[Jeon Seung-min's Science World] Why Yongbyon Became the Heart of North Korea's Nuclear Program

North Korea's movements are becoming increasingly suspicious ahead of the South Korea-US summit. The US government predicts that North Korea will soon conduct its 7th nuclear test. Signs of preparations for the nuclear test are gradually emerging. On the 14th, it was confirmed that the snow on top of buildings related to highly enriched uranium and plutonium production around the 5MW (megawatt) reactor in Yongbyon had melted, leading to analyses that the facility is operational. Although it is mid-May, there are still many places in North Korea where snow falls, making this prediction plausible.

In 2008, North Korea appeared to show its willingness for denuclearization by blowing up the cooling tower of the Yongbyon nuclear facility, but later restarted operations and is currently running three types of reactors. Yongbyon is North Korea's representative nuclear facility because it can produce all the materials needed for nuclear weapons manufacturing.

There are two main methods to make nuclear weapons. The first is the 'enriched uranium' method. Natural uranium ore contains about 0.72% uranium-235 (U235), which can be refined to increase the concentration to over 90%, making it usable as nuclear weapon material. This method can be carried out with high-performance centrifuges and uranium ore alone, so it is possible to produce without a full-scale nuclear facility like Yongbyon. Of course, Yongbyon also has uranium enrichment facilities that enable this process.

The second method uses 'plutonium.' Plutonium refers to uranium-239 (U239), which is rare in nature. Uranium-238 (U238), which is abundant in uranium ore, does not easily undergo nuclear reactions and is difficult to use for power generation. However, when U235 nearby undergoes nuclear reactions, U238 can be converted into plutonium. Plutonium causes powerful nuclear reactions, making it ideal for nuclear weapons. To obtain plutonium, nuclear waste called 'spent nuclear fuel' from power plants must be dissolved in acetic acid to create a liquid, from which plutonium is extracted. This process is called 'reprocessing.' In other words, both power generation and reprocessing facilities are required to obtain plutonium.

Once enriched uranium or plutonium is obtained, the basic preparation for manufacturing a nuclear weapon, i.e., an atomic bomb, is complete. Even when manufacturing a more destructive 'hydrogen bomb,' nuclear facilities like Yongbyon are essential. When making a hydrogen bomb, an atomic bomb made of plutonium or enriched uranium is surrounded by 'tritium.' When the inner atomic bomb explodes, the surrounding tritium undergoes nuclear fusion, causing a much more powerful explosion. The energy from nuclear fusion is theoretically 5 to 7 times that of nuclear fission (atomic bomb), but since the core is an atomic bomb, the actual destructive power is known to be about twice that of an atomic bomb of the same weight.

Tritium does not exist naturally. Therefore, it must be artificially produced using 'deuterium,' which is mixed at about one atom per 6,000 hydrogen atoms. When 'heavy water' containing deuterium is used as the reactor coolant, neutrons flying inside the reactor combine with deuterium to produce tritium. Tritium is produced using the reactor's cooling system.

According to data from the Denuclearization Research Center, North Korea is known to have uranium enrichment facilities in locations such as Pakchon, Yongjeori, Cheonmasan, Taechon, Pyongyang, and Hagap. It has explosion test facilities in Punggye-ri and Geumpyeong-ri, and a light-water reactor in the Kumho district. However, Yongbyon is the only place equipped with various types of reactors, uranium enrichment facilities, nuclear waste storage, explosion test facilities, and reprocessing facilities. From North Korea's perspective, it is an indispensable facility for the manufacturing and development of nuclear weapons.