Entergy Corporation's Pilgrim nuclear power plant in Plymouth, Massachusetts remained off line Friday, one day after it was shut down because of a problem with the electrical system that operates the pumps that supply cooling water to the reactor core. The federal Nuclear Regulatory Commission (NRC) said it appears as if the main feedwater power supply breaker tripped. Entergy said backup pumps automatically activated and plant systems performed as designed. The NRC and plant operators said there was no threat to public safety. The cause of the fault is under investigation and there is no timetable for the plant to restart.