[en] The adsorption of CH₂O at low-coordinated sites (edge and corner) of MgO (0 0 1) surface has been studied using cluster models in the framework of density functional theory. Two adsorption states of CH₂O, i.e. heterolytically dissociative adsorption and molecular adsorption were found. In the former case, the CH₂O adsorbed over Mg_3C-O_3C pair site was dissociated into two separate subspecies, 'CHO^-' and 'H⁺' through the C-H bond cleavage with rather low activation energy, 4.58 kcal/mol. Due to the quite similarity in adsorption energy, it can be expected that both two adsorption states, namely molecular and dissociative adsorption, should simultaneously exist for CH₂O over Mg_3C-O_3C pair site of MgO (0 0 1) surface. In analogy, for CH₄, C₂H₂ and CH₃OH, the edge and corner sites of MgO (0 0 1) surface exhibit the catalytic reactivity toward the C-H bond cleavage, thus leading to the dissociative subspecies, which was reinforced by the quantum chemical calculations and the respective experiments

No abstract available

[en] Decay heat removal system is one of principal engineered safety features of pool-type sodium-cooled fast reactor, it is a main way to carry out the safety function of decay heat remove under some accident conditions for the reactor, such as reactor scram condition, and one of the key equipment of decay heat removal system for fast reactor s sodium-to-sodium decay heat exchanger(DHX). We use the ANSYS FLUENT software to run transient numerical emulations of the DHX in CEFR and the new modified DHX which s setup in hot pool of fast reactor. Through comparing the emulation results the feasibility of the modified DHX design is demonstrated in terms of thermal hydraulics performance. The numerical analysis results are important reference to the design of DHX for large-type size fast reactor. (authors)

[en] The temperature fluctuation in core outlet region of China Experimental Fast Reactor (CEFR) was numerically simulated by the CFD software Star CCM+. With the core outlet temperatures, flows etc. under rated conditions given as boundary conditions, a 1/4 region model of the reactor core outlet region was established and calculated using LES method for this problem. The analysis results show that while CEFR operates under rated conditions, the temperature fluctuation in lower part of core outlet region is mainly concentrated in area over the edge components (steel components, control rod assembly), and one in upper part is remarkable in area above all the components. The largest fluctuation amplitude is 19 K and the remarkable frequency is below 5 Hz, and it belongs to typically low frequency fluctuation. The conclusion is useful for further experimental work. (authors)

No abstract available

[en] The CFD software STAR-CD is used to simulate the normal operating conditions of cold and hot plenums in China Experimental Fast Reactor (CEFR). Complex 3-dimension model is established by using porous medium method. The temperature and velocity distributions of cold and hot plenums are given. These results are compared with the data of the thermal designs of CEFR which have been completed. Meanwhile, the influence of the buoyancy forces is analyzed. The results of the calculation are valuable for the CEFR design and accident analysis. (author)

[en] The thermal stratification can be formed in the upper plenum during the reactor scram transient of CEFR which is the first LMFRR in our country. This will bring a bad effect on the natural circulation of the coolant sodium in the primary circuit because it delay the buildup of the ciucualtion for the cold coolant in the outlet of the reactor core. On the other hand, the thermal stratification in the hot pool can also bring the therrmal stress to the reactor vessel and compents. Based on the detail investigation to this phenonena, the numerical analysis have been performed by using commercial CFD code STAR-CD. From the result, it can be seen that the thermal scarification can be formed after the accident of station blackout. The interface of the clear stratification is located in the level of the upper window of the IHX, but it will never stop the buildup of the natural circulation of the primary circuit. (authors)

[en] As one of the significant equipment of China Experimental Fast Reactor (CEFR) operation system, the cold trap plays an important role on purifying the coolant sodium and ensuring safety and steady operation of reactor. Currently, the existing cold trap of CEFR has some problems which include the aggradation efficiency of impurity is low, the wire mesh is blocked easily, and the cold trap is replaced frequently and so on, and these problems have a bad influence on the long-term operation of CEFR. The reasons for these problems in the current cold trap including: One is the unreasonable flow route of sodium, which can cause the partial blocking in specific area, and the other is about the density and disposal of wire mesh, which can make the aggradation of impurity easy in exterior area leading to block the flow channel. According to the reasons, a modified project was proposed to improve the aggradation pattern of impurity in terms of structure design and hydraulics, and consequently extend the operation lifetime of cold trap. The modified project as follows: About 1/3 rates of orifices on interior canister were occluded in wire mesh area, and two rows of orifices were drilled on upside support shell, thus improving the velocity distribution. Synchronously, the wire mesh was separated to three areas which were top area, middle area and bottom area respectively, and the different densities of wire mesh were used to different areas to fulfill the requirement that the aggradation pattern of impurity was from bottom to top. Through 3D modeling and numerical analysis to the project, and comparing the results to current cold trap of CEFR, it can be concluded that the modified velocity distribution is more reasonable than before, and the new disposal of the wire mesh can also meet the aggradation requirement of impurity. Further correlative study will be done according to the actual operation condition of CEFR. (authors)

[en] Dry etching of 6H silicon carbide (6H-SiC) wafers in a C₄F₈/Ar dual-frequency capacitively coupled plasma (DF-CCP) was investigated. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used to measure the SiC surface structure and compositions, respectively. Optical emission spectroscopy (OES) was used to measure the relative concentration of F radicals in the plasma. It was found that the roughness of the etched SiC surface and the etching rate are directly related to the power of low-frequency (LF) source. At lower LF power, a smaller surface roughness and a lower etching rate are obtained due to weak bombardment of low energy ions on the SiC wafers. At higher LF power the etching rate can be efficiently increased, but the surface roughness increases too. Compared with other plasma dry etching methods, the DF-CCP can effectively inhibit C_xF_y films' deposition, and reduce surface residues

[en] The hydraulic design, test and verification of CEFR primary coolant system were performed based on the requirements of design criteria. The results of calculations and test for core flow rate distribution in CEFR are presented in this paper. A series of pressure drop tests for subassemblies, primary pumps and reactor components were implemented in different test rigs. Based on these tests data and empirical formulas, a steady-state thermal hydraulic analysis code CEFR-DAEMON was developed to calculate primary pumps, core and bypass channels flow rate in several steady states. In CEFR commissioning stage, the test for a mock-up core was performed with a permanent-magnet sodium flow meter of range 5 kg/s. The numerical results of code CEFR-DAEMON showed good agreement with the test data. The test results also proved that pressure drop in the grid plate was very small. A revised edition of this code has been developed to calculate core flow rate reduction or reallocation in other transient states. (author)