A Method of Estimating North Korea’s Potential Thermonuclear Stockpile

Robert Kelley and Vitaly Fedchenko

November 12, 2020

Abstract: There have been many open-source publications estimating the size of the North Korean nuclear weapons arsenal, especially triggered by each of the six nuclear tests conducted between 2006 and 2017. Up to this point these publications relied on an assumption that all Highly Enriched Uraium (HEU) and plutonium stocks in North Korea are allocated to fission-only or boosted single-stage weapons. Such studies normally begin with estimates of stocks of fissile material – in this case, plutonium and HEU – in the North Korean military stockpile, assume how much plutonium or HEU would have to be used in each weapon, and arrive at a number of weapons in an arsenal by dividing the first value by the second one.

In the 14 years that have passed since the first nuclear test in October 2006, estimates of North Korean nuclear arsenal became more complicated. On 3 September 2017, Pyongyang conducted a nuclear test that was accepted by many observers as its first and only test of a thermonuclear explosive device. The methodology outlined above uses the estimates of fissile material mass required for fission weapons but does not account for the material requirements of thermonuclear weapons.

We used the publicly known characteristics of US weapons to develop a new method to calculate fissile material requirements of North Korean thermonuclear weapons. They show that North Korean thermonuclear secondaries are likely to require about three times more highly enriched uranium than a simple fission weapon, and this finding clarifies the possible size and composition of the country’s arsenal.

Bios: Robert Kelley is Distinguished Research Fellow at SIPRI. He is a veteran in the nuclear weapon and disarmament field with over 35 years in the US Department of Energy nuclear weapons complex, most recently at Los Alamos.

Vitaly Fedchenko is a Senior Researcher with the SIPRI European Security Programme, responsible for nuclear security issues and the political, technological and educational dimensions of nuclear arms control and non-proliferation.

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Modelling the Performance of Hypersonic Boost-glide Missiles

Cameron Tracy

Union of Concerned Scientists

October 8, 2020

Abstract: Hypersonic weapons comprise an emerging class of missile technologies—maneuverable vehicles that carry warheads through the atmosphere at more than five times the speed of sound. They have recently garnered a great deal of interest due to their purported advantages over existing missiles, including unmatched speed and the ability to bypass existing early warning systems and defenses. But absent rigorous, independent technical assessment, their precise capabilities remain uncertain and controversial. To elucidate the performance of these weapons, we have developed a computational model of hypersonic missile flight. Simulations show that the fundamental physics of hypersonic flight severely constrain the performance of these missiles. Comparison with existing ballistic missiles reveals that many claims regarding the ostensible advantages of hypersonic weapons lack a clear technical basis.

Bio: Cameron Tracy is the Kendall Global Security Fellow at the Union of Concerned Scientists. His research focuses on fissile material disposal, hypersonic weapons, and the interface between science and nuclear policy. Cameron has previously held fellowships at Harvard University’s Belfer Center for Science and International Affairs and Stanford University’s Center for International Security and Cooperation. He received his PhD in Materials Science and Engineering from the University of Michigan.