Nothing to do with reprocessing. Fast neutron reactors just use fast neutrons, neutrons that are thousands of times faster than the neutrons used in the curren

Nothing to do with reprocessing. Fast neutron reactors just use fast neutrons, neutrons that are thousands of times faster than the neutrons used in the current generation of reactors (called thermal neutrons). A thermal neutron is much more likely to hit a nucleus of Uranium. If it hits U-235, it generally makes it undergo fission, but 18% of the time it is just absorbed and becomes the nasty U-236, which is a very long lived radioactive element. If it hits U-238, it's absorbed, eventually becomes Plutonium-239, which in turns may absorb further neutrons, so a bunch of transuranic elements are produced. That's bad on two counts. The transuranic elements are radioactive and tend to be very long lived so the nuclear waste is long lived. And whenever a nucleus just absorbs a neutron and does not undergo fission, it's a shame, it's energy that's not being produced. Fast neutrons solve both problems. They are about 1000 times less likely to hit a nucleus, but when they do they almost invariably trigger fission for U-235 and very often for U-238 as well. That results in a massively higher burnup, and massively lower amount of transuranic elements in the waste. So, not only will a fast reactor produce much less waste for each GWh of electricity, it will be a much nicer type of waste, one that decays to the background radiation level in a few hundreds of years, rather than millions of years. Again, there is no reprocessing. The TRISO particle are not broken or milled at the end. They become nuclear waste as they are, but after they gave a huge amount of energy.