Emergency Power System (EPS)

The emergency diesel generator (EDG) is part of the standby emergency onsite ac power system and is required to be available as a reliable source of ac power in the event of a loss of normal ac power during all plant modes (operating or shutdown). Normally, each plant has two safety-related buses that power the electrical loads required for safe shutdown and emergency conditions. These buses typically receive power from either the auxiliary or the startup transformers, which are powered from the main generator or offsite power. In the event of the loss of offsite power or the failure of the normal power to the individual safety-related buses, an EDG train will provide a backup source of power to its associated safety-related bus. The EDG train has sufficient capacity to power all the loads required to safely shut the plant down or supply emergency core cooling system (ECCS) loads on a loss-of-coolant accident (LOCA).

An EDG train is required to automatically start upon indication of the following:

  • A loss-of-coolant accident (safety injection signal)
  • A low voltage condition on the safety-related bus

The initial system study is documented in "Emergency Diesel Generator Power System Reliability, 1987-1993" (NUREG/CR-5500, Volume 5 ). The links below provide the current information for the study and latest results.

Current Results (SPAR-based):

Historical Results (SPAR-based):

Historical Results (LER-based):

Supporting Information:

Page Last Reviewed/Updated Wednesday, August 31, 2022