A side question: Why isn’t there more interest in fast breeder reactors? It would seem to me that instead of just dumping the plutonium you’d be better off getting some use from it.
The main objection to it as I understand it is economics. It’s cheaper to store spent fuel than it is to reprocess it (although fuel cost in a nuclear reactor is a much smaller proportion of the total costs than it is in other types of generators; I understand that if the fuel doubled in price, electricity would cost 5% more). According to Stranger, we can keep it around for 40 years when the world’s supply of cheap uranium will be used up and use it then, although it still might be cheaper to use crappy ores than to reprocess.
Rob
As Stranger said, the Uranium used in reactors isn’t enriched enough to make a bomb with, and extracting the U-235 is very difficult because it can’t be done chemically. Extracting the Plutonium can easily be done chemically because it is a different element.
This doesn’t make sense. [sup]14[/sup]C would not be produced in enough quantity and is not hazardous enough to be a problem. It would also have nothing to do with “secondary reactions” or absorption of other elements.
I realize this will be an unpopular question but, how come we don’t just toss spent nuclear fuel into Mariana’s Trench? It’s not like we visit there very often.
Why not use the decay heat from spent fuel rods for something useful-like hot water for laundries? Just pump water through a heat exchanger-there would be no danger of radiation, and you would have a LOT of hot watre.
Following and reading some of the links given above it sounds as if plutonium used in a nuclear reactor is not sufficiently refined for use in a nuclear weapon.
(highlighting mine)
Plutonium is generally a much more dangerous material to humans. Dispersed into droplets it is poisonous as well as radioactive and chemically reactive. It would make a much nastier “dirty bomb”, among other things.
Yeah…we process what’s in the ground to concentrate it – and that’s billions of years old, you know. Even though it degardes somewhat, we can process this stuff to concentrate it when we need/desire.
I foresee some difficulty marketing this idea to people whose concept of clean laundry is informed by the Snuggle Bear™.
In addition to what’s already been said, there’s radiolysis – basically, radioactive bombardment changes the atomic structure. Over time, what was 100% steel casing becomes 99% steel casing and 1% various impurities. Eventually, originally-well-understood engineering materials become a crapshoot in terms of strength and reactivity.
Sailboat
Carbon-14 is a beta emitter, which isn’t too hazardous outside the body (it’ll basically be absorbed in the epidermis). If ingested in even fairly small quantities, however, it can cause serious harm. The major problem with graphite as a moderator, however, is simply that it can catch fire. Unlike steam, which will just evaporate, taking away the excess heat and dispersing the radioactive products it contains, graphite will fall downwind as an ash, bringing with it more toxic products from the fire, and there’s no good way to suppress a graphite fire.
Cost, difficulty, risk.
Again, high level radioactive waste is nasty; not only is it radioactive, but it’s also comprised largely of toxic heavy metals. The better you can keep it isolated and the less you have to handle it, the better. Using the waste heat to produce hot water just isn’t work the effort and risk.
True, but as yoyodyne points out, you can chemically separate plutonium from uranium (whereas it’s extremely difficult and laborous to separare [sup]235[/sup]U from [sup]238[/sup]U), and plutonium is more forgiving of contamination. High quality weapons grade plutonium production does try to minimize the amount of [sup]240[/sup]Pu in the material, but only because it makes the yield difficult to specify and calculate (owing to its high decay rate), and this is done during the production process by strictly controlling the flux and duration of neutrons rather than by active refinement.
You could make a bomb from even reactor grade plutonium, but the yield would be reduced (from an overly fast reaction) and over time the weapon would be more likely to fizzle. A uranium device with too much [sup]238[/sup]U, on the other hand, would fizzle badly and blow itself apart before achieving even a small fraction of potential yield. (It’s also possible to produce [sup]235[/sup]U from the decay of [sup]239[/sup]Pu and chemically separate it out to a high degree of purity.) So, in short, it’s a lot easier to produce a weapon from plutonium, even of sub-weapon grade, than it is to make it from even highly enriched, non-weaponized uranium.
Stranger
Really? Just encase the nuclear waste in concrete blocks, ship it on a barge over the trench, and dump it overboard. Doesn’t seem too costly, difficult, nor risky to me, but I’m admittedly completely ignorant about this sort of thing. Perhaps we are being naive, but it does seem like UncleRojelio’s idea is better than waiting for bureaucratic approval of an expensive storage facility.
How long are those concrete blocks going to keep the material from seeping out and poisoning the surrounding water? What are the long term effects of releasing radioactive material like that into the ocean? And, most importantly, how the hell do we get down there and fix it if we realize in a few decades that it’s a problem?
I seem to recall that one of the major problems with a long term storage site is not the placement of the site itself, it’s getting the various states in between the reactor and the storage facility to agree to transportation of nuclear waste through their state, although my google-fu is failing me this morning and I can’t find a good cite. This problem would still exist for all states that don’t have direct access to the ocean.
All good questions. Sorry if this is a hijack. Here’s a naive person’s take: Assume the material will seep out. I envision a spent fuel rod is pretty heavy, so it’s not going to float up or get swept back to land. Do we care if a spot in the middle of the ocean is poisoned? And the ocean is big… I don’t think even a hundred thousand fuel rods will make any difference that far away from anything. Heck, nuclear weapons were tested in the ocean before. We’ve all seen the video footage. Why don’t we care about the nuclear contamination from that? If it’s okay to explode nukes in the ocean, then use a nuke to blow up the waste material.
How does this supposed risk stack up against other risks like global warming? The only conceivable problem I can see is if the waste is somehow an undilutable contaminator. Like a kilogram of uranium left in the ocean will dissolve and disperse so that the worldwide level of uranium exposure increases measurably. Since uranium already exists in the world, I doubt this is the case. I don’t foresee uranium concentrating up the food chain, either.
As for returning to the waste, the reason you pick a location like the bottom of the ocean over a location like Antarctica is so nobody can go steal the waste.
I specified that it should be into a deep ocean trench where it would ( given enough time ) be subducted back into the earth whence it came.
It’s just not that simple. First of all, you have various types of waste (as I discuss in [post=7123178]this thread[/post]) which have to be contained in different ways. Second, while vitrification should be sufficient containment for concentrated high level waste, even if you can demonstrate that it is fully sealed from the environment you’re going to have to fight a series of political battles every time you transport or attempt to dispose of it; NIMBY (Not In My BackYard) is the Achilles’ heel of the nuclear industry. And then how are you going to dump it four miles down through the ocean and exactly into the subduction zone, rather than have it land on the abyssal plain nearby, potentially disrupting the unique biosystem that lives there? As an engineer, the words “how hard could it be?” are always a harbinger of unseen difficulty and complexity.
On the other hand, author Larry Niven has a modest proposal. I think he’s moderately insane in the same way that water is slightly wet (though I do like his evolution in action concept), but what do I know? 
Stranger
Damn, my solution is just a runner-up to the ultimate solution.
If the waste is vitrified (fused into glass0, I don’t see a problem: glass blocks were reocered from a 5000 year old shipwreck in the Agean sea. and none showed any sign of deterioration.
We could always strap it to the aft end of the odd available nuclear powered submarine and take it a little closer to the target area before discharging it. What could possibly go wrong?
Well, otherwise it’s just burning a hole in your pocket.
It sounds like a great plotline for an Irwin Allen disaster film. 
Stranger
I have to figure that if we can create missiles capable of going 5000+ miles and putting a warhead in a circle the size of Yankee Stadium, if we aimed at the pitcher’s mound, we can handle making some kind of guidance system for that. And… it could even be disposable.
I’d figure that the main stumbling block would be transporting it to the correct site. Can you imagine what would happen if say… a French nuclear waste freighter had problems in the Panama Canal, or got sunk going around Cape Horn?