Study on the difference between B4C powder and B4C pellet regarding the eutectic reaction with stainless steel

The development of Generation IV Sodium-cooled Fast Reactors (SFRs) faces a crucial challenge concerning Core Disruptive Accidents (CDAs). The eutectic reaction between boron carbide (B4C) and Stainless Steel (SS) can lead to boron migration, resulting in the formation of a eutectic melt that may relocate extensively within the core, thereby affecting neutron balance in the disrupted core. The study utilizes a quantitative and high-resolution method using Joule heating to assess the reaction rate to determine the extent of boron migration within the reactor core. Experiments with B4C pellets and SS tubes were conducted in the temperature range of 1450 K–1550 K, comparing them to previous work using B4C powder. Results show that the eutectic reaction between B4C pellet and SS is considerably slower than that between B4C powder and SS. The derived reaction rate constants for pellet case align with literature findings. Additionally, a composition analysis using SEM/EDS was performed on the pellet case to examine microstructures. In the pellet case, the reaction layer exhibits two distinct layers. The first layer is thin and uniform, composed of MeB (Me = Fe, Cr, or Ni) and located adjacent to the B4C region. The second layer is thick and consists of MeB precipitate with Me3B2 grey contrasts. This differs from our previous B4C powder case, where only a single layer of MeB precipitate was observed. Notably, there is no B4C present in the pellet reaction layer. Studying the eutectic reaction mechanism in control rods through assessing the reaction rate and microstructures enhances safety and understanding of CDAs in SFRs.