Chelyabinsk Oblast has been associated with top-secret nuclear research since the 1940s. While there are no nuclear power stations in Chelyabinsk, a number of production reactors were located there starting with the early Cold War. A serious nuclear accident occurred in 1957 at the Mayak nuclear fuel reprocessing plant, 150 km north-west of the city, which led to evacuations and fatalities throughout the oblast, although not in Chelyabinsk city. The province was closed to all foreigners until 1992, with the sole exception of allowing a British medical team in following a two-train rail explosion in the mid-1980s.