Following international diplomatic pressure, North Korea in 2007 abandoned plutonium production. But it later acknowledged that it had built facilities to produce highly enriched uranium, another fissile material that can be used in bombs.
While plutonium is a by-product of nuclear reactors, experts say it can be difficult to build a bomb using the material because specifications have to be precise. Experts say it would be easy for North Korea to make large, if not almost unlimited, quantities of highly enriched uranium.
‘MAY NOT FIND ANYTHING’
Absent the trace evidence that might have been collected by sniffer planes - and without leaked information from within the North Korean testing program - U.S. and allied officials said it would be very difficult for outsiders to determine whether the latest test involved a plutonium or uranium core.
Other key issues include precisely how powerful the device was, how it was configured and how far the North Koreans have advanced in miniaturizing a device they might eventually deploy on long-range ballistic missiles that have been under development.
Officials and experts familiar with the capabilities of sniffer planes said that over the years the North Koreans have become increasingly effective at burying and sealing their tests sites to conceal even the faintest scientific traces.
“History would teach us that the North Koreans do like to hide their secret activities and control the message,” said David Albright, a private nuclear expert who has visited North Korea and talked with officials about its nuclear program.
A European national security official said the North Koreans were becoming “very effective” at hiding evidence that would offer clues to its nuclear secrets.