Prediction of leakage rates from containment buildings under ultimate internal pressure

Accurate modeling of containment leakage is essential for predicting radioactive release during severe nuclear accidents. Although simplified pressure-based methods provide general estimates, they lack the ability to capture damage progression and determine leakage locations caused by structural failures, such as concrete cracking and liner tearing. This study examines the structural response and leakage behavior of a prestressed concrete containment building representative of the APR-1400 under ultimate internal pressure. A comprehensive three-dimensional nonlinear finite-element (FE) model was developed, and the predicted internal pressures corresponding to characteristic strain levels in major components were consistent with those of the Sandia National Laboratories (SNL) test data and simplified calculations, validating the reliability of the FE model. Four leakage prediction methods were employed to evaluate leakage rates, incorporating both permeation-based and crack development approaches. The analysis reveals that leakage initiates primarily at discontinuities, such as equipment hatch, personnel airlocks, and penetrations, and subsequently propagates to free-field regions as pressure increases. In addition, the relationship between predicted leakage rates and liner plate failure was investigated. Lower liner strain thresholds result in earlier onset and greater magnitude of leakage, emphasizing the critical role of the liner plate in containment integrity. These findings enhance the understanding of leakage mechanisms and provide a robust framework for more accurate integrity assessments of containment buildings. Furthermore, FE-based leakage prediction methods show strong potential for integration into severe accident codes, enabling a more realistic representation of the relationship between containment leakage rate and internal pressure.