The United States said Monday that a scientific analysis of North Korea's May 25 nuclear test shows it to have had only a fraction of the explosive force first estimated. The U.S. intelligence report came as President Barack Obama prepared for talks Tuesday on the North Korean nuclear program and other issues with South Korean President Lee Myung-bak. A brief statement from U.S. Director of National Intelligence Dennis Blair said North Korea probably conducted an underground nuclear test on May 25 that had an explosive yield of a few kilotons, the equivalent of a few thousand tons of TNT.
Although it was a sizable explosion, the test was small by nuclear weapon standards and only a fraction of the 10 to 20 kiloton estimate by Russia's Defense Ministry issued a few days after the event. By contrast, North Korea's first nuclear test, in November 2006, was estimated at just one kiloton and is considered by some experts to have been a partial failure.
Although the statement by the U.S. intelligence chief spoke of a "probable" nuclear test, officials say they do not have serious doubts that the May 25 detonation was nuclear, given the difficulty and cost of simulating a blast of that magnitude with conventional explosives.