A circuit is a closed loop through which electric charges can flow. If the loop is opened, then it is called an open circuit and charges no longer flow. A switch is commonly used to open and close a circuit. If a wire breaks, the connection between the wire and another part of the circuit fails, or if a lamp burns out (its filament breaks) then the circuit is opened and there is no current.
The Indian Point Energy Center on the Hudson River in New York state uses nuclear fission to heat water and produce steam. Except for the fuel source, nuclear power plants operate just like any other type of power plant.