Last night's episode of The Simpsons revealed that the Springfield Nuclear Power Plant protects itself the same way Aperture Science does: with turrets.
Unlike at Aperture, though, the turrets are just there to guard office supplies. At the beginning of the episode, Smithers dispatches two of them with a portal gun on the way pick up a paper clip.
This raises some important questions, including "Who would be scarier to work for, Cave Johnson or Mr. Burns?" and "Where the heck did Smithers put the blue portal?"