Vermont Yankee Nuclear Power Plant - Cooling Water

Cooling Water

Vermont Yankee uses the Connecticut River as its source of cooling water for its circulating water and service water systems. The circulating water system removes heat from the power generation process of the plant by cooling the plant's main condenser, while the service water system cools both safety and non-safety related auxiliary components in both the nuclear and turbine sides of the plant and additionally removes decay heat from the reactor in emergencies or in times when the reactor is shutdown. For the circulating water system, water is withdrawn from the pool above the Vernon Dam and pumped to the condenser by the circulating water pumps. It is discharged downstream of the intake structure after cooling the condenser. Two mechanical-draft cooling towers help control the thermal discharge of the plant. The circulating water system at Vermont Yankee is rather unique and can operate in a variety of different configurations controlled by large gates in the discharge structure which can direct some or all water to the cooling towers before it is discharged to the river depending on the gate position. There is also a recirculation line, also controlled by gates in the discharge structure, that can redirect some or all water back to the intake structure instead of it being discharged. Completely closed-cycle cooling with no discharge is possible using the cooling towers and recirculation line. Recirculation is only used during the hottest times of the year between Mid-July and Mid-September. During the cooler months, the cooling towers are not used at all. Due to the mechnaical fans in the cooling towers and booster pumps that are required to pump the water to the top of the towers, use of the cooling towers does reduce the plant's net electrical output.

The plant's service water system utilizes the same intake and discharge structures as the circulating water system, but utilizes separate pumps and piping. After cooling plant loads, the discharge water from this system is also delivered to the discharge structure and can then be either discharged or sent through the cooling towers. One cell of one of the cooling towers, cell B-1, can serve as an alternative heat sink for decay heat and the safety related components in the event the service water system or the Vernon Pool itself is unavailable which could occur if the Vernon Dam was to fail. That one cell is of more robust construction than the rest of the cooling tower and is seismic-rated. Its neighboring cell, B-2, while it does not perform the safety function, is also built safety-rated to protect cell B-1 from damage in the event of a collapse of the rest of the cooling tower due to earthquake or other force. The alternate cooling system using the B-1 cooling tower cell utilizes separate pumps from the normal service water system and is the system that is considered the safety-related heat sink credited for licensing. The normal service water system using the river normally performs this function, but is not built to safety-related standards.