Waterford — A team of special inspectors from the Nuclear Regulatory Commission on Monday began investigating recurring problems with a backup cooling water pump for Unit 3 at the Millstone Power Station.

The pump is the same one that was the focus of a special inspection in February for a different problem, said Neil Sheehan, NRC spokesman. That inspection yielded a preliminary finding on Aug. 28 of a safety violation of low-to-moderate significance. Millstone is not contesting the finding and is awaiting for it to be finalized by the NRC.

The pump failed tests on July 15 and again on Sept. 10, when it started and then stopped unexpectedly, the NRC said in a news release. It was restarted but took 15 minutes to reach full speed.

“A key objective of this inspection will be to learn more about this latest malfunctioning of this safety-related component,” Bill Dean, NRC Region I administrator, said. “The repetitive problems affecting the pump continue to give the NRC concern.”

Sheehan said that because of the malfunction, the plant was placed under “limiting conditions” late last week to make repairs so that the pump would be fully operational within 72 hours. On Saturday, the time limit expired and the plant was two hours into the six-hour shutdown process when Millstone crews were able to complete the repairs and restore the pump to service, Sheehan said.

Crews worked on Saturday to make repairs and retest the pump, and the plant is now at 100 percent power output, Ken Holt, Millstone spokesman, said.

Holt said it is unusual for the same piece of equipment to be the subject of repeated special NRC inspections in the span of a few months. He noted that the problem that prompted the first special inspection was “completely different” from the more recent one, involving a bearing that had been mislabeled by the manufacturer.

While the plant has not been fined for any of the issues with the pump, Millstone owner Dominion is charged by the NRC for the cost of special inspections.

The equipment that is the subject of the inspections is a turbine-driven auxiliary feedwater pump. It is one of several that can be used to draw cooling water from Long Island Sound into the plant after a shutdown.

j.benson@theday.com

Twitter: @BensonJudy