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U.S. finds that North test in May was nuclear

June 17,2009
North Koreans participate in the Pyongyang City People’s Rally, held to denounce the U.S.-led United Nations sanctions against North Korea, at the Kim Il Sung Plaza in Pyongyang in this picture released by North Korea’s KCNA news agency on Monday. The sign reads, “Revenge against sanctions. Total confrontation against confrontation!”[REUTERS]

U.S. intelligence concluded yesterday North Korea “probably conducted” a nuclear test that yielded “a few kilotons” on May 25, but South Korean sources said no radioactive gases have so far been detected.

Dennis Blair, the director of national intelligence, announced that the United States intelligence community “assesses that North Korea probably conducted an underground nuclear explosion” in Punggye-ri, North Hamgyong, and added that the explosion yield was “approximately a few kilotons.”

Shortly after North Korea claimed it had conducted its second nuclear test, the Russian Defense Ministry estimated the yield to be in the 10- to 20-kiloton range. South Korean authorities said they detected an earthquake measuring 4.4 on the Richter scale, or an equivalent of 5.2 kilotons.

The atomic bomb dropped on Japan’s Nagasaki during World War II had the force of some 20 kilotons. North Korea’s first nuclear test yielded about 1 kiloton. Blair said analysis of the second nuclear test will continue.

In 2006, the United States needed only a week to confirm the first nuclear test, a contrast to yesterday’s ambiguous announcement.

South Korean sources said radioactive gases normally emitted after a nuclear explosion have not been detected.

Noble gases like xenon and krypton can leak to the surface and then rise into the atmosphere. They can be detected and then analyzed to determine whether a nuclear test was a success and also to identify the type of device used. A South Korean government source said analysis after the 2006 nuclear test showed the plutonium used had been produced after 2002.

The U.S. Air Force twice dispatched a special reconnaissance jet, the WC-135 Constant Phoenix from Kadena Air Base in Okinawa, Japan, to collect air samples. They are still under examination.

Experts noted the granite walls of the underground testing site in Punggye-ri might have blocked gases from leaking to the atmosphere. Lee Chun-keun, analyst with the Science and Technology Policy Institute, suggested that the second test might have taken place on the west end of the tunnel in Punggye-ri, deeper into the ground than the east end, where the first test was conducted.

“When testing within granite walls, you can keep radioactive gases from spreading as long as you block off the entrance of the tunnel,” Lee said. “North Korea does its tests in tunnels that are parallel [to the ground] rather than vertical tunnels. That might also explain why no gases have been detected.”

A military source here said a northwesterly wind can facilitate collection of air samples. He suggested wind direction might have been unfavorable to the U.S. reconnaissance jet.

In addition, North Korea launched six short-range missiles in the few days following the nuclear test in an apparent attempt by Pyongyang to interfere with detection efforts.

Intelligence sources said the missiles can travel up to only 200 kilometers (124.2 miles) enough to force the jet further away from the test site.

The U.S. intelligence report yesterday came as speculation continued that North Korea would soon carry out a third nuclear test. In response to the United Nations Security Council’s resolution imposing arms and financial sanctions against North Korea and calling for inspection of suspect cargo, Pyongyang said it would start a uranium enrichment program to develop another source of nuclear weapons and would weaponize extracted plutonium.

The New York Times reported yesterday that to enforce the resolution, the Obama administration would order the U.S. Navy to hail and request permission to inspect North Korean ships suspected of carrying arms or nuclear technology. The U.S. Navy, however, will not forcefully board North Korean vessels, according to senior U.S. officials, so as not to escalate tensions.


By Yoo Jee-ho, Yeh Young-june [jeeho@joongang.co.kr]



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