Investigation on jet scrubbing in nuclear reactor accidents: From experimental data to an empirical correlation

The Fukushima accident stressed the significance of suppression pools as passive systems for fission product trapping. Even though pool scrubbing was extensively investigated in the past, there are gaps in the existing data base and modeling that need to be addressed, particularly those relative to high gas injection velocities in the pool. In this paper, the main results of an experimental campaign (PSP tests) on particles scrubbing at the pool inlet region when the carrier gas forms a submerged jet (let scrubbing"), are presented and discussed. The tests have been conducted in the PECA-PS facility of the Laboratory for Analysis of Safety Systems (LASS) and the experimental conditions have been based on two non-dimensional variables: the Weber non-dimensional number, which has been set to values over the threshold from globule to jet regime; and the gas saturation ratio, which has ranged from under saturation to over-saturation. Jet scrubbing efficiency at the pool inlet has been measured to be over 90% whenever the gas enters the pool within the jet regime (We(tect) >= We(c)), regardless thermal boundary conditions. Analysis of gas steam content, though, has not shown any clear trend. Based on the PSP experiments and some others gathered from the open literature, a tentative correlation dependent on nondimensional Stokes number (Stk), which accounts for inertial impaction, and saturation ratio (S), which captures diffusiophoretic deposition, has been proposed as a first step to empirically model jet scrubbing. Finally, some lessons learned for forthcoming experiments have been withdrawn, particularly concerning the high impact of hydrodynamics. This work has been done within the framework of the 7th FWP of EURATOM through the EU-PASSAM project (Grant agreement No. 323217 - Euratom 7FP).