Search Results (12)

This study presents an innovative solution method for ultra-fine group slowing-down equations tailored to stochastic media with double heterogeneity (DH), focusing on advanced nuclear fuels such as fully ceramic microencapsulated (FCM) fuel and Mixed Oxide (MOX) fuel. Addressing the limitations of conventional resonance calculation methods in handling DH effects, the proposed UFGSP method (the ultra-fine group slowing-down method with the Sanchez–Pomraning method) integrates the Sanchez–Pomraning technique with the ultra-fine group transport theory to resolve spatially dependent resonance cross-sections in both matrix and particle phases. The method employs high-fidelity geometric modeling, iterative cross-section homogenization, and flux reconstruction to capture neutron self-shielding effects in stochastically distributed media. Validation across seven FCM fuel cases, four poison particle configurations (BISO/QUADRISO, Bi/Tri-structural Isotropic), and four plutonium spot problems demonstrated exceptional accuracy, with maximum deviations in effective multiplication factor k_eff and resonance cross-sections remaining within ±138 pcm and ±2.4%, respectively. Key innovations include the ability to resolve radial flux distributions within TRISO particles and address resonance interference in MOX fuel matrices. The results confirm that the UFGSP method significantly enhances computational precision for DH problems, offering a robust tool for next-generation reactor design and safety analysis. Full article

This study presents a comprehensive uncertainty and sensitivity analysis of the effective neutron multiplication factor ($k_{\mathrm{eff}}$) in a large-scale sodium-cooled fast reactor (SFR) modeled after the European Sodium Fast Reactor. Utilizing the Serpent Monte Carlo code and the ENDF/B-VII.1 cross-section library, this research investigates the impact of cross-section perturbations in key isotopes (²³⁵U, ²³⁸U, and ²³⁹Pu for both mixed oxide (MOX) and metal fuels. Particular focus is placed on the capture, fission, and inelastic scattering reactions, as well as the effects of fuel temperature on reactivity through Doppler broadening. The findings reveal that reactivity in MOX fuel is highly sensitive to the fission cross sections of fissile isotopes (²³⁹Pu and ²³⁸U, while capture and inelastic scattering reactions in fertile isotopes such as ²³⁸U play a significant role in reducing reactivity, enhancing neutron economy. Additionally, this study highlights that metal fuel configurations generally achieve a higher ($k_{\mathrm{eff}}$) compared to MOX, attributed to their higher fissile atom density and favorable thermal properties. These results underscore the importance of accurate nuclear data libraries to minimize uncertainties in criticality evaluations, and they provide a foundation for optimizing fuel compositions and refining reactor control strategies. The insights gained from this analysis can contribute to the development of safer and more efficient next-generation SFR designs, ultimately improving operational margins and reactor performance. Full article

Double perovskite oxides with mixed ionic and electronic conductors (MIECs) have been widely investigated as cathode materials for solid oxide fuel cells (SOFCs). Classical Fe-based double perovskites, due to their inherent low electronic and oxygen ionic conductivity, usually exhibit poor electrocatalytic activity. The existence of various valence states of B-site ions modifies the material’s catalytic activity, indicating the possibility of the partial substitution of Fe by higher-valence ions. LaBaFe_2−xMo_xO_5+δ (x = 0, 0.03, 0.05, 0.07, 0.1, LBFM_x) is used as intermediate-temperature solid oxide fuel cell (IT-SOFC) cathode materials. At a doping concentration above 0.1, the Mo substitution enhanced the cell volume, and the lattice expansion caused the formation of the impurity phase, BaMoO₄. Compared with the parent material, Mo doping can regulate the oxygen vacancy concentration and accelerate the oxygen reduction reaction process to improve the electrochemical performance, as well as having a suitable coefficient of thermal expansion and excellent electrode stability. LaBaFe_1.9Mo_0.1O_5+δ is a promising cathode material for IT-SOFC, which shows an excellent electrochemical performance, with this being demonstrated by having the lowest polarization resistance value of 0.017 Ω·cm² at 800 °C, and the peak power density (PPD) of anode-supported single-cell LBFM_0.1|CGO|NiO+CGO reaching 599 mW·cm⁻². Full article

TiO₂-based mixed oxide–carbon composite support for Pt electrocatalysts provides higher stability and CO tolerance under the working conditions of polymer electrolyte membrane fuel cells compared to traditional carbon supports. Non-traditional carbon materials like graphene nanoplatelets and graphite oxide used as the carbonaceous component of the composite can contribute to its affordability and/or functionality. Ti_(1−x)Mo_xO₂-C composites involving these carbon materials were prepared through a sol–gel route; the effect of the extension of the procedure through a solvothermal treatment step was assessed. Both supports and supported Pt catalysts were characterized by physicochemical methods. Electrochemical behavior of the catalysts in terms of stability, activity, and CO tolerance was studied. Solvothermal treatment decreased the fracture of graphite oxide plates and enhanced the formation of a reduced graphene oxide-like structure, resulting in an electrically more conductive and more stable catalyst. In parallel, solvothermal treatment enhanced the growth of mixed oxide crystallites, decreasing the chance of formation of Pt–oxide–carbon triple junctions, resulting in somewhat less CO tolerance. The electrocatalyst containing graphene nanoplatelets, along with good stability, has the highest activity in oxygen reduction reaction compared to the other composite-supported catalysts. Full article

Bioethanol, which is currently produced commercially from a growing variety of renewable biomass and waste sources, is an appealing feedstock for the production of fuels and chemicals. The literature clearly shows that bioethanol is a versatile building block to be used in biorefineries. The ethanol conversion using several catalysts with acidic, basic, and redox characteristics results in a diverse assortment of high-value bioproducts. High-acidity tungsten zirconia-based catalysts are stated to compete with traditional zeolitic catalysts and can be employed in the dehydration of ethanol to ethylene, but for a low reaction temperature acetic acid is formed, which causes corrosion issues. WO₃-ZrO₂ (W/Zr = 1, atomic) catalysts modified with MoO₃ were prepared by a sol-gel-like procedure and tested in a gas phase ethanol conversion in the presence of air. The citrate derived xerogels were annealed at 853 K for 12 h, allowing low surface area (<10 m²/g) materials with a Mo-W mixed-oxide-rich surface over tetragonal nanostructured zirconia. Catalysts with MoO3-loading produced mainly acetaldehyde, instead of ethylene, as a result of the high reducibility of Mo⁶⁺ when compared to W⁶⁺. During the reaction, the Mo⁶⁺ becomes partially reduced, but Mo⁶⁺/Mo⁵⁺ species are still active for methanol conversion with increased ethylene selectivity due to the high acidity of tetrahedral MO_X species formed during the reaction. Adding water to ethanol, to simulate bioethanol, only leads to a slight inhibition in ethanol conversion over the MoO₃/(WO₃-ZrO₂) catalysts. The results show that molybdenum oxide deposited on tungstated zirconia catalyst is active, with low sensitivity to water, for the valorization of bioethanol into high-value chemicals, such as ethylene and acetaldehyde, and whose selectivity can be tuned by changing the amount of MoO₃ that is loaded. The MoO₃/(WO₃-ZrO₂) catalysts prepared show catalytic behavior similar to that of noble metal-based catalysts reported in the literature for the dehydrogenation of bioethanol in high-value chemicals. Full article

Mixed oxides of uranium and plutonium (MOX) are currently considered as a reference fuel for the new generation of fast breeder reactors such as ASTRID. The key factor determining the performance and safety of a fuel such as MOX is its operational limits in the application environment which are closely related to the material’s structure and thermodynamic stability. They are in turn closely related to the ambient (zero pressure) melting point $\left(T_m\right)$; thus, $T_m$ is an important engineering parameter. Furthermore, PuO${}_2$ and UO${}_2$ are two endpoints of the phase diagram of MOX; therefore, their ambient $T_m$s are fundamental reference points. However, the current knowledge of the $T_m$ of MOX is limited and controversial as several studies available in the literature do not converge on the unique behavior of $T_m$ as a function of $x.$ Specifically, some studies produced $T_m$ as a monotonically decreasing function of x such that, with $T_m$ of UO${}_2$$(x=0)$ of 3150 K, $T_m$ of PuO${}_2$$(x=1)$ is ∼2650 K, while other studies resulted in $T_m$ having a local minimum at $0.5<x<1$ such that $T_m$ of PuO${}_2$ is ∼3000 K, so that the difference between the two values of $T_m$ is as high as 350 K. In this study, using the ab initio Z method implemented with the Vienna Ab Initio Simulation Package (VASP), we carry out a suite of quantum molecular dynamics simulations to obtain the ambient $T_m$ of MOX at several values of $x,$ $0<x<1,$ including the two end points $(x=0,$ $x=1).$ Our results agree with the behavior of $T_m$ of MOX as a function of x having a local minimum at $x=0.7$ and $T_m$ of PuO${}_2$ of 3050 K. Our study suggests potential ambient density–melting point systematics of MOX which may be useful in subsequent research on MOX such as its thermoelasticity modeling. Full article

TiO₂-based mixed oxide–carbon composite supports have been suggested to provide enhanced stability for platinum (Pt) electrocatalysts in polymer electrolyte membrane (PEM) fuel cells. The addition of molybdenum (Mo) to the mixed oxide is known to increase the CO tolerance of the electrocatalyst. In this work Pt catalysts, supported on Ti_1−xMo_xO₂–C composites with a 25/75 oxide/carbon mass ratio and prepared from different carbon materials (C: Vulcan XC-72, unmodified and functionalized Black Pearls 2000), were compared in the hydrogen oxidation reaction (HOR) and in the oxygen reduction reaction (ORR) with a commercial Pt/C reference catalyst in order to assess the influence of the support on the electrocatalytic behavior. Our aim was to perform electrochemical studies in preparation for fuel cell tests. The ORR kinetic parameters from the Koutecky–Levich plot suggested a four-electron transfer per oxygen molecule, resulting in H₂O. The similarity between the Tafel slopes suggested the same reaction mechanism for electrocatalysts supported by these composites. The HOR activity of the composite-supported electrocatalysts was independent of the type of carbonaceous material. A noticeable difference in the stability of the catalysts appeared only after 5000 polarization cycles; the Black Pearl-containing sample showed the highest stability. Full article

The economic assessment of advanced nuclear power reactors is very important, specifically during the early stages of concept design. Therefore, a study was performed to calculate the total cost estimation of fuel cycle supply for a system modular advanced reactor (SMART) by using the Generation-IV economic program called G4-ECONS (Generation 4 Excel-based Calculation of Nuclear Systems). In this study, the detailed description of each model and methodology are presented including facility, operations, construction matrix, post-production model, and fuel cycle cost estimation model. Based on these models, six Generation-III+ and Generation-IV nuclear reactors were simulated, namely System 80+ with benchmark data, System 80+ with uranium oxide (UOx) and mixed oxide (MOx) fuel assemblies, fast reactor, PBMR (Pebble Bed Modular Reactor), and PWR (Pressurized Water Reactor), with partially closed and benchmarked cases. The total levelized costs of these reactors were obtained, and it was observed that PBMR showed the lowest cost. The research was extended to work on the SMART reactor to calculate the total levelized fuel cycle cost, capital cost, capital component cost, fraction of capital spent, and sine curve spent pattern. To date, no work is being reported to calculate these parameters for the SMART reactor. It was observed that SMART is the most cost-effective reactor system among other proven and advanced pressurized water-based reactor systems. The main objective of the research is to verify and validate the G4-ECONS model to be used for other innovative nuclear reactors. Full article

The exploitation of solar energy, an unlimited and renewable energy resource, is of prime interest to support the replacement of fossil fuels by renewable energy alternatives. Solar energy can be used via concentrated solar power (CSP) combined with thermochemical energy storage (TCES) for the conversion and storage of concentrated solar energy via reversible solid–gas reactions, thus enabling round the clock operation and continuous production. Research is on-going on efficient and economically attractive TCES systems at high temperatures with long-term durability and performance stability. Indeed, the cycling stability with reduced or no loss in capacity over many cycles of heat charge and discharge of the material is pursued. The main thermochemical systems currently investigated are encompassing metal oxide redox pairs (MO_x/MO_x−1), non-stoichiometric perovskites (ABO₃/ABO_3−δ), alkaline earth metal carbonates and hydroxides (MCO₃/MO, M(OH)₂/MO with M = Ca, Sr, Ba). The metal oxides/perovskites can operate in open loop with air as the heat transfer fluid, while carbonates and hydroxides generally require closed loop operation with storage of the fluid (H₂O or CO₂). Alternative sources of natural components are also attracting interest, such as abundant and low-cost ore minerals or recycling waste. For example, limestone and dolomite are being studied to provide for one of the most promising systems, CaCO₃/CaO. Systems based on hydroxides are also progressing, although most of the recent works focused on Ca(OH)₂/CaO. Mixed metal oxides and perovskites are also largely developed and attractive materials, thanks to the possible tuning of both their operating temperature and energy storage capacity. The shape of the material and its stabilization are critical to adapt the material for their integration in reactors, such as packed bed and fluidized bed reactors, and assure a smooth transition for commercial use and development. The recent advances in TCES systems since 2016 are reviewed, and their integration in solar processes for continuous operation is particularly emphasized. Full article

Reprocessing of irradiated nuclear fuel is or has been implemented in several countries with significant numbers of nuclear power plants and installed capacity. In this work, a set of scenarios has been analyzed to find the key variables for the implementation of reprocessing in medium sized fleets. The inventories of the Spanish nuclear fuel cycle scenario were chosen as representative, considering two different reactor lifetimes and reprocessing strategies, with the aim of burning the maximum amount of the Pu mass generated in the cycle. The simulations of the scenarios were performed with the TR_EVOL code developed at CIEMAT. Results show that the lifetime of the reactors has an impact in the possible reduction in the Pu amount. Some scenarios show a shortage of Pu available for mixed uranium-plutonium oxide (MOX) fuel fabrication coming from the reprocessing of UO₂ spent fuel. This work has verified that, for medium sized fuel cycle scenarios, the parameters with the most importance are the reprocessing cost and natural uranium cost. A smaller impact in the comparison is also found for the cost of the final disposal and the possibility of valuing the surplus Pu and reprocessed uranium existent at the end of the cycle. Full article

An efficient burning of the plutonium produced during light water reactor (LWR) operation has the potential to significantly improve the sustainability indices of LWR operations. The work offers a comparison of the efficiency of Pu burning in different reactor configurations—a molten salt fast reactor, a LWR with mixed oxide (MOX) fuel, and a sodium cooled fast reactor. The calculations are performed using the HELIOS 2 code. All results are evaluated against the plutonium burning efficiency determined in the Consommation Accrue de Plutonium dans les Réacteurs à Neutrons RApides (CAPRA) project. The results are discussed with special view on the increased sustainability of LWR use in the case of successful avoidance of an accumulation of Pu which otherwise would have to be forwarded to a final disposal. A strategic discussion is given about the unavoidable plutonium production, the possibility to burn the plutonium to avoid a burden for the future generations which would have to be controlled. Full article

In 2013, the Spanish government created two new taxes on used nuclear fuel. This article aims to present the results of an economic study carried out to compare the costs of long-term storage of used nuclear fuel –open cycle strategy–, with the cost of the strategy of reprocessing and recycling used fuel– closed cycle strategy– taking into account the impact of the new taxes on the global cost of the fuel cycle. The results show that the costs of open-cycle and closed-cycle spent fuel management, evaluated in Spain after the introduction of the taxes, are sufficiently similar (within the bounds of uncertainty), that the choice between both is predicated on other than purely economic criteria. Full article