As part of its 1950s-era Atoms for Peace program, the Unites States provided nuclear technology to foreign nations for peaceful applications in exchange for their promise to forego development of nuclear weapons. The program provided foreign countries with research reactor technology and highly enriched (HEU) needed to fuel civilian nuclear reactors. Initially, the U.S. leased HEU to foreign countries with the explicity provision that the spent fuel be returned for treatment and disposal in the U.S. preventing its use in a weapons program. in 1964, the U.S. changed its policy and began selling its use in a weapon program. In 1964, the U.S. changed its policy and began selling HEU materials to foreign countries without requiring the return of spent fuel.