This report results from a congressionally mandated study (P.L. 112-239, Section 31781) to assess the current status of and progress toward eliminating highly enriched uranium (HEU)2 use in fuel for civilian research and test reactors. The complete study charge is given in Box 1.1.
The continued presence of HEU in civilian installations such as research reactors3 poses a threat to national and international security. Minimization, and ultimately elimination, of HEU in civilian research reactors worldwide has been a goal of U.S. policy and programs since 1978. Today, 74 civilian research reactors around the world, including 8 in the United States, use or are planning to use HEU fuel. Encouragingly, since the last National Academies of Sciences, Engineering, and Medicine (the Academies) report on this topic in 2009 (NRC, 2009), 28 reactors have been either shut down or converted from HEU to low enriched uranium (LEU) fuel.4 Despite this progress, the large number of remaining HEU-fueled reactors demonstrates
1 The American Medical Isotopes Act of 2012, http://www.gpo.gov/fdsys/pkg/PLAW112publ239/html/PLAW-112publ239.htm.
2 HEU is defined as uranium enriched to 20 percent or greater in the isotope 235U; weapon-grade HEU (W-HEU) is enriched to 90 percent or greater.
3 This report refers to “research and test reactors” as simply “research reactors.” The U.S. Nuclear Regulatory Commission (USNRC) differentiates between a research and test reactor by thermal output power level; research reactors operate at 10 megawatts or less, and test reactors operate above this level. For the purposes of this report, this differentiation is not important. For more information on the USNRC’s regulation of research and test reactors, see http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/research-reactors-bg.html.
4 LEU is uranium enriched to less than 20 percent in the isotope 235U.
that an HEU minimization program continues to be needed on a worldwide scale.
Research reactors are important to the U.S. and global scientific and technical enterprise. They fulfill important missions ranging from education to basic scientific research to medical isotope supply to patient treatment. Other mechanisms for producing neutrons with similar spectra and flux levels to fulfill these missions do not currently exist (Finding 3). These characteristics guarantee the enduring importance of research reactors in science and technology.
Most research reactors in use around the world are many decades old. Many, including all of the high performance research reactors (HPRRs5) operating in the United States, were commissioned in the 1950s and 1960s; the youngest U.S. HPRR is more than 45 years old. Additionally, the U.S.based HPRRs (USHPRRs) are managed by different offices and agencies. Given the ages of these reactors and evolving needs for neutrons, it is not surprising that the missions of some USHPRRs have evolved. The capabilities of these reactors have accommodated changing user needs and an expanded user base, with the consequence that reactors are sometimes not specifically designed for current missions (Finding 4). No new USHPRRs are currently planned; therefore, for the foreseeable future, maintenance and relicensing of the existing reactors is the only viable option for continued reactor availability. The situation is quite different in Europe, where the youngest HPRRs are as little as 12 years old and where additional research reactors are under construction or active planning. In short, European countries are developing and executing a strategy for ensuring the continued availability of HPRRs to meet their future needs; the United States has no such strategy and seems to expect the current HPRRs to operate indefinitely.
Conversion of the remaining research reactors has proven to be significantly more difficult than envisioned when the U.S. conversion program began nearly 40 years ago. The nearly 20-year time line to conversion that is currently estimated for some HPRRs is much longer than originally estimated and coincides with their relicensing around 2030. At that time the USHPRRs will be on average 65 years old. Because of the coincidence of relicensing, conversion, and aging issues of the current USHPRRs, it is reasonable to compare the benefit of converting/retrofitting the current fleet of USHPRRs against designing and building new research reactors that use
5 HPRRs are, in the most general sense of the definition, reactors for which available LEU fuels do not currently exist to support conversion without an effect on their performance (Roglans, written communication, September 2015). Editorial note: This report follows convention used by the Department of Energy (DOE) and others by not hyphenating “high performance” in the phrase “high performance research reactors.”
LEU fuel and address the critical missions that current reactors support. In fact, the Department of Energy (DOE) has performed such an analysis, but DOE has authority for one-half of the USHPRRs and this analysis was focused on DOE missions (e.g., research reactors to support the next generation nuclear energy systems). The Office of Science and Technology Policy has the authority to consider an analysis of all USHPRRs and the variety of missions they support. Nevertheless, there is no overarching, long-term, cross-agency strategy for meeting enduring U.S. needs for research reactors (Finding 5).
Recommendation 1: The U.S. Office of Science and Technology Policy should take the lead in developing a 50-year interagency strategy that enumerates and evaluates the importance of anticipated U.S. civilian needs for neutrons and provides a roadmap for how these can best be provided by reactors and other sources that do not use highly enriched uranium.
There are significant technical and nontechnical obstacles associated with eliminating HEU from civilian research reactors. Most of the technical obstacles relate to developing and qualifying very high-density fuel (based on a uranium-molybdenum [UMo] alloy) needed to convert the remaining HPRRs. The timescale for designing, producing, qualifying, and using such fuel to complete conversions is now estimated to be around 15–20 years for U.S. research reactors, resulting in nearly two decades of continued reliance on W-HEU. The fuel type being pursued by the United States faces more manufacturing challenges for qualification than the type being developed in Europe and South Korea and, therefore, the development and qualification time lines have higher uncertainty and risk (Finding 6).
A high-density LEU dispersion fuel is being pursued by a consortium of European countries and separate efforts in South Korea and Russia. In terms of microstructure and manufacturing processes, the new LEU dispersion fuel, also a UMo alloy, is similar to existing, qualified fuels. However, the U.S. fuel development effort requires fabrication methods qualitatively different from those used for any existing fuel. This approach, if successful, will yield a very high-density LEU fuel that can be used in all USHPRRs.
The fuels under development in Europe and South Korea might be suitable for the conversion of some but not all USHPRRs.6 Furthermore, the fuel
6 USHPRRs with lower power density requirements include University of Missouri Research Reactor (MURR), Massachusetts Institute of Technology Reactor (MITR-II), and the Neutron Beam Split-Core Reactor (NBSR); the USHPRRs with the highest power density requirements are the Advanced Test Reactor (ATR) and its critical assembly (ATR-C) and the High Flux Isotope Reactor (HFIR).
being qualified by South Korea may offer modest acceleration in the anticipated conversion time lines for USHPRRs with lower power density requirements. If these fuels become successfully qualified, then they can be used to mitigate technical risks in the current U.S. monolithic fuel development time line by providing alternate high-density LEU dispersion fuel options for those USHPRRs with lower power density requirements (Finding 8).
Recommendation 2: Despite a timescale that is now understood to be much longer than initially expected, the United States should continue to develop a very high-density, low enriched uranium (LEU) fuel to convert as soon as possible the existing generation of U.S. high performance research reactors to LEU operation as well as to enable a new generation of research reactors.
Recommendation 3: The United States should closely monitor the development of low enriched uranium (LEU) dispersion fuels (e.g., in Europe, South Korea, and Russia) and evaluate their possible use as backup options for U.S. high performance research reactor conversions if there are unexpected delays in the development of the U.S. monolithic fuel.
The economic viability of high-density LEU fuel is highly uncertain and is a source of significant concern to the operators of HPRRs worldwide (Finding 7). Not enough is known about the final manufacturing processes for these fuels, particularly for UMo monolithic fuel, including process complexity and yield, to be able to make definitive estimates of fuel cost. However, assuming the current cost model for research reactor fuel continues, one thing is clear: fixed costs associated with the maintenance of a high-density LEU manufacturing line are expected to be borne by the reactor facilities that use the fuel. If the number of research reactors using high-density LEU fuel is markedly different from the number using today’s HEU fuel, or if even one of the reactors that uses large quantities of fuel does not convert, then the cost of high-density LEU fuel could easily become prohibitive for the remaining reactors.
Although DOE has been actively engaged in reactor conversions and shutdowns around the world, there has not been a conversion of a civilian research reactor to LEU fuel in the United States since 2009. This lack of conversions, combined with the long time line for conversion of the USHPRRs, could call into question the level of U.S. commitment to conversion of its own reactors. Based on rough approximations made by the committee, all HPRRs in the United States and Europe but one could probably convert using existing, qualified LEU silicide fuel at enrichments of 45 percent or less without significant impact to the missions they sup-
port; some of the reactors could use fuel enriched to less than 30 percent. European HPRRs have performed calculations to assess feasibility of this option, but the United States has not (Finding 9).
Recommendation 4: To achieve the goal of using as little highly enriched uranium as possible during the many years that it will take to design and qualify appropriate low enriched uranium (LEU) fuel, the United States should pursue an interim solution that reduces the civilian use of weapon-grade material.
- During this interim period, high performance research reactors should use dispersion silicide fuel enriched to the lowest practical level, which can be produced with technologies already known to be reliable. The precise enrichment level can be quickly determined by a focused, small-scale study.
- The United States should downblend the remaining 20 metric tons of highly enriched uranium (HEU) designated for civilian research reactor use to this lowest practical enrichment level as soon as it has been determined.
- The interim solution should be pursued in a way that does not compromise the long-term goal of eliminating HEU usage in civilian applications.
Although the obstacles to conversion of HPRRs are predominantly technical, the obstacles to the conversion of other research reactors are frequently nontechnical. One country of particular concern is Russia. Despite considerable reductions in the number of civilian research reactors fueled by HEU since 2009, Russia remains home to greater than 40 percent of the HEU-fueled civilian research reactors identified by this committee. Many are critical and subcritical assemblies which can pose particular risk because the fuel is lightly irradiated and there can be large amounts of fuel stored on site. Notably the number of these types of facilities has significantly decreased during the past few years. Nearly all research reactors located outside of Russia that use Russian nuclear fuel have been converted to LEU, with most of the Russian-origin HEU returned to Russia. Converting most of the remaining Russian research reactors is possible with existing or soon-to-be-qualified LEU fuel. However, conversion of its domestic research reactors is not a high national priority for Russia (Finding 10).
The Russian-U.S. collaboration on research reactor conversion that progressed for several decades has all but ceased during the past year. Funding of conversions for Russian domestic research reactors has been drastically reduced. Previously, the United States (through DOE) funded these conversions, but the U.S. and Russian governments have mutually ended this program and only limited interaction remains. One particularly
valuable aspect of these collaborations was the development of long-term relationships between U.S. and Russian scientists (Finding 12). Russia is, however, very interested in exporting its nuclear technology, including LEU fuel and radioisotopes. This may be a Russian priority that can be leveraged in continuing bilateral efforts on HEU minimization. Given current international relations in general, and the state of U.S.-Russian relations in particular, the United States and the international community have little influence on Russian prioritization of its domestic civilian research reactor conversions (Finding 13).
Recommendation 5: The United States should encourage and facilitate periodic workshops and meetings that especially engage U.S. and Russian scientists and engineers to continue scientific exchanges and interactions that formed the basis for previous progress in highly enriched uranium (HEU) minimization. These interactions should also seek areas of mutual interest that would result in HEU minimization, jointly study the risks and benefits of low enriched uranium conversion, and identify possible collaborations.
The U.S. Office of Conversion, a component of the recently formed Office of Material Management and Minimization (M3),7 is focused on surmounting the significant technical challenges associated with converting the HPRRs as well as completing the conversion of the remaining HEU-fueled reactors worldwide. The conversion program currently reports annual progress toward its goal of eliminating HEU from civilian research reactors by counting the number of reactors using HEU that have either converted or shut down.8 This metric does not fully convey progress toward minimizing and eliminating the use of HEU fuel for research reactors for three reasons. First, the program definition of a “converted” reactor is one in which at least one LEU fuel element has been inserted. In the case of some reactors, HEU fuel remains in the reactor until the conversion is complete.9 Second, reporting the number of reactors converted or shut down
7 The United States has had a research reactor conversion program since 1978, but it has undergone a number of reorganizations (see Chapter 2). The most recent change was the dissolution of the Global Threat Reduction Initiative (GTRI) and its Convert Program and the creation of M3 and the Office of Conversion.
8 These annual reports of progress are made to Congress through budgetary request documents. Additionally, the Office of Conversion routinely reports its progress at annual international meetings such as the Reduced Enrichment for Research and Test Reactors conference or the European Research Reactor Fuel Management conference.
9 For some reactor cores, fuel replenishment takes place one fuel element at a time. Fully converting a core to LEU fuel can take years, depending on the refueling schedule of the reactor.
does not measure how much HEU fuel is in place at research reactor sites, whether in core or in storage (fresh or spent fuel, respectively). Third, the largest fraction of HEU annual consumption is made by a small number of reactors. No metric provides data on the reduction of the annual consumption of HEU in civilian research reactors.
Recommendation 6: The Material Management and Minimization’s Office of Conversion should augment its annual progress reports to include the following:
- Identification of the number of conversions in progress (i.e., with at least one low enriched uranium [LEU] assembly inserted into the core);
- Identification of the number of conversions completed, including the removal of highly enriched uranium (HEU) fresh and spent fuel from the site;
- Separate reporting of reactors that have fully converted to LEU from those that have been verified as shut down;
- Reduction of the aggregated inventory of HEU fuel at reactor sites (including shutdown reactors) attributable to the conversion program; and
- Reduction in the amount of weapon-grade HEU fuel shipped to HEU-fueled research reactors during the reporting period attributable to the conversion program.
The technical setbacks and increasingly longer time lines for conversion of USHPRRs emphasize the need to develop a robust project management strategy along with regular independent technical and programmatic evaluations (Finding 17). Review teams have been established by the M3 Office of Conversion in recent years to guide program management decisions. Three review teams have been formed to focus on strategic review, cost, and fuel development. Of these three teams, only the fuel development team reviews technical aspects of the program (and its charge is limited to the fuel development pillar). The committee found that the review of fuel development, although technically sound, was not performed by a team with the appropriate independence and institutional diversity needed for critical evaluation and feedback (Finding 18).
Recommendation 7: In-depth independent technical review of each aspect of the fuel life-cycle (from fuel development, fabrication, recycling, and spent fuel management), as well as integration of the technical components, should be conducted to ensure that the newly instituted risk and systems analysis capabilities within the Material Management and Minimization Office of Conversion develop into
robust project and risk management. These reviews should be conducted by qualified, independent, and diverse external experts.
The M3 Office of Conversion has recently initiated a number of important changes in its management of the program, but the impact of these changes could not yet be assessed.