Thermal-hydraulic conditions at and downstream of a quench front during a Loss-of-Coolant Accident in a Pressurized Water Reactor

During a LOCA (Loss of Coolant Accident), the rapid rise in core temperature combined with a drop in external pressure may deform or even rupture the fuel rods of a PWR (Pressurized Water Reactor). To prevent core meltdown and the release of fission products outside the vessel, a safety system injects borated water through the base of the assembly to cool it. This causes intense boiling at the quenching front, generating a vapor-droplet flow that propagates downstream, further cooling the rods. This two-phase flow, known as DFFB (Dispersed Flow Film Boiling), has been previously characterized [1], and recent studies [2–5] have enhanced the understanding of cooling mechanisms associated with it. However, the link between droplet distribution — specifically diameter and velocity profiles — and heat and mass transfer at the quenching front remains unclear. This study investigates thermal-hydraulic conditions at the quench front and downstream under LOCA-like conditions. The project involves designing and constructing a new experimental bench simulating the fuel assembly at a subchannel scale. The platform will enable experiments varying key parameters: water injection temperature, wall temperature, and heat flux applied to the wall. A Phase Doppler Anemometer (PDA) will characterize the dispersed flow (droplet diameter and velocity), and an infrared camera will measure wall surface temperature. An inverse method will estimate the wall heat flux profile. These experimental data will support the development of accurate physical models for predicting droplet behavior, which may eventually be integrated into ASNR’s DRACCAR code, aimed at improving core cooling predictions and safety.

Work In Progress