Reportage. The complex stands along a river, surrounded by a long wall. All around are camps and villages. By 2016, the regime had accumulated material to produce between 13 and 30 bombs.

We traveled to Yongbyon, the heart of North Korea’s nuclear program

It feels as if time has forgotten Kaechon. This 400,000-strong city is suspended in a temporal limbo still hovering between the dark and gray scenery of a coal mining city of the 1980-90s and a revival toward the new opportunities that are challenging North Korea.

In the wide streets, the cars that crowd cities like Pyongyang, Wonsan or Chongjin have not arrived yet. There are a few refurbished buildings, but An Chul-woo, an agronomist who works at the Kaechon Duck Farm, one of the largest farming companies in the country, says apartment prices are already leavening, a sign that the city will also know shortly the entrepreneurial frenzy that already energizes other North Korean centers.

The sleepy city of Kaechon is the focus of attention by international experts, who follow the events of North Korea for several reasons. There are two prison camps near the city: Camp Number 1 and Criminal Colony Number 14, made famous by the Shin Dong-hyuk’s book, Escape from Camp 14, in which the author describes life inside the camp (for the record, in 2015, Shin Dong-hyuk admitted that some facts illustrated in the book had been dramatized).

In addition, in 2004, the Jan. 8 factory would build the Syrian rock engines that were destroyed in the Ryongchon railway accident on April 22 of that year, and also killed 12 people in Damascus.

But I have other reasons to be at Kaechon: The city is just 24 kilometers from the Yongbyon nuclear research center, the heart and the brain of the entire North Korean atomic program. The road to the area is in good condition and, apparently, lightly guarded.

It takes just over half an hour to reach the site; the nuclear power plant, with its unmistakable black chimney, stands out from afar, just beyond the Taeryong River.

A 500-meter-long and 200-meter-wide wall surrounds the entire complex. All around, there are cultivated fields, villages, children with colorful backpacks, people squatting on the street or pedaling on shabby bicycles. These signs indicate how far away from their everyday life is the international tension this nuclear center is creating in the governments of the main global powers.

Globalization has not yet reached these places, which remain suspended in time and space.

About 100 meters from the controversial 5 MW reactor, stands the white dome of the new 30 MW light water reactor that was begun in 2009. The plant is not operational yet and Pyongyang never completed the construction, probably because of the difficulty in financing the project and procuring materials unavailable to North Korea due to international sanctions.

Not far away, I can see the foundations of the cooling tower destroyed in 2008, as the first sign of Pyongyang’s will to stop its nuclear program and receive the oil and fuel aid promised by the United States.

The suspension lasted a few months and in May 2009, the second nuclear test brought North Korea to the front pages of every international newspaper.

Across the river, the research center extends for another three kilometers on an almost circular peninsula. This is where the Yongbyon brain is located, where the departments considered to be the most critical for the country’s nuclear future stand.

The radiochemistry lab is one of the most controversial places. In its buildings, the 8,000 spent fuel bars generated every two years by the 5 MW reactor, are treated to extract the plutonium-239 needed to manufacture nuclear weapons.

The separation process is identical to the one used in the U.S. plants: The fuel bars, after being cooled in the pools for five months, are dissolved in nitric acid and, through currents in different solvents, uranium and plutonium are separated. The last cargo arrived in July 2016 and in three to six months, the North Korean chemists will complete their work.

In each activity cycle, the radiochemical laboratory would be able to separate between 5.5 and 8 kilograms of plutonium-239, enough to set up two or three composite core bombs (that is, mixed uranium-plutonium).

Not far from the lab, another building houses the uranium enrichment plant, built in the mid-1990s. 2,000 centrifuges were sent from Pakistan and, since 2013, it has doubled its production capacity.

Centrifuges are essential for the production of highly enriched uranium, called WGU (Weapons Grade Uranium, uranium with 90 percent uranium-235 isotope). This WGU uranium is necessary for the construction of composite core bombs, that is, nuclear bombs that use both plutonium and uranium as fission products.

The bombs built with this technology and fuel would be much lighter and easier to carry than the traditional uranium nuclear bomb. And that is the goal that Pyongyang seeks to achieve with its nuclear program: to create a small and light enough bomb to be transported onto a missile.

To date, in fact, the North Korean regime had no chance of launching bombs capable of hitting the U.S. territory. Until Sept. 3, when the sixth nuclear test conducted by Pyongyang revealed to the world that yes, the much-feared thermonuclear bomb, or H-bomb (hydrogen), was ready.

A bomb not based on atomic fission, but atomic fusion. With the same amount of potential release of destructive energy, the amount of material needed in the case of nuclear fusion would be tens of times lower than for a fission reaction.

The blast bomb story begins in Hamhung, a town near the eastern coast of the peninsula, where a department within the Hungnam Chemical Fertilizer Complex would operate the production of lithium-6.

Lithium-6 is a metal that, if irradiated inside the Yongbyon reactor, could produce tritium, an essential isotope for fusion. At Yongyong, a plant was built to separate it, which worried the military commands in China, South Korea, Japan, Russia and the U.S.

For now, the little that is known about the Pyongyang nuclear program is fragmentary. From the available data, Pyongyang would have produced around 33 kg of plutonium by the end of 2016 and 175 to 645 kg of WGU purity uranium (the magnitude of the error is due to uncertainty about the number of centrifuges available).

The material would be enough to produce between 13 and 30 nuclear bombs. Each year, assuming the production cycle were 100 percent of its potential, North Korea would be able to add between three and five nuclear bombs to its arsenal.

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