In the reprocessing approach, the irradiated fuel is chemically treated to separate the remaining uranium and plutonium from the fission products and minor actinides. The recovered fissile material is recycled back into the fuel cycle (for example, as MOX fuel), while the fission product waste — which constitutes only about 4% of the total fuel volume but contains over 99% of the radioactivity — is vitrified and stored for eventual disposal.
Countries that have actively pursued reprocessing include France, the United Kingdom, Russia, Japan, and India.
Key Point: The decision between once-through and reprocessing is driven by political, economic, and strategic factors rather than purely technical considerations. Both routes must ultimately deal with long-lived radioactive waste through geological disposal.