Keff Values Research Articles

A criticality assessment through user's routines in FLUKA

In the present paper, a method to obtain the keff value using the FLUKA code is described. It took advantage of the chance to write user defined routines in the standard code. A new algorithm was implemented and tested on the simulation of a research nuclear reactor. Results pertaining to the estimation of keff and neutron fluence are in good agreement with the MCNP's ones.

Assessment of CO2 storage prospect based on physical properties of Rio Bonito Formation rock units

The physical properties of the rock units associated with the Rio Bonito Formation are presented in this study with the focus on modelling reservoir quality based on petrophysics-derived parameters to evaluate CO2 storage potentials. It involves the modelling of the reservoir depths, thicknesses, flow zone indicators (FZI), and effective permeability (Keff) and presenting the CO2 storage efficiency factors peculiar to the rock units of the study location. Research results presented by this study for the stated objectives are not quite common in the region. Keff values range from 200 mD to higher than 2000 mD, and FZI values are generally above 1.0 μm and up to 13.0 μm within the portions covered by the drilled wells. The sandstone units recorded are up to 20 m thick in some cases. The Keff and FZI models indicate the sandstone reservoirs as permeable units to support the injection and circulation of CO2 within the potential reservoir units of the Rio Bonio Formation across São Paulo State. Apart from some points in the southeastern part of the study location, where the Rio Bonito are delineated at depths less than 800 m (minimum CO2 storage depth based on best practices), other portions are deeper, ranging from 950 m to 3500 m. Thin-bedded layers will affect the integrity of the rocks as CO2 storage tanks or reservoir seals/traps/overburden within the region. Sandstone bed thicknesses are up to 20 m in some cases. However, hybrid CO2 reservoir units are feasible, especially in portions where thin siltstone layers are sandwiched between sandstone units to provide considerable thicknesses based on CO2 storage standards. The current study shows that useable areas considering reservoir thickness, depth, and other physical qualities will significantly control the CO2 storage efficiency of the study location. Further studies featuring a detailed geophysical exploration of the site to confirm the availability and saturations of pre-existing fluid (hydrocarbon and water) are encouraged to boost CO2 storage in the region. The related research-based results, as mentioned above, may be combined with the results of this research to determine the area's potentials for CO2 storage or hydrocarbon production with CO2 storage options.

Comparison of Neutron-Physical Parameters of EPR and WWER-1500 using MCNP Computer Code

Three-dimensional calculations of the neutron-physical parameters were performed with the MCNP computer code for two models of a reactor core. The purpose was to determine the coefficient of reproduction of neutrons keff in each of the defined cases, as well as to qualitatively illustrate the neutron flux in axial and radial directions of the reactor core. A generalized analysis of the obtained results is performed, and it can be said that the prepared models, being relatively simple, meet the goal of this paper, namely presenting the basic principles of performing criticality calculations with the MCNP computer code. All calculations for this paper were performed with MCNP5, ver. 1.4. In the present paper, two active core models are considered – one for the EPR reactor and the other for the WWER-1500. Both projects are categorized as Generation 3 nuclear reactors. The following components of the core are included in both models: fuel elements, control rods and coolant. The fuel elements are presented as solid uranium dioxide cylinders coated with zirconium alloy. The fuel elements are grouped in fuel assemblies, in the case of the EPR reactor the fuel elements are arranged in a square grid, and in the case of the WWER-1500 reactor – in a triangular grid (hexagonal geometry). The limits of both models in the radial-azimuthal direction coincide with the inner diameter of the reactor vessel, and in the axial direction the limit is 56 cm in both directions from the end of the fuel elements. The calculations performed in this paper do not aim to quantify the distribution of neutron flux in the core, nor to find with great accuracy the coefficient of reproduction of neutrons keff at different stages of the reactor campaign. The calculations are made in order to verify the accuracy of the compiled input files. A criterion for this could be the demonstration of basic neutron-physical parameters, such as an increase in the value of keff with increasing the fuel enrichment and qualitative illustration of the change in the distribution of the neutron flux when introducing control rods in the core.

Neutronics analysis of UN-PuN fuel for 300MW pressurized water reactor using SRAC-COREBN code

Nuclear Power Plants (NPP) is one of alternative energy that can be used to replace fossil energy. NPP is a clean energy that doesn't emit CO2 as a residue from the power plant. Pressurized Water Reactor (PWR) is the most widely used commercial reactor to date. This reactor usually uses UO2 as fuel with enrich U-235 and produce plutonium as a waste nuclear. In this study, the fuel uses natural uranium and the addition of plutonium from the spent fuel of PWR, calling it Uranium-Plutonium Nitride (UN-PuN) fuel. Plutonium from spent fuel PWR (U-fueled) consists of Pu-238, Pu-239, Pu-240, Pu-241 and Pu-242, which Pu-239 and Pu-241 are fissile material. The aim of using plutonium is to reduce the amount of nuclear waste and prevent the use of plutonium as a nuclear weapon. The addition of neptunium and protactinium is also carried out in the fuel. Neptunium is one of the minor actinide materials which have high toxicity, so add Np-237 it is very useful to reduce the amount of neptunium in the world. And also, the addition of Np-237 and Pa-231 aims to decrease the keff value both in the Beginning of Life (BOL) and End of Life (EOL) in the reactor. This research calculates the neutronic calculations for PWR use SRAC2006 with COREBN Code and Japanese Evaluated Nuclear Data Library 4.0 (JENDL-4.0) for the nuclear data library. The COREBN code is a calculation method based on interpolation of macroscopic cross-section and finite-difference diffusion theory. The optimum design reached the maximum k-eff value 1.017077 and the maximum power density was 58.47 W/cc. The results obtained are the excess reactivity value of 1.68 % smaller than previous study which produces an excess reactivity value of 11.94 %. So this design has the potential to be applied in the PWR design

Testing the validity of the core-shell-surface layer model on the size dependence of effective magnetic anisotropy in magnetic nanoparticles

The stability of the stored information in magnetic recording media depends on the anisotropy energy Ea (=KeffV) of nanoparticles (NPs) of volume V or diameter D. Therefore, it is important to know how the effective anisotropy constant Keff varies with size D of the NPs. In a recent paper [Appl. Phys. Lett. 110, 222409 (2017)], the observed Keff versus D variation in NPs of maghemite (γ-Fe2O3) was explained on the basis of the core-shell-surface layer (CSSL) model given by Eq.: Keff = Kb + (6KS/D) +Ksh{[1-(2d/D)]−3–1}, where Kb,KS, and Ksh are the anisotropy constants of spins in the core, surface layer, and a shell of thickness d, respectively. This CSSL model is an extension of an earlier core-surface layer (CSL) model described by Keff = Kb + (6KS/D) [Phys. Rev. Lett. 72, 282 (1994)] proposed to explain the Keff versus D variation in Fe NPs. For the NPs of γ-Fe2O3, the additional term of the CSSL model involving Ksh was found to be necessary to fit the data for sizes D < 5 nm. In this paper, we report the validity of the CSSL model for NPs of several other systems viz. Co, Ni, NiO, and Fe3O4 using the available data from literature. In selecting the data, care was taken to consider data only for non-interacting NPs since the interparticle interactions generally overshadow the actual value of Keff in NPs. It is shown that the new CSSL model describes very well the Keff vs. D variation for all particle sizes whereas the CSL model fails for smaller particles with the notable exception of Fe NPs. This validation of the CSSL model for the NPs of Co, Ni, NiO, Fe3O4, and γ-Fe2O3 suggests its general validity for magnetic NPs. Discussion is also presented on the comparative magnitudes of the parameters Kb, KS, and Ksh obtained from the fits to the CSSL model.

Temperature dependence of magnetic anisotropy in a cylindrical Fe65Pd35 nanowire array

Fe65Pd35 cylindrical nanowires (NWs) were synthesized in commercial anodic alumina porous templates via potentiostatic electrodeposition. The morphology, composition, and crystalline structure were analyzed by scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction. The NWs obtained are (10 ± 2) μm long and (200 ± 20) nm in diameter, with a polycrystalline microstructure. Magnetic properties were investigated by measuring the Zero Field Cooling-Field Cooling magnetization curves and hysteresis loops in the temperature range 10 K to 350 K. The magnetization easy axis is determined to be along the NWs axis, indicating strong anisotropy in this direction, which cannot be accounted for by only considering shape anisotropy. The hysteresis loops were fitted using the law of approach to saturation, obtaining the effective anisotropy field HA and the effective anisotropy constant Keff value for different temperatures. The blocking temperature TB dependence on the magnetic field H was also analyzed, indicating that a blocked magnetic contribution is present, arising from the smaller grains in the NWs. The observed enhancement in the effective magnetic anisotropy of the array throughout the studied temperature range is explained by considering magnetic interactions among these nanograins.

Generalized correlation for effective thermal conductivity of high porosity architectured materials and metal foams

This paper presents a numerical study on the effective thermal conductivity (keff) of architectured materials typically realized through additive manufacturing. Four different unit cell topologies- Cube, Octet, Face-diagonal Cube, and Tetrakaidecahedron, were simulated for a range of porosity values, and both solid- and fluid-phase thermal conductivities. Numerically predicted keff values were validated against the in-house experiments carried out on single-cell thick 5 × 5 unit cell arrangement samples. These simulations led to a correlation for keff as a function of lattice porosity and thermal conductivities of solid- and fluid-phase materials. For the solid-to-fluid thermal conductivity ratio (ks/kf) greater than 300, the keff showed dependence on only the solid thermal conductivity for any given porosity and unit cell topology. The proposed correlation for the keff of architectured materials is applicable to all the four unit cell topologies with porosities > 0.8, and ks/kf ranging from 102 to 104. For these parameters, the correlation can also predict the keff of high-porosity metal foams obtained via foaming process with an accuracy of ±10%.

Fuel loading pattern optimization of ALLEGRO fast reactor using genetic algorithms

In this work the genetic algorithmic (GA) optimization technique is used to find the optimal fuel loading pattern in the experimental fast reactor ALLEGRO. The penalty function method is used to solve this multi-objective combinatorial optimization problem. To evaluate each loading pattern, an interface between the genetic algorithm code and the ERANOS 2.3 deterministic neutronic simulation code was developed. For the simulation of the fuel cycle in ERANOS, the diffusion approach and a 7-group energy structure are used to reduce the computational cost. An integer variable encoding scheme was defined to represent the fuel loading patterns. Two crossover operators, the partially mapped crossover (PMX) and the order crossover (OX), combined with the random mutation operator were implemented as an alternative to the classical operators used in GA. To evaluate the performance of the code the results are compared using two objective functions and two crossover operators. In the first case the operating cycle length is maximized by maximizing the k-eff value at the EOC by satisfying the constraints on the power peaking factor over the cycle, the excess reactivity at the BOC, and the linear heat generation rate constraints. In addition, a condition was imposed that there should be no more than two contiguous positions in the pattern to preserve the power distribution uniformity and to avoid high power peaking factors. The code works very well, and a good solution was found in a reasonable computation time. The best solution corresponds to the PMX operator, and the running time is twice as short compared to the OX operator. In the second case study, a power distribution flatness term is included in the objective function. In this case, a more uniform radial power distribution is obtained but associated with a decrease in cycle length due to the penalty of the flatness term.

Electrochemical Development and Characterization By SECM of 2D Carbon-Based Materials Architectured for Energy Storage and Conversion

With the fastly-growing social and commercial demands for portable electronic devices and the need for developing environmentally friendly high-power energy sources, new non-critical, non-toxic materials are currently being widely studied [1]. Electrochemical Double Layer Capacitors, also termed as supercapacitors, store energy electrostatically by charge separation at the high-surface-area porous carbon / electrolyte interface, by charging the electrochemical double layer [2]. Carbon-based materials are the most widely used electrode materials for EDLCs because of their desirable physical-chemical properties and low cost. Out of the various carbon structures explored as electrode materials, graphene appears to be a promising candidate thanks to its key properties [3].In this work, in-depth electrochemical characterizations of 2-Dimensional graphene-based materials was achieved using Scanning Electrochemical Microscopy (SECM) technique to study local electrochemical properties: ionic transport and charge transfer properties. 2D carbon materials with tuned interlayer distance were prepared by bridging reduced graphene oxide (rGO) sheets using hexanediamine electroactive molecules acting as pillars. Pillared and non-pillared porous graphene hydrogel (6GH and GHG respectively) composed were also synthetized and tested. Those measurements gave insights about the electroactivity and conductivity of the material’s surface. Also, the influence of the nature and lengths of the pillar on the electrochemical performance have been studied. Preliminary results using conventional electrochemical techniques show that the specific capacitance of raw GHG (170 F g-1) was reduced down to 70F g-1 when adding 6 carbons-hexanediamine pillars during its hydrothermal synthesis to prepare the 6GH (pillared graphene hydrogel). For the rGO, the addition of pillars with different lengths resulted in an increase of specific capacitance from 100 F g-1 to rGO to 140 F g-1 for rGO pillared with 7 atoms pillar diamine pillar (7RP) and 130 F g-1 for rGO pillared with 8 atoms diamine pillar (8RP) .Then, SECM experiments in feedback mode allowed for a fast comparison of the change in local electrochemical activity for the different surfaces through redox reactions between the tip and the electrode surface for all developed materials. Fitting measured approach curves to simulated ones can be used to estimate rate coefficients, as suggested by Chang, Mirkin and Bard [5]. The effective rate coefficient (keff) values for the mediator regenerating surface reaction were estimated using Wittstock's method by fitting the approach curves recorded at different positions. A 10µm diameter platinum-disc microelectrode was the tip connected to the Bio-Logic SECM-150 bipotentiostat and responsible for the approach curve measurement. For the GHG, it was found a 2.3 10-2 cm s-1 effective constant, which is reduced to 1.6 1.8 10-2 cm s-1 for the 6GH. For the rGO, the keff has the value of 3.3 10-2 cm s-1. The next step is to define the effective constant for the pillared rGO 7RP and 8RP. This study contributed to define the key characteristics allowing for the use of electrodes for supercapacitors offering optimal performance in energy density and power density.1- Zhang, Li Li; Zhao, X. S. Carbon-based materials as supercapacitor electrodes. , 38(9), 2520–0, 2009.2- Jiang Yang, Sundaram Gunasekaran. Electrochemically reduced graphene oxide sheets for use in high performance supercapacitors,Carbon, 2013.3- Zhu, Y.; Murali, S.; Stoller, M. D.; Ganesh, K. J.; Cai, W.; Ferreira, P. J.; Pirkle, A.; Wallace, R. M.; Cychosz, K. A.; Thommes, M. Carbon-Based Supercapacitors Produced by Activation of Graphene, 2011. 4-TAKAHASHI, Yasufumi. Development of High-Resolution Scanning Electrochemical Microscopy for Nanoscale Topography and Electrochemical Simultaneous Imaging. Electrochemistry, 2016.5- C. Wei, A.J. Bard, M.V. Mirkin, Scanning electrochemical microscopy. 31. Application of SECM to study of charge transfer processes at the liquid/liquid interface, J. Phys. Chem. 99 Figure 1

Monte Carlo calculation analysis of PWR-type fuel assembly mockup cores loaded with Gd2O3-UO2 fuel rods in B&W 1810 series critical experiments

ABSTRACT To extend the information on the validation of the JENDL-4.0 nuclear data library, continuous-energy Monte Carlo calculation was applied to the analysis of the twenty-two PWR-type fuel assembly mockup cores in the Babcock and Wilcox (B&W) 1810 series critical experiments which provided the benchmark data for the validation of the nuclear tools about using Gd2O3-UO2 fuel rods. The critical analysis results showed that the effective neutron multiplication factors (keff ) ranged from 0.99933 to 1.00040 and the average value was 0.99969. The keff values were scrutinized against the numbers of the Gd2O3-UO2 fuel rods, the insertion of the Ag-In-Cd absorber rods and the B4C absorber rods, and partially loading the 4.020 wt% UO2 fuel rods. The analysis results of the core radial fission rate distributions of the six cores indicated that the calculations generally well reproduced the measurements of the fuel rods in the central fuel assemblies. It was observed that the relative differences between the calculated and measured fission rates of the Gd2O3-UO2 fuel rods were larger than those of the neighboring UO2 fuel rods. This trend was examined by comparing with the results of the precedent studies of the Monte Carlo and deterministic transport calculations.

Comparison of thorium nitride and uranium nitride fuel on small modular pressurized water reactor in neutronic analysis using SRAC code

Comparison of thorium nitride (ThN) and uranium nitride (UN) fuel on small modular PWR in neutronic analysis has been carried out. PWR in module is one type of reactor that can be utilized because of its small size so that it can be placed on demand. Neutronic calculations were performed using SRAC version 2006, the data library using JENDL 4.0. The first calculation was fuel pin (PIJ) calculation with hexagonal fuel pin cell type. And the second calculation was reactor core (CITATION) calculation using homogeneous and heterogeneous core configurations. ThN and UN fuels use heterogeneous configurations with 3 fuel variations. The reactor geometry was used in two fuels are the same, with diameter and height active core was 300 cm and 100 cm. In this research, Np-237 was added as a minor actinide in the UN fuel to reduce the amount of Np-237 in the world and also reduce the k-eff value. For ThN fuel, Pa-231 also added in the fuel to reduce the k-eff value. The optimum configuration of UN fuel reached when used heterogeneous core configuration case four with percentage of U-235 in F1=5.5 %, F2=7 % and F3=8.5 % also with the addition of Np-237 0.2 % and fuel fraction 56 %. It has a maximum excess reactivity value 12.56 % %∆k/k. And then, the optimum configuration of ThN fuel reached when used heterogeneous core configuration case three with percentage of U-233 in F1=2 %, F2=4 % and F3=6 % with the addition of Pa-231 0.5 % and fuel fraction 53 %. It has a maximum excess reactivity value 7.67 % %∆k/k. The comparison of optimum design of UN and ThN fuel shows that the ThN fuel has the k-eff value closer to critical than UN fuel. Therefore, in this study, ThN fuel is more suitable for use in PWR reactors because it has a small excess value and can operate for 10 years without refueling

Spectral dependence of UV light penetration into powder TiO2 anatase

The penetration depth of UV monochromatic light into deposited TiO2 anatase powder was investigated. The light penetration depth was considered in units of numbers of surface hole, Ns, and electron, NO2, centers activated during irradiation. The numbers of hole centers Ns were obtained from photostimulated oxygen isotope exchange reaction registered by means of mass spectrometry. The numbers of electron centers NO2 were obtained from subsequent thermo-programmed desorption spectroscopy of photoadsorbed oxygen O2-. It was shown that the depth D of UV light penetration into UV absorbing TiO2 powder coat depends on the wavelength and intensity I0 of incident UV light and obeys to the equation DI0=1kefflg(I0/Im) obtained from the Beer–Lambert–Bouguer law with effective extinction coefficient keff and minimal value of light intensity Im, below which the photoactivation is considered negligible. Commonly, the value Im has an order of a few microwatts/cm2 for activation of electron and hole type centers except for a case of 334 nm falling into the band of the first direct band-to-band transition of anatase, where relatively high threshold value Im=0.063 mW/cm2 for photoactivation of hole centers was revealed. Effective extinction coefficient keff may be considered proportional to the absorption coefficient of TiO2 in the region of fundamental absorption, whereas, in the non-fundamental absorption region, keff exceeds significantly that of TiO2 due to, probably, dominating scattering processes. At small intensities of the incident light, there is a strong sensitivity of the penetration depth (and activated surface) to the intensity.

Neutronic analysis of the unfolding process of the LOTUS reactor design

The LOTUS reactor is a novel small thermal reactor concept designed for heat supply in winter. This pool-submerged reactor can unfold passively into four parts along its central axis solely under the buoyancy and gravity. When facing accidents like loss of coolant in the primary loop or in the pool, the unfolding process is expected to make the operational core sub-critical by reducing the volume of the fuel under the critical level and shut down the reactor immediately, which keeps the fuel assemblies in contact with water and delays the exposure in the air to ensure the safety. In this study, we implemented selected analyses using Serpent surrounding the unfolding process of the LOTUS reactor, including stepwise steady-state and transient calculations. This work showed that the fission power, keff value, flux, and reaction rate in the core decreased definitely as the reactor unfolded. The discrepancy between the results from the two modes of Serpent, however, indicated that in such dynamic behavior, considering the delayed neutrons and neutron moderation was crucial to the analysis, particularly to the water of the pool, which had a certain value of power deposited when the core power dropped during the unfolding process.

Perhitungan Burn Up Model Assembly Heksagonal pada Reaktor SCWR Menggunakan Bahan Bakarr Thorium

The research about the calculation of burn-up model of the hexagonal assembly in SCWR reactor using thorium as fuel materials has been done. This research uses thorium-232 and uranium-233 as fuel materials. Calculations were performed using the ASMBURN code in the SRAC program, by determining fuel enrichment, cell radius, analyzing atomic density after burn up, increasing burn up level, and change of linear heat. The calculation results obtained show the value of efficient fuel enrichment at 4% enrichment, with 0.3902 cm of fuel cell radius, 0.4508 cm of cladding, and 0.5586 cm of moderator. The atomic density of Th232 decreased for each burn-up period meanwhile, the atomic density of U233, U235, and Pu239 increased. The keff value will decrease along with the addition of burn-up and greater change of linear heat.

Study of the relationship between magnetic anisotropy and composition ratio of Fe oxide to Fe at CoFeB/MgO film interface

Ta (5)/CoFeB (1)/MgO (2)/Ta (2) (in nm) multilayers were deposited on silicon substrates by magnetron sputtering, and the MgO layer was prepared by two methods at the same argon gas flow rate: the radio frequency (RF) sputtering method of MgO target and the reactive sputtering method of direct current (DC) sputtering Mg target with introducing oxygen at the same time. The sample prepared by the former method was denoted as Sample A, and the latter was denoted as Sample B. The results indicate that as-deposited Sample A shows in-plane magnetic anisotropy (IMA) with Keff = -0.79 × 106erg/cm3. However, the as-deposited Sample B shows perpendicular magnetic anisotropy (PMA) with Keff = 1.69 × 106erg/cm3, and the Keff value increases to 3.17 × 106erg/cm3 after annealing at 250℃. X-ray photoelectron spectroscopy (XPS) results illustrate that the films show PMA when the composition ratio (ε) of Fe oxide to Fe in CoFeB/oxide interface of Sample A and B annealed below 300 ℃, is approximately in the range of 0.65–0.75. When ε is beyond the above range, the film shows IMA. Moderate oxidation state at the interface results in the formation of PMA and it was improved by forming effective orbital hybridization of Fe 3d and O 2p. High resolution transmission electron microscopy (HRTEM) analysis reveals that no crystallization appears in CoFeB and MgO layer of the film before and after annealing, and crystallization has no effect on the interface chemical states in this system.

A computational investigation for the impact of particle size on the mechanical and thermal properties of teak wood dust (TWD) filled polyester composites

The prime object and novelty of this investigation are to analyze the effect of particle size on the mechanical and thermal properties of teak wood dust (TWD) reinforced polyester composites. Teak woods are ground into powder form and sieved to three different sizes (58, 110, and 155 μm) by a sieve shaker. Poly + TWD composite specimens are prepared with different filler content (0, 5, 10, 20, 25 wt%) and (0, 3.35, 6.52, 11.95, 17.33 vol%) separately for tensile and thermal conductivity test respectively. The effective thermal conductivity and tensile strength of the composites are measured by Unitherm™ Model 2022 and universal testing machine (UTM) respectively. Thermal conductivity and tensile of the composites decrease with increase in TWD content. The solution casting method is used for the fabrication of composites. It is observed that the tensile strength and thermal properties of the composites improve with an increase in the particle size of the teak wood dust. For computational investigation, multi finite element Digimat-FE software is also utilized to analyze the tensile and thermal behavior of the composites. The computational predicted results are also compared with the measured values for confirmation of findings. The presence of higher stress concentration is marked in the polymer matrix at a larger particle size of TWD particles. The finding of the simulated effective thermal conductivity (Keff) value of the composites is also compared with other theoretical models. It is found that the numerical predicted findings are nearly concurrent with the thermal conductivity value calculated by other models and experimental results.

Impact of H in H2O thermal scattering data on criticality calculation: uncertainty and adjustment

In this paper, the impact of the thermal scattering data for H in H20 is estimated on criticality benchmarks, based on the variations of the CAB model parameters. The Total Monte Carlo method for uncertainty propagation is applied for 63 keff criticality cases, sensitive to H in H20. It is found that their impact is of a few tenth of pcm, up to 300 pcm maximum, and showing highly non-linear distributions. In a second step, an adjustment is proposed for these thermal scattering data, leading to a better agreement between calculated and experimental keff values, following an increase of scattering contribution. This work falls into the global approach of combining advanced theoretical modelling of nuclear data, followed by possible adjustment in order to improve the performances of a nuclear data library.

Effect of increasing interaction interface on perpendicular magnetic anisotropy of Pd/Co2MnSi/Pd multilayers

Interfacial interaction induced perpendicular magnetic anisotropy (PMA) is one of the research hotspots of magnetic recording thin films. The PMA of Pd/Co2MnSi(CMS)/Pd multilayers can be improved by increasing the interfaces of heavy metal/ferromagnetic (HM/FM). In order to study the effect of adding HM/FM interface on the PMA of multilayers, a Pd layer was inserted into the CMS of Pd/CMS/Pd film to form Pd/CMS(t/2)/Pd/CMS(t/2)/Pd multilayer structure with quadruple Pd/CMS interface, and the [Pd/CMS(t/2)]N was inserted into the Pd/CMS(t/2)/Pd film to form Pd/CMS(t/2)[Pd/CMS(t/2)]N/Pd multilayer structure. The results showed that the PMA and MS of Pd/CMS(t/2)/Pd/CMS(t/2)/Pd multilayers were enhanced. The maximum Keff was 52.3% higher than that of the Pd/CMS(t)/Pd structure. The increase of MS can effectively reduce the switching current density of the magnetic tunnel junction, and then reduce the energy consumption of magnetic record writing. For the Pd/CMS(3.5)/[Pd(0.8)/CMS(3.5)]N/Pd multilayers, the PMA peaked at N = 1. With the increase of N, the PMA decreases and gradually changes from PMA to IMA. This indicates that the increase of more Pd/CMS interfaces does not increase the PMA further. In addition, when N = 3 and 4, the expression of Keff values is inconsistent with the corresponding hysteresis loops, and the exchange bias effect of in-plane hysteresis loops appears at N = 4 and N = 5.

Development and application of TaSNAM 2.0 for advanced pressurized water reactor

The Nuclear Thermal-hydraulic Laboratory (NutheL) at Xi’an Jiaotong University developed a Temporal and Spatial Neutronics Analysis Module (TaSNAM) based on the User Defined Function (UDF) and User Define Scalar (UDS) in Fluent. The neutron diffusion equations were solved based on the Finite volume method (FVM). In this paper, the TaSNAM is extended the original function to solve 3D problems and obtain neutron parameters based on the neutron parameters library, and improved to TaSNAM 2.0. The 3D-IAEA benchmark problem was selected and simulated to validate. The calculated results show good agreement with the reference values and the difference from the reference value of keff is 40pcm. A three-dimensional steady-state simulation of the whole core in AP1000 was completed employing the TaSNAM 2.0. The calculated results of important parameters agree well with the design values and the detailed three dimensional distributions of neutron flux and power were achieved.

Core Configuration Analysis for Modular Gas-cooled Fast Reactor (GFR) using OpenMC

The core configuration analysis of modular Gas-cooled Fast Reactor (GFR) has been done to understand GFR performance. The modular GFR used a fast neutron spectrum and high-temperature helium gas, providing higher thermal efficiency than the other generation IV reactor candidates. In this paper, the variation of core configuration and dimension for core design has been applied in radial, axial, and radial-axial directions. The Monte Carlo method, named OpenMC code, has been used for the criticality and isotope evaluation of design core GFR. The OpenMC code provides the probabilistic solution to solve the neutron transport equation in a 3D model and non-homogenous physical volumes using Evaluated Nuclear Data File (ENDF/B-VII.b5) and continuous energy spectrum. The neutronics parameters characterized are the value of keff, fission rate and neutron flux distribution, and fissile material evolution to know of GFR core design’s performance. The analysis showed that the core configuration in radial direction gives a good understanding of the feasibility of GFR core design.