Nuclear energy forms when atoms of uranium are split in a nuclear reactor through a process called fission. Small, hard ceramic particles containing uranium fuel are inserted into the reactor to produce steam, which turns the turbines in the reactor to produce electricity.
A ceramic matrix, which has pellets with approximately 3 percent Uranium (U-235), releases nuclear energy in the power plants. The pellets are replaced every three to four years, and the nuclear reactor core is kept cool by being submerged in water. The two main types of nuclear reactors are pressurized (PWR) and boiling water (BWR) reactors. In pressurized water reactors, water is heated under pressure by the nuclear reactions. Water does not boil under pressure, so the water in this type of reactor heats the water in the steam generator side. In contrast, a boiling water reactor causes the water to boil, which in turn powers a turbine. In both reactors, the water is reused. One of the main benefits of nuclear power is that it does not produce greenhouse gases as coal- or diesel-powered plants do. However, nuclear fuel is radioactive, which presents some challenges during disposal. According to HowStuffWorks, there were 443 operating nuclear power reactors spread across the planet in 47 different countries, as of March 1, 2011.