Reprocessed uranium
Reprocessed uranium is the uranium recovered from nuclear reprocessing, as done commercially in France, the UK and Japan and by nuclear weapons states' military plutonium production programs. This uranium actually makes up the bulk of the material separated during reprocessing. Commercial LWR spent nuclear fuel contains on average only four percent plutonium, minor actinides and fission products by weight. Reuse of reprocessed uranium has not been common because of low prices in the uranium market of recent decades, and because it contains undesirable isotopes of uranium.
| Isotope | Proportion | Characteristics |
| uranium-238 | 98.5% | Fertile material |
| uranium-237 | 0% | Around 0.001% at discharge, but half-life only 1 week. Produces soluble, long-lived neptunium-237 which is hard to contain in a geological repository. |
| uranium-236 | 0.4%-0.6% | Neither fissile nor fertile. Affects reactivity. |
| uranium-235 | 0.5%-1.0% | Fissile material |
| uranium-234 | >0.02% | Fertile material but can affect reactivity differently |
| uranium-233 | trace | Fissile material |
| uranium-232 | trace | Fertile material, decay product thallium-208 emits strong gamma radiation making handling difficult |
Given sufficiently high uranium prices, it is feasible for reprocessed uranium to be re-enriched and reused. A higher enrichment level is required to compensate for the 236U which is lighter than 238U and therefore concentrates in the enriched product.
Also, if fast breeder reactors ever come into commercial use, reprocessed uranium, like depleted uranium, will be usable in their breeding blankets.
There have been some studies involving the use of reprocessed uranium in CANDU reactors. CANDU is designed to use natural uranium as fuel; the 235U content remaining in spent PWR/BWR fuel is typically greater than that found in natural uranium, which is about 0.72% 235U, allowing the re-enrichment step to be skipped. Fuel cycle tests also have included the DUPIC fuel cycle, where used fuel from a Pressurized Water Reactor is packaged into a CANDU fuel bundle with only physical reprocessing but no chemical reprocessing.