Deep Freeze Spawns Rare Frazil Ice That Hobbles Nuclear Reactor

(Bloomberg) -- The arctic blast wreaking havoc across much of the U.S. was cold enough to shut down a nuclear reactor, thanks to a rare phenomenon called frazil ice.

Public Service Enterprise Group Inc. shut one unit at its Salem nuclear plant in southern New Jersey early Thursday after intake screens froze over, restricting the flow of water needed to cool the reactor, according to spokesman Joe Delmar. A second unit at the station on the Delaware river was powered down because of the same problem.

The 60-foot (18-meter) tall intake screens rotate in and out of the water, preventing debris like floating wood from entering the plant. Under extreme conditions like this week -- overnight low temperatures at the station fell into the single digits -- the frazil ice can accumulate on the screens, blocking the flow. That caused water circulators to shut down and prompted Newark-based Public Service to take the plant offline.

“We had the heaters running, we had folks out there, and we lost the four circulators within five minutes,” Delmar said. He wouldn't say when Salem 2 is expected to go back into service.

Public Service last shut a unit at Salem for frazil ice in 2010. Regular ice that forms on the surface of lakes or rivers won't cause the same problem -- the whole screen has to freeze over, blocking all or most of the water intake.

“I would characterize this as a rare occurrence,” said Chris Earls, senior director of regulatory affairs at the Washington-based Nuclear Energy Institute. “Once it warms up a little bit, it takes care of itself.”

Temperatures in the region are expected to climb into the mid-20's Friday and a balmy 40 degrees Fahrenheit (4 Celsius) Saturday, according to AccuWeather Inc.

To contact the reporter on this story: Jim Efstathiou Jr. in New York at jefstathiou@bloomberg.net

To contact the editors responsible for this story: Lynn Doan at ldoan6@bloomberg.net, Will Wade, Patrick McKiernan