Operators powered down unit 1 at the Salem nuclear plant in New Jersey Thursday because of a small leak in the reactor coolant system.

According to a report filed with the Nuclear Regulatory Commission, leakage at 4 gallons per minute necessitated the manual shutdown at about 4:30 p.m. The plant also reported that pressure in the primary containment structure briefly exceeded regulatory limits. No emergency was declared, and NRC records indicate the reactor was fully powered down on Friday.

After an initial inspection, plant workers suspected the leak originated in packing on a pressurizer spray valve in the RCS, according to the NRC. The valve had been replaced and the air operator rebuilt during a refueling outage this spring.

PSEG operates two 1,100 megawatt Westinghouse reactors at the Salem plant. It is part of the Artificial Island complex south of Wilmington, Del., that also includes the Hope Creek plant.