Passive containment cooling system (PCCS) response with Drywell Gas Recirculation System (DGRS) activated during a postulated Loss of Coolant Accident (LOCA)

Passive Containment Cooling Systems (PCCS) are characterizing the design of several advanced LWR such as SBWR, ESBWR, ABWR-II, etc. These systems should ensure the mitigation of postulated accidents both under Design Basic Accident (DBA) and Beyond DBA (BDBA) conditions. Some ALWR designs integrated in the PCCS a system called Drywell Gas Recirculation System (DGRS). The DGRS works like a fan, with inlet flow lines connected to the Passive Cooling condenser (PCC) vent lines and the outflow line connected to the Drywell (DW). The present paper presents the experimental results of an integral containment test performed in the PANDA facility. The initial conditions (temperature, pressure, gas composition, decay heat, etc.) for the test represent the containment situation 1 h after a Loss of Coolant Accident (LOCA). The test consists of two phases (6 h each) for a total duration of about 12 h. In the first phase has been simulated the response of the PCCS to a LOCA, in the second phase the DGRS has been activated and has been investigated the effect of such activation on the overall PCCS response. The test shows that the activation of the DGRS has an effect on the overall PCCS characteristics, i.e. composition of gas mixture in the PCC tubes, stratification in the Wetwell (WW), DW–WW pressure differences, timing for the opening of the Vacuum Breakers (VB) and overall containment pressure.