Breeder Reactor - Reprocessing

Reprocessing

Fission of the nuclear fuel in any reactor produces neutron-absorbing fission products, and because of this it is necessary to reprocess the fuel and breeder blanket from a breeder reactor if one is to fully utilise its ability to breed more fuel than it consumes. The most common reprocessing technique, PUREX, is generally considered a large proliferation concern because such reprocessing technologies can be used to extract weapons grade plutonium from a reactor operated on a short refuelling cycle. For this reason, the FBR closed fuel cycle is often seen as a greater proliferation concern than a once-through thermal fuel cycle.

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.

Furthermore, several countries are developing more proliferation resistant reprocessing methods that don't separate the plutonium from the other actinides. For instance, the pyrometallurgical process when used to reprocess fuel from the Integral Fast Reactor leaves large amounts of radioactive actinides in the reactor fuel. Removing these transuranics in a conventional reprocessing plant would be extremely difficult as many of the actinides emit strong neutron radiation, requiring all handling of the material to be done remotely, thus preventing the plutonium from being used for bombs while still being usable as reactor fuel.

Thorium fueled reactors may pose a slightly higher proliferation risk than uranium based reactors because, while Pu-239 will fairly often fail to undergo fission after neutron capture and produce Pu-240, the corresponding process in the thorium cycle is relatively rare. Thorium-232 converts to U-233, which will almost always undergo fission successfully, meaning that there will be very little U-234 produced in the reactor's thorium/U-233 breeder blanket, and the resulting pure U-233 will be comparatively easy to extract and use for weapons. However, the opposite process (neutron knock-off) happens as a matter of course, producing U-232, which has the strong gamma emitter Tl-208 in its decay chain. These gamma rays complicate the safe handling of a weapon and the design of its electronics; this explains why U-233 has never been pursued for weapons beyond proof-of-concept demonstrations.