Unraveling North Korea's Centrifuge Program

Although North Korea's centrifuge project is a certain fact, it raises quite a few questions: What is the scope of this project? Are they developing nuclear weapons based on enriched uranium? And to what extent are the Iranians involved?

Construction work on the Light Water Reactor at Kumho, North Korea (Photo: AP)

The uranium enrichment program of North Korea had emerged at some point in the mid-1990s, in the form of a knowledge exchange transaction between Dr. Abdul Qadeer Khan, known as the "Father of the Pakistani Bomb" and North Korea. Dr. Khan provided the North Koreans with the technology of the Zippe-type gas centrifuges used in the enrichment of uranium, in exchange for the technology of the Nodong ballistic missile, whose Pakistani version is the Ghauri missile. At that time, KRL (Khan Research Laboratories – named after the founder, Dr. Khan) located near the city of Kahuta in Pakistan, operated two centrifuge types on an industrial scale: P1 – a first-generation centrifuge with an aluminum alloy rotor, and P2 – a centrifuge fitted with a maraging steel rotor. The P2 centrifuge is more powerful and rotates faster, thereby increasing the uranium throughput per machine relative to the P1 centrifuge.

According to Indian journalist Shyam Bhatia, who was a close friend of Benazir Bhutto, following Bhutto's election, in the autumn of 1993, for a second term as Prime Minister of Pakistan, she visited Pyongyang in order to meet with Kim Il-Song, the supreme leader of North Korea, to discuss North Korean assistance to Pakistan in the development of ballistic missiles. Following the advice of Dr. Khan, Bhutto carried with her CDs that contained sensitive centrifuge-related data as an incentive for the negotiations with Pyongyang regarding the missile issue. According to Dr. Khan (after 2003, when the clandestine, illicit centrifuge technology trafficking network he had established and through which he sold centrifuge technology to Iran and Libya was revealed), in 1993 and 1994, missile specialists from North Korea came to the laboratories in Pakistan in order to train the Pakistani engineers and technicians in the manufacture of the missile parts. At the same time, the workshops where the North Korean specialists trained the Pakistanis were also the site where centrifuge parts were manufactured and assembled and where centrifuge sub-assemblies and complete centrifuges were assembled and tested. The North Korean specialists were keenly interested in the centrifuge technology, and during the period they spent at KRL as instructors, they also studied the more advanced P2 type centrifuges under the best Pakistani specialists. Indeed, the former President of Pakistan, Pervez Musharraf, confirmed in his memoirs that the North Koreans were regular guests at KRL and that Dr. Khan supplied them with twenty P1 type centrifuges, four P2 type centrifuges, flowmeters and control devices so that they may gain experience in the operation of centrifuges, as well as with computer software for this activity.

The US intelligence community had suspected since the late 1990s that North Korea was developing a uranium enrichment centrifuge program. This issue was first publicized in 2002, after Kang Sok-Ju, North Korea's deputy foreign minister, admitted that the program existed for the first time, in response to the accusations of US government officials who had visited Pyongyang. Admittedly, Kang and other North Korean officials hastened to deny those admissions, but the genie had already jumped out of the bottle. Subsequently, in November 2002, an unclassified CIA report was disseminated to the US Congress, stating that "North Korea was constructing a plant that could produce enough weapons-grade uranium for two or more nuclear weapons when fully operational – which could be as soon as mid-decade."

Incriminating Indications

The first indications received since the late 1990s and during the first decade of the 21st century, upon which the estimates of the US intelligence community had been based, were as follows: the twenty-four centrifuges as well as the instrumentation Dr. Khan had transferred to the North Koreans; the visits by the North Korean engineers to KRL; the attempt to purchase two electrical frequency converters from a Japanese manufacturer in 1999; another attempt, four years later, to purchase three electrical frequency converters; the importation of 150 tons of high-strength aluminum tubes for the centrifuge housings from a Russian trader (North Korea allowed the Americans, in 2008, to inspect them in order to prove that they were not intended for uranium enrichment, but the American scientists found traces of enriched uranium on them); the blocked shipment of 22 tons of high-strength aluminum tubes in April 2003 as well as the unfulfilled orders of other shipments, and the purchasing of instrumentation compatible with uranium feed-and-withdrawal systems for an enrichment plant. Moreover, according to European government officials, North Korea had also purchased ring magnets for use as the upper bearings of the centrifuge rotor; epoxy resins used in the assembly of centrifuge parts, e.g. Araldite, and a range of equipment for operating centrifuges individually or in cascades, such as vacuum pumps, valves, specialized UF6 resistant oils, uranium hexafluoride (the uranium compound which, at a temperature of about 60 degrees Celsius and under low pressure sublimes and turns into gas, which makes it applicable to the process of enriching uranium using the centrifuge method), as well as power supply units or the components thereof. It should be noted that North Korea had also purchased various metal processing machines, including CNC lathes. Of particular interest was the purchase of a flow-forming machine used in the manufacture of thin-walled tubes – an item of critical importance to the manufacture of maraging steel centrifuge rotors. Owing to the fact that these machines have a limited use other than the manufacture of centrifuge rotors, the number of manufacturers producing them, worldwide, is very small. It is reasonable to assume that the North Korean machine had been purchased from the German manufacturer Leifeld, which is known to have sold such machines to other third-world countries.

The aforementioned indicators notwithstanding, a long time passed until it could be ruled unequivocally that North Korea had already begun operating a uranium enrichment centrifuge plant. Only in 2009, after the second nuclear test they had conducted, did Pyongyang announce publicly that they intended to begin enriching uranium soon, following the "satisfactory success achieved in the development of uranium enrichment technologies," which, according to North Korea, were intended for the manufacture of nuclear fuel for the experimental light water reactor (LWR) they were about to erect. Conversely, according to a report in the Washington Post in late 2009, Dr. Khan said that "North Korea may have been enriching uranium on a small scale by 2002, using 'maybe 3,000 or even more' centrifuges, and that Pakistan helped the country with vital machinery, drawings and technical advice for at least six years." According to Albright Brannan, owing to the sanctions imposed on North Korea by the West, "North Korea frequently procures for its uranium enrichment program using various subterfuges, either directly in China or by using China as a transshipment point." Procurement was carried out using smuggling networks. The North Korean company NCG (Nam Chongang Trading Company), whose exploits were exposed by the western intelligence services, played a key role in organizing a wide range of illicit and legitimate procurement activities in connection with ballistic missiles and nuclear technology, in particular for the enrichment program. In order to minimize the visibility of the procurement activities vis-à-vis the western intelligence services, North Korea made the payments for the procurement transactions using secret accounts in overseas banks. One of those banks was a Kuwaiti bank.

In November 2010, a delegation from the Stanford University was invited to visit the Yongbyon Nuclear Scientific Research Center in North Korea. The head of the delegation was Professor Siegfried Hecker, formerly the Head of the Los Alamos National Laboratory, where during World War II the first American atomic bomb had been developed. Professor Hecker had devoted his career to the development of US nuclear weapons. The uranium enrichment plant erected at the Yongbyon center was presented to the American delegation. According to Professor Hecker, he was surprised by what he saw, which was nothing short of amazing: "Instead of seeing a few small cascades of centrifuges, which I believed to exist in North Korea, we saw a modern, clean centrifuge plant of more than a thousand centrifuges all neatly aligned and plumbed below us." Additionally, the control room of the centrifuge plant looked every bit like a modern American control room. According to the chief engineer of the centrifuge plant, 2,000 centrifuges had been installed there in six cascades, all of the parts and components of which had been manufactured domestically in North Korea, but modeled after the centrifuges at the URENCO enrichment plant in Holland, at Almelo and at the Japanese Nuclear Fuels Limited's uranium enrichment plant in Rokkasho-Mura. The control room of the plant, according to Professor Hecker, was "astonishingly modern". Professor Hecker noted that he had gathered from his hosts that the centrifuges at the plant were the more advanced P2 model, intended to enrich uranium to a grade of 3.5% – a low enrichment grade suitable for the manufacture of nuclear fuel for power reactors. The American delegation was also told that construction of the plant had begun in April 2009, and that it was activated just shortly before their visit.

Inside The Tractor Plant

As for tube flow forming machines being available to North Korea, according to reports in the Arms Control Wonk website (Jeffrey Lewis, June 24, 2013; Joshua Pollack, September 23, 2013), in September 2006 North Korean television ran a clip of the late supreme leader of North Korea, Kim Jong-Il, in which he could be seen inspecting a more primitive flow forming machine at the Kusong Machine Tool factory. That machine looked more like an early prototype; it appeared to lack fancy CNC controls. It was difficult to determine whether the machine filmed had been purchased from the Leifeld Company of Germany or from another foreign company, or had been manufactured locally. However, a more modern machine was observed later, during a visit by Kim Jong-Il in December 2009 to the Ye Kangg General Tractor Plant in Jagang Province – a remote area of North Korea. This machine featured a portable CNC panel. In any case, the official name of the plant notwithstanding, it was difficult to assume that it was actually engaged in the manufacture of tractors or their parts. A tractor factory does not have to be built inside an underground tunnel. Additionally, tube flow forming machines have no use whatsoever in a tractor factory. Accordingly, it is very reasonable to assume that the "tractor" factory actually manufactured maraging steel rotors for P2 type centrifuges. Like father like son: the present supreme leader of North Korea, Kim Jong-On, visited a tractor factory in June 2013, and was filmed inspecting a large, state-of-the-art tube flow forming machine that appears to be a part of an assembly-line fabrication process for making thin-walled components. The machine, as could be seen from the footage, was located safely in an underground tunnel. This machine could be the same machine filmed in December 2009, but in 2013 it included a large panel. It should be noted that in another area of the "tractor" factory, a hot piercer milling machine could be seen. This machine takes raw feedstock and produces thick-walled seamless tubes. Thick-walled seamless tubes serve as preforms for the flow forming machines. Notably, Kim Jong-On's visit to the "tractor factory" and to other industrial plants in the area engaged in the manufacture of metal components and machining, were accompanied by massive propaganda in the North Korean media, and were even covered and reported by local television

In August 2015, a significant upgrade of the uranium enrichment plant at the Yongbyon Center was reported, in the form of a second centrifuge hall. The new centrifuge hall appears to be very similar to the centrifuge hall presented to Professor Hecker's delegation in November 2010. Accordingly, it may be assumed that the new hall contains 2,000 centrifuges. The new hall was exposed in early 2015 by satellite images showing melted snow accumulating around the hall. This may lead to the conclusion that a heat source of some kind was in operation inside the hall, hence the possibility that the centrifuge hall may have been active already.

Joshua Pollack stated in his article that the images of the North Korean tube flow forming machine presented in December 2009 and in June 2013 help explain the surprise of the Stanford University delegation headed by Professor Hecker during their visit, in November 2010, to the modern, state-of-the-art centrifuge plant at the Yongbyon Center. Additionally, this may explain how the North Koreans had managed to double the size of their centrifuge plant within such a short time.

Despite Pyongyang's statements to the effect that the North Korean uranium enrichment program was intended for the fueling of electrical power reactors, the Americans are concerned that North Korea had established a parallel uranium enrichment plant where uranium is being enriched to weapons grade. The questions that arise from the concerns of the US intelligence community at the present time are: the number of centrifuges currently installed at the Yongbyon Center and whether that centrifuge plant serves a civilian program for the production of fuel for light water reactors – or a military program; the scope and operation history of the clandestine enrichment plant, if such a plant exists (according to Professor Hecker's estimate, as of September 2016 North Korea has a stock of uranium enriched to military grade that could be sufficient for about 6 nuclear weapons, plus plutonium for about 16 additional weapons); whether there are any hindrances to the effective operation of the centrifuges in North Korea, and whether the North Koreans used enriched uranium cores in their latest nuclear tests. Finally, a very troubling question concerns the nuclear cooperation between Pyongyang and Tehran. 


Lt. Col. (res.) Dr. Rafael Ofek is an expert in the physics and technology of nuclear power. He served in the Israeli intelligence community as a senior researcher and analyst.