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Fluoride-salt-cooled high-temperature reactor coupled with SCO2 Brayton cycle power generation system has the advantages of high inherent safety, high efficiency, compact structure, and waterless cooling. However, the cold end of the SCO2 Brayton cycle system operates near the critical point and is very sensitive to the cold end parameters, which seriously affects the performance of the cycle system. In addition, when the cold end parameters cross the critical point, the liquefied mass can seriously threaten the safety of the compressor and even the cycle system, therefore, the investigation of the characteristics of the cold end parameters during the dynamic process becomes the key to the safe and stable operation of the SCO2 Brayton cycle system. This paper took the SCO2 Brayton cycle system of a small fluoride-salt-cooled high-temperature reactor as the research object. Matlab/Simulink software was used as the simulation platform, and the Refprop interface was embedded to calculate physical properties. The one-dimensional dynamic simulation model was established for compressors, turbines, heat exchangers, reactors, and other thermal equipment through energy conservation and mass conservation. On this basis, the dynamic characteristics of the system under the disturbance of the cooling water flow of the SCO2 pre-cooler were studied, and the influence of the cold end parameters on the system performance during the variable load was explored. The results show that the disturbance of the cooling water flow of the SCO2 pre-cooler directly affects the inlet temperature of the main compressor, which in turn seriously affects the stable operation of the whole system, so it is necessary to impose certain control means to ensure the stability of the pre-cooler outlet temperature during the operation of the system. Due to the role of the thermal inertia of the reactor and the interaction between the reactor and the heat exchanger, the hot end of the system fluctuates obviously and then affects the cold end, so the reactor is the main reason for the longterm fluctuations of the cold end. In the process of load reduction, the cold end parameters of the system gradually approach the critical point, resulting in increasingly drastic changes in carbon dioxide density at the inlet of the main compressor, which leads to the sensitivity of the main compressor to the inlet temperature and inlet pressure gradually increases. At the low load state, the main compressor inlet temperature is disturbed by 1 ℃, the highest change of main compressor inlet density is 262 kg/m3, the highest change of main compressor outlet pressure is 7 MPa, and the highest change of main compressor efficiency is 6.82%. The main compressor inlet pressure is disturbed by 0.1 MPa, the highest change of main compressor inlet density is 228 kg/m3, the highest change of main compressor outlet pressure is 6.33 MPa, and the highest change of main compressor efficiency is 6.23%. However, the inlet temperature and inlet pressure of the main compressor have a small and almost negligible effect on the outlet temperature.

To explore the flow and heat transfer characteristics of liquid lead-bismuth eutectic (LBE) in the hexagonal rod bundle assembly, an experiment on liquid lead-bismuth heat transfer was carried out at 0.250 kPa of operation pressure, 200-300 ℃ of inlet temperature, 0.47 071.48 W·m-2 of heat flux, 0.4 kg·s-1 of mass flow rate, and 300-600 of Peclet number (Pe). The experimental facilities and operating conditions were introduced in detail, and the uncertainty of this experiment was analyzed to ensure the accuracy of the results. The heat transfer characteristics of liquid lead-bismuth in the rod bundle under different measuring points, heat flux, and inlet temperature were analyzed, and the relevant experimental results were obtained. The simplified Reynolds averaging equation of turbulent flow and heat transfer were also introduced to analyze the characteristics of LBE based on experimental results. The experimental data show that different inlet temperatures have little effect on the flow and heat transfer characteristics of LBE. At high Pe operating condition, the difference of heat transfer of LBE under different wall heat fluxes is also not significant. Based on the experimental measurements of flow and heat transfer characteristics in the rod bundle channel, the flow and heat transfer empirical relations of liquid metal in the world were calculated and evaluated. The results show that the relation of Mikityuk has the best prediction to this experiment which is introduced in this article. This is because that Mikityuk sorts and analyzed the previous heat transfer relations for liquid metals, and obtains a new form to describe the heat transfer relations for liquid metals. Therefore, a new heat transfer relation of LBE was fitted with reference to the basic form of relation of Mikityuk. The applicability and reliability of the new empirical relation were checked out and evaluated by the experimental data of Karlsruhe Institute of Technology (KIT) in Germany under 19 rods bundle operating condition. The calculation results show that the deviation of the new empirical relation for the KIT 19 rod bundle is ±20%, which proves that the new empirical relation has the high applicability and reliability. Finally, based on the similarity principle of fluid mechanics, the reason for the deviation between the empirical relationship fitted in this article and the KIT 19 rod bundle experiment data was also analyzed. The experimental data and the new empirical relation in this article can provide the references and technical supports for the design and research of flow and heat transfer characteristics of LBE in rod bundle channel of hexagonal assembly in the liquid metal cooled reactor in China.

The power system of heat pipe cooled nuclear reactor can be divided into dynamic conversion system and static conversion system. Thermoelectric generator (TEG) is a typical static conversion device, which can directly convert heat energy into electric energy. The combination of heat pipe cooled nuclear reactor and TEGs can bring many advantages, such as compact structure, high inherent safety, no auxiliary mechanical equipment and low noise. However, the maximum core temperature could exceed 1 000 K, and ordinary thermoelectric generators can not operate in such high temperature. To solve this problem, the use of segmented thermoelectric generator (STEG) in the power system of heat pipe cooled nuclear reactor is a method worthy of research. STEG can play an important role in the heat pipe cooled nuclear reactor. But there is not enough literature to study the application of STEG in heat pipe cooled nuclear reactor. STEG usually splices two or three thermoelectric materials with the highest power generation efficiency in different temperature ranges. In this way, STEG can obtain a high thermoelectric conversion efficiency in a wide temperature range (usually above 600 K). Therefore, a kind of STEG for heat pipe cooled nuclear reactor was designed. In this paper, a conceptual design of a heat pipe cooled nuclear reactor with STEGs was proposed. The single STEG and single channel model were explored by COMSOL software. A three-dimensional finite element model of STEG’s performance in heat pipe cooled nuclear reactor was established. STEG was designed to compose of bismuth telluride and skutterudite, and its geometric structure and performances were optimized. Numerical simulation was carried out under steady-state conditions to determine the optimal STEG’s geometry. Then, the optimized STEG was connected with the heat pipe to form a single channel model for simulation to explore its performances. When the temperature difference reaches 550 K, the maximum STEGs’ output power reaches 0.374 W, and the maximum conversion efficiency is 15.75%. In single channel model, when the heating power is 300 W, the maximum STEGs’ output power reaches 47.29 W, and the maximum conversion efficiency is 15.63%. The simulation also show that the maximum stress of single STEG and single channel model are 270 MPa and 547.5 MPa, respectively. And the maximum stress appears on the copper conductor near the hot side. This paper could provide a preliminary basis for the numerical simulation of the combination of STEG and heat pipe cooled nuclear reactor. This paper can also be used as a reference for the thermoelectric conversion of heat pipe cooled nuclear reactors.

Lead-cooled fast reactor (LFR) is known as a typical reliable new type reactor by the US Department of Energy (DOE), and the potential accidents of LFR are necessary to assess. Steam generator tube rupture (SGTR) accident can cause high-pressure hyperbaric steam-water jetting into liquid lead bismuth eutectic (LBE) pool, and leads to a rapid pressure rising in the reactor primary system together with a potential pressure wave crashing the structures. This paper focuses on the computational fluid dynamics (CFD) analyses of SGTR experimental research on the LIFUS5/MOD2 experiment facility. A two-dimensional symmetrical slice with 1 million 570 thousand structured mesh was established for the experimental reaction vessel, and each side except the injection nozzle were set as adiabatic no slip boundary in order to achieve the non-decompression process. In the aspect of multiphase model settings, the Eulerian-Eulerian two-phase flow model was adopted to track the steam-LBE interface in the transient simulation, and the CSF surface tension polynomial together with Lee substituted evaporation model were considered. In addition, the injection of high-pressure water in each time step was separated to two parts: latent heat and injected steam, so as to calculate both endothermic and jet of flash evaporation simultaneously. Among them, the latent heat was realized by user-defined functions (UDF), and the injected steam was adopted as compressible real gas with R-K gas state equation. Based on the above settings, three established thermal-hydraulics phenomena including pressure rising of LBE environment together with pressure wave spreading, level fluctuation of liquid environment with argon entrainment and level rising of liquid environment and diffusion of injected steam were analyzed. From the results a conclusion can be reached that CFD numerical simulation has little error on calculating pressure rising with pressure wave spreading. In addition, the peak value of pressure wave rises with back pressure of water increasing, and the pressure of partial steam cavity is lower than that of LBE pool around it, in turn inhibits the occurrence of its explosion. Meanwhile, LBE in the middle firstly washes up and impacts the structures, and then entrains the argon when it falls back, in turn causes the combination of argon and steam cavity, or the secondary segmentation to small argon bubbles. Moreover, the diffusion of the steam cavity along the radial direction becomes more intense with the increase of the axial height, accompanies by the steam cavity divided from the center to the edge along the radius.

The safety injection (SI) system might be put into use under the loss of coolant accident (LOCA) in nuclear reactor and the thermo-hydraulic phenomena while the subcooled water is mixed with pure steam in high temperature will directly affect the judgement on reflooding of core. For enhancing core competitiveness of nuclear power research and development design, China General Nuclear Power Group (CGN) independently developed and designed a system code of the hydraulic system of two-phase flow analysis named LOCUST, and the current version is LOCUST 1.2. The LOCUST code is written in C language and uses two-fluid model as the conservation equations, treats the gas and liquid phases as separate single phases, and calculates the interphase interactions. This code is generally used for the safety analysis of accident conditions such as LOCA. Nuclear safety regulations require that computer codes used in the safety analysis of nuclear power plants must be fully verified and validated. The use of experimental data is essential for the validation of the safety analysis code for the thermal-hydraulic system. As an important validation for LOCUST, the thermal mixing test of emergency core cooling (ECC) system based on the ECCS-XJTU test facility in Xi’an Jiaotong University was introduced in this paper. Based on this test facility, the ECC thermal mixing tests were conducted, which were mainly focused on the mixing between subcooled water injected from the SI pipe with a range of 25 to 125 kg/h in mass flow and the pure steam in the primary pipe with a range of 100 to 500 kg/h in mass flow. Besides, the modeling, calculations for ECC tests by using LOCUST code and analysis for calculation results and experimental results were performed. The experimental results show that the temperature stratification in the vertical direction is observed in fluid field after mixing, and the main temperature fluctuations concentrated at the lower part in the primary pipe. This is mainly due to the hydraulic jump phenomenon and the effect of gravity. The temperature of the measurement point at the lowest location (point Ⅳ at cross-section with six measurement points, point Ⅱ at cross-section with two measurement points) is much less than the saturated steam temperature, which could be regarded as the fluid temperature and compared with the fluid temperature calculated in LOCUST. The comparison between tests and simulations shows that the maximum relative error of LOCUST in mass flow of liquid is within 13.8%, and that in temperature is within 8%, which validates the reliability and accuracy in simulations of LOCUST for two-phase thermal mixing in LOCA.

Slope runoff of colluviums is the premise for gully runoff erosion, and is the main mode of the sheet-flow erosion in Benggang basin. Studies on characteristics of slope runoff and sediment transportation mechanism in Benggang basin are important for understanding Benggang erosion process and for erosion prevention and control. In this study, an artificial rainfall simulation experiment was carried out in field to investigate the slope runoff process and soil moisture distribution in Benggang basin. Liantanggang Benggang in Wuhua County of Guangdong Province was taken as the study area. In this area, 7 different colluvial deposits were selected including old and new deposits. The 7 deposits had slope of 4°-48°. The old deposits were developed for more than 5 years with dark color and the new deposits were less than 5 years with pale red color. In general, the structure was more stable in the old deposits than the new deposits. These 7 deposits were used for observations of runoff time under the artificial rainfall simulation. A portable rainfall simulator was used with rainfall duration from 0.6 to 60 min and rainfall amount from 2.4 to 60 mm. A total of 28 simulated rainfall experiments were preformed in the field, and the runoff time as well as soil moisture were observed and measured. The results showed that: 1) A negative power function could describe the relationship between the rainfall intensity and slope runoff (P< 0.01), and the runoff time decreased rapidly with the increase of rainfall intensity; 2) A negative logarithmic function could reveal the relationship between runoff time and initial soil water content in depth of 10 cm for the old colluviums; 3) Based on the initial soil water content and rainfall intensity, the 3D surface model may be used to estimate the runoff time of the colluviums; 4) When the rainfall intensity reached 3.5 mm/min or above, the runoff time showed a linearly negative correlation with the slope of the colluviums, and the runoff time became shorter with increasing slopes. 5) After runoff of the colluviums, soil moisture was obviously different between the old and new deposits at the depth of 10 cm, and the soil moisture was over 20% in the old colluviums, and less 20% in the new colluviums; and 6) In the end of precipitation and after 24 h of rainfall, the wetting depth of the new colluviums were higher than that of the old colluviums, indicating that the instable depth of the new colluviums is larger than that of the old colluviums when rainfall occurs. The results provide rich information for understanding slope runoff process and method for erosion forecast in Benggang basin. [ABSTRACT FROM AUTHOR]

Three-dimensional laser scanner (Leica ScanStation 2) was used to measure Liantanggang collapsing hill and erosional gully in Wuhua County of Guangdong Province for 6 times during 2011-2013. About half a year as an interval, and through ArcGIS, high-solution analyses of measurements was conducted to study the spatial and temporal variations of the erosional processes and sediment yield in the watershed of Liantanggang. The average erosional volume was 499 m3 in rainy season, and was 291 m3 in dry season. During the 3 years measurement, the average annual erosional amount was 833 m3 and the erosional modulus was 222 408 t/(km2.a). The heavy rainstorm more than 100 mm within 24h greatly influenced the collapses. Rainfall of rainstorm during each measuring period was positively correlated with the erosional amount. The intense erosional zones located on the colluvial cones at the elevations between 111-131 m, accounting for 55.6% of the total erosional amount, which indicates that the erosional rate in the middle-lower parts of the watershed is the greatest. The slopes of 40°-50° was the largest erosional amount, then the slopes of 50°-60°, and both them accounting for 49% of the total erosional amount of 1 019 m3. The sediment yield per square meter increased with the gradient, which means the erosional processes are more intense in steeper slopes. The average maximum erosional amount per square meter was located on the slopes of 70°-80°. The average erosional depth for each measuring period was 0.105 m. During the period of all the measurements, the severe erosion was found in the main and branch channels including their sides, and at the gully heads. The accumulative erosional depth was greater than 1 m, and the maximum depth was more than 2.5 m. Within the period of five measurements, the erosional modes showed as in the first 3 measuring periods, rapid down-cutting, lateral and retreated erosions were the main modes. In the last 2 measuring periods, there were dominantly gravitational erosions with small-scale landslips. The total erosional amount firstly declined and then increased. The watershed now is in its maturity stage. Morphometric terrain may be the major factor affecting its current evolution. Topographic condition may lead to the transformation between gravitational erosion and hydraulic erosion. The combination of gravitational and hydraulic erosions and their alternations may make the erosional volumes to be fluctuating changes. [ABSTRACT FROM AUTHOR]

For the performance testing of cabin pressure control system (CPCS), a high-altitude simulation cabin (HASC) system based on the virtual instrument is established to simulate the atmospheric pressure which varies with aircraft flight states. On the basis of SCXI virtual instrument platform, a digital proportion-integration-differentation (PID) controller is developed in Labview to accomplish the HASC pressure control. The performance test of digital-pneumatic cabin pressure controlling system is carried out with the HASC system. The results show that the HASC system can accurately simulate the atmospheric pressure of flight states which is very important in CPCS performance tesing. [ABSTRACT FROM AUTHOR]

The boiling heat transfer characteristics of a multi-port extruded tube are experimentally investigated. To test the boiling heat transfer characteristics of the tube in equivalent diameter 0. 63 mm, a boiling heat transfer test system with refrigerant R134a is built as the working medium. Tests are performed with a mass flux of 116. 5-466. 0 kg ⋅ m-2 ⋅ s-1 and a heat flux of 13-52. 7 kW/m². The experimental results are compared with the calculation results of the formulas that suit for boiling heat transfer in small size channel. It shows that the experimental data of boiling heat transfer coefficient fit well with the calculations of Bertsch correlation, and only in the big mass flux, the data are close to the calculations of the Cooper correlation and Liu and Winterton correlation. [ABSTRACT FROM AUTHOR]