SIEGFRIED HECKER, a professor who used to run America’s nuclear laboratory at Los Alamos, recalls the most recent of the seven trips he has made to North Korea, in 2010. His hosts were showing off their sprawling Yongbyon atomic-energy complex. With a blend of shyness and defiance, they displayed an astonishing spectacle: a hall with 2,000 brand-new centrifuges, machines that enrich uranium, either for electricity or nuclear bombs.

Apparently assembled in another, unsuspected site, they had appeared in Yongbyon since Mr Hecker’s previous trip in 2008. This implied that, besides its existing plutonium-based technology, the country could make nuclear bombs from uranium. He was also shown the beginnings of a light-water reactor that could produce more plutonium. The message: “We have more nuclear capacity than you think, and you’ll never know how much…”

North Korea’s arsenal has since grown. Estimates range from 20 to 60 warheads, and its latest test was apparently of a…Continue reading
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