4
Managing Proliferation Risks and Maintaining Missions
The final session (Session 4) of the symposium focused on possible futures for research reactors and how the proliferation risks associated with them can be managed. Five briefings presented at the symposium (Appendix A) on these topics are summarized in this chapter:
• A. Zrodnikov (Rosatom Institute for Physics and Power Engineering) discussed missions for future research reactors (Zrodnikov, 2011);
• R.P. Kuatbekov (Dollezhal Scientific Research and Design Institute of Energy Technologies [NIKIET]) and P. Lemoine (Commissariat à l’Énergie Atomique) provided Russian and French perspectives on future research reactor plans and designs (Kuatbekov, 2011; Lemoine, 2011); and
• A.N. Chebeskov (Rosatom Institute for Physics and Power Engineering) and Robert Bari (Brookhaven National Laboratory) provided Russian and U.S. perspectives on proliferation risks associated with highly enriched uranium- (HEU-) fueled research reactors (Bari, 2011; Chebeskov, 2011).
Following these briefings, symposium participants engaged in a discussion about future opportunities for the United States and Russia related to research reactor conversion. This discussion is summarized in the last section of this chapter.
FUTURE MISSIONS FOR RESEARCH REACTORS
A. Zrodnikov
Research reactors in the United States and Russia serve a variety of industrial and biomedical missions and enable research in fields such as physics and nuclear engineering. Missions mentioned during the course of the symposium that seem likely to continue include silicon doping, radioisotope production, notably including molybdenum-99, and neutron therapy. It is essential to maintain the capability to meet these research and industrial needs. Other means (e.g., particle accelerators) may be developed in the future for generating some radioisotopes and producing neutron beams, but research reactors will be far more difficult to replace for some other applications. In particular, future research related to nuclear energy and the nuclear fuel cycle will necessitate maintaining and improving current research reactor capabilities in the United States and Russia as well as in other countries. Research reactors are especially needed to conduct basic research for nuclear power development.
Nuclear power generation faces major challenges in the coming decades. Increasing quantities of commercial spent nuclear fuel are being accumulated around the world, and in the long-term, supplies of uranium-235 will begin to decrease. Fast neutron reactors (“fast reactors”) are being studied in the United States and in Russia for their potential to help meet these challenges. Such reactors have the potential to “burn” long-lived actinides in spent fuel and also to produce and operate using plutonium, thereby extending current fuel supplies. However, more research remains to be done on these topics to effectively design the needed facilities and processes.
Beyond the design and testing of future fast reactors, further research could also help to extend the capability of nuclear power plants to meet new tasks. For example, research on heat- and radiation-resistant materials could lead to the deployment of high-temperature nuclear plants to meet the needs of heat-intensive industrial processes, including water desalination, production of synthetic fuels, and hydrogen production. If fossil resources that currently fuel these processes are exhausted, nuclear power will be needed to fill the gap.
Several research problems related to these topics will need to be investigated in the coming decades, including improving the scientific understanding of:
1. Nuclear physics of the interaction of radiation with matter.
2. Radiation damage of metallic and nonmetallic reactor materials.
3. Changes in macroscopic material properties caused by neutron and charged particle irradiation.
Research reactors will also be used in theoretical, computational, and experimental studies on thermo-physical, physical-chemical, corrosion, and physical-mechanical properties of advanced high-temperature coolants, fuel materials, and core structural materials. Moreover, data generated from such studies will help researchers to develop complete nuclear data libraries. This knowledge can be used to develop new nuclear technologies.
Much of the research work involving fast reactors may require capabilities that only a few current research reactors possess. A research reactor with a stationary steady-state fast neutron flux of about 1016 neutrons/cm2-s will be required to support this research.
In the subsequent discussion, Thomas Newton (Massachusetts Institute of Technology [MIT]) agreed that this need for fast neutrons was also true at MIT, and observed that, after conversion, MIT plans to take advantage of the harder neutron spectrum that can be acquired with low enriched uranium (LEU) for fast neutron experiments.
FUTURE RESEARCH REACTOR PLANS AND DESIGNS
R.P. Kuatbekov
Current research reactors are unlikely to meet all needed missions over the next few decades. Many of the currently operating research reactors are ageing, and many missions are projected to grow in importance. Consequently, there is a need to design and build new research reactors. In many cases, particularly for industrial applications, new reactors can be designed from the beginning to use LEU rather than HEU fuel. In other cases, particularly if HEU or even plutonium fuel is required to retain essential performance characteristics, alternative solutions may need to be found to meet nonproliferation goals.
The customers of research reactors do not care whether the reactor is fueled by HEU or LEU—they simply need the results within a reasonable period of time and at reasonable cost. This is true whether the results are completed research, produced materials, or medical isotopes. Consequently, two key qualifications for any new research reactor will be: (1) its ability to meet customer needs; and (2) economic and technical feasibility. With respect to economics, both initial costs and refueling costs of the reactor should be considered to be reasonable by the operator.
In addition, not all countries can afford to perform experiments to optimize fuel for their research reactors, as the United States and Russia have done, and these countries are likely to be a major market for certain types
of research reactors in the coming decades. For these reasons, NIKIET is using reliable and tested fuel types and design solutions in its new research reactor designs. At the same time, proliferation concerns will need to be accounted for.
NIKIET is in the process of designing several new types of LEU-fueled research reactors for industrial, biomedical, training, and research applications. The focus is on the development of pool-type reactors with integrated passive safety systems. Pool-type reactors are convenient for the end-user because they allow for flexibility in the core configuration and easy access to experimental positions. NIKIET uses standardized components in its reactor designs, which reduces costs and simplifies future repairs.
NIKIET is focusing on narrow-purpose reactor designs that optimize each reactor for the customer’s primary end use. There are two end uses that are in highest demand, both mentioned elsewhere in this report: medical isotope production and silicon doping. NIKIET is focusing on optimizing designs of two reactor types for these applications: (1) a low-power (500 kW or less) reactor with natural circulation for silicon doping and (2) a 15 MW reactor for isotope production. Some preliminary computations have been carried out on these reactor designs, and NIKIET plans to improve these designs in the future with additional computations and design work.
It is feasible to meet most customer needs using LEU-based research reactors. Designing reactors to use LEU from the start will not be as much of a challenge as retrofitting some current HEU-fueled reactors. In fact, modifying research reactor cores that were originally designed to use HEU can be very expensive and technically challenging, as illustrated by the case studies in Chapter 3. If the core is optimized during the design stage, then it can simultaneously be optimized for its missions. For example, if the core is initially designed to use LEU fuel, then differences in neutron fluxes and spectra can be accounted for from the initial design stages.
In fact, NIKIET has found that several of its designs for new LEU reactors maintain high flux levels to meet customer requirements and achieve reliable operation with high fuel burnups. NIKIET has now proven computationally that these LEU reactors should operate as well as similar HEU reactors.
On the other hand, some cutting-edge research requires reactors with unique designs or higher fast or thermal neutron fluxes. This research may not be able to be carried out using the types of standardized designs described here. In many cases, unique LEU-fueled reactors can be designed from the start to meet these needs; however, it was suggested by some at the symposium that maintaining a small number of special-purpose reactors fueled by HEU or plutonium could have value, particularly for fast reactor research.
Discussion
N.V. Arkhangelsky noted that a provision formulated at the start of RERTR—backed both by Russia and the United States—acknowledges that there are a number of reactors that will not lend themselves to conversion, including fast breeders. This provision remains in effect. One example of such a reactor is the Russian BOR-60 with an HEU and plutonium core. Before the end of this decade, a multipurpose fast reactor of this type will have been built in Dmitrovgrad. V. Ivanov stated that this reactor must also be viewed as unique or qualifying for special treatment, because the work done there will be important to future advances in nuclear technology.
Another participant noted that very few reactors of such unique types are likely to be needed. Several delegates at the symposium suggested that large international centers could be used to house a small number of research reactors operating using HEU or plutonium. These high-performance reactors would be pursued on an international basis, making adequate capacity available for the international research community. This approach could eliminate the need for the United States and Russia to duplicate their capabilities in this area and allow top-quality personnel and the highest standards of physical protection and materials protection, control, and accounting to be focused at a small number of sites.
NEW RESEARCH REACTOR CASE STUDY: THE JULES HOROWITZ REACTOR
P. Lemoine
The Jules Horowitz Reactor (JHR) is a 100 MW multipurpose materials testing reactor that was commissioned to replace another reactor, OSIRIS, which was built in the 1960s. JHR was initially designed to operate with a new high-density LEU fuel; however, because of difficulties in the development and qualification of this fuel, the reactor will begin operation with HEU fuel instead as described in the paragraphs to follow.
The JHR fuel elements consist of eight circular rings of curved fuel plates, each 1.37 mm thick (see Figure 4-1). The fuel elements have a 98 mm external diameter and a 600 mm active height. The nominal hydraulic gap (“coolant gap” in Figure 4-1) between the fuel plates is 1.95 mm; light water, which streams upward through the gap at a speed of 15 meters per second, is used for both cooling and moderating the core.
The core can contain 34 to 37 fuel elements and has up to 10 experimental positions (see Figure 4-2). The designed neutron fluxes are 5.5 × 1014 fast neutrons per square centimeter per second (n/cm2-s) in the core and up to 4.5 × 1014 thermal n/cm2-s in the reflector.
FIGURE 4-1 Schematic illustration of a JHR fuel element. The 1.37-mm-thick fuel plates form eight concentric rings, with coolant gaps of 1.95 mm between the plates. The center of the fuel element contains aluminum filler, a hafnium control rod, or an experimental position. SOURCE: Lemoine (2011).
The reactor was designed in 2002 using a reference fuel of high-density (8 grams uranium per cubic centimeter [gU/cm3]) UMo dispersion LEU fuel. Original plans had called for this fuel—in development under the RERTR program—to be qualified in 2006. In 2004, however, problems with the fuel’s irradiation behavior indicated that it would be unlikely to be available in time for JHR’s completion. At the time of this symposium, UMo dispersion LEU fuel was still under development by the European initiative LEONIDAS, which is supported in part by the U.S. Department of Energy (DOE). Further optimization still needs to be done to qualify this fuel and demonstrate that it will be available at reasonable cost.
JHR still intends to use UMo dispersion LEU fuel when it becomes available. However, for the time being, JHR plans to use a neutronically equivalent uranium silicide (U3Si2) dispersion fuel enriched to 27 percent uranium-235. The higher enrichment of the silicide fuel is intended to balance its lower density (4.8 gU/cm3) relative to UMo dispersion LEU fuel. The neutron-equivalent U3Si2 fuel is currently under qualification. Although this fuel has been used in other reactors, qualification for JHR is needed because its operating level is much higher than the operating levels of other reactors that use this fuel.
FIGURE 4-2 Schematic illustration of the JHR core. The fuel elements are shown in purple. Ten experimental positions are shown in yellow, with seven located in the center of individual fuel elements. Three “triple” experimental positions are available in fuel element positions. The core is surrounded by a beryllium reflector with additional fixed experimental positions and eight cross water channels for mobile devices. SOURCE: Lemoine (2011).
METHODS TO IMPROVE THE ASSESSMENT OF THE RISKS POSED BY HEU-FUELED RESEARCH REACTORS
If research reactors will continue to be needed in the foreseeable future it is important to understand as clearly as possible their risks. As noted previously, conversion of research reactors from HEU to LEU lowers risk. However, some reactors may not be able to be converted, so it is important to understand the risks associated with their continuing operation. This risk goes beyond the reactor itself to involve all facilities and associated infrastructures, including fuel manufacturing; transportation; fresh fuel storage; irradiated fuel storage; and reprocessing or final repository placement.
Robert Bari described two different types of risk associated with research reactor facilities and infrastructures (systems) as follows (Bari, 2011):
• Proliferation risk of an HEU-fueled research reactor’s fuel cycle is associated with the diversion or undeclared production of nuclear material or misuse of technology by a host state seeking to acquire nuclear weapons or other nuclear explosive devices.
• Terrorism risk of an HEU-fueled research reactor’s fuel cycle is associated with the theft of materials suitable for nuclear explosives or radiation dispersal devices and the sabotage of facilities and transportation by sub-national entities and/or non-host states.
The following sections describe two methodologies to structure and improve the understanding of proliferation and terrorism risk: First, assessing the relative attractiveness of various nuclear materials; and second, proliferation risk assessment methods.
Material Attractiveness
A.N. Chebeskov
As noted in Chapter 1, the lack of availability of special nuclear material (SNM) that can be used to build a nuclear weapon is widely agreed to be a major barrier to nuclear proliferation (see Chapter 1). Thus, an essential part of understanding the proliferation risk associated with a research reactor involves understanding how straightforward it would be for a host state or terrorist organization to successfully misuse the reactor’s fuel material.
The attractiveness of a nuclear material from a proliferator’s point of view is determined in large part by a material’s ability to sustain a nuclear chain reaction. Material attractiveness is also influenced by whether it is necessary to process the material to make it usable in a nuclear weapon. To categorize fissile materials qualitatively, four categories (classes) might be used: very attractive, attractive, low attractive, and unattractive.
Several variables are relevant to the attractiveness of SNM. For example, for a given quantity of uranium, its attractiveness is proportional to both its enrichment and its mass. Higher-enriched materials are more attractive than lower-enriched materials; for example, HEU enriched to 90 percent uranium-235 is far more attractive than LEU, which is regarded to be unattractive. Similarly, higher masses are more attractive than lower masses for a given level of enrichment. In general, the higher the enrichment, the less mass is required to obtain an equivalent amount of uranium-235.
Of course, nuclear weapons can be constructed using plutonium as well, but it is difficult to compare the attractiveness of different materials. Different grades of plutonium can be rated relative to one another as reactor grade (less attractive) and weapons grade (more attractive). However, very highly enriched uranium is the most desirable material for a potential proliferator, because of the relative simplicity of constructing a nuclear explosive device using HEU as opposed to plutonium.
As an example, at the MEPhI reactor, the small size and mass of very highly enriched fuel assemblies represent a higher theft risk than heavier power reactor fuel assemblies, especially for fresh fuel assemblies. The uranium contained in the MEPhI fuel assemblies would not need further enrichment to be usable in a nuclear explosive device. For irradiated fuel assemblies this risk is smaller because of the presence of strong radiation.
Risk Assessment
Robert Bari
Quantitative risk assessment has been used successfully to estimate safety risks, for example, at nuclear power plants. However, more research is needed before proliferation and terrorism risks can be effectively estimated using such a methodology. Such risk assessment methods are easier to apply to safety, for several reasons:
• The likelihood of an accident is more easily estimated than the likelihood of a deliberate attack. A deliberate attack depends on the choices of an intelligent adversary, making likelihoods and methods of failure difficult to estimate.
• Inherent features and engineered systems with known characteristics provide safety, whereas both intrinsic (i.e., barriers intrinsic to the technologies themselves) and extrinsic (e.g., guns, guards, gates, safeguards) systems provide security. The effectiveness of some extrinsic measures, particularly those that involve human action, can be difficult to estimate.
• For safety, defense in depth and safety margins are universally embraced.
Workable proliferation risk models still need significant development.
The methodology summarized here is one of several possible approaches and is analogous to the approach developed for the Generation IV Forum: Proliferation Risk and Physical Protection (PR&PP).
To perform an effective risk assessment, it is important to gather a great deal of information about the research reactor facility as well as the country in which it is located. There are many countries with research reactors, each
having its own national and geopolitical interests that could impact the potential for proliferation. In addition, a number of key assumptions need to be considered in the analysis. These include assumptions about potential threats, such as diversion, misuse, breakout, theft, and sabotage; extrinsic factors such as sources of fresh fuel supply, spent fuel disposition, and fuel transportation; and facility design and operational information that impact proliferation risk.1
The assessment itself involves building a range of scenarios by which proliferation could occur; analyzing specific scenarios to determine whether an attempted proliferation was successful and the barriers that were encountered along the way; then using the responses to construct a risk estimate.
The key elements of an effective proliferation risk assessment include:
• Gather information on facility design.
• Define country (or countries) context.
• Establish/define international safeguards design.
• Establish/define physical protection design.
• Define adversary mission success.
• Identify facility targets (for adversary).
• Perform pathway analysis to define potential scenarios for proliferation.
• Evaluate pathways for each threat and measure.
• Assess and interpret results.
Further research will be needed before this type of analysis can be carried out in a dependable way for research reactors. The range of possible scenarios has not been explored in much detail. In addition, combining the information produced by each stage of the analysis described above to produce an overall understanding of risk remains challenging. However, such a risk assessment process can still be worthwhile to perform. In particular, the process itself can provide useful insights, not just the final result.
Discussion
Many measures that can be taken to reduce the risk of proliferation from research reactors are already well known. Some measures mentioned by symposium attendees included avoiding the use of HEU fuel where possible in favor of LEU fuel; maintaining adequate nuclear materials
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1 For example, one facility might require only very few radiation protection measures to isolate nuclear materials, whereas another facility might require more sophisticated measures. These operational characteristics affect the proliferation risk of the facility.
protection control and accountability (MPC&A) and physical protection measures; and using appropriate insider prevention methods, as practical.
Many of the participants at the symposium observed that the principal means of reducing proliferation risk is conversion of research reactors to LEU; however, as noted previously, this may not be possible in all cases. Other participants noted that some risk also accompanies the use of LEU. Consequently, appropriate MPC&A and physical protection measures will continue to be needed, although to a lesser extent than with HEU fuel.
A symposium participant posed a question about the relative priorities between conversion to LEU and better physical protection. In particular, is it possible to compensate for HEU use through improved security? Robert Bari’s reply was that one cannot separate conversion from physical protection. Clearly, maintaining HEU fuel poses a greater risk, but LEU use does not mean zero risk. Richard Meserve clarified that at a gross overview level, conversion lowers risks as well as the costs for physical protection.
FUTURE OPPORTUNITIES FOR THE UNITED STATES AND RUSSIA
Near the close of the symposium, participants were asked to summarize important ideas that had been mentioned over the preceding three days and to identify potential future opportunities for both the United States and Russia on the conversion of research reactors from HEU to LEU fuel. During this discussion, many key points were brought up by individuals in attendance at the symposium. These points include the following:
• Many symposium participants from both the United States and Russia emphasized the importance of reducing and, where possible, eliminating the use of HEU in research reactor fuel. Over the past few decades, the trend in research reactor development—as well as in civilian applications as a whole—has been to reduce the use of HEU.
• Research reactors currently serve important purposes for research and industry, and they will to continue to serve important purposes into the future. In some cases, accelerators or other sources of neutrons could be used to replace research reactors for medical isotope production and other applications. However, for scientific research, some types of irradiation phenomena, and advanced fuel cycle work, research reactors will continue to be invaluable into the foreseeable future. Several workshop participants stated that these reactors must continue to operate safely and cost effectively and fulfill their missions in ways that meet the needs of customers.
• Collaboration between the United States and Russia on conversion of research reactors will continue to be essential and fruitful. Daniel Wachs observed that past collaborative U.S.-Russian work on fuel development has provided opportunities to advance conversion of both countries’
reactors; he stated that the cross-fertilization of ideas, lessons learned, and technological advances has been helpful and should continue to be encouraged. In addition to technical collaboration, one participant observed that there is significant potential for collaboration on the regulatory aspects of conversion as well. Alexander Adams and V. Bezzubtev noted that Russia will face many challenges in regulating its to-be-converted reactors; the United States has previously faced many similar challenges and may have helpful advice for Russia on this issue.
• The United States and other nations have been able to convert research reactors to LEU fuel while maintaining performance required for key missions, e.g., research as well as medical and industrial applications. H.-J. Roegler observed that prior to conversion of many research reactors in Europe there were a number of concerns about maintaining needed functionality after conversion. However, in the end, the performance of many research reactors was improved as a result of the conversion process through design changes and better understanding of reactor behavior. P. Adelfang added that an analogy might be made to molybdenum-99 production. In 2001, Argentina’s Cómision Nacional de Energía Atómica (CNEA) made the decision to convert its domestic production from HEU targets to LEU targets. At that time, it was considered to be infeasible to produce molybdenum-99 in significant quantities using LEU; however, CNEA showed that it could be done. After nine years it has become abundantly clear that high-quality molybdenum-99 production is possible with LEU targets.
• The economic and performance challenges associated with conversion are likely to be surmountable, particularly with government assistance and the involvement of reactor operators and customers. Research reactor conversions have been successfully completed in many countries, but many of these efforts would have been unlikely to occur without U.S. government support. B. Myasoedov and Jeffrey Chamberlin agreed that government involvement is critical to future conversion successes in Russia and the United States. Jordi Roglans noted that governments’ decisions regarding future HEU use would likely be influenced by the potential for economic and other upheavals if a terrorist event involving HEU occurred related to research reactors or otherwise.
• Some facilities may not be easily convertible to LEU fuel, including fast reactors, fast critical assemblies, reactors with small core volumes, and reactors with high specific power per unit volume of active core. The feasibility of conversion depends to some extent on policy choices by the host nation’s government. Several workshop participants suggested that one way of minimizing the use of HEU for essential or unique missions would be to create major international nuclear centers to house the few reactors needed for these missions and to ensure that those facilities have strong security and safeguards protection. A. Zrodnikov observed that international
centers would complement conversion, because a large international facility would allow research to be done that would be more challenging than at a smaller facility. In addition, he observed that at such facilities it would be easier to manage high-quality MPC&A as well as physical protection because of the international attention that such facilities would receive, especially if such facilities were placed in nations with well-developed nuclear infrastructures. The suggestion regarding major international centers received support from several Russian participants.
REFERENCES
Bari, R. 2011. Estimation of Risk for Research Reactors. Presentation to the Research Reactor Conversion Symposium. June 10.
Chebeskov, A. 2011. An Approach to Proliferation Risk Assessment for Research Nuclear Reactors. Presentation to the Research Reactor Conversion Symposium. June 9.
Kuatbekov, R.P. 2011. Types and Designs of Prospective Research Reactors with LEU Fuel. Presentation to the Research Reactor Conversion Symposium. June 10.
Lemoine, P. 2011. Fuel Design and LEU Development for the Jules Horowitz Reactor. Presentation to the Research Reactor Conversion Symposium. June 10.
Zrodnikov, A. 2011. Power Development and Missions of Prospective Research Reactors. Presentation to the Research Reactor Conversion Symposium. June 10.
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