Analyses of PACTEL passive safety injection experiments GDE-21 through GDE-25

Abstract In advanced light water reactors (ALWR), gravity-driven passive safety injection systems (PSIS) replace pump-driven emergency core cooling systems. PSISs often rely on small density differences and driving forces for natural circulation. In a typical loss-of-coolant accident (LOCA), interactions between different parts of the emergency core cooling system also take place. VTT Energy in Finland, in co-operation with the Lappeenranta University of Technology (LUT), performed five experiments in the PACTEL loop to study PSIS performance during SBLOCAs. The purpose of the PSIS, a passive core make-up tank (CMT), was to provide high-pressure safety injection water to the primary circuit. The purpose of these experiments was to produce data to validate the current thermal-hydraulic safety codes, and to study the effects of break size on the PSIS behaviour. In all experiments the CMT ran as planned. No problems with rapid condensation in the CMT, as seen in earlier passive safety injection experiments in PACTEL. The main reason was the new CMT arrangement, with a flow distributor (sparger) installed. The analyses of the test data supported the use of McAdams correlation for calculating the heat transfer from the hot liquid layer to the CMT wall. The use of Nusselt film condensation correlation for condensation at the CMT walls seems correct. The APROS code simulated successfully the overall primary system behaviour in the GDE-24 experiment, such as timing of the core heat-up at the end of the experiment. The code had some problems, in the simulation of thermal stratification in the CMT.