Global Security Newswire

A new study involving measurements of airborne radioisotopes suggests North Korea could have secretly carried out two underground nuclear detonations in 2010, Nature reported on Friday. The conclusion has been questioned by a number of nonproliferation specialists (see GSN, Feb. 3).

Atmospheric researcher Lars-Erik De Greer examined radioisotope data collected by surveillance stations in Japan, South Korea and Russia. The Swedish Defense Research Agency scientist also analyzed weather data from the same period.

A year of analysis led him to the theory that the North conducted two limited nuclear explosions in April and May 2010 that were each as powerful as the detonation of between 50 and 200 metric tons of TNT. 

The Stalinist state is known to have already conducted two nuclear tests -- one in 2006 that was judged largely to be a failure and another in 2009 and was seen as more successful. Pyongyang in May 2010 proclaimed it had successfully produced a nuclear fusion reaction. At the time, the announcement was widely mocked by international scientists who doubted the isolated and poor country could have achieved such an exceptional feat (see GSN, May 12, 2010).

However, researchers in South Korea had during that period identified a small amount of xenon that could indicate a nuclear operation in the North, Nature reported.

The kinds of isotopes found in the atmosphere and their levels point to efforts by Pyongyang to assess what sorts of substances and technological processes would increase the explosive power of its nuclear bombs, De Geer said. The kind of limited detonations that the radioisotope analysis indicates could have been geared toward producing a tritium-enhanced warhead, he speculated.

His study is to be published in the April/May edition of the Science and Global Security journal.

De Geer's conclusion has faced questions from some nuclear arms specialists. Princeton University physicist Frank von Hippel allowed that De Greer's research offers serious indications that some sort of nuclear fission activities occurred in the North. However, he does not believe the activities are unquestionably related to nuclear detonations or fusion enhancing efforts.

"I hope that other experts will analyze it and see whether they can put forward alternative, simpler explanations," von Hippel said.

Retired geophysicist Ola Dahlman noted that De Geer's theory does not account for the absence of any earth movement that is likely to have occurred following an underground nuclear detonation. The Korean Peninsula is so closely monitored for nuclear tests that the smallest seismic event should be detected, Dahlman said. "It should have been able to see something."

Nonproliferation expert Jeffrey Lewis said De Geer's theory "doesn't feel right to me."

The global nuclear testing surveillance apparatus by itself cannot confirm that the heightened radioisotope levels were the result of a nuclear test and and not the result of another atomic activity, for instance a reactor incident, said Lewis, of the California-based Center for Nonproliferation Studies.

A large number of atomic power plants are active in East Asia, Lewis said. Absent any physical checks of the area and seismic information it is not feasible to confirm from where the isotopes originated, he added. "You need other data'" (see GSN, June 21, 2010).

Though De Geer based his case to some degree on information gathered by the global monitoring system managed by the Preparatory Commission for the Comprehensive Test Ban Treaty Organization, the nonproliferation entity has not formally studied the information, said Lassina Zerbo, who heads the CTBTO data center in Vienna, Austria.

A request from a state party to the CTBT regime would be required for an official study to be conducted; none of the treaty's 182 member states have taken that step, Zerbo said. Additionally, the data collected by South Korean surveillance centers, which De Geer partly based his analysis on, is not delivered to the CTBT organization, he said (Geoff Brumfiel, Nature, Feb. 3).