Experimental investigation of surface inclination effects on ablation of a solid impacted by a hot liquid jet

Abstract

In sodium-cooled fast reactors (SFRs), the potential consequences of a severe accident with core meltdown are now considered during the reactor design phase. Such events lead to the formation of a corium , a radioactive mixture of molten nuclear fuel and structural materials. Two protective devices can be implemented in advanced SFR designs: discharge tubes, used to transfer the corium to the lower part of the reactor vessel to prevent recriticality, and a core catcher, designed to receive the corium to facilitate its long-term cooling. However, with such new mitigation designs, the corium may impinge on the core catcher as a high-temperature liquid jet ( ∼ 3000 K ), which can lead to localized thermal ablation of the core catcher. Some design proposals for the core catcher include angled baffles intended to dissipate the jet’s kinetic energy. The ablation of such inclined surfaces must be understood to ensure the structural integrity of the core catcher during the corium relocation phase. The present study investigates the influence of surface inclination on the ablation dynamics induced by a hot free-surface liquid jet impinging on an inclined solid target. Experiments were conducted using the HAnSoLO facility, in which water and ice serve as simulant materials, with a water jet impinging on a transparent ice block. The experimental conditions cover Reynolds numbers from 3.7 × 1 0 4 to 1.47 × 1 0 5 , Prandtl numbers from 2.5 to 5.4, and surface inclination angles from 0° to 45°. Results show that surface inclination strongly affects the filling of the cavity as well as the flow circulation before the pool regime. A new intermediate regime, absent for horizontal impacts, was identified. The results show that surface inclination is not necessarily beneficial in terms of ablation reduction and that, at the highest Reynolds numbers investigated, inclination can lead to an increase in the ablation velocity. These findings provide a first experimental basis for understanding the influence of surface inclination on jet-induced ablation and for guiding further investigations toward reactor-relevant conditions. Their extension to corium conditions will require a progressive validation approach combining numerical simulations and prototypical experiments.