Large Scale experimental facility for assessment the performances of the vacuum vessel pressure suppression system of ITER

The nuclear fusion reactor ITER (International Thermonuclear Experimental Reactor) foresees a Pressure Suppression System (PSS) in order to manage a Loss of Coolant Accident (LOCA) in the Vacuum Vessel (VV). The VVPSS (Vacuum Vessel Pressure Suppression System) has a key safety function because a large internal pressure in the VV could lead to a breach of the primary confinement barrier. Differently by the applications in the nuclear fission reactors, the steam condensation occurs in ITER at sub-atmospheric pressure conditions. No previous applications of direct steam condensation at sub-atmospheric conditions have been done. Therefore, experimental assessment of VVPSS was necessary simulating the direct condensation of the steam in the ITER thermal-hydraulic conditions. Under financial support of ITER Organization, an experimental program has been performed at the Department of Civil and Industrial Engineering (DICI) of the University of Pisa using a small-scale experimental rig (1/22 scale factor). In order to assess the scale laws elaborated by means of the experimental results obtained in the small scale facility, a Large Scale facility was built at University of Pisa following an international tender launched by ITER Organization. This facility is about a full scale from the geometric point of view (1/1.09 scale factor) and it is 1/10 scale factor from the steam mass flow rate point of view. This paper illustrates the results of the first test campaign. A 1/10 scale sparger system SPS-A (having a diameter DN125 and 100 holes) has used with a maximum steam mass flow rate of 0.5 Kg/s. This experimental configuration is representative of real operating conditions on the base of the results of elaborated similitude analysis. The preliminary analysis of the experimental results confirms the agreement in terms of the condensation regimes between the two reduced scale (1/22 and 1/10 scale) as foreseen by the elaborated scale laws.