Xingkang Su

Reliable heat removal from tightly packed fuel assemblies is a central safety requirement for liquid-metal fast reactors. Low flow or a local obstruction can produce strongly nonuniform cooling, yet conventional subchannel formulations based on downstream-only flow and uniform rod-surface heat flux cannot represent upstream coupling, internal flow reversal, or heat redistribution through the solid. This work develops the Liquid-Metal Blockage Sub-Channel Code (LMB-SAC), a lumped-parameter code for sodium, lead-bismuth eutectic (LBE), and lead. Mass, axial-momentum, and enthalpy conservation are coupled to temperature-dependent fluid properties. A Newton solver covers the full axial domain and solves signed mass flow, pressure, enthalpy, buoyancy, and axial conduction together. The formulation also includes low-Prandtl-number transport, distributed blockage resistance, multilayer radial and circumferential rod conduction, local rod-fluid coupling, and conservative wake heat release. Without fitting coefficients to measured temperatures, 92.8% of the predictions for an unblocked LBE bundle are within 20 °C of the measurements. The extreme low-flow calculation resolves five internal control volumes with reversed flow. For an impermeable blockage closing six central subchannels, conjugate heat transfer preserves the measured hot-cold wall partition and reduces the root-mean-square error (RMSE) from 93.3 °C with a non-conjugate rod formulation to 30.0 °C. The streamwise momentum-flux change contributes 51.4 kPa, equivalent to 22.7% of the total pressure drop. Coupling momentum and energy with conjugate heat transfer extends assembly-scale subchannel analysis to low-flow reversal and severe local blockage. Subject to the stated closure limits, LMB-SAC is suitable for thermal-hydraulic design and safety analysis of liquid-metal reactor fuel assemblies.

High-current cyclotron low-energy beam transport must preserve transverse acceptance while compressing a continuous beam into the center-region radio-frequency (RF) phase acceptance. This study presents the complete design from the ion sources to the final diagnostic plane (D8) of the independently developed CYCLZU-30 multi-ion axial-injection line and evaluates its self-consistent space-charge (SC) response for α ²⁺ , H ^- , and D ^- at 40 keV. The common lattice combines species-specific electron cyclotron resonance (ECR) and multicusp ion-source branches with signed magnetic setpoints and a three-harmonic buncher. Staged optimization based on three-dimensional particle-in-cell tracking determines the species-specific waveforms of the first buncher (BUN1). Independent numerical sensitivity scans for the PIC grid and time step establish numerical independence at the declared production resolution. At that resolution, buncher retuning raises the best obtained longitudinal capture efficiency with space-charge effects by 1.3–2.0 percentage points relative to the previous-design waveforms evaluated at the same resolution. Fine-step calculations support near-converged production results for all three ion species. Matched-waveform controls indicate species-dependent space-charge capture losses whose ordering is consistent with generalized perveance, with the weakest response obtained for D ^- . The 80% core phase width likewise exhibits a species-dependent response rather than universal broadening. Strong solenoidal focusing keeps the combined D8 2 σ _r change below 5.9%, mainly through transverse waist shifts. Cohort-tracked 4D covariance analysis nevertheless indicates residual nonlinear coupled 4D RMS emittance growth in all three species, with the smallest excess for D ^- . The resulting source, magnetic, and RF setpoints define the resolution-tested unneutralized operating baseline for the CYCLZU-30 axial-injection line.

Vacuum-sliding electrical contacts find extensive application in aerospace components, yet they face limitations related to inadequate lubrication performance. In this study, we analyzed the design of an emerging conductive lubricant material, NbSe₂. A series of NbSe₂-Ti films with varying doped Ti contents were prepared through magnetron sputtering technology. We investigated the correlation between the sputtering current and composition, microstructure, mechanical properties, and current-carrying tribological properties of the films. The results indicate that under vacuum and current-carrying conditions, the NbSe₂-Ti films demonstrate significant advantages over existing electrical-contact lubrication materials. Compared with electroplated gold films, the NbSe₂-Ti films reduced the coefficient of friction from 0.25 to 0.015, thereby improving the wear life by more than six times. This result demonstrates that magnetron-sputtered NbSe₂ film can be used as a lubricant for space current-carrying sliding contacts.

The present study focuses on the thermal hydraulic characteristics of fuel assemblies in the China Initiative Accelerator Driven subcritical System (CiADS), which utilizes grid-type spacers to support lead bismuth eutectic (LBE) cooled fast reactors. While the structural design and mechanical analysis of CiADS triangular fuel assemblies with grid-type spacers have been preliminarily investigated, there is a pressing need to study the thermal hydraulic behavior of liquid LBE within these fuel assemblies. This analysis is crucial for assessing the safety and economy of the CiADS subcritical reactor. The sub-channel analysis code, based on the lumped parameter method, plays a vital role in rapidly evaluating the safety features of LBE-cooled fast reactor fuel assemblies. To comprehensively evaluate the thermal hydraulic performance of fuel assemblies with grid-type spacers in the CiADS LBE cooling system, the flow pressure drop model, turbulent mixing model, and convective heat transfer model for the fuel assembly structure with grid-type spacers were incorporated into the existing CiADS sub-channel analysis code. This enhanced code has been successfully employed in the thermal hydraulic analysis of fuel assemblies utilizing wire-type spacers in the CiADS system. To verify the validity and accuracy of the modified CiADS sub-channel analysis code in calculating triangular fuel assemblies with grid-type spacers, the code was first utilized to replicate a 19-rods flow heat transfer experiment with grid-type spacers cooling liquid LBE. A comparison between the simulation and experimental results confirms that the CiADS sub-channel analysis code can predict the coolant temperature and fuel rod surface temperature in fuel assemblies with grid-type spacers. Subsequently, the structure and thermal hydraulic design of the latest CiADS fuel assembly with grid-type spacers were reviewed. Finally, taking into account the aforementioned enhancements to the CiADS sub-channel analysis code, a comprehensive thermo-hydraulic calculation of the CiADS fuel assembly with grid-type spacers was conducted. The results demonstrate that the coolant outlet temperature, maximum cladding temperature, and maximum fuel pellet temperature all fall within the design parameters of CiADS. Furthermore, the impact of the number of rods in different rod bundles (91, 61, 37, and 7 rods) on thermal hydraulic performance was analyzed. The findings indicate that, while ensuring calculation accuracy and efficiency, the results obtained from the 37-rod bundle can effectively reflect the thermal hydraulic behavior of the reactor core.