Potential Impact of North Korea’s Nuclear Attack on Seoul

The biggest obstacle to peace on the Korean Peninsula is North Korea’s nuclear arsenal. Recently, during the Supreme People’s Assembly, North Korea openly declared its intention to enhance its nuclear capabilities by enshrining its nuclear policy in the constitution. In response, the government has warned that “if North Korea prays for nuclear use, it will face the end of the regime.”

How much damage would occur if North Korea provoked by firing a nuclear weapon? It was confirmed that North Korea conducted a test last March to maximize the lethality of a short-range ballistic missile (KN-23) equipped with a mock tactical nuclear warhead by detonating it in the air at an altitude of 800 meters, targeting South Korea.

At the time, the Korean Central News Agency in North Korea reported that after loading a mock nuclear warhead on a North Korean version of the Iskander ballistic missile (KN-23) within the strike range of South Korea, it detonated it in the air, stating that it was “a comprehensive tactical simulation training for nuclear counterattack involving a mock launch training for a nuclear strike against enemy major targets.” The typical method of a nuclear attack is to detonate a nuclear warhead in the air, and this report was interpreted as North Korea demonstrating its ability to use missiles equipped with tactical nuclear warheads in actual combat.

According to the Korean Central News Agency, North Korea launched a missile test in Dongchang-ri, Cholsan County, Pyonganbuk-do. The media outlet stated, “A comprehensive tactical training was conducted to master the procedures and processes for carrying out tactical nuclear attack missions,” and “the missile warhead exploded exactly at an altitude of 800m above the target point in the East Sea, verifying the reliability of the nuclear explosion control device and the detonation device of the nuclear warhead part.”

In response, an official from the Korea Defense Research Institute evaluated, “800m is a considerable threat to us as it is an altitude that can maximize the killing radius when a nuclear warhead that North Korea claims to be able to load on KN-23 explodes.” The media especially raised the threat level by disclosing the specific flight specifications and operating procedures of KN-23, stating that they conducted “nuclear counterattack simulation training.”

There is an analysis that, if the report of the North Korean media outlet is accurate, there is a possibility that a small tactical nuclear weapon more potent than the atomic bombs “Little Boy” (15 kt) and “Fat Man” (20 kt)” (1 kt is the destructive power of 1000t of TNT) that fell on Hiroshima and Nagasaki, respectively, during World War II, has been completed.

The Little Boy and Fat Man, which were dropped on Hiroshima and Nagasaki, respectively, during World War II, both exploded at an altitude of 550m. At the time, the United States set the explosion altitude to maximize the destructive power of the 15-20 kt atomic bombs. The greater the power of the nuclear bomb, the more damage it can cause to the target by detonating it at a higher altitude. Tactical nuclear weapons are known to have a destructive power of 10-20 kt.

So, how powerful would it be if a nuclear warhead exploded in the sky over Seoul? We ran an actual simulation.

According to the analysis of the nuclear explosion simulation program Nukemap, if a tactical nuclear weapon with a power of 10 kt explodes at an altitude of 800m over the Seoul City Hall area, the estimated number of deaths is estimated to be 44,000. People within a radius of 1.47-2.12 km can suffer thermal radiation damage and get third-degree burns. Ultimately, it was estimated that the number of deaths would be between 44,000 and 115,000, and the number of injured would be between 300,000 and 420,000.

Nukemap is a program developed by Professor Alex Wellerstein of Stevens Institute of Technology in the United States. Major think tanks use it to estimate the results of nuclear explosions. Nuclear experts explained, “It seems that they set 800m as the explosion altitude to imply the development of a tactical nuclear weapon with a stronger force than what was dropped on Hiroshima and Nagasaki,” and “it can be seen as a force that can reach more than 50 kt.”

If North Korea changes its target and targets the presidential office in Yongsan, Seoul, the scale of damage will change again.

Assuming that a missile carrying a 10 kt tactical nuclear warhead exploded at an altitude of 400m near the presidential office in Yongsan, Seoul, it was predicted that there would be 46,510 deaths and 164,850 injuries. A crater is likely to be formed in a radius of 153 meters from the explosion point, and residential buildings within 1.36 km are likely to collapse. Including minor injuries, the final damage area was estimated to expand south of the Han River, reaching 41.7 km² in the Dongjak-gu area.

If we assume a situation where a 20 kt nuclear warhead, which can maximize the killing power at an altitude of 800 meters, explodes, the simulation result is that there are about 114,600 deaths and a total of 534,600 casualties. It is revealed that the presidential office in Yongsan-gu (3.6 km) is included within a radius of 5.29 km (87.8 km²) that falls under the direct damage of the nuclear explosion. In this area, a huge mushroom cloud rises to a height of 7.21 km, and it is expected that there will be a large number of casualties who will die within a month of exposure within a radius of 1.16 km, including the Seoul Government Complex and Myeongdong.

It was estimated that people within a radius of 2.12 km, including Huam-dong, Yongsan-gu, and Namsan Tower, would suffer significant injuries, such as third-degree burns and the need to amputate parts of their bodies.

More importantly, if a 20 kt nuclear bomb explodes at an altitude of 800m in Yongsan, targeting the presidential office, it is revealed that the presidential office, the Ministry of National Defense, and the Joint Chiefs of Staff would suffer damage to the extent of disappearing from the map. The area within a radius of 1.91 km, including universities and apartments in Yongsan-gu, is directly exposed to building collapses and fire damage caused by nuclear explosions.

On September 2, last year, North Korea launched a long-range strategic cruise missile, presumed to be an Arrow-1 or 2 type, to the west. At the time, North Korean media emphasized that it “detonated in the air at a set altitude of 150m above the target island.” Military experts are speculating that this cruise missile is the Arrow-1 or 2 type that North Korea is developing. It is believed that it is possible to load a 10-kt tactical nuclear warhead on it.

Recently, North Korea has often mentioned the word “explosion in the air” in public reports after missile test launches. It claims to have performed a nuclear strike mission by setting various air explosion altitudes of missiles from 150m to 800m. Military experts are expressing concern about this move. The National Intelligence Service also mentioned in the report to the National Assembly Information Committee that “testing with tactical nuclear capabilities suggests a potential direction for threats in case of future provocations against South Korea.” This means examining the target and purpose of South Korea’s strike, aiming to find the optimal altitude for an airborne explosion to achieve the most effective nuclear lethality.

According to Nukemap results, if a nuclear warhead-equipped Arrow missile penetrates Seoul at low altitude, evading interception, and then successfully detonates at an altitude of 150 meters (about 492 feet) above Seoul City Hall, it is estimated that 60,910 people would die and another 113,870 would be injured. This suggests that detonating a nuclear weapon at a relatively high altitude could maximize the kill radius and increase the effectiveness of the blast.

Conversely, lowering the detonation altitude proves more effective in destroying sturdy structures like underground bunkers, while the kill radius may decrease. Nukemap analysis indicates that to collapse concrete structures with a 10 kt tactical nuclear weapon, the optimal altitude for an airborne explosion would be 102 meters (about 335 feet), and for causing casualties, 1010 meters (about 3314 feet).

In March of the previous year, North Korea unveiled the tactical nuclear cartridge Hwasan-31 with an estimated yield of 10 kt, along with successive public tests of missile launches with airborne explosions. North Korea claims that the Hwasan-31 can be mounted on eight different types of missiles, including the KN-23, KN-24, KN-25, and Arrow-1 and 2, demonstrating their capability to operate tactical nuclear warheads like loading bullets into a gun.

North Korea is conducting test launches with different strike purposes for each missile type based on theoretical figures to simulate the power of airborne explosions. In essence, North Korea is repeatedly seeking the “most dangerous altitudes” that could cause maximum human and material damage to South Korea.

To date, North Korea has conducted six nuclear tests, with the most recent, the sixth hydrogen bomb test, estimated to have a yield of between 100 and 300 kt. Yang Uk, a senior researcher at the Asan Institute for Policy Studies, explained that the North Korean military would likely choose a time when the wind blows south to prevent nuclear fallout from reaching North Korea.

A nuclear explosion releases a massive amount of energy in a nanosecond, generating a heat storm of approximately 100 million degrees Celsius (180 million degrees Fahrenheit), spreading nuclear fission-generated high-temperature radiation and fallout, and causing significant damage to nearby ground areas. The direct damage radius of the explosion reaches up to 4.26 kilometers (about 2.65 miles).

Moreover, the casualties from a strategic nuclear explosion, which has a much greater yield, are expected to increase significantly.

38 North, a U.S.-based North Korea monitoring website, estimates that if North Korea were to launch a single nuclear missile (with a yield of 250 kt) toward Seoul, the devastating impact would result in 783,197 deaths and 2,778,009 injuries. This potential damage far exceeds the human losses of the Korean War (death toll of 373,599, 229,625 injured, and 387,744 kidnapped or missing) and Japan’s World War II casualties (500,000 to 800,000 deaths).

The outlet estimated that North Korea’s sixth nuclear test in 2017 had a yield estimated between 108 and 250 kt and proceeded to simulate future nuclear weapon yields up to 250 kt. The scenarios calculated were based on warhead yields ranging from 15 to 250 kt across seven scenarios, with Seoul’s population estimated to be 24,105,000. However, the simulations also considered the potential unreliability of the missile system and South Korea’s deployment of the THAAD (Terminal High Altitude Area Defense) system against North Korean nuclear and missile attacks.

Simulations, assuming a 20%, 50%, and 80% chance of North Korean nuclear missiles hitting their target without being intercepted, estimated the damage in Seoul. With a 20% hit rate, casualties would range from 220,000 deaths and 790,000 injuries at a 15-kt yield to 1.22 million deaths and 4.33 million injuries at a 250-kt yield. At a 50% likelihood, the death toll could range from 550,000 (at 15 kt) to 1.75 million (at 250 kt), with injuries between 1.98 million (at 15 kt) and 6.23 million (at 250 kt). In an 80% hit scenario, the estimated casualties could range from 880,000 deaths (at 15 kt) to 2.02 million (at 250 kt), with injuries from 3.17 million (at 15 kt) to 7.19 million (at 250 kt).

A military official commented, “If North Korea’s claims are true, ballistic missiles equipped with nuclear warheads are nearing operational use. However, this could also be an exaggeration by North Korea to instill a sense of threat.”