 Later, China, after its nuclear tests, similarly rejected North Korean requests for help with developing nuclear weapons.Soviet engineers took part in the construction of the Yongbyon Nuclear Scientific Research Center and began construction of an IRT-2000 research reactor in 1963, which became operational in 1965 and was upgraded to 8 MW in 1974.In 1979, North Korea began to build a second research reactor in Yongbyon, as well as an ore processing plant and a fuel rod fabrication plant.