Simulation-Based Heat Transfer Optimization for Mass Concrete in Nuclear Power Station Construction: A Case Study

The construction of mass concrete foundations for nuclear power plants faces significant challenges in controlling hydration heat and preventing early-age thermal cracking. This study develops an integrated framework combining high-fidelity thermal–mechanical simulation, real-time temperature monitoring, and construction process optimization to address these issues. Focusing on the VVER-1200 reactor raft foundation in the Xudapu NPP Phase II Project, an innovative center-to-periphery synchronous pouring method is proposed, departing from conventional inclined or layered pouring by strategically utilizing stage time lags to moderate the radial temperature gradient. Numerical simulations demonstrate that this method significantly reduces the peak temperature and thermal stress. Field validation shows that the maximum core-to-surface temperature difference is controlled within 19.8 °C, well below the critical threshold of 25 °C, and the peak concrete temperature remains at 66.7 °C, safely below the risk level for delayed ettringite formation (82–85 °C). The cracking risk coefficient K remains below 0.65, indicating a low probability of thermal cracking. Post-construction inspection confirms the absence of thermal cracks in the 5240 m3 monolithic pour. The proposed methodology offers a reliable, science-based approach for thermal crack mitigation and serves as a valuable reference for similar large-scale mass concrete structures in nuclear and other critical infrastructure projects.