Answer to Question #8770 Submitted to "Ask the Experts"

In the event of an atmospheric detonation of a nuclear device, are domestic nuclear power plants (I live within 18 kilometers [km] of one) able to withstand the electromagnetic pulse without (1) losing their facility controls resulting in a meltdown or (2) overloading the facility when the output demand drops to zero, resulting in a meltdown?

At a nuclear power plant, the control systems for safety-related equipment are located in robust concrete structures designed to shield the equipment from external effects. In the unlikely event that an electromagnetic pulse were to cause a control-system disturbance, the equipment is designed to "fail safe," meaning that the reactor would shut down automatically and the safety-related equipment needed for core cooling would automatically actuate. 

The electromagnetic pulse would likely cause a loss of off-site power due to the grid disturbance and effects on other generating plants on the electrical grid. While nuclear power plants utilize power from the grid to support plant operations, they also have multiple on-site backup power supplies that are designed to automatically start and power safety-related equipment if power from off-site is interrupted. As with all electric generation plants, nuclear power plants are designed to accommodate a sudden loss of electrical load. The reactor protection system senses the power being generated by the station and the power being supplied to the electrical grid. If there is a mismatch, the reactor is automatically shut down. Separate protection circuits would also cause the turbine-generator to shut down, which would send another signal to shut the reactor down.  

After a nuclear plant shuts down, cooling water is provided by auxiliary feedwater systems that would start automatically following the reactor shutdown. These systems can also be operated manually, if necessary, and the systems contain multiple components that use separate means of operation to ensure that the single failure of any component would not prevent the system from operating as designed. The cooling water supplied by the auxiliary feedwater systems absorbs the heat from the core and is turned to steam. Automatic control systems normally transfer the steam to a condensing tank, removing the heat from the reactor. In the event that the normal steam control system is not available, main steam safety relief valves would open if necessary to remove heat from the reactor core. These valves are passive, needing no power or controls to operate. These same systems would be used to handle other events, such as weather, fires, aircraft impact, etc. Because of the design of these safety systems and others, including the containment structure surrounding the reactor, there should be no releases to the environment from this type of event.

Eric Goldin, CHP
Greg Guliani