On Tuesday, North Korea vowed to restart a nuclear reactor capable of making one bomb's worth of plutonium per year in an act of brinksmanship even China called "regretful." But the Yongbyon reactor, a Soviet-era relic that has been idle for six years, is no spring chicken. Is it even operable? How much of a fixer-upper is it? Experts who've studied satellite imagery and visited the Yongbyon site's facilities disagree on the timetable for getting the reactor up and running (some say six months, others say longer than a year). But these are the major factors:
A New Cooling Plant
The Yongbyon reactor was originally shut down in a disarmament-for-aid deal with the United States in 2007, which preceded the complete dismantling of the cooling tower in 2008 (See GIF). It's believed that North Koreans extracted enough plutonium before the reactor was shuttered for six to eight bombs. But to bring the reactor back online, a functioning cooling system is a must, says Mark Fitzpatrick of the International Institute for Strategic Studies. "A new cooling tower or an alternative cooling system would have to be built and a fresh fuel load would have to be prepared by resizing and cladding a stash of fuel rods that were prepared many years ago for a different reactor project," Fitzpatrick writes in a new essay. It's always conceivable that North Korea has been working on fuel rods in secret, but it's unlikely that it built a cooling system without notice (the prying eyes of spy satellites tend to pick up on that sort of thing).
One reason North Korea's announcement is a big deal is that bringing the plant back online now gives the country two sources of fuel for atomic weapons: highly enriched uranium and plutonium. Unfortunately, when it comes to uranium, it won't take long for the country to kickstart its enrichment process, according to Siegfried Hecker, a senior fellow at the Center for International Security and Cooperation who visited the Yongbyon facility in 2010. "The uranium enrichment facilities could be readily converted to produce highly-enriched uranium (HEU) bomb fuel," he wrote at the time. "North Korea could produce up to 2 tonnes of LEU [low-enriched uranium] or, if the cascades are reconfigured, up to 40 kg HEU [highly-enriched uranium."
Before it was shut down, the Yongbyon reactor was a primary source of plutonium bomb fuel for the country. It's unclear why North Korea de-prioritized its plutonium program relative to its uranium program, but it may be because certain types of uranium bombs are easier to construct. In any case, now that it's been shut down for years, you can't just flip the switch back on and start churning out plutonium. As Hecker discovered, no new fuel had been produced since 1994 and the 5 MWe reactor hadn't been restarted since July 2007. "My assessment is that they could resume all plutonium operations within approximately six months and make one bomb's worth of plutonium per year for some time to come," he wrote. Fitzpatrick agrees. "His judgement that six months would be required for re-start is probably still correct."
When you're dealing with secretive, U.N.-defying regimes, there's always an X factor. In this case, no one knows what North Korea might be hiding. One of the key differences between plutonium and uranium is that uranium enrichment facilities are easier to conceal. If North Koreans have been secretly enriching uranium, it would throw off everyone's timetables, as Hecker notes. "The greatest concern is that a facility of equal or greater capacity, configured to produce HEU exists somewhere else," he writes. "Such a facility would be difficult to detect as demonstrated by the fact that this facility was undetected in the middle of the Yongbyon fuel fabrication site." On the other hand, we could also be over-estimating the regime. As Reuters notes, it's not even clear that Yongbyon is connected to the country's "antiquated electricity grid at all." So it could go either way, which is a frustrating conclusion, but that's why they call the DPRK "one of the most isolated and unpredictable states in the world."