WMD Junction: Thorium reactors are often promoted as being an alternative form of nuclear power that limits nuclear weapon proliferation risks. Unfortunately, that isn’t true. Thorium reactors begin with thorium-232, a nonfissionable material. Irradiating the thorium with neutrons (typically from a “seed” source such as uranium 235) creates protactinium-233, a highly radioactive isotope with a half-life of 27 days, which decays into uranium-233. In molten salt thorium reactors, highly pure uranium-233 is obtained by removing the protactinium-233 while it decays in order to prevent it from absorbing further neutrons (and producing protactinium-234 as a result). That makes obtaining fissionable material a relatively easy process. Although uranium-235 is the preferred source of fissionable material for weapons, enriching it is an intensely industrial process that is easily detectable. And a US test in 1955 showed that uranium-233 can be used in a nuclear weapon, albeit with a lower-than-expected yield. However, advances in industry and technology suggest that the yield could easily be adjusted upward.
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I have never heard any proponent of Thorium LFTR design claim that U233 could not be used for a bomb. What they do claim is the gamma radiation from the U233 would fry any people and electronics near the U233.
In a fluoride reactor, all of the fuel processing equipment will be located in a containment region containing the reactor and its primary heat exchangers, under very high radiation fields, and under the high heat needed to keep the fuel liquid. Once the system is properly designed to direct uranium-233 created in the outer regions of the reactor (the “blanket”) to the central regions of the reactor (the “core”) there will be no possibility of redirection of the material flow. Such a redirection would necessitate a rebuild of the entire reactor and would be vastly beyond the capabilities of the operators. Furthermore, the nature of U-233 removal and transfer from blanket to core involves the operation of an electrolytic cell that will allow very precise control and accountability of the material in question. Unlike solid-fueled reactors the uranium-233 never needs to leave the secure area of the containment building or come in contact with humans in order to continue the operation of the reactor. This is another important point that the authors have failed to distinguish as they have ignored the existence or implications of fluid-fueled thorium reactors.
To claim that uranium-233 is just as effective as plutonium-239 for nuclear weapons is gross simplification bordering on outright deception. They have similar values for critical mass, but this leaves out a very important point. The nuclear reactions that consume uranium-233 also produce small amounts of uranium-232, a contaminant that will later be mentioned by the authors but ignored at this stage of the criticism. U-232 has a decay sequence that includes the hard gamma-ray-emitting radioisotopes bismuth-212 and thallium-208. Indeed, the half-life of U-232 is short enough that this decay chain begins to set up within days of the purification of the uranium, and within a few months that gamma-ray flux from the material is intense. These gamma rays destroy the electronics of a nuclear weapon, compromise the chemical explosives, and clearly signal to detection systems where the fissile material is located. This is one of the key reasons why no operational nuclear weapons have ever been built using uranium-233 as the fissile material.
The above comments were authored by Dr. Alexander Cannarahttp://energyfromthorium.org/ieer-rebuttal/#comment-162
No, obtaining the U-233 from an operating commercial power thorium molten salt reactor is hardly “a relatively easy process”. A weapons-intent state would use less expensive, less risky, technologically proven approach to obtaining fissile material, as demonstrated by India, Pakistan, North Korea, and (soon) Iran. Commercial power reactors based on thorium molten salt technology will not increase proliferation risk.
And, no, enriching uranium is not an “intensely industrial process that is easily detected”. One such centrifuge enrichment plant in Iran was not known until revealed by the government. And new laser-enrichment technology will use even less power, with less heat signature.
This is covered in THORIUM: energy cheaper than coal, described at http://www.thoriumenergycheaperthancoal.com