Boron Carbide-Stainless Steel Eutectic Interactions During Severe Accidents in Sodium-Cooled Fast Reactors: From...

Eutectic reactions between core materials strongly influence the progression of severe accidents in sodium-cooled fast reactors (SFRs). Contacting constituents, namely metallic fuel with steel cladding and boron carbide (B₄C) absorber with stainless steel (SS), form liquid phases several hundred kelvin below the melting points of the individual materials. The resulting low-temperature liquefaction leads to early failure of cladding and control-rod structures, relocation of fuel and absorber, and changes in core reactivity, and therefore affects both the recriticality evaluation and the in-vessel retention (IVR) strategy. This focused narrative review mainly covers studies published in the last decade and earlier foundational work. It concentrates on B₄C-SS reaction mechanisms, kinetics, thermodynamics, properties, experiments and models, with metallic fuel-cladding interaction as context. A transferability analysis distinguishes reactor-independent material-couple evidence from geometry-dependent and oxidation-specific results obtained mainly in post-Fukushima boiling water reactor studies. The principal limitations are the predominance of unirradiated small-scale tests in controlled atmospheres, incomplete multicomponent thermodynamic and transport-property data, and limited validation from single-rod to bundle and reactor scales. These uncertainties propagate through melt composition and boron redistribution to reactivity and IVR, defining priority needs for future SFR experiments and coupled modeling.