Suspicious activity has been spotted in two areas of North Korea′s main nuclear site that are key to the production of plutonium for building nuclear weapons. Lee Ji-won reports. According to satellite images and analysis from U.S.-based North Korea monitoring website 38 North,... trucks loaded with cargo appear to have been going in and out of a building at the Yongbyon nuclear research center that houses a five megawatt reactor. Another image shows vehicle tracks and trucks around the Radiochemical Laboratory complex. This is where plutonium is turned into the raw material for building nuclear weapons. 38 North says it′s impossible to determine to exact reason for the activity,... but one possible explanation could be that North Korea is unloading spent fuel rods from the reactor for the purpose of producing new plutonium. It says a full core of spent fuel rods at the reactor could produce enough plutonium for up to two additional nuclear bombs. The website says the latest developments are concerning and should be monitored closely by the international community. It′s thought North Korea has collected enough plutonium-based fissile material from Yongbyon over the years to arm up to ten small nuclear bombs. Lee Ji-won, Arirang News.