Системные возможности быстрых натриевых реакторов в двухкомпонентной ядерной энергетике

Most nuclear reactors under operation are thermal reactors, which consume 235U in once-through fuel cycle resulting in ineffective resource utilization and dramatic SNF volume growth. However, sustainable nuclear energy system (NES) should provide NFC closing for all hazardous radionuclides to minimize its life-time within NES and to make risk to be proportional to NES capacity, rather than total energy produced. These two basic principles require enough amount of neutrons for both energy generation and hazardous radionuclides transition to fission products. Therefore, taking into account politic, economic and technological risks and uncertainties, these issues can be solved in terms of two-component NES consisting of both thermal and fast reactors. In this work two methods to estimate neutron balance in NES are discussed. The fist method is based on the analysis of nuclear transformation chain due to radioactive decays and neutron induced reactions. The second one is the most complete one and relies on reaction rates comparison. Neutron balance estimation approach is demonstrated for two-component NES case study.

The paper presents the results of a case study on evaluating performance and sustainability metrics for Russian nuclear energy deployment scenarios with thermal and sodium-cooled fast reactors in a closed nuclear fuel cycle. Ten possible scenarios are considered which differ in the shares of thermal and sodium-cooled fast reactors, including options involving the use of mixed uranium-plutonium oxide fuel in thermal reactors. The evolution of the following performance and sustainability metrics is estimated for the period from 2020 to 2100 based on the considered assumptions: annual and cumulative uranium consumption, needs for uranium enrichment capacities, fuel fabrication and reprocessing capacities, spent fuel stocks, radioactive wastes, amounts of plutonium in the nuclear fuel cycle, amounts of accumulated depleted uranium, and the levelised electricity generation cost. The results show that the sustainability of the Russian nuclear energy system can be significantly enhanced through the intensive deployment of sodium-cooled fast reactors and the transition to a closed nuclear fuel cycle. The authors have highlighted some issues for further considerations, which will lead to more rigorous conclusions regarding the preferred options for the development of the national nuclear energy system.

Fabrication of Pu-bearing ceramic fuels for thermal and fast reactors for Indian nuclear power programme

One of the main reasons for the reprocessing of spent uranium oxide fuel is that of resource conservation. The fuel is termed 'spent' when it has been irradiated in a reactor for up to three years and is reaching the stage of diminishing efficiency in the production of heat through the fission of atoms. If retained in the reactor after this period heat is produced less efficiently and so the fuel is removed. 97 per cent of this irradiated fuel is uranium, up to 1 per cent is plutonium and 2–3 per cent is radioactive waste (Allday, 1977). As the fuel has been enriched — i.e. it has had uranium 235 added — it contains far more U235 after irradiation in a thermal reactor than is found in natural uranium. Reprocessing frees this uranium and plutonium from other actinides and fission products so that they may be reconverted into fuel for re-use in fast reactors and, conceivably, in thermal reactors. The effect of re-using the reprocessed fuel in a thermal reactor is to enable 30–40 per cent more power to be generated from the original material. However, such fuel can only used once. On the other hand recycling this material in a fast reactor would give an energy saving 50 times greater than that elicited from a thermal reactor (Allday, 1977). Hence the uranium and plutonium in spent oxide fuel is self-evidently a valuable source of energy if it can be recovered at a cost which permits the recycled U and Pu to have a value such that their use in thermal or fast reactors would provide power at a competitive price.1KeywordsFission ProductOxide FuelThermal ReactorSpend FuelUranium OxideThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Evolution of the CYCLE code for the system analysis of the nuclear fuel cycle

The accelerated fuel qualification (AFQ) methodology is applied by simulating accelerated fuel tests of the General Atomics Electromagnetic Systems’ fuel system for its 44-MW(electric) gas-cooled, fast-spectrum fast modular reactor (FMR). This fuel is comprised of UO2 pellets in SiGA® cladding, a silicon carbide ceramic matrix composite. Fast reactors, like the FMR, offer many benefits, including high fuel utilization and flexibility, but may require a lengthy material design process if tests are performed using fast neutron irradiation alone. A thermal neutron irradiation can instead be used to rapidly test how well key components of the current material models extend to high burnup. Thermal neutrons produce a different radial power distribution within the pin than fast neutrons. However, the temperature and burnup values for the two neutron types are comparable, and the differences between the simulated fuel responses are relatively small, demonstrating the weak sensitivity of the physics-based fuel model calculations on the neutron type and the irradiation rate. Furthermore, the deformation of the SiGA cladding saturates after about 1 displacement per atom for both neutron spectra. In an accelerated fuel test, the irradiation time required to reach the target fuel burnup can be reduced by a factor of 3 by using a small rodlet with a 45% smaller pellet diameter while maintaining the same linear power. Therefore, the time for data collection up to high burnup can be significantly reduced while maintaining the same temperature profile, which largely determines the material response. Tests of fuel rodlets of standard and compact size will be carried out in the Idaho National Laboratory’s Advanced Test Reactor (ATR), including full size and compact rodlets with varying gap sizes. By applying physics-based mechanistic modeling and simulation in accordance with the AFQ methodology, this type of compact rodlet testing in a thermal test reactor captures the necessary phenomena to test fuel material models up to high burnup and to simulate the expected impact of fast neutron radiation on the fuel in FMR operations. This approach to testing fast reactor fuels in existing thermal test reactors, paired with advanced physics-based mechanistic modeling and simulation, is expected to be applicable to a range of advanced fuels and will decrease the overall fuel qualification timeframe from decades to years.

The paper describes the approach to the assessment of nuclear energy systems based on the integral indicator characterizing the level of their sustainability and results of comparative assessment of several nuclear energy system options incorporating different combinations of nuclear reactors and nuclear fuel cycle facilities. The nuclear energy systems are characterized by achievement of certain key events pertaining to the following six subject areas: economic performance, safety, availability of resources, waste handling, non-proliferation and public support. Achievement of certain key events is examined within the time interval until 2100, while the key events per se are assessed according to their contribution in the achievement of sustainable development goals. It was demonstrated that nuclear energy systems based on the once-through nuclear fuel cycle with thermal reactors and uranium oxide fuel do not score high according to the integral sustainable development indicator even in the case when the issue of isolation of spent nuclear fuel in geological formation is resolved. Gradual replacement of part of thermal reactors with fast reactors and closing the nuclear fuel cycle results in the achievement of evaluated characteristics in many subject areas, which are close to maximum requirements of sustainable development, and in the significant enhancement of the sustainability indicator.

The access to reliable sources of energy is the key to sustainable development of mankind. The major part of the energy consumed by people is generated with a chemical reaction of fossil fuel burning. This leads to quick depletion of natural resources and progressing environmental pollution. The contribution of the renewable energy sources to the general energy production remains insignificant. A modern 1,000 MW coal-fired thermal power plant (TPP) burns 2.5 million tons of coal per year and produces significant amount of solid and gaseous waste. TPPs are the largest consumers of atmospheric oxygen and sources of carbon dioxide. A nuclear power plant (NPP) of the same power consumes less than 50 tons of fuel per year. Environmentally significant NPP’s waste (liquid, solid and gaseous) is carefully collected, reduced in volume (evaporation, filtering, compaction, incineration, etc.) and securely isolated from the environment at the plant. The annual volume of waste for storage is less than 100 m3. The waste is under the control of a special NPP’s service and regulatory authorities. The energy of fission reaction millions of times exceeding the energy of burning has an enormous potential that mankind can receive. Four hundred and thirty-three nuclear power units with a total capacity of about 400 GW exist in the world. The accident at the Fukushima Daiichi NPP in Japan in March 2011 caused anxiety about nuclear safety throughout the world and raised questions about the future of nuclear power. Now, it is clear that the use of nuclear power will continue to grow in the coming decades, although the growth will be slower than was anticipated before the accident. Many countries with existing nuclear power programmes plan to expand them. Many new countries, both developed and developing, plan to introduce nuclear power. Some countries, such as Germany, plan to abandon nuclear energy. The IAEA’s latest projections show a steady rise in the number of NPPs in the world in the next 20 years. They project a growth in nuclear power capacity by 23% by 2030 in the low projection and by 100% in the high projection [1,2]. The basis of modern nuclear power comprises water-cooled nuclear reactors which use the energy potential of natural uranium inefficiently (thermal reactors). The thermal reactors use isotope U-235 in which the content of natural uranium is <1%. Breeder reactors are capable of using the significant part of energy potential, which is unavailable to thermal light water reactors. As a result, the same starting quantity of uranium can produce 50 times more energy. These reactors can transform U-238 into fissile Pu-239 in larger amounts than they consume fissile material. This feature is called ‘breeding’ [3]. The key problem of using the basic benefitsv of nuclear power is to ensure the safety of its use, as well as decommissioning and reliable isolation of process waste from the biosphere. The long-term large-scale nuclear power should possess guaranteed safety, economic stability and competitiveness, absence of the raw material base restrictions for a long period of time and environmental sustainability (low waste). The nuclear power systems with fast neutron reactors and liquid metal coolant can satisfy these conditions. More than 40 years of Russian experience in the field of construction and operation of sodium fast reactors makes it possible to summarize and analyze the ecological features of reactors of this type, the possibility of their use for sustainable energy supply of mankind and solving environmental problems.

The accumulated experience in the operation of NPP, including those with fast reactors, shows that during normal operation, with due regard for possible operational difficulties and accidents, they ensure a significantly lower level of risk for personnel and the surrounding population than is present in industrial regions and those prone to natural disasters. Therefore, the dangers connected with the widespread development of nuclear power arise not so much from a real risk as from a risk which in principle can be realized in very improbable accidents. From this point of view sodium-cooled fast reactors have certain advantages. The probability of the maximum accident of the rupture of pipelines in high-pressure reactors must be considerably higher. Here a single event, and one difficult to detect, such as the failure to detect a flaw in manufacture, is enough to initiate the very dangerous first step of an accident. The rupture of equipment in the primary loop of a fast reactor at practically atmospheric pressure is considerably less probable, and the integral assembly is quite safe. All the other chains of development of maximum accidents in a fast reactor require the simultaneous realization of several events in systems and devices which are constantly being monitored (SS and power supply systems, etc.). The above considerations together with such important properties of sodium as the large reserve before the boiling point and the practically inertialess transport of heat from the reactor to structural elements and heat-transfer devices under natural circulation conditions gives one confidence that the level of risk for future industrial NPP with fast reactors will be at least no higher than that for NPP with thermal reactors.

In the Fast Reactor Cycle Technology Development (FaCT) project, a sodium-cooled fast reactor (SFR) with mixed-oxide (MOX) fuel and an SFR with metal fuel were selected as the primary and the secondary candidates, respectively, for the Japan Sodium-Cooled Fast Reactor (JSFR). The present study focuses on the effects of transuranium (TRU) composition in the design for the JSFR core with MOX fuel. In the transitional stage from light water reactor (LWR) to fast breeder reactor (FBR), there is the possibility for FBR fuel to have high minor actinide (MA) content due to the recycling of LWR spent fuel. High MA content affects core and fuel designs as follows: the neutronic reactivity characteristic changes; the linear power limit is reduced because of decreases of the melting point and thermal conductivity in the fuel; the gas plenum length is extended because of an increase in He gas generation. Thus, to evaluate the effects quantitatively, design studies for cores with two TRU compositions were conducted: an FBR multirecycle composition with ~1 wt% (in heavy metal) of MA content and an LWR recycle composition for which 3 wt% of MA content was assumed as a tentative target. The results show that the change from the FBR multirecycle composition to the LWR recycle composition leads to a sodium void reactivity increase of 10%, a linear power limit decrease of 1 to 2%, and a gas plenum length increase of 5%. As a result, the effects of TRU composition on the core and fuel designs were revealed to be benign.

The Russian Government approved the Energy Strategy of the Russian Federation (Government Decree No.1523-r of June 9, 2020). The Strategy envisages the use of both thermal (TR) and fast (FR) reactors. The Strategy points out that the problems of nuclear power are associated with po-tential high expenses for irradiated fuel and radioactive wastes management. The previously de-signed model of the Russian nuclear energy development suggested that fast reactors only would operate at NPPs after 2010. Radiological equivalence, expressed as the equivalence of lifetime radiation risks to the public from radioactive wastes and from primary uranium ore, was shown to be achieved after 100-year storage. The burnup of 241Am, 237Np и 242Сm in closed nu-clear fuel cycle with fast reactors is a key part in the achievability of radiation risks equivalence. Scenarios of the Russian nuclear energy development through to 2100 with account of uncertain-ty factors in the measurement of contribution of fast and thermal reactors to the electric energy production are considered in the paper. The following three scenarios were developed: uncer-tainty is replaced by FRs; uncertainty is replaced by TRs; 50 per cent of FRs and 50 per cent of TRs replace uncertainty. If the energy is produced by fast reactors only (scenario 1) radiological equivalence was found to be achieved in 412 years. In two other scenarios radiological equiva-lence will be achieved after more than 1000 years. Contribution of main dose-forming radionu-clides and relevant ratios of potential biological hazards is included in models regardless of whether uncertainty in nuclear energy development is taking or not taking into account. Results of the study of conditions for radiological equivalence achievement should be used for amending Strategic plan of Russian nuclear power development through to 2100 that meets requirements of radiation ecology and radiation protection of the public.

A review of irradiation testing vehicle approaches and designs that have been incorporated into past Sodium-Cooled Fast Reactors (SFRs) or envisioned for incorporation has been carried out. The objective is to understand the essential features of the approaches and designs so that they can inform test vehicle designs for a future U.S. Fast Test Reactor. Fast test reactor designs examined include EBR-II, FFTF, JOYO, BOR-60, PHÉNIX, JHR, and MBIR. Previous designers exhibited great ingenuity in overcoming design and operational challenges especially when the original reactor plant’s mission changed to an irradiation testing mission as in the EBRII reactor plant. The various irradiation testing vehicles can be categorized as: Uninstrumented open assemblies that fit into core locations; Instrumented open test assemblies that fit into special core locations; Self-contained closed loops; and External closed loops. A special emphasis is devoted to closed loops as they are regarded as a very desirable feature of a future U.S. Fast Test Reactor. Closed loops are an important technology for irradiation of fuels and materials in separate controlled environments. The impact of closed loops on the design of fast reactors is also discussed in this report.

The Plutonium Recycle and Fast Reactor Programs at present in the U.S. are reviewed. This report includes radiophysical and nuclear data, reactor physics and estimated values of plutonium in thermal and fast reactors. The technical and economical feasivilily of plutonium recycle in thermal reactors, especially in light water reactors, will be established by 1970. A competitive fast reactor fueled with plutonium is also expected to be built around 1975. It is worthwhile to notice the “dual economy” of light water reactors and fast reactors.

Authors

The long-term issues of nuclear power systems are the effective use of uranium resources and the reduction of radioactive waste. Important radioactive wastes are minor actinides (MAs: 237Np, 241Am, 243Am, etc.) and long-lived fission products (LLFPs: 129I, 99Tc, 79Se, etc.). The purpose of this study was to show a concept that can simultaneously achieve the breeding of fissile materials and the transmutation of MAs and LLFPs in one fast reactor. Transmutation was carried out by loading innovative Duplex-type MA fuel in the core region and LLFP-containing moderator in the first layer of the radial blanket. Breeding was achieved in the core and axial blanket. As a result, it was clarified that in this fast breeder reactor, a breeding ratio of approximately 1.1 was obtained, and MAs and LLFPs achieved a support ratio of 1 or more. The transmutation rate was 10.3%/y for 237Np, 14.1%/y for 241Am, 9.9%/y for 243Am, 1.6%/y for 129I, 0.75%/y for 99Tc, and 4%/y for 79Se. By simultaneously breeding fissile materials and transmuting MAs and LLFPs in one fast reactor, it will be possible to solve the long-term issues of the nuclear power reactor system, such as securing nuclear fuel resources and reducing radioactive waste.