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Investigating the surface properties of heteroatom-doped carbon materials is essential because these versatile materials have found use in a variety of energy and environmental applications; an understanding of these properties would also lead to an improved appreciation of the direct interaction between the reactant and the functionalized surface. Herein, we explore the effect of boron (B) doping on the surface properties of activated carbon (AC) materials based on their water adsorption behavior and oxygen reduction reaction. In the high-temperature B doping process, B-doped AC materials at 1400 °C exhibit an open pore structure with B-O bonds, whereas at a temperature of 1600 °C, a nonporous structure containing a large amount of B-C bonds prevails. The B-O species act as active sites for water adsorption on the carbon surface. On the basis of the isothermal adsorption heat, we suggest that B atoms are present at the pore openings and on the surfaces. The B-O moieties at the open edges improve the electrocatalytic activity, whereas the B-C bonds at the closed edges decrease the electrocatalytic activity because of the stable structure of these bonds. Our findings provide new evidence for the electrocatalytic properties associated with the structure of B-doped edges.

Nitrogen (N)-doped nanostructured carbons have been actively examined as promising alternatives for precious-metal catalysts in various electrochemical energy generation systems. Herein, an effective approach for synthesizing N-doped single-walled carbon nanohorns (SWNHs) with highly electrocatalytic active sites via controlled oxidation followed by N2 plasma is presented. Nanosized holes were created on the conical tips and sidewalls of SWNHs under mild oxidation, and subsequently, the edges of the holes were easily decorated with N atoms. The N atoms were present preferentially in a pyridinic configuration along the edges of the nanosized holes without significant structural change of the SWNHs. The enriched edges decorated with the pyridinic-N atoms at the atomic scale increased the number of active sites for the oxygen reduction reaction, and the inherent spherical three-dimensional feature of the SWNHs provided good electrical conductivity and excellent mass transport. We demonstrated an effective method for promoting the electrocatalytic active sites within N-doped SWNHs by combining defect engineering with the preferential formation of N atoms having a specific configuration.

In the fabrication of safe, but powerful lithium ion batteries (LIBs), graphene-related materials are being actively examined in order to meet the demand for applications such as electric vehicles and smart grids. However, most of this work has focused on liquid-phase exfoliated graphene and reduced graphene oxide. Herein, we demonstrate a simple, but effective route for significantly improving the electrochemical performance of currently available LIBs by coupling current collector with catalytically grown large-area graphene. When coating current collectors with large-area three-layered graphene, a reduction in the internal resistance (or effective electron transfer) between the current collector and active materials was observed. The graphene also protected the underlying collector from corrosion, greatly improving the power capability and cyclability of LIBs. The three-layered graphene provided the best electrochemical performance and corrosion resistance because of its high electrical conductivity and mechanical stability during the transfer process. We believe that our approach using interfacial graphene coating can be used with all kinds of electrochemical energy-storage systems, in which high corrosion resistance, electrical conductivity, and flexibility are critical.

The low density of porous carbon nanomaterials for supercapacitor electrodes has limited their widespread application, despite their ultra-high gravimetric capacitance. In this work, we successfully prepared highly densified composite electrodes of graphene and single-walled carbon nanohorns (SWCNHs) using a simple spray-drying method that is suitable for mass production. To prepare the high-density composite electrodes, water-based mixtures of oxidized SWCNHs (NHOs) and graphene oxides (GOs) were spray-dried in heated air; after spray-drying, GOs dispersed in water were agglomerated in spherical clusters containing NHO nanoparticles. The reduced spray-dried GO/NHO (rS-GO/NHO) composite electrodes exhibited an extremely high bulk density of 1.23 g·cm−3, which is almost double that of commercial activated carbon (AC) and reduced NHO (r-NHO) electrodes, and three times higher than that of rS-GO electrodes. Of the materials tested, the rS-GO/NHO composite electrode had the highest volumetric capacitance (80 F·cm−3 at 1 mA·cm−2) and a low sheet resistance (0.005 Ω· sq.−1), which are far superior to those of commercial AC (57 F·cm−3 at 1 mA·cm−2 and 0.293 Ω·sq.−1, respectively), without the need for a conductive material, such as carbon black. We expect that these high-density graphene/SWCNH composite electrodes with high volumetric capacitances can be substituted for commercial AC materials in energy storage devices, such as supercapacitors.

Nitrogen enriched carbon nanofibers have been obtained by one-step carbonization/activation of PAN-based nanofibers with various concentrations of melamine at 800 °C under a N2 atmosphere. As synthesised carbon nanofibers were directly used as electrodes for symmetric supercapacitors. The obtained PAN-MEL fibers with 5% melamine stabilised at 280 °C and carbonized at 800 °C under a nitrogen atmosphere showed excellent electrochemical performance with a specific capacitance of up to 166 F g−1 at a current density of 1A g−1 using 6 M KOH electrolyte and a capacity retention of 109.7% after 3000 cycles. It shows a 48% increase as compared to pristine carbon nanofibers. Two electrode systems of the CNFM5 sample showed high energy densities of 23.72 to 12.50 W h kg−1 at power densities from 400 to 30 000 W kg−1. When used as an anode for Li-ion battery application the CNFM5 sample showed a high specific capacity up to 435.47 mA h g−1 at 20 mA g−1, good rate capacity and excellent cycling performance (365 mA h g−1 specific capacity even after 200 cycles at 100 mA g−1). The specific capacity obtained for these nitrogen enriched carbon nanofibers is higher than that for pristine carbon nano-fibers.

A generalized perturbation theory (GPT) formulation suited for the Monte Carlo (MC) eigenvalue calculations is newly developed to estimate sensitivities of a general MC tally to input data. In the ...

The continuous-energy Monte Carlo (MC) sensitivity and uncertainty (S/U) analysis conducted using the multigroup covariance matrices has a theoretical pitfall in that it is inconsistent with the principle of continuous-energy MC neutronics calculations because the use of the multigroup covariance matrices means treating covariance data as multigroup variables rather than continuous-energy variables. As a way to get around this deficiency and perform the MC S/U analysis on the theoretically consistent principle, this paper presents a new continuous-energy MC S/U formulation which directly utilizes the continuous-energy covariance data in the evaluated nuclear data libraries instead of the multigroup covariance matrices produced by nuclear data processing codes. The validity of the new MC S/U formulation is examined in terms of the input-nuclear-data-induced k uncertainty of the Godiva critical assembly and the TMI-1 pin cell problem by inputting the continuous-energy covariance data of nuclides inv...

Si-based composites wrapped in multiple graphene shells were successfully fabricated as binder-free anodes for Li-ion batteries (LIBs). Reduced graphene oxide (rGO) and Si nanoparticles were prepared as spherical composite structures using a facile spray-drying process. The microspheres were homogeneously incorporated into a 3D porous graphene aerogel (GA) structure using an aerogel synthesis process. The inner rGO shell surrounding the Si nanoparticles promoted an effective electron transfer from the surface of the Si nanoparticles to electrolytes and suppressed the continuous formation of an unstable solid–electrolyte interface layer. Moreover, the 3D, porous GA framework, which demonstrated high electrical conductivity and mechanical stability, promoted the homogeneous dispersion of the Si nanoparticles, an effective and fast Li+ ion diffusion, and the suppression of volume expansion during lithiation. The rGO/Si/GA composite anode constructed by multiple graphene shells had an extremely high initial discharge capacity (1217 mAh g−1), excellent cyclic stability (462 mAh g−1 at 1.0 C after 200 cycles), and superior rate capability (819 mAh g−1 at 10 C) owing to its multilayered structure. We expect that our simple and scalable approach for fabricating Si-based anodes wrapped in multiple graphene shells can contribute to the development of high-performance LIBs for use in electric vehicles.

The low energy density of commercially available activated carbon-based supercapacitors has limited their widespread applications. In the current work, we demonstrated fabrication of carbon nanofiber-based supercapacitors that exhibited ultra-high energy density by rationally tailoring their pore structure in an ionic liquid system. To gain control on the pore structure, three different methods were employed for the synthesis of an electrospinning-derived freestanding carbon nanofiber web. They are incorporation of a pore generator (i.e., tetraethyl orthosilicate) in the electrospinning step, physical activation (e.g., H2O or CO2), and hydrogen treatment. We observed finely tuned pore sizes ranging from 0.734 to 0.831 nm and accompanying changes in BET surface areas ranging from 1160 to 1624 m2 g−1. The entrapped TEOS within the electrospun organic nanofiber web provided high tuning ability of the pore structure in the following carbonization step, and decreased the activation energy of the pore formation. Both high specific capacitance (161 F g−1) and ultra-high energy density (246 W h kg−1) were achieved when the pore size on the surface of carbon nanofibers matched with the ionic size of the electrolyte. Our results demonstrate the importance of a finely tuned pore structure to secure high-temperature operable carbon nanofiber-based supercapacitors with ultrahigh energy density using ionic liquids as electrolytes.

Mesopore-enriched activated carbon nanofiber mats incorporating RuO 2 (RuPM-ACNF) are prepared by a simple electrospinning method with the help of poly(methyl methacrylate) (PMMA), and their electrochemical property electrodes are investigated as a supercapacitor electrode. The microstructure of RuPM-ACNF is changed in terms of high specific surface area, narrow pore size distribution, and tunable porosity. The textural parameters affect the electrochemical properties significantly through the variation in PMMA concentration. The active sites, RuO 2 and abundant mesopore structures of RuPM-ACNF not only increase the specific capacitance but also enhance the high-rate electrochemical performance by fast electrolyte ion diffusion into the pores with increasing PMMA concentration. The RuPM-ACNF electrode also exhibits good cycling stability after 3000 charge–discharge cycles, which demonstrates the good stability, long lifetime and high degree of reversibility in repetitive charge–discharge cycling of the RuPM-ACNF electrodes. Therefore, the cooperation of large mesopores induced by PMMA and RuO 2 in the ACNF electrode materials synergistically improves the electrochemical performance because of the electric double-layer capacitance of porous ACNFs and the pseudocapacitance of RuO 2 , resulting in high rate capability, high capacitance, and long cycling life.

McCARD is a Monte Carlo (MC) neutron-photon transport simulation code developed exclusively for the neutronics design and analysis of nuclear reactor cores. McCARD is equipped with the hierarchical modeling and scripting functions, the CAD-based geometry processing module, the adjoint-weighted kinetics parameter and source multiplication factor estimation modules as well as the burnup analysis capability for the neutronics design and analysis of both research and power reactor cores. This paper highlights applicability of McCARD for the research reactor core neutronics analysis, as demonstrated for Kyoto University Critical Assembly, HANARO, and YALINA.

RuO 2 -containing activated carbon nanofibers with hollow cores (PMRu-ACNFs) are prepared through one-step electrospinning using polyacrylonitrile (PAN), poly(methyl methacrylate) (PMMA), and ruthenium(III) acetylacetonate followed by thermal treatment. The porous PMRu-ACNF composites exhibit an improved morphological structure and textual properties due to the increased surface area, unique nanotexture, and presence of several functional groups such RuO 2 in the ACNFs. Electrochemical measurements of PMRu-ACNF reveal a maximum specific capacitance of 180 Fg −1 and high energy densities of 20-14 Whkg −1 in the power density range of 400 to 10,000 W kg −1 in aqueous KOH electrolyte. In contrast, the ACNF electrodes show a lower specific capacitance and the energy density rapidly drops to 2 Whkg −1 at power densities of 4,000 Wkg −1 . Therefore, the PMRu-ACNF composite electrodes may be more suitable as supercapacitors than regular ACNFs are, due to the synergistic effect between the electric double-layer capacitance of porous ACNFs and the pseudocapacitance of RuO 2 .

In the last decades, carbon fibers with light weight and high strength have experienced the largely increased uses in various industrial applications. However, their expected uses in the automotive industry and building are largely limited because of their high production cost. Herein, we have demonstrated an effective method of making low cost carbon fibers via the melt spinning of petroleum-processing residue (pyrolyzed fuel oil, PFO)/lignin blends. Careful selection of tetrahydrofuran as the solvent to dissolve both PFO and lignin was made to optimize the miscible blend. The melt spinnable blend with a softening point of 260–280 °C exhibited good spinning ability at 280 °C. The plasticizing function of PFO allowed the highly cross linked lignin-based pitch to have high fluidity in the melt spinning process. Based on detailed TEM observations, the thermally treated fiber prepared at 2800 °C exhibited a shell–core structure, consisting of a highly crystalline surface from PFO and an amorphous disordered core from lignin. Such a crystalline surface structure gave rise to a high modulus value (up to 100 GPa) to the prepared carbon fibers.

•Preparation of ZnO/ACNF composites by one-step electrospinning and spontaneous sol–gel processing of zinc acetate.•Investigation of the morphological, textual structure, and electrochemical performance of the ZnO-ACNFs.•Superior supercapacitor performance of the ZnO-CCNFs due to well-distributed ZnO on ACNF and suitable pore size distribution.

Carbon fibers are considered as one of the promising heating elements in various industrial applications because of their excellent thermal stability and electrical conductivity. In order to achieve controllability of the power output, gas-phase carbon deposition was carried out on the surface of carbon fibers by flowing a mixture of liquefied petroleum gas and hydrogen via electro-conduction chemical vapor deposition. We confirmed the tuning ability of the temperature ranging from 800 to 1330 °C. The microtexture of the deposited carbon was sequentially changed; the initial layer with small-sized domains, the intermediate layer with medium crystallinity, and the top layer with large-sized domains and high crystallinity. However, the linear decrease in the electrical conductivity of the heating elements was ascribed to the change in the growing direction of the crystallites from a longitudinal to a perpendicular direction with respect to the fibers. The wide range of power output for our carbon fiber composites from 270 to 448 W at 50 V will be useful for various industrial electric heating applications.

The hybridization of an electrochemically active metal oxide with electrically conductive carbon nanofibers (CNFs) has been utilized as a solution to overcome the energy density limitation of carbon-based supercapacitors as well as the poor cyclic stability of metal oxides. Herein, we have demonstrated the growth of binary metal oxide nanosheets on the engineered surface of CNFs to fully exploit their electrochemical activity. Metal oxide nanosheets were observed to grow vertically from the surface of CNFs. The high structural toughness of the CNF–metal oxide composite under strong sonication indicated strong interfacial binding strength between the metal oxide and the CNFs. The rationally designed porous CNFs presented a high specific surface area and showed high capacity for adsorbing metal ions, where the active edge sites acted as anchoring sites for the nucleation of metal oxides, thereby leading to the formation of a well dispersed and thin layer structure of binary metal oxide nanosheets. Excellent electrochemical performance (e.g., specific capacitance of 2894.70 F g−1 and energy density of 403.28 W h kg−1) was observed for these binary metal oxide nanosheets, which can be attributed to the large increase in the accessible surface area of the electrochemically active metal oxide nanosheets due to their homogeneous distribution on porous CNFs, as well as the efficient charge transfer from the metal oxide to the CNFs facilitated the improvement in the performance.

Zinc oxide (ZnO)-based porous carbon composite nanofibers (ZnO–CCNFs) are prepared by one-step electrospinning and subsequent thermal treatment using zinc acetate, as the pore generator and ZnO precursor. In particular, the PAN-based nanofiber paper contains in-frame incorporated nitrogen surface functionalities, due to its large residual nitrogen content in the char. The N functionalities doped at the graphite edges enhances their capacitance by the pseudocapacitive effect. Therefore, the ZnO–CCNFs showed higher capacitance (163 F g−1 at 1 mA cm−2) and energy density (20.80–14.80 W h kg−1 in the power density range of 400–20,000 W kg−1) than the control sample of carbon nanofibers (CNFs) in aqueous electrolyte. The combination of the high surface area of CNFs with the large capacity of surface functional groups such as N, O, and ZnO as the faradic electrode material affords the advantages of both the double layer capacitance and the pseudocapacitance, thereby offering potential applications for supercapacitors.

Porous carbon nanofibers (PCNFs) were prepared from electrospinning both without and with a pore generating inorganic material. Next, they were activated with different activation media (N2, H2O, or CO2). The pore size was tailored from 0.64 to 0.81 nm under various activation conditions, and the specific surface area ranged from 404 to 1624 m2·g−1. To determine the charging mechanism of the supercapacitor in an aqueous electrolyte, the normalized capacitance was calculated, and it was compared with the adsorption behavior of the solvent, H2O, separately. The normalized capacitance showed a trend similar to that of H2O adsorption at a low relative pressure (P/P0 = 0.1), which was expected to be driven by the filler–pore wall interaction, indicating that the ions were strongly solvated by the solvent, H2O. The highest normalized capacitance value (32 μF·cm−2 at 1 mA·cm−2) was achieved from PCNFs having a pore size of 0.64 nm, similar to the electrolyte solvated ion sizes. It was observed that both the capacitance and H2O adsorption were achieved near the pore size of 0.64 nm and at a high functionality. It was understood that the adsorption of the solvated ions was primarily driven by the interaction of the solvent, H2O, with the surface functional groups.

The multiobjective simulated annealing (MOSA)–based fuel assembly loading pattern (LP) optimization method, employing the discontinuous penalty function (DPF), is extended for multicycle applications by introducing an adaptively constrained discontinuous penalty function (ACDPF). A discontinuous point in the penalty function is adaptively shifted to a better direction during the course of MOSA such that the search can be more efficient. The advantages of the ACDPF-based MOSA algorithm over the original DPF-based algorithm are first examined with a real single-cycle LP optimization problem of an operating reactor, as well as with a simple LP optimization problem that has known solutions. A direct multicycle LP optimization method is then formulated with an application to the first four cycles of the Younggwang Nuclear Unit 4 (YGN4) core. The rearrangement method is devised as a fuel shuffling method that can avoid drastic changes in the LPs of the subsequent cycles of a seed cycle. It is demonstrat...

It is well known that the sample variance of a tally mean in Monte Carlo (MC) eigenvalue calculations is biased because of the intercycle correlations of the fission source distribution (FSD). This...

Organic-inorganic hybrid composite carbon nanofibers (CCNFs) are prepared by one-step electrospinning and subsequent thermal treatment using polyphenylsilane (PPS) as an inorganic precursor. We investigate the structural properties and electrochemical behavior of these CCNF materials when applied as supercapacitor electrodes as a function of the carbonization temperature ranging from 800 to 1000 °C. The introduction of PPS induces thermal stability for the organic-inorganic hybrid CCNFs via the incorporation of a porous structure with stabilized functional structures such as silicon oxynitride (SiOxNy) and silicon oxycarbide (SiOxCy). This phenomenon is attributed to the synergistic effect of both the double-layer capacitance and the pseudo-capacitive effect induced by the porous carbon layer and the some surface functionalities), thereby providing high charge capacity, power and energy density.

The B1 theory-augmented Monte Carlo (MC) method has been recently presented as a new MC method to generate homogenized few-group diffusion theory constants (FGCs) of nuclear systems such as a fuel pin cell or a fuel assembly (FA). It is demonstrated that it can produce FGCs that are well qualified for highly accurate two-step core neutronics analyses. However, it is unavoidable for FGCs from it to carry uncertainties that are ascribed to statistical uncertainties, as well as nuclear cross-section and nuclide number density input data uncertainties, of MC calculations pivotal in the new MC method. In order to evaluate the impact of these uncertainties of FGCs on the core neutronics design applications, therefore, it becomes essential to present their uncertainties quantitatively in addition to FGCs themselves. The purpose of this paper is to develop a mathematical formulation for separately quantifying contributions of statistical and input data uncertainties to uncertainties of FGCs from the new M...

The effects of alignment of polyacrylonitrile (PAN) nanofibers and a two-step drawing process on the mechanical properties of the fibers were evaluated in the current study. The alignment was achieved using a high-speed collector in electrospinning synthesis of the nanofibers. Under optimal two-step drawing conditions (e.g., hot-water and hot-air stretching), the PAN nanofiber felts exhibited large improvements in both alignment and molecular chain-orientation. Large increase in crystallinity, crystallite size, and molecular chain orientation were observed with increasing draw ratio. Optimally, stretched PAN-based nanofibers exhibited 5.3 times higher tensile strength and 6.7 times higher tensile modulus than those of the pristine one. In addition, bulk density of the drawn PAN nanofibers increased from 0.19 to 0.33 g/cm3. Our results show that fully extended and oriented polymer chains are critical in achieving the highest mechanical properties of the electrospun PAN nanofibers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43945.

The vanadium pentoxide (V 2 O 5 )/carbon nanofiber composites (CNFCs) were prepared from polyacrylonitrile/V 2 O 5 in N,N-dimethylformamide by a simple electrospinning method, and their electrochemical properties as supercapacitor electrodes were investigated. Different loadings of V 2 O 5 , the microstructures of the CNFCs (e.g., nanometer-size diameters, high specific surface areas, narrow pore size distributions, and tunable porosities) were changed, and the textural parameters significantly affected the electrochemical properties of the composites. The CNFC capacitors delivered the high specific capacitances of 150.0 F g −1 for the CNFCs in an aqueous, with promising energy densities of 18.8 Wh kg −1 , over a power density range of 400–20,000 W kg −1 . The CNFCs simultaneously exhibited excellent capacity retention.

Graphene/carbon composite nanofibers (CCNFs) with attached TiO2 nanoparticles (TiO2–CCNF) were prepared, and their photocatalytic degradation ability under visible light irradiation was assessed. They were characterized using scanning and transmission electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and ultraviolet–visible diffuse spectroscopy. The results suggest that the presence of graphene embedded in the composite fibers prevents TiO2 particle agglomeration and aids the uniform dispersion of TiO2 on the fibers. In the photodegradation of methylene blue, a significant increase in the reaction rate was observed with TiO2–CCNF materials under visible light. This increase is due to the high migration efficiency of photoinduced electrons and the inhibition of charge–carrier recombination due to the electronic interaction between TiO2 and graphene. The TiO2–CCNF materials could be used for multiple degradation cycles without a decrease in photocatalytic activity.

In this study, we have developed an economically viable and technologically sound process for the production of low-cost carbon fibers (CFs) made of lignin copolymer with acrylonitrile (AN). Initially, lignin, a by-product of the pulp and paper industry, is copolymerized with AN in dimethysulfoxide (DMSO) by the radical copolymerization. The resulting copolymer was confirmed by a Fourier transform infrared (FT-IR), 13C, and 1H nuclear magnetic resonance (NMR) spectroscopy, showing the presence of the C N group of polyacrylonitrile (PAN) co-eluting with ether, hydroxyl, and aromatic groups that are attributed to lignin. This provided evidence that a PAN–lignin copolymer was synthesized. Using a wet-spinning process, the PAN–lignin copolymers are then spun into fibers with an average tensile strength of 2.41 gf/den, a tensile strain of 11.04%, and a modulus of 22.92 gf/den. The CFs are prepared by the subsequent thermal treatment of the spun fibers. Differential scanning calorimeter (DSC) analysis of the PAN–lignin copolymer-based spun fibers displays a downshifted exothermic peak at 285.83 compared with the homopolymer PAN-based as-spun fibers, which provides evidence that lignin is cooperated with the oxidative stabilization reactions. The stabilized fibers are carbonized by heating from room temperature to 800 °C in a nitrogen atmosphere. This study shows the potential for a number of recycled and renewable polymers to be incorporated into wet-spun fibers for production of CF feedstocks, thereby reducing the supply cost using the current commercial technology.

McCARD is a Monte Carlo (MC) neutron-photon transport simulation code. It has been developed exclusively for the neutronics design of nuclear reactors and fuel systems. It is capable of performing the whole-core neutronics calculations, the reactor fuel burnup analysis, the few group diffusion theory constant generation, sensitivity and uncertainty (S/U) analysis, and uncertainty propagation analysis. It has some special features such as the anterior convergence diagnostics, real variance estimation, neutronics analysis with temperature feedback, B1 theory-augmented few group constants generation, kinetics parameter generation and MC S/U analysis based on the use of adjoint flux. This paper describes the theoretical basis of these features and validation calculations for both neutronics benchmark problems and commercial PWR reactors in operation.

TiO 2 /carbon nanofiber (CNF) composites containing Ag nanoparticles (Ag–TiO 2 /CNF) were prepared and their photocatalytic degradation ability upon visible light irradiation assessed. The reduction of methylene blue (MB) adsorption in an aqueous solution by the photocatalysts occurred due to the combined effects of MB adsorption in the pores of CNFs and decomposition by the photocatalysts throughout the process. The Ag–TiO 2 /CNF photocatalyst degraded MB 17 times faster than the TiO 2 /CNF composites with no Ag nanoparticles after 3 h under visible light illuminations.

A new formulation aimed at quantifying uncertainties of Monte Carlo (MC) tallies such as keff and the microscopic reaction rates as well as nuclide number density estimates in MC depletion analysis...

The electron beam (EB) irradiation effects of TiO2 deposited on carbon nanofibers (CNFs) were studied aiming the improvement of the photocatalytic activity. The EB irradiation contributed to an increase in crystallinity of the anatase resulting an improvement of the photocatalytic activity through the oxidation (ionization) of the doped TiO2 and leading to uniform distribution TiO2 particles on the CNFs surface. The photoactivity of the catalyst was measured by the decoloration of the methylene blue (MB) with time under UV irradiation.

The SiC/SiO 2 deposition was performed to improve the oxidation resistive properties of carbon nanofiber (CNF) from electrospinning at elevated temperatures through sol–gel process. The stabilized polyacrylonitrile (PAN) fibers were coated with SiO 2 followed by heat treatment up to 1000 and 1400 °C in an inert argon atmosphere. The chemical compositions of the CNFs surface heat-treated were characterized as C, Si and O existing as SiC and SiO 2 compounds on the surface. The uniform and continuous coating improved the oxidation resistance of the carbon nanofibers. The residual weight of the composite was 70–80% and mixture of SiC, SiO 2 and some residual carbon after exposure to air at 1000 °C.

The Monte Carlo Wielandt method has the potential to eliminate most of a variance bias because it can reduce the dominance ratio by properly controlling the estimated eigenvalue ( k e ). However, it requires increasingly more computation time to simulate additional fission neutrons as the estimated eigenvalue becomes closer to the effective multiplication factor ( k eff ). Therefore, its advantage over the conventional Monte Carlo (MC) power method in the calculation efficiency may not always be ensured. Its efficiency of the tally estimation needs to be assessed in terms of a figure of merit based on a real variance as a function of k e . In this paper, the real variance is estimated by using an inter-cycle correlation of the fission source distribution for the MC Wielandt calculations. Then, the tally efficiency of the MC Wielandt method is analyzed for a 2 × 2 fission matrix system and weakly coupled fissile array problems with different dominance ratios (DRs). It is shown that the tally efficiency of the MC Wielandt method depends strongly on k e , there is a k e value resulting in the best efficiency for a problem with a large DR, and the efficiency curve as a function of L, the average number of fission neutrons per history, follows a long tail after the best efficiency.

The problem of multiobjective fuel loading pattern (LP) optimization employing high-fidelity three-dimensional (3-D) models is resolved by introducing the concepts of discontinuous penalty function...

The sample variance of a tally in Monte Carlo eigenvalue calculations is biased because of an intercycle correlation between the fission source distributions (FSDs). How to estimate the variance bi...

Conformal mapped nodal simplified P 3 equations are derived and implemented for the two-dimensional neutronics analysis of fast reactor cores where hexagonal assemblies are loaded. The one-dimensional simplified P 3 equations are solved by using the nodal expansion method. The partial currents response matrices are constructed for the coupled simplified P 3 equations by applying the relationship between the partial currents and the surface-averaged fluxes. These matrices are then solved non-linearly. This method has been demonstrated for three two-dimensional fast reactor problems, and it was observed that the conformal mapped nodal simplified P 3 method can be effectively applied for the neutronics analysis of fast reactors with a substantial improvement in computational accuracy over the diffusion method.

A new optical technique based on the heterodyne polarimetry is developed for fast inspection of uniformity of lithography masks in semiconductor industry. Sub-wavelength periodical structure of a sample acts as a wire-grid polarizer, making both the amplitude and phase of the reflected laser beam dependent on geometrical dimensions and optical properties of the mask pattern. The heterodyne technology based on the cross-polarized two-frequency Zeeman laser is used to simultaneously measure the amplitude and the phase of the reflected laser beam. A two-dimensional map of spatial variations can be obtained via point-by-point scanning of the sample. The technique is applicable not only to exact periodical structures like diffraction gratings, but also to double-periodical patterns consisting of large number of periodically distributed small areas of sub-wavelength gratings. Theoretical background, simulation, and experimental results are presented.

Polyacrylonitrile-based carbon fibers, embedded with multi-wall carbon nanotubes (MWCNTs) in different concentrations, have been prepared by an electrospinning technique. The samples were subjected to oxidative stabilization followed by carbonization and graphitization at temperatures from 1000 to 3000 °C. Scanning electron microscopy, X-ray diffraction, and positron annihilation spectroscopy were used to investigate the samples. Positron annihilation studies, viz. analysis of positron lifetime and Doppler broadened spectrum line shape, provide deeper insight on defect specific aspects of the material as a function of temperature. Positron lifetime spectra for all the samples give a best fit for two-lifetime components. The trapping of positrons at specific sites in the nanotubes embedded in the fibers indicates the exact regions of open volume defects in the samples. Carbonization and graphitization are enhanced by embedding nanotubes in the fibers and could be an effective way of tailoring the properties of this system.

Two new stopping criteria designed to terminate automatically inactive cycle runs in Monte Carlo (MC) neutronics eigenvalue calculations are derived in terms of the covariance matrix of stochastic ...

The Numerical Nuclear Reactor (NNR) was developed to provide a high-fidelity tool for light water reactor analysis based on first-principles models. High fidelity is accomplished by integrating full physics, highly refined solution modules for the coupled neutronic and thermal-hydraulic phenomena. Each solution module employs methods and models that are formulated faithfully to the first principles governing the physics, real geometry, and constituents. Specifically, the critical analysis elements that are incorporated in the coupled code capability are a direct whole-core neutron transport solution and an ultra-fine-mesh computational fluid dynamics / heat transfer solution, each obtained with explicit (sub- fuel-pin-cell level) heterogeneous representations of the components of the core. The considerable com- putational resources required for such highly refined modeling are addressed by using massively parallel computers, which together with the coupled codes constitute the NNR. To establish confidence in the NNR methodology, verification and validation of the solution modules have been performed and are continuing for both the neutronic module and the thermal-hydraulic module for single-phase and two-phase boiling conditions under prototypical pressurized water reactor and boiling water reactor conditions. This paper describes the features of the NNR and validation of each module and provides the results of several coupled code calculations.

The purpose of this study is the development and verification of the coupled code system SCAN and RELAP-CANDU for transient analysis of a Canada deuterium uranium (CANDU) reactor. For this purpose,...

Polyacrylonitrile (PAN)-based carbon fibers, embedded with multi-wall carbon nanotubes (MWCNT) in different concentrations, have been prepared by an electrospinning technique and investigated using scanning electron microscopy, Raman, and positron annihilation spectroscopy. An analysis of the positron lifetime and Doppler broadened spectral line shape has been made. Positron lifetime spectra for all the samples give best fit for three distinct lifetime components. Raman data has been used to estimate the sp2 mole fraction in the fiber. It is found that the gradual changes incorporated in the fiber due to the addition of MWCNTs are reflected as well defined changes in the positron lifetime and the S parameter of the Doppler broadened spectral line. Annihilation parameters are discussed from the point of view of formation of distinct positron trapping sites in the form of vacancy type defects at the interfaces of MWCNTs and the PAN matrix, and their variations in concentration due to different amount of MWCNTs added.

The objective of this study is to find the optimal configuration of a He-cooled molten Li (HCML) blanket in terms of tritium breeding ratio (TBR). A parametric optimization study is performed to assess the impact of thickness and position of neutron reflectors. As the neutron reflector, Be, 11 B 4 C, graphite, and TiC are considered. In spite of some unfavorable material properties, Be appears to be far superior to others from the TBR point of view. It is shown that a graphite-reflected HCML blanket can provide a sufficient TBR without a neutron multiplier if the reflector is utilized in an optimal way. For a graphite-reflected HCML blanket, the impact of the Li-6 composition on TBR is also investigated. In addition, the blanket neutron energy multiplication factor (NEM) and the distribution of nuclear heating are evaluated.

A feasibility study has been performed to devise a He-cooled solid breeder (HCSB) blanket without a Be neutron multiplier. To achieve the self-sufficient tritium breeding ratio (TBR), natural lead is introduced as an alternative neutron multiplier and a graphite neutron reflector is employed to minimize the neutron leakage. For the Be-free blanket concept, various neutronic analyses have been done with a Monte Carlo code to characterize its neutronic performance. It is found that a self-sufficient TBR can be achieved in a He-cooled solid breeder (Li 4 SiO 4 ) blanket with a relatively thin lead neutron multiplier.

As an efficiency enhancement numerical scheme of transient nonlinear nodal calculations, a three-grid correction scheme (3GCS) using a modified W cycle based on three grid structures of three-dimensional (3-D) four-node-per-assembly (4N/A), 3-D 1N/A, and two-dimensional (2-D) 1N/A is developed. Its computational efficiency is compared with a single-grid biconjugate gradient stabilized (BICGSTAB) iteration scheme in popular use in terms of 3-D 4N/A nonlinear analytical nodal method solutions to Nuclear Energy Agency Committee on Reactor Physics pressurized water reactor rod ejection benchmark problems. It is shown that in computational efficiency, the 3GCS excels the BICGSTAB iteration method using preconditioners such as Jacobi, incomplete lower and upper (ILU), and 3-D block incomplete lower and upper (BILU3D) preconditioners. It is also shown that coarse-grid residual equations based on the 3-D 1N/A grid structure can predict temporal truncation errors as accurately as the 3-D 4N/A fine-grid residual equation but with considerably less overhead computing time for variable time-step size control calculations by a step doubling method. In addition, incorporation of preconditioners into the 3GCS is shown to enhance further efficiency of the nonpreconditioned 3GCS. From these results, it is concluded that the temporal adaptive 3GCS employing coarse-grid residual equations for temporal step-size control as wellmore » as the preconditioner like the BILU3D can provide a very efficient iterative solution scheme for transient nonlinear nodal calculations.« less

A least-squares method that solves both the core neutronics design equations and the in-core detector response equations on the least-squares principle is presented as a new advanced online flux-ma...

The two popular transverse integrated nodal methods (TINMs), the nodal expansion method (NEM) and analytical nodal method (ANM), and the analytic function expansion nodal (AFEN) method are integrat...