Preliminary Study on the Cooling Performance of Passive Emergency Core Cooling System

The H-SIT ensures emergency coolant injection into the core in the high-pressure region between the reactor coolant system (RCS) operation pressure (15.0 MPa) and the MP-SIT operation pressure (4.2 MPa). While its tank design is identical to that of a conventional SIT, the upper part of the tank and the cold leg are connected with a pressure balancing line (PBL), and the gravity-driven injection of cooling water from the tank into the reactor takes place at high pressure. In this study, an integral effect test (IET) was conducted on a loss of coolant accident (LOCA), which requires the operation of the primary makeup system, in order to confirm the performance of each PECCS component. A LOCA is an accident caused by a pipe break in the reactor coolant pressure boundary that results in a loss of reactor coolant at a rate in excess of the capability of a normal reactor coolant makeup system. A classic small break LOCA (SBLOCA) scenario with a break area of 0.024 square feet (two-inch break) was selected for PECCS performance analysis. In this study, the simulation of transient accident was performed on the two-inch cold leg break selected from the ATLAS-based SBLOCA scenarios to assess the cooling performance of the passive emergency core cooling system. The H-SIT (SITs #1 and #3) injection starts successfully at the moment when the primary side pressure falls to 10.0 MPa, and the MP-SIT (SITs #2 and #4) injection starts when the pressure falls further to 4.21 MPa. The operation condition such as PCT for ADVs #1 – #4 constituting the auto depressurization system (ADS) needs to be added.