A detailed study of anticipated transients without scram (ATWS) has been carried out in the Federal Republic of Germany based on a boiling water reactor (BWR) and a pressurized water reactor (PWR) reference plant. The study includes transient calculations as well as reliability analyses of the entire scram system (sensors, logic, actuating system). In addition, the influence of other safety related systems (pressure relief system, pump control system in a BWR) has been evaluated. During all ATWS, system pressure does not exceed 110% of design pressure. Only for short periods (several seconds) and only in small areas of the core might film boiling occur. The availability of the scram systems for both a BWR and a PWR is on the order of 10−5 per demand. From these results it is concluded that no independent second scram system is necessary. However, the detailed analysis has given an indication of where hardware measures could be taken to mitigate the transients (e.g., increase of valve capacity) or further improve the availability of the scram system.