Multi-scale Thermal-hydraulics Methodology and its Application to Marine Small Nuclear Reactor

[Background] Marine-based small nuclear reactors face unique thermal-hydraulic challenges due to periodic fluid oscillations and complex maritime movements, posing difficulties in design and safety assessments. [Purpose] This study develops a multi-scale analysis method for systematically evaluating thermal-hydraulic behavior and safety of marine SMRs under dynamic marine conditions. [Methods] First, system, subchannel, and CFD codes were modified for marine-specific factors impacting system behavior, component heat transfer, and fuel bundle analysis. Then, targeted methods for system-level, component-level, and fuel bundle scales were established, with a cross-scale data transmission mechanism enabling multi-scale simulation. [Results] Analysis reveals significant thermal-hydraulic changes under marine conditions, especially periodic oscillations in thermodynamic parameters and enhanced heat transfer coefficients under oscillatory conditions. The study further demonstrates that coupling CFD with system and subchannel codes enhances cross-scale accuracy and data coherence. [Conclusions] The proposed multi-scale analysis method effectively evaluates the safety of marine nuclear power reactors and provides theoretical support for design optimization.

[背景] 海洋小型核反应堆因周期性流体振荡与复杂海洋运动而面临独特的热工水力挑战，给设计与安全评估带来困难。
[目的] 本研究针对动态海洋条件下海洋小型核反应堆（SMR）的热工水力行为与安全性，开发一种系统评估的多尺度分析方法。
[方法] 首先，针对影响系统行为、部件传热及燃料棒束分析的海洋特有因素，对系统级、子通道级及计算流体动力学（CFD）代码进行了改进。随后，建立了系统级、部件级及燃料棒束级的针对性分析方法，并通过跨尺度数据传输机制实现多尺度模拟。
[结果] 分析表明，海洋条件下热工水力特性发生显著变化，尤其是热力学参数的周期性振荡及振荡条件下传热系数的增强。研究进一步证实，将计算流体动力学（CFD）与系统级及子通道级代码耦合可提升跨尺度精度与数据一致性。
[结论] 所提出的多尺度分析方法可有效评估海洋核动力反应堆的安全性，并为设计优化提供理论支撑。