North Korea: Are alarm bells ringing?
Nuclear experts are trying to reach a balanced view about the revelation that North Korea has built a modern plant for the enrichment of uranium.
They say it does not prove that North Korea will use this for nuclear weapons but add that in theory it could.
The balance of probability at the moment appears to be that the alarm bells should not be too loud.
Another question is how North Korea managed to do this, an issue I will discuss later.
First, the balanced view: this is certainly the approach of the scientist who was shown the new facility, Siegfried Hecker, a former director of the Los Alamos National Laboratory where US nuclear weapons are designed, and now of Stanford University.
He says he was "stunned" by what he saw, but that appears to be because nobody had expected the North Koreans to have got so far so fast, even though it was known they were exploring the enrichment of uranium.
In his report on his visit to the enrichment plant at Yongbyon with two colleagues, he states: "These facilities appear to be designed primarily for civilian nuclear power, not to boost North Korea's military capability."
In an apparent bout of breast-beating, North Korean engineers told him they had failed in the past "to contribute to the national demand for electricity" and that they were simply trying to do so now.
Prof Hecker was also shown a light-water reactor under construction that was meant, he was told, to take the low-enriched uranium from the new plant as fuel.
He further concludes: "I believe that although this peaceful programme can be diverted to military ends, the current revelations do not fundamentally change the security calculus of the United States or its allies at this time."
His reasons are based on the fact that there are two routes to a nuclear bomb - highly-enriched uranium [HEU] and plutonium. North Korea has, he says, "frozen" its programme of producing plutonium from which it could already have made "four to eight primitive nuclear weapons".
It could, he agrees, use the new plant to produce HEU - but it would have problems placing a uranium-based nuclear warhead on its missiles.
He says: "Building more sophisticated bombs that can be mounted on a missile is better done with plutonium."
However, he adds: "The production of large quantities of HEU and additional nuclear tests would allow them to increase the size of their arsenal." And he concedes that there could be a secret plant producing HEU elsewhere.
A white elephant?
A similar nuanced view is taken by Mark Fitzpatrick, the nuclear watcher at the International Institute for Strategic Studies in London.
He too says he was "stunned" by the revelation but says: "I do not want either to be too alarmist or to downplay the significance of this. There are several reasons to take a cautious view.
"One is that North Korea might have given up on its plutonium programme and therefore bomb-making by that method.
"Another is that it might not able to operate these sophisticated centrifuges easily and the third is that it would need to do a lot of work before it could put an HEU bomb on its missiles or produce a thermonuclear device.
"It's also possible that the plant might be used as a bargaining chip to get aid in any future negotiations, and might even be a white elephant produced for prestige purposes in honour of the 100th anniversary of the birth of Great Leader Kim Il-sung in April next year."
Nevertheless, the US military has reacted strongly, arguing that the revelation indicates that the North is interested in developing the uranium route to a bomb.
Admiral Mike Mullen, chairman of the Joint Chiefs of Staff said: "The assumption certainly is that they continue to head in the direction of additional nuclear weapons."
The other issue here is how the North did this and what implications it might have for the proliferation of nuclear weapons technology.
Prof Hecker says: "Even more troubling would be the potential of export of fissile materials or the means of producing them, which now include centrifuge technologies."
The North Koreans told Prof Hecker that they did all the work themselves, but Mr Fitzpatrick says this is unlikely.
"The 2,000 centrifuges appear to be of the P2 design, and North Korea got that design along with samples and a list of black-market suppliers from the AQ Khan network, supported by Pakistan, before 2004. In return Pakistan got North Korean missiles.
"That network has since been closed down but the North has been able to activate the suppliers, perhaps with the help of Chinese middlemen. North Korea has a number of companies active in this.
"North Korea it must be realised has a very strong intellectual base and they can manufacture some parts themselves but not all, I think.
"There are 100 parts to a centrifuge. I assume they have got help from Iran with the frequency converters needed to run the centrifuges at supersonic speed. But remember that the Stuxnet worm was meant to attack those converters and North Korea might also be infected."
The implication of the North Korean success, along with that of Iran, is that countries minded to develop nuclear technology outside the confines of the Nuclear Non-Proliferation Treaty (which the North has left) have found it possible to do so.
Sanctions might have slowed them but have not stopped them.