Core Pressure Research Articles

Comparison of the Thermo-Hydraulic Response of MELCOR 1.8.6 and 2.1 for SBO Accident for APR 1400 Reactor

An analysis of thermohydraulic response during a station blackout (SBO) accident for the APR 1400 nuclear power plant is performed using MELCOR version 1.8.6. MELCOR 1.8.6 results for the SBO scenario are benchmarked with MELCOR 2.1. The simulation of the SBO accident with MELCOR 2.1 was done by the APR 1400 reactor designer company (KEPCO). This research consists of two parts; the first part is related to the results of MELCOR 1.8.6, and the thermo-hydraulic analysis of MELCOR1.8.6 has been done. Analysis of thermohydraulic response is focused on investigating thermohydraulic parameters, such as core pressure, fuel clad temperature, water mass flow rate in the core, time of fuel clad failure, time of lower head failure, and time of containment failure. In the second part, the results of MELCOR version 1.86 have been benchmarked with the results of MELCOR 2.1. The results of the analysis of containment pressure changes in version 1.8.6 showed that the effect of pressure increase in containment is mostly due to the increase in carbon dioxide mass, but in version 2.1, the increase in pressure is more due to water vapor.

Sub-core permeability estimation from coreflooding experiments: Numerical analysis for evaluating accuracy and improving methods

Coreflooding experiments are one of the primary methods for reservoir rock characterization and have been developing in recent years, providing increasing detail. An advanced analysis of coreflooding experiments consists of constructing three dimensional permeability (k) maps of the core sample with sub-core resolution. Such detailed characterizations provide important information on the core heterogeneity and enable the construction of accurate numerical flow models that can reproduce experimental results. This work presents a method for estimating k, combining data from multiple coreflooding experiments, and studies the estimation accuracy considering a large number of test cases consisting of synthetic data obtained by numerical experiments. Cases include varying parameters, such as: fluid injection flow rates and types, relative permeability curves, capillary pressure functions and core heterogeneity. The new method is shown to significantly improve the estimation accuracy in comparison to methods that incorporate data only from a single experiment. Furthermore, a method for improving k estimations in regions where water is trapped is presented and its implementation is shown to increase the overall accuracy of k estimation. An additional method is considered, that requires only single-phase flow solutions, thus increasing the computational efficiency. However, it is shown to be applicable only for a small subset of cases.

High‐Pressure Melting Experiments of Fe3C and a Thermodynamic Model of Fe‐C Liquids for the Earth's Core

AbstractMelting experiments of Fe3C were conducted to 85 GPa in laser‐heated diamond anvil cells with in situ X‐ray diffraction and post‐experiment textural observation. From the determined pressure‐temperature conditions of the melting curve for Fe3C, together with literature data on the melting point of diamond and eutectic point of the system Fe‐Fe3C/Fe7C3 under high pressures, we established a self‐consistent thermodynamic model for high‐pressure melting of the system Fe‐C including the mixing parameters for liquids. The results show that mixing of Fe and C liquids is negatively nonideal from 1 bar to the pressure at the center of the Earth. The departure from ideal mixing becomes progressively larger with increasing pressure, which leads to greatly stabilized liquids under core pressures. The modeled carbon content in eutectic melts under core pressures is 3.3–4.4 wt%. From the Gibbs free energy, we derived an internally consistent parameters for Fe‐C outer cores which included the crystallizing points at their bottoms, isentropic thermal profiles, and densities and longitudinal seismic wave speeds (Vp). While the addition of carbon in excess of the eutectic melt composition effectively reduces the density of iron liquid, the Vp of iron liquid is not greatly changed. Therefore, the low density and high Vp of PREM relative to pure iron cannot be reconciled by an Fe‐C liquid. Therefore, the Earth's core cannot be approximated by the system Fe‐C and should include another light element.

Experimental study on optimizing tailwater reinjection technology for weakly consolidated sandstone geothermal reservoirs

The difficulty of recharging the weakly consolidated sandstone geothermal reservoirs (WCSGR) is a macroscopic manifestation of the interplay of multiple factors associated with both fluids and formation properties. However, current studies predominantly focus on the influence mechanisms of individual factors on the reinjection of WCSGR. To address this limitation, a high temperature–pressure core flow experimental platform, combined with an orthogonal experimental design, is employed to investigate the dynamic reinjection process of WCSGR under the combined effects of multiple factors. The research indicates that high temperatures significantly impact the movement of 3 μm microspheres, leading to a rapid decrease in core permeability. Additionally, in experiments conducted at flow rates of 2 mL/min, 3 mL/min, and 4 mL/min, the pH stabilization time of the outflow solution decreased, while both the pH value and turbidity of the outflow solution increased, compared to the experiments conducted at flow rate of 0.5 mL/min and 1 mL/min. The permeability damage rate (%) was used as the experimental evaluation index. The primary and secondary order of influence of each factor on the permeability is: microsphere size > flow rate > turbidity > confining pressure > temperature. The optimal levels for each factor are 5 μm, 4 mL/min, 2 mg/L, 1.4 MPa, and 25 °C, respectively. Consequently, the reinjection technology of GT in WCSGR is optimized.

Investigation on the plugging mechanism of nanocomposite polyacrylate copolymers in water-based drilling fluids: Experiments and applications

The plugging of nanopores and cracks in shale formation has become the critical technology that promotes the development of shale gas. Herein, nanocomposite polyacrylate (Poly-TALC) copolymers were successfully prepared by emulsion polymerization using butyl acrylate and triallyl isocyanurate as the raw material. Poly-TALC was characterized by fourier transform infrared spectroscopy (FTIR), laser light scattering particle size analysis, scanning electron microscope (SEM) and thermogravimetric analysis (TGA). The rheological properties and plugging performance of Poly-TALC were evaluated by a six-speed rotational viscometer, filter cake permeability test, core permeability test and pressure transfer experiment. Results revealed that Poly-TALC exhibited a particle size distribution ranging from 75.27 to 95.29 nm, while maintaining notable stability at 327.75 °C. Upon the addition of Poly-TALC to the drilling fluid, both the apparent viscosity and plastic viscosity insignificantly changes. At a Poly-TALC dosage of 1.0%, the filter cake's permeability was 1.2 × 10−5 μm2 with a plugging rate of 56.9%, while the permeability of the core was 1.2 × 10−6 μm2 with a plugging rate of 84.0%. The decrease in permeability was not significant beyond a Poly-TALC dosage of 1.0 wt%. Pressure transfer experiments demonstrate that Poly-TALC is able to form a multi-stage dense seal within the rock core, which can effectively prevent formation water from immersing into shale formation and improve shale wellbore stability.

Thermal conductivity of iron under the Earth’s inner core pressure

Abstract The thermal conductivity of ε-iron at high pressure and high temperature is a key parameter to constrain the dynamics and thermal evolution of the Earth’s core. In this work, we use first-principles calculations to study the Hugoniot sound velocity and the thermal transport properties of ε-iron. The total thermal conductivity considering lattice vibration is 200 W/mK at the Earth’s inner core conditions. The suppressed anharmonic interactions can significantly enhance the lattice thermal conductivity under high pressure, and the contribution of the lattice thermal conductivity should not be ignored under the Earth’s core conditions.

POWER ACCUMULATOR FOR STABILIZATION OF THE PRESSING PRESSURE OF THE CORE OF A POWERFUL TURBOGENERATOR WITH BUILT-IN METER

In this paper present described features of stabilization and restoration of pressing force of the stator core of a powerful turbogenerator (TG). Weakening of the pressing forces is the cause of a number of negative phenomena, such as increased vibration and loosening of the core sheets with their subsequent destruction (cracking), which is often the cause of generator damage. It is shown that to assess the state of the pressing force in the core of the TG stator, force meters in the clamping prisms of the core, built into the design of the power accumulator (PA) for stabilizing the pressing force of the core, can be used. The design of the package of disc springs used in PA consists of a package of plate springs and allows to stabilize the pressure in the stator core of a powerful TG to a given level without additional control with probes and fixation by tightening the adjustment nuts. Describes the advantages and features of using PA with a package of disc springs for pressure stabilization, installed under the tightening nuts or instead of them on the threaded ends of the tightening prisms. Proposed to use a built-in force measuring transducer, which consists of an elastic sensitive element (ESE) and a capacitive sensor (CS) into PA structure. The purpose of this article is to create a force meter in the clamping prisms of the stator core of a powerful TG using an elastic sensitive element and a capacitive sensor built into the design of a "caseless" power battery to stabilize the pressing pressure of the stator core of a powerful turbogenerator. A number of TG and PA parameters, which should know to calculate the mechanical characteristics of the disc spring unit outlined. The dependence of the force of the spring block on the displacement of the pressure plate of the stator core is determined. Showing that the assessment of the force in the tightening prism performed by measuring the electrical capacity between the potential electrode CS and the grounded element of PA. Measuring the height of the block during planned repairs or operation of the turbogenerator allows you to determine with high accuracy the amount of tension on each tightening prism and therefore the compression force of the core and, if it necessary to adjust the pressing force by tightening the springs. The conversion function of the force converter is determined, taking into account the geometric dimensions of the ESE and CS. The calculation of ESE for mechanical strength was carried out. The use of pressure gauges in tightening prisms allows you to effectively restore and maintain the pressing force of the final packages of the stator core, control the pressure during operation and adjust it without stopping the turbogenerator. The obtained results can be used in systems for stabilizing the pressing force of the stator core with power accumulators and in the system for assessing the current state of the stator core of powerful turbogenerators of the TGV-200 and TGV-300 type. Increasing the accuracy of measurements and reducing operational risks will contribute to the rapid and effective restoration of critical infrastructure and ensure the stable operation of energy facilities.

An Experimental Evaluation of the APR1000 Core Flow Distribution Using a 1/5 Scale Model

The experimental data of core flow distribution are indispensable for obtaining licensing and facilitating the design of fluid systems of nuclear reactors. In this study, an Advanced power reactor Core flow and Pressure (ACOP) test facility was established to experimentally simulate the internal flow of the Advanced Power Reactor 1000 (APR1000) on a reduced length scale of 1/5. The core region was simulated by using 177 core simulators representing the fuel assemblies of the APR1000. The APR1000 flow distributions were synthetically identified by accurately measured parameters: the core inlet flow rate and outlet pressure under the four-pump balanced and unbalanced flow conditions. The overall inlet flow rates ranged from 87.7% to 112.0% relative to the averaged flow rate. Here, we scrutinize the flow distributions considering the flow conditions and internal structures and briefly describe the applied scaling method and design concept of the test facility.

Investigation on flow structure and pressure fluctuation of gas-liquid two-phase flow in a mixed flow pump

Abstract Mixed flow pump is characterized by high-efficiency operation and wide range of flow rate conditions, while research on transporting gas-liquid two-phase flow is quite limited. The present work investigates the energy performance, two-phase flow pattern and pressure fluctuations of a mixed flow pump, on basis of the numerical method of inhomogeneous Eulerian-Eulerian multiphase flow model. Results show that the pump head and efficiency decline with the increase of gas volume fraction. In impeller, gas phase is mainly distributed at the tip clearance, the blade pressure side and suction side, and the hub outlet. The low pressure of tip leakage vortex core leads to the gas phase concentration and the formation of gas strip. Moreover, X-shaped gas strip appears at high gas volume fraction (GVF). In guide vane, gas phase is mainly distributed at the leading edge of blade pressure side, the blade suction side, and the middle of passage. As the inlet GVF increases, the spatial-temporal evolution of the gas phase shows obvious differences. The strong gas-liquid interaction causes broad low-frequency fluctuations, and the rotor-stator interference causes significant blade passing frequencies in the mixed flow pump.

Dissolved Methane Diffusion Drives Hydrate-Bearing Pressure Core Degradation during Long-Term Storage in Water

Dissolved Methane Diffusion Drives Hydrate-Bearing Pressure Core Degradation during Long-Term Storage in Water

Sealing performance analysis of pressure controller in pressure core sampling for seafloor drill

In order to improve the working reliability of pressure controller in the pressure core sampling for the seafloor drill, the challenges faced by the pressure controller in the working phase are analyzed. The working parameters of Y-ring on the pressure-retaining performance are analyzed. The optimization scheme of the working parameters for Y-ring is obtained and verified by sea trial. The conclusions are as follows: The gap extrusion degree of Y-ring is proportional to the working pressure. When the working pressure exceeds 20 MPa, the increase rate of the maximum contact stress increases. Under the condition that the friction coefficient is 0.1–0.4, the safety margin of the maximum contact stress is proportional to the friction coefficient. When the friction coefficient increases from 0.4 to 0.5, the safety margin decreases. Under the condition that the interference is 0.66–0.76 mm, the growth rate of the maximum Mises stress is slow. when the interference is 0.7 and 0.76 mm, the safety margin decreases. When the extrusion gap is 0.4–0.6 mm, the increase trend of safety margin is more obvious. When the extrusion gap is 0.6 mm, the growth rate of the maximum Mise stress increases. The success rate of the sealing cap installation is about 80%.

Analysis of Breaking Characteristics of C4F7N/CO2 Mixture Gas in Circuit Breaker

In recent years, the C4F7N mixed gas has attracted considerable attention for its outstanding insulation and arc-extinguishing capabilities, positioning it as a potential substitute for sulfur hexafluoride, SF6. However, there remains a limited understanding of the arc-extinguishing and insulation performance of C4F7N/CO2 mixed gas. In addition, there is limited research on high-current breaking in circuit breakers. Therefore, this study aims to investigate the arc characteristics and breaking behavior of 10%C4F7N/90%CO2 and 15%C4F7N/85%CO2 mixed gases using a magnetohydrodynamic model based on the 252kV air pressure circuit breaker. The dynamic characteristics of this mixed gas are compared with pure SF6 under short-circuit current breaking conditions, while analyzing different parameters of the C4F7N configuration. The results indicate that the mixed gas exhibits lower levels in terms of arc temperature, axial diffusion distance and pressure difference at the moment of arc initiation compared to pure SF6. Furthermore, increasing the inflating pressure can effectively enhance the breaking performance of the circuit breaker with 0.6 MPa, making it more suitable. Additionally, increasing the proportion of C4F7N in the mixed gases will cause the arc temperature to rise slightly at the initial arc and current crossing zero, but decrease at the peak current. The core pressure also rises significantly, with a greater pressure difference established in the compressor at moment of arc initiation. This study provides a reference for the design of an environmentally friendly circuit breaker and the selection of the mixed gas ratio.

Wellbore Instability Analysis to Determine the Safe Mud Weight Window for Deep Well, Halfaya Oilfield

Wellbore instability is one of the most common issues encountered during drilling operations. This problem becomes enormous when drilling deep wells that are passing through many different formations. The purpose of this study is to evaluate wellbore failure criteria by constructing a one-dimensional mechanical earth model (1D-MEM) that will help to predict a safe mud-weight window for deep wells. An integrated log measurement has been used to compute MEM components for nine formations along the studied well. Repeated formation pressure and laboratory core testing are used to validate the calculated results. The prediction of mud weight along the nine studied formations shows that for Ahmadi, Nahr Umr, Shuaiba, and Zubair formations ranges between 12.5 to 15 ppg. The predicted safe mud weight value seems to be narrow with a well deviation higher than 350. Therefore, for Ahmadi, Nahr Umr, Shuaiba, and Zubair formations, the wellbore appears unstable compared to other formations. The results of stability analyses indicate that the breakout mud weight wasn’t affected by wellbore azimuth because of low-stress contrast. Furthermore, shear failure can be prevented by drilling the well with an inclination of less than 350. As well as, to prevent breakdown the well should be drilled with an inclination between 25o to 65o in the direction of minimum horizontal stress. These outcomes could be used to prevent wellbore instability and determine a safe mud-weight window when planning to drill nearby wells in the future.

Study on the factors affecting the performance of oil-filled pressure sensitive core

PurposeThe performance of oil-filled pressure cores is very much affected by the corrugated diaphragm and the oil filling volume. The purpose of this paper is to show the effects of different corrugated diaphragms, different oil filling volumes and different treatments of the corrugated diaphragms on the performance of pressure sensors.Design/methodology/approachPressure-sensitive cores with different diaphragm diameters, different diaphragm ripple numbers and different oil filling volumes are produced, and thermal cycling is introduced to improve the diaphragm performance, and finally the performance of each pressure-sensitive core is tested and the test data are analyzed and compared.FindingsThe experimental results show that the larger the diameter of the corrugated diaphragm used for encapsulation, the better the performance. For pressure-sensitive cores using smaller diameter corrugated diaphragms, the performance of one corrugation is better than that of two corrugations. When the number of corrugations and the diameter are the same size, the performance of the outer ring of the diaphragm with concave corrugations is better than that with convex corrugations. At the same time, the diaphragm after thermal cycling treatment and appropriate reduction of encapsulated oil filling can improve the performance of the pressure-sensitive core.Originality/valueBy exploring the effects of corrugated diaphragm and oil filling volume on the performance of oil-filled pressure cores, the design of oil-filled pressure sensors can be guided to improve sensor performance.

Equation of State of Liquid Fe7C3 and Thermodynamic Modeling of the Liquidus Phase Relations in the Fe‐C System

AbstractWe calculated the pressure‐volume relations of liquids Fe and Fe7C3 up to ∼360 GPa and 3000–8000 K based on the first‐principles molecular dynamics simulations. The results demonstrate that liquid Fe7C3 is similar in compressibility and thermal expansivity to liquid Fe at the Earth's core pressure range. We then obtained a thermodynamic model of the liquidus phase relations in the Fe‐C system at high pressures by using the thermal equation of state (EoS) of liquid Fe7C3 as well as that of liquid Fe3C estimated by interpolation between the volumes of Fe and Fe7C3 calculated in this study. The previously reported eutectic points in the Fe‐Fe3C system are reproduced with interaction parameters that are dependent on temperature but independent on pressure at >∼50 GPa. The melting curve of Fe7C3 should be close to that of Fe, which leads to a change in the eutectic system from Fe‐Fe3C to Fe‐Fe7C3 above 250 GPa as observed by previous experiments. The thermodynamic model also suggests that the solidus and liquidus of Fe3C are relatively low. The Fe‐Fe7C3 liquidus phase relations at the Earth's inner core boundary (ICB) pressure indicate the Fe7C3 inner core is unlikely. While the carbon content in the Earth's outer core may be small, the addition of 1 wt% C to liquid Fe drops the liquidus temperature to crystallize hcp‐Fe by ∼450 K, suggesting that the presence of carbon in the outer core is preferable for a relatively low core‐mantle boundary (CMB) temperature.

Kinetic-ballooning-bifurcation in tokamak pedestals across shaping and aspect-ratio

We use a new gyrokinetic threshold model to predict a bifurcation in tokamak pedestal width-height scalings that depends strongly on plasma shaping and aspect-ratio. The bifurcation arises from the first and second stability properties of kinetic-ballooning-modes that yields wide and narrow pedestal branches, expanding the space of accessible pedestal widths and heights. The wide branch offers potential for edge-localized-mode-free pedestals with high core pressure. For negative triangularity, low-aspect-ratio configurations are predicted to give steeper pedestals than conventional-aspect-ratio. Both wide and narrow branches have been attained in tokamak experiments.

Building 1D Mechanical Earth Model for Subba Oilfield in Iraq

At the Subba oil field, wellbore stability is the main concern while drilling. The wellbore's instability causes several issues, including: (inefficient hole cleaning, tight hole, stuck pipe, mud losses, caving, bad cementing, and well kick or blowout). This increases Non-Productive Time (NPT) and well-drilling costs; hence the operator's main goal is to create a drilling program that reduces these problems and therefore reduce drilling cost. The study aims to build a 1D mechanical earth model to predict the wellbore failure and design optimum mud weight to improve the drilling efficiency for future wells. The model includes pore pressure, stress state, and rock mechanical parameters (such as UCS, angle of friction, Young-Modulus, and Poisson-Ratio). To achieve this aim, the study utilised offset well data including log data (Gama-Ray Logs (GR), Caliper Logs (CALI), Density Logs (RHOZ), and Compressional Sonic (DTCO) and Shear Sonic (DTSM)), Core tests, Mini-frac field tests, Drilling Reports, Mud Reports, and Mud Log Reports (master log) to estimate and calibrate the profiles of formation pore pressure, rock mechanical properties, and in-situ stresses. The 1D mechanical earth model was built using the Excel program for three wells data set, where all the necessary parameters to create the model was calculated, calibrated for the calculated variables with core data and pressure test points, and finally the safe mud window was detected. The results showed that the Eaton Slowness method to predict pore pressure perfectly matches the pressure test points. The most common fault regimes in the Subba oilfield are normal and strike-slip faults. The Modified Lade criteria showed a compatible match with drilling events and calliper log in predicting the failure zones, so it is the best criterion in determining minimum and maximum mud weight. Based on the results of this study and in comparison with the mud window used in drilling operations in the field, it is necessary to change the mud window used in drilling and adopt the safe MWW of this study in drilling new wells in this field and the area adjacent to the field.

Pion and kaon electromagnetic and gravitational form factors

A unified set of predictions for pion and kaon elastic electromagnetic and gravitational form factors is obtained using a symmetry-preserving truncation of each relevant quantum field equation. A key part of the study is a description of salient aspects of the dressed graviton + quark vertices. The calculations reveal that each meson’s mass radius is smaller than its charge radius, matching available empirical inferences; and meson core pressures are commensurate with those in neutron stars. The analysis described herein paves the way for a direct calculation of nucleon gravitational form factors.

Unveiling the effect of Ni on the formation and structure of Earth’s inner core

Ni is the second most abundant element in the Earth's core. Yet, its effects on the inner core's structure and formation process are usually disregarded because of its electronic and size similarity with Fe. Using ab initio molecular dynamics simulations, we find that the bcc phase can spontaneously crystallize in liquid Ni at temperatures above Fe's melting point at inner core pressures. The melting temperature of Ni is shown to be 700 to 800 K higher than that of Fe at 323 to 360 GPa. hcp, bcc, and liquid phase relations differ for Fe and Ni. Ni can be a bcc stabilizer for Fe at high temperatures and inner core pressures. A small amount of Ni can accelerate Fe's crystallization at core pressures. These results suggest that Ni may substantially impact the structure and formation process of the solid inner core.

Empirical evaluation of the strength and deformation characteristics of natural and synthetic gas hydrate-bearing sediments with different ranges of porosity, hydrate saturation, effective stress, and strain rate

Evaluating the mechanical properties of gas (primarily methane) hydrate-bearing sediments is essential for commercial production as a next-generation resource and understanding the global carbon cycle. Triaxial and uniaxial compression tests have been conducted on synthetic gas hydrate and natural core samples recovered from deep-sea beds using pressure coring techniques. The results show that four factors are vital in establishing the strength of hydrate-bearing sediments: hydrate saturation, effective confining stress, porosity, and strain rate. However, no study has evaluated these factors in a unified and quantitative manner, and even if the physical properties of the reservoir are known in detail from logging, predicting the strength has been challenging. In this study, pressure cores were drilled and recovered from the Eastern Nankai Trough in April 2018 after Japan’s second offshore production test, and triaxial or uniaxial compression tests were performed on 12 pressure core samples brought back to the laboratory. The mechanical properties of the hydrate-bearing sediments were classified with previous obtained results from 53 pressure cores and 223 synthetic cores, and empirical equations for triaxial compressive strength and deformation modulus were proposed as functions of gas hydrate saturation, effective confining pressure, porosity, and strain rate. The obtained equations were found to correlate well with the experimental data and can predict the strength and deformation modulus from logging data.