Third Korean nuclear test – why the big deal?

Hayley Channer and Rod Lyon at the ASPI’s new blog, The Strategist, argue that North Korea may be about to conduct another nuclear test and that such a test would be “a game changer”, prompting a variety of responses from South Korea and Japan, possibly including requests for the USA to deploy tactical nuclear weapons in the region, and increasing pressures on those two countries to build their own indigenous deterrent.

Nobody except a few North Koreans high up in the regime could possibly think another North Korean nuclear test is a good thing. But it’s frankly hard to see it as the “game-changer” Channer and Lyon fear.

North Korea’s first nuclear test was, by all reports, a fizzer. Or, technically, a “fizzle”. Something went wrong, though only the North Koreans, and possibly people in the intelligence communities of the nuclear powers, would have any idea as to what. Their second test had a bigger explosive yield (Channer and Lyon cite a figure of 4.6 kilotons), but it’s not clear whether this was a fully successful test of a small device, or a still only partly successful test of a larger one.

Channer and Lyon argue that demonstrating a bomb that yields something more akin to the 16-20 kiloton yields of the Hiroshima and Nagasaki bombs would:

After a test of that size, it’s going to be harder for critics to claim that North Korea isn’t yet a real nuclear power—something the US has always stressed, even after the first two tests.

I don’t buy this.

For one thing, a 4.6 kiloton weapon delivered to the middle of downtown Seoul or Tokyo would still kill tens of thousands, probably hundreds of thousands of people. It would create a fireball that would incinerate everyone within a 500-metre radius. Out to a radius of 1.1 kilometres, the radiation dose would have a roughly 50% chance of killing you, even with medical treatment (and in those circumstances the odds of getting proper medical treatment aren’t great). A 16 kiloton weapon’s fireball radius would be around 700 metres (so the area of total devastation roughly doubled) and the lethal prompt radiation dose would extend to 1.4 kilometres (so the area receiving the dose is, again, roughly doubled). Yes, the larger weapon does more damage, but in terms of the credibility of the threat it doesn’t matter a lot. In both cases we’re talking about mass casualties on a scale unseen in either country since WWII and the Korean War respectively (and that’s even compared to the recent earthquake and tsunami in Japan).

I don’t have time to go into the details, but I would also note that it is, by all reports, easier to build a Hiroshima-scale weapon than a reliable smaller one, regardless of whether you are building an implosion weapon or a gun-type bomb (the gun design is really very simple). Apparently, if you don’t know exactly what you’re doing and you design conservatively, the extra fissile material you have as a “safety” margin is likely to result in a bigger bang.

So, in a nutshell, a larger-scale test a) doesn’t represent a qualitatively different threat to North Korea’s neighbours, and b) doesn’t necessarily indicate substantial progress in their nuclear weapons program.

For North Korea to go from an existential to a minimum deterrent (as I understand the terms) they need to demonstrate two things – that they can build a delivery vehicle that has a reasonable chance of reaching its target, and that they can build a weapon that fits on the delivery vehicle and functions with a reasonable degree of reliability.

Simply detonating one more device of unknown physical size underground does neither of those things, and it doesn’t seem to me that it would provoke dramatic changes in defence arrangements in north-east Asia whatever flowery rhetoric might follow a test.

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2 Responses to Third Korean nuclear test – why the big deal?

  1. wilful says:

    Robert, quite a lot of diplomatic hoo har is divorced from physical realities (I’m sure there’s a witty aphorism that could be applied). Another example is the threat that Israel will attack Iran’s nuclear program. This completely ignores that fact that it’s a 3000 km round trip and the IAF F-15s simply cannot carry a bombload that far, let alone across Iraqi and Saudi airspace and having to fight through Iranian SAMs . It’s pure fantasy to suggest otherwise. Not that this stops pundits from having a go.

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