COLUMBIA, S.C. - Water with traces of a radioactive hydrogen isotope has leaked at a nuclear power plant in South Carolina, but federal regulators said Thursday workers and the public were not at risk.

The leak was reported Wednesday at the Oconee Nuclear Station, a three-reactor site near Seneca run by Duke Energy. Water was being transferred from one chemical treatment pond to another when it leaked and began seeping from the ground, according to the U.S. Nuclear Regulatory Commission.

Officials did not say exactly how much water leaked, saying only that it was more than 100 gallons of water. Duke spokeswoman B.J. Gatten said the company voluntarily reported it to state and federal agencies.

All the leaked water was contained on site, Gatten said. And the level of tritium in the water is well below limits that would make it dangerous to drink, according to regulators.

"There's no implication for either worker safety or public safety," NRC spokesman Roger Hannah said.

Tritium is a byproduct of atomic fission. Drinking water containing high levels of tritium can increase the risk of developing cancer, according to the U.S. Environmental Protection Agency.

Savannah River Site Watch, a group focusing on nuclear issues, called on Duke to figure out why the leak happened and prevent future spills.

"Of greater concern than a single tritium spill is the question of why tritium is leaking from the reactors and what Duke is doing to halt all such leakage from piping on the site," group director Tom Clements said in a news release. "Immediate steps must be taken to halt leakage of tritium from the reactors into the environment."

Last year, two tritium leaks were reported at another Duke-run facility, Catawba Nuclear Station in York County. In both instances, NRC officials said the tritium levels were less than half the federal limit for safe drinking water.

The pipes at Oconee will be inspected and repaired, Gatten said.

One of Oconee's three reactors is currently shut down for a planned refueling outage. Its other two reactors are currently operating normally, Gatten said.