This heat is removed by passing a liquid or gas through the reactor. Carbon dioxide, water and liquid sodium are all used. In a nuclear submarine the turbines also drive the propeller. Originally it was thought that nuclear reactors would be so efficient that everybody would have free electricity. Now nuclear reactors are becoming unpopular.
People are worried about the small amounts of radioactive liquids and gases that they emit.
They a lso create quantities of highly radioactive waste products that are expensive and dangerous to store. Sometimes a reactor can get out of control a nd catch fire. This leads to a vast release of radioactive material into the atmosphere. Material from Chernobyl made sheep in Wales too radioactive to eat.