Full scale test facility for operability verification of tokamak pressure suppression system at sub-atmospheric conditions

The reliable and safe operation of tokamak fusion reactors is mainly based on radioactive contaminants confinement, achieved preserving the integrity of robust barriers, among which the Vacuum Vessel (VV) performs an essential role. The VV protection against postulated over pressurization events is guaranteed by the safety functions implemented in the Pressure Suppression System (PSS), in which steam from VV is discharged and Direct Contact Condensation (DCC) occurs at sub-atmospheric conditions. Aiming to verify the VVPSS performance of ITER machine (i.e. steam condensation efficiency at different DCC regimes with/without non-condensable), in steady state and transient conditions relevant for fusion reactor postulated events, and contribute to fill the knowledge gap regarding sub-atmospheric condensation, an extensive experimental research activity is ongoing with the Large and Full Scale Test Facility (LSTF and FSTF): designed, assembled, instrumented and commissioned at Laboratory B. Guerrini at DICI University of Pisa. This facility is mainly composed of a Steam Generator (up to 500 g/s, about 1.8 MW), three different steam lines for wide mass flowrate regulation, two air lines for mixed condensation characterization, Experimental Test Tank (92 m3, where steam condensation is investigated adopting two different spargers, scaled and full scale with 100 and 1000 holes, respectively), Auxiliary Tank (10 m3 for plant conditioning), Vacuum Pump, Chiller and Water Storage Tank (15 m3). Two Steam Storage Tanks (15 m3 each) allow to accumulate and provide the foreseen steam peak flowrate value (of 5 kg/s) in the postulated accident. FSTF is highly instrumented (81 thermo-resistances, 28 thermocouples, 35 pressure transmitters, 18 strain gauges and 4 vortex flow meters) and fully remotely controlled (64 on-off and control valves) by a dedicated Data Acquisition and Control System (DACS). Six video cameras and 4 led lights assure steam injection video-recording, for detailed characterization of condensation regimes. Preliminary results are shown for 50 g/s of steam injected through the scaled sparger into water pool at 30 °C with cover gas at 0.1 bar absolute, providing a condensation efficiency of about 100% and verifying instable chugging condensation regime.