MONTPELIER, Vt. – Unplanned shutdowns an hour apart at nuclear plants in Vermont and New York — one due to a small leak of radioactive water inside the plant, the other due to a transformer explosion — show the challenge of managing aging nuclear plants, an expert said.

Both plants are 38 years old and owned by New Orleans-based Entergy Corp. No one was hurt at either plant and each was expected to be back online quickly.

In Vermont, Entergy said the leak’s source was a 2-inch metal access plug on a pipe that had been welded over in 1972. The pipe was part of a closed-loop system that feeds water to the nuclear reactor, where it is heated and then sent to spin turbines that make electricity, said plant spokesman Larry Smith.

The weld was leaking about 60 drops a minute, he said. Repairs were expected to take 24 hours, he said.

It was too soon to tell what caused the transformer explosion Sunday at the Indian Point 2 reactor, built in 1972 north of New York City. No one was hurt and no radioactive material released. The explosion was outside the nuclear portion of the plant.

David Lochbaum, director of the nuclear safety program for the Union of Concerned Scientists, said both problems were probably due to their age. As plants get older, they face more and more such challenges, said Lochbaum.

The Nuclear Regulatory Commission called the two shutdowns a coincidence and said agency inspectors were monitoring the repair plans at the Vermont Yankee plant in Vernon and at Indian Point 2, where a spare transformer was on site.