[en] The operating head of the fast reactor fuel assembly plays an important role in balancing pressure, moderating pressure drop and reducing vibration, which has a significant impact on the safety of fast reactor. Furthermore, it has the function of fixing and snatching during the process of replacing and hoisting fuel assembly. At present, there is no uniform design standard of the operating head. In this study, the computational fluid dynamics (CFD) was used to investigate the flow characteristics of the closed and open operating head. The results show that the outlet hole at the top of the operating head can effectively balance the pressure inside the operating head, moderate the pressure drop and reduce the vibration to avoid harmful impact on the structure. In addition, with the increase of outlet-hole diameter, the flow performance has been significantly improved inside the open operating head, which enhances the heat transfer and avoids the potential safety risks caused by heat accumulation. Moreover, it is suggested that the structure design of fast reactor fuel assembly can be optimized using the open operating head with outlet-hole diameter in 30 mm. In the engineering, the outlet hole provides a flow channel for discharging residual gas before the injection of sodium coolant for the first time. (author)

[en] Due to its ability to achieve large pressure drop in a small space, labyrinth throttle is well used in the primary cooling system of a sodium-cooled fast reactor to adjust pressure drop. For selection of labyrinth throttle in design, it is necessary to evaluate the pressure drop. Usually the pressure drop is determined by experiment, but it is a time-consuming work. Flow information also cannot be obtained during experiment due to the restriction of measure conditions. As a result, recently numerical simulation becomes a common method for calculation of the pressure drop. Although numerical method is very convenient, its accuracy is affected by many factors, especially the choice of turbulence models. Numerical results have rarely been validated by experiments. On the other hand, pressure drop of labyrinth throttle is determined by various factors, including distance between adjacent plates, height of each plate, number of plates and mass flow rate. Relationship between pressure drop and these factors is still unknown. Based on above recognition, a numerical modeling was studied for simulating the pressure drop, where standard k-ε was selected as the most reliable model via comparison between numerical results and experimental ones. Using the validated numerical modeling, hydraulic characteristics of the labyrinth throttle varying with various factors were analyzed. Empirical formulas for pressure drop changing with these factors were fitted by multiple regression method consequently. (authors)

[en] The entry tube locates at the coolant inlet of the fast reactor fuel assembly, which directly determines the flow rate of the sodium coolant entering the interior of the fuel assembly to cool the fuel-rod bundles. It has important influence on the pressure drop and flow-velocity distribution of the fuel assembly. At present, the research on fast reactor fuel assembly is mostly focused on the thermal-hydraulic characteristics of the fuel-rod bundles, while there is lack of the research about the entry tube, especially there is no uniform design standard. Therefore, it is necessary to further study the flow characteristics about the entry tube of fast reactor fuel assembly to provide a reference for structure design. In this study, the distribution of resistance coefficient and the relationship between flow rate and pressure drop of entry tube with different diameter are studied by hydraulic experiment. The results show that the diameter of the entry-tube hole has the significant impact on the flow characteristics of sodium coolant, so the inlet flow rate of the fuel assembly in different core-region can be adjusted by changing the diameter of the entry-tube hole to achieve the balance of pressure drop of fuel assembly. In addition, a dimensionless contraction coefficient of the entry tube is introduced and the empirical correlations of the resistance coefficient are formulated which are used to estimate the pressure drop of the in fast reactor fuel assembly. Finally, based on the design requirements of pressure drop and flow-velocity limitation, a recommended program is presented of diameter selection about the entry-tube hole, which can be used as a reference for relevant experiments or engineering. (authors)

[en] The control assembly is an important safety component of sodium-cooled fast reactor. The entry-tube geometrical structure has a significant effect on flow characteristics. The flow characteristics of plate-throttle entry-tube were investigated by hydraulic experiment, and the fluid-structure coupling numerical simulation was verified by experiment data. The results show that reducing the thickness of throttle plate and increasing the diameter of connecting rod can effectively improve the entry-tube throttling capacity. Considering the limitation of flow velocity, the dimensionless thickness-diameter ratio of 0.5 and connecting rod diameter of 20 mm are regarded as the optimum structure parameters of entry-tube. Due to the shortage of plate-throttle entry-tube in experiment, an alternative project of square-groove entry-tube was proposed. It is verified that this project is feasible with the similar flow velocity and pressure distribution in two types of entry-tubes. (authors)

[en] The computational fluid dynamics (CFD) was used to simulate the labyrinth-seal structure of right angle trapezoid with different spacing in this paper. Then, the comparative research was conducted including the effects of spacing on sealing performance, flow field distribution, pressure field distribution and control of flow velocity, and the effect of eccentricity on sealing performance was analyzed at the optimal spacing. The results show that increasing the spacing of the labyrinth-seal structure can effectively reduce the leakage flow, improve the sealing performance, achieve better control of flow velocity and can also significantly improve the flow performance near the wall surface and enhance the cooling of the outer wall surface of fuel assembly. As the spacing exceeds 3.02 mm, the improvement of sealing performance is very limited, indicating it is impossible to continue to improve the sealing performance of the labyrinth-seal structure by increasing the spacing when the spacing exceeds a certain limit. It is necessary to select the reasonable spacing in structural design and engineering application. The eccentricity leads to the imbalance of flow velocity and pressure distribution in the flow region, and as the eccentricity increases, the unevenness tends to expand, which not only adversely affects the sealing performance, but also exacerbates the vibration of the fuel assembly. (authors)

[en] Highlights: • For the entry tube of fast reactor fuel assembly, there is lack of available resistance-coefficient experiment data, empirical correlation and criterion equation. This study tries to fill this gap. • A new plate-throttle entry tube for fast reactor fuel assembly is designed. • The flow characteristics of fuel assembly are experimentally investigated. • The resistance coefficient empirical correlations are obtained. • The empirical criterion equation are obtained by regression analysis. - Abstract: The entry tube of fast reactor fuel assembly plays an important role in controlling flow rate, adjusting pressure drop and limiting flow velocity, which has a significant effect on safety and economy of fast reactor. Due to some shortcomings of traditional straight-through entry tube, an optimized plate-throttle entry tube is designed and manufactured in the current investigation. Reynolds number from 8.99 × 10⁴ to 1.65 × 10⁶ is considered and experiment data are generated from hydraulic experiment conducted at constant water temperature (84 °C). The experiment results indicate that the flow characteristics of plate-throttle entry tube is excellent, i.e. it can significantly increase pressure drop with the large-diameter entry-tube holes to avoid excessive vibration. It is verified that the pressure drop of plate-throttle entry tube is more sensitive to the width of plate throttle rather than the diameter of entry-tube holes. In the experiments or practical engineering applications, the pressure drop should be adjusted by changing the width of plate throttle as much as possible to reduce cost. A dimensionless number called the throttling-area ratio is introduced to represent the geometrical parameters effect on flow characteristics of plate-throttle entry tube. The resistance-coefficient empirical correlations and an empirical criterion equation are obtained by regression analysis of experiment data, which can be used for structure design of sodium-cooled fast reactor and preliminary estimation of entry-tube flow characteristics.

[en] The multi-hole entry tube widely used in engineering has some shortcomings in adjustment of flow characteristics and processing accuracy. In this paper, an alternative method of few-hole entry tube was proposed. By hydraulic experiment, the flow characteristics of multi-hole and few-hole entry tubes, such as the distribution of resistance coefficient, the corresponding relationship between flow rate and pressure drop, were compared and studied. The results show that the flow characteristic of the few-hole entry tube with 12.0 mm in diameter is almost the same as that of the multi-hole entry tube with 6.2 mm in diameter, which all can meet the design requirements. It is verified that the alternative method of few-hole entry tube proposed in this paper is feasible. In addition, the flow characteristics can be more effectively adjusted by the few-hole entry tube. Moreover, the empirical correlation between the resistance coefficient of the entry tube and its structure parameters is formulated, which can be used in relevant experiment or engineering. (authors)

[en] The pursuit of multifunctional, stable, more efficient, and safer cancer treatment has gained increasing interest in the research of nanoparticle-mediated photothermal therapy. Many nanoparticles have good absorption chracteristics in the near-infrared region, because of the high light-to-heat conversion efficiency; they could destroy tumor cells by heat; thus, they are often treated as a potential photothermal therapy agent. In this work, a kind of polypyrrole (PPy)-coated gold nanoparticles particles (PPy-GNPs) with high photothermal conversion capability was prepared. Their particle sizes were about 90 ± 11.2 nm. The temperature of PPy-GNPs solution in a concentration of 0.25 mg/ml rises 13.6 °C, and the nanoparticles could significantly inhibit the proliferation of SKOV-3 cells under irradiation of 25 W·cm⁻² laser (808 nm) for 10 min, with the maximum cell viability value is maintained at 87.6% by MTT assay. In the same photothermal and cultured conditions, the photothermal conversion efficiency and cytostatic effect of the gold nanoparticle are much lower than that of the PPy-GNPs group. The atomic force microscopy (AFM) was used to identify the function of nanoparticles for the structural changes of the cells. The SKOV-3 cell of adhesion forces decrease by 21%, and Young’s modulus increases by 26% compared with control. These results suggest that PPy-GNPs are effective targeted photothermal therapeutic agents for cancer treatment.