Even under a worst-case scenario, with a core meltdown , a critical mass of fuel would not be present and the fuel would burn into the ground. Refuelling can be done by removing fuel bundles from the pressure tubes and replacing them with new bundles. Heavy water contains deuterium , an isotope of hydrogen having one neutron in the nucleus. Heavy water also transfers heat from the fuel into a heat exchanger which heats ordinary water to produce steam. The steam produced is used to turn turbines which are connected to electric generators.
Condensers change the steam back into water so it can be cycled back to the steam generator.
If excess heat builds up in the calandria, the heavy water can be drained out. This causes the chain reaction to stop, because the moderator is no longer present. Supporters of the use of nuclear energy feel that it is a safe and effective way to produce energy. With the demand for energy increasing, and the problems associated with burning fossil fuels, such as acid precipitation and the greenhouse effect, they regard the use of nuclear energy as being necessary. Nuclear energy avoids some of the problems of generating hydro-electric power.