About 30 people gathered outside the nuclear plant near Harrisburg for a vigil, offering prayers for tsunami-devastated Japan and people forced from their homes by the crisis at the Fukushima Dai-ichi nuclear complex.
An equipment failure and operator errors led to a partial core meltdown at the plant's Unit 2 reactor on March 28, 1979. It took five days to contain the crisis.
No one was immediately hurt in the incident.
The accident had a huge impact on the nuclear industry and led to more stringent standards.
The Associated Press contributed to this report.