The Democratic People’s Republic of Korea (North Korea)’s 3 September nuclear bomb test – its sixth, closely following its inflammatory 28 August test launch of a Hwasong-12 intermediate-range ballistic missile over Japan’s northern island of Hokkaido – raised North Korean bellicosity and menace to a new level. Overall, North Korea’s confrontation with the United States and its regional allies, the Republic of Korea (South Korea) and Japan, has reached crisis proportions. Although there is still insufficient data to validate the ecstatic claim by North Korean state media that the device tested was a ‘perfect hydrogen bomb’, the powerful seismic tremor the test generated – with a magnitude between 6.1 and 6.3 on the Richter scale – indicated that it was almost surely a hydrogen bomb at an early stage of development.
Early press reports ascribing a 100-kiloton yield to the bomb probably underestimated its power. Without knowing the depth of the explosion and the geology of the test site, the yield is difficult to calculate. But reasonable estimates range up to 500 kilotons, with 140kt being the US intelligence community’s approximation and 300kt being the estimate from two different models. The US nuclear arsenal includes some bombs with yields in this range. A 300kt bomb could produce deadly thermal radiation across an area of 126 square kilometres. If dropped in the middle of Tokyo, it would cause hundreds of thousands of instant deaths and third-degree burns for everyone from the Tokyo Dome to Setagaya, some 15km away. The measurable impact of such weapons has produced and continues to inspire humanitarian initiatives to ban nuclear weapons, and illuminates the danger and cynicism of Pyongyang’s attempts to use active threats to use such weapons for achieving strategic objectives.