[en] Since the end of last century, the size of integrated devices has become smaller and smaller and semiconductor industry had been experiencing great challenge on Moore law. New materials and technology in semiconductor industry had become significant in the development in network communication and auto control. Finding new materials with excellent electronic natures other than silicon had been a hot spot of the research. With the discovery of Graphene, two-dimensional material system becomes important in the research. Study the optical and electronic properties of two-dimensional materials, especially the carrier mobility, which can help to design proper two-dimensional materials. This paper introduces how the theoretical computation of the mobility for two-dimensional materials was developed. Specifically, the Bloch theorem, density functional theory, the first-principle calculation and deformation potentials theorem. (paper)

[en] The advanced fuel design, such as accident tolerant fuel (ATF) was design concept to withstand the high temperatures for extreme condition. When it was equipped in reactor core, the heat removal by radiation would be quite considerable. The radiation heat removal in a simplified SMR core was studied in the present study. The calculation was assumed to be 2D and at steady state. The calculation models were established from fuel assembly to fuel rod. The radiation heat flux was calculated based on the heat balance model when the limitation temperature in the core was reached. The results showed that the radiation heat flux contribute large proportion when the limitation temperature on fuel clad was high. The radiation heat flux was increased with fuel clad temperature limitation value. The higher the emissivity was, the more radiation heat flux removed. (author)

[en] In this paper, we use the rod-power distribution obtained by the nuclear design and the 202 tables and 205 cards of RELAP5/MOD3 to realize the change of the relative power share of each axial node in the heat of the RELAP5/MOD3. The 'variable power distribution' analysis method is successfully realized in RELAP5/MOD3, and the method is used to analyze the rod withdrawal accident of a reactor. The maximum fuel temperature obtained by this method is significantly lower than the fixed power distribution method. (authors)

[en] The digital reactor is an integral numerical simulation platform for the performance of nuclear reactor systems. In the first part of this paper, the development history of the nuclear reactor simulation technology is reviewed. The three technical elements constituting the digital reactor are elaborated, including the target scenario, advanced models and multi-physics coupling technology, and the integrating environment. Although there are several challenges for the development of digital reactors, such as the difficulties in multi-physics and multi-scale computation, the complexity in design optimization, and the insufficient database, the digital reactor can help better analyze key problems that limiting the reactor performances and safety, and better understand the mechanism of the phenomena that cannot be observed or measured experimentally. (authors)

[en] It is necessary to use the computed fluid dynamic (CFD) method to study the problems considering the U-tube distribution, such as the reverse flow in the steam generator. But it is difficult to model all the U-tubes in a steam generator because of the huge number of the U-tubes and the limited capability of computers. This paper discussed a simplified modeling approach for single-phase fluid flow in U-tubes, using a square tube instead of a round tube. The result of a reverse flow calculation for a steam generator using the simplified modeling approach is basically the same as the result using a non-simplified model, which indicates that the approach can be used in CFD analysis of this kind of problems. (authors)

[en] A 5 × 5 rod bundles with 7 spacer girds which structure mixing gird (MG) and mid span mixing gird (MSMG) are arranged alternant are studied by two phase computational fluid mechanic (CFD), and bubbles coalescence and breakup, and heat transfer are considered in the calculation, but not the interface mass change. In order to choose the reasonable two phase model parameters, 5 × 5 rod bundles with 2 spacer girds (MG and MSMG) based on AFA3G fuel assembly isstudied by two phase CFD, and the sensitivity and uncertainty analysis is conducted on max bubble size, bubbles coalescence and breakup model parameters, non-drag force model, drag force model parameters, inlet bubble diameter and inlet void fraction distribution. Use this model setting, the study of the two phase performance is conducted on AFA3G fuel assembly with 7 spacer grids. The calculation shows that the bubble through the spacer grid is without periodicity, but the void fraction fields of every MSMG upstream are similar and the MG upstream shows the same situation. This research is useful to choose the model setting and geometry size for the rod bundle with spacer girds in the two phase calculation, for geometry size it is possible to analyze the two phase performance on rod bundle with 2 or 3 spacer grids. Finally, the void fraction distribution of AFA3G fuel assembly and advanced fuel assembly are compared, and evaluated in terms of the improvement of the CHF. It agrees well with the experiment, which verifies the evaluation method, the research is the base for the establishment of the evaluation guideline for the thermal hydraulic performance of the fuel assembly by two phase CFD calculation. (authors)

[en] In order to study the accuracy of the prediction of flow field distribution in bundle channels using Computational Fluid Dynamics (CFD) methods, STAR-CCM+ code is utilized to analyze the single-phase 4 × 4 bundle flow experiments conducted by Korea Atomic Energy Research Institute. Based on generating meshing scheme determined by meshing sensitivity study, standard k-ε (SKE), realized k-ε (RKE), standard k-ω (SKW) and SST turbulence model are adopted to simulate the bundle flow, and comparisons are conducted for the simulation results and experimental data for lateral and axial velocity. The results show that, four turbulence models can well predict velocity field distribution inside the bundle channels, the relative deviation for SKE and RKE is 19.6% to predict the lateral velocity, and SKE is better for simulating the lateral velocity analysis at zone near grids, otherwise RKE is better. For axial velocity prediction, SKE simulation is with the minimum relative deviation of 4.9%. All four models underestimate RMS velocities, but can predict RMS velocity distribution law inside the bundle channels, and RKE is suitable for near-grid zone, otherwise SST is suitable. The results provide references to the set-up of best practice guide for CFD analysis of single-phase bundle flow. (authors)

[en] Three primary design principles, meanwhile the design features, are carried through the R and D process of Chinese Small Module Reactor (ACP100): integral layout, compact design and modularized configuration. As a substantial demonstration of the above design conceptions, an upper plenum built-in pressurizer is proposed for the pressure control system design for Chinese SMR. In this design, branches with large diameters connected to the primary loop (i.e. surge line, etc.) are eliminated, and this will significantly reduce the LOCA possibility due to the pressure boundary breach. This study mainly focuses on the feature of responses of the built-in pressure control system during the system transients, such as step load increase/decrease, ramp load increase/decrease and partial loss of electrical load. Initial status of the plant, assumptions, postulated transient condition and methodology of this analysis are described in the first section. Important thermal hydraulic parameters that can picture the transient characteristics of the coolant system are given in the second section. It shows that, during those transients, no reactor safety related signals or safety guard features are triggered or actived. It also shows that Nuclear/thermal power response rapidly and stably, and average coolant temperature and system pressure are welled controlled within the range of normal deviation of the set point values of safety related system. This study results get a good agreement with the operating experiment study of the build-in pressure control system. (author)

[en] Spacer grids with mixing vanes are generally used in fuel assemblies of Pressurized Water Reactor (PWR), because that mixing vanes could enhance the lateral turbulent mixing in subchannels. Thus, heat exchangements are more efficient, and the value of departure from nucleate boiling (DNB) is greatly increased. Actually turbulent mixing is composed of two kinds of flows: swirling flow inside the subchannel and cross flow between subchannels. Swirling flow could induce mixing between hot water near the rod and cold water in the center of the subchannel, and may accelerate deviation of the bubbles from the rod surface. Besides, crossing flow help to mixing water between hot subchannels and cold subchannels, which impact relatively large flow area. As a result, how to accurately capture and how to predict the complicated mixing phenomenon are of great concernments. Recently many experimental studies has been conducted to provide detailed turbulent mixing in rod bundle, among which Laser Doppler Velocimetry method is widely used. With great development of Computational Fluid Dynamics, CFD has been validated as an analysis method for nuclear engineering, especially for single phase calculation. This paper presents the CFD simulation and validation of the turbulent mixing induced by spacer grid with mixing vanes in rod bundles. Experiment data used for validation came from 5 x 5 rod bundle test with LDV technology, which is organized by Science and Technology on Reactor System Design Technology Laboratory. A 5 x 5 rod bundle with two spacer grids were used. Each rod has dimension of 9.5 mm in outer diameter and distance between rods is 12.6 mm. Two axial bulk velocities were conducted at 3.0 m/s for high Reynolds number and 1.0 m/s for low Reynolds number. Working pressure was 1.0 bar, and temperature was about 25degC. Two different distances from the downstream of the mixing spacer grid and one from upstream were acquired. Mean axial velocities and turbulent intensities (W_rms) were measured in the test as well as the pressure drop of spacer grids. Sensitivity study showed that geometry of spring structure made a great importance for pressure drop calculation while has little impact on downstream mixing flow. Thus mixing flow comparison were based on simplified springs, and pressure drop comparison were based on real springs. This simulation employed the ANSYS code CFX 14.5. RANS models such as K-epsilon, RNG K-epsilon, Shear-Stress Transport (SST) K-omega and BSL Reynolds-stress turbulence model were chosen for validation. Validation results showed that RANS models were nearly adequate for prediction of mean velocities, while K-epsilon and RNG K-epsilon are more accurate under low Re condition, and Shear-Stress Transport (SST) K-omega and BSL RSM have better performance under high Re condition; as to turbulent intensities, all RANS models underestimate them; as to the pressure drop comparison results, RANS models have more prediction under high Re condition, especially for RNG K-epsilon, but they have large deviation under low Re condition. (author)

[en] Objective: To evaluate the clinical application of preoperative multi-slice computed tomography (MSCT) and multi-slice computed tomography portography (MSCTP) in performing transjugular intrahepatic portosystemic stent shunt (TIPSS) combined with gastric coronary vein embolization (GCVE). Methods: A total of 126 patients with cirrhosis complicated by upper gastrointestinal bleeding or massive ascites due to portal hypertension were enrolled in this study. The patients were arranged to receive TIPSS together with GCVE. Before the treatment, MSCT and MSCTP were performed in all patients. By using post-processing techniques, including maximum intensity projection (MIP), multiplanar reformation (MPR), volume rendering (VR) and surface shade display (SSD), the anatomy of liver was comprehensively evaluated. Results: Both MSCT and MSCTP could clearly display morphologic changes of liver, the spatial relationship of the portal and hepatic veins, the degree and extent of portal collateral circulation, and the severity of ascites, which provided important anatomical information for preoperative evaluation of TIPSS and GCVE. Conclusion: MSCT and MSCTP are non-invasive and reliable examinations for the diagnosis of cirrhosis with portal hypertension, it can further clarify the diagnosis and guide the performance of TIPSS and GCVE. (authors)