Why doesn’t the United States reprocess spent nuclear fuel? Those in charge cite proliferation concerns since reprocessing makes plutonium, but it’s not like reprocessing facilities are going to leave it by the roadside with a sign that says, “Free to a good home.” I would expect these sites to be at least as well-defended as reactor facilities are (which I hear is pretty good). Are there other concerns arising from the process such as toxic reagents and other byproducts? What makes reactor fuel go bad anyway? Doesn’t it keep putting out heat for a long time?
While were on the topic of nukes, what is the likelihood of ever developing a viable fusion reactor? I often hear that these will be around in 2050, or is it simply the case that no reactor could possibly be online before that date barring some unforeseen breakthrough?
If you can fit it in, can you discuss pebble bed reactors? Do they adequately address fission reactor concerns? Are they feasible? How soon could they be online?
I’m going to give you my best answer regarding civilian nuclear power, since we aren’t allowed to talk about the military. I apologize if my answers are slightly dated - I’m studying thyroids and anesthetics these days instead of neutrons and isotopes as I once did. Also I’m going to shoot for fairly non-technical answers here - I hope that’s what you wanted? I am really tired of getting uber-technical answers to my simple questions, don’t know about you.
My understanding about the reprocessing thing is that it produces a tremendous amount of nuclear waste in the form of throw-away parts and materials that have to be stored in shielded waste facilities for the next several hundred thousand years, which is very expensive. If we were short of uranium it might be worth it to incur this extra cost, but as it stands we have plenty and it’s cheaper to do it the present way. Sort of like the oil situation - until it gets REALLY expensive we won’t get serious about looking for alternatives, even though there are other more viscerally satisfying options out there.
The question added on to your first question is a non-trivial one. Yes, once a core is activated, it “never” stops putting out heat (unless you’re measuring in eons, and we won’t go there today). The problem is, how much heat? It only makes a usable amount for a finite period of time, because the products of those fission reactions build up in there and contaminate the core. They suck up neutrons which then can’t go on to be part of the chain reaction. So this question is a smarter version of one my dad once asked when looking at the steam coming out the stack of an oil refinery near our house. He said, “Boy are they stupid! Why don’t they just put a turbine up there and get all the energy out of that steam?” Answer: First, because you can’t ever get out “all” the energy - you can only get it closer and closer to about-atmospheric-temperature water. Second, because the source of that energy is not very organized - it’s a low temperature vapor, which means the equipment to “mine” those $2 worth of energy per day would cost tens of thousands of dollars - not worth it. It’s a simliar case with the nuclear reactor - once it’s below a certain temperature, it’s just not cost-effective to use any more energy out of it. As with reprocessing, it’s a matter of dollars, not physics.
The fusion thing - I certainly hope we work that out, and soon. I’m sure someone will answer this more technically, but the essential problem is that a fusion core is hot. I mean REALLY hot. So hot that we don’t have a solid material that can hold it. The solution is this fancy thing called a plasma bottle, and the issue right now is that it takes about as much power to create the plasma bottle as you get out of the reactor. Production is pretty good, but the net stinks. If the poplular media can be believed (har har har) the Japanese are probably the farthest ahead on this one. No idea about likelihood or timing - it’s all a matter of 10% inspiration and 90% perspiration, and until somebody supplies that first 10% we’re out of luck.
I apologize - I have no inside knowledge about your last question, so I won’t insult your intelligence with a Google gather ‘n’ dump here.
You might want to look into something called a Breeder Reactor. These nuclear reactors solve a great deal of the nuclear waste issue associated with current light water reactors.
So, why don’t we have Breeder Reactors? One of the nifty tricks of a Breeder Reactor is it produces more fuel than it consumes (this is not to say it will run forever without being replenished but that the process of “burning” the fuel produces more nuclear material that can be recycled back into the reactor). Basically these reactors convert U-238 into Pu-239. Pu-239 is what you want when building a nuclear weapon. As a result President Carter banned development of Breeder Reactors in the United States for fear that the plutonium could be stolen (or somehow appropriated) by people who we do not want to have such things.
It has been awhile since I read up on this stuff but IIRC there are breeder reactor designs that address the worries about proliferation of plutonium. Basically, while they create plutonium-239 the plutonium is mixed in with other things such that extracting the pu-239 for weapons use is hugely difficult (difficult to the point you are FAR better off building a reactor specifically to make pu-239). Note the “mixed in with other things” is not something that has to be done after the fact but is how it comes out of the reactor. Even if someone got their hands on this stuff and walked away with it there wouldn’t be much they could do with it weapons wise (not to mention at this point it is all extremely radioactive and not easily handled in its own right…throw it in your backpack and walk out and you won’t live very long). This fuel however can be used by the Breeder Reactor to produce more energy.
Better still are there are passively safe Breeder Reactor designs. Essentially the reaction is self limiting so no matter what disaster scenario you can think up about coolant pumps and such breaking the core will not explode but rather slow itself down via the physics of the reaction.
Ultimately, like anything, there are byproducts produced by such a reactor but what needs to be thrown away in the end is less in quantity and, more importantly, has radioactive half-lives on the order of a few hundred years (rather than thousands for conventional nuclear waste). If you use an Integral Breeder Reactor design all fuel handling can occur at the facility so no need to cart around plutonium and other nastiness to be reprocessed at other facilities (meaning security can be much tighter and it is much harder to “lose” some material).
Other countries (Japan and Great Britain come to mind) are developing and using these reactors so whatever their flaws it is more anti-nuclear anything sentiment in the United States holding this stuff back (or so it seems to me…Clinton put a stop to it during his presidency but I forget why).
During Clinton’s presidency, he tried to introduce something called the IFR which was a combination fast breeder reactor and fuel reprocessing plant at the same site. If you didn’t have to move the fuel in order to reprocess it, it would be that much more secure. I think that died because less contraversial energy sources were abundant and we didn’t really have to consider it.
As the previous poster noted, one of the problems with reprocessing fuel is that it is cheaper to mine and purify new fuel than it is to reprocess spent fuel. I found an article on PBS’s website written by one of the men who advised Carter to abandon breeder reactors and fuel reprocessing that said this. Proliferation was just icing on the cake. One plan is to take all that spent fuel and bury it in Yucca Mountain for 10,000 years. I think it would be better to stockpile that fuel and then start to reprocess it in 50 years when we run out of easily extractable uranium. Will the spent fuel be worthless in 50 years? Would it be better to subsidize reprocessing now rather than accumulating a bunch of radioactive junk? How much does electricity have to cost before we can stick the stuff in a bunch of RTGs and connect them to the grid?
Even with a breeder reactor there are isotopes besides simply the usuable Pu-238, U-238 and U-235 that are produced. Fission product poisons still have to be seperated out, then disposed of.
The problem is that while it’s fair to think of spent fuel as a highly enriched ore for getting such isotopes from, they’re not the only isotopes that are going to have to be seperated out. And, as Spacekat points out, there’s really no way to economically utilize the energy of such fission products. Then there’s the real (If overblown, IMHO) concern about what the uses for such waste might be. Let’s be honest here, even getting a hold of the crud* that’s mostly relatively short-lived Co-60 from a reactor core would make for a hellagood “dirty bomb.”
I may think the risk of this is overblown, but it’s not a concern being made up out of whole cloth.
Heck, there was an interesting article in SciAm about a year ago about a proposed “solution” to long-term fission product isotopes: “burn” them in a liquid lead reactor. That would allow for some of the energy potential in such materials to be used, but again, the article’s authors made the point that unless the political climate changes, and people are willing to consider reprocessing spent fuel, it’s just a neat idea.
Let’s also be a bit cold-blooded here. In the US we’ve got so many untapped natural resources (coal, oil in nature preserves, etc…) that there’s the metaphorical room to consider options that are less than ideal from the standpoint of economy and energy production, that other countries may not be able to consider. Thus Japan, England and other nations may have more pressure to look to nuclear power options to reduce reliance upon foreign sources of power or raw material than the US does.
sweeteviljesus, I see your point, but that’s not going to happen in the US until after a lot more of the known domestic coal, oil shale, and simple oil deposits are used up. I may be wrong, but I believe most US environmental types would rather see the Great Lakes, Yosemite, and Alaska opened up for more drilling/mining than to allow more reactors to be built.
*yup, that’s the proper technical term - it’s wear and corrosion products that go into solution in a PWR or BWR, and then get deposited on the core surfaces and activated. Crud.
I don’t have a clearance, so I can talk about the military all I want. Nyah, Nyah, Nyah.
Seriously, what is so special about military nuclear power that it should be a secret? I guess that making subs run quiet probably involves classified information, but does that have anything to do with the reactor? I saw a documentary about submarines once and they noted that cameras were not allowed in the reactor room which I assume is not for safety reasons.
That and the the building materials around and within the core deteriorate faster than usual due to the radioactive bombardment. You also have other “fun stuff” all around. A plant in Ohio was closed for 2 years recently due to leaking boric acid.
So you have steel, concrete, pipes, pumps and such all wearing out in a couple decades. It’s a lot more costly to replace these because of the induced radioactivity. Ergo, the plant becomes no longer economically viable. One of the all time classic examples of this was the Trojan plant in Oregon. Opened 1976. Closed 1992, 20 years earlier than planned. Leaky steam pipe.
The bottom line is that almost all aspects of nuclear power plants are stretching our scientific and engineering expertise. We are like the Egyptians building the earliest pyramids but haven’t yet figured out that the slope needs to be lower.
In a general way, those of us with military reactor experience can talk about alloy composition, specific fuel and poison loading concepts and plans, and a few other specific details associated with NAVSEA 08 plants that Uncle Sam would prefer we not mention.
To be a nuclear plant operator in the Navy one has to have an active Confidential clearance. And discharge doesn’t release us from those restrictions.
Therefore, we keep our mouths shut. It’s not about preventing damage to national interests (At least not for me.) because most of the data that I could give is out there in the public domain, if one really looks. It’s about keeping me at liberty to oogle pretty women.
Out of curiosity, how much consideration would be given to the thought that various countries we are/were not on the best terms with (ie: China and Russia during the Cold War) in regards to a decision to make a breeder reactor that happened to produce material which could be used in nuclear weapons? I suppose such a thing might make them nervous, but I’m not sure how much plutonium we happen to have just lying around anyways, and then there’s the line in a Tom Clancy book somewhere about how a gun with 13 bullets isn’t necessarily more dangerous than a gun with 5 bullets in it.
I ramble, but I think the question in there is coherent enough.
Otto, I don’t disagree, but if they had to choose one or the other, I think most go with the emotional “nukes eeeeevil” reaction. I do know I’ve gotten into more than one argument with self-labelled greens who think that coal is greener than nuclear power. For that matter, wasn’t it just last year that the latest world meeting about global warming endorsed nuclear power as a good way to start reducing greenhouse gasses? Certainly I haven’t seen much change, here in the US, towards nuclear power after that. Even from those still pushing Kyoto. Raguleader - I think part of the lack of concern for Russia and China is because there’s damn-all we can do to stop them from getting the capability to make nukes, or dirty bombs. Certainly when the concern was for fission or fusion bombs there wasn’t that much concern about “briefcase” bombs, because the reaction to that would have been the same as the reaction to an ICBM bomb - MAD. Since reactor isotope ratios tend to be a bit idiosyncratic AIUI, it would have been very, very hard to disguise where one’s nuclear bomb came from.
With a dirty bomb, we’re no longer looking at manufactured elements like Pu. We’re looking at Co-60, and other relatively short-lived, high energy isotopes. There’s more room to spoof people about where such isotopes came from than the rarer Pu or U.
For that matter, I really don’t think that there’s much immediate concern about the nuclear power and weapon programs of India and Pakistan as a US security issue. (This isn’t to say that the fact that two countries that basically have a long standing cold war going nuclear is a good thing, but we’re not really concerned about either country going after us.) The problem is when a country that is rather strongly irrational in its leadership is going after such capability - and when it’s been pushing rhetoric that’s more than a bit confrontational. Like, say, Iran, or North Korea. And in both countries, since such programs are in their infancy, it’s still possible (or may still be possible) to prevent them from gaining the capability.
In general, Navy-used reactor designs are very compact (obviously, in order to fit within the hull of a ship or a submarine) and require active control to maintain stability. One of the largest sources of noise on a submarine is the pump(s) on the coolant loop of a submarine. In power-generating nuclear fission reactors a coolant–some kind of fluid like high pressure steam or liquid sodium–is run through the core, extracting the heat (and keeping the temperature of the core low enough that the elements don’t “meltdown”). The coolant then runs through a heat exchanger–basically, a big, double-ended radiator–where it transfers its energy to the outer loop. This loop runs through a cycle that drives the generator which in turn serves to make power that drives the powershaft, provides HVAC and systems power, et cetera.
For most US submarines, the reactor system is designed such that under most regimes the coolant moves through the loops under “natural convection”, i.e. it keeps moving without having to actively pump it, and thus eliminates the pump vibration; this translates into a very silent boat, to the point that some US submarines actually radiate less noise than the ambient environment. Soviet subs, on the other hand, were noted for the amount of noise their reactors make; the deep diving, high speed Alfa class “interceptor” boats, for instance, used a high pressure steam loop that was phenomonally noisy at max cruising speed. The later subs like the Akula and the Delta-IIIs were much quieter because of better pump isolation, anechoic hull tiles, and noncavitating screw designs, but AFAIK they never developed effective natural convection reactor systems.
Reprocessing nuclear waste is expensive, somewhat hazardous, and adds more links in the security chain. On the other hand, stuffing high grade radioactive material in a crack in the ground isn’t necessarily the brightest idea, either. At the time that Carter approved a ban on breeder reactors the designs ran on unstable or marginally stable modes which were strongly opposed by the anti-nuke environmentalists as well as sensible, caution-minded experts. There are modern designs that are passively stable (that is, they can’t go critical by failure of some subsystem–overheading results in boiling off the moderator or somesuch which then slows the reaction) but the US hasn’t approved new nuclear powerplant construction since the mid-Seventies and as others have already noted, until the fossil fuel supplies are sufficiently depleted to warrant the expense and bureaucracy of building nuclear plants that probably won’t change.
The production of potential weapon products is more or less a nonissue; one can readily produce a fuel that is appropriate for power generation but nonweaponizable (i.e. won’t sustain the kind of supercritical reactor that results in an explosion). One could produce a dirty bomb from radioactive products, of course, but you hardly need highly enriched plutonium to do so; see The Nuclear Boy Scout for the story of how a teenage boy built a nuclear hazard in his backyard shed.
Controlled energy-generating fusion has been perpetually “20 to 30 years away” since the Fifties, and despite advances in computer elecromagnetic fluid dynamics simulation and superconductor materials is likely to remain out of reach in the foreseeable future. We can create fusion reactions easily enough (as the residents of Nevada are well aware) but making a controlled, sustainable reaction is tough. Also, as Spacekat notes, the reaction is extremely hot (and for the D-T cycle, produces a lot of neutrons which results in material degredation and neutron activation of radioactive isotopes of otherwise inert materials). It is, in fact, far too hot to run a coolant loop through as detailed above, so you have to extract the energy via some other process where you either stage down the temperature of the products to a level that is managable by normal materials, or you extract energy inductively from the charged plasma via a magnetoelectrodynamic generator. Both of those will require advances in the state of the art of technology, so even if you could control nuclear fusion today you’d still have years of effort into making a safe, reliable system for turning raw energy (in the form of an energetic plasma) into electricity. So, don’t be buying up shares in General Atomics in hopes of paying next year’s Christmas bill with them.
The irony of this is that a coal-fired plant pumps out into the atmosphere substantially more radioactives–in the form of [sup]14[/sup]C and radioactive isotopes that are naturally found in coal and shale–than any properly functioning nuclear fission plant.
I like it. I’m familiar with the basics of the plan, and really like that the designs I’ve seen specs for use helium as a heat transfer mechanism. That eliminated, forex crud, and activated crud, since it can’t carry wear and corrosion products. It’s also a naturally low corrosion environment.
But, remember, my understanding is based on a few popular articles on the subject, and a technician’s understanding of the engineering and science behind nuclear power. I’m not uneducated, but there are gaps in my education which may lead me to miss important factors. (i.e., I don’t know why MIT doesn’t have a design they’d back in the real world, yet but I’m not about to second guess them, either.)
I like it. I’m familiar with the basics of the plan, and really like that the designs I’ve seen specs for use helium as a heat transfer mechanism. That eliminated, forex crud, and activated crud, since it can’t carry wear and corrosion products. It’s also a naturally low corrosion environment.
But, remember, my understanding is based on a few popular articles on the subject, and a technician’s understanding of the engineering and science behind nuclear power. I’m not uneducated, but there are gaps in my education which may lead me to miss important factors. (i.e., I don’t know why MIT doesn’t have a design they’d back in the real world, yet but I’m not about to second guess them, either.)
Pebble Bed Modular Reactor. Here’s a list of the standard criticisms of PBMRs by someone with a clear axe to grind on the whole nuclear industry. I’m not an expert on nuclear power plant designed, but from my barely informed opinion it seems to have the advantages of being mechanically uncomplex, passively moderated, and reasonable scalable. The criticisms listed are valid but mitigatible, IMHO. Whether the system can be made safe and reliable in operation is an emperical exercise, but from a functionality standpoint its clearly less complex to operate than a traditional rod element in pool type of core.
My limited understanding of PBMR’s is that their one serious downfall is a need to constantly refuel them (as in refuel them weekly). In a world worried about proliferation would non-stop truckloads of uranium driving about be a good idea?
