Mayak is the name for a number of nuclear facilities, which are about from Ekaterinburg, in Russia. The facilities were also known as "Chelyabinsk-65", or "Chelyabinsk-40". Mayak was built between 1945 and 1948. It was the first plant that could produce nuclear material in the Soviet Union. At times, up to 25.000 people worked at Mayak. They produced the plutonium fuel that was used for the first Soviet atomic bomb, amongst other things.