North could have 60 nuclear warheads

North Korea is capable of building as many as 60 nuclear warheads, according to South Korean and U.S. intelligence authorities, based on an assessment that it has been secretly producing more highly enriched uranium than previously estimated.

According to a secret report by intelligence and military authorities exclusively acquired by the JoongAng Ilbo on Wednesday, Pyongyang has 758 kilograms (0.83 tons) of highly enriched uranium and 54 kilograms of plutonium, based on 2016 figures.

Military experts in Seoul and Washington estimate that between four to six kilograms of plutonium and 16 to 20 kilograms of highly enriched uranium are needed to make one nuclear warhead.

Taking into consideration the government’s analysis of the plutonium and weapons-grade uranium that North Korea is stockpiling, the regime should be able to build between 46 to 60 nuclear warheads.

The atomic bomb dropped on Nagasaki in August 1945 during World War II required around six kilograms of plutonium.

It is the first time that such specific intelligence on Pyongyang’s highly enriched uranium reserves has been revealed.

The figure is much higher than average estimates by defense experts that North Korea possessed around 300 to 400 kilograms of highly enriched uranium and 40 to 50 kilograms of plutonium.

Seoul and Washington through intelligence-sharing last year calculated how much nuclear material North Korea has using various data including U.S. information on a new North Korean uranium enrichment facility, as well its expanded existing facility in Yongbyon in North Pyongan Province.

“South Korea and the United States have been continuously tracking the trend of North Korea’s facilities that produce nuclear materials,” a South Korean intelligence official said. “And they concluded that the amount of nuclear materials possessed by North Korea far exceeds the amount estimated by experts.”

North Korea is known to have been reprocessing plutonium at its 5-megawatt reactor and producing highly enriched uranium at its uranium centrifuge facility at the Yongbyon nuclear complex.

But government officials deduced that Pyongyang is likely to be operating another secret facility to produce highly enriched uranium, taking into consideration the sharp increase in its stockpile of nuclear materials.

This second uranium enrichment facility is believed to be located near Panghyon air base in Kusong, a city also in North Pyongan Province.

A large-scale facility is needed in order for plutonium production, but centrifuges producing highly enriched uranium only requires around 600 square meters, so Seoul’s intelligence officials believe Pyongyang is concealing more uranium enrichment facilities.

In 2010, nuclear expert Siegfried S. Hecker, a professor of management science and engineering at Stanford University, visited the Yongbyon nuclear complex and its uranium enrichment facility with 2,000 centrifuges. He estimated that the site could have produced 40 kilograms of highly enriched uranium.

Seoul and Washington concluded in following years that Pyongyang expanded the facility by a factor of two between 2013 and 2014 and that the Yongbyon complex alone produced around 80 kilograms of highly enriched uranium yearly since 2014.

Military experts have estimated that North Korea produced some 300 to 400 kilograms of weapons-grade uranium since 2005. However, the Yongbyon facility alone would not be enough to produce 758 kilograms of highly enriched uranium, hence the possibility of a second or even third uranium enrichment facility, according to experts.

“A second facility [for uranium enrichment] definitely exists, and we are sharing the information with the United States,” an intelligence official told the newspaper.

North Korea’s uranium ore deposits are estimated to be 26 million tons.

“Highly enriched uranium can be mass produced for relatively little cost, and 1,000 centrifuges can be operated in a relatively small amount of space of around 600 square meters, so it is easy to conceal,” said Lee Chun-geun, a research fellow with the Science and Technology Policy Institute.

The South’s Ministry of National Defense last month claimed in its 2016 defense white paper that North Korea’s stockpile of plutonium was around 50 kilograms, an increase of 10 kilograms from 2014.

It estimated that Pyongyang has enough plutonium to manufacture 10 such nuclear bombs.

But this biennial white paper released on Jan. 11 only said that North Korea possessed “a considerable level” of highly enriched uranium without specifying a number.

North Korea conducted a fourth nuclear test on Jan. 6, 2016 and fifth on Sept. 9.

The South Korean government Thursday said it was not able to confirm the details of the intelligence report on North Korea’s nuclear materials.

“We are concerned about North Korea’s increasing nuclear capabilities and observing the situation closely,” an official of the Ministry of Unification said. “South Korea and the United States routinely evaluate [North Korea’s nuclear capabilities] and closely share information. We cannot speak on this information in detail.”

Moon Sang-kyun, a Defense Ministry spokesman, said in a briefing the same day, “The content is related to security matters, so we cannot confirm the details.”

BY JEONG YONG-SOO, LEE CHUL-JAE AND SARAH KIM [kim.sarah@joongang.co.kr]