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The American Experience
Three Mile Island: How a Nuclear Reactor Works

schematic of reactor

At the heart of every nuclear power plant lies the radioactive core. The core is a nuclear furnace, generating heat as its atoms split during a controlled chain reaction. At Three Mile Island, the core stands 12 feet high and weighs 100 tons.

Control rods are lowered into or raised out of the core to control the rate at which the atoms split, and therefore the amount of heat generated by the core. Lowering the rods slows down the reaction; raising the rods increases the reaction.

Water in the primary loop flows around the core, absorbing the heat generated. Because it comes in contact with the core, the water in the primary loop is radioactive. Pumps move the water through the primary loop. The PORV is a pressure release valve. The EIW, or Emergency Injection Water, allows water to enter the system in the event of a "loss of coolant."

Heat transfers from the water in the primary loop to water in the secondary loop. The water in the secondary loop turns to steam. The steam powers a turbine, which is connected to a generator.The generator produces electricity. Pumps move the water through the secondary loop and back to where the heat is exchanged. Water in the secondary loop does not mingle with the water in the primary loop and therefore is not radioactive.

Surrounding the core and much of the primary loop is a four-foot-thick, concrete containment structure.

What Happened: Step-by-Step (Shockwave activity)

Text version of "What Happened: Step-by-Step Feedback