Helical Fuel Rod Dynamics in Lead-Bismuth Eutectic-Cooled Reactors
The safe and efficient operation of nuclear reactors greatly depends on the thermal-hydraulic performance of the nuclear fuel. Lead-bismuth eutectic (LBE) coolant has emerged as a promising candidate for advanced reactors due to its excellent thermal properties and compatibility with fast reactor systems. This study focuses on an innovative helical fuel design, aiming to optimize flow and heat transfer characteristics. Through experimental investigations and numerical simulations, this research provides insights into the complex dynamics of LBE-cooled systems and paves the way for high-performance fuel assembly designs.
Experimental Methodology and Test Sections
To comprehensively analyze the flow and thermal behavior, three distinct test sections were developed and tested under controlled conditions. These sections were designed to replicate real-world fuel configurations, including helical cruciform geometries. Parameters such as temperature, pressure drop, and volumetric flow rate were meticulously measured to establish a reliable experimental dataset. The experimental setup enabled evaluation of flow resistance, convective heat transfer, transverse mixing, and flow distribution, which are critical for validating numerical models and improving reactor design.
Flow Resistance and Reynolds Number Independence
A significant finding from the experiments is the apparent independence of the resistance coefficient from inlet temperature when both Reynolds number (Re) and Péclet number (Pe) are held constant. This suggests that within the specified flow regime, geometric factors and turbulence dominate resistance characteristics more than thermal conditions. The resistance correlation was found to align well with prior studies on cruciform helical geometries, reinforcing the repeatability and reliability of the novel fuel rod structure under turbulent LBE conditions.
Heat Transfer Performance and Nusselt Number Stability
The convective heat transfer performance was evaluated using the Nusselt number (Nu), which also exhibited negligible variation with inlet temperature under constant Re and Pe. This thermal stability is crucial for reactor operation, as it ensures consistent cooling regardless of minor inlet fluctuations. The robust nature of Nu behavior further confirms the thermal efficiency of the helical design and supports its viability in LBE-cooled fast reactors, where stable heat transfer is a key safety requirement.
Transverse Mixing in Subchannels
Transverse mixing plays a vital role in thermal uniformity and prevention of hot spots within the core. Experiments conducted in a four-rod test section demonstrated that mixing efficiency between subchannels is influenced by flow conditions and geometric configurations. The findings highlight that mixing intensity varies with experimental parameters, offering a deeper understanding of inter-subchannel transport phenomena, which is often overlooked in simplified reactor models.
Flow Distribution Analysis and CFD Validation
Flow distribution experiments revealed a consistent average flow distribution ratio of 1.89 between inside and outside subchannels, independent of Reynolds number in turbulent flow regimes. This insight is critical for predicting coolant behavior in full-core assemblies. Complementing the experiments, CFD simulations were performed using the Realizable two-layer k−ε turbulence model. The simulation results showed strong agreement with measured data, validating the accuracy of the numerical approach and reinforcing confidence in CFD as a predictive tool for LBE reactor design.
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