Experimental investigation of depressurization characteristics on the 1/28 scaled simplified HTGR reactor building Model

Reactor Buildings (RBs) for the Next Generation Nuclear Plant (NGNP) High Temperature Gas Cooled Reactor (HTGR) consisting of Reactor Pressure Vessel (RPV) and Steam Generator Vessel (SGV) can be designed as Vented Low Pressure Compartments (VLPCs). In cases of Depressurized Loss of Forced Cooling (D-LOFC) accidents, for instances breaks in the helium pressure boundary, there is a possibility of air ingress into the RPV through the RB vent path. Air ingress into the RPV causes oxidation of the fuel elements and other nuclear-grade graphite components, and its impacts on graphite oxidation are important for assessing safety consequences. In order to predict when oxidation may occur inside the RPV more accurately, close investigation of the helium/air mixture characteristics inside the RB after the D-LOFC event is required. In the present study, RB depressurization characteristics were investigated experimentally on the 1/28 scaled simplified HTGR RB facility. The initial scaled RB pressure was set at 1.2 psig. The natural leak rate of the facility was matched to the conceptual NGNP HTGR RB design criteria: leaking 1 entire volume per day under 1 psig.