North Korea's Mystery Bomb

Exactly how North Korea gathered both the materials needed and the plans to build such a facility is not clear. Some of the scientists who operate the Yongbyon facility were originally trained in Russia but the present generation appears to have been trained in North Korea. The construction of the first reactor began in 1980. The choice of its fuel—natural, unenriched uranium–was dictated by the limitations of the country: at the time there was no enriched uranium and no supply of heavy water. Using open-source information, the North Koreans copied the design of the first British plutonium producing reactors, which had been built in the 1960s with the intent of producing weapons-grade plutonium. These reactors, called Magnox reactors, were long ago abandoned in Britain but they continue to function in North Korea today. Magnox is an alloy of magnesium with a small amount of aluminum that is used to clad the fuel elements, which are made of unenriched uranium.