Uranium atoms are split to produce energy. This energy heats water which passes through a steam generator and then back to the reactor. Steam is formed from a separate water volume in the steam generator. The steam pushes against the blades of a turbine causing them to turn. An electric generator is attached to the turbine; as the turbine spins, electricity is produced.
The uranium fuel is in long metal fuel rods (1). Each rod is 12 feet long. There are 208 fuel rods in a fuel assembly. The reactor core (2) is made up of 177 fuel assemblies. The reactor core is inside the reactor vessel (3). The reactor vessel is filled with purified water.
Control rods (4) located on top of the reactor start and stop the chain reaction that produces heat. When the rods are withdrawn, the nuclear chain reaction occurs, producing heat.
Davis-Besse is a pressurized water reactor. This means that the water inside the reactor is under pressure so the water will not boil. The water temperature is heated as it passes through the core. The water then travels along tubes through the steam generator (5) and back to the reactor. This is known as the primary loop (green). After it has passed through the steam generator, the water has “cooled” down. The average temperature in this cycle is maintained at 582°F.
When the water passes through the steam generator, its heat is transferred to the secondary loop (blue). The heat is transferred, without the water in the primary loop and secondary loop ever coming in contact with the other. These are known as closed loops. The water in the secondary loop boils to steam in the steam generator. This steam flows to the turbine generator (6). It is here that the steam’s energy is made into electricity.
When the steam leaves the turbine, it comes in contact with pipes carrying cooling water. As the steam cools, it changes back into water. The third loop (yellow) contains the water that is cooled by the large cooling tower (7) located at Davis-Besse. The water vapor you see rising from the cooling tower IS NOT radioactive.
After about 24 months of operating time, some of the used fuel is replaced. This is known as refueling. During the refueling, about one-third of the used fuel assemblies are replaced with fresh fuel.
The used fuel is placed in a reinforced and steel-lined concrete pool of water. In early 1996, the oldest used fuel assemblies were removed from the Davis-Besse pool and placed in a dry fuel storage system.
In this system, used fuel is sealed in a metal container. The container is then housed in a thick concrete structure. The system location is in a secured area at the Davis-Besse plant.