Unit 1 back online at Limerick nuclear plant [updated]

Unit 1 at Exelon Nuclear's resumed operation at about 3:15am today, a representative for the company said by telephone this morning.

Unit 1 had been offline since a "scram" at 10:21am Friday. The unplanned shutdown took place less than 24 hours after the plant reactivated Unit 2, which had shut down because of a faulty turbine valve actuator on May 29.

"Limerick operators and maintenance technicians worked around the clock performing numerous tests to identify and ensure the problem associated with the turbine coming offline was due to an instrumentation anomaly," the company said in a statement.

"There was no risk to the public, and operators restored the unit to service safely and without incident," the company said.

A reactor status page maintained by the Nuclear Regulatory Commission (NRC) showed Limerick Unit 1 at 20 percent power early this morning.

Asked about the nature of the "instrumentation anomaly," NRC spokesperson Neil Sheehan said the circuitry used to protect the turbine falsely indicated that the turbine was operating abnormally, triggering an automatic system that shut down the reactor for its protection.

"There was not actually anything wrong with the main turbine. Rather, there was an incorrect signal indicating that was the case," Sheehan said via e-mail.

The company said in a second statement issued this morning that "corrective measures were implemented to prevent recurrence" of the problem.