20% [sup]235[/sup]U) which obligates a long enrichment cycle and is technically “weapon-grade” (although an efficient weapon requires >80% [sup]235[/sup]U). The specific configuration depends on what types of fuels it is intended to process; most use NaK or helium as the working fluid for the energy conversion cycle to prevent thermalizing (slowing down) the neutrons. I would classify this as a combination of engineering and empirical science; the basic theory of neutron absorption and fission is well-understood, but the behavior of different fuel compositions under novel neutron influx is always subject to some previously unanticipated phenomena, especially thermal state or crystalline boundary structure phase transitions.
The whole point (besides burning down persistent nuclear waste to low grade or very short half-life residues) is to be energy positive. While the electrostatic fusor isn’t close to energy positive, it can produce neutrons at a modest energy input, which can provide enough energy to bump fissionable materials to fission, releasing more energy than put into them. This is like the rider encouraging the horse; while he can’t himself run 15 miles an hour, much less carry the horse along at that speed, he can dig his heels into the horse’s withers and cause it to run, propelling them both at the horse’s expense.
Stranger
Is anyone considering a research reactor? What are the efficiencies we are talking about here (and in this case, I mean how much juice for the fusor for how much fission in the fuel, not how effectively it heats the working fluid)?
I also like the fact that we can use nice, safe helium as the working fluid vs. liquid metal, water, etc… I assume this is because helium resists neutron capture due to its low cross section, correct?
Thanks,
Rob
P.S. How do I make my own table-top research reactor? 