The addition to the centrifuge plant makes the overall length and width of the building approximately 393 feet by 50 feet -- about double the size of the original building, the Institute for Science and International Security said in a release Wednesday.
The ISIS said it construction on the extension appears to have begun sometime in March 2013, shortly before North Korea announced plans to do some "readjusting and restarting all the nuclear facilities in Yongbyon including uranium enrichment plant and 5MW graphite moderated reactor."
North Korea has said that the plant produces low enriched uranium, apparently to fuel an experimental light water reactor under construction at the Yongbyon nuclear complex.
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