April 09, 2011
The Thorium Solution
China likes Thorium based nuclear reactors. So they are doing research.
If the reactor works as planned, China may fulfill a long-delayed dream of clean nuclear energy. The United States could conceivably become dependent on China for next-generation nuclear technology. At the least, the United States could fall dramatically behind in developing green energy.This of course is somewhat misleading. It is true there are no fuel rods to melt down. That is because the fuel in the reactor is already melted down. If there was a cooling loss could that blob of molten metal and fluorine melt the reactor vessel from decay heat? Sure. Why not? Fission fragment heat removal is the same (more or less) for any reactor. The next article linked does point out that liquid Thorium Reactors can be designed for passive cooling in the event of an accident. Such a passive system is exactly what I have suggested should be a design criteria for future nuclear reactors in many of my previous posts.
In an article on how Thorium is safer for nuclear reactors the author talks about fundamental safety for nuclear plants.
The ongoing Fukushima Daiichi disaster is naturally making many people wonder about the safety of nuclear power. It's a good illustration of how unexpected failures happen in practice, and also shows how Liquid Fluoride Thorium Reactor (LFTR) is a fundamentally safer approach. When building a reliable system, you must assume it will fail. Regardless of how many layers of safety you build into something, what really determines its fundamental safety is what happens if all safety systems fail at once. For a nuclear facility, aside from specifically hardening against disasters like hurricanes, tornadoes, terrorist-flown airplanes, tsunamis, earthquakes, malicious actors, etc., you must also make a fundamental engineering assumption that it will melt down. No matter how improbable you think you've made it for a meltdown to occur, the most important feature of any nuclear facility is what happens when a meltdown does occur. And not only that, but there should be contingency plans for what happens when the plant is hit with God's flyswatter, not because such a thing is likely or even possible, but because you can't really be too paranoid about engineering for such scenarios.I agree on the design criteria for safer nuclear plants. You can read the rest of the article to see why the author thinks Thorium is a better idea.
These folks don't like Thorium. I will say now that they are generally a bunch of hysterics. OTOH I didn't find anything in the parts I have quoted that I disagree with. My background is: Naval Nuclear Power Trained. Reactor Operator Qualified.
Contrary to the claims made or implied by thorium proponents, however, thorium doesn't solve the proliferation, waste, safety, or cost problems of nuclear power, and it still faces major technical hurdles for commercialization.So you need enriched Uranium to kick start the reaction and what you have left over after the fuel is spent is the usual fission fragments plus plutonium from the Uranium kick start.
It has been claimed that thorium fuel cycles with reprocessing would be much less of a proliferation risk because the thorium can be mixed with uranium-238. In this case, fissile uranium-233 is also mixed with non-fissile uranium-238. The claim is that if the uranium-238 content is high enough, the mixture cannot be used to make bombs without a complex uranium enrichment plant. This is misleading. More uranium-238 does dilute the uranium-233, but it also results in the production of more plutonium-239 as the reactor operates. So the proliferation problem remains - either bomb-usable uranium-233 or bomb-usable plutonium is created and can be separated out by reprocessing.So Thorium reactors will have a proliferation problem. Chemical extraction of Plutonium is easier than centrifuge extraction of U-235. Except for the radiation problem.
Proponents claim that thorium fuel significantly reduces the volume, weight and long-term radiotoxicity of spent fuel. Using thorium in a nuclear reactor creates radioactive waste that proponents claim would only have to be isolated from the environment for 500 years, as opposed to the irradiated uranium-only fuel that remains dangerous for hundreds of thousands of years. This claim is wrong. The fission of thorium creates long-lived fission products like technetium-99 (half-life over 200,000 years). While the mix of fission products is somewhat different than with uranium fuel, the same range of fission products is created. With or without reprocessing, these fission products have to be disposed of in a geologic repository.Well the above is a little hysteric. Radioactivity decreases with increasing half life. Generally substances with a half life of over 50 years are not thought to be sufficiently radioactive to be a serious hazard. Which is why we worry about releasing tritium to the environment (half life on the order of 13 years) and why the fact that Uranium is everywhere in our environment (in beach sand say) is not a serious concern. The five hundred year number is correct though. That is 10 half lives and means a reduction of radioactivity by a factor of 1,000 from substances with a 50 year half life and rather more for shorter lived radioactive elements. For instance a substance with a 25 year half life kept for 500 years would see a decrease of radiation by a factor of a million.
I wish the Chinese luck. I'd also like to see ALL their data when they are ready to sell those reactors to the rest of the world. It might also be a good idea to buy one and test it to destruction before they are generally approved for use in the US. And do I worry about China making money selling us reactors? No. We will gain far more from the electrical power production of the reactors than the profits on the reactors will cost us. Because if we can't profit from the reactors what would be the point of buying them?
Cross Posted at Power and Control
posted by Simon on 04.09.11 at 07:44 PM
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A small step on the road to restoration of independence?
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A knee sock jihad might be premature at this time
People Are Not Rational
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The Thorium Solution
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