Final answer:
The safety valve is a device that relieves excessive steam pressure, usually found on top of a steam boiler to prevent accidents by letting out steam when the pressure gets too high.
Step-by-step explanation:
The safety valve is a device used to relieve excessive steam pressure when it builds up in a system. It is typically located on or near the top of a steam boiler. For example, in a pressurized water reactor used for generating electricity, the control rods adjust neutron flux to maintain criticality. Should the reactor overheat and boil the water to steam, these control mechanisms, including the safety valve, ensure the chain reaction is terminated to prevent accidents. Steam pressure can also be relieved in household devices like pressure cookers, which is a similar yet simpler application of pressure and safety control.