Is Thorium an Energy Alchemist's Dream?
27 Mar, 2009 02:20 pm
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Reduce text sizeAdvocates say that already existing thorium fuel and reactor technology could provide centuries and perhaps millennia of safe, abundant nuclear power. Are they right?
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Their work revealed that nuclear fuels could be multiplied through a process called breeding in which nonfissile elements--ones not subject to nuclear fission--such as thorium-232 and uranium-238 are deliberately introduced into a reactor. Their bombardment with particles emitted by fissile elements such as uranium-235 and plutonium-239 turns them into fissile fuels--ones capable of being split--such as uranium-233 (from thorium-232) and plutonium-239 (from uranium-238). (The splitting, of course, is what results in such a huge release of energy. The controlled version is a nuclear reactor while the uncontrolled version is, as most people know, a nuclear bomb.)
Breeding would be unimportant were it not for the fact that uranium contains only about 0.7 percent uranium-235, the only naturally occurring fissile fuel. It takes a lot of work and energy to enrich uranium to the point where it contains enough uranium-235 to be useful for a nuclear reactor. And, the rarity of uranium-235 calls into question the longevity of the world's uranium fuel supply.
Thorium by contrast appears to be far more abundant than uranium, perhaps three times more abundant than all isotopes of uranium combined. And, it is theoretically possible to turn all of the available thorium into fissile material meaning the total supply on any human time scale is vast.
Besides availability, thorium has three additional distinct advantages over uranium fuel. First, thorium fuel elements can be designed in a way that make it difficult to recover the fissile uranium produced by breeding for bomb making. This reduces the likelihood of nuclear weapons spreading to nonnuclear nations that adopt thorium-based fuel technologies.
Second, the waste stream can be considerably smaller since unlike current reactors which often use only about 2 percent of the available fuel, thorium-fueled reactors with optimal designs could burn nearly all of the fuel. This is the main reason besides its sheer natural abundance that thorium could provide such long-lived supplies of fuel for nuclear power.
Third, the danger from the waste of the thorium fuel cycle is potentially far less long-lived. The claim is that the reprocessed waste will be no more radioactive than thorium ore after about 300 years. This claim is based on the idea that virtually all of the long-lived radioactive products of breeding will be consumed in the reactor before the final round of reprocessing takes place.
So, with all these advantages, what is holding back development of thorium-based fuels? First, most commercial reactors run on uranium. Thorium fuels have been used in some commercial reactors with success. But no fuel-producing infrastructure yet exists for supplying thorium commercially, and so it remains for more economical and reliable to use uranium. (One small company has been trying to change that with limited success.)
Second, the advantages of thorium come from the reprocessing and extraction of the uranium-233 produced by breeding. This reprocessing has proven challenging because of the highly radioactive byproducts produced during breeding and the resulting high costs associated with processing fuel and building fuel assemblies.
There are also practical hurdles for reprocessing solid fuel. But advocates of the so-called molten salt reactor claim that this design lessens the problem of reprocessing since the products of breeding can be continuously extracted and processed from the molten liquid stream inside a closed fuel cycle. They also claim that the design is far less prone to accidents which might release radioactive materials into the environment. None of this, of course, solves the problems of existing reactors that use solid fuel assemblies. But it does suggest a plausible course for vastly expanding nuclear power generation with little worry about fuel supplies and fewer concerns about nuclear weapons proliferation.
The end of the fossil fuel era is coming sooner than most people believe as exponentially increasing fossil fuel consumption brings us ever closer to the day when production will peak for oil, natural gas and coal and then begin irrevocable declines. The only options left for powering a modern technical society will then be solar, wind, tidal, hydroelectric, geothermal and nuclear. And of these, only nuclear can conceivably be located wherever it is needed at the scale required.
The main concern about these replacements is whether they can be built fast enough to head off an overall reduction in the amount of energy available to society. A second concern is the size of the footprint for renewables such as solar and wind, footprints which are orders of magnitude greater than what we are used to with fossil fuel power generation.
Given the history of the nuclear industry I have my doubts whether much will be done to maintain, let alone increase, the share of power generation that nuclear now supplies. Still, the possibility of a vastly expanded and viable long-term nuclear industry seems now to lie with thorium and the small band of advocates who are making the case for its use.
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Add to Newsvine| [1] | Comment by Irving Smith - 27 Mar, 2009 04:48 pm Thank god a few knowledgeable people are writing and speaking on this subject. At this rate it will take ages to overcome public anti-nuclear power prejudice. Where are you, Al Gore? |
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| [2] | Comment by Charles Barton
- 28 Mar, 2009 01:59 am Kurt, The solution to the rapid deployment problem is simple. Factory build small, easily transportable Liquid Fluoride Thorium Reactors, and site them at existing power plant locations. You are invited to join the conversation at Energy from Thorium, or read more about it at Nuclear Green. |
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| [3] | Comment by Patrick Kennedy
- 28 Mar, 2009 06:52 am Senators Harry Reid (D-NV) and Orrin Hatch (R-UT) have recently introduced legislation that would pave the way for U.S.-based thorium nuclear-fuel reactors. it states in part: "The Thorium Energy Independence and Security Act of 2008 would establish offices at the Nuclear Regulatory Commission and the Department of Energy to regulate domestic thorium nuclear power generation and oversee possible demonstrations of thorium nuclear fuel assemblies." This legislation needs support, perhaps a grass roots campaign by bloggers to encourage citizens to contact their Senators is needed. |
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| [4] | Comment by Robert Hargraves
- 28 Mar, 2009 03:17 pm There is a tutorial presentation on the liquid fluoride thorium reactor at the Aim High web site. It also provides links to other resources. |
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| [5] | Comment by Zack Moitoza - 29 Mar, 2009 08:35 am Another option, closer to fruition, is the Integral Fast Reactor, or IFR. We have enough depleted uranium of the enrichment process of U-235 to power these reactors for hundreds of years. So, for hundreds of years we wouldn't even need to mine more fuel, and could burn up our nuclear waste or U-238 depleted uranium. I recommend "Prescription for the Planet," by Tom Blees, for more info, or just google Integral Fast Reactor. |
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| [6] | Comment by J. Speaker
- 29 Mar, 2009 08:57 pm The tutorial presentation that Robert Hargraves mentioned can be found by clicking on his name and then when the "The site you have requested could not be found" message is obtained, changing the internet address to omit the "www" part. |
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| [7] | Comment by Niels Colding - 30 Mar, 2009 08:53 am I wonder how many - say 1000 MW reactors - would be needed to replace 50 % of the world's total fossile energy consumption? Can anyone out there give me a qualified answer? I know that we would have been better off in Denmark with one single nuclear reactor than wiht our 5000 almost useless unreliable windmills. |
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| [8] | Comment by mdf - 2 Apr, 2009 02:42 pm Mr. Colding, humanity is burning about 80 million barrels of oil per day. At 7 barrels per tonne, and 42GJ per tonne of oil, and 86400 seconds per day, this amounts to a power dissipation of about 5000GW. That's thermal; to get the electric (which is how power plants are usually accounted), divide by about 3. A couple of thousand nuclear power plants is a big job, but hardly unachievable. Once the manufacturing pipeline begins, though, we can expect accelerations in terms of time and cost reductions. |
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