Civilian HEU Reduction and Elimination Resource Collection

December 14, 2020

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The NTI Civilian HEU Reduction and Elimination Resource Collection tracks global civil highly enriched uranium (HEU) holdings, discusses common applications and alternatives, and profiles countries that produce, utilize, or export civil HEU. It also describes in detail domestic and international efforts designed to address civil HEU security, and remaining implementation challenges.

Civilian HEU Reduction and Elimination Resource Collection

Why Is Civilian Highly Enriched Uranium a Threat?

The most difficult challenge for a terrorist organization seeking to build a nuclear weapon or improvised nuclear device (IND) is obtaining fissile material, either plutonium or highly enriched uranium (HEU). HEU, uranium that has been enriched to increase the proportion of the U-235 isotope to over 20%, is required for the construction of a gun-type nuclear device, the simplest type of nuclear weapon. The higher the enrichment level, the less material is needed for a nuclear explosive device. Weapons-grade uranium generally refers to uranium enriched to at least 90%, but material of far lower enrichment levels, found in both fresh and spent nuclear fuel, could be used to build a nuclear explosive device.

Twenty-three countries have stocks of highly enriched uranium. In addition to military use, HEU has numerous civilian applications. According to a 2015 report by the Institute for Science and International Security (ISIS), global stocks of civilian HEU are as high as 137 tons, but this estimate has significant error margins given that no comprehensive inventory of civil HEU exists (total global HEU, including military stockpiles, is estimated at 1,335 tons). [1] [2] Civil HEU reduction efforts are greatly hindered by poor global accounting. According to the U.S. Government Accountability Office (GAO), even the United States has failed to maintain an accurate inventory of the HEU that it has exported over the years, and attempts to balance the books could only account for 10 percent of the material. [3]

The global inventory of civil HEU is sufficient to build nearly 5,000 nuclear bombs. [4] Many civilian facilities that use or store HEU on-site lack adequate security. These facilities are often located in universities or other publicly accessible research centers. Given the difficulty posed by reconfiguring sites that were not built with physical protection in mind, upgrading security measures is not a simple task and can be cost-prohibitive.

Weapons-useable material can be obtained from HEU that is fresh (unirradiated), and irradiated (also referred to as spent fuel). HEU spent fuel is often even less secure than fresh fuel stocks, as it has no further economic value to the facilities that use it at this stage. Traditionally, spent fuel was considered “self-protecting” due to the radioactive dose thieves would receive. The increased threat of suicide terrorism requires that security measures evolve to meet spent fuel challenges. As such, the IAEA no longer recommends that a state factor in “self-protection” when determining necessary physical protection measures. [5]

The four head-of-state level Nuclear Security Summits, held from 2010 to 2016, helped to raise awareness of global fissile material stockpiles, but no comparative global effort has emerged to replace them. Despite worsening relations between the United States and Russia, U.S. Department of State Assistant Secretary Christopher Ford in 2018 called HEU minimization “a good example of how cooperation is possible between Washington and Moscow on shared interests.” [6] National and international efforts to secure and minimize the use of civil HEU are discussed in detail in Past & Current Civil HEU Reduction Efforts.

Current Civil HEU Uses

A wide variety of civil reactors use HEU fuel. HEU is also frequently utilized for the production of medical isotopes, in Russian icebreakers for propulsion, and in some space propulsion research.

HEU Use in Research and Test Reactors

Significantly less powerful than commercial power reactors, research reactors use smaller amounts of uranium for neutron production. While many research reactors initially used low enriched uranium (LEU) fuel, the LEU fuel technology used in the 1950s soon reached its limits. In order to improve the performance of the reactors with existing technology, and to enable more powerful reactors to be built, HEU fuel soon became the standard among the vast majority of research reactors. [7] The amount of HEU fuel used in research reactors varies dramatically, from just 1 kg in Miniature Neutron Source Reactors (MNSR), to approximately 10 kg per year in many pool reactors, up to more than 100 kg per year in some of the most powerful reactors. Some of these reactors also have stocks of fresh and spent fuel on site, which makes them potentially attractive targets for criminals or terrorists seeking access to weapons-useable nuclear material.

In addition to research reactors, low powered reactors that frequently utilize HEU fuel include critical assemblies, subcritical assemblies, pulsed reactors, and test reactors. Low powered reactors pose unique proliferation challenges; because they consume their fuel very slowly, they frequently have what are termed “lifetime cores.” As a consequence, existing facilities with low powered reactors have no natural window of opportunity or economic incentive to transition to LEU fuel. The cost of conversion is substantial, as the irradiated HEU fuel from reactor cores needs to be extracted, stored, and replaced with high-density LEU fuel. Moreover, Russian operators have an interest in keeping their facilities running on HEU, since higher uranium enrichment levels have been linked to higher employee salaries. [8]

The largest concentrations of HEU-fueled reactors are found in the former Soviet Union, the United States, and the European Union. In 2007, 140 research reactors were using HEU fuel. According to a report by the National Academies of Sciences in early 2016, 74 civil reactors still use HEU nearly a decade later. [9] Moreover, many of the HEU research reactors that have been shut down but not decommissioned continue to have spent HEU fuel on-site, posing ongoing security risks. [10]

Although there is no international agreement banning the use of HEU in future research reactors, no new HEU-fueled civilian research reactors with a power level of more than 1 MW have been built in Western countries since the early 1980s, with the exception of Germany’s FRM-II reactor. Germany’s program has presented a setback for global civil-HEU reduction and elimination efforts, as prior to its construction there had been a de facto global norm against building civil HEU reactors. For more information see Civil HEU: Germany.

HEU in Radioisotope Production

HEU continues to play a role in the production of radioactive isotopes for medical applications, both as fuel for reactors and as targets. HEU targets are irradiated in a reactor, producing the fission product molybdenum-99 (Mo-99). Mo-99 has a 66 hour half-life wherein it decays to 6-hour half-life technetium-99m, a gamma ray emitter frequently used in medical imaging. [11]

The international community has made substantial progress in phasing out the use of HEU in medical isotope production. In many cases, this fulfills national commitments made during the Nuclear Security Summit process. South Africa – a major exporter – was one of the first countries to make the conversion to LEU. In 2010, it converted its Safari-1 reactor to rely on both LEU targets and LEU fuel for the production of medical isotopes. Other countries, including Australia, the Netherlands, Indonesia and Egypt, produce medical isotopes with LEU targets. [12] Canada, until recently an important Mo-99 exporter, stopped production of medical isotopes in 2018. [12] But as of 2020 was making “significant progress” towards the Mo-99 production at Ontario Power Generation’s Darlington plant that will be the first large-scale nuclear power station to produce the medical radioisotope. [13]

HEU Use in Fast Reactors and Future Nuclear Power Reactors

A number of countries, including China, France, Germany, India, Japan, and Russia have constructed or are developing fast reactors. [14] [15] Fast reactors, like the China Experimental Fast Reactor (CEFR), start-up with an initial HEU fuel load. [16] Most, if not all such future reactors, will ultimately rely on plutonium or U-233-based fuels, which pose similarly serious proliferation risks to HEU.

A critical question for the future is whether the next generation of nuclear power reactors, whether fast reactor designs or not, will require HEU. In the United States, the Department of Energy has launched the Gen IV Nuclear Energy Systems International Forum, an initiative to explore new technological approaches to nuclear power generation. [17] The IAEA has also undertaken the Project on Innovative Nuclear Reactors and Fuel Cycles (INPRO), which is likewise exploring new nuclear power technologies. [18] None of the reactors under consideration by these initiatives use HEU as a fuel.

HEU in Icebreaker Propulsion Reactors

Russia is the only country that employs nuclear propulsion for civilian vessels. It launched its first nuclear-powered icebreaker, the Lenin, in 1957. The OK-150 reactors that initially powered the Lenin used low-enriched fuel (5%). [19] Later designs have utilized HEU enriched up to 90%. [20] Some ships carry up to 200 kg of U-235 in their cores. [21] Russia’s current fleet is composed of four operational nuclear icebreakers (Vaygach, Yamal, Taymyr, and 50 let pobedy). [22] The rest of Russia’s fleet has been decommissioned and is in the process of being dismantled. [23] Russia plans to build more icebreakers, and is expected to use HEU fuel for its icebreaker fleet for at least another decade. [24]

HEU in Space: Power and Propulsion

Fission reactors have been used to power satellites orbiting earth. Weapons-grade HEU has been exclusively used for such reactors due to the size constraints imposed by space launches. [25] The United States launched a single satellite powered by a fission reactor in 1965; it was the first of its kind. [26] Such reactors were used extensively during the Cold War by the USSR to power 33 Radar Ocean Reconnaissance Satellites (RORSATs); these reactors used weapons-grade HEU fuel. [27] A second-generation TOPAZ reactor was also built (using 96% enriched fuel), and two satellites using this reactor were deployed by the Soviet Union. [28] In 2015, the United States began development of the Kilopower Reactor Using Stirling Technology (KRUSTY), a small fission reactor with a 30kg U-235 reactor core to power space travel. The KRUSTY system was tested in January 2018. Nonproliferation advocates criticized NASA’s decision to use HEU technology for space exploration, and have urged the adoption of LEU technologies. [29] These advocates worry that U.S. use of HEU for space applications could be used by other countries to justify their own production of HEU for civilian purposes. [30]

[1] Albright, Davis, Kelleher-Vergantini, Serena, “Civil HEU Watch: Tracking Inventories of Civil Highly Enriched Uranium,” 7 October 2015,; David Albright and Serena Kelleher-Vergantini, “Plutonium and Highly Enriched Uranium, 2015,” Institute for Science and International Security, 2015.
[2] “Fissile material stocks,” International Panel on Fissile Materials, 14 July 2020,
[3] “U.S. Agencies Have Limited Ability to Account for, Monitor, and Evaluate the Security of U.S. Nuclear Material Overseas,” Government Accountability Office, GAO 11-920, September 2011,
[4] International Atomic Energy Agency (IAEA) safeguards standards define 25 kilograms (kg) of U-235 (approximately 28kg of 90% HEU) as the amount for which, taking into account unavoidable losses during fabrication, “the possibility of manufacturing a nuclear device cannot be excluded.” This estimate of about 5,000 weapons is based upon the IAEA standard of 25 kg. It should be noted however, that while State programs are capable of manufacturing a nuclear weapon using less than this “significant quantity,” about 40 to 60 kg would be needed for the manufacture of a crude nuclear device using a design within the technical reach of a terrorist group.
[5] “Nuclear Security Recommendations on Physical Protection of Nuclear Materials and Nuclear Facilities (INFCIRC/225/Revision5),” IAEA Nuclear Security Series No.13, International Atomic Energy Agency, 2011.
[6] “Nonproliferation Lessons Learned,” Dr. Christopher Ashley Ford, Assistant Secretary, Bureau of International Security and Nonproliferation, 19 September 2018, remarks delivered at the Vienna Center for Disarmament and Non-Proliferation, Vienna Austria,
[7] A number of research reactors historically used fuel with a very high enrichment level, approximately 90% U-235, while many now use fuel enriched to approximately 36%.
[8] Alan J. Kuperman, “Global HEU Phase-Out: Prospects and Challenges,” in Nuclear Terrorism and Global Security: The Challenge of Phasing Out Highly Enriched Uranium, Alan J. Kuperman, ed. (Abingdon: Routledge, 2013), p. 16, 22.
[9] “Reducing the Use of Highly Enriched Uranium in Civilian Research Reactors,” Committee on the Current Status of and Progress Toward Eliminating Highly Enriched Uranium Use in Fuel for Civilian Research and Test Reactors, The National Academies Press, 28 January 2016.
[10] The IAEA database notes that over 20,000 spent fuel assemblies from research reactors are enriched to levels above 20 percent. Nearly half of these stored fuel assemblies are enriched to levels at or above 90 percent.
[11] International Atomic Energy Agency, “Annex VII: Production and Supply of Molybdenum-99,” Annex to the Nuclear Technology Review 2010, 2010, p. 150,
[12] Nuclear Research and Consultancy Group, “NRG Keeps Its Promise to Obama: Production of Medical Isotopes Using Only Low-Enriched Uranium,”
[13] “Canadian firms make progress with radioisotope production,” World Nuclear News, 25 September 2020,
[14] One example of a fast reactor that currently uses HEU fuel is Russia’s BN-600 reactor at Beloyarsk Nuclear Power Plant (NPP). The 600 MW reactor requires three types of fuel for an inner core, an intermediate core, and an outer core. The enrichment level for these fuels varies between 17%, 20%, and 26% U-235. The BN-600 reactor can also use a hybrid core with 75% uranium and 25% MOX fuel to dispose of some of Russia’s plutonium. According to the June 2005 IAEA report, the BN-600 annually consumes 6 tons of uranium fuel with U-235 assays, including 4 tons of HEU. At Beloyarsk NPP, the Russians are also constructing the BN-800 reactor, which current documents indicate will use MOX fuel. According to the plan established by the 2000 Plutonium Management and Disposition Agreement and its 2010 protocol, the BN-600 and BN-800 are to begin disposing of 34 metric tons of surplus Russian weapons-grade plutonium at a rate of 1.3 metric tons per year by 2018.
[15] IAEA Fast Reactor Database,
[16] “China Experimental Fast Reactor (CEFR),” Nuclear Threat Initiative, 25 July 2012,
[17] Gen IV Nuclear Energy Systems, U.S. Department of Energy, Office of Nuclear Energy, Science, and Technology,
[18] International Project on Innovative Nuclear Reactors and Fuel Cycles, International Atomic Energy Agency, Nuclear Power Technology Development Section,
[19] Nikolay Khlopkin, Boris Pologikh, Yuriy Sivintsev, and Vladimir Shmelev, “Preliminary Study of Sea Radioactive Contamination from Dumped Nuclear Reactors,” Kurchatov Institute Report No. 31/1-1949-93, 1993, as cited in Ole Reistad, Morten Bremer Mærli, and Nils Bøhmer, “Russian Naval Nuclear Fuel and Reactors: Dangerous Unknowns,” Nonproliferation Review, vol. 12, no. 1 (March 2005), pp. 174-176.
[20] Ole Reistad, Morten Bremer Mærli, and Nils Bøhmer, “Russian Naval Nuclear Fuel and Reactors: Dangerous Unknowns,” Nonproliferation Review, vol. 12, no. 1 (March 2005), pp. 181-183.
[21] “Nuclear Waste in the Arctic: An Analysis of Arctic and Other Regional Impacts From Soviet Nuclear Contamination,” Office of Technology Assessment-ENV-623, Washington D.C.: U.S. Government Printing Office, September, 1995, p. 134.
[22] Charles Digges, “One of Russia’s New Nuclear Icebreakers Facing Delays,” Bellona, 10 September 2018,
[23] Christine Egnatuk in Alan J. Kuperman, Nuclear Terrorism and Global Security – The Challenges of Phasing Out Highly Enriched Uranium (London: Routledge, 2013), p. 73.
[24] Christine Egnatuk in Alan J. Kuperman, Nuclear Terrorism and Global Security – The Challenges of Phasing Out Highly Enriched Uranium (London: Routledge, 2013), p. 79.
[25] R. Blake Messer, “Space Reactors,” Nuclear Terrorism and Global Security: The Challenge of Phasing out Highly Enriched Uranium, ed. Alan J. Kuperman (Abingdon: Routledge, 2013), p. 211-212, 216-217.
[26] R. Blake Messer, “Space Reactors,” Nuclear Terrorism and Global Security: The Challenge of Phasing out Highly Enriched Uranium, ed. Alan J. Kuperman (Abingdon: Routledge, 2013), p. 211-213.
[27] R. Blake Messer, “Space Reactors,” Nuclear Terrorism and Global Security: The Challenge of Phasing out Highly Enriched Uranium, ed. Alan J. Kuperman (Abingdon: Routledge, 2013), p. 213.
[28] R. Blake Messer, “Space Reactors,” Nuclear Terrorism and Global Security: The Challenge of Phasing out Highly Enriched Uranium, ed. Alan J. Kuperman (Abingdon: Routledge, 2013), p. 213.
[29] David Irvin Poston, Patrick Ray McClure, “White Paper – Use of LEU for a Space Reactor,” Los Alamos National Laboratory, 11 August 2017,
[30] Alan J. Kuperman, “Avoiding Highly Enriched Uranium for Space Power,” Nuclear Proliferation Project, LBJ School of Public Affairs, University of Texas, 26 February – 1 March 2018,

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