Use of the MARS-KS Code for the Prediction of Condensation Heat Transfer in a Passive Cooling Heat Exchanger

The Passive Auxiliary Feedwater System (PAFS) is new conceptual design of auxiliary feedwater system in APR+ nuclear power plan. Although PAFS is relatively a simple system composed of one heat exchanger and several valves, it is designed to be capable of performing safety functions of which the conventional Auxiliary Feedwater System (AFS) did by active components. Furthermore, PAFS carry out safety functions during the period of the total loss of electrical power (i.e. SBO). PAFS provides cooling water into a steam generator to remove the residual heat under transient and accident conditions. During operation of PAFS, the phase change occurs at the Passive Cooling Heat Exchanger (PCHX) which located at the inside of the Passive Condensation Cooling Tank (PCCT). Then, the condensate water flows into the steam generator by gravity and it evaporates in the steam generator again. Therefore, the characteristics of heat transfer inside the PCHX is a main issue of PAFS. The schematic diagram of PAFS is in Figure 1. This paper addresses a preliminary investigation of the applicability of the thermal-hydraulic system analysis code 'MARS-KS' for predicting the thermalhydraulic characteristics of PCHX and PCCT in the PAFS. In addition, the heat transfer performance of PCHX during operational transients has been investigated