Study on the thermo-hydraulic behaviors of the new-pattern fuel assembly in lead-based fast reactors based on OpenFOAM

To improve the heat transfer efficiency of the coolant in lead-based fast reactors,this study optimized the configuration and rotational direction of the spacer wires in fuel assemblies to design a new-pattern fuel assembly.This study conducted detailed comparisons between traditional and new pattern fuel assembly rod bundles utilizing the open-source computational fluid dynamics platform,OpenFOAM.The results indicated that the new design may significantly reduce the pressure drop along the rod bundle,which is beneficial for lowering the pressure drop.Furthermore,this new design improved coolant mixing in the subchannels,which facilitated a more uniform temperature distribution and lower thermal gradients at the assembly outlet.These factors collectively reduced the thermal fatigue and creep in nearby internal components.Overall,the newpattern fuel assembly proposed in this study may have better heat transfer performance,thereby enhancing the Integrated Thermal-Hydraulic Factor by 48.2% compared to the traditional pattern.

CFD analysis of a CiADS fuel assembly during the steam generator tube rupture accident based on the LBEsteamEulerFoam

Steam generator tube rupture(SGTR) accident is an important scenario needed to be considered in the safety analysis of lead-based fast reactors. When the steam generator tube breaks close to the main pump, water vapor will enter the reactor core, resulting in a two-phase flow of heavy liquid metal and water vapor in fuel assemblies. The thermal-hydraulic problems caused by the SGTR accident may seriously threaten reactor core's safety performance. In this paper, the open-source CFD calculation software OpenFOAM was used to encapsulate the improved Euler method into the self-developed solver LBEsteamEulerFoam. By changing different heating boundary conditions and inlet coolant types, the two-phase flow in the fuel assembly with different inlet gas content was simulated under various accident conditions. The calculation results show that the water vapor may accumulate in edge and corner channels. With the increase in inlet water vapor content, outlet coolant velocity increases gradually. When the inlet water vapor content is more than 15%, the outlet coolant temperature rises sharply with strong temperature fluctuation. When the inlet water vapor content is in the range of 5–20%, the upper part of the fuel assembly will gradually accumulate to form large bubbles. Compared with the VOF method, Euler method has higher computational efficiency. However, Euler method may cause an underestimation of the void fraction, so it still needs to be calibrated with future experimental data of the two-phase flow in fuel assembly.

All-fiber ultrafast laser generating gigahertz-rate pulses based on a hybrid plasmonic microfiber resonator

Ultrafast lasers generating high-repetition-rate ultrashort pulses through various mode-locking methods can benefit many important applications,including communications,materials processing,astronomical observation,etc.For decades,mode-locking based on dissipative four-wave-mixing(DFWM)has been fundamental in producing pulses with repetition rates on the order of gigahertz(GHz),where multiwavelength comb filters and long nonlinear components are elemental.Recently,this method has been improved using filter-driven DFWM,which exploits both the filtering and nonlinear features of silica microring resonators.However,the fabrication complexity and coupling loss between waveguides and fibers are problematic.We demonstrate a tens-to hundreds-of gigahertz-stable pulsed all-fiber laser based on a hybrid plasmonic microfiber knot resonator device.Unlike previously reported pulse generation mechanisms,the operation utilizes the nonlinear-polarization-rotation(NPR)effect introduced by the polarization-dependent feature of the device to increase intracavity power for boosting DFWM mode-locking,which we term NPRstimulated DFWM.The easily fabricated versatile device acts as a polarizer,comb filter,and nonlinear component simultaneously,thereby introducing an application of microfiber resonator devices in ultrafast and nonlinear photonics.We believe that our work underpins a significant improvement in achieving practical low-cost ultrafast light sources.