This standard provides functional@ performance@ and design requirements for the fuel oil system for diesel generators that provide emergency onsite power for light water reactor nuclear power plants. This standard addresses all mechanical equipment associated with the fuel oil system@ but does not include that portion of the fuel oil system which is factory assembled@ engine mounted@ and supplied by the diesel generator manufacturer. Also@ it includes the instrumentation and control functional requirements. It excludes motors@ motor control centers@ switchgear@ cables@ and other electrical equipment used in the operation of the fuel oil system@ except to define interface requirements. Purpose. The purpose of this standard is to define those features of fuel oil systems required to ensure an adequate fuel supply to emergency diesel generators and to provide performance and design criteria that ensure sufficient fuel is available for supply to the emergency diesel generators under all plant conditions.