Graphite Core Research Articles

Utralow coefficient of thermal expansion in a spheroidized natural flake graphite based isotropic graphite

With the development of high-temperature gas-cooled reactors, the coefficient of thermal expansion (CTE) of nuclear-grade graphite plays an increasingly important role in reactor design. A lower CTE enhances both the integrity of the graphite core structure and reactor efficiency. In this paper, we present a new isotropic graphite grade with a low CTE, utilizing spheroidized natural flake graphite (SFG) as a filler material. The ultralow isotropic CTE of 2.6-2.9×10−6 K−1 in the SFG-based graphite, owing to the ability of the slit-shaped pores within the SFG particles to accommodate cross-plane thermal expansion. To enhance the baking performance of the SFG-based graphite, hybrid fillers of SFG/coke or SFG/microcrystalline graphite (MG) were used to prevent cracking of the green bodies. In particular, the addition of MG prevents cracking without changing the low CTE value of the SFG-based graphite. This research contributes to the development of new graphite materials with low CTE that can be used in nuclear engineering, the semiconductor industry, and other high-temperature environments.

Seismic modeling and simulation of the graphite core in gas-cooled micro-reactor

To evaluate the structural safety of the graphite core in a gas-cooled micro-reactor and to assess its structural response under seismic loads, a study was conducted. By comparing the acceleration and velocity curves obtained from small-sized graphite block collision experiments and collision simulations, it was determined that the simulation results accurately represent the real collision behavior of graphite blocks. The collision stiffness and damping parameters were derived from these curves. Subsequently, simulations of graphite components in the core were performed to establish the stiffness and damping parameters of the graphite blocks, which were then incorporated into the core analysis calculations. To validate the accuracy of the core numerical model and simplify the vibration form, the core model was divided into in-plane and axial models. A full-core model calculation was then carried out to determine the forces between graphite components. The final results confirm that the graphite core adheres to the ASME design specifications under seismic loads.

Internal stress analysis of irradiated graphite cores in a gas-cooled microreactor

The structural integrity of core graphite under high-temperature irradiation conditions is crucial for the safe operation of the reactor. This paper presents a simulation of the hexagonal core graphite structure, developed using the UMAT program. Design factors, including irradiation, high temperature, dimensional strain, and creep strain, are analyzed separately through the control variable method. The results indicate a positive correlation between the magnitude of the irradiation field gradient and the resulting stress effects. Stress concentration within the temperature field is observed to occur near the inner side of the hexagonal prism. Among the four types of graphite examined, PCIB demonstrates the least stress and deformation, making it more suitable for specific applications. The selection of graphite should consider the particular service period requirements. Choosing a graphite material that exhibits minimal shrinkage and a high turnaround dose is advisable. The primary creep parameter is negligible when compared to the secondary creep parameter; selecting graphite with a larger secondary creep parameter enhances reactor safety. The findings of this study provide a solid foundation for the design of a graphite core and offer recommendations for graphite candidates in the development of microreactors in China.

Nodular Graphite Dissolution and Nucleus Observation: High-Temperature Dynamics of Ductile Iron Recycling

This investigation examines the dynamic behavior of the nodular graphite structure in ductile cast iron at elevated temperatures during the recycling process. It comprises a systematic analysis of the impact of high temperature on the change in chemical composition, followed by a set of examinations of the nodular graphite structure dissolution mechanism at the early phase of the remelting process. The results indicate that prolonged holding at higher temperatures affects the carbon or silicon concentration due to oxidation, which correlates with the operating temperature and the dynamic concentration proportion of those two main alloying elements. It is also substantiated that the dissolution of nodular graphite, the only carbon source during the ductile cast iron remelting process, does not occur primarily in the liquid state but has already started during the solid phase because of austenitization. This dissolution is governed mainly by a surface reaction, as indicated by the residual graphite structure with preserved nonmetallic nuclei. Hence, this approach also provides an alternative method for observing the nodular graphite core by intentionally partially dissolving the graphite structure.

Crack growth in sandwich-structured foam core graphite epoxy laminate composite using a phase-field modelling approach

The laminated sandwich composites have wide structure-making applications in the automotive and aviation fields due to their lightweight and superior flexural rigidity properties. Making grooves or holes to assemble more than one structure induces crack discontinuities near the stress concentration region in these sandwich structures. The present work examines the effect of crack discontinuities on the mechanical performance and failure process of the sandwich structures under different loading conditions. Phase field method (PFM) has been presented and implemented using in-house developed MATLAB code. The effect of holes, multiple cracks, number of cores, and loading conditions are analyzed for the mechanical and fracture behavior of the structure. Load-carrying capacity, threshold displacement value for crack initiation, crack propagation trajectory, and energy absorption capacity are compared for various crack discontinuities under different loading conditions. Approximately 35% increase in load carrying capacity is observed in equivalent multiple core sandwich structures.

Core Optimization for Extending the Graphite Irradiation Lifespan in a Small Modular Thorium-Based Molten Salt Reactor

The lifespan of core graphite under neutron irradiation in a commercial molten salt reactor (MSR) has an important influence on its economy. Flattening the fast neutron flux (≥0.05 MeV) distribution in the core is the main method to extend the graphite irradiation lifespan. In this paper, the effects of the key parameters of MSRs on fast neutron flux distribution, including volume fraction (VF) of fuel salt, pitch of hexagonal fuel assembly, core zoning, and layout of control rod assemblies, were studied. The fast neutron flux distribution in a regular hexagon fuel assembly was first analyzed by varying VF and pitch. It was demonstrated that changing VF is more effective in reducing the fast neutron flux in both global and local graphite blocks. Flattening the fast neutron flux distribution of a commercial MSR core was then carried out by zoning the core into two regions under different VFs. Considering both the fast neutron flux distribution and burnup depth, an optimized core was obtained. The fast neutron flux distribution of the optimized core was further flattened by the rational arrangement of control rod channels. The calculation results show that the final optimized core could reduce the maximum fast neutron flux of the graphite blocks by about 30% and result in a more negative temperature reactivity coefficient, while slightly decreasing the burnup and maintaining a fully acceptable core temperature distribution.

Study on tritium transport characteristics in fluoride-salt-cooled high-temperature advanced reactor

Fluoride-salt-cooled high-temperature reactors (FHRs) are a promising reactor class that combines prominent attributes from the Gen-Ⅳ reactors, raising attractive interests of the international community. However, tritium control has been a major challenge in FHRs because of the neutron reactions of lithium. It's necessary to study the transport characteristics of tritium in the fluoride-salt-cooled high-temperature advanced reactor (FuSTAR) and to provide theoretical support for appropriate tritium control measures and safe operation of the FHRs. In this paper, the inclusive transport characteristics of production, graphite adsorption, diffusion, dissolution, and permeation on tritium in the primary loop are analyzed. The mathematical and physical model of the tritium transport phenomenon is established, and an analysis model of tritium transport characteristics is also developed. Then, the tritium transport characteristics in the FuSTAR primary loop are analyzed. The results show that the tritium in the FuSTAR primary loop mainly exists in the form of Diatomic Tritium (T2), and it's found that Tritium Fluoride (TF) and T2 are adsorbed by graphite after being generated in the core, and this process reaches saturation in about 150 Effective Full Power Days (EFPDs). It also indicates that almost 48% of tritium penetrates the secondary loop through the heat exchanger, and only about 3.8% of tritium is adsorbed on the core graphite. TF makes the corrosion of the heat exchanger and downcomer more serious. Finally, the safety of tritium transport in FuSTAR is conservatively estimated, with a tritium emission dose of 0.1674 mSv/a. This study can provide a theoretical reference for the structural design, tritium recycling, and radiation protection of FHRs.

Kinetic modeling of IG-110 oxidation in inert atmosphere with low oxygen concentration for innovative high-temperature gas-cooled reactor applications

ABSTRACT The oxidation behavior of IG-110, a graphite core component, was investigated at temperatures ranging from 400 to 1000°C in a 10 ppm Ar/O2 flow to simulate the oxidation process between the graphite core component and helium coolant with low O2 concentrations employed in advanced High-Temperature Gas-cooled Reactors (HTGRs). The results reveal that IG-110 undergoes significant mass loss at temperatures above 700°C, resulting in total mass changes of −1.5%, −5.3%, and −9.0% at 700, 800, and 1000°C, respectively, during a 10-hour oxidation period. No significant mass loss is observed below 600°C. To understand the oxidation mechanism of IG-110 under low O2 concentrations, we propose a kinetic model as the current chemical kinetic-controlled model does not fully explain the oxidation behavior observed in our research. Our analysis shows lower estimated reaction rates compared to studies at higher O2 concentrations; the activation energy values exhibit good agreement. The proposed kinetic model sheds light on the oxidation mechanism of IG-110 under 10 ppm Ar/O2 flow. This study provides new insights into the oxidation behavior of graphite core components in HTGRs and highlights the importance of controlling the O2 concentration in the helium coolant to prevent severe degradation of SiC-matrix fuel compacts.

Monte Carlo modelling of a prototype small-body portable graphite calorimeter for ultra-high dose rate proton beams

Background and purposeAccurate dosimetry in Ultra-High Dose Rate (UHDR) beams is challenging because high levels of ion recombination occur within ionisation chambers used as reference dosimeters. A Small-body Portable Graphite Calorimeter (SPGC) exhibiting a dose-rate independent response was built to offer reduced uncertainty on secondary standard dosimetry in UHDR regimes. The aim of this study was to quantify the effect of the geometry and material properties of the device on the dose measurement. Materials and methodsA detailed model of the SPGC was built in the Monte Carlo code TOPAS (v3.6.1) to derive the impurity and gap correction factors, kimp and kgap. A dose conversion factor, DwMC/DgMC, was also calculated using FLUKA (v2021.2.0). These factors convert the average dose to its graphite core to the dose-to-water for a 249.7 MeV mono-energetic spot-scanned clinical proton beam. The effect of the surrounding Styrofoam on the dose measurement was examined in the simulations by substituting it for graphite. ResultsThe kimp and kgap correction factors were 0.9993 ± 0.0002 and 1.0000 ± 0.0001, respectively when the Styrofoam was not substituted, and 1.0037 ± 0.0002 and 0.9999 ± 0.0001, respectively when substituted for graphite. The dose conversion factor was calculated to be 1.0806 ± 0.0001. All uncertainties are Type A. ConclusionsImpurity and gap correction factors, and the dose conversion factor were calculated for the SPGC in a FLASH proton beam. Separating out the effect of scatter from Styrofoam insulation showed this as the dominating correction factor, amounting to 1.0043 ± 0.0002.

Growth and property evaluation of nickel–graphite core–shell nanoparticles based on temperature parameters for utilization in silver paste

Growth and property evaluation of nickel–graphite core–shell nanoparticles based on temperature parameters for utilization in silver paste

Seismic response prediction using intensity measures: Graphite nuclear reactor core model case study

Seismic response analyses of structures have conventionally used the peak ground acceleration or spectral acceleration as an intensity measure to estimate the engineering demand parameters. An extensive shaking table test program was carried out on a quarter-sized advanced gas-cooled reactor (AGR) core model to investigate the global dynamic behavior of the system with degraded graphite components while subjected to seismic excitation. Evaluation of the most widely considered intensity measures, with respect to their capability for predicting the seismic response of an AGR core–like structure, is performed. Twenty intensity measures of 16 distinct seismic input motions are formulated and correlated, with experimental measurements describing the dynamic response of the reactor core model. Linear correlations are constructed for each intensity measure to statistically determine the best metric for predicting the seismic response of the AGR core model, and statistical analysis indicates that the acceleration spectrum intensity (ASI) is best suited to characterize and describe the structural demand of an AGR core-like structure when subjected to seismic loading. A response prediction tool is developed, based on empirically derived linear correlations, to estimate column distortions and determine the critical input motion for further experimental and numerical studies. Statistical analysis indicates that predicted column distortions, compared against direct experimental displacements, are significant, repeatable, and accurate.

Computational method for added mass of single graphite brick in molten salt reactor

The fluid–structure interaction (FSI) that occurs in the graphite core submerged in molten salt has a great influence on the vibration of the core under seismic conditions in thorium molten salt reactor-liquid fuel (TMSR-LF1). The added mass method is an important way to study the phenomenon. In this paper, a bidirectional fluid–structure coupling method was established to calculate the added mass of the graphite brick, and the numerical simulation results were in good agreement with the experimental results. On this basis, the sensitivity analysis of added mass factors was carried out, such as the size of gaps between components, the geometric shapes of graphite bricks and the molten salt temperatures, etc. The results show that these factors influence the added mass in different degrees and the size of the gap is the most important factor affecting the added mass. The results can provide FSI parameters for structural dynamic analysis and offer the assistance for the design and manufacture of the graphite core.

Damage tolerance in the graphite cores of UK power reactors and implications for new build

Damage tolerance in the graphite cores of UK power reactors and implications for new build

POLYETHYLENE FILTER FOR THE TNF2 THERMAL NEUTRON FACILITY.

The Standard Thermal Neutron Flux Unit, TNF2, in (LNMRI/IRD)(1, 2), was built for neutron detector and survey meter calibrations. The facility's fluence is achieved by moderation of four 241Am-Be with a graphite core and paraffin/graphite blocks surrounding it. Due to the small channel dimensions, it is impossible to calibrate personal dosemeters and survey meters for thermal neutrons. A polyethylene filter construction was carried out to allow the external irradiation of personal dosemeters and neutron survey meters. The polyethylene filter was constructed with 29 stacked discs with diameters ranging from 5 to 34cm. Different thicknesses were simulated to provide the desired effect. This new irradiation configuration was also experimentally tested and compared with simulation results with MCNPX(3).

Observations of high burnup structure in AGR fuel

Nuclear power plants (NPPs) within the UK are largely of the commercial advanced gas-cooled reactor (AGR) design. The key elements of the reactor and fuel design differ somewhat to those seen in Light Water Reactors (LWRs), most markedly the cladding, an austenitic stainless steel, and annular ceramic UO2 fuel pellets. The graphite moderated AGR cores also experience much higher temperatures than PWR (Pressurised water reactor) cores.In order to fully understand the requirements for enhanced fuel performance and interim/long term spent fuel storage, some efforts must be made to compare and contrast the two fuel types, to understand if LWR data are fully applicable to AGR data in various operational and storage scenarios. One such microstructural effect requiring assessment is a fuel microstructure commonly referred to as high burnup structure (HBS).The current study describes a series of post-irradiation examinations (PIE) undertaken on AGR fuel. A total of circa 30 AGR samples are examined in which HBS is present, and a further similar size of samples in which no HBS was present. Observations include SEM (scanning electron microscopy) and LOM (light optical microscopy) providing a characterisation of the appearance of HBS in AGR. The results are supported by burnup profile modelling, and assessment of fuel temperature from metallographic markers.The results are consistent with AGR outer ring fuel exhibiting an onset of HBS at a rod average burnup of ∼30 MWd/kgU and a 100 μm HBS thickness at a rod average burnup of 40 MWd/kgU. These values are lower than the comparable (pellet average) burnup for PWR fuel. The difference in burnup is shown to be due to the neutron spectrum in AGR fuel elements, and which also leads to a marked variation in HBS thickness around the circumference of AGR fuel. There is no suggestion that the local onset burnup for HBS formation differs between the two fuel types.

Effect of Graphite Exfoliation Way on the Efficiency of Exfoliated Graphene for the Determination of Hydroxychloroquine in Urine and Waste Water

Graphene oxide (GO) electrodeposited on graphite electrode has been used as a sensor for the detection of hydroxychloroquine (HCQ). It was synthesized via a simple and low-cost electrochemical approach by exfoliation of graphite pencil core in aqueous solution of Na2SO4 using a direct current (DC) and alternating current (AC), then electrodeposited at the graphite electrode surface by cyclic voltammetry. The electrochemical performance of the DC−GO and AC−GO toward HCQ oxidation was tested. Graphene oxide (GO) and reduced graphene oxide (rGO) were characterized by UV–vis absorption spectroscopy (UV–vis), Fourier transform infrared spectroscopy (FTIR), and X-ray powder diffraction (XRD). Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to study the HCQ oxidation mechanism as well as electron transfer and HCQ quantification at the modified electrode AC−rGO@CPE, respectively. Parameters, such as potential range, scan rate, and the number of segments (half cycle) in cyclic voltammetry were optimized for the electrodeposition of GO. The AC−rGO@CPE shows good sensitivity toward HCQ in the range from 4.0 × 10−7 to 4.0 × 10−6 mol l−1. The detection limit was calculated to be 3.2 × 10−8 mol l−1 with an RSD of 3.47%. Furthermore, the modified electrode was successfully used to detect HCQ in human urine and wastewater.

A surrogate machine learning model for advanced gas-cooled reactor graphite core safety analysis

A surrogate machine learning model was developed with the aim of predicting seismic graphite core displacements from crack configurations for the advanced gas-cooled reactor. The model was trained on a dataset generated by a software package which simulates the behaviour of the graphite core during a severe earthquake. Several machine learning techniques, such as the use of convolutional neural networks, were identified as highly applicable to this particular problem. Through the development of the model, several observations and insights were garnered which may be of interest from a graphite core analysis and safety perspective. The best performing model was capable of making 95% of test set predictions within a 20 percentage point margin of the ground truth.

Electrochemical exfoliation of graphene using dual graphite electrodes by switching voltage and green molten salt electrolyte

In this study, the switching voltage (sV) technique was applied for graphite exfoliation in eutectic molten salts of NaOH and KOH at 300 °C. Dual graphite pencil cores were used as anode and cathode with two commercial time relays to swap between positive and negative voltages at various application times. The exfoliated graphene samples were analyzed using several characterization techniques. Results indicated that the sV technique was efficient to achieve better exfoliation efficiency compared to the constant voltage (cV). At the optimum voltage application times for anode and cathode relays, few-layer graphene with respective high production yields of 0.50 and 0.43 g min−1, low ID/IG ratios of 0.31 and 0.58, and good electrical conductivities of 75.28 and 182.62 S m−1 were obtained on both anode and cathode, respectively. Moreover, the SEM characterizations showed that the sV technique efficiently produced smooth graphene flakes, with less agglomeration, crumbling, and wrinkling than those exfoliated at a constant voltage. The XRD patterns confirmed that the crystallite size of the exfoliated graphene prepared by the sV method was smaller than those of pristine graphite and the graphene obtained at a cV. The AFM analysis revealed that the thickness of the exfoliated graphene developed by the sV technique was significantly lower than that obtained at cV. The XPS analysis showed that the quality and the purity of the exfoliated graphene obtained using the sV technique was higher than that prepared at a constant voltage due to the effective suppressing of the cations and ions stacking between the graphite layers.

Microwave Synthesis, Characterization and Perspectives of Wood Pencil-Derived Carbon

More than 14 billion pencils are manufactured and used globally every year. On average, a pencil is discarded after 60% of its original length has been depleted. In the present work we propose a simple and affordable way of converting this non-neglectable amount of waste into added value carbon product. In particular, we demonstrate the microwave synthesis of carbon from the wood pencil with and without chemical activation. This could be a process stage before the final recycling of the expensive graphite core. In the latter case, irradiation of the wood pencil in a domestic microwave oven heats up the pencil’s graphite core, thus inducing carbonization of its wood casing. The carbonized product consists of amorphous carbon nanosheets having relatively low surface area. However, if the wood pencil is soaked in 50% KOH aqueous solution prior to microwave irradiation, a significantly higher surface area of carbon is obtained, consisting of irregular-shaped porous particles. Consequently, the obtained carbon can easily decolorize a methylene blue aqueous solution, can be used to make pocket warmers or gunpowder, and lastly, serves as an excellent adsorbent towards Cr(VI) removal from water, showing a maximum adsorption capacity of 70–75 mg/g within 24 h at 23 °C, pH = 3.

A Surrogate Machine Learning Model for Advanced Gas-Cooled Reactor Graphite Core Safety Analysis

A Surrogate Machine Learning Model for Advanced Gas-Cooled Reactor Graphite Core Safety Analysis