Deconstruction and cleanup of the first former uranium enrichment complex in the world is complete, U.S. Secretary of Energy Dan Brouillette announced Tuesday at an event marking the historic cleanup milestone of the former K-25 site at the East Tennessee Technology Park in Oak Ridge.

Built secretly in the 1940s as part of the Manhattan Project, the campus once was home to a complex of facilities that enriched uranium for the world’s first atomic weapon. From 1945 to 1985, the plant produced enriched uranium for commercial nuclear power. The U.S. Department of Energy closed the site in 1987, and facilities fell into a dangerous state of disrepair.