Heat transfer inside a blocked region of a rod bundle during a LOCA-simulations and experiments

International audienceThis study focuses on the coolability of a partially deformed fuel assembly of a PWR reactor through an accident causing the loss of coolant primary (LOCA). Beyond the dryout point during the reflooding phase, the core is cooled mainly by a vapor/droplets flow. The thermal-hydraulic features of this two-phase flow, as well as the damaged cladding characteristics, are important parameters to estimate the core coolability through the fuel assemblies. In order to analyze experimentally the influences of the cladding deformation on the heat transfer by a vapor/droplet flow, a setup is developed at the sub-channel scale. Measurements are carried out using optical techniques to characterize the droplet's flow. Along the blocked zone, temperature measurements of the tube surface are performed in order to estimate the total internal heat transfer. One-dimensional mechanistic model, accounting for the heat transfer mechanisms in a post-dryout region, is also developed. This is a necessary step in order to analyze correctly the experimental data and it helps us to better understand heat transfer within the tube