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12 Feb. 2013: Testing times in North Korea

The considerable uncertainty about the technical characteristics of the most recent test blast will need to be resolved in the coming days and weeks. For now, international attention will be focused on two main technical questions which will shed light on whether the North is poised to improve its rudimentary nuclear weapon capabilities, both in terms of numbers and quality.

1. What was the fissile material used by North Korea for the explosion? 

There has been considerable speculation that North Korea is seeking to build nuclear weapons using highly enriched uranium (HEU) as the fissile material (rather than plutonium, which is believed to have been used in the first two tests). While it is not known whether North Korea has produced HEU for use in nuclear weapons, the country is believed to have an active uranium enrichment programme. By using HEU for nuclear weapons, North Korea could potentially overcome the constraints posed by its limited stock of weapon-grade plutonium. North Korea currently has enough separated plutonium to construct 6–8 nuclear explosive devices. A test using HEU could pave the way for an expanded future arsenal.

It will be unclear for at least some days whether the latest test used uranium or plutonium. Initial indications are that the underground test was relatively shallow and may not have been well contained. If so, this will help the use of airborne sampling techniques outside the country to determine the material used for the test. This will in turn give greater insight into North Korea’s nuclear weapons capabilities.


2. What was the design of the explosive device?

According to the official press statement, the test used a ‘miniaturized and lighter nuclear device with greater explosive force than previously’. This is consistent with the widespread view that North Korea is trying to develop a device that is compact and light enough fit on top of a ballistic missile—something that has long been considered out of the North’s technical reach. 

While it will be technically challenging for outside experts to confirm the design of the device, a successful North Korean test of such of a compact design would bring it one step closer to being able to build a long-range ballistic missile capable of delivering a nuclear weapon. In December 2012, North Korea successfully tested a multi-stage satellite launcher, suggesting that it was gradually mastering the technology needed to develop such a missile. 



Shannon N. Kile is a Senior Researcher in the SIPRI Weapons of Mass Destruction Programme.