III—9. Postulated in-vessel steam explosions are generally judged not to threaten the integrity of the containment.

III-10. Failure of the reactor vessel at high or low pressures, in conjunction with the presence of water within the reactor cavity, may lead to interactions between fuel and coolant with the potential for rapid steam generation or steam explosions. Rapid steam generation may give rise to the pressurization of containment compartments beyond the capability of the containment to relieve the pressure, so that the containment fails due to local overpressuri­zation. Steam explosions may be caused by the rapid mixing of finely fragmented core material with surrounding water, resulting in the rapid vaporization and acceleration of the surrounding water, creating substantial pressure and impact loads.

III-11. The presence of water in the reactor cavity can be avoided by means of a suitable layout if important components of the containment, such as the supporting reactor cavity wall and the containment liner, are not capable of resisting these high impulse loads.