About halfway to revving the reactor back to full operation after valve repairs, operators at the Oyster Creek Nuclear Power Plant in Lacey Township shut it down manually to address another matter.

Oyster Creek nuclear plant (Excelon)

According to the Nuclear Regulatory Commission (NRC), the plant had reached about 55 percent operating capacity at 3:12 AM today, when operators detected less than optimal vacuum conditions in the condenser.

NRC spokesman Neil Sheehan said that the situation poses no immediate safety risk and is geared more toward operational efficiency.

However, he added, the agency is changing its performance indicator for unplanned scrums (shutdowns) per 7,000 hours from "green" - meaning compliance with all cornerstone objectives - to "white" - meaning low-to-moderate safety significance and  tighter federal oversight.

The condenser processes reactor-generated steam after it's passed through the turbine. Sheehan said that it operates under vacuum conditions for maximum efficiency.

Operations halted in late June to replace several valves housed in the dry well surrounding the reactor.