IPFM International Panel on Fissile Materials

[This entry is drawn from Chapter Eight of the 2006 Global Fissile Material Report: "Global Cleanout of Highly Enriched Uranium." The printed version includes endnotes and, in some cases, additional figures. Entries are updated to reflect current data.]

Global Cleanout of Highly Enriched Uranium

Major efforts are being made to upgrade the security of the sites where fissile material can be found. The United States, which has taken a leadership role in this respect, launched in 1993 a cooperative "materials, protection, control and accounting" program that is currently spending more than $400 million per year on security upgrades of sites with fissile material in the former Soviet Union (such as shown in Figure 1) . The status and progress of the various efforts have been well summarized by the Project on Managing the Atom at the Harvard Kennedy School and by RANSAC.

Increasing the security of fissile materials in storage is a vital undertaking. In the long run, however, the most effective approach to the risk of diversion or theft is to eliminate the material from as many locations as possible. This section discusses the feasibility of a global cleanout of civilian highly enriched uranium, still held at more than a hundred civilian sites worldwide -- primarily in research-reactor fuel cycles.

These cylinders in a Russian institute’s storage facility contain huge quantities of plutonium and highly enriched uranium. The portability of the cylinders increases the risk of theft. (Source: Strategic Plan 2006, Office of International Material Protection and Cooperation, National Nuclear Security Administration, U.S. Dept. of Energy, 2005).

During the 1950s and 1960s, as part of their competing Atoms for Peace programs, the United States and the Soviet Union built hundreds of research reactors domestically and for export to more than 40 other countries. In response to demands for longer-lived fuel and maximum reactor performance, export restrictions on fissile materials were relaxed and most of these reactors shifted to fuel containing weapon-grade HEU. As a result, HEU is still used today as a research-reactor fuel in about 140 civilian reactors worldwide. In addition, HEU often remains at sites of shut down, but not yet decommissioned reactors. Taken together, the global inventory of civilian HEU reactor fuel is very roughly 50 metric tons, widely distributed around the globe (see Figure 2 and IPFM Fissile Material Atlas). According to a U.S. Government study, in 2004 there were around the world at least 128 sites associated with research reactors with at least 20 kilograms of HEU.

FIGURE 2. Civilian HEU is still distributed around the globe in large quantities. International efforts to convert HEU-fueled research reactors to low-enriched uranium have reduced the annual demand of the material by about 250 kg of HEU per year. Yet, there are still more than 100 sites worldwide, where the material can be found in significant quantities at operational or shut down but not yet decommissioned HEU-fueled reactors.
Click on figure to go to IPFM Fissile Material Atlas and explore interactive map.

Reactor Conversion to Low-Enriched Fuel

Since 1978, an international effort has been directed at converting HEU-fueled reactors to low-enriched fuel in the Reduced Enrichment for Research and Test Reactor (RERTR) program. Almost all new reactors designed since that time use LEU fuel. By the end of 2005, the RERTR program had converted or partially converted 42 research reactors. The world's remaining research reactors consume about 1,000 kilograms of HEU per year -- virtually all supplied by the United States and Russia. RERTR program analysts believe that 41 more reactors can be converted using existing LEU fuels. Of the Western-designed reactors, about ten, which consume the bulk of the HEU, cannot be converted, however, until advanced LEU fuels are developed. These research reactors have compact, high-powered cores designed to maximize neutron intensity for testing reactor fuels and materials to high irradiation levels and for neutron-scattering measurements.

The primary approach of the RERTR program has been to develop 20-percent enriched LEU fuels in which uranium-238 is added to dilute the U-235 in the fuel. As a result, the concentration of uranium in the nuclear fuel is increased approximately five-fold. Fortunately, the uranium densities in the HEU fuels that have to be replaced are mostly quite low: 3-6 percent of the density of solid uranium -- or about 0.6-1.2 grams uranium per cubic centimeter (g/cc). The most advanced fuel commercialized thus far has an effective uranium density of 4.8 g/cc. Because of unexpected poor irradiation performance of a candidate fuel with a higher uranium density that was to be commercialized in 2006, the expected availability of fuels with the densities required to convert research reactors with compact, high-powered cores has slipped to around 2010. The most promising fuel currently under development, solid uranium alloyed with molybdenum, has a uranium density of more than 16 g/cc and could be used to convert almost all remaining high-powered research reactors. If these fuels can be successfully developed and qualified, the main technical obstacle for a global HEU cleanout would be removed.

Decommissioning Unneeded HEU reactors

Most of the world's aging fleet of HEU-fueled reactors is no longer needed – and the total number of these research reactors worldwide could be reduced, in principle, from hundreds to tens. Just shutting down an HEU-fueled reactor is not sufficient, however. To complete the cleanout, the HEU fuel must be removed, i.e. the reactor must be "decommissioned". To make a decommissioning program attractive in Russia and elsewhere, it may be necessary for concerned countries to invest in strengthening the surviving research-reactor centers. Such assistance should be conditioned, however, on the management being willing to allow research groups from decommissioned facilities to become "users groups" on a nondiscriminatory basis. Such arrangements are standard in the United States and Western Europe but are still foreign to Russia, where, if a group does not have its own reactor, it does not have an opportunity to do experiments. Russia accounts for about one third of the world's HEU-fueled reactors and probably over one half of the HEU associated with civilian HEU-fueled reactors.

Beyond RERTR: Other Types of HEU Reactors

Conversion efforts have thus far been focused almost entirely on HEU-fueled reactors that are refueled regularly and therefore can be converted by refueling them with LEU instead of HEU fuel. This excludes critical assemblies and pulsed-power reactors that have lifetime cores that can contain huge quantities of barely-irradiated HEU (see Figure).

The BFS2 (shown) and BFS1 critical assemblies in Obninsk Russia share ton quantities of HEU and plutonium – mostly in the form of tens of thousands of small disks that are stacked up in columns to simulate fuel of different enrichments and mixes of uranium and plutonium (from Institute of Physics and Power Engineering website).		The shutdown Zero Power Physics Reactor at the Idaho National Laboratory (shown at right) similarly has ton inventories of plutonium and HEU associated with it that are loaded into drawers (from Argonne National Laboratory website).

There are about 45 HEU-fueled critical assemblies worldwide that are listed by the IAEA as "operating". In 2005, the IAEA hosted a consultation on the future need for critical assemblies. The consultation concluded that, given the greatly increased capabilities of computer simulations, and the large numbers of criticality "benchmark" experiments that have been performed, there should be joint workshops of reactor designers and critical- and sub-critical assembly experts to consider which existing facilities are no longer needed and to modernize the facilities that are still needed. Decommissioning the redundant critical assemblies would be much less costly than decommissioning other types of research reactors since their uranium fuel is barely irradiated.

There are also about 20 HEU-fueled pulsed reactors that similarly contain large inventories of barely irradiated HEU and could similarly be either decommissioned or converted to LEU. The All-Russian Institute of Experimental Physics (VNIIEF) in Sarov, Russia has proposed a feasibility study on the conversion of the BIGR pulsed reactor, which has an HEU inventory of 833 kilograms of weapon-grade uranium.

Russia also uses HEU fuel in seven nuclear-powered icebreakers. LEU fuel has been developed for a proposed floating nuclear power plant that would be powered by a reactor derived from one of the reactor types (the KLT-40) used on the icebreakers. The privately funded Nuclear Threat Initiative has offered to support the adaptation of this fuel for the icebreakers.

Converting HEU-fueled military propulsion reactors would further extend the scope of the global cleanout initiative discussed in this section. China is believed to use LEU -- or HEU fuel barely above 20 percent enrichment -- in its submarines and France is shifting to LEU fuel. U.S. and U.K. naval reactors are fueled with weapon-grade uranium but are unlikely to be converted since they mostly have lifetime cores. Future naval reactors could be designed to use LEU but, in 1995, the then director of the U.S. Naval Nuclear Propulsion program argued that LEU-fueled reactor cores using the same fuel technology would have to be three times larger in volume than cores fueled with weapon-grade uranium and that this would lead to a ten percent cost increase in the Navy's new Virginia-class attack submarines.

Because of the highly classified nature of naval-reactor fuel design, it has been impossible for independent analysts to review this conclusion. However, approaches by which such cost increases could be mitigated have been proposed, including adopting a compact system design in which steam generators are inside the reactor pressure vessel. This design has allowed France to deploy the world's smallest nuclear-powered attack submarines (the Rubis class). The impact of a larger reactor core should be relatively small on the cost of larger U.S. nuclear-powered ships, such as ballistic-missile submarines and aircraft carriers.

Russia's submarines reportedly use HEU fuel with enrichments ranging from 21 to 45 percent. This, along with the fact that Russia's submarine, like France's are refueled at five to ten year intervals, should make it easier to convert them to LEU.

Toward a Comprehensive HEU "Global Cleanout" Program

In 2004, the U.S. Department of Energy responded to Congressional concern about how slowly the HEU-cleanout programs were moving by combining its reactor-conversion and spent HEU-fuel take back efforts into a Global Threat Reduction Initiative (GTRI) program.

This initiative would achieve complete elimination of HEU-fuel shipments to research reactors outside Russia by 2014. Critical assemblies and pulsed reactors containing huge quantities of barely irradiated uranium are not yet formally being targeted, however, and Russia has not yet agreed to convert or decommission its own HEU-fueled reactors.

What is needed is a broader international effort to: (1) decommission HEU-fueled research reactors that are no longer needed, (2) accelerate the conversion of operating research reactors for which replacement LEU fuel is available, (3) assure that fuels are developed to convert all the remaining HEU-fueled research reactors that are still needed, and 4) maximize the security and minimize inventories and enrichments of any HEU-fueled reactors that remain in operation.

Consideration also needs to be given to making more attractive the effort to decommission or shut down little-used HEU-fueled reactors by concentrating research-reactor or accelerator neutron services in regional centers of excellence that are available on a nondiscriminatory basis to user groups from institutes whose research reactors have been shutdown.

The key countries whose cooperation is required are those that have built and exported or operate high power HEU-fueled research reactors, large critical assemblies, or pulsed reactors. The United States, Russia, United Kingdom, France, China, Germany and Japan account for more than 90 percent of the global civilian HEU inventories and demand. Their joint engagement in an accelerated conversion and clean-out effort would likely bring along the other countries that receive or have received fuel from the major HEU suppliers.

The reluctance of Russia's government to give this effort high priority domestically -- at the same time that the leading Russian nuclear institutes have been asking for funding for projects to convert and decommission their HEU-fueled reactors illustrates the importance of working directly with the institutes as well as on a government-to-government level. This "bottom-up" approach, in which Russian institutes help get their government's approval, has been key to virtually all successful cooperative nuclear security initiatives. Unfortunately, Russia's security services increasingly have been blocking collaboration between Russia's nuclear institutes and U.S. Government programs working on HEU cleanout. This makes it even more important for other countries to become more seriously engaged with this agenda.