Heterogeneous Material Distribution Research Articles

Ground motion characteristics of subshear and supershear ruptures in the presence of sediment layers

SUMMARY We investigate the impact of sediment layers on ground motion characteristics during subshear and supershear rupture growth. Our findings suggest that sediment layers may lead to local supershear propagation, affecting ground motion, especially in the fault parallel (FP) direction. In contrast to homogeneous material models, we find that in the presence of sediment layers, a larger fault normal (FN) compared to FP particle velocity jump, reflects shear propagation at depth but does not rule out shallow supershear propagation. Conversely, a large FP compared to FN particle velocity jump indicates supershear propagation at depth. In the presence of a shallow layer, we also uncover a non-monotonic behaviour in the sediment’s influence on supershear transition and ground motion characteristics. During supershear propagation at depth we observe that sediment layers contribute to enhancing FP velocity pulses while minimally affecting the FN component. Furthermore, in the limit of global supershear propagation we identify local supersonic propagation within the sediment layers that significantly alters the velocity field around the rupture tip as observed on the free surface, creating both dilatational and shear Mach cones. In all our models with sediments we also find a significant enhancement in the fault vertical component of ground velocity. This could have particular implications for hazard assessments, such as in applications related to linear infrastructure, or a higher propensity to tsunami wave generation. Our research unravels the importance of considering heterogeneous subsurface material distribution in our physical models as they can have drastic implications on earthquake source physics.

Optimizing heterogeneous elastic material distributions on 3D models

Optimizing heterogeneous elastic material distribution on a 3D part to achieve desired deformation behavior is an important task in computer-aided design and additive manufacturing. This paper presents a solution to this problem, which involves interactive design, automatic deformation generation, and optimization of spatial distribution of heterogeneous elastic materials. Our method improves previous techniques in three aspects. First, we incorporates a geometric deformation-based interactive design into FEM-based optimization, which makes the solution less dependent of initial guesses of Young’s modulus values and it more likely to produce the target design even with sparse user input of displacements and forces at a limited set of mesh vertices. Second, we formulate the problem as an L2- or L0-optimization problem. The L2 formulation outputs smoothly varying heterogeneous material distribution that accommodates multiple functions within a single part. The L0 formulation achieves the computation of sparse material distribution in one step, which is beneficial for additive manufacturing with multi-material printers. Third, we utilize the adjoint method to derive formulae for efficiently computing the gradient of the objective functions, making it possible to quickly solve the optimization problem in the full-dimensional space of materials, which was previously infeasible. The experiments demonstrate the robustness and efficiency of our approach.

A Numerical Simulation of Evolution Processes and Entropy Generation for Optimal Architecture of an Electrochemical Reaction-Diffusion System: Comparison of Two Optimization Strategies

Employment of electrochemical energy devices is being expanded as the world is shifting toward more sustainable power resources. To meet the required cost efficiency standards for commercialization, there is a need for optimal design of the electrodes. In this study, a topology optimization method is proposed to increase the performance of an electrochemical reaction-diffusion system. A dimensionless model is developed to characterize the transport and rate processes in the system. Two optimization strategies are introduced to improve system performance using a heterogeneous distribution of constituents. In addition, an entropy generation model is proposed to evaluate the system irreversibilities quantitatively. The findings show that the system performance could be enhanced up to 116.7% with an optimal tree-root-like structure. Such a heterogeneous material distribution provides a balance among various competing transport and rate processes. The proposed methodology could be employed in optimal design of electrodes for various electrochemical devices. This study also offers a fundamental comprehension of optimal designs by showing the connection between the optimal designs and the entropy generation. It is revealed that a less dissipating system corresponds to a more uniform current and entropy generation. Some recommendations are also made in choosing a proper optimization approach for electrochemical systems.

Universal self-assembly of graphene-based composites as free-standing hierarchical electrodes for high-performance aqueous hybrid capacitors

For the development of aqueous hybrid capacitors, it is essential to fulfill the role of active materials and concentrate on the device's performance. However, these goals are challenging because the conventional electrodes meet a heterogeneous distribution of active materials and large-portion passive components. We develop a universal method to prepare free-standing hierarchical graphene-based composited electrodes here. Compared to conventional electrodes, this hierarchical electrode can distribute active materials effectively, improve ion diffusion, increase charge transfer, reduce parasitic reactions, decrease passive components, etc., which facilitates fulfilling the role of active materials and increases the device performance. Typically, the hierarchical electrodes show higher capacity for Fe3O4, NiCo-LDH, PANI, and active carbon. In addition, the hierarchical electrodes can generate a high energy density of 43.7 Wh kg−1 (based on the whole electrodes instead of active materials). Also, the preparation method of hierarchical electrodes is facile, energy-saving, eco-friendly, etc., facilitating the practical application. Such a universal preparation method and high electrochemical performance hold great potential for developing high-performance energy storage devices.

Mechanical Slowing Down of Network-Forming Phase Separation of Polymer Solutions.

Phase separation is a fundamental phenomenon leading to spatially heterogeneous material distribution, which is critical in nature, biology, material science, and industry. In ordinary phase separation, the minority phase always forms droplets. Contrary to this common belief, even the minority phase can form a network structure in viscoelastic phase separation (VPS). VPS can occur in any mixture with significant mobility differences between their components and is highly relevant to soft matter and biomatter. In contrast to classical phase separation, experiments have shown that VPS in polymer solutions lacks self-similar coarsening, resulting in the absence of a domain-coarsening scaling law. However, the underlying microscopic mechanism of this behavior remains unknown. To this end, we perform fluid particle dynamics simulations of bead-spring polymers, incorporating many-body hydrodynamic interactions between polymers through a solvent. We discover that polymers in the dense-network-forming phase are stretched and store elastic energy when the deformation speed exceeds the polymer dynamics. This self-generated viscoelastic stress mechanically interferes with phase separation and slows its dynamics, disrupting self-similar growth. We also highlight the essential role of many-body hydrodynamic interactions in VPS. The implications of our findings may hold importance in areas such as biological phase separation, porous material formation, and other fields where network structures play a pivotal role.

Two-phase reactive transport modeling of heterogeneous gas production in a low- and intermediate-level waste repository

Abstract. The widely proposed approach to dispose of low- and intermediate-level radioactive waste is to store it in a deep underground repository with multiple barriers. A typical gallery is filled with concrete containers accommodating cemented steel drums of waste. Inside a container, different gases may be produced by (bio)chemical reactions, which include pH-dependent anoxic corrosion of metals and the degradation of organic matter. Both reactions consume water and may lead to pressure buildup and transport of gas, both within and around the repository. In order to investigate the controlling factors of this gas production process, a coupled reactive transport model of component-based two-phase flow in the OpenGeoSys framework is adopted here. The numerical study of Huang et al. (2021) has shown that a realistic internal structure of a waste package, including the heterogeneous distribution of materials with different chemical and hydrological properties, and the exchange of mass at the boundaries are key factors that determine the evolution of the waste package. Based on the study of Huang et al. (2021), the geometric configuration of the model has been further extended to reflect the various conditions of a multi-container disposal in a gallery. In a two-dimensional setup several model scenarios have been designed and simulated to study the change in gas production rate over time in relation to water availability in various geological and waste storage setups. In this presentation, we show simulation results covering the geochemical evolution of a waste package over 500 years. It is found that the initial water content in the waste compartment only controls the gas production rate for the first 40 to 60 years. The early pressure buildup and gas release rates are largely controlled by several critical parameters, including the permeability of cement material and water availability at the boundary. The sensitivity of these parameters is currently being investigated in detail.

Investigations on the compression-shear coupled stress waves propagating in heterogeneous rock

In order to investigate the heterogeneous responses in complex rocks, a compression-shear coupled constitutive relationship with four coupled parameters is established and a generalized wave equation is obtained. Based on the generalized self-consistent theory, the approach to determine the four coupling parameters related to local stress and strain state in the heterogeneous rock with multiphase components is proposed. A meso finite element model (meso-FEM) is employed to calibrate the calculation process according to four load paths. Based on the generalized wave equation, three characteristic wave velocities of 3-D plane waves are derived to describe the compression-shear coupled effect on wave propagation. These wave velocities (e.g. the primary wave and secondary wave) are different from those of the conventional compression wave and shear wave due to the coupled effects. As an example, the theoretical method is further employed to investigate wave velocities in the heterogeneous granular medium due to particle rotation. It indicates that wave velocities in the looser medium are related to local rotation and local strain. Particle rotation has significant effects on the wave velocities, which causes severe heterogeneity and compression-shear coupling effect in particle material. Both the heterogeneous distribution of internal materials and particle rotation affect wave velocities. The results provide a profound theoretical explanation for the heterogeneity of rock and are expected to provide a comprehensive understanding of the physical mechanism of the effect of heterogeneity on wave velocity.

Derivation of heterogeneous material distributions and their sensitivity to HM-coupled two-phase flow models exemplified with the LASGIT experiment

Advective gas transport in bentonite, a possible buffer material in repositories for radioactive materials, is difficult to simulate in numerical continuum models, partly due to the complicated microstructure of bentonite. To generate reliable models of repositories nevertheless, spatially distributed heterogeneous material properties can be used to allow localization of gas flow. In this study, a pore-size-dependent stochastic approach of the gas entry pressure is derived from Mercury Intrusion Porosimetry, which is used to replicate measurements from the LASGIT experiment. In addition, three benchmark tests are simulated to investigate the dependence of heterogeneous distributions of material properties on the mesh discretization, the temporal dependence, and the coupling between the processes influenced by the heterogeneous parameters. The numerical modeling results of the LASGIT experiment show that the onset of gas flow into the system and the subsequent increase in pressure and stress can be well reproduced using heterogeneous distributions. Compared to a model with homogeneous material properties, heterogeneous distributions may allow the generation of dilatancy-controlled microfractures—an important feature with regard to the advective gas flow in bentonites. However, it can be observed that the heterogeneous distributions in LASGIT are less significant, as technical gaps or differences in material types could have a greater impact.

The Dielectric Properties of Martian Regolith at the Tianwen‐1 Landing Site

AbstractMars' surface is characterized by a weathered layer of regolith and exposed rock exposures that are the results of long‐term geological processes. The Mars Rover Penetrating Radar (RoPeR) on board the Zhurong rover of China's first Mars mission (Tianwen‐1) has been investigating the fine structure and dielectric properties of the martian regolith in the southern Utopia Planitia. The permittivity of the regolith within 5 m of the landing zone is , and the average loss tangent is 0.0060 ± 0.0002, 0.0087 ± 0.0002, and 0.0114 ± 0.0002 using the geometric compensation of R2, R3, R4, respectively. The permittivity distribution map has been derived to show permittivity varying with depth and location. The high dispersion of both permittivity and loss tangent values along the traverse path indicates relatively heterogeneous material distribution on the landing site compared to an airless body such as the Moon.

A Variational Formulation of Physics-Informed Neural Network for the Applications of Homogeneous and Heterogeneous Material Properties Identification

A new approach for solving computational mechanics problems using physics-informed neural networks (PINNs) is proposed. Variational forms of residuals for the governing equations of solid mechanics are utilized, and the residual is evaluated over the entire computational domain by employing domain decomposition and polynomials test functions. A parameter network is introduced and initial and boundary conditions, as well as data mismatch, are incorporated into a total loss function using a weighted summation. The accuracy of the model in solving forward problems of solid mechanics is demonstrated to be higher than that of the finite element method (FEM). Furthermore, homogeneous and heterogeneous material distributions can be effectively captured by the model using limited observations, such as strain components. This contribution is significant for potential applications in non-destructive evaluation, where obtaining detailed information about the material properties is difficult.

Biomechanical modeling of rice seedling stalk based on multi-scale structure and heterogeneous materials

Rice seedling stalks are biologically characterized by multilayer porous structure and multiphase inhomogeneous material properties. This biological properties make it challenging to reveal the biomechanical behavior and damage mechanism of rice seedling stalks under mechanical load. In this research, the mechanical properties of the cell wall in each leaf sheath of rice seedling stalk were measured by nanoindentation, and a three-dimensional (3D) structure model of rice seedling stalk was established using micro-computed tomography (Micro-CT). According to the gray value difference in the CT images, rice seedling stalk was defined as three types of materials: protoplasts, parenchyma cell wall and collenchyma cell wall. A 3D finite element model of rice seedling stalk with heterogeneous material distribution was established based on the mapping relationship of gray value-density-elastic modulus. The accuracy of the model was verified by radial compression and axial tensile tests from three aspects: macroscopic mechanical response, microscopic mechanical behavior, and actual load effect. The results show that the modeling method is fast and reliable, and effectively improves the analytical accuracy of biomechanical properties for living plant materials with multi-layer porous structure characteristics, heterogeneous anisotropic material properties, and high moisture content. It also provides a useful tool for revealing the damage mechanism and quantitative damage evaluation of living plants under mechanical loading. This will be of great help to the optimization of the structure and working parameters of transplanting mechanism.

Preliminary results of the first lithic raw material survey in the piedmont zones of Kazakhstan

The study of raw materials was comprehensively studied in European and African Palaeolithic. However, systematic research of raw material sourcing has not been undertaken for the Palaeolithic of Kazakhstan, such surveys being embedded in reconnaissance works aimed at discovering new Palaeolithic sites. Our work presents preliminary results of the first lithic raw material survey in Kazakhstan. This study distinguishes the geographic patterns of land-use and their correlation with the stone tools from stratified sites. We describe primary and secondary sources of raw materials and compare macroscopically with the lithic assemblages. The survey results show a heterogeneous distribution of raw materials throughout the study regions. Macroscopic observations of lithic assemblages, and data extracted from literature suggest that hominins primarily selected local raw materials. Regional differences in the utilisation of a particular type of raw material which can be observed through the macroscopic examination of the lithic collections are confirmed by survey results.

The Application of a Multi-Material Flexible Chain Mail for the Design of an Artificial Spinal Disc to Reproduce Natural Nonlinear and Anisotropic Rotational Behavior.

Inspired by the potential of architected materials for achieving biomimicking functionalities and the advancement of multi-material additive manufacturing to fabricate parts with complex structures and heterogeneous material distributions, this study investigates the feasibility of using a multi-material, flexible chain mail sheet for the design of an additively manufactured artificial spinal disc for reproducing patient-specific anisotropic and nonlinear rotational behaviors. The application of a chain mail-based structure is motivated by its similarities in behaviors compared with a natural disc's fiber network that likewise has negligible bending stiffness and shape-changing ability. The proposed approach for the chain mail sheet design includes an initial characterization of the uniaxial tensile responses of the chain mail unit cell defined as the basic building block of the chain mail sheet, modeling and response calculation, and material optimization. Results show that the additively manufactured chain mail sheet is not only able to exhibit a natural strain-stiffening rotational response but also is able to reproduce natural anisotropy of three natural disc specimens in the six most common rotational scenarios in daily life. This study shows the potential of additively manufactured mechanical-metamaterials-inspired structures for implant design to restore natural mechanics.

Nonlinear material identification of heterogeneous isogeometric Kirchhoff–Love shells

This work presents a Finite Element Model Updating inverse methodology for reconstructing heterogeneous material distributions based on an efficient isogeometric shell formulation. It uses nonlinear hyperelastic material models suitable for describing incompressible material behavior as well as initially curved shells. The material distribution is discretized by bilinear elements such that the nodal values are the design variables to be identified. Independent FE analysis and material discretization, as well as flexible incorporation of experimental data, offer high robustness and control. Three elementary test cases and one application example, which exhibit large deformations and different challenges, are considered: uniaxial tension, pure bending, sheet inflation, and abdominal wall pressurization. Experiment-like results are generated from high-resolution simulations with the subsequent addition of up to 4% noise. Local optimization based on the trust-region approach is used. The results show that with a sufficient number of experimental measurements, design variables and analysis elements, the algorithm is capable to reconstruct material distributions with high precision even in the presence of large noise. The proposed formulation is very general, facilitating its extension to other material models, optimization algorithms and meshing approaches. Adapted material discretizations allow for an efficient and accurate reconstruction of material discontinuities by avoiding overfitting due to superfluous design variables. For increased computational efficiency, the analytical sensitivities and Jacobians are provided.

Modeling Early Clustering of Impact-induced Ejecta Particles Based on Laboratory and Numerical Experiments

Abstract A projectile impact onto a granular target produces an ejecta curtain with heterogeneous material distribution. Understanding how the heterogeneous pattern forms is potentially important for understanding how crater rays form. Previous studies predicted that the pattern formation is induced by inelastic collisions of ejecta particles in early stages of crater formation and terminated by the ejecta’s expanding motion. In this study, we test this prediction based on a hypervelocity impact experiment together with N-body simulations where the trajectories of inelastically colliding granular particles are calculated. Our laboratory experiment suggests that pattern formation is already completed on a timescale comparable to the geometrical expansion of the ejecta curtain, which is ∼10 μs in our experiment. Our simulations confirm the previous prediction that the heterogeneous pattern grows through initial inelastic collisions of particle clusters and subsequent geometric expansion with no further cluster collisions. Furthermore, to better understand the two-stage evolution of the mesh pattern, we construct a simple analytical model that assumes perfect coalescence of particle clusters upon collision. The model shows that the pattern formation is completed on the timescale of the system’s expansion independently of the initial conditions. The model also reproduces the final size of the clusters observed in our simulations as a function of the initial conditions. It is known that particles in the target are ejected at lower speeds with increased distance to the impact point. The difference in the ejection speed of the particles may result in the evolution of the mesh pattern into rays.

Targeting mixtures of jarosite and clay minerals for Mars exploration

AbstractTerrestrial thermal environments can serve as analogs for subsurface environments in the search for life because they regularly host microbial communities, which may leave behind biosignatures. This study focused on an acid-sulfate hydrothermal site as an analog for a potentially habitable environment on Mars. A weathered boulder in the thermal area was dissected, revealing an interior marked with disconnected horizons of differently colored materials, very low pH, and increasing temperature. The mineralogy comprised weathering products from andesite (kaolinite, quartz, clinoptilolite) along with sulfate salts (alunite, jarosite, tschermigite, and copiapite) formed by oxidation of sulfide and ferrous iron. Characterization of organic matter in this boulder and several soil samples yielded interesting but surprising results. Both mass spectrometry and Raman spectroscopy identified organic compounds in portions of the soils and the boulder. Jarosite-associated samples showed more numerous and diverse organic signatures than did Al-bearing silicate samples, despite the lower total organic carbon content of the jarosite-associated soils (0.69 ± 0.07 wt% Corg) compared to the Al-bearing samples (1.28 ± 0.13 wt% Corg). Results from our geochemical, mineralogical, and spectroscopic study of hydrothermal alteration products and salts inform the heterogeneous distribution of inorganic and organic materials that could delineate habitats and demonstrate the limits on organic matter detectability using different analytical techniques. Furthermore, we relate our measurements and results directly to current and upcoming martian missions, and we provide recommendations for detection and characterization of minerals and organics as biosignatures on Mars using instruments on future missions.

Seismic-scale finite element stress modeling of the subsurface

The stress field in rock formations of the subsurface is a key element to understand for the planning of underground operations in a safe and sustainable way. Such operations include the drilling of wells, hydrocarbon production, fluid injection for enhanced oil recovery and CO2 storage, hydraulic stimulation for unconventional resources, geothermal reservoirs, and many more. Modeling the subsurface stress field using 3D finite element (FE) simulations is common practice in the oil and gas and other industries. It allows to understand the prevailing in-situ stress and changes in terms of stress, deformation and rock failure that could result from planned operations. Such modeling is thus key to guide safe subsurface operations of many types and it is paramount that all available data and known complexity is captured in the highest possible resolution in these models. This results in a continuous quest for larger numerical simulations, which in turn demand software and linear solver technology to keep pace and ensure those do not become a limiting factor for computing the in-situ stress field.In this study, a FE simulator for 3D geomechanical modeling is optimized in multiple aspects to efficiently solve high resolution numerical stress simulations on large scales consisting of hundreds of millions of elements. This capability is demonstrated using a real-world dataset from the Gulf of Mexico to generate multiple geomechanical models from 500 million to over 1 billion elements. The models include fully heterogeneous material distributions and are built directly from seismic inversion data following a new direct modeling workflow that significantly facilitated pre and postprocessing. Using state-of-the-art high-performance compute (HPC) infrastructure, such models can be solved in less than 4 h with more than 3000 processors by applying hybrid parallelization methods. This demonstrates feasible turnaround times for such large stress simulations that enable geomechanical investigations in sufficient detail to improve the safety and sustainability of subsurface operations.

New approach for the high electrochemical performance of silicon anode in lithium-ion battery: A rapid and large surface treatment using a high-energy pulsed laser

Silicon nanoparticle based anode is effective to extend cycle life by reducing pulverization of silicon particles during lithiation and de-lithiation. However, it is hard to handle nano-scale materials during a series of manufacturing processes in the industry. Particularly, during the drying process, inhomogeneous material distribution within electrode is prone to form a dense surface region by agglomeration of the nanoparticles, causing degradation of electrochemical performances. In this work, we report the effects of laser surface treatment on the dense surface region formed by heterogeneous distribution of materials within the silicon anode based on nanoparticles during the drying process. Laser surface treatment enhanced the cycle life (laser-treated, 1000 mAh g−1 vs. original, 250 mAh g−1 at 200 cycles), rate capability and columbic efficiency considerably. From mechanism study on physicochemical changes at the surface region during laser surface treatment, it is revealed that the characteristics of the laser-treated surface contributes to the reduction of internal resistances and thickness of the solid electrolyte interphase layer, and improves diffusion characteristics.

Thickness of orthopyroxene-rich materials of ejecta deposits from the south pole-Aitken basin

The South Pole-Aitken (SPA) basin is the largest impact structure on the Moon and is believed to have excavated the orthopyroxene (Opx)-rich lower crust and/or upper mantle materials. For the complex craters outside of the SPA transient cavity, the origin of the Opx-rich central peaks is possibly from either the Opx-rich materials of the SPA ejecta deposits or the unexcavated lower crust and/or upper mantle. To estimate the thickness of the Opx-rich materials of the SPA ejecta deposits, this study investigated large complex craters (dozens of kilometers) that have penetrated the Opx-rich materials and exposed deeper mafic-poor crustal material based on spectra extracted from small fresh craters (sub-kilometer scale). The amount of foreign material introduced to these large complex craters by other lunar impact events was estimated to guarantee the least influence on the compositional analysis. The study results suggest that a 56 km-diameter crater at ~640 km northwest of the SPA center is large enough to penetrate the Opx-rich materials of the SPA ejecta deposits, which are thinner than ~4.7 km at this location. This result also indicates that the intense bombardment history of the large craters and basins outside of the SPA transient cavity excavated and redistributed a large amount of crustal material across the basin, possibly resulting in the heterogeneous distribution of mafic-rich and mafic-poor materials on the SPA surface.

Heterogeneous effects in simulating a fast nuclear reactor on the BFS test facility

Simulating fast neutron reactor cores for comparing experimental and calculated data on the reactor neutronics characteristics is performed using zero power test stands. The BFS test facilities in operation in Russia (Obninsk) are discussed in the present paper. The geometrical arrangement of materials in the cores of the simulated reactors (fuel pins, fuel assemblies, coolant geometry) differs from the simulation assembly on the BFS. This can cause differences between the experimental results obtained at the BFS and theoretical calculations even in the case when homogenized concentrations of all materials of the reactor are thoroughly observed. The resulting differences in neutronics parameters due to the geometry of arrangement of materials with the same homogeneous concentrations are referred to as the heterogeneous effect. Heterogeneous effects tend to increase with increasing reactor power and its size, mainly due to changes in the neutron spectra. Calculations of a number of functional values were carried out for assessing the heterogeneous effects for different spatial arrangements of the reactor materials. The calculations were performed for the following cases: a) heterogeneous distribution of materials in accordance with the design of a fast reactor; b) heterogeneous arrangement of materials in accordance with the capabilities and design features of the BFS test facility; c) homogeneous representation of materials in the reactor core and breeding blankets. The configuration of materials in accordance with the design data for fast reactors of the BN-1200 type was accepted as the basic calculation option, relative to which the effect called the heterogeneous shift of the functional value (HSF) was calculated. The effect of neutron leakage on the HSF obtained as the result of calculations using different boundary conditions was estimated. All calculations were carried out for the same homogeneous concentrations of all materials for all the above three configurations. Calculations were carried out as well for the case when plutonium metal fuel was used in the BFS. The values of the following functionals were calculated for different cases of arrangement of materials: the effective multiplication factor (reactivity), the sodium void reactivity effect, the average energy of fission-inducing neutrons, and the ratios of radioactive capture cross-sections to fission cross-sections for 239Pu. The calculations were performed using the Serpent 2.1.30 (VTT, Finland) Monte Carlo software package for neutronics simulations and ENDF/B-VII.0 and JEFF-3.1.1 evaluated nuclear data libraries. The effects of various options of material arrangement on the values of keff were found to be the greatest (about 1.6%) for the case when fissile material in the form of dioxide is replaced with metal fissile material. Homogenization of the composition reduces the keff value by about 0.4%. The average energy of fission-inducing neutrons depends to a significant extent on the leakage of neutrons and the presence of sodium (the average energy of neutrons increases and reaches in the presence of sodium about 100 keV, that is, it increases by about 11–13%). Replacing fissile material metal with its dioxide in the BFS test facility (while maintaining homogeneous concentrations, including that of oxygen) allows reducing the average energy of fission-inducing neutrons by about 60 keV. The highest values of HSF, reaching 65%, are observed when calculation of sodium void reactivity effect is performed with materials distributed homogeneously; however, HSF is equal to 1.5% when calculation of the reactor mock-up assembled on the BFS is performed. In the absence of neutron leakage (infinitely extended medium), the sodium void reactivity effect becomes positive and the HSF is equal to 4–7%. The heterogeneous effect of α for 239Pu noticeably (6–8%) depends only on the replacement of metallic plutonium with its dioxide (maintaining, of course, the homogeneous concentrations).