Vapor and water containing 13 different radioactive substances was found late Friday coming from a pipe in a hole workers dug to find the source of an earlier leak.
"This was a new leak," Vermont Yankee spokesman Larry Smith said in an e-mail Saturday. "The leak has been stopped. ... There is no threat to public health or safety."
The federal Nuclear Regulatory Commission also said the public faced no danger.
Spokeswoman Diane Screnci said an NRC inspector will arrive Tuesday to help the two agency inspectors assigned to the plant year-round. She said they will look at company efforts to find what caused the leak, the repair of the piping, and remediation of any effects of the leak.
"The observed short duration and small volume of leakage from the drain line appears to indicate that the event did not result in any impact to public health and safety," according to an NRC statement.
Vermont Yankee was recently off line for routine maintenance and refueling. It went back in operation and was reconnected to the New England power grid early Saturday. Smith said the plant is expected to be running at 100 percent within the week.
The leak was the second mishap connected with the startup. On Wednesday, the reactor "scrammed" - went into automatic shutdown - when a problem developed with equipment in the switchyard where it connects to the power grid.
In January, plant officials announced that radioactive tritium, which can cause cancer when ingested in large amounts, had turned up in a monitoring well. In investigating, the company spent months digging wells, only to find more tritium and other radioactive substances.
Meanwhile, plant officials acknowledged they had misled state regulators and lawmakers regarding whether the plant had underground pipes that carried radioactive substances. The radioactive tritium was found in an underground pipe.
Vermont is the only state with a law authorizing the Legislature to vote on renewing the license of a nuclear plant. In February, the state Senate voted against a bill to give the plant the green light.
Consequently, the plant could close when its current license expires in March of 2012, although supporters of Vermont Yankee hope lawmakers will take the question up again in 2011.
The 38-year-old plant's 650-megawatt reactor produces electricity used throughout the northeastern New England states. Owned by New Orleans-based Entergy Corp., the plant is located on the Connecticut River in southeast Vermont, not far from the Massachusetts border.