SEOUL, South Korea (AP) - Abnormal radiation was detected near the inter-Korean border days after North Korea claimed last month to have achieved a nuclear technology breakthrough, South Korea's Science Ministry said Monday.
The ministry said it failed to find the cause of the radiation but ruled out a possible underground nuclear test by North Korea. It cited no evidence of a strong earthquake that must follow an atomic explosion.
On May 12, North Korea claimed its scientists succeeded in creating a nuclear fusion reaction - a technology necessary to manufacture a hydrogen bomb. The technology also one day could provide limitless clean energy because it produces little radioactive waste, unlike fission, which powers conventional nuclear power reactors.
South Korean experts doubted the North actually made such a breakthrough. Scientists around the world have been experimenting with fusion for decades, but it has yet to be developed into a viable energy alternative.
On May 15, however, the atmospheric concentration of xenon - an inert gas released after a nuclear explosion or radioactive leakage from a nuclear power plant - on the South Korean side of the inter-Korean border was found to be eight times higher than normal, according to South Korea's Science Ministry.
South Korea subsequently looked for signs of a powerful, artificially induced earthquake - something that should have been detected if North Korea had conducted a nuclear test. Experts, however, found no signs of a such a quake in North Korea, a ministry statement said.
"We determined that there was no possibility of an underground nuclear test," it said. The ministry did not mention any possible health hazard from the release.
Earlier Monday, South Korea's mass-circulation Chosun Ilbo newspaper reported that North Korea may have conducted a small-sized nuclear test, citing the abnormal radioactivity. The paper cited an atomic expert it did not identify.
North Korea - which is believed to have enough weaponized plutonium for at least a half-dozen nuclear weapons, conducted two underground nuclear tests in 2006 and 2009, drawing international condemnation and U.N. sanctions.
The news of the detected radiation comes as tension is running high on the Korean peninsula over the deadly sinking of a South Korean warship blamed on a North Korean torpedo attack. North Korea flatly denies the allegation and has warned any punishment would trigger war, with the U.N. Security Council reviewing Seoul's request to punish Pyongyang over the sinking.
A Science Ministry official said the wind was blowing from north to south when the xenon was detected.
But the official - speaking on condition of anonymity, citing department policy - said xenon could have come from Russia or China, not necessarily from North Korea, as South Korea was unable to find the reason for the high-level of the gas.
The official also said that there was no possibility that the xenon could have originated from any nuclear power plants in South Korea.