Experimental investigation of reflood heat transfer characteristics on CRUD-deposited surfaces

Abstract

This study experimentally investigates the influence of CRUD on reflood heat transfer performance under bottom reflood conditions following the actuation of ECCS during LOCA in a PWR. To simulate the in-reactor environment, CRUD-deposited test specimens were fabricated under prototypical PWR water chemistry conditions, and reflood experiments were conducted using a single heated rod configuration. Key thermal-hydraulic parameters-including quench front propagation speed, rewetting temperature, critical heat flux, and film boiling heat transfer coefficient-were quantitatively evaluated through high-speed flow visualization and inverse heat conduction analysis based on wall temperature measurements from an embedded thermocouple. The experimental results revealed that, on CRUD-deposited surfaces, the quench front formed earlier and propagated upward at a speed up to 2.3 times faster than that observed on bare surfaces. The CHF increased by up to 1.9 times, while the rewetting temperature rose by as much as 80 degrees C. The film boiling heat transfer coefficient in the post-CHF region was enhanced by up to 13.6 %, and the overall quenching time was reduced by approximately 50 %. High-speed visualization revealed frequent local vapor film collapses and direct liquid-surface contact events on the CRUD-deposited surfaces. These results indicate that the porous microstructure and hydrophilic surface characteristics of CRUD may promote coolant supply and induce vapor film destabilization, thereby enhancing reflood heat transfer performance of overheated fuel rods during LOCA.