Cooling

A lot of people don't realize that the powerplant is cooled by ocean water, and that water travels through two 3 mile long tunnels. The tunnels were dug from the construction site out to the ocean. They each are 19 ft in diameter. The intake tunnel is 17,140 ft long and the discharge tunnel is 16,483 ft long. The intake and discharge vertical shafts were constructed before the tunnels. The first picture shows roughly how the tunnels are situated. The water temperature increases about 34 degrees at the plant but by the time it gets back to the ocean it is only 5 degrees warmer then the intake after exiting through the diffuser nozzles.

This picture shows the three intake shafts.

Three miles out and 160' below the water's surface. Out at the end of the Intake Tunnel.

The three intake structures before they were lowered to the ocean floor.

Two men on top of one intake structure. Good for seeing the size of the intake. After Seabrook Station began operation seals would swim into the intake, down into the tunnel and get lost. The width beween the bars is 16". The flow of the water is slow enough at the intake not to suck in wild life, but it doesn't stop the curious.

To keep the seals from swimming into the intake structures, seal deterrent barrier panels were created. This is a mockup showing the panels bolted to the original (blue) bars. The distance between the bars is 5". Since being installed in Aug, 1999 no seals have been trapped in the tunnels.

Closeup of a seal deterrent barrier panel installed. It's easy to see how much of a difference 5" is than 16".

If were sitting on a boat, out at the buoy marking the intake structures, this is what it would look like. You can see Unit 1 and Unit 2 containment buildings in the distance.

The discharge diffuser nozzles are quite different than the intakes. Heated cooling water is discharged out of eleven of these spaced about 100 ft apart. The openings of each nozzle are about 2.5 ft in diameter. The diffuser nozzles jet the warmer water out at about 10 feet per second at a point about 50 feet below the ocean surface. The surface water temperature rise is limited to no more than 5 degrees fahrenheit above the ambient ocean surface water temperature.