Why Is Highly Enriched Uranium a Threat?

The most difficult challenge for a terrorist organization seeking to build a nuclear weapon or improvised nuclear device is obtaining fissile material, either plutonium or highly enriched uranium (HEU). HEU, uranium that has been processed 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 greater the proportion of U-235 (i.e. 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, can be used to create a nuclear explosive device.

In 2002, the U.S. National Research Council warned that "crude HEU weapons could be fabricated without state assistance," noting that "the primary impediment that prevents countries or technically competent terrorist groups from developing nuclear weapons is the availability of [nuclear material], especially HEU."[1] Creating a nuclear weapon from HEU is technically easier than building a plutonium weapon. Moreover, current technology is unlikely to detect a shielded nuclear device on a truck or boat. Therefore, securing and eliminating stocks of HEU is the surest way to decrease the risk that terrorist groups could use this material to create a nuclear explosion.

Where Is Civilian HEU Located?

Experts estimate that approximately 70 tons of HEU are used in civilian applications worldwide. [2] As little as 25 kilograms (kg) of U-235 (which amounts to about 28kg of HEU enriched to 90%) is needed to produce a nuclear weapon; about 40-60kg is needed for a cruder nuclear device. [3] Bomb-grade material can be obtained from HEU that is fresh (unirradiated), and irradiated (also referred to as spent). Fresh and lightly irradiated fuel (such as fuel used in critical assemblies and pulse reactors) is not significantly radioactive, and is therefore relatively safe to handle. Although using nuclear fuel in high-powered reactors initially makes it highly radioactive and thus very difficult to handle safely (often this fuel is referred to as "self-protecting"), spent fuel loses its radioactivity over time, making it easier to handle and potentially more attractive to terrorists.

HEU is currently used in the civilian sphere to fuel research reactors, critical assemblies, pulsed reactors, and a few fast reactors. According to the International Atomic Energy Agency (IAEA), 263 research reactors are in operation or temporarily shut down across 57 countries. A further 455 reactors have been shut down or decommissioned, while ten are planned or under construction. [4]

Many of the research reactors that have been shut down, but not decommissioned, have spent HEU fuel on-site. 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.[5] That said, there is no current comprehensive, authoritative inventory of civil HEU globally, which is a major obstacle to progress in this area. According to the Government Accountability Office, even the United States has failed to maintain an accurate inventory of the HEU that it has exported over the years as attempts to balance the books could only account for 10 percent of the material. [6]

The United States and the Soviet Union supplied much of the HEU fuel used in research reactors world-wide. Other producers include China (which sent HEU fuel for research reactors to Nigeria, Ghana, Iran, Pakistan, and Syria, as well as enriched uranium to South Africa, and Argentina); France (to Chile and India); the United Kingdom (to Australia, India, and Japan); and South Africa (which did not export this fuel).[7] Before 1978, when Washington and Moscow became concerned about the implications of their exports of highly enriched fuels, most of the fuel supplied by the United States (the bulk of which went to North American and the Asia-Pacific), was of very high enrichment levels (90% and above). The Soviet-supplied fuel, chiefly sent to Eastern Europe, was typically 80% enriched. Under several U.S.-led initiatives, many countries have returned HEU fuel, both fresh and spent, to its country of origin in order to reduce the risk of theft.

HEU is also used in targets in reactors that produce medical isotopes. HEU is used for this purpose annually in reactors in Belgium, Canada, France, the Netherlands, and Russia.[8] Other countries, including Australia and Indonesia, have begun producing these isotopes with LEU targets, and still other countries, such as Egypt, are currently developing and implementing their LEU target-based production process. [9] In particular, South Africa—a major exporter—converted its Safari-1 reactor to rely on both LEU targets and fuel for the production of medical isotopes. Most of the other major producers of medical isotopes, including Canada, the Netherlands, and France, utilize LEU fuels in their reactors, but continue to rely on HEU targets. However, a number of these countries, particularly in Western Europe, have pledged to convert to LEU targets. While a Russian project had initially aimed to produce enough molybdenum-99 using HEU fuel and targets to satisfy 20 percent of global demand by 2015. Russia subsequently announced a number of steps to convert to LEU fuel and targets over the next few years. [10]

In addition to use in research and test reactors and for medical isotope production, HEU is used in naval propulsion and space propulsion research. The material is also used for testing fast reactor core designs using mixed oxide (MOX) fuel. For further information on HEU in civilian applications, see Civilian Uses of HEU.

Security of Civilian HEU

Many civilian facilities with HEU on-site do not have adequate security. The IAEA reported that during one of its missions, it discovered a research reactor with HEU that "was observed to have essentially no physical protection." [11] The IAEA assisted the facility with enhancing its security, but reported that overall, "deficiencies remain in the legal, administrative, and technical arrangements for controlling and protecting nuclear materials ... in many countries." [12] The U.S. Department of Energy has been assisting with physical protection upgrades for 22 foreign research reactors through the Global Research Reactor Program. A September 2009 GAO report found that while most sites that have received upgrades generally met IAEA security guidelines, in some cases, critical security weaknesses remained. [13]

It is not a simple matter to upgrade security measures; the majority of the world's research reactors are located in universities or other publicly accessible research centers. While security concerns have dramatically increased since 9/11, it is difficult to reconfigure a site that was not built with physical protection in mind. Storage of spent fuel stocks is generally even less secure than fresh fuel stocks, as until a few years ago spent nuclear fuel was considered "self-protecting" and few facilities wanted to spend money securing a material that was no longer of economic value. It is far more effective to remove this material from vulnerable locations than to attempt to increase security on-site.

Programs to Reduce and Eliminate HEU

There have been efforts to reduce the amount of HEU at civilian facilities since 1978, when Washington initiated the Reduced Enrichment for Research and Test Reactors (RERTR) Program. Moscow also began its own program to reduce enrichment at Soviet-built research reactors outside of the Soviet Union, and changed its HEU export policies, supplying these reactors with 36% HEU in lieu of 80% HEU. In the past 25 years, many countries have cooperated with the RERTR program or initiated their own, similar programs.

In May 2004, the U.S. Department of Energy launched the Global Threat Reduction Initiative (GTRI), which the IAEA, Russia, and others have since joined. Among its goals, the GTRI seeks to "minimize and eventually eliminate any reliance on HEU in the civilian fuel cycle, including conversion of research and test reactors worldwide from the use of HEU to the use of LEU fuel and targets." As of early 2012, U.S.-led efforts have converted to LEU or verified the shut down of 88 HEU-fueled facilities.[14]

The RERTR  program is also working on the conversion of a handful of medical isotope producers that use HEU targets in their reactors. The program includes some of the largest producers of medical isotopes, located in Europe. To date, the RERTR program has helped to successfully convert isotope-producing reactors in Argentina and South Africa. At present, most of the technical barriers to conversion to LEU have been eliminated, with remaining issues primarily political and financial in nature.  [15]

Besides converting facilities to use LEU fuel and targets, there have also been efforts to consolidate fresh and spent HEU fuel at a smaller number of relatively secure locations. This has involved removing the fuel, mostly to the United States and Russia, from other countries, as well as consolidating the fuel within countries. U.S. programs in this area (the Russian Research Reactor Fuel Return program to repatriate fuel to Russia, and the Foreign Research Reactor Spent Nuclear Fuel Acceptance Program to repatriate U.S.-origin fuel), have all been subsumed under the 2004 GTRI initiative. Together, the two programs have returned over 2,735kg of spent and fresh HEU fuel to the United States and Russia as of 2012. [16] According to the IAEA's definition of the quantity of HEU necessary to construct a nuclear explosive device, the amount of repatriated HEU is equivalent to up to 80 weapons. [17]

Despite the progress of these efforts, many HEU sites remain worldwide, with a significant portion of them located in Russia. [26] A related program, the Material Consolidation and Conversion (MCC) project, established in 1999, reduces this excess Russian civilian HEU by blending it down into LEU. As of the end of 2011, approximately 13.5 of an estimated 17 tons of U-235 in excess Russian civilian HEU had been blended down. [18]

Both the United States and Russia also have large quantities of excess HEU from their defense programs. In Russia, excess HEU from weapons has been blended down to LEU within the framework of the Megatons to Megawatts program (also known as the HEU-LEU program). The resulting LEU is then released for civilian use. The program will end in 2013, at which point 500 tons of HEU will have been downblended. [19] The United States initially declared some 174 metric tons of HEU as excess to military needs, designating this material as civilian. [20] An additional 200 metric tons were officially removed from the U.S. weapons stockpile in November 2005. [21]

Since the amount of HEU that is actually excess to military needs is likely far greater than the amount that has officially been declared to date, there have also been calls to speed up the various downblend programs. [22]

For further information on programs to reduce and eliminate HEU, see Past and Current Civilian HEU Reduction Efforts.

International Proposals to Eliminate the Civilian Use of HEU

At the 2005 Non-Proliferation Treaty (NPT) Review Conference IAEA Director General Mohamed El-Baradei called on countries "to minimize, and eventually eliminate, the use of high enriched uranium in peaceful nuclear applications." [23] Many national governments have since called for the elimination of HEU in the civilian sphere. These efforts have included reactor conversions, fuel return, and the development of HEU-free medical isotope production.

The opening statement from Kyrgyzstan at the 2005 NPT Review Conference noted that "the Kyrgyz Republic believes this Review Conference should consider means to enhance the security of existing stockpiles of highly enriched uranium, while consolidating them, reducing their size, and moving toward the elimination of the use of highly enriched uranium in the civilian nuclear sector." [24] This call was taken up by other countries, especially Iceland, Lithuania, Norway, and Sweden. [25] Norway reiterated its call in its statement to the IAEA General Conference in September 2005, as well as calling for the IAEA to develop guidelines for the management of HEU in the civilian sector. The U.S. statement, too, called to "phase-out the commercial use of highly enriched uranium," a policy the United States has been promoting since 1992, when it restricted exports of HEU in order to promote conversion to LEU.

Civilian use of HEU did not figure prominently in the next NPT Review Conference, held in May 2010, but states did agree to place the issue in the consensus action plan. Action 61 of the plan "encourages" states to further minimize HEU in civilian stocks, voluntarily, where technically and economically feasible. [26]

In April 2010, 47 heads of state or government attended the Washington Nuclear Security Summit, an unprecedented high-level meeting that dealt with the HEU issue, among others. Participating states agreed to consider, "where appropriate," the conversion of nuclear facilities utilizing HEU to LEU, and to collaborate on the development of LEU-based technologies for the production of medical or other isotopes. In addition, states pledged individual measures to reduce their use of HEU or secure existing supplies.[27]

A second Nuclear Security Summit was held in March 2012 in Seoul, South Korea, and was attended by 53 heads of state. At this summit, the participant states reported on their accomplishments and pledged to speed up their HEU reduction efforts. Several states committed to convert their isotope-producing reactors by 2015. The Summit's Communiqué encouraged "states to take measures to minimize the use of HEU, including through the conversion of reactors from highly enriched to low enriched uranium (LEU) fuel, where technically and economically feasible, taking into account the need for assured supplies of medical isotopes, and encourage States in a position to do so, by the end of 2013, to announce voluntary specific actions intended to minimize the use of HEU. [It also encouraged] States to promote the use of LEU fuels and targets in commercial applications such as isotope production, and in this regard, welcome[d] relevant international cooperation on high-density LEU fuel to support the conversion of research and test reactors." [28] However, more dramatic measures, such as France's advocacy of HEU management guidelines similar to existing plutonium guidelines, proved controversial at this time. A follow-on summit will be held in the Netherlands in 2014.

For further information on international efforts to reduce HEU use, see the International Politics of Civilian HEU Elimination.

Further Reading

• Office of Global Threat Reduction U.S. National Nuclear Security Administration
• International Panel on Fissile Materials Reports
• Fissile Materials Working Group
• "Global HEU Phaseout," a Nuclear Proliferation Prevention Project at the University of Texas at Austin
• "Reduced Enrichment for Research and Test Reactors," Argonne National Laboratory
• 2012 Nuclear Security Summit website
• "Securing the Bomb 2010: Securing All Nuclear Materials in Four Years"
• Medical Isotope Production without Highly Enriched Uranium, National Academy of Sciences, February 2009
• Future of the Nuclear Security Environment in 2015: Proceedings, National Academy of Sciences and Russian Academy of Sciences, February 2009
• Charles Ferguson and William Potter, eds., The Four Faces of Nuclear Terrorism (Abindgdon, Oxfordshire, UK: Routledge, June 2005), www.nti.org
• Miles A. Pomper, "The 2012 Seoul Nuclear Security summit and HEU Minimization," US-Korea Institute at SAIS, January 2012

Sources:
[1] Committee on Science and Technology for Countering Terrorism, Making the Nation Safer: The Role of Science and Technology in Countering Terrorism (Washington, DC: National Academy Press, 2002), pp. 40, 45, as cited in Charles Ferguson and William Potter, eds., The Four Faces of Nuclear Terrorism, p. 132.
[2] "Global Fissile Material Report 2011," International Panel on Fissile Materials, 2011, pp. 9, www.fissilematerials.org.
[3] The IAEA defines significant quantities of nuclear material as "the approximate quantity of nuclear material in respect of which, taking into account any conversion process involved, the possibility of manufacturing a nuclear explosive device cannot be excluded." The standard, generally speaking, is 8kg of plutonium, 25kg of U-235 in HEU, and 75kg of U-235 in natural or low-enriched uranium. See: Limits to the Safeguards System, www.iaea.org.
[4] Research Reactor Database, International Atomic Energy Agency, http://nucleus.iaea.org, 18 March 2013.
[5] Research Reactor Database, International Atomic Energy Agency, http://nucleus.iaea.org, 18 March 2013.
[6] "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, www.gao.gov.
[7] Chinese exports consist of approximately 1kg. of 90% HEU fuel for use in Miniature Neutron Source type reactors. Sources: Greg Webb, "Nigeria Commissions Research Reactor; HEU-Fueled Facility Goes Against U.S.-Led Nonproliferation Effort," Global Security Newswire, 1 October 2004, www.nti.org; Ann MacLachlan, "Operators of small reactors to meet to discuss conversion to LEU fuel," NuclearFuel, 25 April 2005, p. 5; "Research Reactors" Briefing/Information Paper, December 2004, World Nuclear Association, www.world-nuclear.org; Judith Miller, "U.S. is Holding up Peking Atom Talks," New York Times, 19 September 1982; Michael Brenner, "People's Republic of China," in William Potter, ed., International Nuclear Trade and Nonproliferation, 1990, p. 253; and Leonard Spector, Nuclear Ambitions, 1990, p. 274, as cited in Steven Dolley, "China's Record of Proliferation Misbehavior," 29 September 1997, Nuclear Control Institute, www.nci.org.
[8] Office of Nonproliferation, National Nuclear Security Administration, "RERTR Program Project Execution Plan," 16 February 2004.
[9] Nuclear and Radiation Studies Board, Medical Isotope Production without Highly Enriched Uranium (Washington, DC: The National Academies Press, 2009), p. 112, www.nap.edu.
[10] Miles A. Pomper and William C. Potter, "Medical Isotope Production: The U.S. Must Follow South Africa's Lead," Bulletin of the Atomic Scientists, 17 December 2010, www.thebulletin.org; Nicholas Arkhangelskiy and Jeff Chamberlain, RERTR Meeting, 2012.
[11] "Promoting Nuclear Security: What the IAEA is doing," IAEA.org.
[12] "Promoting Nuclear Security: What the IAEA is doing," IAEA.org.
[13] "National Nuclear Security Administration Has Improved the Security of Reactors in its Global Research Reactor Program, but Action Is Needed to Address Remaining Concerns," GAO Report GAO-09-949, September 2009, www.gao.gov.
[14] Jeff Chamberlain, "The Role of International Cooperation in International HEU Minimization," Second Symposium on HEU, January 24, 2012, www.nti.org.
[15] "DOE Needs to Take Action to Further Reduce the Use of Weapons-Usable Uranium in Civilian Research Reactors," GAO-04-807, July 2004, www.gao.gov; Miles A. Pomper, "The 2012 Seoul Nuclear Security summit and HEU Minimization," US-Korea Institute at SAIS, January 2012.
[16] Jeff Galan, "US-Origin Nuclear Fuel Removals," presentation at the Southern States Energy Board, November 2011, www.sseb.org.
[17] "IAEA Safeguards Glossary," International Atomic Energy Agency, 2001, p. 23, www.iaea.org.
[18] U.S. Department of Energy, FY 2013 Congressional Budget Request: National Nuclear Security Administration, DOE/CF-0071, Vol. 1 (Washington D.C.: DOE, February 2012), pp. 421-422.
[19] "Highly Enriched Uranium Disposition," National Nuclear Security Administration, accessed 12 April 2011, http://nnsa.energy.gov.
[20] For information on the U.S. program, see "Reducing Excess Stockpiles: U.S. Highly Enriched Uranium Disposition," in Securing the Bomb 2005, www.nti.org.
[21] "Global Fissile Materials Report 2010," International Panel on Fissile Materials, 2010, p. 34, www.fissilematerials.org.
[22] Steven Aftergood and Frank N. von Hippel, "The U.S. Highly Enriched Uranium Declaration: Transparency Deferred but not Denied," The Nonproliferation Review 14/1, 2007, pp. 149-161.
[23] Mohamed El-Baradei Statement, Treaty on the Non-Proliferation of Nuclear Weapons 2005 Review Conference, United Nations, New York, 2 May 2005, IAEA.org.
[24] Statement by H.E. Nurbek Jeenbaev, Permanent Representative of the Kyrgyz Republic to the UN at the 2005 Review Conference of the Parties to the Treaty on the Nonproliferation of Nuclear Weapons (New York, 3 May 2005), www.un.org.
[25] Norwegian Position Paper, Treaty on the Non-Proliferation of Nuclear Weapons, 2005 Review Conference, 5 May 2005.
[26] Final document of the 2010 Review Conference of the Treaty on the Nonproliferation of Nuclear Weapons, May 2010, p. 29, www.reachingcriticalwill.org.
[27] "Highlights of the National Commitments Made at the Nuclear Security Summit," The White House, 13 April 2010, www.whitehouse.gov.
[28] "The Seoul Nuclear Security Summit Communiqué," March 27, 2012, www.un.org.