World War II by Soviet and captured German engineers working in detention. The centrifuge process was the first isotope separation method considered for the Manhattan project, but was abandoned due to technical challenges early in the project. When German scientists and engineers were released from Soviet captivity in the mid-1950s the West became aware of the ultra centrifuge design and began shifting uranium enrichment to this much more efficient process. As centrifuge technology advanced, it became possible to carry out uranium enrichment on a smaller scale without the vast resources that were necessary to build and operate 1940s and 1950s "K" and "Y" style separation plants, a development which had the effect of increasing nuclear proliferation concerns. Centrifuge cascades began operating at Oak Ridge in 1961. A gas centrifuge test facility (K-1210) opened in 1975, followed by a larger centrifuge plant demonstration facility (K-1220) in 1982. In response to an order from President Lyndon B. Johnson to cut production of enriched uranium by 25 percent, K-25 and K-27 ceased production in 1964, but in 1969 K-25 began producing uranium enriched to 3to 5percent for use in nuclear reactors. Martin Marietta Energy replaced Union Carbide as the operator in 1984. Gaseous diffusion ceased on 27 August 1985. The Oak Ridge Gaseous Diffusion Plant was renamed the Oak Ridge K-25 Site in 1989, and the East Tennessee Technology Park in 1996. Production of enriched uranium using gaseous diffusion ceased in Portsmouth in 2001, and at Paducah in 2013. Nowadays all commercial uranium enrichment in the United States is carried out using gas centrifuge technology. The United States Department of Energy (DOE) contracted with British Nuclear Fuels Ltd (BNFL) in 1997 to decontaminate and decommission the facilities. Its subsidiary Reactor Sites Management Company Limited (RSMC) was acquired by EnergySolutions in June 2007. Initially K-29, K-31 and K-33 were to be retained for other uses, but it was subsequently decided to demolish them. Bechtel Jacobs, the environmental management contractor, assumed responsibility for the facility in July 2005. Demolition of K-29 began in January 2006, and was completed in August. Demolition of K-33 began in January 2011, and was completed ahead of schedule in September 2011. It was followed by the demolition of K-31, which began on 8October 2014, and was completed on 26 June 2015. Bechtel Jacobs was contracted to dismantle and demolish the K-25 facility in September 2008. The contract, valued at $1.48