Documents show the Nuclear Regulatory Commission gave the Vermont Yankee nuclear plant a new license last month knowing that electrical cables to key safety systems had been submerged in water for long periods of time.
The nuclear watchdog group New England Coalition, says the issue has new urgency since the nuclear disaster in Japan was caused by tsunami flooding that knocked cooling systems out of service at the Fukushima nuclear plant.
NRC documents show the agency has been concerned about submerged electrical cables at U.S. nuclear plants for years. But an agency report issued in December said it would not require any changes.
The coalition raised the issue before the NRC decided last month to give Vermont Yankee a 20-year license extension.