OAK RIDGE, Tenn. — K-25, once the world’s largest building under one roof, reflects less of its former title every day. Due to the partnership between the U.S Department of Energy (DOE) Office of Environmental Management (EM) cleanup team and Oak Ridge’s prime environmental management contractor, URS | CH2M Oak Ridge, LLC (UCOR), the 44-acre, multi-level uranium-enrichment superstructure is in the advanced stages of demolition.