[en] The retained dose and compositional depth profile were studied in the context of cylindrical target with different plasma density treated by plasma-based ion implantation (PBII). Nitrogen was implanted into silicon wafer clamped on the samples in order to acquire high quality profiles. Auger electron spectroscopy (AES) was used to acquire the nitrogen depth profile at the middle of Si wafer. A method, that combined fluid dynamic model to simulate plasma sheath expansion during high voltage pulse and TRIM code to simulate incident ion distribution in the solid was presented to simulate the experimental results. Both retained dose and N depth profile were compared with the results of theoretical simulation. The agreement between them for all three cases is good; that is, the model can give a good prediction and explanation to the experimental results. The retained dose for cylinder increases with increasing plasma density. The continuously distributed energy of incident ions and low N⁺/N₂ ratio in the plasma shift the N depth profile nearer to the surface and reduce the range significantly

[en] In this paper, the effect of the pulse waveform on plasma sheath evolution around a diamond-shaped target has been simulated using fluid dynamic model in the context of plasma-based ion implantation (PBII). The implanted parameters of ions such as ion-implanted energy, impact angle and impact current have also been studied under different pulse shapes. Understandably, the longer pulse rise time would result in the lower ion impact energy, and less sheath expanding extent. By comparing the sheath structure under different pulse rise time, we found that long pulse rise time would enhance the conformation of the sheath to the target at the earlier stage of the pulse and would reduce the tendency of the ion depletion in the plasma sheath. Accordingly increase the ion impact current at the later stage of the pulse, which is quite important for the PBII process, when the ions have been accelerated adequately

[en] After turning and milling the 1LD14 work piece, burrs of different lengths generate at the milling part of the parts. The burrs have a bad impact on the machining accuracy, assembly accuracy, use requirements, operation safety and appearance quality of the parts. At present, it mainly uses manual polishing to deal with the burrs. But this has caused a lot of problems, such as large labor volume, low efficiency and poor security. In this paper, to solve this problem, we searching for automatic grinding method to instead of manual grinding, it can reduce people participation, cost and improve efficiency. What is more automatic grinding method can remove ob stance for automated production lines, and lay the foundation for the smooth implementation of the follow-up scientific research projects. (author)

[en] A predictive model of the initial point of net vapor generation, incipient point of net vapor generation (IPNVG) for low-flow subcooled boiling is developed in this paper. The IPNVG established in this model meets both the thermodynamic and hydrodynamic conditions. The thermodynamic condition is described by the heat balance at IPNVG. The amount of heat for steam generation is equal to that for bubble condensation at IPNVG. The force balance of the detached bubbles at IPNVG or the hydrodynamic condition is established to provide the diameter of the detached bubbles and the interfacial heat transfer coefficient for the calculation of heat transfer at IPNVG. This mechanism of the present model makes it applicable to low-flow subcooled boiling. Several coefficients involved in the proposed model are identified by Freon-12 experimental data. This model is compared with the experimental data obtained from different works. The data cover two working media of steam-water and Freon-12, two flow conditions of natural and forced circulations and relatively wide ranges of pressure, mass flux and heat flux. The predictions of this model agree with the data quite well

[en] Highlights: • The low-power-laser was used to obtain the excellent coatings with different amount of Y_2O_3 addition. • The addition of rare earth oxide Y_2O_3 refined and purified the microstructure of the coatings, meanwhile, increased the thickness of the coatings and reduced the dilution of cladding materials from based alloy. • The primary phases in the coatings are Mg_3_2Al_4_7Cu_7, MgCu_6Al_5, Al_2CuMg and Al_1_2Mg_1_7. The A_l_4MgY and MgAl_2O_4 phase can be found in Y_2O_3-modified coatings. • The micro-hardness and the abrasion resistance of the coatings with Y_2O_3 had been improved obviously compared with the coatings without Y_2O_3. • The corrosion resistance of the AZ91D magnesium alloy had been improved by laser cladding. And the effect of Y_2O_3 on the corrosion potential of the coatings was less than the effect of Y_2O_3 on corrosion current density of the coatings. - Abstract: Due to the low-melting-point and high evaporation rate of magnesium at elevated temperature, high power laser clad coating on magnesium always causes subsidence and deterioration in the surface. Low power laser can reduce the evaporation effect while brings problems such as decreased thickness, incomplete fusion and unsatisfied performance. Therefore, low power laser with selected parameters was used in our research work to obtain Al–Cu coatings with Y_2O_3 addition on AZ91D magnesium alloy. The addition of Y_2O_3 obviously increases thickness of the coating and improves the melting efficiency. Furthermore, the effect of Y_2O_3 addition on the microstructure of laser clad Al–Cu coatings was investigated by scanning electron microscopy. The energy-dispersive spectrometer (EDS) and X-ray diffractometer (XRD) were used to examine the elemental and phase compositions of the coatings. The properties were investigated by micro-hardness test, dry wear test and electrochemical corrosion. It was found that the addition of Y_2O_3 refined the microstructure. The micro-hardness, abrasion resistance and corrosion resistance of the coatings was greatly improved compared with the magnesium matrix, especially for the Al–Cu coating with Y_2O_3 addition.

[en] A prismoid-shaped target was treated by plasma based ion implantation (PBII) with nitrogen plasma, in order to study the lateral homogeneity in the near region of square corner after treatment. Auger electron spectroscopy was used to execute sputter depth profiling to obtain nitrogen depth distribution and retained dose on the silicon wafer. It showed that, in addition to process parameters of PBII such as pulse voltage, pulse width and radio frequency power, treatment homogeneity is strongly dependent on the shape and dimensions of the workpiece being treated. The ion retained dose and its gradient of distribution are a strong function of the factors mentioned above. Due to enhanced sputtering effect induced by the oblique ion impact, lower retained dose and shallower implantation depth were observed in the vicinity of the edge contained by square corner. The gradient of retained dose distribution exhibits a higher value with higher pulse voltage, lower plasma density, longer pulse width and smaller target size. Aided by the results of numerical simulation, sheath expanding tendency and ion impact mode under various conditions were discussed. Through conformal condition analysis of plasma sheath and the resulting characteristic of ion impingement, a better understanding of the treatment homogeneity can be achieved

[en] Highlights: • Heat flows after mixing TBP with nitric acid are of different orders of magnitude. • Thermodynamics and kinetics of tributyl phosphate-nitric acid mixtures are derived. • Tributyl phosphate directly reacts with nitric acid and form organic red oil. • Thermal runaway could occur at 79 °C with a high nitric acid concentration. - Abstract: During PUREX spent nuclear fuel reprocessing, mixture of tributyl phosphate (TBP) and hydrocarbon solvent are employed as organic solvent to extract uranium in consideration of radiation contaminated safety and resource recycling, meanwhile nitric acid is utilized to dissolve the spent fuel into small pieces. However, once TBP contacts with nitric acid or nitrates above 130 °C, a heavy “red oil” layer would occur accompanied by thermal runaway reactions, even caused several nuclear safety accident. Considering nitric acid volatility and weak exothermic detection, C80 micro calorimeter technique was used in this study to investigate thermal decomposition of TBP mixed with nitric acid. Results show that the concentration of nitric acid greatly influences thermal hazard of the system by direct reactions. Even with a low heating rate, if the concentration of nitric acid increases due to evaporation of water or improper operations, thermal runaway in the closed system could start at a low temperature.

[en] In the experimental research of reactor thermohydraulic behavior on test facility, an electric heater is always used instead of a nuclear reactor. There are many inherent reactivity feedback in a real reactor, such as temperature coefficient feedback and void coefficient feedback, so when an electric heater is used as a nuclear fuel in a test facility, it is required to simulate the reactivity feedback. An analysis of effect of reactivity feedback is made and a method of simulating reactivity feedback is proposed

[en] Void fraction distribution characteristics in rod bundle with grid spacer is one of the important aspects in reactor thermal hydraulic characteristics research. A test using a specially designed 3*3 rod bundle test section with AFA-2G structure spacer has been performed under air water two-phase flow. The RBI optical probes were used to measure void fractions and the distribution regularity also has been analyzed. The results show that the grid spacer, especially the mixing vane, has a significant influence on the flow and phase distribution. The results should be the basis for further researching on vapor-water two-phase flow and heat transfer and development of the fuel subassembly with high thermal hydraulic performance

[en] Since the distribution of void fraction is important in the technology of two phase flow, some experiments have been developed. But these experiments can only be taken under limited conditions, so the descriptions of foundational phenomena are also only limited in some special experimental conditions. Here the authors analyzed some results of these experiments and described the radial distribution of void fraction in vertically upward two phase flow. According to the analysis, got the typical relationship between the void fraction curve and flow pattern in the vertical upward flow, and after the comparison with the former results, proved that the relationship is reasonable both from the angle of the results of experiments and mechanistic analysis