Thinning behavior of solid boron carbide immersed in molten stainless steel for core disruptive accident of sodium-cooled fast reactor

Boron carbide (B4C)-stainless steel (SS) eutectic reaction behavior is one of the most important issues in the core disruptive accidents (CDAs) of sodium-cooled fast reactors (SFRs). In this study, the immersion experiments using B4C pellets with molten SS were conducted to evaluate the CDA sequences such as contact event of solid B4C with degraded core materials including SS at very high temperature. The immersion experiment aims at understanding the kinetic behavior of solid B4C-liquid SS reaction based on the reduced thickness of B4C pellet after the experiment in the temperature ranges from 1763 to 1943 K, which is higher than the temperature of solid B4C-solid SS reaction. Based on the kinetic consideration of the reaction rate constants for solid B4C-liquid SS reaction, it was found that similar temperature dependency was identified between solid B4C-liquid SS and solid B4C-solid SS. Besides, the reaction rate constants of solid B4C-liquid SS were smaller than those of solid B4C-solid SS extrapolated in higher temperature region by two or more orders of magnitude due to two different evaluation method for B4C side/SS side. It was confirmed that this difference was reasonable through the consideration of previous reaction tests in solid-solid contact for B4C side/SS side.