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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."
"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.
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.
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.