By 1984, Sweden had signed and ratified the Antarctic Treaty. The Treaty was established in 1961 to ban all military activity in Antarctica. The Antarctic Treaty was not, however, the first "nonarmament" treaty that Sweden signed. Previously it had participated in the establishment of the Outer Space Treaty in 1967, which restricts the placement of nuclear weapons or other types of weapons of mass destruction in space. The 1986 Chernobyl nuclear disaster evoked fears of radiation and safety. As a reaction to it, the Social Democratic-led Swedish government set 1995/1996 as years to start the implementation of a phase-out plan, including the shut-down of two nuclear reactors. Additionally, in 1999 and 2005 two other nuclear reactors (Barsebäck I and Barsebäck II, respectively) were closed. In 1992, in order to improve safety of Russian nuclear power plants, Sweden started cooperating with Russia on nuclear safety, radiation protection, nonproliferation, and proper nuclear waste management.