Abnormally cold weather in late January led to operational problems at two nuclear power plants, requiring Nuclear Regulatory Commission (NRC) notification.

In one incident, which began at 3:01 am EST on January 31, the Unit 2 reactor at the Salem nuclear station in New Jersey manually tripped offline from 100% power due to icing conditions that required removing four circulating water pumps from service. Salem Unit 1 shut down one circulating water pump and reduced power to 88% as so-called "frazil ice" developed. Frazil ice forms in water that is too turbulent to freeze solid.

The Salem facility is a two-unit pressurized water reactor nuclear power plant owned by PSEG Nuclear and Exelon Generation. The pressurized water reactors were built by Westinghouse, and have a combined generating capacity of 2,275 megawatts (MW).

In the filing, the operators reported that the Unit 2 trip was "not complex" and that all systems responded normally. After the unit tripped offline, the plant's auxiliary feedwater system was activated due to low levels measured in a steam generator. Operations responded to the event and stabilized the plant, according to the report. Decay heat was being removed from the plant by the main steam dumps and auxiliary feedwater system.

The second incident occurred southwest of Chicago. At 09:10 pm on January 30, the Dresden Station heater boiler 'B' tripped while placing a second heater boiler in service. With cold temperatures, the density of the supply air increased and contributed to a greater quantity of air entering the reactor building than what was previously supplied with a heating steam system in place.

According to the NRC filing, the reactor building differential pressure (DP) fell below 0.25 inches water column vacuum. Operators initiated the plant's standby gas treatment system to assist with reactor building DP control, the filing said. As a result, reactor building DP was restored to greater than 0.25 inches water column vacuum.

Both units at the power plant were reported to be operating at 100% power after the event. Dresden consists of two GE supplied boiling water reactors with a combined generating capacity of nearly 1,800 MW. The plant is owned and operated by Exelon.