Fast breeder: Encyclopedia II - Fast breeder - Proliferation

Fast breeder - Proliferation

It is generally agreed that—if designed incorrectly—the FBR poses a greater risk of proliferation of nuclear weapons than light water-moderated reactors. Water-moderated reactors must shutdown and refuel every four months or less to produce weapons grade plutonium, relatively pure Pu-239, because the level of Pu-240 in the fuel increases over time. Pu-240 undergoes spontaneous fission at a relatively high rate and is unsuitable for nuclear weapons production. An FBR can more easily produce weapons grade material, depending on its design. However, to date all known weapons programs have used far more easily built thermal reactors to produce plutonium, and there are some designs such as the SSTAR which avoid proliferation risks by both producing low amounts of plutonium at any given time from the U-238, and by producing three different isotopes of plutonium (Pu-239, Pu-240, and Pu-242) making the plutonium used infeasible for atomic bomb use. Dirty bomb would still be a possibility, although ordinary high-level radiation waste can be used for this purpose as well.

Thorium reactors may pose a slightly higher proliferation risk than uranium based reactors, if improperly operated. The reason for this is that Pu-239 will fairly often fail to fission up on neutron capture, producing Pu-240, which contaminates the fuel, making it difficult to use in nuclear weapons. Thorium-232, however, converts to U-233, which will almost always fission successfully, meaning that there will be very little U-234, or higher actinides mixed with the reactor's thorium/U-233 breeder blanket, and the resulting pure U-233 will be comparatively easy to extract and use for weapons. Uranium-238 can be mixed with this blanket to make the resulting material less useful for weapons purposes (as then the U-233 would require isotopic separation), so properly operated, a thorium reactor should be less suceptable to proliferation.

Adapted from the Wikipedia article "Proliferation", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki