Nuclear Notions: North Korea’s Growing Nuclear Arsenal

By David Albright

North Korea closely guards the number of nuclear weapons that it has built or deployed. Complicating matters, it also carefully hides its production of weapon-grade uranium (WGU) and has been evasive about the amount of plutonium it has made, both key nuclear explosive ingredients in its nuclear weapon and combined indicative of the overall number of North Korean nuclear weapons. As a result, estimating the size and characteristics of North Korea’s nuclear arsenal, as well as its future growth is challenging. Today, however, most believe it will likely continue to grow in size and sophistication, even likely growing faster than in the past.

North Korea’s nuclear weapons program reached fruition in the late 1980s. However, its nuclear arsenal grew slowly during the next few decades1. After producing at most one or two nuclear weapons in the late 1980s and early 1990s, the US/DPRK Agreed Framework froze further production for over a decade. With the demise of this agreement in 2003, North Korea was estimated to have built five to 13 plutonium-based weapons as of late 2005, utilizing both plutonium stored during the Agreed Framework period and produced after 20032. There was another pause created by the Six Party talks, but this pause ended in the late 2000s. By this time, North Korea had brought into the equation a uranium enrichment capability to make weapon-grade uranium. Its enrichment capacity has allowed it to produce nuclear weapons at a faster rate. By the end of 2017, North Korea had an estimated 26 to 44 weapons composed of either plutonium or weapon-grade uranium, where the range reflects uncertainties, particularly in uranium enrichment capacity. This type of estimate is now called a traditional method because it does not take into account the varying plutonium or WGU requirements of more sophisticated nuclear weapons3.  

During the last 10 years, in particular, the uncertainties in these estimates have grown dramatically, largely due both to a lack of knowledge about the size and operational experience of North Korea’s uranium enrichment program and to the type of nuclear weapons North Korea has built. The ability of North Korea’s nuclear weaponeers, showed in six underground nuclear tests, means that it has progressed beyond building relatively simple fission weapons with estimated diameters of 50-60 centimeters and estimated explosive yields of less than 15 kilotons, powered by either separated plutonium or weapon-grade uranium. The test in September 2016 achieved an explosive yield in the range of 15 to 25 kilotons, greater than any of the three earlier ones. The last test in 2017 achieved anywhere from 70-280 kilotons, suggesting that North Korea may be building thermonuclear weapons, albeit probably rather crude ones.

North Korean statements have boasted of a wide variety of nuclear weapons and their delivery vehicles—tactical, strategic, miniaturized fission, and thermonuclear weapons, and even a nuclear-armed underwater drone. North Korea has also proclaimed it has an interchangeable tactical nuclear warhead able to be deployed on several different missiles.

With North Korea known to be producing more sophisticated nuclear weapons, a traditional estimate no longer suffices. One way to account for different possibilities is to consider a range of nuclear arsenal types.

After estimating plutonium and WGU stocks through 2023, the composition of North Korea’s nuclear arsenal is posited. Three representative nuclear arsenals have been identified4. They are (1) a traditional estimate assuming that the arsenal is composed of relatively simple fission weapons, ones made only with plutonium and others made only with weapon-grade uranium; (2) one with every nuclear weapon composed of both plutonium and WGU, a “composite” nuclear weapon; and (3) an estimate with a set of single-stage thermonuclear weapons, in addition to simple fission weapons. See table 1 for medians and ranges for each estimate.

Given that each of the three main estimates is a reasonable possibility, based on currently available information, they can be transformed into a single distribution by averaging, where each distribution receives equal weight. The result is a slightly skewed distribution with a median of 50 weapons and a range of 38 to 68 nuclear weapons at the end of 2023.

Table 1. The arsenal types and estimate ranges of North Korea’s nuclear weapons arsenal, as of the end of 2023. 

What does the future hold? North Korea is well situated to increase the rate it can build nuclear weapons. Its current average rate varies, depending on the type of nuclear weapons North Korea is building. However, it can be as small as two nuclear weapons per year and as large as six nuclear weapons a year, or an average of four nuclear weapons per year. 

Its Experimental Light Water Reactor (ELWR) at Yongbyon can significantly boost this annual production rate. After years of delay it started operation late last year, discharging warm water, indicative of achieving criticality according to the IAEA5. Once fully operational—a date still too early to predict, the ELWR could allow a surge in plutonium quantities at an estimated rate of about 20 kilograms of plutonium per year.  Separating the ELWR plutonium would likely require the expansion of separation capabilities, which would likely take place at the Yongbyon Radiochemical Laboratory.  But once the ELWR is fully operational and plutonium separation is underway, this reactor could produce enough plutonium for 5 to 10 nuclear weapons per year. The range reflects a choice that each nuclear weapon has two to four kilograms of plutonium, where the former number would entail a weapon made from both plutonium and WGU. This rate would more than double or triple the current production rate, resulting in a new total rate (rounded) of roughly 10 to 15 nuclear weapons a year. 

North Korea’s leadership is charting a nuclear arms buildup reminiscent of the Cold War days in the 1950s and early 1960s, when the United States and Russia misguidedly explored a myriad of nuclear weapons and delivery methods, recklessly increased production of nuclear explosive materials, and contemplated fighting battlefield nuclear wars. 

About the Author

David Albright is founder and President of the non-profit Institute for Science and International Security in Washington, D.C. He directs the project work of the Institute, heads its fundraising efforts, and chairs its board of directors. In addition, he regularly publishes and conducts scientific research. He has written numerous assessments on secret nuclear weapons programs throughout the world.

Albright has published assessments in numerous technical and policy journals, including the Bulletin of the Atomic Scientists, Science, Scientific American, Science and Global Security, Washington Quarterly, and Arms Control Today. Research reports by Albright have been published by the Environmental Policy Institute in Washington, D.C. and Princeton University’s Center for Energy and Environmental Studies.

Albright has co-authored four books, including the groundbreaking World Inventory of Plutonium and Highly Enriched Uranium,1992, (SIPRI and Oxford University Press) written in collaboration with Frans Berkhout, of Sussex University, and William Walker, of the University of St. Andrews. A second, greatly-expanded edition entitled Plutonium and Highly Enriched Uranium 1996: World Inventories, Capabilities and Policies was published in March 1997. Albright is also a co-editor and contributor to Challenges of Fissile Material Control (Institute Press, 1999) and Solving the North Korean Nuclear Puzzle (Institute Press, 2000), which one leading expert on North Korea called “the definitive unclassified analysis of the North Korean nuclear program.”

During his career, Albright has testified numerous times on nuclear issues before the U.S. Congress. He has spoken to many groups, technical workshops and conferences, briefed government decision- makers, and trained many government officials in non-proliferation policy making. The media frequently cite Albright, and he has appeared often on television and radio. A National Journal profile in 2004 called him a “go-to guy for media people seeking independent analysis on Iraq’s WMD programs.”

Albright cooperated actively with the IAEA Action Team from 1992 until 1997, focusing on analyses of Iraqi documents and past procurement activities. In June 1996, he was the first non-governmental inspector of the Iraqi nuclear program. On this inspection mission, Albright questioned members of Iraq’s former uranium enrichment programs about their statements in Iraq’s draft Full, Final, and Complete Declaration. In the spring of 2003, after the fall of Baghdad, he initiated a successful effort to retrieve the only complete set of classified Iraqi documents, hidden since the 1991 Gulf War, about making gas centrifuges to enrich uranium for nuclear weapons.

From 1990 to 2001, Albright was a member of the Health Advisory Panel appointed by Colorado Governor Roy Romer. The Panel, responsible to the state’s Health Department, oversees a historical assessment of the toxicological and radiological doses received by the population near the Rocky Flats nuclear weapons production site. On this panel, Albright oversaw the development of ‘source’ terms, which describe the type and amount of dangerous materials that left the plant during daily releases, accidents, or large-scale fires.

In 1996, Albright was appointed to the Department of Energy Openness Advisory Panel, which operates under the auspices of the Secretary of Energy Advisory Board. The panel is charged with reviewing the Department’s Openness policy, which was started in 1993, with the aim of lifting the veil of Cold War secrecy that has surrounded many of the DOE’s activities without jeopardizing national security.

Prior to founding the Institute, he worked as a Senior Staff Scientist at the Federation of American Scientists and as a member of the research staff of Princeton University’s Center for Energy and Environmental Studies. In the early 1980s, he taught physics at George Mason University in Virginia. He has served as a consultant or contractor to the Environmental Policy Institute, the Congressional Research Service, the International Task Force on Prevention of Nuclear Terrorism, Los Alamos National Laboratory, and the International Atomic Energy Agency.

He is an American Physical Society (APS) Fellow. He was the 2006 recipient of the APS’s Joseph A. Burton Forum Award. He received a 1992 Olive Branch Award for a series of articles he wrote, along with Mark Hibbs, on the Iraqi nuclear weapons program for the Bulletin of the Atomic Scientists. He was also a Bulletin contributing editor and was a guest editor of special editions of the magazine.

Prior to founding the Institute in 1993, Albright was a Senior Staff Scientist at the Federation of American Scientists and a member of the research staff of Princeton University’s Center for Energy and Environmental Studies. In the early 1980s, he taught physics at George Mason University. Albright received a Masters of Science in physics from Indiana University in 1980, a Masters of Science in mathematics from Wright State University in 1977, and a Bachelor of Science from Wright State University in 1975. In addition to the Outstanding Alumni Award, Albright also received an Honorary Doctorate of Humane Letters from Wright State University in 2007.