Visualization Experiments of Radiation Heating on the Eutectic Reaction Between B4C-SS and Its Relocation Behavior

Generation IV Sodium-cooled Fast Reactor (SFR) development faces a critical challenge with Core Disruptive Accidents (CDAs). Boron migration resulting from the eutectic reaction between boron carbide (B4C) and Stainless Steel (SS) can lead to molten pool formation, affecting neutron balance within the core. This study employs quantitative, high-resolution visualization using radiative heating to observe eutectic behavior and melt structure during boron migration. Experiments, simulating control rod design, cover the temperature range of 1150 ℃ to 1372 ℃, focusing on long-duration melting and relocation behavior. Results show the eutectic temperature for pellets surpassing that of powder, unaffected by heating rate. Two failure mechanisms are identified: SS peeling off B4C, forming molten droplets, and B4C pellets breaking into pieces due to thermal stress, with sintering in the powder case. Visualization accurately determines eutectic melting onset, pointing to differing values for pellets and powder. This study enhances understanding of eutectic reaction mechanisms, contributing to CDA safety in SFRs.