"Ever since the first nuclear reactor was created, however briefly, under the stands of a football field at the University of Chicago on Dec. 2, 1942, much of the world has become reliant on nuclear energy for its electrical grids, warships and doomsday scenarios," according to the introduction to a new photo gallery at LIFE.com reproduced here in part and with permission. "But though nuclear power provides 20 percent of the United States' electrical needs, few Americans have actually been inside a reactor."

LIFE.com pulls together photos from various photographers, agencies and generations to offer a glimpse inside some of this country's most guarded and secure locations. From Three Mile Island to New York's Brookhaven National Laboratories to the San Onofre Nuclear Generating Station near San Clemente, California, these images provide a look at the work being done by men and women everyday to feed this nation's need for power.

View more photos at LIFE.com.

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