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Cleaning Uranium Waste with Bacteria
Roland Piquepaille writes "Nuclear bombs can kill people even if they're not used. In the U.S. alone, the Department of Energy estimates that more than 2,500 billion liters of groundwater are contaminated with uranium as a consequence of nuclear weapons production. In "Uranium 'pearls' before slime," scientists from the Pacific Northwest National Laboratory (PNNL) say they discovered that some common bacteria could "convert deadly heavy metal into less threatening nano-spheres." In fact, these bacteria can convert soluble radioactive uranium into a non-toxic solid form called uraninite. Still, more research needs to be done before using these bacteria on a large scale, but it's a step in the good direction. Read more for additional references and photos showing how Shewanella oneidensis can help us to decontaminate groundwater at nuclear waste sites."
It may be radioactive, but at least it won't get in people's drinking water.
"Nuclear bombs can kill people even if they're not used. In the U.S. alone, the Department of Energy estimates that more than 2,500 billion liters of groundwater are contaminated with uranium as a consequence of nuclear weapons production. Ok, let's be scientific here. First, the proposed problem is not that unused nuclear bombs can kill people themselves, but that the production of nuclear weapons creates a radioactive byproduct that is alleged to be dangerous. Where is this byproduct located? Is it contaminating known in use reservoirs? Is it all far away from any humans that would use this groundwater? Or is it somewhere in between? Assuming people are ingesting the radioactive byproduct, how many rads are they irradiated with? Is it a neglible amount? Are they dying in their showers? This story hasn't bothered to be consistent with its own terminology, and I don't think it's too early to call it hysterical fearmongering sans hard data.
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If you want to get a decent dose from uranium you are either going to need a lot of uranium around you or a very long time to be exposed.
Actually perhaps even further back than you might imagine! I submitted something that seems quite similar... back in 1999?
Fission reactors operate at a few hundred degrees - which is probably still enough to kill the bacteria even before we start asking questions about the radiation levels. You may be thinking of fusion reactors, which use ultra-hot plasmas, but they don't contain or produce uranium and are pretty much vaporware at the moment anyway.
I am a physicist. I've worked as aerospace engineer on spacecraft hardening and earth-resources monitoring; as chemical engineer on groundwater contamination and chemical remediation; as nuclear engineer as nuclear contamination monitor and waste containment engineer. This is baloney. Bugs which could digest chemicals could help for spills but will not alter or even contain the emitters. You'll only make a sludge full of it. And that won't go away. It all depends upon the type of emitters and whether or not there is mixing and other "digestion". Unless you believe in creationism, better not to believe there's a good way to move this crap back down into the earth where it comes from. This just tries to get a biological mechanism to put it back. Bad idea, 'cause life moves things up.
There are several uses of billion which may or may not add up to 2.5 trillion. The British and American system's billion is not the same.
I like muppets.
Wrong. In the commonly used system today, 2500 billion (2,500,000,000,000) IS equal to 2.5 Trillion (2,500,000,000,000) as 1 billion would equal 1,000,000 * 1,000. However, in the old system 2.5 Trillion would equal 2,500,000 Billion, as 1 billion would equal 1,000,000 * 1,000,000
I am Spartacus
Uranium is primarily an alpha emitter. Alpha particles can be stopped by a layer of clothing. Sure, its radioactive, but it won't turn you into the Toxic Avenger unless you consume it and it can directly irradiate your innards from the inside.
Politely, no. The organism is filtering free ions in solution, and using them for its energy needs, in the process precipitating out less-soluble minerals. This may be the origin of uranium deposits which are mined, at least in some cases.
So, the purpose here is if you have a mess such as Hanford, i.e. millions of gallons of highly radioactive soluble waste, this bacterium can help precipitate is as uranite, and take it out of your water supply. It's not going to dine on fuel rods. I'm not sure you'd want that anyway, as it would be fairly annoying to hear about rolling blackouts due to a bacterial infestation eating a reactor core.
the more accurate the calculations became, the more the concepts tended to vanish into thin air. R. S. Mulliken
Uranium in reactors is inside fuel pellets that are encased in a zirconium cladding (kind of like the chocolate inside an M&M candy). Those fuel pellets are then embedded or sandwiched in fuel plates made from various forms of stainless steel with zirconium cladding as well. The uranium fuel does not move around. I doubt the bacteria could penetrate those materials to get to the uranium. In theory, the uranium and its fission products (gases and solids) should never leave the confines of the fuel pellets. Overheating of the fuel plates can cause steam crevice corrosion (in a pressurized water reactor at least) which leads to blistering and swelling of the fuel plates which could then release uranium and the fission products to the primary coolant. The primary source of long term radiation in the primary coolant is not from the uranium itself, it is from the alpha, beta, and gamma energy and particles released that make other materials around the core and suspended in the primary coolant radioactive. Basically, small particles of rust and corrosion from the piping becoming activated. If I remember correctly, cobolt60 is the biggest offender. Of course cleanup and disposal of the coolant has nothing to do with what is left behind and contained in those fuel pellets!
If you ever are in a position that you need to shut down a reactor really quick, inject some boron or borated water into the core. That will absorb the thermal neutrons preventing them from being reflected back into the fuel pellets and stopping the chain reaction.
Second, U-238 is 99.28% of natural uranium. U-235 is 0.72% Weapons grade, or enriched uranium is natural uranium that has a much higher percentage of U-235.
Suddenly, the hairy finger of a familiar monkey tapped me on the shoulder. It was time.--G. T.
Uranium isn't particularly radioactive and what it emits from radioactive decay isn't particularly dangerous (mostly alphas, which are blocked by everything, including your skin and a couple inches of air) - it has a long half life, but there's millions of tons of the stuff all over the planet and you aren't dead yet. Most Geiger counters will go 'nuts' at almost anything that's big enough to handle, since they're usually designed to find trace amounts of radioactive material; a large lump of anything will test them effectively, but uraninite is fairly safe to handle so it's a good choice.
Uranium *fission* is dangerous but that doesn't happen unless somebody wants it to. Nuclear reactor waste fuel is dangerously radioactive primarily due to the assorted byproducts of fission that are still stuck in it (and most of those will decay in a few months or years - highly radioactive things have short half lives, by definition).
Uranium is a dangerous element to deal with because most of the forms it's used in happen to be extremely poisonous without needing to decay. Getting it into a non-toxic form is a good idea. (Shoving it back into a reactor is a better idea, but it's cheaper to bury it than to reprocess it)
Reading through the comments so far, there seems to be some misunderstanding of the work by the PNNL crowd and of bioremediation in general. My research group here at Argonne National Laboratory (which outside of Chicago) collaborates with the folks from PNNL. In fact, I am writing this very early on a Sunday morning while measuring the oxidation state of uranium using X-ray Absorption Spectroscopy at the Advanced Photon Source in samples from a collaborator at Oak Ridge National Laboratory, which, like PNNL, is a center of research into uranium bioremediation.
First, a few words about the concept of bioremediation. The Department of Energy became interested in bioremediation of metallic contamination after the extensive success of bioremediative techniques for cleaning up organic contamination -- things like benzene or trichloroethylene. The basic idea is that you dose the ground with bacteria that can metabolize the organic contaminant, let the bugs happily live their lives, then in the end the ground is much cleaner than before. Variations on this technique are in wide use for many organic contaminants and in many places around the world.
The Department of Energy's started several years ago to fund research into using similiar concepts to clean up ground water contamination associated with various sites where materials for nuclear weapons or nuclear fuel were produced. There are several sites in the US where the groundwater has elevated levels of uranium and other metals. Bioremediation is attractive because it involves remediation in situ. The ground doesn't need to be dug up, which introduces a whole slew of other problems into the mix.
Unfortunately, metals are different from organics. When a bacterium metabolizes benzene, the benzene goes away. When a dissimilatory metal reducer, like Shewanella, respires on a uranium compound, the most it can do is change the chemical state of uranium. It is impossible to turn the uranium into some other element. As several other posters have pointed out, uraninite (the end product of Shewnella's respiration of uranium compounds) is still radioactive and it is still toxic.
However, uraninite is not soluble. The uranium in the ground water is in a soluble form and therefore will flow through the ground and find its way into rivers and into drinking water supplies. Uraninite is highly insoluble. When Shewnella converts soluble uranium into uraninite, the uraninite particles adhere to the rocks in the ground.
Thus uranium bioremediation is a containment-in-place strategy. The danger of the contaminated sites is that the contamination will spread. The uranium-polluted site will still be polluted after the Shewnella has done its thing, but at least the uranium will not move out of the contaminated site. And that's the point of the DOE's bioremediation strategy -- to keep a problem that exists from spreading and becoming a bigger problem.
I suppose that you could say that for the first millionth of a second or so after a fission, a very localized area around a fission event might have a temperature of tens of millions of degrees. This is because any fission fragment will typically have a kinetic energy of about 60-80 MeV after a fission event (which accounts to a speed of about 1/30th that of light). As it rams into neighboring atoms it will obviously impart a lot of energy in a very small area (it is said that a single fission event can cause a grain of sand to visibly jump). But after that very brief period of time the heat will transfer to the surroundings.
The highest temperature in a fuel element is called the peak fuel centerline temperature (PFCT or PCT). Except for inert gas cooled reactors this value will not be higher than roughly 2500 F. The reason is simple if you are familiar with the design of steam plants (note: PWR is assumed for the rest of this discussion though you should be able to see that the BWR analysis is similar in results). This might seem like a large jump in topic considering that we were talking about the fuel element before, but as in many things in nuclear engineering, they are releated. Assuming saturated non-supercritical steam (to simplify the analysis), and assuming the Ideal Gas Law Applies (technically we need the van der Waal's equation of state, but we won't be that far off with the Ideal Gas Law), and assuming the steam stops are shut on the steam generator, we have a confined gas in a finite volume container which is bounded by the steam stop to the water level. It's pressure will be determined by its temperature. Well, this is not entirely true since as the temperature rises more water is going to boil off. This in turn raises the pressure which raises the temperature of the boiling point. But you should get the general gist: look up in a steam table what pressure a steam generator would be at if it had a temperature of 500 C, for example. Could you design it to have a reasonable volume (so that you could output a lot of steam to spin your turbines)?
Ok, back to our first part, primary water cools the fuel elements. This goes on to heat the steam generator. In order to keep the primary liquid, you have a pressurizer, which has the same requirements as the steam generator discussed before. You additionally have primary piping that has a pressure limit. Hence, you don't want your water coming off the fuel elements to be too hot otherwise you will start boiling water in the primary loop. You can raise that level by increasing the pressure, but there is a limit. The steam generator discussion comes in in the fact that it will have the temperature of roughly the mean between the water that comes off of your fuel elements and the water before it cools your fuel elements. To prevent heating your water too much you must have a sufficient flow rate of water to cool the fuel elements. Therefore the outside of your fuel elements will have a temperature only a little higher than the temperature of your steam generator. Now the easy part: with a constant power output (from your steam generators in steam), you can calculate the PCT solely from the current reactor power. PCT will follow it almost linearly. If you get bored and want to read a book on nuclear engineering you will find that it will typically be less than 2500 F.
Second, when people say fuel elements are hot, they are using slang. 'Hot' in the nuclear industry is synonymous with highly radioactive. It is true that fuel elements generate heat by radioactive decay after a reactor is shutdown (called decay heat), but any simple cooling system could take care of that. They are put in big pools because water is a cheap radiation shield. And it cools the fuel elements at the same time.