Enriched uranium was first manufactured in the early 1940s when the United States and Britain began their nuclear weapons programs. Later in the decade, France and the Soviet Union began their nuclear weapons and nuclear power programs. Depleted uranium was originally stored as an unusable waste product (uranium hexafluoride) in the hope that improved enrichment processes could extract additional quantities of the fissionable U-235 isotope. This re-enrichment recovery of the residual uranium-235 is now in practice in some parts of the world; e.g. in 1996 over 6000 metric tonnes were upgraded in a Russian plant.