Containment Capacity and Failure Modes for Conditions beyond Design Basis

Under internal over‐pressure loading, experimental studies have demonstrated that the most probable ultimate failure mode of concrete containments of nuclear power plants is leakage instead of a catastrophic break. For steel containments, scaled model tests have shown instantaneous catastrophic failure. However, due to simplistic representations of scaled models, the data base is not conclusive for interpreting full‐scale steel containment behavior. Rather it serves primarily as a technical basis for method validation. Structurally, analytical and experimental data have shown that both concrete and steel containments can withstand two to three times internal design basis pressures without failure. Experimental data on external seismic loading plus internal overpressure loading is limited. Most of the findings are based on analytical studies. Because of geometric complexity (3‐D features, local stiffness discontinuities, etc.) and nonlinear behavior (geometric nonlinearity and material nonlinearity) under extreme loadings, containment capacity and failure‐mode prediction requires qualified and validated analytical tools, together with sound engineering judgment.