Plutonium inventories can be estimated with good confidence because reactor details are well known and satellite imagery tells you when it is operating. Outside experts, including international inspectors, have been in North Korea's reactor complex facilities. I have also visited the plutonium facilities and met their technical staff several times. I estimate that North Korea has 20 to 40 kilograms of plutonium, sufficient for 4 to 8 bombs.

Estimates of highly enriched uranium are very uncertain. Centrifuge facilities are virtually impossible to spot from afar and the only access to one of the North's centrifuge facilities was that given to our Stanford University delegation in November 2010 when the North unveiled a shockingly modern centrifuge hall. Highly enriched uranium estimates based on that visit and additional circumstantial evidence from satellite imagery are in the range of 200 to 450 kilograms. The combined plutonium and highly enriched uranium inventories may give the North sufficient bomb fuel for 20 to 25 nuclear devices today and the capacity to produce an additional one every six to seven weeks.

We know even less about their ability to weaponize – that is, to build the bomb. However, the bottom line is that they have conducted five underground nuclear tests and the last two had destructive power equivalent to the bombs that destroyed Hiroshima and Nagasaki. We know little else, but with five nuclear tests over 10 years, I believe that North Korea can build nuclear warheads small enough to mount on their short and some medium-range missiles. They have greatly stepped up their missile-testing program and although many of the recent launches failed, we must assume they can reach all of South Korea and Japan with a nuclear-tipped missile. Reaching the U.S. mainland is still some years away.

How? Although North Korea had an early assist for peaceful nuclear technologies from the Soviet Union and later took advantage of a leaky international export control system to acquire some key materials, they have for the most part built the facilities and bombs themselves. They require no outside help at this point to make their arsenal more menacing. The sophistication of the arsenal is primarily limited by nuclear and long-range missile tests. 

When? The nuclear program has been 50 years in the making. In the first few decades, North Korea was building capability. That effort slowed down and to some extent was reversed as a result of diplomatic initiatives during the Clinton administration. Pyongyang broke out and built the bomb when confronted by the Bush administration and then dramatically stepped up the program and built a menacing nuclear arsenal during the Obama administration.

MEDIA CONTACTS