Basic Operation. The operation of a nuclear power plant is in many respects similar to that of a coal, natural gas or oil fired plant. All have a heat source that boils water.
The primary difference between these plants is the fuel used. At a nuclear plant the fuel is uranium.
The containment structures for both Units 2 and 3 are made of reinforced concrete 4 ½ feet thick. Inside the structure is an 8-inch thick steel reactor vessel which houses the reactor.
Inside the reactor, fuel rods and control rods are surrounded by pressurized water. 
Control rods are moved out from between the fuel rods starting the nuclear fission process to heat up the pressurized water flowing within the reactor.
This pressurized water is pumped from the reactor into the steam generator where the heat from the pressurized water transfers to a second source of water which then boils into steam.
The pressurized water now returns back to the reactor to heat up once again.
Traveling through the steam line, the high-pressure steam enters the turbine where the propeller-like blades inside spin to generate electricity.
Simultaneously, a loop of ocean water is used as a coolant to condense the steam back into water for recycling to the steam generator.
The electricity travels from the turbine generator to the electrical switchyard, across a series of transmission lines and substation transformers until it is delivered into consumers' homes and businesses.
The control room is the nerve center for all these aspects of electrical generation at SONGS.