The construction site of the Yongbyon nuclear reactor in 2010(DigitalGlobe)
The impoverished nation desperately needs energy, but the reactor could also be run to produce weapons-grade plutonium.
The reclusive regime has based its nuclear weapons programme on plutonium and has tested two nuclear bombs since 2006, triggering repeated international crises.
Pyongyang has also said that it is building a uranium enrichment plant to produce low-enriched fuel for the new reactor.
Scientists believe the accompanying site could be converted to produce highly enriched uranium, giving North Korea a second way to make nuclear weapons.
The Yongbyon nuclear facility in Yongbyon, North Korea in November 2010 (left) and in April 2012 (Geoeye/AP)
The steel-reinforced concrete reactor dome was placed on top of the reactor's containment structure "at some point between June 21 and August 6," Puccioni said.
"The cloud cover from weather patterns that caused extensive flooding in the region during late June and July precluded imagery analysis over the territory at Yongbyon during that time.
"Indeed, the river levels around the reactor building on August 6 were significantly higher than previously observed during any season over the past four years, extending to within 100 metres of the reactor building itself."
AFP
