The German risk study. Pt. 1

With reference to a representative PWR plant of the 1300 MWe-type some 100 accident sequences leading to core melt have been investigated. An overall core melt frequency of about 9 x 10-5 per reactor and per year has been obtained as a mean value. According to the analysis performed the main contributions to the core melt frequency result from uncoped small LOCAs in the reactor coolant loops, and some transients (e.g. Loss of Offsite Power). Furtheron, assuming failure of engineered safety features, the course of core melt accidents and potential containment failure modes (overpressure, leakage, steam explosion) are analyzed. Thereby the course of a core melt accident leading to overpressure failure of the containment is discussed in some detail. The activity release in the environment resulting from different accident sequences is determined. (orig./RW)