Catherine DillNorth Korean Uranium Conversion: History and Process, Part 1

This is a guest post by my colleague Jamie Withorne. Jamie is a Research Assistant at the James Martin Center for Nonproliferation Studies. Her work focuses on emerging technology, North Korea’s sanctions evasion, and North Korea’s nuclear fuel cycle.

This is the first of a three part series that aims to provide an in-depth review of North Korea’s uranium conversion capabilities, including addressing what details presently remain unknown. While this series does not attempt to identify North Korea’s uranium hexafluoride production capabilities, it does analyze other North Korean uranium conversion operations, processes, and associated locations.

This series is divided into three parts: 1) a historical review of North Korea’s uranium conversion from 1983-2002 2) a historical review of North Korea’s uranium conversion from 2003-2010 and 3) a comprehensive technical analysis of North Korea’s uranium conversion processes.

Part One: North Korea’s Uranium Conversion Before and During the Agreed Framework (1983-2002)

During the 1983-2002 time period, North Korea declared its conversion operations to the International Atomic Energy Agency (IAEA) and nominally froze its conversion activities.

Figure 1: Timeline of North Korea’s conversion activity from 1983 to 2002

Timeline of North Korea conversion activity from 1983 to 2002

Before the Agreed Framework negotiations took place, North Korea declared the technical specifications of its nuclear program to the IAEA in 1992. This declaration was followed by an on-the-ground visit from the IAEA in May 1992.[1] With respect to conversion, in the declaration and during the visit, North Korea provided details on a uranium tetrafluoride (UF₄) production line located at the Yongbyon Fuel Fabrication Plant (FFP).[2] Construction of the FFP began in the early 1980s, and the facility was operational sometime between 1985-1987.[3] Before 1985, North Korea operated a pilot fuel fabrication plant from 1983 to 1986 which included a UF₄ production line, but North Korea claimed to have lost and/or destroyed the records from this facility in 1991.[4]

The dossier, Solving the North Korean Nuclear Puzzle, provides one of the earliest technically specific and publicly available descriptions of North Korea’s uranium conversion capabilities, including facility identification.[5] Citing this publication, Dr. Siegfried Hecker describes the material flow at the FFP and North Korea’s uranium conversion processes as follows.[6]

Figure 2: The process flow at North Korea’s Yongbyon Fuel Fabrication Plant [7]

Uranium conversion process flow at Yongbyon

According to this analysis, yellowcake was produced at Pyongsan and then transferred to the FFP by rail. The yellowcake was then brought to Building 1 by an internal rail system where it was reduced first to uranium trioxide (UO₃) and then to uranium dioxide (UO₂). The UO₂ was brought to Building 2 for purification and uranium tetrafluoride (UF₄) production. Hydrogen Fluoride (HF) was produced in the building labeled “HF production.” The UF₄ was then converted into uranium metal in Building 3, shaped into fuel rods in Buildings 4 and 5, and the fuel rods were stored in Building 6.

Both reports contain assumptions in their assessments, including assumptions on specific uranium conversion details such as equipment and chemical requirements. Part 3 of this series will more thoroughly consider the implications of these assumptions.

Given these descriptions, North Korea was likely implementing a uranium conversion process that employed wet UO₂ and wet UF₄ production from the early 1990s until 1994. There was no declared or observed UF₄ production or other conversion-related activity at the FFP during the Agreed Framework freeze, from October 1994 until October 2002. However, during the freeze the IAEA had limited access to technical buildings at Yongbyon and had difficulty gaining regular access to some of the “frozen” facilities, including conversion-related facilities.[8] Consequently, it is possible North Korea was operating aspects of its nuclear fuel cycle, including parts of the conversion line, covertly during this time frame.

While North Korea did not declare a UF₆ production line during this time period, there is the Libya variable to consider. From the 1980s until 2003, Libya made several efforts to create an indigenous nuclear program. In late 2003, when Libya declared to the IAEA that it was giving up its nuclear program, it did not have indigenous UF₆ production capabilities.[9] In a 2004 visit, the IAEA stated Libya had procured UF₆ from illicit shipments in 2000 and 2001.[10] It was later revealed these shipments were procured by means of the A.Q. Khan illicit trade network. In 2011 the IAEA confirmed that it was very likely the UF₆ shipment from 2001 originated in North Korea.[11] Press reports suggested that plutonium had been found on the outside of another canister, potentially indicating multiple canisters had been in North Korea (specifically at Yongbyon) at one point in time.[12] Some reports suggest North Korea, Pakistan, and A.Q. Khan worked together as early as the autumn of 1993 to improve their respective nuclear weapons capabilities, though the full extent of this cooperation is unclear.[13] In a statement given by A.Q. Khan, he claimed that North Korea gave Pakistan UF₆ as early as 1998. However, this is the only statement detailing North Korea UF₆ production capabilities prior to 2000, and this statement could potentially be purposefully misleading or inaccurate.[14]

Given this collaboration and presence of North Korea-linked UF₆ in Libya, it is possible that North Korea was able to produce UF₆ prior to 2001 at an unknown and undeclared facility. However, there are several key pieces of information missing regarding this claim. For example, it is unclear what form the uranium was in (i.e. UF₆ or some other uranium product, like yellowcake) when it left North Korea and was transferred through Pakistan to Libya.[15]

Considering these factors, it is possible North Korea took steps to extend its uranium conversion line to include UF₆ production during the Agreed Framework years. However, it remains unknown as to whether or not North Korea was able to actually begin UF₆ production prior to 2002.

 [1] “IAEA footage of Director General Hans Blix Touring North Korean Nuclear Sites in 1992,” Institute for Science and International Security YouTube, December 3, 2018, <>.

[2] The term “fuel fabrication plant” refers to the entire complex of buildings located in the southern part of the Yongbyon nuclear site, whereas “fuel fabrication facility” refers only to individual buildings (Buildings 4 and 5, identified in Figure 2 below) at the fuel fabrication plant.

[3] Joseph Bermudez, “North Korea’s Nuclear Infrastructure,” Jane’s Intelligence Review, February 1, 1994. 

[4] IAEA, “Application of Safeguards in the Democratic People’s Republic of Korea,” GOV/2011/53-GC(55)/24, September 2, 2011. 

[5] David Albright and Kevin O’Neill, Solving the North Korean Nuclear Puzzle, (Washington, DC: Institute for Science and International Security, 2000), p. 146.

[6] Chaim Braun, Siegfried Hecker, Chris Lawrence, Panos Papadiamantis, “North Korea Nuclear Facilities After the Agreed Framework,” Center for International Security and Cooperation at Stanford University, May 27, 2016 <>.

[7] This graphic is a reproduction of Figure 9 from Chaim Braun et al.

[8] GAO, “Nuclear Nonproliferation: Difficulties in Accomplishing IAEA’s Activities in North Korea,” GAO/RCED-98-210, July, 1998.

[9] IAEA, “Implementation of the NPT Safeguards Agreement of the Socialist People’s Libyan Arab Jamahiriya,” GOV/2004/12, February 20, 2004.

[10] IAEA, “Implementation of the NPT Safeguards Agreement of the Socialist People’s Libyan Arab Jamahiriya,” GOV/2004/33, May, 28 2004.

[11] GOV/2011/53-GC(55)/24.

[12] Jeffrey Lewis, “Can North Korea Produce UF6?” Arms Control Wonk Blog, October 5, 2005, <>.

[13] David Albright and Paul Brannan, “Taking Stock: North Korea’s Uranium Enrichment Program,” The Institute for Science and International Security, October 8, 2010, <>.

[14] “A.Q. Khan’s Thirteen-Page Confession,” Fox News, November 17, 2014, <>.

[15] Jeffrey Lewis, “A Financial Link in That AQ Khan-North Korea-Libya UF6 Daisy Chain?” Arms Control Wonk Blog, April 1, 2005, <>.

This work is part of an ongoing joint project between the Verification Research, Training and Information Centre (VERTIC), the James Martin Center for Nonproliferation Studies (CNS) at the Middlebury Institute of International Affairs (MIIS), and the Royal United Services Institute (RUSI). The project seeks to update and systematize analysis of North Korea’s nuclear complex, using remote sensing data and industry-standard nuclear fuel cycle modelling to generate independent models of plausible scenarios for that complex, in the past, present and future, and to use those results to assess priorities for control and verification. The project is generously funded by Global Affairs Canada.