Onsite Standby Power System

The VZS, which provides ventilation and eooling of the diesel generator building, and ventilation and heating of the diesel oil transfer mod lule enelosure to support operation of the onsite standby power system. 

The onsite ac power system (ECS) is a non-class IE system comprised of a normal, preferred, maintenance and standby power supplies. The normal, preferred, and maintenance power supplies are included in the main ac power system. The standby power is included in the onsite standby power system. 

Two onsite standby diesel generator units, each furnished with its own support subsystems, provide power to the selected plant ac loads. Power supplies to each diesel generator subsystem components are provided from separate sources to maintain reliability and operability of the onsite standby power system. 

Offsite power, main ac power, and onsite standby power systems. 

Two onsite standby diesel generators power the onsite standby power system. This supplies power to selected loads in the event of the loss of the normal or the preferred ac power supplies. These loads provide defence-in-depth functionality. The diesel generators are automatically started and connected to their respective buses. In the event of a fast bust transfer, the diesel connection to the bus is delayed such that the fast bus and residual transfer is allowed to initiate. 

The onsite standby diesel generator backed 400 Vac distribution system provides the normal ac power to the battery chargers. Industry standard stationary batteries are provided to supply the dc power source in case the battery chargers fail to supply the dc distribution bus system loads. The batteries are sized to supply the system loads for a period of at least two hours after loss of all ac... 

Power is supplied to the main control room/control support area HVAC subsystem by die plant ac electrical system. In the event of a loss of the plant ac electrical system, the main control room/control support area ventilation subsystem can be transferred to the onsite standby diesel generators. The convection heaters and duct heaters are not transferred to the onsite standby diesel generator. 

Regulatory Guide 1.6, "Independence Between Redundant Standby (Onsite) Power Sources and Between Their Distribution Systems", U.S. Nuclear Regulatory Commission. 

The EFW system is also highly reliable and is designed to function in the event of a loss of offsite and onsite power. The design accommodates a coincident failure of a single active mechanical or electrical component. In addition, the EFW system is capable of maintaining the plant in a hot standby condition for eight hours and then providing for an orderly cooldown to shutdown conditions (see CESSAR-DC, Section 10.4.9.1.2). 

USNRC Regulatory Guide 1.6, "Independence between redundant standby (onsite) power sources and between their distribution systems. ... 

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