SILFIDE experiment: Coolability in a volumetrically heated debris bed

The SILFIDE facility was designed at EDF R&D to study the coolability of a debris bed in multidimensional configurations. The choice of induction heating mode was motivated by the necessity for the heat to be generated primarily within the solid particles instead of using external heaters. Particles were simulated by steel beads with diameters ranging from 2 to 7 mm. Coolability is significantly better in terms of CHF values in comparison with the Lipinski 1D formulation applied to the conditions (especially when considering vertically integrated power) where the dryout occurs first. The experiments also show that bottom coolant injection is at least two times more efficient than top coolant injection. With increasing thermal power, steady temperature overheats up to 200 °C above saturation were observed, and the bed was still coolable. Combined phenomena considered as responsible are discussed: steam flow cooling with or without entrained liquid droplets in post-dryout regime, and preferential paths of fluid in porous media. As a consequence, the critical heat flux definition under such conditions must be considered with care. Especially, a failure of coolability cannot necessarily be concluded only from the occurrence of dry zones.