How we generate electricity
Like an oil fired or coal fired power unit, a nuclear power unit produces steam which actuates the turbines. In oil and coal-fired units, the heat comes from burning oil or coal. In a nuclear power station, heat is generated in the reactor core. The heat, which brings the water to boil and generates steam, comes from the energy that is released when the atomic nuclei are split (nuclear fission).
All three reactors at Oskarshamn are Swedish designs from ABB Atom (today a subsidiary of Westinghouse). This type of reactor is known as a Boiling Water Reactor (BWR), or as a Light Water Reactor (LWR). The primary pipe systems in the unit are sealed and the same water is therefore constantly circulating the system.
The water is pumped through the reactor vessel, where it is heated until it boils. The steam generated passes through pipes from the vessel to the turbine. The reactor vessel is about 20 meters high, 5 meters in diameter and is made from high grade steel, 15 centimeters thick.
Fuel elements and control rods
The water is heated by the energy released by nuclear fission in the fuel elements. The chain reaction in the reactor core is controlled by inserting control rods between the fuel elements. These control rods are an essential part of the extensive safety systems at the Oskarshamn power plant.
Steam turbine and electric generator
The hot steam from the reactor vessel drives the turbine. The rotating motion of the turbine is transmitted via a shaft to a generator which transforms the motion into electricity.
When the steam has been used in the turbine, it goes to a condenser, where the steam is cooled down into water again. This cooling is achieved by sea water, which is pumped through the condenser in a separate system of pipes. Consequently, the reactor steam never comes into direct contact with the sea water. With all three Oskarshamn units running, a total of 90 000 litres of water passes through the condenser every second. The sea water temperature rises by approximately 10 degrees Centigrade on its way through the condensers.
The control room is the heart of the process and the control room operators consequently have to meet high standards. The average OKG employee spends 2 percent of his or her working hours undergoing training. For control room operators, the figure is 8 percent. An important part of operator training is carried out in full scale simulators.