The report on 38 North, the website of U.S.-Korea Institute at Johns Hopkins University, says new satellite imagery of the nuclear complex indicated the Communist country is probably restarting its 5 megawatt gas-graphite plutonium production reactor.
North Korea agreed to end its nuclear weapons program and scrap its Yongbyon facility several years ago in return for international aid. However, it has continued with nuclear testing, having conducted its third nuclear test in February that drew heavy U.N. Security Council sanctions. In April, amid heightening tensions with the United States and South Korea, the North, under its new leader Kim Jong Un, announced its intention to restart the reactor.
The U.S.-Korea institute said since that announcement, "work has progressed rapidly over the spring and summer to bring the facility back into operation."
The New York Times reported the satellite photograph showed steam emerging from a newly reconstructed nuclear reactor and if that establishes the restart of the reactor, North Korea may be able to start building plutonium weapons. It would also mean four U.S. presidents have not been able to end its nuclear program.
Talks among the six nations involved in the North's denuclearization remain stalled, although the North has indicated its willingness to return to them. Involved in the negotiations are the two Koreas, the United States, China, Russia and Japan.
The Times said the North Koreans, however, have not clearly spelled out whether they would agree to eventual disarmament.
The United States, along with South Korea and Japan, have said the six-party talks can resume only if North Korea shows readiness to accept the complete and verifiable elimination of its nuclear program.
Analysts told the Times said the latest development about the steam at the plant could also be a ploy by the North to try to force the United States and its allies to return to the talks to secure economic aid. However, they said the North's effort could backfire as U.S. President Barack Obama is reluctant to take steps that would reward North Korea.
David Albright, head of the Washington research group Institute for Science and International Security, told the Times he has also studied the satellite images, which implied the reactor is restarted, but which needs to be confirmed.
"You want to get confirmation because you never know. They can surprise you, but I can't think of any alternative explanations," he said, adding the reactor would need two or three years of operation to make plutonium in its core.
The Times quoted a South Korean intelligence official the government needs more time to determine if the reactor has restarted, but also said both the United States and his country have increased monitoring of Yongbyon.