CONTAINMENT CAPACITY AND FAILURE MODES FOR CONDITIONS BEYOND DESIGN BASIS

Under internal over-pressure loading, experimental studies have demons trated that the most probable ultimate failure mode of concrete contai nments of nuclear power plants is leakage instead of a catastrophic br eak. For steel containments scaled model tests have shown instantaneou s catastrophic failure. However, due-to simplistic representations of scaled models, the data base is not conclusive for interpreting full-s cale steel containment behavior. Rather it serves primarily as a techn ical basis for method validation. Structurally, analytical and experim ental data have shown that both concrete and steel containments can wi thstand two to three times internal design basis pressures without fai lure. Experimental data on external seismic loading plus internal over pressure loading is limited. Most of the findings are based on analyti cal studies. Because of geometric complexity (3-D features, local stif fness discontinuities, etc.) and nonlinear behavior (geometric nonline arity and material nonlinearity) under extreme loadings, containment c apacity and failure-mode prediction requires qualified and validated a nalytical tools, together with sound engineering judgment.