Reprocessed uranium (RepU) 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 (excluding cladding) 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.
As of April 2007, uranium prices had begun to rise again, and if the price becomes high enough, it is possible that reprocessed uranium will be re-enriched and reused. A higher enrichment level will be required to compensate for the 236U which is lighter than 238U and therefore will concentrate 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 U-235 content remaining in spent PWR/BWR fuel is typically greater than that found in natural uranium, which is about 0.72% U-235, allowing the re-enrichment step to be skipped. Fuel cycle tests also have included the DUPIC (Direct Use of spent PWR fuel In CANDU) fuel cycle, where used fuel from a Pressurized Water Reactor (PWR) is packaged into a CANDU fuel bundle with only physical reprocessing (cut into pieces) but no chemical reprocessing.