Tube plugging effects on the thermal–hydraulic characteristics of a CAP1400 steam generator with a three-dimensional primary–secondary coupled heat-transfer model

In steam generators (SGs), heat transfer tubes are about 1 mm thick and operate under severe conditions. Therefore, preventive tube plugging is routinely applied to limit tube failure risk. However, most studies of SG tube plugging still rely on one-dimensional system codes, which cannot capture the impact of plugged-tube distribution on three-dimensional thermal–hydraulic performance. In this study, a three-dimensional primary–secondary coupled heat-transfer model is developed for tube plugging conditions. After validation, the effects of plugging location and plugging ratio on the thermal–hydraulic characteristics of the CAP1400 SG are systematically investigated. The tube bundle region is modeled as a porous medium, and the plugged tubes are represented in the cross-section by an annular region. A mesh-mapping method is proposed to enable robust coupled heat-transfer calculations between the two nonconformal sides. The results show that SG thermal power and outlet steam mass flow decrease as the plugged region moves outward and as the plugging ratio increases. Tube plugging has little effect on the secondary-side pressure drop, whereas the primary-side pressure drop increases with plugging ratio. At a plugging ratio of 20%, SG thermal power and outlet steam flow decrease by up to 7.20% and 6.43%, respectively, while the primary-side pressure drop increases by up to 36.36% relative to the normal condition. This study conducts the first systematic numerical study of tube plugging in the CAP1400 SG. The results support the safe operation of CAP1400 units and provide a modelling framework for future digital-twin studies of nuclear power systems.