BERWICK, Pa. — A nuclear reactor at a Pennsylvania power plant has had to be shut down for the second time in a week.

The U.S. Nuclear Regulatory Commission says Unit 2 at PPL’s Susquehanna nuclear facility near Berwick was shut down around 5:30 p.m. Wednesday because of lowered water levels in the reactor.

Officials say it was returning to service and was at 18 percent capacity when it shut down automatically. It had been shut down Sunday due to a valve problem with its main turbine.

The NRC is investigating. The plant is about 95 miles northwest of Philadelphia.