Reworked device a few months off, U.S. analysts say

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North Korean scientists will only need a few months at most to correct technical problems connected with the Oct. 9 test of the country's first nuclear device, U.S. analysts estimate.

U.S. government and private analysts are still trying to gauge the effectiveness of the test, which sparked global condemnation and a drive to impose new sanctions on the isolated Northeast Asian state.

"North Korea's nuclear test was a partial success," said David Albright, a former inspector for the International Atomic Energy Agency, the United Nations' nuclear watchdog, and president of the Washington-based Institute for Science and International Security. "They will fix the problem, and maybe try again."

U.S. intelligence officials have confirmed the explosion was a nuclear device, but basic questions about the test remain. Pyongyang reportedly told Chinese officials before the test that it would be a 4-kiloton blast, but the actual measured explosion was estimated at less than 1 kiloton.

The smaller blast suggests a problem with the chain reaction, Mr. Albright said at a forum on the North Korean nuclear program at Johns Hopkins University earlier this week. "It blew apart before [the] optimal time."

The most likely cause of the failure was a component that initiates the chain reaction that produces the explosion, Mr. Albright said.

Frank N. von Hippel, a nuclear physicist and professor of public and international affairs at Princeton University, said a successful nuclear blast requires an intricate sequence of events that must be timed perfectly for complete detonation.

"There are lots of things that could have gone wrong," he said in a phone interview. The timing may have been off, or something else could have started the chain reaction, he said.

Daryl Kimball, executive director of the D.C.-based Arms Control Association, said the test could have developed problems even before the chain reaction started, owing to the poor quality of the plutonium used or faults with the detonators.

"We can't say what was the cause or what the device was expected to do," Mr. Kimball said.

It also is not clear exactly how much the North Koreans expected the device to yield, analysts said.

"We don't know what they meant when they said 4 kilotons. They may have meant 4 to 10 kilotons," Mr. Albright said. By comparison, the nuclear bomb dropped on Nagasaki, Japan, in 1945 was 20 kilotons.

All of the U.S. analysts agreed that it would take the North Koreans only a few months to fix these types of problems.

It is possible that a crude 4-kiloton nuclear device can be carried by North Korea's Nodong missile, Mr. Albright said. Such a missile could easily reach U.S. allies Japan or South Korea and "threaten American assets" in the region.

He estimated that North Korea has enough weapons-grade plutonium to make between four and 13 nuclear weapons.

Mr. Kimball said the North Koreans "learned a lot from the test, even if it did not detonate fully."

"This was a political test. Whether it performed exactly as designed or not, the world now knows North Korea has nuclear weapons," he said.