The spill at the Salem 1 nuclear plant in Lower Alloways Creek Township, N.J., was confined to the containment building, with no threat to the public or workers, the commission said in a statement Friday.
The plant was shut down Thursday evening, The (Newark) Star-Ledger reported. It remains out of service.
The leak, determined to come from a pressurized spray valve, was recorded at 4 gallons per minute, exceeding the operating requirement of 1 gallon per minute, forcing the shutdown, said Neil Sheehan, an NRC spokesman.
In a statement, Joe Delmar, a spokesman for plant operator PSEG Nuclear, stressed there was no release of radioactivity into the environment, and added a repair plan was in progress, although he did not provide a time frame for the plant's return to service.