North Korea on Thursday threatened a "high-level" nuclear test, triggering frenzied speculation among pundits what that may mean.
North Korea's nuclear test back in 2006 involved a bomb of less than 1 kt and was considered a failure, but in the second test in 2009, the bomb was between 2 and 6 kt. One government source here said, "The 'high-level nuclear test' North Korea is talking about could be aimed at measuring the power of a bomb, testing miniaturized lighter warheads, or detonating multiple bombs."
In order for its nuclear arms to be viable, the North needs to build a warhead measuring just 88 cm in diameter and weighing less than a ton. South Korean and U.S. officials had believed the North's nuclear bombs weighed between two to three tons, which is too heavy to mount on a missile.
If North Korea conducts a nuclear test, South Korean and U.S. agencies can measure the seismic waves, sound signatures and radioactive particles to gauge whether it succeeds or not, and to determine whether plutonium or uranium is used. But it is not easy to determine how big it is if it is detonated in an underground test site.
The final step before a nuclear test is to seal off the entrance to the test shaft. "We haven't been able to confirm whether the shaft at the nuclear test site" in Pungye-ri, North Hamgyong Province "has been sealed yet," the government source said.
The source added that sandbags can also be used to seal the shaft. "We believe a nuclear test could take place within days if North Korea really wants to."