"Built in the 1940s and 1950s, the Y-12 National Security Complex, located in Oak Ridge, Tennessee, is the National Nuclear Security Administration's (NNSA) primary site for enriched uranium activities. Because Y-12 facilities are outdated and deteriorating, NNSA is building a more modern facility-known as the Uranium Processing Facility (UPF). NNSA estimates that the UPF will cost up to $3.5 billion and save over $200 million annually in operations, security, and maintenance costs. NNSA also plans to include more advanced technologies in the UPF to make uranium processing and component production safer.GAO was asked to (1) assess NNSA's estimated cost and schedule for constructing the UPF; (2) determine the extent to which UPF will use new, experimental technologies, and identify resultant risks, if any; and (3) determine the extent to which emerging changes in the nuclear weapons stockpile could affect the UPF project. To conduct this work, GAO reviewed NNSA technology development and planning documents and met with officials from NNSA and the Y-12 plant. "