Second North Korean nuclear reactor appears to be operational, IAEA says

A new reactor in North Korea appears to be operating for the first time, the U.N. nuclear watchdog and independent experts said.

A new reactor at North Korea's Yongbyon nuclear complex appears to be operating for the first time, the U.N. nuclear watchdog and independent experts said on Thursday, which would mean an additional potential source of plutonium for nuclear weapons.

North Korea has for years used spent fuel from a 5-megawatt nuclear reactor at Yongbyon to produce plutonium for its nuclear arsenal but a telltale discharge of warm water from a larger light-water reactor suggests it is coming online, too, the International Atomic Energy Agency said.

"The discharge of warm water is indicative the reactor has reached criticality," IAEA chief Rafael Grossi said in a statement, meaning the nuclear chain reaction in the reactor is self-sustaining.

The IAEA has not had access to North Korea since Pyongyang expelled its inspectors in 2009. The agency now observes the country mainly using satellite imagery. Without access, the IAEA cannot confirm the reactor's operational status, Grossi said.

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The IAEA says it has observed a strong outflow of water from the light-water reactor's cooling system since October, suggesting ongoing commissioning of the reactor. More recent indications are that the water was warm, Grossi said.

"The LWR, like any nuclear reactor, can produce plutonium in its irradiated fuel, which can be separated during reprocessing, so this is a cause for concern," he said, adding that the advancement of North Korea's nuclear program was "deeply regrettable".