Loss of offsite power in pressurized water reactors, a combined probablistic and thermal-hydraulic analysis

The pressurized water reactor (PWR) loss of offsite power initiating event was studied at the Idaho National Engineering Laboratory as a part of the U.S. Nuclear Regulatory Commission's (NRC) Severe Accident Sequence Analysis Program. An event tree was developed and used as a basis for investigating high risk accident sequences initiated by a loss of offsite power. Specific high risk accident sequences for further study were determined by assigning probabilities to events within the tree. The thermal-hydraulic responses of three PWRs of different vendors were calculated for these high risk sequences using the RELAP4/MOD7 computer code. Actions to mitigate the consequences of certain sequences were identified and the critical times for their implementation were determined