[Yang Nak-gyu's Defence Club] How South Korea and the US Will Act If North Korea Conducts a Nuclear Test

On the 24th, officials from North Korea's Nuclear Weapons Research Institute carried out demolition work to close the Punggye-ri nuclear test site in Kilju County, North Hamgyong Province. At the moment of the demolition of the Punggye-ri nuclear test site control command facility, wooden buildings were blown apart and shattered. On that day, seven control command facility buildings were demolished. Officials from North Korea's Nuclear Weapons Research Institute explained that "Tunnel No. 4 was prepared for the most powerful nuclear test." /

[Asia Economy Yang Nak-gyu, Military Specialist Reporter] As North Korea prepares for its 7th nuclear test, intelligence agencies have entered an emergency state. North Korea is currently holding an expanded meeting of the 5th plenary session of the 8th Central Committee of the Workers' Party, and it is expected that a decision regarding the nuclear test will be announced. Additionally, there is analysis that internal public sentiment needs to be appeased due to food shortages and COVID-19, and that a decision must be made before the rainy season begins.

If North Korea shows signs of a nuclear test, intelligence agencies will inevitably accelerate their movements to identify the test's materials, scale, and power.

For North Korea to conduct a nuclear test, the process proceeds in the order of ▲site selection and tunnel excavation ▲installation of nuclear weapons and measuring equipment ▲cable connection and tunnel backfilling ▲conducting the nuclear test. With only the decision of Chairman Kim Jong-un, the installation of measuring equipment and cable connections can be completed within a few days.

The South Korean and U.S. military authorities can detect whether the test will be conducted 1 to 2 hours before through signals interception and other means. However, there is a possibility that North Korea may attempt to disrupt by spreading false information.

A nuclear test causes an earthquake. This is an artificial earthquake. Artificial earthquakes occur when explosives are detonated underground, liquids infiltrate the crust, or reservoirs form due to dams. In contrast, natural earthquakes occur due to sudden crustal movements inside the Earth.

The Korea Meteorological Administration (KMA) detects artificial earthquakes. KMA has invested 300 million won each in three locations: Inje in Gangwon Province, Yeoncheon, and Ganghwa in Gyeonggi Province, installing seismic observation stations 100 meters underground. The seismometers installed at these stations detect vibrations as small as about 0.25g, capturing tremors from all directions every second.

The Arirang-2 satellite photographs the area around the Punggye-ri nuclear test site in Kilju County, North Hamgyong Province, which is suspected to be the nuclear test location. Arirang-2 is equipped with a satellite camera capable of identifying objects measuring 1 meter by 1 meter. Orbiting the Earth 14 times a day at an altitude of 685 km, it attempts to capture images. However, if the test is conducted in complex tunnels, confirming the test is not easy.

In the air, the Korea Institute of Geoscience and Mineral Resources operates an infrasound measuring device installed at the Ganseong Observatory in Goseong County, Gangwon Province, to measure 'airborne infrasound.' Airborne infrasound is generated when explosives detonate and does not occur during natural earthquakes. If airborne infrasound is detected, it is highly likely to be an artificial earthquake.

The Korea Institute of Nuclear Safety also takes action. Since North Korea conducted its first nuclear test in October 2006, the institute has introduced 'SAUNA.' This device detects xenon and krypton gases that leak into the air after a nuclear test. If North Korea conducts a nuclear test, radioactive particles will linger over the Korean Peninsula for 3 to 4 days. Through these radioactive particles, the materials used in the nuclear test can be identified. However, detection may fail depending on the detection location, wind direction and speed, and radiation concentration.

The Nuclear Safety and Security Commission analyzed radioactive nuclides collected on land, sea, and air after North Korea's 6th nuclear test on September 3, 2017, and judged that the trace amounts of xenon-133 (Xe-133) detected were related to the nuclear test, but they ultimately could not confirm the specific type of nuclear test.

The U.S. Air Force's special reconnaissance aircraft also participates. It is the WC-135 (Constant Phoenix). The WC-135W belongs to the 82nd Reconnaissance Squadron under the 55th Wing at Offutt Air Force Base in Nebraska but is on standby at Kadena Air Base in Okinawa, Japan, flying over the East Sea. The U.S. government owns only two WC-135W aircraft, and their primary mission is nuclear test detection.

The WC-135W is better known by its nickname 'Sniffer.' It detects radioactive materials using an engine-shaped air sample collection device mounted on the side of the fuselage. By lowering the internal temperature of the air component collector inside the reconnaissance aircraft to below minus 50 degrees Celsius, nuclear materials in the air adhere to it. It collects and measures radioactive substances such as xenon (Xe-135), krypton (Kr-85), and cesium (Cs-137), which are released when atoms artificially break during a nuclear explosion, determining not only whether a nuclear test occurred but also distinguishing between enriched uranium, plutonium, and hydrogen bombs.

Since North Korea's first underground nuclear test in October 2006, the WC-135W has been dispatched over the East Sea to collect radioactive materials and conduct related activities. The WC-135W played a key role in tracking radiation leaks during the 1986 Chernobyl nuclear disaster in the Soviet Union. It also flew during nuclear tests conducted by India and Pakistan in 1998.