The North Korean Nuclear Program in Transition

The recent moratorium on missile and nuclear tests and uranium enrichment agreed between the US and the DPRK on February 29, 2012 failed its first test when North Korea launched, albeit unsuccessfully, a satellite on April 13. This article provides a snapshot of North Korea’s enrichment program and the various steps that the DPRK could take vis-à-vis its nuclear program, should it seek yet another occasion to ratchet up pressure on its interlocutors.


When North Korean leadership transitioned late last year from Kim Jong Il to his son Kim Jong Un, Pyongyang experienced change in more ways than one. Kim Jong Il presided over a nuclear program that produced two plutonium bomb detonations and, towards the end of his reign, ramped up its uranium enrichment program. Today, Kim Jong Un helms a nuclear program that has transitioned from graphite moderated reactors and plutonium to light water reactors (LWR) and uranium enrichment.

The moratorium announced by the DPRK on February 29, 2012 on missile tests, nuclear tests, and operations at the uranium enrichment plant at Yongbyon, in return for nutritional aid from the United States, provided the signal as well as the lever with which to reengage the diplomatic process. The hoped for quid pro quo was that North Korea would curb additional progress in its nuclear weapon program.

The Agreed Framework by and large brought the North Korean plutonium program to a halt from 1994 until 2002, when its implementation collapsed. While the 2007 agreement reached in the Six Party Talks initiated the dismantlement of its plutonium program, North Korea was, at the same time, working on a parallel secret indigenous light water reactor (LWR) program centered around an experimental 100 MWth reactor[1] and a Uranium Enrichment Workshop (UEW) that was built in 2009.[2] North Korea has long sought LWRs. It first tried to acquire them from the Soviet Union and then later used their acquisition as part of the bargain with the United States under the Agreed Framework.[3] However, since this type of reactor fuel requires low enriched uranium (LEU),[4] it opened another door to a weapons option since the centrifuge facilities needed to produce that fuel can also be reconfigured in a short period of time to produce weapons-grade highly enriched uranium (HEU).[5] Therefore, by choosing the uranium route, Pyongyang has found itself an excusable recourse to a viable dual-track option—LEU for producing nuclear electricity with LWRs and HEU as a second route to the bomb to augment its small plutonium inventory.

What We Know about North Korea’s Light Water Reactor Project

Satellite imagery analysis has revealed that North Korea has made important progress in its LWR construction at Yongbyon over the past year.[6] Nevertheless, the reactor will probably not be ready for commissioning for another two to three years. As of November 2011, the North seemed able to complete external construction in six to twelve months. In order to do so, heavy equipment remains to be brought in and installed in the reactor building. That will require manufacturing key nuclear components, and delivering them to the site.

Barring any hiccups in this process or any unexpected acceleration, it will most likely take an additional five to ten years before new plutonium production from a LWR could materialize. The parameters setting the timeline for the production of additional plutonium are calculated when the reactor is completed, fuel irradiated and then cooled. In the meantime, North Korea’s reprocessing plant at Yongbyon could be modified[7] for plutonium separation from the LWR fuel without major difficulties. Current stocks are estimated to be 24 to 42 kilograms plutonium.[8] This amount would be sufficient for four to six nuclear weapons. Once the 100 MWth LWR is operational, it could produce up to 12 kilograms of plutonium annually. This would mean producing sufficient fissile material for a little more than one bomb per year.

What We Know About North Korea’s Enrichment Program

There is some evidence that North Korea began research and development in uranium enrichment in the late 1980s, including acquisition of vacuum equipment from European companies. While such equipment was primarily meant for North Korea’s fuel fabrication plant then under construction, some of the vacuum pumps and valves had specifications that could have been useful for uranium enrichment experiments. These procurement efforts were coordinated through the DPRK’s Embassies in (East) Berlin and in Vienna. North Korean companies involved were Lyongaksan, and Daeson 6th Trading Corporation. The leadership and engineers of the Chongchongang Chemical Plant, whose location is not known, were also involved.  Mr. Yun Ho Jin, a North Korean diplomat based in Vienna during that period, was a key figure in organizing meetings with European vendors. He is also known to have been involved in later proliferation cases.[9]

After this initial phase, Pyongyang received another boost in its enrichment efforts from Pakistan in the mid-1990s, when deliveries of P-1 and P-2 centrifuges, special oils, and other equipment flowed from Pakistan to North Korea. Former Pakistani President General P. Musharraf acknowledged this in his memoirs, In the Line of Fire. President Musharraf wrote that, separately, North Korean engineers were provided training at A.Q. Khan’s Research Laboratories in Kahuta under the auspices of a government-to-government deal on missile technology. There has been speculation that Pyongyang also received the blueprints for centrifuges and other related process equipment from the A.Q. Khan network during that time period.

Figure 1: Approximate 3D Visualization of the Uranium Enrichment Facility at Yongbyon (Click arrows to navigate slides. Click on the “More” in the menu bar to display the feature in full screen mode.)

*Visualization done by Tamara Patton, Graduate Research Assistant at the James Martin Center for Nonproliferation Studies.[10]

New attempts by the North Koreans to purchase vacuum technology in 2002 strongly pointed to the acquisition of additional equipment destined for uranium enrichment purposes. Information on North Korea’s procurement activities in the late 1990s to the early 2000s showed its objective was to achieve a semi-industrial[11] scale enrichment capacity, based on the Pakistani P-2 centrifuge design. In 1997, the North attempted to acquire large amounts of maraging steel suitable for manufacturing centrifuge rotors. In 2002/2003, Pyongyang successfully procured large quantities of high strength aluminum from Russia and the United Kingdom, another requirement for making centrifuges. A simple tally of the amounts and types of equipment and material sought by North Korea suggests that it planned to develop, at least, an A.Q. Khan HEU production scheme, which requires about 5900 centrifuges. That means a 5000 centrifuge strong enrichment capacity. (The rest is spares and those which do not pass quality control tests.) [12]

This appears not only consistent with a separate earlier enrichment offer A.Q. Khan had made to Libya, but the timing and pattern of acquisitions is also interesting. Iran, Libya and North Korea appear to have started initial acquisition of enrichment technology through vendors in Europe around 1987. Then, between 1993 and 1996, these countries turned to the A.Q. Khan network and acquired larger deliveries of raw materials and probably also obtained more advanced P-2 technology.

Implications of North Korea’s Enrichment Capabilities

It is highly likely that the UEW at Yongbyon is not the only uranium enrichment installation in North Korea. At least one other workshop would have been needed to serve as a test bed for pilot cascades of P-1 and P-2 centrifuges prior to the beginning of semi-industrial scale enrichment operations. Such an installation should have a few hundred centrifuges. While no uranium hexafluoride (UF6)[13] fabrication plant has been located in the North, its existence has been traced as far back as 2000, when subsequent investigations revealed that North Korea had shipped UF6 to the Libyan enrichment program.[14] Concerns over high enrichment were also prompted by the detection of HEU particles from aluminum samples handed over by the North Koreans to a US monitoring team in 2007 as part of the Six Party Talk agreement.[15] As contamination could have resulted from either tainted imported centrifuge equipment or from indigenous enrichment, its source remains unknown.

In any event, work at the UEW site has never been monitored. A glimpse of the facility was revealed when North Korea invited a group of visitors from Stanford University (including Professor Siegfried Hecker, the former Director of the Los Alamos National Laboratory) to a brief visit in 2010. If commissioning of the UEW has been successful, North Korea would have at present at least 3.5 tons of UF6, enriched to 3.5% U-235. This output is consistent with the annual needs of the 100 MWth LWR currently under construction. By 2013, there should be enough material, about four tons of uranium dioxide (UO2), for the first core of the 100 MWth LWR.

Such an enrichment plant could also be easily modified to produce HEU for nuclear explosives. If we look at possible future HEU production in North Korea, there are several permutations to consider from a technical standpoint depending on the availability of vital raw materials such maraging steel. The following are three possibilities with regard to operations at the UEW:

  • Utilize the current LEU cascades and install additional cascades to enrich LEU to weapons-grade HEU;
  • Modify the existing cascades to produce HEU;
  • Utilize the current LEU configuration at the workshop and construct additional cascades for LEU and HEU production.

The first, most straightforward option would be to install an additional 1000[16] centrifuges to convert the annual production of 1.8 tons of LEU at Yongbyon to 40 kilograms of HEU. This is an amount sufficient to generate the necessary fissile material for one to two additional nuclear bombs per year.[17] Such a step-wise scheme was foreseen in Libya by enriching 3.5% enriched uranium first to 20%, then from 20% to 60%, and finally from 60% to 90% U-235.[18] The actual conversion of 3.5% to 90% would take only a couple of months. This scenario would require the availability of additional raw materials and key equipment. Here we are faced with a few unknowns. For instance, we do not know the source and amount of maraging steel—a key raw material for manufacturing additional centrifuges—available to North Korea.

Second, the existing UEW could be reconfigured to produce HEU by recycling LEU. This would be a viable option if North Korea lacks the key materials to manufacture new centrifuges. However, this scenario would not be able to take full advantage of the installed centrifuges since the cascades for HEU production have a different layout, which forces the operator to leave a number of centrifuges unused. Consequently, the time needed to produce HEU would increase under this scenario.

Third, for the DPRK to fully optimize its HEU production following the A.Q. Khan scheme, it would install an additional 2000 centrifuges that could produce 3.5% enriched uranium with an extra 1900 centrifuges[19] for HEU production. This option, using 5900 centrifuges, would turn all natural UF6 into HEU and produce up to 80 kilograms of HEU annually or an amount sufficient for four nuclear bombs.  However, there are no indications that the DPRK has required key raw materials to be able to manufacture thousands of additional centrifuges. Such a scenario would require, for instance, an additional 60 tons of maraging steel.

Next Steps by North Korea

The DPRK has invited the International Atomic Energy Agency (IAEA) to monitor its moratorium on uranium enrichment, but it appears that arrangement will not go forward with the collapse of the February 29 agreement. If it does, IAEA inspectors will likely be limited by the DPRK to prior arrangements implemented in 2007, which would mean that the IAEA would verify that the UEW is shutdown, but it will neither be permitted to verify the inventory of LEU nor establish the historical production of enriched uranium. Under such circumstances, the IAEA would only have access to the UEW. Any other installations, including conversion and (potential undisclosed) enrichment facilities, would not be included. Access to those facilities would have to be negotiated within the Six Party Talks.

With the April 13 satellite launch, North Korea has stepped determinedly towards a confrontational course with its Six Party Talk partners, and the United Nations Security Council has issued a Presidential Statement condemning its actions. Under such circumstances, what are the nuclear-related options North Korea can exercise if it chooses to raise the stakes even further? Conduct another nuclear test? This is certainly possible, but one that would further deplete Pyongyang’s precious plutonium stocks. What about the alternative of a uranium bomb test? This assumes that the North Koreans have succeeded in producing HEU (in sufficient quantities as well) and have a bomb design.[20] Yet another step is for North Korea to forge ahead with the production of HEU and demonstrate that capability to the international community short of a bomb test.[21]

As governments, diplomats and experts assess how to deal with North Korea’s new leadership under Kim Jong Un, the message that everyone should remain mindful of is that the DPRK’s nuclear program has transitioned from solely relying on the production of plutonium to adding a new feature, the growing production of enriched uranium. Transitioning away from this ominous onward march through a slowdown, suspension and gradual turnaround will be the ultimate test of a true transition that will eventually integrate North Korea back to the international community.

[1] S.S. Hecker, C. Braun, R.L. Carlin, “North Korea’s Light-Water Reactor Ambitions,” Journal of Nuclear Materials Management, Spring 2011, Volume XXXIX, No.3,  pp. 18-25.

[2] Siegfried S. Hecker, “A Return Trip to North Korea’s Yongbyon Nuclear Complex,” Center for International Security and Cooperation, Stanford University, November 20, 2010.

[3] As a part of the October 1994 Agreed Framework, the United States undertook to make arrangements for the provision to the DPRK of a LWR project with a total generating capacity of approximately 2,000 MW(e) by a target date of 2003.

[4] LWR fuel is enriched generally up to 4% U-235.

[5] Highly enriched uranium, HEU, contains 90%  U-235. Uranium in nature has 0.7% U-235.

[6]North Korea Makes Significant Progress in Building New Experimental Light Water Reactor (ELWR),” 38 North, US-Korea Institute at SAIS: Johns Hopkins University, November 14, 2011,

[7] Modifications are mainly required to the so-called head end, which includes fuel chopping and dissolution. Much of the needed information is available in open literature, e.g. from the Eurochemic plant, which operated  from 1966 to 1974  in Dessel, Belgium. The DPRK used already this information for the design of the original Reprocessing Plant in Yongbyon.

[8] S. Hecker, “Lessons learned from North Korean nuclear crises,” Daedalus, Winter 2010, 44-56.

[9] J. Solomon, “North Korean Pair Viewed as Key to Secret Arms Trade,” The Wall Street Journal Asia, August 31, 2010.

[10] Sources: and

[11] Semi-industrial enrichment plants are used to demonstrate that the process is working properly before proceeding with a full scale expensive investment. In the chemical industry, this is often called to a pilot plant. Semi-industrial plants have customarily about 1000 centrifuges when the full size enrichment plants can have tens of thousands of centrifuges.

[12] The total number could be as high as 7000 centrifuges, but a reserve for the replacement of failed centrifuges and small test cascades is also required.

[13] Uranium hexafluoride is the feed gas for the centrifuges.

[14] “Application of Safeguards in the Democratic People’s Republic of Korea,” IAEA, Board of Governors General Conference, GOV/2011/53 – GC(55)24, September 2, 2011.

[15] G. Kessler, “New Doubts On Nuclear Efforts by North Korea,” Washington Post, March 1, 2007.

[16] The scheme could be as follows: 3.5-20% four cascades, each 164 centrifuges, 20-60% two cascades, each 114 centrifuges, and 60-90% two cascades, each 64 centrifuges.

[17] A nuclear weapon design, which was floating in the A.Q. Khan network, required less than 20 kilograms of HEU.

[18] Annexure to a plea agreement of Mr. Daniel Geiges available from

[19] The scheme could be as follows: 3.5-20% eight cascades, each 164 centrifuges, 20-60% four cascades, each 114 centrifuges, and 60-90% two cascades each 64 centrifuges.

[20] In 2004, the IAEA became aware that some computers of the members of the A.Q. Khan had some design drawings of a more advanced uranium device, which had likely been developed around mid-1990s.

[21] The DPRK can also follow the playbook of Iran by claiming that it is enriching uranium for its old Soviet-made IRT research reactor. The IRT reactor, which is also located in Yongbyon, has not received new fuel in last three decades. The IRT reactor fuel is 36% (U-235) enriched uranium.

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