A cooling tower in North Korea being demolished as a sign of commitment to a nuclear deal, Pyongyang, North Korea, June 27, 2008.
Kyodo / Reuters

On November 12, during my most recent visit to the Yongbyon nuclear complex, North Korean scientists showed me and my colleagues, John W. Lewis and Robert Carlin, a small, recently completed, industrial-scale uranium-enrichment facility and an experimental light-water reactor (LWR) under construction. 

I was stunned by the sight of 2,000 centrifuges in two cascade halls and an ultramodern control room. But it was not until the long drive back to Pyongyang that the political implications of these findings hit home. It will be more important than ever to limit Pyongyang's nuclear progress and calm tensions on the Korean peninsula. This is particularly true in light of the clash in the Yellow Sea between the two Koreas late last month.

Although I and other nonproliferation experts had long believed that North Korea possessed a parallel uranium-enrichment program -- and there was ample evidence for such a belief -- I was amazed by its scale and sophistication. Instead of finding a few dozen first-generation centrifuges, we saw rows of advanced centrifuges, apparently fully operational. Our hosts told us that construction of the centrifuge facility began in April 2009 and was completed a few days before our arrival. That is not credible, however, given the requirements

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  • SIEGFRIED S. HECKER is Co-Director of the Center for International Security and Cooperation at Stanford University. He was director of the Los Alamos National Laboratory from 1986 to 1997.
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