WASHINGTON (AP) -- New satellite imagery offers further signs that North Korea has restarted a nuclear reactor capable of producing plutonium for bombs, a U.S. research institute said Wednesday.
North Korea announced plans in April to restart the reactor at Nyongbyon that was shuttered in 2007 under a disarmament deal. Satellite imagery at the end of August showed steam coming from an adjacent generator building, suggesting North Korea was in the process of starting it up.
The U.S.-Korea Institute at Johns Hopkins School of Advanced International Studies says that a satellite photo from Sept. 19 shows hot water being released through a drainpipe that is part of a cooling system for the five megawatt reactor. That most likely shows that the reactor is now operating and its generators are producing power.
The findings were being published on the institute's website, 38 North, and were based on analysis by Nick Hansen, a retired intelligence expert who closely monitors developments in the North's weapons programs.
North Korea has yet to announce that the reactor is working again. The United States has said that any move to do so would be a "very serious matter" and violate U.N. Security Council resolutions.
The reactor can be used both to generate electricity and produce fissile material for nuclear weapons. Once it is operating, it can produce about 6 kilograms of plutonium a year, enough for one or two bombs. North Korea has conducted three nuclear test explosions since 2006, and experts estimate it already has enough plutonium for between four to eight crude weapons.
According to the 38 North analysis, hot water from the drainpipe reaches the bank of the nearby Kuryong River and produces white foam that is visible in the overhead imagery. Although the water is used to cool the reactor, that doesn't mean it is radioactive.
The United States and South Korea on Wednesday agreed to work together to strengthen the South's ability to deter threats from North Korea. Their defense chiefs also endorsed a new military strategy to better coordinate the response to a nuclear, chemical or other attack from North Korea.
In February, North Korea conducted its third nuclear test, prompting the Security Council to tighten penalties. That angered the North, which threatened nuclear strikes on the U.S. and its allies.
Tensions have since eased, and the North now appears more willing to engage in diplomacy. It wants to hold aid-for-disarmament negotiations without preconditions, but the U.S. says the government of young leader Kim Jong Un should first take concrete steps to show it serious about disarming.
Analysts say restarting the reactor could be part of an attempt by the North to assert itself as a nuclear power and extract concessions in negotiations that have been on hold for five years.
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