On Mon, 2009-12-28 at 10:25 -0800, Phil Hays wrote: Yea, I'm talking to myself.
> BTW: A thorium fueled fast neutron reactor seems to me to be a very very > odd choice. Thorium, unlike uranium, doesn't need fast neutrons to have > a breeding ratio greater than one in a reactor. Both light water cooled > and heavy water cooled reactors have been operated with thorium fuel > rods, and have been shown to produce more fuel (U233) than consumed. > Fast neutron reactors are more complex and expensive, but have the > advantage of being able to breed more fuel (plutonium) from uranium > (U238) than they consume (plutonium and U235). Why used a more expensive > and complex reactor with the advantage of being able to breed fuel from > uranium to breed fuel from thorium when cheaper and more reliable > reactors can do that? I don't understand at all. Now, my interest in > nuclear power comes from the fact that it seem to be a requirement to > solve the global warming issue. I'm no expert on the details of nuclear > power, so perhaps someone can point me to a discussion explaining this > choice. Some quality time with Google let me find an answer to my question. Light water thorium breeder reactors have breeding ratios only a little over 1. The Shippingport reactor, for example, ran at a breeding ratio 1.01. As such it would require reprocessing to operate. Heavy water thorium breeder reactors are somewhat better, and can operate with only thorium fuel after startup, allowing reprocessing to be delayed for decades or even centuries to allow for most of the very radioactive elements to decay. Thorium breeders of any sort need to be fueled during startup with a mix of thorium and either enriched uranium or plutonium. For India, with little uranium resources and having had strict limits on importing uranium, and with massive thorium resources, this poses a startup problem for thorium based nuclear power. So India has designed and is constructing fast neutron breeder reactors mostly fueled with thorium to produce plutonium from India's very limited uranium to more quickly start the thorium fueled power cycle. Such fast neutron reactors would be not needed, or even useful in a steady state, or with the abundant and cheap enriched uranium outside India. The limits on importing uranium were imposed to limit/punish Indian nuclear weapon production. Longer term, limits on uranium might be probably counterproductive. To reduce the risk of U233 produced by a thorium breeder reactor being used for nuclear weapons, the fuel mix could include some depleted or natural uranium, which can't be chemically separated from the U233, but could only be separated by isotopic enrichment. The reprocessed fuel from a thorium only breeder reactor would be more usable for nuclear weapons than reprocessed fuel from a thorium/uranium fueled breeder reactor. -- Phil Hays <[email protected]> -- You received this message because you are subscribed to the Google Groups Global Change ("globalchange") newsgroup. Global Change is a public, moderated venue for discussion of science, technology, economics and policy dimensions of global environmental change. Posts will be admitted to the list if and only if any moderator finds the submission to be constructive and/or interesting, on topic, and not gratuitously rude. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/globalchange
