Power level effects on CAP1400 steam generator thermohydraulics with primary-secondary coupled heat transfer

Abstract

The thermohydraulic characteristics of the steam generator (SG) in a pressurized water reactor (PWR) directly influence the safe operation of the nuclear power plant. However, as a pressurized water reactor in its initial commercial operation phase, the thermohydraulic characteristics of the CAP1400 SG under low-power conditions remain insufficiently explored. To address this gap, a simplified three-dimensional primary-secondary coupled porous media model is developed for both sides of the CAP1400 SG. Following validation with operational PWR data, the model is used to investigate the impact of power levels on flow and heat transfer. Primary-to-secondary side heat transfer is computed by coupling parameters at corresponding positions, while flow resistance in local components, including the tube sheets, tube bundle, support plates, and anti-vibration bars (AVB), is simplified through momentum source terms. Numerical simulations closely match measured data, with relative errors within 2.17 %, confirming the model's accuracy. Notably, the uneven flow distribution caused by the lower head structure on the primary side intensifies the non-uniform heat transfer on both sides. Moreover, an analysis of cross-flow energy associated with flow-induced vibration (FIV) shows that the risk of vibration-induced damage to the outermost tube bundle increases with power. The peak cross-flow energy is concentrated on the hot side, and the angle between the peak cross-flow energy and the horizontal plane increases from 37° at 30 % full power (FP) to 68° at 100 % FP. These findings provide valuable data and practical recommendations for ensuring the safe operation of the CAP1400 across a range of power levels.