Yesterday, evidence that North Korea is preparing for a third nuclear test in North Hamkyung Province was released by South Korean intelligence sources, lending weight to the idea that Pyongyang plans a test to follow the launch of a long-range rocket later this week.

Intelligence sources say that recent images taken of the area by the U.S.-owned ‘Quickbird’ commercial imaging satellite show the digging of a third shaft at the nuclear test site near Pungye-ri, part of Kilju County in North Hamkyung Province. They say that a growing pile of earth and sand at the entrance to the shaft has been brought in from elsewhere; in the case of a test, that earth would be used to fill the shaft.

Experts suspect that North Korea wishes to conduct the test because it plans to use an enriched uranium (HEU) device, rather than its limited stocks of plutonium as in the past.

Ham Hyung Pil, a research fellow with the Korea Institute for Defense Analyses, explained to Daily NK, “There is no evidence yet that North Korea has produced HEU,” but added, “If North Korea produced HEU with its centrifuges then there is no reason to use its plutonium for the test now.”

In addition, it is considered likely that North Korea will conduct its next nuclear test with an implosion-type device. The ‘Little Boy’ which was dropped on Hiroshima was a gun-type uranium device, but implosion designs are far more effective, safer and can be much lighter; however, they require higher technical standards to be met and must be tested.

Ham went on, “The implosion method needs only a small amount of uranium and is the most destructive but they are technologically difficult. Ultimately it’s a miniaturization technology; a uranium bomb of this type is the most efficient to mount on an ICBM.”