How did North Korea's nuclear program begin?
North Korea began its nuclear program using a graphite-moderated reactor and a reprocessing plant in which they separated the plutonium from irradiated natural uranium. It's been said that the design for North Korea's reactor was copied from a design the British used to make plutonium weapons. The British later added the ability to produce electricity from these reactors. North Korea did this, too, although because their reactor is small it generated a relatively small amount of electricity, presumably supplied to a village adjacent to the Yongbyon reactor site.***
Where did the North Koreans get the designs, expertise and equipment needed to build their reactor?
The U.S. and the U.K. made their reactor designs public information as part of the Atoms for Peace conferences. [These conferences were launched following a December 1953 speech by President Dwight D. Eisenhower to promote nuclear energy worldwide. The Atoms for Peace program led to the declassification of hundreds of nuclear studies and reports.] Of course, building a reactor requires an effort to master certain technologies and to make, for example, very pure graphite so it won't absorb neutrons. For that North Korea sent quite a few people to the Soviet Union to be trained. The North Koreans saw nuclear as a path to energy and military independence.
How does North Korea's nuclear weapons arsenal compare with the world's other nuclear powers?
We're talking about enough plutonium to make 10 weapons or less. So not very much—but enough to ruin your day. The U.S. and Russia have thousands while other nuclear countries like the U.K., France, China, India, Pakistan and Israel have weapons numbering in the low hundreds.
Based on what we know about North Korea's nuclear arsenal, what is the extent of the damage it could inflict?
Their arsenal is a deterrent. They have the potential to blow a Hiroshima-sized hole in a city in South Korea or Japan, or several holes maybe. The question of whether they have designed these warheads so they can be carried by the missiles they have is unanswered. But I think nobody would bet against it. They've also been working on missiles that could reach the U.S., although without having a successful test to prove this.
What has been the rest of the world's reaction to North Korea's attempts to build a nuclear arsenal?
In response to Western concerns about the reactor, which had been discovered by surveillance satellites in the 1980s, Russia successfully pressed North Korea to sign the Non-Proliferation Treaty, which it did in 1985. They were then expected to set up a system whereby the IAEA [International Atomic Energy Agency] could inspect North Korean nuclear facilities, although they really didn't want the IAEA to look at evidence of their activities relating to past plutonium production. It got to be a cat-and-mouse game with inspectors.
Concerns over North Korea's nuclear program built up over a period of nine years until 1994, when the U.S. considered bombing the site. That was when Jimmy Carter parachuted—not literally, of course—into Pyongyang and reached an agreement with Kim Jong-il's father, Kim Il-sung, to freeze their atomic program. As part of the Agreed Framework, North Korea said it would freeze operation and construction of nuclear reactors, which were suspected of being part of a covert nuclear weapons program. In exchange they were supposed to get two light-water nuclear power reactors that couldn't be used to make weapons. In the meantime, we were also supposed to send them heavy fuel oil to compensate for the energy they weren't getting from the reactors they had shut down.
The U.S. claims that in October 2002 North Korea admitted to having a uranium-enrichment program that could be used to make nuclear weapons. North Korea denied having said it has such a program, but the damage was done. How did the Agreed Framework fall apart?
We stopped sending the heavy fuel oil. Meanwhile the schedule for completing the new reactors had slipped [from 2003 to 2008]. North Korea kicked out the IAEA inspectors and started reprocessing the irradiated fuel that had been in the reactor when it had shut down. They were able to capture something like 30 kilograms or so of additional plutonium for a few more bombs, perhaps 10 kilograms of which they used for their nuclear tests in 2006 and 2009. Subsequently, North Korea irradiated more uranium in the Yongbyon reactor and produced 20 to 25 kilograms more plutonium.
*** In the mid-1960s Kim Il-sung built the Yongbyon Nuclear Scientific Research Center 90 kilometers north of Pyongyang with help from engineers trained in the Soviet Union. By 1985 U.S. intelligence reports indicated North Korea had built a fully functioning nuclear reactor.