More nuclear material remains at the former Soviet nuclear test site in Kazakhstan, but collaboration between the US and Russia has locked down most of it.
While all things in North Korea are cloaked in secrecy, it appears that this new reactor could produce material for nuclear weapons – potentially expanding North Korea's small stockpile.
The last tangible thread of cooperation between Pyongyang and Seoul was cut today, with South Korea announcing it would pull the remaining workers from a sprawling factory complex in the North.
North Korea says it plans 'higher level' test as part of its military deterrent in its confrontation with the United States. South Korea says that's code for multiple nuclear tests.
Once completed, the North Korean reactor would be able to produce enough plutonium for a new bomb every year, according to the US-Korea Institute at Johns Hopkins University.
Following President Obama's State of the Union message, in which he insisted 'North Korea keeps its commitment to abandon nuclear weapons,' South Korea and the US are showing a united front on North Korea.