Operators at the Susquehanna nuclear power plant shut down Unit 1 early Wednesday morning (7/8) to make modifications to monitoring instruments.

"The instruments are 16 acoustical monitors that signal whether the safety relief valves in the unit's reactor are open or closed," said Herbert D. Woodeshick, PP&L, Inc.'s special assistant to the president for Susquehanna. One of the monitors intermittently is showing that a valve is open when it is not.

"We know the signal is false because separate monitoring devices show the valve to be closed," Woodeshick said.

The safety relief valves would release steam from the reactor to the unit's suppression pool in the event of a sudden unplanned shutdown of the reactor. When the unit is shut down normally, steam pressure is reduced gradually, and the safety relief valves are not needed, Woodeshick said. The suppression pool, located beneath the reactor, provides water for emergency cooling systems.

In addition to the work on the acoustical monitors, crews will perform plant maintenance that only can be done while the unit is out of service, he added. Unit 2 at the plant is continuing to produce electricity.

The Susquehanna plant, jointly owned by PP&L, Inc. and Allegheny Electric Cooperative, Inc., is located about five miles northeast of Berwick along Route 11.