Vermont ? Radioactive tritium, a carcinogen discovered in potentially dangerous levels in groundwater at the Vermont Yankee nuclear plant, has now tainted at least 27 of the nation’s 104 nuclear reactors — raising concerns about how it is escaping from the aging nuclear plants.

The leaks — many from deteriorating underground pipes — come as the nuclear industry is seeking and obtaining federal license renewals, casting itself as a clean-green alternative to power plants that burn fossil fuels.

Tritium, found in nature in tiny amounts and a product of nuclear fission, has been linked to cancer if ingested, inhaled or absorbed through the skin in large amounts.

The Nuclear Regulatory Commission said Monday that new tests at a monitoring well on Vermont Yankee’s site in Vernon registered 70,500 picocuries per liter, more than three times the federal safety standard of 20,000 picocuries per liter.