A tiny, remote controlled device with a video camera found a crack in a tube that may have been the source of a radioactive leak at the Indian Point 2 nuclear power plant, Westchester, N.Y., earlier this month.
Radioactive water from the reactor contaminated the clean water that is turned to steam to drive turbines.
A minute amount of the resulting radioactive steam escaped into the atmosphere, according to Con Edison, which owns and operates the plant.
An alert is the second of four ascending levels of nuclear emergency.
The crack was found by one of eight snake-like devices threaded through the thousands of tubes in the steam generator. Testing is expected to continue for several days, officials said.
"Preliminary, this leak appears to be consistent with the leak that caused the Feb. 15 event," said Stephen Quinn, vice president of Con Edison. "As somebody that's looking for a needle in a haystack, it's really nice when you find the needle."
Meanwhile Tuesday, officials from New York's northern suburbs met with the Nuclear Regulatory Commission but "did not get the reassurance they wanted" about safety at the Indian Point nuclear reactors, according to a spokeswoman.
The plant, 35 miles north of New York City declared the first alert in its 26 years of operation on Feb. 15 and is expected to remain out of operation for several weeks.