Development of the CAT code - YGN 5 and 6 CVCS analysis tool

The CAT code has been developed for the analysis of the Chemical and Volume Control System (CVCS) of the Yonggwang Nuclear Power Plant Units 5 and 6(YGN 5 and 6). The code is able to simulate the system behaviors in the operating conditions which should be considered in the design of the system. It has been developed as a stand alone code which can simulate CVCS in detail whenever correct system boundary conditions are provided. The code consists of two modules, i.e. control and process modules. The control module includes the models for the Pressurizer Level Control System, the Letdown Backpressure Control System, the Charging Backpressure Control System, and the Seal Injection Control System. Thermal-hydraulic responses of the system are simulated by the process module. The modeling of the system is based on a node and flowpath network. The thermal-hydraulic model is based on the assumption of homogeneous equilibrium mixture. The major system components such as valves, orifices, pumps, heat exchangers and the volume control tank are explicitly modeled in the code. The code was validated against the measured data from the letdown system test performed during the Hot Functional Testing at YGN 3. The comparison between the measured and predicted data demonstrated that the present model can predict the observed phenomena with sufficient accuracy. (author)