Reactors are devices used to initiate and control nuclear reactions, primarily for generating energy. They are commonly found in nuclear power plants, where they convert nuclear energy into heat, which is then used to produce steam that drives turbines for electricity generation. There are different types of reactors, such as pressurized water reactors and boiling water reactors, each with unique designs and operational methods. Safety is a crucial aspect of reactor design, with multiple systems in place to prevent accidents and manage radioactive materials effectively.