A review of containment accidents

Abstract The consequences of severe reactor accidents depend greatly on containment safety features and containment performance in retaining radioactive material. If the containment function is maintained in a severe accident, the radiological consequences will be minor. If the containment function does fail, the timing of failure can be very important. The longer the containment remains intact relative to the time of core melting and radionuclide release from the reactor coolant system, the more time is available to remove radioactive material from the containment atmosphere by engineered safety features or natural deposition processes. Delay in containment failure or containment bypass also provides time for protective action, a very important consideration in the assessment of possible early health effects. Thus, in evaluating the performance of a containment, it is convenient to consider no failure, early failure, late failure, and containment bypass as separate categories characterising different degrees of severity. The paper reviews the containment challenges posed by the severe accidents, on the basis of an extensive list of references. First the phenomena that could lead to early containment failure are described: direct containment heating, steam explosions, hydrogen combustion, and isolation failures. Then the late containment failure modes are treated: gradual overpressurization, basemat meltthrough, and overheating. Finally, some words are said about containment bypass.