Thermal shock studies associated with injection of emergency core coolant following a loss-of-coolant accident in PWRs

The thermal shock resulting from injection of emergency core coolant following a loss-of-coolant accident may, under certain circumstances, result in propagation of preexisting cracks on the inner surface of pressurized-water-reactor (PWR) pressure vessels. At Oak Ridge National Laboratory, studies being conducted in connection with this problem include the thermal shock testing of 533-mm-OD by 241-mm-ID steel test specimens. Four experiments have been conducted thus far. The results have revealed no significant anomalies and tend to validate with reasonable accuracy the methods of analysis used for predicting the behavior of PWR vessels under thermal shock conditions. Analysis indicates that in present generation and future PWR vessels crack propagation will not occur as a result of thermal shock, but in older vessels it may. However, it appears that a phenomenon known as warm prestressing will prevent excessive crack penetration.