Nuclear Power Generation Systems Research Articles

Power Generation with Renewable Energy and Advanced Supercritical CO2 Thermodynamic Power Cycles: A Review

Supercritical CO2 (S-CO2) thermodynamic power cycles have been considerably investigated in the applications of fossil fuel and nuclear power generation systems, considering their superior characteristics such as compactness, sustainability, cost-effectiveness, environmentally friendly working fluid and high thermal efficiency. They can be potentially integrated and applied with various renewable energy systems for low-carbon power generation, so extensive studies in these areas have also been conducted substantially. However, there is a shortage of reviews that specifically concentrate on the integrations of S-CO2 with renewable energy, encompassing biomass, solar, geothermal and waste heat. It is thus necessary to provide an update and overview of the development of S-CO2 renewable energy systems and identify technology and integration opportunities for different types of renewable resources. Correspondingly, this paper not only summarizes the advantages of CO2 working fluid, design layouts of S-CO2 cycles and classifications of renewable energies to be integrated but also reviews the recent research activities and studies carried out worldwide on advanced S-CO2 power cycles with renewable energy. Moreover, the performance and development of various systems are well grouped and discussed.

UTOP accident analysis and mitigation measures of lead-cooled fast reactor considering coupling effect with SCO2 Brayton cycle

The lead-cooled fast reactor (LFR) coupled with SCO2 Brayton cycle is an advanced nuclear power generation system which has high efficiency and high compactness. The purpose of this study is to investigate the impact of coupling effect between LFR and SCO2 cycle on the safety analysis of unprotected transient overpower (UTOP) accident, and to propose mitigation measures to UTOP accident with the aid of SCO2 cycle. Firstly, the dynamic simulation model of a 100 MW small modular natural circulation LFR coupled with SCO2 Brayton cycle was developed using APROS software, and was verified through the steady-state and transient simulations. Secondly, the UTOP accident of the LFR coupled with SCO2 Brayton cycle was analyzed, including a comparative case which simplified SCO2 cycle as a fixed boundary in the analysis. Finally, two measures to mitigate the UTOP accident by charging more SCO2 to the circulation loop from the storage tank and by maintaining constant SCO2 temperature at the inlet of in-reactor heat exchangers (IRHXs) were proposed. The results indicate that the conventional method of simplifying power generation system as the fixed boundary underestimated the severity of accident. Specifically, the maximum fuel cladding temperature was about 40 °C higher when considering the coupling effect of reactor and SCO2 cycle than that of assuming SCO2 cycle as the fixed boundary, which greatly exceeded the safety limit. Moreover, within the scope of present UTOP accident conditions, the measures proposed in this study could mitigate the severity of accident. The maximum cladding temperature was reduced by 15–23 °C in the condition of maintaining constant SCO2 temperature at IRHX inlet, and was reduced by 5–7 °C in the condition of charging more SCO2 to the circulation loop, compared with the condition not applying any measures.

Dawn of clean energy: Enhanced heat transfer, radiative cooling, and firecracker-style controlled nuclear fusion power generation system

Global climate change has become a major environmental threat and development challenge facing humanity. Controllable nuclear fusion is a globally recognized ideal solution for clean energy, but its required high-energy triggering conditions and intense energy release prevent existing technologies from achieving safe, stable, and long-term continuous operation. Here, inspired by the traditional Chinese firecrackers, we propose a pulsed fusion reaction flywheel energy storage multi-reactor relay operation to drive the steam turbine to continuously and stably generate electricity for a long period of time; meanwhile, to install cleaning rotors in the cooling medium pipeline to enhance heat exchange, and to apply radiative cooling technology on the surface of the cooling tower to improve cooling efficiency and to reduce energy consumption, thereby improving system safety and overall energy efficiency. Proposing the combination of original technologies at both the hot end and the cold end of the system, we strive to open up a new way for controllable nuclear fusion power generation.

Exploring energetic, exergetic, economic and environmental (4E) performance of waste heat power generation in nuclear power plant systems: A perspective of pattern recognition

Combined cogeneration systems are employed to recover waste heat from the sCO2 cycle in nuclear power generation systems. However, dealing with their multidimensional and nonlinear design and optimization spaces is a complex challenge for designers. In this study, the combined cogeneration system is parameterized and modeled: 4E models including energetic, exergetic, economic and environmental are established for sCO2 combined Organic Rankine Cycle (sCO2/ORC) and trans-critical CO2 Cycle (sCO2/tCO2) respectively. Several decision variables and five performance indicators are selected. To gain a deeper understanding of the mechanisms and optimize the combined cogeneration system, pattern recognition methods including the Self-Organizing Map (SOM), an unsupervised competitive learning approach, and Statistical Sobol Global Sensitivity Analysis methods are proposed. These techniques help identify key parameters and system patterns within the design space. Then, the Non-Dominated Sorting Whale Optimization Algorithm (NSWOA) is adopted to build a Pareto-optimal decision space, and the SOM and PCPs are proposed to visualize and mining based on pattern recognition and graph visualization interaction. The design parameters of the top cycle, P2, PRc, and x, have been confirmed as having a substantial impact on the system's performance. The multiple attributes, criterions and objectives problems in the combined cogeneration system are ultimately simplified to “Economy-Environment”, double objectives problem, and three trade-offs’ solutions are discussed: prioritizing economics, prioritizing the environment, and finding a balanced economic-environmental compromise. Pattern recognition method provides decision-makers with a fresh perspective for gaining a deeper understanding of the multi-criteria objectives space and potential trade-offs. The integration of pattern recognition into the thermodynamic, economic, and environmental models outlined in this paper represents a substantial and valuable advancement in the analysis and optimization of combined cogeneration cycles.

Tritiated water removal method based on hydrate formation using heavy water as co-precipitant

A separation method of tritium has been developed based on co-precipitation of tritiated water on porous heavy water (D2O) based clathrate hydrate. The tritium was semi-continuously removed by a circulating flow of tritium-containing light water through the D2O hydrate media crystallized in advance. The tritium concentration of 4.77 × 105 Bq/kg was reduced to 1.55 × 103 Bq/kg with HFC-134a hydrate at 0.35 MPa for 1 h, while tritiated water treatment at a concentration of 1010 Bq/kg or greater is eligible with the conventional detritiation methods. Near the D2O hydrate surfaces, solid solutions with higher concentrations of tritiated water were deposited on the hydrate substrate than those in the liquid phase. The semi-serialized operation of hydrate based detritiation is capable of high-rate processing as well as energy and resource saving. This method could be a candidate treatment for huge quantities of water with low concentration tritium discharged from nuclear fusion power generation system.

Multi–length scale characterization of point defects in thermally oxidized, proton irradiated iron oxides

A key for the success of safe nuclear power generation system is to consider structural materials that are economical, meet mechanical property needs, possess good corrosion resistance, and are radiation tolerant. Nevertheless, fundamental insights that elucidate the details of radiation damage on materials corrosion performance are lacking. This includes the behavior of surface oxides which often regulate corrosion. For example, it is unclear how non-equilibrium point defects, oxide structure, mass transport in oxides, and subsequent oxidation behavior are altered by the radiation. In this work, some of the effects of proton irradiation on the attributes of point defects, iron oxide microstructures, and the physical nature of the oxidation product were correlated with corrosion behavior. Iron oxides, fabricated by thermal oxidation in air at 400°C and 800°C for 1 h, were subjected to 200 keV, 0.03 dpa (displacements per atom) of proton irradiation, and subjected to corrosion reactivity assessment using AC and DC electrochemical methods. Experimental methods that target materials information at different length scales, such as positron annihilation spectroscopy (atomistic), transmission electron microscopy (mesoscopic), and electrochemical methods (macroscopic), were coupled to shed light on the impact of radiation-induced defect modifications and structural changes in oxides on corrosion reactivity which ultimately affects durability in harsh environments.

Modeling, Analysis, and Identification of Armature Winding Interturn Fault in Multiphase Brushless Exciters

As the core of large-capacity nuclear power generation system, the multiphase annular brushless exciter (MPABE) may cause a serious catastrophe to the nuclear power plant if it fails. In order to effectively protect the armature winding of MPABE, a rapid simulation model and a sensitive diagnosis method of armature winding short-circuit (AWSC) fault are studied systematically in this article. First, this article proposes a general and rapid simulation model of MPABE with AWSC fault. To verify the correctness of this model, corresponding simulations and experiments of AWSC faults are carried out, respectively, through which the fault characteristics are obtained. Then, a detailed mechanism analysis is presented, which explains the induction process of the related harmonics in the stator and rotor currents. The variation law of the characteristics value when the number of short-circuited coils changes is also analyzed. Finally, a new method to diagnose AWSC fault of the MPABE is proposed and then optimized. The test results on the prototype show that this method can sensitively diagnose even the slightest AWSC fault. Therefore, it can provide a reliable basis for the monitoring and protection of MPABE in nuclear power plants.

Convectively cooled solidification in phase change materials in different configurations subject to internal heat generation: Quasi-steady analysis

Phase change phenomena involving internal heat generation are of central interest in various applications, including freeze drying, preservation of biological tissues, microwave/Joule heating processes, materials processing using lasers, and nuclear power generation systems. In this work, mathematical models are developed to study the solidification processes driven by convective cooling effects on the exterior surface of phase change materials (PCM) in different geometric configurations, where both the solid and the liquid phases are subject to volumetric heating. By invoking a quasi-steady assumption and performing a simplified unified analysis, new semi-analytical approximate solutions for this unique Stefan problem in planar, cylindrical, spherical, and semi-infinite geometries of the PCM are obtained and studied. The interface evolution depends on the characteristic dimensionless parameters, such as the Biot number, Bi, internal heat generation parameter, Q, Stefan number, St, and the thermal conductivity ratio, κ. The effects of all the dimensionless parameters, viz., Bi, Q, St, and κ are systematically investigated for each geometrical configuration of the PCM. In particular, the results show the significant role of the Biot number on the transient evolution as well as the steady-state thickness of the solidifying front in the presence of an inhibiting internal heat generation. In addition, a simple and unified condition relating the dimensionless internal heating rate (Q) and the external convective cooling rate (Bi) for the onset of remelting for the special case of κ = 1 applicable for all the above geometries of the PCM is deduced.

Solution of issues in emergy theory caused by pathway tracking: Taking China's power generation system as an example

Emergy theory is effective to evaluate sustainabilities by tracking all the resources of a product formation process and converting them to solar emergy baseline. Emergy transformity (Tr) is essential to obtain the emergy value of a product. However, a secondary product coming from different production pathways will have various Trs, making it difficult to select a representative Tr when it is used as an input of other systems. Different methods for representative Tr are used in previous studies without considering the characters of different pathways. A method to obtain representative Tr is proposed in this study by classifying the pathways for a secondary product into the technological-impacted-systems and environmental-impacted-systems with the advanced and average values adopted as the representative Trs, respectively. Based on the market share and representative Tr of each pathway, the weighted average value could be obtained as the representative Tr of the product. The on-grid power generation system of China is taken as a case study. The nuclear and coal-fired power generation systems belong to technological-impacted-systems, while the renewable power generation systems belong to environmental-impacted-systems. According to the proposed method, the representative Tr of electricity generated in China is 1.13 × 105 sej/J.

Study on thermal deformation of hybrid printed circuit heat exchanger for advanced nuclear reactor

The intermediate heat exchanger (IHX) is one of the key components in advanced nuclear reactor power generation system. Printed circuit heat exchanger (PCHE) with mini-channels is a good candidate for the IHX. But the whole PCHE with tens of thousands of mini-channels is hard to be modeled and calculated at high temperature. Thus, the homogenization method, which can calculate the thermal deformation of the whole hybrid mini-channel PCHE, is conducted in this study and both the elastic and elastic-plastic finite element analysis methods are used. Here, the performance of the PCHE is assumed to be isotropic in the simulation. The results show that the macroscopic thermal deformation of the whole PCHE follows a gradually downward trend from hot side to cold side, while obvious thermal stress concentration is observed around the junctions between the PCHE core and cover plate. The stress and strain calculated by elastic and elastic-plastic methods under different constraints show quite different patterns. For the thermal deformation analysis of PCHE under weak constraint or small temperature difference conditions, the stress and strain results by elastic analysis and elastic-plastic analysis are similar so that the elastic analysis can be used. Under the strong condition, the stress of PCHE calculated by elastic analysis is much higher than that of elastic-plastic analysis, while the strain is lower than that of elastic-plastic analysis. The relative deviations of stress are 100.883% and 120.786% along path 1 and path 2 respectively. And the relative deviations of strain are 6.987% and 10.139% along path 1 and path 2 respectively. The elastic-plastic analysis should be used instead of the elastic analysis.

Thermodynamic-Dynamic coupling of a Stirling engine for space exploration

As the new space era advances, there is an increasing demand for long-term missions beyond Earth’s orbit, such as on Mars and the Moon. The level of complexity of these missions is higher than conventional missions in terms of duration, particularly the energy demand required. To become viable, power generation systems must have a high power density, that is, high power associated with low mass. From this perspective, dynamic nuclear power generation systems coupled with electric propulsion are considered the most promising systems for deep-space exploration and colonization missions. Thus, to provide valuable information for the development of a dynamic energy conversion system for space, this study carried out thermodynamic modeling of a nuclear-powered Stirling cycle coupled with a dynamic engine model for space purposes. By means of numerical modeling, the constructive parameters of the Stirling engine, such as regenerator efficiency, compression ratio, heat exchanger thermal conductance, engine frequency, piston stroke, and area, are varied to understand the impact of these parameters on the final system performance. The results show that the regenerator efficiency can provide significant gains in the engine efficiency. However, a very high regenerator efficiency reduces the power of the cycle. The engine compression ratio tends to increase the engine efficiency, but a compression ratio above six provides marginal gains for cycle efficiency. From the results obtained, the best parameters yielded a system with a power output of 260.5 kW and a power density of 35.38 kg∙kW-1. This study can serve as a theoretical guideline for the future design of nuclear-powered Stirling engines for space applications, providing insight into the constructive parameters that influence the overall performance of the system.

Overview and current perspectives for the use of the GFR reactor in research and electricity generation in Brazil / Panorama e perspectivas atuais para o uso do reator GFR em pesquisa e geração de energia elétrica no Brasil

The Gas Cooled Fast Reactor (GFR) is one of the ambitious projects of Generation IV nuclear reactors, which aims to develop a sustainable, safe, reliable, economical and proliferation-resistant nuclear power generation system. This project is currently in a theoretical phase, being reported in this work a history from its idealization to the present moment. Presently, the project that is in a more advanced development stage, ALLEGRO, is in the final design phase and with the licensing process in progress. In the Brazilian perspective, it is known that an increase in investment is necessary to develop the nuclear area and a greater engagement in research and development groups of fast neutron reactors, aspects which are compatible with a GFR generation IV project.

Optimization of a recompression supercritical nitrous oxide and helium Brayton cycle for space nuclear system

Long life, high energy density, high efficiency, and compact power system is necessary for space exploration to achieve a future goal. Recompression supercritical Brayton cycle has excellent potential for application of space nuclear power generation systems. However, it faces the choice of cycle working fluid which limits the cycle thermal efficiency and quality. In order to improve the thermal efficiency of the nuclear power system, a new composition of the working fluid, nitrous oxide and helium (N2O–He) mixture is used in the system. Comprehensive studies and optimization are performed for the significant parameters, including the split ratio, pressure ratio, minimum operating temperature, maximum operating temperature, and minimum operating pressure. Optimum values have been obtained at which the maximum thermal efficiency and minimum Brayton rotating unit (BRU) mass of the cycle occur. Results show that the thermal efficiency improves with an increase in the split ratio, main compressor pressure ratio, and maximum operating temperature, and decreasing minimum operating temperature and minimum operating pressure. The proposed novel working fluid cycle has superior performance compared with N2O (deviation of 5.1%) and CO2 (deviation of 6.5%). The optimized thermal efficiency and BRU mass are calculated as 42.67% and 3584.80 kg at optimum conditions.

Numerical research on thermal stress of steam cooler tube sheet mechanical structure

Steam cooler is one of the most important mechanical equipment in thermal power generation system and nuclear power generation system. The steam cooler bears a huge temperature gradient load when the working conditions are switched. In order to analyze the thermal stress of steam cooler tube sheet with high temperature load under harsh working conditions, the thermal-structural coupling analysis model of steam cooler tube sheet is constructed with finite element method. The results show that the stress concentration exists at the position connection between heat exchanger tube and cylinder. The maximum stress is located at the outermost heat exchanger tube with the peak stress of 320MPa. The heat exchanger tube layout alone cause higher stress. This situation should be avoided in the design of heat exchanger tube sheet. Furthermore, the strength and safety of the steam cooler tube sheet are evaluated with the stress linearization method. The steam cooler tube sheet design meets the safety requirements of structural strength under high temperature load.

Numerical study on particle decontamination from spherical bubbles in scrubbing pools by using Eulerian–Lagrangian method

Pool scrubbing is conducted to remove contaminated aerosols/particles released from nuclear power generation systems in severe accidents. Gas-entrained particles pass through the pools in three stages: 1) injection into the pools through a vent, 2) decontamination process in bubbles rising in the pools, and 3) secondary entrainment into the atmosphere at the pool surface. The particle separations in the rising bubble swarm constitute the primary process for aerosol decontamination. The dynamics of the particles contained in the rising bubble swarm are crucial. Numerical modeling of particle transportation in bubbles in three-phase systems is complex and challenging. This study aimed to investigate the particle flow dynamics in scrubbing pools to understand the particle decontamination mechanism, which can guide equipment design to achieve high aerosol separation efficiency. In this study, particle decontamination in bubbles is simulated by using the Eulerian–Lagrangian method. This numerical method is used to investigate the mechanisms of flow dynamics, coagulation, and separation of particles in the bubbles, as well as the particle decontamination affected by the operation parameters such as the bubble velocity, and gas and particle properties. In addition, the decontamination factor is predicted for aerosol particles in the small bubbles of the rising swarm, which agrees with the calculated experimental DF of the bubble swarm.

Influence of non-ideal gas characteristics on working fluid properties and thermal cycle of space nuclear power generation system

Space nuclear Closed Brayton Cycle (CBC) power generation system with Helium-xenon gas (He–Xe) as a work fluid has attracted much attention with the development of space technology. The appropriate thermophysical property model of He–Xe is the key to achieve high-precision simulation of CBC power generation system. The thermophysical property model based on virial coefficient was developed and proposed. It was compared with the ideal gas model to clarify the differences and non-ideal gas characteristics of He–Xe. The deviations of He–Xe thermophysical parameters, main cycle parameters under different temperatures and pressures were compared numerically with these models. Based on non-ideal gas properties, a thermodynamic model was developed to analyze the influence of non-ideal gas characteristics on the efficiency of a 3.0 MWth lithium-cold fast reactor power system. The results showed that He–Xe physical parameters deviated from ideal gas characteristics significantly under the molar mass of more than 40 g/mol. Lower temperature (<500K) or higher pressure (>3.0 MPa) tends to make non-ideal gas characteristics on thermophysical parameters more effective. The thermophysical property model with non-ideal gas characteristics improves the system simulation accuracy about 4.91 %. This work can be used as reference for the development, accurate simulation and assessment of space nuclear CBC power generation system.

Development of a civil infrastructure resilience assessment framework and its application to a nuclear power plant

Recent disruptive events, such as earthquakes or floods, have caused severe damage to civil infrastructure systems. Thus, there is a need to extend the focus of traditional design practices to include resilience-based design approaches which can help in defining preventive actions and measures to mitigate the consequences caused by such disruptive events. This paper presents a Civil Infrastructure Resilience Assessment Framework (CIRAF) to assess the seismic fragility and resilience of a single or multiple interconnected civil infrastructure systems following a disruptive event. Once the information regarding the infrastructure system, hazards, fragility functions, component's damage state correlation, recovery models, and upgrade models are identified, then the framework can be used to quantify the loss of functionality, recovery time, repair cost, and overall resilience using a Bayesian Network approach. A state-of-the-art engineering tool is also developed using the framework that would enable the stakeholders to compare different upgrade strategies through an easy to use web interface and thus easing the decision-making process. A case study of a hypothetical nuclear power generation system is used to assess the seismic fragility and resilience using the proposed framework.

Evaluating the two-phase flow development through orifices using a synchronised multi-channel void fraction sensor

Understating two-phase flow through flow restricting orifices is critical in evaluating the piping degradation mechanisms in nuclear power generation systems. Characterizing the instantaneous changes of the two-phase local parameters across flow restricting orifices is critical in evaluating the piping structure dynamics. A multi-channel void fraction sensor was developed to investigate the effect of flow restricting orifices on flow pattern development in a 25.4 mm horizontal pipe. Instantaneous void fraction measurements were obtained at multiple locations upstream and downstream of the flow restricting orifices with area ratios of 0.062, 0.14, 0.25, and 0.56. Additionally, pressure measurements and flow visualizations were carried out to investigate the dynamics flow characteristics through the orifice. A liquid superficial velocity of 0.526, and 1.08 m/s and a gas superficial velocity ranging from 0.164 to 2.795 m/s were selected to represent the intermittent flow pattern. The results revealed that as the gas superficial velocity increased, the flow pattern downstream of the restriction changed to dispersed bubbly, or liquid jet and annular-dispersed liquid for an intermittent flow upstream of the orifice. The flow pattern development along the test section was affected significantly in the region close to the orifice, especially at a lower area ratio. Analysis of statistical characteristics of the slug flow pattern such as slug velocity, elongated bubble length and slug frequency were determined from the void fraction data and presented. The slug velocity upstream of the orifice decreased non-linearly as the area of the flow restriction decreased for the same flow condition upstream. The pressure variations along the pipe for different two-phase flow conditions across the orifices were obtained and different correlations to predict pressure drop across the orifices were evaluated. The Simpson et al. [1] correlation was the best as it predicted 93% of the experimental data with a 25% error.

Pluto Orbiter–Kuiper Belt Explorer: Mission Design for the Gold Standard

A mission design study was conducted demonstrating for the first time the feasibility of a combined Pluto orbiter–Kuiper Belt explorer mission using present-day electric propulsion (EP) performance and launch vehicles, assuming that radioisotope thermoelectric generator (RTG)–sourced electricity would power the EP system, a not-yet-demonstrated but low-risk capability. This mission breaks the scientific conundrum between desires to study the Pluto system in more detail using an orbiter and desires to reconnoiter other bodies in the Kuiper Belt. This study also includes the first demonstration that a wide suite of Pluto orbiter scientific objectives can be accomplished with an orbital trajectory primarily using Charon gravity-assist maneuvers to maneuver in the system. The study further demonstrates that Pluto system escape back into the Kuiper Belt can be accomplished using Charon gravity assists, thereby further reducing onboard propulsion requirements. The primary technical challenges for this mission are the long (75 years) mission duration imposed by current-day RTG nuclear systems required to power the spacecraft and its EP system, and the need for high-bit-rate communications () to make the Pluto orbiter continuously effective. As discussed in this study, the communications challenges can be overcome without new systems developments or unreasonable mass challenges. More reasonable mission durations (e.g., ) will require the development of multi-kilowatt nuclear fission reactor power generation systems; still shorter mission durations require both more power and higher EP thrust, as in multiple electric engines operating simultaneously.

Molecular dynamics study of mechanism of density fluctuation in supercritical fluid

With the rapid development of supercritical fluid, it has been widely applied to various industrial technology fields such as supercritical fluid extraction, thermal and nuclear power generation systems, air conditioning and refrigeration, and solar power generation because of its unique physical and transport properties. At present, some studies have found that the speed of sound sharply changes near the supercritical point and the supercritical region can be divided into “liquid-like” and “gas-like” regions, and the concept of “pseudo-boiling” was proposed. However, the structural characteristics of supercritical fluids in different regions and their evolution laws versus time are rarely available in the literature. Therefore, in this paper, the density fluctuations in the “liquid-like” and “gas-like” regions of a supercritical fluid at different isotherms and densities have been investigated and analyzed by molecular dynamic simulation. The results show that near the critical temperature, the density time series curve has a large fluctuation at the “pseudo-critical” point. As the system temperature and the deviation from the “pseudo-critical” point increase, the density fluctuation gradually decreases. In addition, with the density increase or decrease, the difference of density fluctuation between different isotherms decreases. This can indicate that the degree of density deviation from the “pseudo-critical” point is the main reason for density fluctuations. Moreover, supercritical fluid is a type of a heterogeneous medium with considerable density fluctuation and can be regarded as a mixture of high density (“liquid-like”) and low density (“gas-like”) fluids; therefore, the heterogeneous character declines with temperature, and the deviation from the “pseudo-critical” point increases. In this paper, nonlinear analysis has been based on the time series of density and the autocorrelation function, attractor phase diagram, and recurrence plots have been mainly used to conduct it. The studies confirm that the density fluctuations in the different region are deterministic chaotic or stochastic systems. Based on the time delay obtained from the autocorrelation function, the chaotic and stochastic characteristics of the calculated conditions can be preliminarily interpreted. It is demonstrated that the lower system temperature and closer to the pseudo-critical point, the time series curve has strong predictability. All of the time series only showed two different non-linear characteristics according to the phase diagram of the attractor and the recurrence plots. The result reveals that when the isotherm is near the critical point, a large density range represent chaotic characteristics and as the temperature increases, this range gradually decreases. Moreover, when T =1.075 T c, all the calculation conditions exhibit stochastic systems and chaotic systems no longer exist. Finally, a study on the sample entropy of different calculation conditions was conducted indicating a change trend in which the sample entropy of the chaotic system is less than that of the stochastic system. Additionally, as the deviation from the pseudo-critical point increases, the entropy converges in a small region and the difference between the different isotherms is reduced. At the same time, the effect of the system temperature on the sample entropy gradually decreases, and the system density plays a dominant role. This illustrates that a certain ordered structure in the chaotic system and a stronger disordered structure in the stochastic system exists and proves that this special structure of supercritical fluid exists in a certain range of temperature and pressure. These finding may facilitate to understand the characteristics of supercritical fluids and provide theoretical support for further exploration.