Efforts to convert civilian research reactors from weapon-grade highly enriched uranium (HEU) to low enriched uranium (LEU) fuels are taking significantly longer than anticipated, says a report from the National Academies of Sciences, Engineering, and Medicine. The report calls for the federal government to take immediate steps to convert civilian research reactors currently using weapon-grade HEU fuel to a lower-enriched HEUfuel while awaiting the qualification of new LEU fuel. Additionally, the White House Office of Science and Technology Policy (OSTP) should develop a long-term strategy to evaluate future civilian needs for neutrons to meet U.S.science and technology objectives and how these could best be provided by research reactors and other sources, said the committee that conducted the study and authored the report.
The NAS reports that since 1978, U.S. policy and reactor conversion programs have worked to minimize, and phase out where possible, the use of HEU in fuel for civilian research reactors. These reactors use weapon-grade HEU — which is enriched to 90 percent or greater uranium-235 — to produce neutrons vital to research and other civilian applications. Eliminating HEUuse in these reactors by converting them to fuel containing LEU — enriched to less than 20 percent uranium-235 — would reduce the risks that this material could be diverted for illicit use, for example in nuclear explosive devices. Worldwide, over 90 civilian research reactors have been converted to LEU fuel or shut down. However, 74 civilian research reactors, including eight in the United States, continue to use HEU fuel.
Obstacles for converting the remaining civilian research reactors from HEUto LEU fuel are both technical and nontechnical, the report notes. Some reactors using HEU fuel require the successful development of new, higher-density LEU fuel to maintain performance after conversion; these reactors are referred to as high performance research reactors. For others, progress toward conversion is hindered by nontechnical obstacles such as economic and political motivations.
The United States is developing high-density LEU fuel that could be used to convert all of the currently operating U.S. high performance research reactors, but manufacturing this fuel will be challenging, the report notes. Somewhat lower density LEU fuels in development in Europe and South Korea might be suitable for the conversion of some, but not all, U.S. high performance research reactors. The Office of Conversion, which is part of theU.S. Department of Energy’s (DOE) Material Management and Minimization Office, should monitor the development of European and South Korean LEUfuels for possible use as a backup option if there are unexpected delays in theU.S. fuel development effort.
DOE now estimates that it will take another 20 years to convert the remainingHEU-fueled civilian research reactors throughout the world and over fifteen years to convert those in the United States to LEU fuel. The report recommends an interim solution to accelerate the removal of weapon-gradeHEU from civilian applications until new high-density LEU fuel is available: convert the high performance research reactors in the United States and Europe using an existing, qualified HEU fuel with uranium-235 enrichments of 45 percent or less. Nearly all of the high performance research reactors currently operating with HEU fuel could use this intermediate fuel without significant impact to their missions, the report estimates.
NAS notes that the current fleet of aging U.S. research reactors fueled by HEUis managed by a number of different universities and U.S. government agencies. DOE, for example, has authority over only half of these reactors. Therefore, the report recommends that OSTP take the lead in developing a 50-year cross-agency strategy to ensure the future availability of U.S. neutron sources, potentially including civilian research reactors.
Over 40 percent of the remaining HEU-fueled civilian research reactors in the world are located in Russia. However, conversion of its domestic reactors has both technical and nontechnical obstacles: Russia has several high performance research reactors and conversion is not a high priority for the Russian government. U.S. collaborations with Russia on research reactor conversion have all but ceased during the past year, and U.S. funding to support conversion of Russian civilian research reactors has decreased. The report recommends that the United States encourage and facilitate periodic workshops and meetings to bring Russian and U.S. scientists together to jointly study the risks and benefits of LEU conversion and identify opportunities for collaborations.
The report recognizes the challenges faced by the DOE’s Office of Conversion, which is responsible for managing the U.S. government’s LEU fuel development and civilian research reactor conversion efforts. The conversion program is expected to operate for several more decades based on current time lines and has many technical risks. This program can be strengthened by utilizing qualified, independent, and diverse external experts to conduct technical reviews of all aspects of the program, including LEU fuel development and fabrication, material recycling, and spent-fuel management, the report says.
NAS says that the American Medical Isotopes Production Act of 2012 mandated that the Academies carry out an assessment of the progress being made by DOE and others to eliminate all worldwide use of HEU in research reactor fuel and medical isotope production facilities. It was later determined that two separate studies would be conducted to support this mandate. The current report examines the status of conversion of research reactors to LEU. Another report examining the status of medical isotope production without HEU targets will be issued later this year.
— Read more in Reducing the Use of Highly Enriched Uranium in Civilian Research Reactors (National Academies Press, 2016)