WASHINGTON  The discovery of water flowing across the floor of a building at the Indian Point 2 nuclear plant in Buchanan, N.Y., traced to a leak in a buried pipe, is stirring concern about the plant’s underground pipes and those of other aging reactors across the country.

A one-and-a-half-inch hole caused by corrosion allowed about 100,000 gallons of water to escape from the main system that keeps the reactor cool immediately after any shutdown, according to nuclear experts. The leak was discovered on Feb. 16, according to the plant’s owner, Entergy Nuclear Northeast, a subsidiary of the Entergy Corporation.

Entergy and the federal Nuclear Regulatory Commission emphasized that the Indian Point reactor could still have been shut down safely with either of two other backup systems, although operators generally avoid using both.

They also stressed that the supply pipe was quickly repaired after the leak was found and that the water itself, which is cleaner than tap water, posed no environmental threat. Yet the leak’s discovery has prompted Entergy and the regulatory commission to begin studying how the chief system for cooling during shutdowns, so important that the Indian Point 2 has three pumps in place to do the same job, could be endangered by the failure of a single part.