Blog 38 North, a forum run by university researchers examining North Korea, reports that commercial satellite imagery of North Korea indicates workers may be putting final touches on an experimental light water reactor.
"While the reactor seems designed to produce electricity for the civilian economy, it will have a residual capability to produce plutonium that can be used for nuclear weapons," researchers said.
Previous research by the Johns Hopkins team said the North Koreas may be able to produce weapons-grade plutonium "if they decided to do so." Under this scenario, North Korea may have enough material to produce more than two dozen nuclear weapons by 2016.
North Korea sparked international concern when it conducted an underground nuclear test in February.
Johns Hopkins researchers say that a lot depends on whether North Korea has enough reactor fuel. It's not clear to what extent North Korean engineers have mastered some of the technology involved in nuclear research, they say.
"If the start-up period proceeds smoothly, the (light-water reactor) could become fully operational during the first half of 2014," researchers said.