As multinational talks aimed at ending North Korea's nuclear ambitions remain stalled, fears are growing that Pyongyang may conduct its first nuclear test.
Recent news reports say that intelligence experts in the United States and Asia are seeing signs that North Korea may soon conduct an underground nuclear test. U.S. spy satellites have reportedly captured images of excavation activity at a suspected test facility in the northeastern part of the country, and even the construction of a reviewing stand, where military leaders and dignitaries might sit while a test is conducted.
But because so little is known about North Korea's activities, experts say determining whether the North will actually conduct its first nuclear weapons test remains, to a large extent, guesswork.
However, scientists have enough information about Pyongyang's nuclear capabilities to at least sketch out what a test might look like - an underground blast using a plutonium device.
Estimates vary, but North Korea is believed to have reprocessed as much as 40 or 50 kilograms of plutonium from spent fuel rods from its Yongbyon reactor. That could be enough fissile material for 10 weapons.
Dan Pinkston, a Korea specialist at Center for Nonproliferation Studies in Monterey, California, says if North Korea tests a device, its scientists would have to calculate carefully the size of the explosion.
"They have a small inventory of fissile material, so they don't want to waste any of the fissile material, he said. "But, if they test a bomb, they want it to work. It would be bad if they were to test a bomb and it failed or they had a low yield."
British nuclear scientist John Large says North Korea might test a device containing a sphere of plutonium about the size of a grapefruit. When surrounding explosives are detonated, the plutonium would set off a nuclear chain reaction, releasing destructive force and radioactive material.
Mr. Large says from North Korea's perspective, the ideal test may be a missile launch, rather than an underground one, because it accomplishes two things.
"Preparing for an underground test gives too much forewarning …. The North Koreans may say: 'Oh no, we don't want to do that, because the American scientists may say it's not very good….' A missile test would prove that the weapon not only worked, but it was matched to a deployment system … that would be a direct demonstration of its nuclear capability," explained Mr. Large.
Other experts say an underground test is more realistic, because too many things could go wrong with a missile test. For instance, the missile could misfire. They say because the Korean peninsula is so densely populated and surrounded by neighbors, Pyongyang would need to hold the test deep underground to contain the nuclear fallout.
Professor Pinkston in Monterey, however, notes it is possible there will be no test. He says the construction activity could be just for show, intended to discredit U.S. intelligence if North Korea does not test.
"You know, then they can say, oh, look, U.S. intelligence is wrong, they don't know what they're talking about. So, other things that U.S. intelligence says or that U.S. policy makers say are also flawed," said Professor Pinkston.
Still, scientists and weapons experts say a test can not be ruled out.
Kim Tae-woo, a senior researcher at the Korea Institute for Defense Analyses in Seoul, says although there is still reason to believe North Korea is bluffing, the threat must be taken seriously. Mr. Kim says North Korea has taken a lot of risks in developing its nuclear capability, suggesting that it genuinely feels threatened and feels it needs a nuclear bomb to protect itself.
For two years, the United States, South Korea, Japan, China and Russia have been trying to persuade Pyongyang to comply with its previous commitments to not develop nuclear weapons. North Korea, however, has withdrawn from nuclear disarmament talks with the other five countries.
Pyongyang says it needs nuclear weapons to deter what it considers a hostile United States. Officials in the Bush administration have said many times, however, that the United States has no intention of attacking or invading North Korea.
Washington and its regional partners say a North Korean nuclear test would deal a severe blow to attempts to resolve the stalemate peacefully and diplomatically.
On Friday, the Japanese foreign minister said it might be necessary to take the issue to the United Nations Security Council, which possibly could impose sanctions on Pyongyang.
North Korea has never tested a nuclear weapon, despite having declared itself a nuclear state. Experts say regional seismograph readings will probably be the only way means of knowing for sure if North Korea proves its nuclear capability.