The anatomy of North Korea’s nuclear test tunnels released for the first time

Posted on : 2013-02-05 15:55 KST Modified on : 2019-10-19 20:29 KST
The Ministry of National Defense diagram believed to show the composure of the test area
The view from Odusan observation post in Paju
The view from Odusan observation post in Paju

By Kim Kyu-won, staff reporter

The structure of the tunnels used for North Korea’s nuclear tests has come to light for the first time. The horizontal tunnels include nine doors and ten corners to absorb the shock of the blast.

On Feb. 4, the Ministry of National Defense released a two-dimensional diagram of what is believed to be the tunnel used in North Korea’s second nuclear test in May 2009. The plan was based on an analysis by South Korean and US nuclear experts of a nuclear testing diagram that appeared in part four of “Naega Bon Nara (The Country I Saw),” a film broadcast on Korean Central Television on Sept. 8, 2010.

Judging from the film’s content and the structure of the tunnel, it is believed to be the site used for the 2009 test. The film’s plotline includes propaganda and justification for that test.

Based on the ministry’s analysis, the entrance to the tunnel is located approximately halfway up Mt. Mantap, a 2,205-meter mountain in the Punggye village of Kilju county, North Hamgyong province. Unlike other countries that have conducted nuclear tests by digging anywhere from several hundred to a thousand meters vertically underground, North Korea developed its tunnels and testing system by digging horizontally in a mountainous region.

A ministry official called this a “unique method” that made use of the country’s mountainous topography. Mt. Mantap is a granite peak, and the tunnel is known to have been built by boring into the granite.

Believed to be two to three meters wide and high and hundreds of meters long, the tunnel roughly forms the shape of a hammer, with the testing installation located where the head would be. To conduct the tests, the nuclear device and equipment to measure radioactivity and seismic waves are placed in the deepest part of the tunnel. This testing site is then linked to a control center outside the tunnel via cables weighing thousands of tons. The hole is then sealed with earth, gravel, sand, plaster, cement, and similar materials, after which the control center detonates the explosive.

The area with the weapon is sealed off by three steel doors. The measuring equipment is also placed inside this area.

The hundreds of meters of tunnel and nine doors or bulkheads are designed to absorb the entire blast. First, the tunnel includes four right-angle turns, one after each of the first four doors. After that is the first containment vessel, designed to absorb the blast wind and debris.

Because the area from the detonation site to the third and fourth doors absorbs the brunt of the blast, the tunnel bends at right angles to reduce the force.

A ministry official said the first door was believed to consist of three layers of steel, but added that nothing was known for certain as to whether the second through ninth divisions were doors or bulkheads.

“The tunnels and doors would be completely wiped out through the third to fourth divisions as the granite melted from the intense heat of the blast,” the official explained.

After the fifth door, the tunnel bends slightly, heading in a generally southward direction. The fifth through ninth doors lie between this area and the western entrance, with two more traps along the way to absorb the blast and debris. The shock wave from the explosion is believed to be absorbed completely along the way.

The ministry official said the most crucial task after a nuclear test is ensuring that no radioactive gases, such as xenon or krypton, leak out afterwards. It is believed that the angled tunnel was used for the second test to successfully prevent leaks after radioactive gases did escape during the first test in 2006, when the tunnel followed a straight-line path.

The ministry official said, “South Korean and US nuclear experts concluded after analyzing the floor plan that it did indeed look like the structure of North Korea’s actual nuclear testing site.”

Former Los Alamos National Laboratory director Siegfried Hecker, who visited North Korea in 2010, was one of the participants in the examination, the ministry said.

 Gyeonggi province
Gyeonggi province


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