Supercritical Reactor Research Articles

An innovative system by integrating the gasification unit with the supercritical water unit to produce clean syngas for solid oxide fuel cell (SOFC): System performance assessment

Existence of impurities in the product gas hinders the application of the system which combines gasification with solid oxide fuel cell (SOFC). A new method is proposed to produce qualified syngas, which integrates the gasification unit with the supercritical water unit (SWU). The SWU contains supercritical water mixer, separator, reactor (SWR) and expander. To analyze performance of the proposed process from a systematic perspective, downstream operating units primarily including SOFC, burner, heat recovery steam generation and steam cycle are designed. Model for the whole system is developed by using Aspen Plus and a mathematical model for the SOFC. Sensitivity analysis regarding the fuel utilization factor (Uf) and the mass ratio of tars to supercritical water (T/W) are conducted in terms of system electrical efficiency, SOFC electrical efficiency and cell voltage. Results show that combustible components in the obtained syngas mainly contain CH4, H2, and CO. Tars are completely decomposed and only slight amount of light hydrocarbons (except CH4) are present. One SWR can undertake the functions of water gas shift, tar reforming and methane synthesis concurrently. The integrated process can offer a combustible components efficiency of 78.2%, and the system electrical efficiency is predicted to be 46.3%. Uf has a significant influence on the SOFC electrical efficiency, while it has slight influence on system electrical efficiency. As the T/W rises from 1.6% to 2%, system electrical efficiency, SOFC electrical efficiency and cell voltage slightly increase.

Evolution of Dislocation Loops in AL-6XN Stainless Steels Irradiated by Hydrogen Ions

AL-6XN stainless steels, one of the candidate structure materials for supercritical water-cooled reactor, were irradiated from 0.5 to 5 dpa using 100 keV H2 + ions at 290 and 380 °C. Microstructures were characterized by transmission electron microscopy (TEM). Dislocation loops were the dominant radiation-induced defects. All the dislocation loops had 1/3 <111> type Burgers vector. Number density and size of the loops have been measured. Nucleation and evolution of dislocation loops were also investigated. Voids were observed only in the condition of 5 dpa at 380 °C. Different evolution mechanisms of the radiation-induced dislocation loops were discussed. Effects of hydrogen and elevated temperature on the microstructural evolution were also investigated. Besides, the formed voids have a further effect on the evolution of dislocation loops.

Understanding bottom-up continuous hydrothermal synthesis of nanoparticles using empirical measurement and computational simulation

Continuous hydrothermal synthesis was highlighted in a recent review as an enabling technology for the production of nanoparticles. In recent years, it has been shown to be a suitable reaction medium for the synthesis of a wide range of nanomaterials. Many single and complex nanomaterials such as metals, metal oxides, doped oxides, carbonates, sulfides, hydroxides, phosphates, and metal organic frameworks can be formed using continuous hydrothermal synthesis techniques. This work presents a methodology to characterize continuous hydrothermal flow systems both experimentally and numerically, and to determine the scalability of a counter current supercritical water reactor for the large scale production (>1,000 T·year–1) of nanomaterials. Experiments were performed using a purpose-built continuous flow rig, featuring an injection loop on a metal salt feed line, which allowed the injection of a chromophoric tracer. At the system outlet, the tracer was detected using UV/Vis absorption, which could be used to measure the residence time distribution within the reactor volume. Computational fluid dynamics (CFD) calculations were also conducted using a modeled geometry to represent the experimental apparatus. The performance of the CFD model was tested against experimental data, verifying that the CFD model accurately predicted the nucleation and growth of the nanomaterials inside the reactor.

Application of Radiation Chemistry to Some Selected Technological Issues Related to the Development of Nuclear Energy.

The most important contributions of radiation chemistry to some selected technological issues related to water-cooled reactors, reprocessing of spent nuclear fuel and high-level radioactive wastes, and fuel evolution during final radioactive waste disposal are highlighted. Chemical reactions occurring at the operating temperatures and pressures of reactors and involving primary transients and stable products from water radiolysis are presented and discussed in terms of the kinetic parameters and radiation chemical yields. The knowledge of these parameters is essential since they serve as input data to the models of water radiolysis in the primary loop of light water reactors and super critical water reactors. Selected features of water radiolysis in heterogeneous systems, such as aqueous nanoparticle suspensions and slurries, ceramic oxides surfaces, nanoporous, and cement-based materials, are discussed. They are of particular concern in the primary cooling loops in nuclear reactors and long-term storage of nuclear waste in geological repositories. This also includes radiation-induced processes related to corrosion of cladding materials and copper-coated iron canisters, dissolution of spent nuclear fuel, and changes of bentonite clays properties. Radiation-induced processes affecting stability of solvents and solvent extraction ligands as well oxidation states of actinide metal ions during recycling of the spent nuclear fuel are also briefly summarized.

The study of microalgae Nannochloropsis salina fatty acid composition of the extracts using different techniques. SCF vs conventional extraction

The extraction of lipids and other valuable components from microalgae (Nannochloropsis salina) has been performed using various conditions: pure SC-CO2; SC-CO2+acetone (at 32MPa and 40°C); Soxhlet apparatus with n-hexane; and Soxhlet apparatus with chloroform. Small amounts of co-solvents (3.2wt.% of acetone) were added to modify the polarity and solvent strength of the supercritical CO2 to increase the solute solubility and to minimize operating costs of the extraction process. The extractions of lipids from algae were performed using a laboratory scale SCF extraction experimental apparatus. High pressure supercritical reactor with volume of 993cm3, which made from stainless steel, was used. The flow rate of SCF was maintained constant (1.5±0.05kg/h). The extraction time was within 1.5h. Four extracted lipid fractions were collected separately for each extraction conditions (for pure CO2 and CO2+co-solvents) and analyzed using GC–MS. The experimental results showed that extraction technique is negligible small affecting on total extract yields and fatty acids content.

Improved Scaling Analysis for Heat Transfer in a Circular Tube With Various Supercritical Fluids Using Computational Fluid Dynamics Simulations

ABSTRACTThe operating conditions of supercritical water cooler reactor (SCWR) are well above the critical point of water, so it is not possible to investigate its heat transfer aspects through laboratory experiments without industry-scale support. The most feasible alternative can be to scale-down the operating parameters by fluid-to-fluid scaling with a suitably chosen scaling fluid. However, it is impossible to incorporate all phenomenological factors of an intricate system like the SCWR through simple analytical scaling. This study demonstrates the limitation of fluid-to-fluid scaling in such situations and suggests the incorporation of computational fluid dynamics simulation as a subsequent step for better scaling. A scaling methodology from the published literature is adopted. Carbon dioxide and R134a have been considered as scaling fluids to identify the parameter ranges suitable for lab-scale simulation of the SCWR. A circular tube of 8 mm diameter and 1500 mm length is taken for simulation. A grid dependency test is done and the standard κ − ϵ turbulence model is selected. The developed computational model showed amicable agreement with existing experimental data. Analytically scaled-down parameters failed to simulate the axial and radial temperature profiles of the prototype. Increase in wall heat flux and reduction in mass flow rate are suggested as two possible options for achieving better profile matching. The modified values of scaled parameters with respect to a particular prototypical condition are reported. Profiles with CO2 as model fluid show better agreement with water as compared to R134a and hence this is recommended for use in lab experiments.

A SOLID MODERATOR PHYSICS ASSESSMENT FOR THE CANADIAN SCWR

The Canadian supercritical water-cooled reactor (SCWR) is Canada’s contribution to the Generation-IV (GEN-IV) International Forum’s research and development effort toward the study and eventual deployment of advanced nuclear energy systems. All GEN-IV concepts including the SCWR target enhanced safety, improved economics, improved sustainability, and enhanced security relative to present day nuclear reactors. A loss of coolant accident in the SCWR will shut down the reactor due to a large decrease in reactivity. This highly negative coolant void reactivity (CVR) is a contributor to the enhanced safety of the reactor, but it can complicate reactor control. The use of a solid moderator, namely zirconium hydride, as a means of coolant void reactivity adjustment is assessed here. Results suggest that a solid moderator is a viable option for CVR adjustment, provided materials obstacles can be overcome.

Stress corrosion cracking behavior of annealed and cold worked 316L stainless steel in supercritical water

The supercritical water reactor (SCWR) is one of the more promising designs considered by the Generation IV International Forum due to its high thermal efficiency and improving security. To build this reactor, standardized structural materials used in light water reactors (LWR), like austenitic stainless steels, have been proposed. These kind of materials have shown an optimum behavior to stress corrosion cracking (SCC) under LWR conditions except when they are cold worked.It is known that physicochemical properties of water change sharply with pressure and temperature inside of the supercritical region. Owing to this situation, there are several doubts about the behavior of candidate materials like austenitic stainless steel 316L to SCC in the SCWR conditions.In this work, alloy 316L was studied in deaerated SCW at two different temperatures (400°C and 500°C) and at 25MPa in order to determine how changes in this variable influence the resistance of this material to SCC. The influence of plastic deformation in the behavior of alloy 316L to SCC in SCW was also studied at both temperatures.Results obtained from these tests have shown that alloy 316L is susceptible to SCC in supercritical water reactor conditions where the susceptibility of this alloy increases with temperature. Moreover, prior plastic deformation of 316L SS increased its susceptibility to environmental cracking in SCW.

Assessment of subchannel code ASSERT-PV for supercritical applications

The Canadian subchannel code ASSERT-PV has been modified and used in the development of a fuel assembly concept for the Canadian Supercritical Water-cooled Reactor (SCWR). This paper describes the modification to ASSERT-PV for the SCWR applications, and presents an assessment of the code against available experimental data. Full-bundle tests for the SCWR fuel assembly are not yet available; therefore, partial-bundle tests with a reduced number of rods and a shortened channel length were considered in the assessment. Three heat transfer experiments at supercritical pressures were selected for the assessment: (i) a Japanese 7-rod bundle water experiment; (ii) a Chinese 2×2 rod bare-bundle water experiment; and (iii) a Russian 7-rod bare-bundle Freon experiment. The rod surface temperature was taken as the key parameter in the assessment since the maximum fuel cladding temperature is a key criterion used in developing the SCWR fuel assembly concept. The ASSERT-PV predictions of rod surface temperature were compared against experimental data of measured wall temperatures. Six widely-known heat transfer correlations were assessed for their suitability in predicting the wall temperatures in rod bundles under conditions relevant to the Canadian SCWR. Overall, the Jackson correlation was found to be the most suitable for predicting the wall temperatures in the range of conditions covered by the selected experiments.

Numerical Analysis on Heat-Transfer Deterioration of Supercritical Fluid in the Vertical Upward Tubes

Heat-transfer characteristics are especially significant among all issues for the supercritical water-cooled reactors (SCWRs). The two-peak wall-temperature phenomenon that could be verified by Shitsman and Jackson’s experiments occurred in the regions of tb&lt;tpc&lt;tw for vertical upward flow under the extreme heating conditions or accident cases (i.e., q/G&gt;0.6 kJ/kg for water). However, so far the special two-peak result has not been paid much attention due to the difficulty of the experiments. Hence, in this study, numerical analysis was carried out to investigate the characteristics of heat-transfer deterioration (HTD) two-peak phenomenon of supercritical pressure water/carbon dioxide in the conditions of high q/G. The results showed that the higher the heat fluxes were, the more temperature peaks might appear and more unstable flow might be presented. Finally, the mechanism of two-peak HTD was studied through quantitatively analyzing the distribution of flow parameters and thermophysical properties in the near-wall region.

Development of a new empirical correlation for the prediction of the onset of the deterioration of heat transfer to supercritical water in vertical tubes

Heat transfer to supercritical water is relevant for modern power applications such as supercritical water reactors, supercritical boilers in fossil-fired power plants or future concepts for supercritical solar-thermal power plants. The phenomenon of deteriorated heat transfer (DHT), caused by the strong variation of fluid properties at pressures above the critical pressure is still not thoroughly understood to date. At the same time it is of great importance for plant design and operation. Disagreements exist regarding its definition, its prediction and the mechanisms leading to its occurrence. This study evaluates the performance of empirical correlations for the a-priori prediction of the heat flux causing the onset of DHT in heated vertical tubes with an internal upward flow of supercritical water and proposes a new correlation. Also, definitions from literature are discussed, and the most frequently used quantitative definition: α<0.3·αNHT is selected for correlation analysis and development. It is emphasized that the predictive capability of a correlation for the deterioration of heat transfer is limited when no definition for this phenomenon is provided. For the evaluation of the existing correlations and the development of the new correlation, heat transfer data consisting of 4455 data points from 14 independent references is considered. This data set is reduced to 32 independent experiments reflecting the heat flux causing the onset of DHT. The newly developed correlation has a mean average relative deviation of 12.9% and predicts 78.1% of the DHT data within ±20%. This is a significant improvement compared to the best existing correlation with a mean average relative deviation of 23.4% and which predicts 56.3% of the DHT data within ±20%.

EVOLUTION OF THE CANADIAN SCWR FUEL-ASSEMBLY CONCEPT AND ASSESSMENT OF THE 64 ELEMENT ASSEMBLY FOR THERMALHYDRAULIC PERFORMANCE

Canada has participated in the Generation IV (Gen-IV) International Forum with a main focus on the pressure-tube type supercritical water-cooled reactor (SCWR) concept. The Canadian SCWR concept is a heavy water moderated and light water cooled reactor. The research and development framework for development of the Canadian SCWR fuel-assembly concept includes experiments, analysis, subchannel code development, and applications, as well as coupled neutronic and thermalhydraulic analyses. The evolution of the Canadian SCWR fuel-assembly concept is summarized in this paper to demonstrate the enhanced performance characteristics and to show that the peak fuel cladding temperature is within allowed limits. The peak cladding temperature is a limiting thermalhydraulic parameter for the Canadian SCWR fuel assembly and is calculated using the ASSERT-PV subchannel code under steady state normal operating conditions with axial and radial power profiles corresponding to the beginning and the end of the fuel cycle. The power profiles were obtained from WIMS AECL/RFSP and MCNP physics code calculations. Using the ASSERT-PV subchannel code, the geometry of the Canadian SCWR fuel assembly has been further optimized to reduce the peak fuel cladding temperature for axial and radial power profiles of interest to the Canadian SCWR concept.

European Project “Supercritical Water Reactor–Fuel Qualification Test”: Results of Fuel Pin Mock-up Tests

The main target of the EURATOM FP7 project “fuel qualification test for supercritical water-cooled reactor” was to make significant progress toward the design, analysis, and licensing of a fuel assembly cooled with supercritical water (SCW) in a research reactor. Within the project, fuel pin mock-ups of a future fuel qualification test facility were designed and manufactured by Centrum Výzkumu Řež (CVR). Following that, it was decided to conduct three different types of tests considering two possible accident scenarios. Simulation of loss of external pressure was the target of Test 1. The autoclave was depressurized as fast as possible from 20 to 1 MPa by opening the close valve located behind the cooling part of the high-pressure part of the loop. Pressure inside the pin was held at a constant value of 20 MPa by pumping high-pressure water via the pin and in parallel via a separate relief valve that was connected directly to the pin using the filling pressure tube. A similar approach was chosen when the opposite case, i.e., loss of internal pressure in the pin, was simulated in Test 2A. Eventually, Test 2A was repeated with modified setup to determine the lower limit of the internal pin pressure (i.e., collapse/buckling of the pin due to external overpressure) more accurately. The presented paper summarizes the results of all three performed tests.

Prediction of Volumetric Data in Supercritical Reactors

Pressure-intensified processes are characterized by handling mixtures whose density is highly dependent on the operating conditions. In addition, fluid behavior in this type of equipment is clearly nonideal. Therefore, the frequent assumption of ideal mixing for calculating the mixture density is inaccurate. Prediction of volumetric information on mixtures is important for the design of continuous supercritical reactors and other process equipment such as heat exchangers, high-pressure pumps, compressors, etc. The isochoric method is a simple and reliable procedure to measure mixture densities and find conditions of homogeneous operation of supercritical chemical reactors at high temperature and pressure. Moreover, it also provides PvT properties simultaneously. It is well-known that the two-parameter equations of state (2P-EoS), like Soave–Redlich–Kwong or Peng–Robinson, have limitations to describe accurately the PvT properties of different fluids together with the phase transitions. The three-parameter...

An innovative system by integrating the gasification unit with the supercritical water unit to produce clean syngas: Effects of operating parameters

Advanced technologies such as solid oxide fuel cells generally have a strict requirement on syngas quality especially the concentration of impurities. It is common to sacrifice economy and efficiency to achieve a qualified syngas by applying several cleaning and conditioning steps. The objective of this work is to propose a combined process by integrating the gasification unit with the supercritical water unit (SWU) to provide qualified syngas. The SWU includes supercritical water mixer, separator, supercritical water reactor (SWR) and expander. Detailed operating methods and appropriate equipment are presented. The whole process is modeled by using Aspen Plus to investigate effects of SWR inlet temperature, operating pressure, and mass ratio of tars to supercritical water (T/W) on the final product composition and on the outlet temperature of SWR. Results show that higher SWR inlet temperature facilitates achieving a higher H2 and CO yield while lower inlet temperature assists in obtaining a higher H2/CO ratio. Lower SWR operating pressure benefits to achieve a higher H2 and CO yield and a higher H2/CO ratio. Lower T/W benefits to have a higher H2 yield and a lower CO yield, leading to a higher H2/CO. Tars could be completely decomposed at the given operating conditions in the proposed process. Higher inlet temperature, higher pressure and larger T/W lead to an increased SWR outlet temperature. Combustible components in the syngas mainly contains H2, CO, and CH4.

An experimental investigation of supercritical heat transfer in a three-rod bundle equipped with wire-wrap and grid spacers and cooled by carbon dioxide

Heat transfer measurements in a three-rod bundle equipped with wire-wrap and grid spacers were obtained at supercritical pressures in the Supercritical University of Ottawa Loop (SCUOL). The tests were performed using carbon dioxide, as a surrogate fluid for water, flowing upwards for wide ranges of conditions, including conditions equivalent to the nominal and near-normal operating conditions of the proposed Canadian Super-Critical Water-Cooled Reactor. The test section contained three heated rods and three unheated rod segments with an outer diameter of 10mm and a pitch-to-diameter ratio of 1.14; the heated length was 1500mm. Detailed surface temperature measurements along and around the three heated rods were collected using internally traversed thermocouples. The following ranges of test conditions were covered, with equivalent water conditions given inside parentheses: pressure from 6.6 to 8.36MPa (19.7–25MPa); inlet temperature from 11 to 30°C (330–371°C); mass flux from 200 to 1175kgm−2s−1 (340–1822kgm−2s−1); and wall heat flux from 1 to 175kWm−2 (11–1847kWm−2). For one set of tests, the heated rods were fitted with a 1.3mm OD wire wrap, having an axial pitch of 200mm along the entire heated length; for a second set, the heated rods were fitted with grid spacers having a 5.3% flow blockage and located at 500mm axial intervals. The effects of spacer configuration on heat transfer at supercritical pressures were documented and analyzed. The observed experimental trends were compared to those obtained in a experiment in a heated tube at similar conditions and with predictions of a supercritical heat transfer correlation. Heat transfer was observed to deteriorate near the start of the heated section of the rod bundle equipped with either type of spacers as well as in a circular tube for mass fluxes between 200 and 700kgm−2s−1. The onset of deterioration occurred at a higher heat flux for the wire-wrapped bundle than for the one with grid spacers, and at the lowest heat flux for the tube. Normal heat transfer in either of the rod bundles behaved similarly to the one in the tube and was also compatible with the predictions of the correlation of Jackson. The grid spacers introduced a strong local enhancement, but their effects disappeared only about 10 rod diameters downstream.

Validation of the ATHLET-SC code by trans-critical transient data

Abstract For the safety analysis of Supercritical Water-Cooled Reactor (SCWR), one of the challenge tasks is to predict the trans-critical behavior of the reactor system during some accidents. The current safety codes have some shortcomings when the pressure decreases from the supercritical condition to the subcritical state due to the void fraction discontinuity across the critical point. Another challenge is the validation of the system code, which needs the transient experimental data. To overcome the above-mentioned challenges, this paper validates the modified code ATHLET-SC, which is developed based on the pseudo two-phase method. The trans-critical transient data from SWAMUP test facility in Shanghai Jiao Tong University (SJTU) are adopted to compare with the simulation results. The results obtained so far shows that the ATHLET-SC code has good feasibility to the trans-critical simulation of SCWR, and it can be used for transient analysis of SCWR in the future.

CSR1000 single channel thermal hydraulic stability analysis using response matrix method

To analyze the thermal-hydraulic stability of CSR1000 (a Chinese supercritical reactor), a Single Channel Thermal-Hydraulic Stability Analysis Code has been developed. This code follows the system response matrix method to determine the stability in time domain, by linearizing the perturbed conservation differential equations. The stability is represented as decay ratio, which is calculated axially at each node in the single channel. A parametric study is performed and it is found that system becomes stable by increasing mass flow rate and decreasing reactor power. The analysis becomes less sensitive for greater values of inlet orifice diameter ratios. The size of mesh has a great effect on the results of analysis. Increasing the system pressure also tends to stabilize the reactor. Using the results of this code, a method is devised to design and realize the concept of inlet orifice in CSR1000.

A novel fractional technique for the modified point kinetics equations

Abstract A fractional model for the modified point kinetics equations is derived and analyzed. An analytical method is used to solve the fractional model for the modified point kinetics equations. This methodical technique is based on the representation of the neutron density as a power series of the relaxation time as a small parameter. The validity of the fractional model is tested for different cases of step, ramp and sinusoidal reactivity. The results show that the fractional model for the modified point kinetics equations is the best representation of neutron density for subcritical and supercritical reactors.

Corrosion behaviour of IN625 in superheated steam at 800°C

Concerns with greenhouse gas emissions and the uncertainty of long-term supply of fossil fuels have resulted in renewed interest in nuclear energy as an essential part of the energy mix for the future. Canada is currently undertaking the design of Generation IV supercritical water-cooled reactor (SCWR) with improved higher thermodynamic efficiency and considerable plant simplification. The identification of appropriate materials for in-core and out-of-core components to contain the SCWR coolant is one of the major challenges for the design of Canadian SCWR. This study is carried out to evaluate the oxidation/corrosion behaviours of Inconel 625 (IN625) under superheated steam (SHS) at a temperature of 800°C (0.1 MPa) for up to 3000 hours. The results show that chromium-based oxide forms on the surface after exposure in SHS for 800, 2000 and 3000 hours. The oxide formation leads to initial weight increase followed by weight loss after extended exposure, likely due to chromium oxide dissolution. No localised oxide spallation was observed on all samples examined. Despite the slight weight reduction, a dense and adhered oxide layer, consisting primarily of Cr2O3 with some spinel (Ni(Cr,Fe)2O4), remained on IN625 after 3000 hours in SHS.