Flow analysis in a 37-pin wire-wrapped rod bundle for sodium-cooled fast reactor using magnetic resonance velocimetry. I. Validation and gross behavior

The sodium-cooled fast reactor (SFR), a fourth-generation nuclear reactor, utilizes liquid sodium as a coolant and offers advantages like operation at atmospheric pressure and the use of spent nuclear fuel. Understanding flow characteristics around fuel rod bundle is crucial for securing cooling performance and safety. This study investigates the flow characteristics in a 37-pin wire-wrapped fuel rod bundle of SFR from three-dimensional flow fields measured by magnetic resonance velocimetry. Aimed at enhancing the understanding of coolant flow dynamics crucial for reactor safety and efficiency, the study successfully captures and validates three-dimensional, three components of mean velocities. Key discoveries include phase differences between wire position and high velocity regions, evidence of upstream flow influence by wire structures, and secondary flows such as edge swirling induced by wire blockage. The research offers detailed insights into subchannel velocities and flow split factors, contributing to improved SFR design and safety.