North Korea has continued to advance its nuclear weapons program, demonstrating significant progress and resilience despite international sanctions and diplomatic efforts aimed at curbing its development. Since 2006, North Korea has announced and carried out six nuclear weapon tests. These tests occurred in 2006, 2009, 2013, 2016, and 2017, with yields ranging from less than 1 kiloton in 2006 to as much as 250 kilotons in 2017. In addition, North Korea declared that it was closing and dismantling the Punggye-ri test site, a significant move that drew international attention.
The nuclear explosive devices designed and tested by North Korea have been the subject of extensive analysis and scrutiny. The devices’ design, yield, and the materials used are crucial to understanding the capabilities and intentions of North Korea’s nuclear program. The modeling and measurement of North Korea’s nuclear warhead design have provided valuable insights into the country’s nuclear capabilities.
In a presentation at Princeton University’s Program on Science and Global Security’s Brown Bag Seminar on October 23, 2019, Senior Research Associate and Nonproliferation Review Editor Joshua H. Pollack discussed three distinct streams of evidence regarding North Korea’s nuclear-weapon program: seismic and other observational data, insider accounts, and official North Korean statements. By comparing these streams, a largely consistent picture emerges, suggesting that North Korea likely has four designs: three implosion devices and one two-stage device.
The Program on Science and Global Security (SGS), based in the Woodrow Wilson School of Public and International Affairs, conducts scientific, technical, and policy research to advance national and international policies for a safer and more peaceful world. SGS has a long history of working on nuclear arms control, nonproliferation, and disarmament to reduce the dangers from nuclear weapons and nuclear power. In recent years, SGS has also focused on biosecurity issues and the challenges posed by disruptive technologies such as new biotechnologies, information and communications technologies, autonomous weapons, artificial intelligence, and space-based systems.
Joshua Pollack, who joined the Middlebury Institute of International Studies (MIIS) in April 2016, has an extensive background in issues related to weapons of mass destruction, including proliferation, arms control, and deterrence. Before joining MIIS, Pollack served as a consultant to the US government and worked as a defense policy analyst at DFI International, Science Applications International Corporation, and Constellation West. His clients included the Defense Threat Reduction Agency, the Office of the Under Secretary of Defense for Policy, the Department of Homeland Security, the National Nuclear Security Administration, and the Plans and Policy Directorate (J5) of U.S. Strategic Command. In 2015, he was named an Associate Fellow of the Royal United Services Institute and has been a frequent commentator in major media outlets.
The six nuclear tests conducted by North Korea provide a timeline of the country’s nuclear development. The first test in 2006 had an estimated yield of less than 1 kiloton, indicating a relatively rudimentary device. The second test in 2009 showed an increased yield of approximately 2 to 6 kilotons, suggesting improvements in design and efficiency. The 2013 test further increased the yield to about 6 to 16 kilotons, demonstrating continued progress. The tests in 2016 and 2017 were particularly significant, with yields estimated at 20 to 30 kilotons and up to 250 kilotons, respectively. The 2017 test, in particular, marked a significant milestone, as it was believed to be a hydrogen bomb, a much more powerful two-stage thermonuclear device.
The Punggye-ri test site, located in the mountainous region of North Hamgyong Province, was the site for all six of North Korea’s nuclear tests. The site’s closure and dismantling in 2018 were viewed as a positive step towards denuclearization. However, the extent to which the site was rendered unusable remains unclear, and some analysts suggest that North Korea could still resume testing at other locations if it chooses to do so.
The design and development of North Korea’s nuclear warheads have been informed by various sources of evidence. Seismic data from the nuclear tests provide information about the yield and characteristics of the explosions. Insider accounts, though difficult to verify, offer insights into the internal workings of North Korea’s nuclear program. Official statements and media releases from North Korea also provide clues about the country’s nuclear capabilities and intentions.
The three implosion devices reportedly developed by North Korea include a single-stage fission device with a yield of around 10 to 20 kilotons, similar to the bombs dropped on Hiroshima and Nagasaki. The two-stage thermonuclear device, or hydrogen bomb, represents a significant advancement, with a yield potentially exceeding 250 kilotons. This design involves a primary fission explosion that triggers a secondary fusion reaction, resulting in a much more powerful explosion.
North Korea’s choice of fissile material and its boosting capabilities are still unknown. Fissile material, such as highly enriched uranium or plutonium, is essential for sustaining a nuclear chain reaction. Boosting involves injecting a small amount of fusion fuel, such as deuterium and tritium, into the core of a fission bomb to increase its yield. If North Korea has developed boosted fission weapons, it could significantly enhance the destructive power of its arsenal.
The international community continues to monitor North Korea’s nuclear program closely. Diplomatic efforts, such as the summits between North Korean leader Kim Jong-un and US President Donald Trump in 2018 and 2019, have sought to address the issue through dialogue and negotiation. However, these efforts have yielded limited results, and North Korea’s commitment to denuclearization remains uncertain.
As of July 15, 2024, the Federation of American Scientists (FAS) released the latest edition of the Nuclear Notebook, published in the Bulletin of the Atomic Scientists. The authors, Hans Kristensen, Matt Korda, Eliana Johns, and Mackenzie Knight, estimate that North Korea may have produced enough fissile material to build up to 90 nuclear warheads. However, the country has likely assembled fewer than that, potentially around 50. This estimation follows the trendline researchers have been tracking over the years, with no significant change from previous estimates in 2021 and 2022.
North Korea’s nuclear policy has undergone notable shifts, particularly with the abandonment of its no-first-use policy. This change aligns with the country’s recent efforts to develop tactical nuclear weapons, indicating a more aggressive nuclear posture. The development of tactical nuclear weapons suggests that North Korea is looking to enhance its flexibility and options for nuclear use, which could lower the threshold for nuclear conflict.
Warhead Preparation and Delivery
North Korea has developed a highly diverse missile force across all major range categories. This includes short-range tactical missiles, sea-based missiles, and new launch platforms such as silo-based and underwater platforms. The advancements in solid-fuel missile technology are particularly significant as they improve the survivability and mobility of North Korea’s missile force. Solid-fuel missiles can be launched more quickly than liquid-fuel missiles, which require longer preparation times and are more vulnerable to pre-emptive strikes.
Since 2006, North Korea has detonated six nuclear devices, updated its nuclear doctrine to reflect the irreversible role of nuclear weapons for its national security, and continued to introduce a variety of new missiles test-flown from new launch platforms. Hans Kristensen, director of FAS’s Nuclear Information Project, notes that the size and composition of North Korea’s nuclear stockpile depend on warhead design and the number and types of launchers that can deliver them.
Disco Balls, Peanuts, and Olives
North Korea’s nuclear warhead designs have been informally referred to as the disco ball, peanut, and olive, based on their appearance in North Korean state media. These nicknames describe the visual characteristics of the supposed warhead designs. The “disco ball” is a single-stage implosion device, the “peanut” is a two-stage thermonuclear warhead, and the “olive” is a new miniaturized warhead called the Hwasan-31. The Hwasan-31, first showcased in 2023, demonstrates North Korea’s progress towards developing and fielding short-range, or tactical, nuclear weapons.
While North Korea’s warhead design and stockpile makeup are not verifiable, it is possible that most weapons are single-stage fission weapons with yields between 10 and 20 kilotons of TNT equivalent, similar to those demonstrated in the 2013 and 2016 tests. A smaller number of warheads could be composite-core single-stage warheads with a higher yield.
The development of the Hwasan-31 and other tactical nuclear weapons indicates North Korea’s intent to strengthen its regional deterrence posture. Tactical nuclear weapons provide options for nuclear use below the strategic level, which can complicate the security calculus for neighboring countries and the United States. The pursuit of these weapons suggests that North Korea is preparing for potential conflict scenarios where limited nuclear use could be considered.
North Korea’s missile force includes a range of delivery systems capable of carrying nuclear warheads. This includes short-range ballistic missiles (SRBMs), medium-range ballistic missiles (MRBMs), intermediate-range ballistic missiles (IRBMs), and intercontinental ballistic missiles (ICBMs). The diversity of North Korea’s missile force enhances its ability to threaten targets at various distances, from regional adversaries like South Korea and Japan to the continental United States.
The development of sea-based missile platforms, such as submarine-launched ballistic missiles (SLBMs), adds another layer of complexity to North Korea’s nuclear strategy. SLBMs can be launched from submarines, making them more difficult to detect and pre-empt. This capability enhances the survivability of North Korea’s nuclear forces and strengthens its second-strike capability.
North Korea has also invested in mobile missile launchers, which can be moved to different locations to evade detection and increase the survivability of its missile forces. Mobile launchers can launch missiles from various locations, making it more challenging for adversaries to target and destroy them before they are launched.
The advancements in solid-fuel missile technology are a critical component of North Korea’s missile development program. Solid-fuel missiles have several advantages over liquid-fuel missiles, including shorter launch preparation times, greater mobility, and enhanced survivability. These characteristics make solid-fuel missiles a more credible and responsive component of North Korea’s missile force.
North Korea’s nuclear and missile programs have been the subject of numerous international sanctions and diplomatic efforts aimed at curbing their development. Despite these efforts, North Korea has continued to advance its capabilities, demonstrating a high level of technical expertise and determination.
The international community remains deeply concerned about North Korea’s nuclear and missile programs. The potential for miscalculation or escalation in the region poses significant risks to global security. Diplomatic efforts to address North Korea’s nuclear ambitions have been met with varying degrees of success, but the path to denuclearization remains fraught with challenges.
In conclusion, North Korea’s ongoing modernization and expansion of its nuclear weapons arsenal highlight the persistent and evolving threat posed by the country’s nuclear and missile programs. The development of new warhead designs, advancements in missile technology, and shifts in nuclear doctrine all underscore the complexity and urgency of addressing this issue. The international community must continue to work towards a peaceful resolution while remaining vigilant against the potential threats posed by North Korea’s growing nuclear capabilities.
