During its war of words – at least so far – with the US, the North Korean government said that it was considering a nuclear test in the Pacific Ocean. This would involve firing a ballistic missile over Japan and detonating it somewhere above sea level.
Not only is this incredibly provocative, it’s also insanely risky. If this missile fails above Japan, the consequences would be horrific; if it succeeds in reaching its target, it would be the first above-ground nuclear test since China’s final atmospheric detonation in 1980 – and as a new simulation shows, its radioactive fallout would be spread far and wide.
Lassina Zerbo, the executive secretary of the Comprehensive Nuclear Test Ban Treaty Organization, tweeted what he referred to as a “rough simulation” of the spread of such a radioisotopic cloud over the course of about two weeks. As is clear, the radiation spreads across much of the Northern Hemisphere within just a few days.
Thanks to sustained stratospheric air currents and jet streams, the most prominent nuclear fallout first spreads across the Eastern Pacific Ocean towards Canada and the contiguous United States, before circling around the world and weakening as it drifts over Europe and Russia. Soon, Japan, parts of China, and even Hawaii will see some fallout. Ultimately, two weeks after the detonation, the strongest radiation lingers over much of North America.
This radioactive cloud will contain, among others, decaying strontium, zirconium, rubidium, and caesium. If these radioactive particles mix within the cloud line, it will eventually precipitate out as black rain.
Although many of these can take millennia to fully decay, or longer, fallout from the explosion is the most intense in the first few hours. Generally speaking, nukes follow the “rule of seven”, which states that the intensity of the radiation falls by a factor of 10 seven hours after the blast.
That means that after seven hours, the radiation is 90 percent less intense. According to the simulation, then, this means that the Pacific Ocean will get the worst of it. Taking shelter will not be required.
The amount of fallout is dependent on the type of device detonated, as well as its yield. Although the regime claims they have tested a hydrogen bomb on several occasions, seismic data suggests that they haven’t quite managed it yet.
However, the latest estimates suggest their most recent underground test was an atomic bomb with a yield of 250 kilotons, which is 17 times the one dropped on Hiroshima. If this was detonated in-atmosphere, it would release a considerable amount of radioactive material.
It’s not certain whether North Korea is able to – or currently wants – to conduct an atmospheric nuclear test in this way. Let’s hope it stays that way.