108. The K-25 plant produced enriched uranium until 1987, and its design was copied for two additional plants located at Paducah, Kentucky, and Portsmouth, Ohio. As an industrial process it was vastly superior to the calutrons at Y-12, but there were still better methods available. The ultra-centrifuge, which was a known method before the war, is now the uranium enrichment process of choice for the United States, Europe, and any spoiler state looking to build an atomic bomb.