The Allentown-based utility says a worker fixing a water line was evacuated after higher-than-acceptable levels of nitrogen were detected inside the room. The worker had been using a device containing the gas at the time.
PPL says workers used the plant's ventilation system and fans to return oxygen levels to normal.
They were then able to get into the room and shut off the source of the nitrogen, and the alert ended immediately after.
The company says both reactors at the plant continued to operate normally and no injuries were reported. PPL says a follow-up investigation will be done.