Fast Reactor Transmutation Research Articles

Performance indices optimization of l ong‐lived fission products transmutation in fast reactors

Performance indices optimization of l <scp>ong‐lived</scp> fission products transmutation in fast reactors

Estimation of uncertainty in transmutation rates of LLFPs in a fast reactor transmutation system via an estimation of the cross-section covariances

ABSTRACT A new concept of transmutation system for six long-lived fission products (LLFPs: 79Se, 93Zr, 99Tc, 107Pd, 129I, and 135Cs) consisting of three small-size fast reactor cores was proposed. In order to establish a method to estimate the effects of cross-section uncertainties on the transmutation rates of the LLFPs, cross section covariances for the six LLFPs were estimated using a T6 system which includes resonance and statistical models via propagation of model uncertainties, and the uncertainties of transmutation rates and support factors of the six LLFPs in the three fast reactors were estimated based on a Total Monte Carlo (TMC) method. It was made clear that some of the transmutation rates of these LLFPs have large uncertainties indicating that the accuracy of cross sections for them is not enough, and hence the strategy for efficient transmutation may have to be reconstructed. It is concluded that the T6 system and the TMC method used in this study are quite effective not only to estimate the uncertainties of cross sections but also to assess the effect of error propagation throughout the series of calculations conducting in this study.

A fast reactor transmutation system for 6 LLFP nuclides

A fast reactor transmutation system with enhanced transmutation efficiency for six long-lived fission products (LLFP: 79Se, 93Zr, 99Tc, 107Pd, 129I, and 135Cs) was evaluated. A new fast reactor transmutation system concept consisting of three fast reactor cores was constructed by loading six LLFP nuclides on a radial blanket, axial blanket and shield using YD2 and YH2 moderators. By combining three MONJU-class fast reactors, the ratio of the amount of transmuted nuclides in the three reactors to the amount of nuclides produced in the three reactors were achieved 1 or more for all six LLFP nuclides, and the effective half-lives were significantly reduced.

A comparison of curium, neptunium and americium transmutation feasibility

Minor actinides transmutation is the process of decreasing the long term radiotoxicity of the nuclear spent fuel by submitting it to a neutron flux so as to achieve fission of the heavy nuclides concerned. In the case of a closed fuel cycle, minor actinides are the main contributors to the spent fuel radiotoxicity after a few centuries. The isotopic vector of the minor actinides feed to be transmuted depends heavily on the fuel cycle considered: PWRs with UOX fuels will mainly lead to neptunium and americium production while MOX fueled reactors will produce mainly americium and curium. Americium is the main element currently considered for transmutation due to its relatively short half-life and significant production level. On the other hand, neptunium is seen as a secondary candidate for transmutation due to its very long half life and low activity while Curium transmutation is generally ruled out due to the high activity of curium isotopes. Two modes of transmutation in fast reactors are generally opposed, namely the homogeneous approach in which minor actinides are directly mixed with the fuel while in the heterogeneous approach, the minor actinides are loaded in dedicated targets. It is shown in this paper that the impacts on the fuel cycle of heterogeneous americium transmutation are similar to the one of homogeneous curium transmutation. It is further shown that given the quantities of curium in the fuel cycle, only a limited number of reactors would be required to effectively transmute the curium production of fast reactors with americium bearing blankets. Curium transmutation thus appears a feasible option in a completely closed fuel cycle without significantly higher fuel cycle impacts than with only americium transmutation. It is finally verified that neptunium transmutation can be achieved regardless of the approach considered.

Optimization of Minor Actinide–Bearing Radial Blankets for Heterogeneous Transmutation in Fast Reactors

A methodology dedicated to the optimization of the transmutation of minor actinides (MAs) in dedicated blankets is discussed here. This methodology relies on recently developed optimization tools. In the so-called heterogeneous transmutation approach, MAs are loaded into specific assemblies located at the periphery of a fast reactor core. Thus, the resulting perturbation of the core behavior is limited and the management of MAs is entirely decoupled from standard fuel management. This also allows greater flexibility in the blanket design, in terms of material, volume fraction, and neutron spectrum to be used. On the other hand, the low neutron flux level experienced at the periphery of the core slows down the transmutation process. If this effect can be compensated for by an increase of the MA fraction loaded in the blankets, this also strongly increases their decay heat and neutron source level, which complicates spent fuel reprocessing and handling. An optimization is carried out with regard to the neutron spectrum and americium concentration in the blankets, with the dual objective of maximizing the transmuted MA mass while minimizing the total MA inventory in the fuel cycle by limiting the cooling time of such blankets. Artificial neural networks are coupled with a genetic algorithm to reduce the total calculation time. It is shown here that regardless of the MA mass to be loaded, a slightly moderated neutron spectrum is the most promising option for heterogeneous transmutation. This result is confirmed by full-core calculations. An analysis of the irradiation time is also performed, and it is shown that maximization of the irradiation time should be sought in the specific case studied here. It is concluded that from a purely physical point of view, no breakthrough can be obtained for heterogeneous transmutation.

Analysis and optimization of minor actinides transmutation blankets with regards to neutron and gamma sources

Heterogeneous loading of minor actinides in radial blankets is a potential solution to implement minor actinides transmutation in fast reactors. However, to compensate for the lower flux level experienced by the blankets, the fraction of minor actinides to be loaded in the blankets must be increased to maintain acceptable performances. This severely increases the decay heat and neutron source of the blanket assemblies, both before and after irradiation, by more than an order of magnitude in the case of neutron source for instance. We propose here to implement an optimization methodology of the blankets design with regards to various parameters such as the local spectrum or the mass to be loaded, with the objective of minimizing the final neutron source of the spent assembly while maximizing the transmutation performances of the blankets. In a first stage, an analysis of the various contributors to long- and short-term neutron and gamma source is carried out whereas in a second stage, relevant estimators are designed for use in the effective optimization process, which is done in the last step. A comparison with core calculations is finally done for completeness and validation purposes. It is found that the use of a moderated spectrum in the blankets can be beneficial in terms of final neutron and gamma source without impacting minor actinides transmutation performances compared to more energetic spectrum that could be achieved using metallic fuel for instance. It is also confirmed that, if possible, the use of hydrides as moderating material in the blankets is a promising option to limit the total minor actinides inventory in the fuel cycle. If not, it appears that focus should be put upon an increased residence time for the blankets rather than an increase in the acceptable neutron source for handling and reprocessing.

Analysis and optimization of minor actinides transmutation blankets with regards to neutron and gamma sources

Heterogeneous loading of minor actinides in radial blankets is a potential solution to implement minor actinides transmutation in fast reactors. However, to compensate for the lower flux level experienced by the blankets, the fraction of minor actinides to be loaded in the blankets must be increased to maintain acceptable performances. This severely increases the decay heat and neutron source of the blanket assemblies, both before and after irradiation, by more than an order of magnitude in the case of neutron source for instance.We propose here to implement an optimization methodology of the blankets design with regards to various parameters such as the local spectrum or the mass to be loaded, with the objective of minimizing the final neutron source of the spent assembly while maximizing the transmutation performances of the blankets. In a first stage, an analysis of the various contributors to long and short term neutron and gamma source is carried out while in a second stage, relevant estimators are designed for use in the effective optimization process, which is done in the last step. A comparison with core calculations is finally done for completeness and validation purposes. It is found that the use of a moderated spectrum in the blankets can be beneficial in terms of final neutron and gamma source without impacting minor actinides transmutation performances compared to more energetic spectrum that could be achieved using metallic fuel for instance. It is also confirmed that, if possible, the use of hydrides as moderating material in the blankets is a promising option to limit the total minor actinides inventory in the fuel cycle. If not, it appears that focus should be put upon an increased residence time for the blankets rather than an increase in the acceptable neutron source for handling and reprocessing.

Uncertainty analysis of minor actinides transmutation in fast reactor cores

The uncertainty of minor actinides transmutation in fast reactors has been estimated for individual nuclides of minor actinides (MA). The burn-up dependent sensitivities of MA number densities are calculated using the generalized perturbation theory, and a method is derived to transform the sensitivities to the sensitivities of minor actinides transmutation. The sensitivities are used to obtain the uncertainties of minor actinides transmutation together with the cross-section covariance data of JENDL-4. The method is applied to the two MA transmutation fast reactor cores with MA content of 6% and 11%. It is seen that the uncertainties of the total MA transmutation amounts are about 3% and 4% for the two cores because the uncertainties of Np-237 and Am-241 transmutations which mainly contribute the total transmutation are small (about 3%).The contribution to the uncertainties is mainly caused by the Np-237 and Am-241 capture cross-sections.The transmutation uncertainties for Np-239, Am-233, Cm-243, and Cm-245 are rather large. However the transmutation amounts of these nuclides are very small, and the large uncertainties are not the problem in practice. However, it is found that the transmutation amount of Cm-244 has large uncertainties of 10% and 13% for the cores with MA content of 6% and 11%, and this large uncertainties have to be considered when MA fuels are fabricated and reprocessed because Cm-244 produces large decay heat and neutron emission.

New trends in the reprocessing of spent nuclear fuel. Separation of minor actinides by solvent extraction

&lt;p&gt;Recycling of actinides from spent nuclear fuel by their selective separation followed by transmutation in fast reactors will optimize the use of natural uranium resources and minimize the long-term hazard from high-level nuclear waste. This paper describes solvent extraction processes recently developed, aimed at the separation of americium from lanthanide fission products as well as from curium present in the waste. Depicted are novel poly-N-heterocyclic ligands used as selective extractants of actinide ions from nitric acid solutions or as actinide-selective hydrophilic stripping agents.&lt;/p&gt;

Characterization of metallic fuel for minor actinides transmutation in fast reactor

The METAPHIX programme is a collaboration between the Central Research Institute of Electric Power Industry (CRIEPI, Japan) and the Joint Research Centre - Institute for Transuranium Elements (JRC-ITU) of the European Commission dedicated to investigate the safety and effectiveness of a closed nuclear fuel cycle based on Minor Actinides (MA: Np, Am, Cm) separation from spent fuel, incorporation in metal alloy fuel and transmutation in fast reactor.Nine Na-bonded experimental pins of metal alloy fuel were prepared at ITU and irradiated at the Phenix reactor (CEA, France) achieving 2.5 at.%, 7 at.% and 10 at.% burn-up. Four metal alloy compositions were irradiated: U-Pu-Zr used as fuel reference, U-Pu-Zr + 5 wt.% MA, U-Pu-Zr + 2 wt.% MA + 2 wt.% Rare Earths (RE: Nd, Y, Ce, Gd), and +5 wt.% MA + 5 wt.% RE, respectively. RE reproduce the expected output of a pyrometallurgical reprocessing facility.Post Irradiation Examination is performed using several techniques, covering properties ranging from the macroscopic morphology of the fuel matrix to the microanalysis of phases and elemental redistribution/segregation. The irradiated fuel is characterized by many phases occurring along the fuel radius. The fuel underwent large redistribution of the fuel constituents (U, Pu, Zr) and many secondary phases are present with a variety of compositions. The distribution of phases in the irradiated fuel containing minor actinides and rare earths is essentially similar to that observed in the basic ternary alloy fuel.

Comparative Fuel Cycle Analysis of Critical and Subcritical Fast Reactor Transmutation Systems

Fuel cycle analyses are performed to evaluate the impacts of further transmutation of spent nuclear fuel on high-level and low-level waste mass flows into repositories, on the composition and toxicity of the high-level waste, on the capacity of high-level waste repositories, and on the proliferation resistance of the high-level waste. Storage intact of light water reactor (LWR) spent nuclear fuel, a single recycle in a LWR of the plutonium as mixed-oxide fuel, and the repeated recycle of the transuranics in critical and subcritical fast reactors are compared with the focus on the waste management performance of these systems. Other considerations such as cost and technological challenges were beyond the scope of this study. The overall conclusion of the studies is that repeated recycling of the transuranics from spent nuclear fuel would significantly increase the capacity of high-level waste repositories per unit of nuclear energy produced, significantly increase the nuclear energy production per unit mass of uranium ore mined, significantly reduce the radiotoxicity of the waste streams per unit of nuclear energy produced, and significantly enhance the proliferation resistance of the material stored in high-level waste repositories.

Transmutation characteristics of MA and LLFP in a fast reactor

Systematic studies were implemented to investigate the flexibility and attractive core concepts of MA and LLFP transmutation in fast reactors. The MA transmutation in the fast reactor core has no serious drawbacks in terms of core performance, provided that the homogeneous loading method can be employed with a small fraction of MA fuel (2~5wt%). The recycling of MA in the fast reactor is feasible from neutronic and thermal-hydraulic points of view. For FP transmutation, the introduction of target subassemblies using duplex pellets — a moderator annulus surrounding a Tc-99 core — gives the maximum transmutation rate of Tc-99 in the radial shield region of the fast reactor. The fast reactor has an excellent potential for transmuting MA and LLFP effectively. The fast reactor will be able to play an important role for reduction of environmental burden in future energy system.

Nuclear fuel considerations for the 21 st century

There are many external influences that may control the path that nuclear power deployment follows. In the next 50 years several events may unfold. Fear of the consequences of the greenhouse effect may produce a carbon tax that would make nuclear power economically superior very quickly. This, in turn, would increase the rate at which uranium reserves diminish due to the increased rate of nuclear power deployment. However, breakthroughs in the extraction of uranium from the sea or deployment of fast breeder reactors would greatly extend the uranium reserves and, as well, utilize the thorium cycle. On the other hand, carbon sequestering technology breakthroughs could keep fossil fuels dominant for the remainder of the century. Nuclear power may only then continue, as today, in a lesser role or even diminish. Fusion power or new developments in solar power could completely displace nuclear power as we know it today. Even more difficult to predict is when the demand for mobile fuel for transportation will develop such that hydrogen and hydrogen rich fuel cells will be in common use. When this happens, nuclear power may be the energy source of choice to produce this fuel from water or methane. In a similar vein, the demand for potable and irrigation water may be another driver for the advent of increased deployment of nuclear power. With all these possibilities of events that could happen it appears impossible to predict with any certainty which path nuclear power deployment may take. However, it is necessary to define a strategy that is flexible enough to insure that when a technology is needed, it is ready to be deployed. For the next few decades there will be an evolutionary improvement in the performance of uranium oxide and mixed uranium oxide-plutonium oxide (MOX) LWR fuels. These improvements will be market driven to keep the cost of fuel and the resulting cost of nuclear power electricity as competitive as possible. The development of fuels for accelerator transmutation and for reactor transmutation with inert matrix fuels is in its infancy. A great deal of research has been initiated in a number of countries, which has been summarized in recent conferences. In Europe the work on these fuels is directed at the same problem as their utilization of MOX; namely to reduce the inventory of separated plutonium, minor actinides, and Long Lived Fission Products (LLFP). In the United States there is no reprocessing and thus no inventory of separated civilian plutonium. However, in the United States there is a resistance to a permanent spent fuel repository and thus accelerator transmutation presents a possible alternative. If nuclear power does have a long-term future, then the introduction of the fast reactor is inevitable. Included in the mission of the fast reactors would be the elimination of the inventory of separated plutonium while generating useful energy. The work that is ongoing now on the development of fuel concepts for assemblies that contain actinides and LLFP would be useful for fast reactor transmutation. There is still a great deal of work required to bring the fast breeder reactor option to maturity. Fortunately there is perhaps a fifty-year period to accomplish this work before fast breeders are necessary. With regard to fast reactor fuel development, future work should be considered in three stages. First, all the information obtained over the past forty years of fast reactor fuel development should be completely documented in a manner that future generations can readily retrieve and utilize the information. Fast reactor development came to such an abrupt halt world-wide that a great deal of information is in danger of being lost because most of the researchers and facilities are rapidly disappearing. Secondly, for all of the existing fast reactor fuels, and this includes, oxides, carbides, nitrides, and metallic fuels, the evolutionary work was far from being completed. Although mixed oxide fuels were probably the furthest advanced, there were many concepts for improved claddings and advanced fabrication methods that were never fully explored. Finally, with such an extended period before fast reactors are needed there is ample time for truly innovative fuels to be developed that are capable of performing over a wide range of conditions and coolants.

Study on MA and FP transmutation in fast reactors

Feasibility studies have been performed to develop an optimized fast reactor core for reducing long-term radiotoxicity of nuclear waste by minor actinide(MA) and long-lived fission product(FP) transmutation, taking into consideration fuel cycle technology. Systematic parameter survey calculations were implemented to investigate the basic characteristics of MA and FP transmutation in a fast reactor core. The hybrid MA-loading method, where Np nuclide is dispersed uniformly in the core and target subassemblies containing Am, Cm and rare earth nuclides are loaded into the blanket region, has the potential to achieve the maximum transmutation of MA with no special fuel design considerations. The introduction of target subassemblies using duplex pellets - a moderator annulus surrounding a 99Tc core - has a great potential to transmute long-lived fission products in the radial blanket region of the fast reactor core.