Also, it had an emergency cooling system (the isolation condenser) which could work passively without pumped water. Unfortunately the failsafe logic made the va

Also, it had an emergency cooling system (the isolation condenser) which could work passively without pumped water. Unfortunately the failsafe logic made the valves to the isolation condenser close when electricity was lost, and then without electric power the reactor operators could neither open the valves, nor monitor whether the valves were opened or closed, so it didn't work and the operators were confused about why. [https://www.ncbi.nlm.nih.gov/books/NBK253938/ https://www.ncbi.nlm.nih.gov/books/NBK253938/]