By Samuel Burke, CNN
After weeks of bellicose rhetoric, North Korea announced Tuesday that it will restart a nuclear reactor it had shut more than five years ago.
Siegfried Hecker, one of the world's most prominent nuclear scientists, was one of the last Western observers to visit the Yongbyon nuclear complex. He believes that the North Koreans could restart the plant within six months to a year.
“They would have to rebuild the cooling tower, they would also have to prepare the fresh fuel to put in, but in my opinion it could be done in six months to a year’s time,” Hecker told CNN’s Christiane Amanpour in an interview on Tuesday.
Hecker is the former director of United States' Los Alamos National Laboratory.
Amanpour reported from Yongbyon in 2008, which North Korean officials made a big show of shutting down – the cooling tower was blown up in front of television cameras.
She asked Hecker if the North Koreans had deceived the world at that time.
“No, I believe they were actually serious in what they called the ‘disablement’ of those facilities,” Hecker told Amanpour, adding that while they have always kept the contingency to be able to restart it.
“So they went ahead and disabled it and not dismantled it,” he said. “So for the last five years they’ve had it mothballed, but at any of those times they could have actually had the technical capacity to restart it.”
In his best estimate, the North Koreans have perhaps four to eight bombs worth of plutonium, which Hecker based on his visits to the country and discussions with North Korean specialists.
“Right now they cannot build anymore plutonium bombs, because they’ve reprocessed all the plutonium – there’s none in the pipeline. “I think that’s why they said they’d restart the reactor.”
If they did restart it, within that sixth-month-to-year time period that Hecker laid out, he believes the best the North Koreans could do is to build one bomb’s worth of fissile material per year.
“However, it would take them about three years before they’d actually be able to reprocess more. So let’s say in three years time, then they could then potentially build one more bomb’s worth a year. That’s it.”
Because of that Hecker, says he was neither surprised by North Korea’s announcement on Tuesday, nor does he believe that it fundamentally changes the nuclear threat.
Hecker does not believe that there are any other plutonium reactors or reprocessing plants in North Korea; but when it comes to enriched uranium capabilities, which he calls “the second path to the bomb,” he is not sure of the Hermit Kingdom’s capacities.
“In 2010 they showed me a very modern facility, but they said it was dedicated to making reactor fuel. However, I’m quite convinced that they do have a covert uranium enrichment facility somewhere and in most likelihood they’ve made at least some highly enriched uranium for bombs.”
In other words, it is possible that the facility that Hecker saw in 2010 could be changed from making reactor fuel into making highly enriched uranium.
The bombs that North Korea fielded so far are quite primitive, according to Hecker. He said they are not sufficiently militarized to put on a missile and unable to reach the United States.
He said they could reach South Korea, but not using a missile. “In most likelihood they’d have to deliver that in a van, boat or by airplane.”
He believes North Korea would be unlikely to pull it off.
While he emphasized that he is a technical person, not a policy person, he did offer up some advice to the world: He believes North Korea is not going to give up the bomb, so the world should focus on diplomacy to make sure things don’t get worse, which is exactly what North Korea is signaling they might attempt to do with Tuesday’s announcement.
He suggested diplomacy focus on what he calls “The Three No’s:” Make sure North Korea doesn’t build any more bombs; prevent them from surpassing any improved bomb technology that they currently have; and don’t allow them to export any bombs or technology.
You can read more about Hecker's work regarding North Korea at his website.