Experimental and numerical analysis of boron diffusion in eutectic melt under uniform radiative heating of B4C-SS control rod composites

In Sodium-cooled Fast Reactors (SFRs), a key challenge during Core Disruptive Accidents (CDAs) is the eutectic interaction between boron carbide (B4C) and stainless steel (SS) control rod. This reaction lowers the melting point, redistributes boron, and raises recriticality risk. However, diffusion-driven boron relocation under uniform prototypic heating remains poorly understood. Earlier experiments lacked representativeness, and most models focused on complex 2D/3D multiphase behaviour without isolating the key 1D transport mechanisms. This study presents a novel experimental approach, employing hollow cylindrical B4C-SS composites subjected to uniform radiative heating in an argon atmosphere. Melt relocation was recorded using high-speed imaging, while boron redistribution was quantified with Laser-Induced Breakdown Spectroscopy (LIBS). An in-house 1D MATLAB model was developed, coupling radiative heat transfer with Fick diffusion kinetics and employing an Arrhenius-based diffusivity of 2 × 10−8 m2/s at 1500 K. Eutectic melting occurred between 1505 and 1550 K, depending on the heating configurations. In both cases, the SS cladding fully liquefied and flowed downward, with LIBS showing 4–8 wt% boron in the solidified melt, matching model predictions (6–8 wt%, <10 % error). Although the heat flux direction shifted the onset temperature and increased boron concentration in the B4C-heated case by ∼20 %, the eutectic mechanism was consistent across configurations.