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.