What we know about North Korea’s nuclear tests

Last week North Korea claimed to have conducted its second nuclear test, but how big an explosion was it?

Some indications can be found by looking at the first nuclear test the North Koreans conducted in October 2006.

The North Koreans told the Chinese in advance to expect a 4-kiloton yield but the first public estimates were way off. Russia’s defense minister Sergey Ivanov claimed that the test was the equivalent of 5–15 kilotons of TNT.

But geologists of the South Korean and French governments, who used better seismic data, rapidly downsized the explosion yield to 0.5–0.8 kilotons. In other words, the explosive device was believed to be a dud and a relative failure compared with other nuclear tests.

This finding was backed up by the office of US Director of National Intelligence who released a statement on 16 October 2006 : “Analysis of air samples collected on October 11, 2006 detected radioactive debris which confirms that North Korea conducted an underground nuclear explosion in the vicinity of P’unggye on October 9, 2006. The explosion yield was less than a kiloton.”

What type of bomb was the first test?

Siegfried Hecker , the former director of Los Alamos National Laboratory, and who had traveled to North Korea to see its nuclear facilities, stated that he thought the underground test was not of a basic implosion device , which is simple to build if you have the nuclear material, but of a more advanced design based on plutonium suitable for delivery on a missile.

The North Koreans are believed to have reprocessed all 8000 fuel rods they removed from International Atomic Energy Agency seals earlier this decade. The rods are estimated to have 25–30 kg of plutonium metal, enough for 3-4 bombs. Since they kicked out the IAEA inspectors, the North Koreans have been creating more plutonium, producing enough for possibly 6 to 12 devices.

Hecker told a Congressional committee that he thought the North Koreans would learn something useful from this first test, despite being unsuccessful.

Estimating the second test

“Earthquakes and nuclear bombs have quite different seismographs,” said David Booth of the British Geological Survey to the Guardian’s James Sturcke . “Earthquakes happen along fault lines and you get compression waves, known as P–waves, and shear waves from the movement. With a bomb it is mostly just compression waves meaning the seismograph is a lot less complicated.” (see left image for the seismic signature of North Korea’s second nuclear test)

Martin Kalinowski says—based on what is now known of the first test, and the 4.7–magnitude underground earthquake that was located in northeastern North Korea, about 40 miles northwest of the city of Kimchaek at North Korean’s testing facility—this second test most likely has a yield of 4 kilotons.

Andreas Persbo at the Verification, Implementation and Compliance blog thinks it’s even smaller, possibly as low as 1.6 kilotons. The Russian conclusions, he says, could be based on not accounting for the shallow water table in the region .

More than 16 seismic stations picked up traces of the explosion, and sent data to the Comprehensive Nuclear-Test-Ban Treaty Organization’s International Data Centre in Vienna, Austria. The latest refinement of the data , released earlier today, has narrowed down the location of the explosion.

In the right-hand image, the estimation of the origin of the 2009 event (red) is much more precise than in 2006 (green). The other two ellipses show the first automatic estimation of the 2009 event (blue) and the second (yellow).

Political Impact

Following the Democratic People’s Republic of Korea’s announcement that it conducted a nuclear test, Peter Shannon, chairman of the Preparatory Commission for the Comprehensive Nuclear–Test–Ban Treaty Organization (CTBTO), called the nuclear test “a clear challenge to the international community’s efforts to advance global nuclear disarmament and non-proliferation.”

The Wall Street Journal reported the United Nations Security Council held an emergency meeting shortly after the test and “voiced their strong opposition to and condemnation of the nuclear test,” said the current council president, Russian ambassador Vitaly Churkin.

Churkin said in a statement that council members “demand that [North Korea] comply fully with its obligations” not to conduct tests, under a Security Council resolution passed after Pyongyang announced its first test blast in October 2006.

But the biggest political fallout occurred hours earlier today when North Korea apparently helped break a 12-year stalemate on the fissile-material cut-off treaty . “After more than a decade of deadlock the Conference of Disarmament today took the historic decision to restart work,” Britain’s ambassador to the arms talks, John Duncan, said in a “tweet ” on Twitter.

The conference , which will go on until next thursday, is the only multilateral forum on disarmament issues. The following days will see discussions on global nuclear disarmament, reinserting the doctrine of not using nuclear weapons on nonnuclear states, and a revision to the Outer Space Treaty , which bans space-based weapons. North Korea’s ambassador Ri Tcheul’s influence on these nuclear issues will be closely watched over the coming week.

Paul Guinnessy