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Microbes for Bioremediation
The San Francisco Chronicle has a piece discussing current efforts to clean up nuclear waste sites with microbes. Current treatment procedures generally involve pumping out the contaminated groundwater, filtering it, and pumping it back, which is rather expensive.
So, as it currently stands, there's not much that microbes could do to "cure" Hiroshima. It's already highly populated after having to recover from near-total population loss, and I seem to recall reading somewhere that it has a birth defect rate that's the same as other Japanese cities. So much for the nuclear waste zone.
"God, root, what is difference?" - Pitr, userfriendly
OK, enough of the silly "Microbes will take over" and Frankenfood-inspired comments.
Having read the article, it seems like a good way to precipitate soluble U ions as U oxides, or complex uranyl compounds. It appears to offer a way to mitigate impacts upon human health and the environment by precipitating U ions traveling in ground water so they do not discharge to surface water or pumped by potable wells.
Bioremediation is nothing new. It works well with chlorinated solvents (PCE and TCE), especially in reduced, iron-rich ground water. The caveat for those compounds is, however, that they break down only so far, often leaving vinyl chloride -- a demonstrated carcinogen -- as the final step before there is not enough energy for them to survive by reductive dehalogenation. Basically, the microbes die becuase they do not have a source of "food."
The same goes for aerobic microbes, like these appear to be; they combine dissolved metals with oxygen to precipitate them. That gets even more expensive, because you have to maintain the proper redox level by introducing O2 with hydrogen peroxide or ozone. It's expensive and prone to mechanical failure or the vagaries of the subsurface.
These microbes may die out once their source of "food" depletes. However, the by-products should be assessed before they try to use this in a live environment, because sometimes the cure can be worse than the problem. There is also no economic analysis for this research, but it is likely way to early to determine how much it would cost to implement. It may be more reliable and cheaper to precipitate dissolved U by simply pumping a lot of oxygen into the ground water.
The story sounds like its using a method that the copper industry has been using for years, expect in this case with microbes that crave uranium instead if copper. They don't eat or destroy the uranium, just chemically transform it into insoluble forms that can be easily filtered out of groundwater.
Biological heap leaching is an inexpensive way to extract the metal from low-grade ores where copper is bound in a sulfide matrix. As the microbes chew up the ore, which has been treated with sulfuric acid to encourage them, the copper is released and concentrated in a solution that flows into a catch basin. The metal is extracted, and the acid solution is recycled.
I'd be a little surprised if the concern with the uranium concentration is really the radiation; perhaps at the Oak Ridge, but almost certainly not at the mine tailings. If the concentration of non-refined U is so high radiation becomes a concern, you're more likely to die due to the fact uranium is poisonous in the same sense mercury and arsenic are poisonous. In any case, U isn't a good thing to have in the water supply.
Groundwater is poluted by engine oil, petrol, and jp5 jet fuel leaking from storage tanks in all 50 states and every country on the globe.
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Hydrocarbon groundwater pollution is a much more widespread problem than soluable uranium. People with water wells 10 miles from Miami International Airport (MIA) can smell JP5 jet fuel in their well water. This is clear cut opportunity for bioremediation. People store and therefore leak hydrocarbons where they can and do use them.
As population and water needs rise, and supply dwindles, the US Federal Government has been forced to act. In the 1990's, to reduce the hydrocarbon pollution of groundwater, the US Government forced every gas station (petrol filling station) to dig up every storage tank and the soils surrounding the tank, and leave the dirt in piles to "off gas" the hydro carbons for months. And after off gassing, station owners had to replace the tanks with less leaky modern tanks.
Because water is essential for life, yet difficult to move economically, there will be increased border wars and politcal fights to control rivers and aquafers. We are watching a war for control of the oil rich country of Iraq. We will see similar fights and politcal disputes for control of rivers and dams on many international rivers. We will also see a marked rise in the trade of grain, one of the few water intensive commodities that can be traded economically.
All of this spells a golden opportunity for bioremediation of hydrocarbons, to help cities, farms, and countries to improve supply of potable water.
Mac refugee, paper MCSE, Linux wanna be
and first person to mention knoppix on
You said: "Canadian reactors use weapons grade plutonium and uranium, rather than whatever it is that other reactors use (which is how India and Pakistan got their hands on nuclear material -- from nuclear reactors bought from Canada). I remember there was a big fuss during the Clinton administration, because the plutonium and uranamium from a number of decomissioned nuclear weapons was going to be shipped to Canada, and people on both sides of the border weren't too keen on that."
Canadian reactors are not initially fueled with plutonium. They are just not highly enriched (where the fraction of the isotope U-235, which occurs 0.7% naturally, is increased). The consequence of this is that in order to have a self-sustaining chain reaction (criticality), the neutron flux must be higher. This is because the Candu reactor uses slow-fission which utilizes U-235 as a fuel and not U-238. In order for the core to remain critical (where on average one neutron from a fission event goes on to cause another fission vice being absorbed by another nucleus or escaping the boundary of the core) it has to be very large size and have a very high neutron flux (as compared to a more enriched core which could be smaller and have a lower neutron flux and stay critical).
One consequence of a core with a very high neutron flux is that U-238 can absorb a neutron (which is helped because the core utilizes slow fission unlike a nuclear bomb), become U-239, undergo 2 beta decays and form Pu-239. Pu-239 can also undergo fission like U-235 and be used as a fuel (odd numbered atomic mass numbers of very heavy elements will undergo slow fission but even numbers will not). This is one of the reasons why natural uranium and thorium (which would produce U-233) could potentially create more fuel over time in the reactor (as the U-235 is depleted). Since it is much easier to make a nuclear bomb from plutonium than the brute force method of seperating U-235 from natural uranium this is obviously a potential threat for nuclear weapons poliferation around the world if these reactors are sold.
You asked: "So -- as far as environmentally friendliness is concerned, how do the different types of reactors stack up?"
When you think about environmental friendliness there is short term safety (immediate event of casuality) and long term (groundwater and storage of waste) concerns.
In the short term the major concerns are preventing the reactor from breaking and spilling its fission fragments (which is the VERY highly radioactive waste in a reactor compared to everything else which is relatively lowly radioactive), and if it does break, by containing it. Preventing the reactor from breaking is pretty much controlled by good engineering practice of operating it and by competent design. If we've learned anything from the Chernobyl accident, the least of which is that *only* the people who are trained to operate and know the most about the reactor should be allowed to do any test (or any operation for that matter). Once management steps in and decides that they know how to operate the reactor better than the operators themselves, there is a serious problem. Containment is much simpler. You put up several barriers to prevent radioactive fission gasses from escaping. The final one, the most obvious one, is the cement dome that covers nuclear power plants. But other methods of containment are also useful, such as the pebble bed design where each fuel particle is encased in a ceramic sphere that can contain all fission product gases ever produced by that particle. In the worst case accident the particle will not melt or lose any of its ability to hold the gasses. Future reactors will be much safer due to designs like this (in fact the NRC has rated some as requiring "no evacuations under any accident condition", meaning that they don't think a meltdown can occur).
For long term concerns, continuous sampling and monitoring as well as storage of radioactive waste are the concerns. As long as there is
Suddenly, the hairy finger of a familiar monkey tapped me on the shoulder. It was time.--G. T.
What those who speak in praise of the city haven't mentioned is that the swan pond that I'm looking at is surrounded by a fence, that you can't fish anywhere downstream of the labs for miles and miles, and that there are still barrels of STUFF that we don't even know exist buried around the countryside. Sure, on the surface things are fine, but that's because the heavy metals have long since sunken into the earth.
It's not like the situation hasn't gotten infinitely better since the initial mismanagement of the lab (alluded to by a previous poster and by Richard Feynmann's 'The Pleasure of Finding Things Out'). We built an onsite waste management facility, as part of the cleanup led by Bechtel Jacobs. It was a step in the right direction for the lab, as it allows us not only to repair damage already done, but to prevent causing further harm to the environment as research on radioactive materials continues. (side note: we prefer the term 'rare isotope'... It doesn't scare the populace). The cleanup process was not painless, as this proposal by Bechtel Jacobs (the company leading the multi-billion dollar effort) and article from the Knoxville News-Sentinel indicate. We're nearly done, though. Occasionally something surprises us, but the situation's better than it was.
So, on to the article at last... These microbes don't have a huge utility value here, but they have great potential. Chernobyl, anyone? If there's another uncontained meltdown, these little buggers can be deployed almost immediately (via aerosol spray delivered in an overfly by crop dusters) to begin to counteract the fatal seep of irradiated cadmium and contaminated nickel. It's not of use now, but it's a valuable tool to have in our box.
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