Unit 1 at the Susquehanna nuclear power plant near Berwick returned to service Monday (8/5) after a four-day outage to replace a sensor that monitors vibration in the unit's main turbine.

Unit 1 shut down automatically early Thursday morning (8/1) when the sensor failed and improperly indicated high vibration in the unit's turbine, said Herbert D. Woodeshick, special assistant to the president for Pennsylvania Power & Light Co., which operates the plant.

"The unit shut down safely as it is designed to do when the monitoring equipment in the turbine, which is on the non-nuclear side of the plant, indicates even minor changes in vibration," Woodeshick said. When abnormal vibrations are detected, the turbine shuts down and that leads to the automatic shutdown of the reactor.

"In this case, an investigation showed that a failed sensor in the monitoring equipment was giving an erroneous reading," he added. Unit 1 had operated continuously for 238 days before the outage.

Susquehanna Unit 2, which returned to service Thursday (8/1) after an 18-day outage, is expected to reach full power tonight (8/5). It had operated continuously for 266 days before the outage.

The Susquehanna plant, located in Luzerne County about five miles north of Berwick, is owned jointly by PP&L and Allegheny Electric Cooperative Inc.