The Oyster Creek nuclear power plant remains on "alert" status even as the rising waters that caused problems with the reactor's pumping system continue to abate, a spokesman for the U.S. Nuclear Regulatory Commission said Tuesday. Despite the "alert" status, which is the second least serious level, the reactor, located in Lacey Township, Ocean County, is considered "safe," he said.

The Oyster Creek facility was impacted by the storm in three ways - rising water in intake canals affected pump performance in an intake structure; a power outage in the area also hit the plant, causing it to switch to back up generator to power the facility, and winds and weather took out 21 of about 50 warning sirens positioned in a 10-mile radius of the plant, said spokesman Neil Sheehan.

But the brunt was not as bad as it could have been because the plant was already on shutdown mode, having been closed for previously scheduled maintenance and refueling. Sheehan said such closures are routine and occur about every 18 months.

Even in a shutdown, he said, water needs to be pumped to keep spent fuel in storage areas cool. "That's still running around the clock," he said.

Plant operators "started to see water pile up in the intake structure," he said. When the water reaches a level of 4.5 feet, Sheehan said, federal regulations require the plant to declare an "unusual event." That happened at about 4 in the afternoon on Monday. By about 8:45 p.m., waters had risen to above 6 feet, the threshold for triggering an "alert." At 6.5 feet, Sheehan said, pump operations begin to be affected. Waters reached a peak of 7.4 feet at 12:45 a.m. Tuesday.

Sheehan said that if pumps are affected, backup portable generators can be used, but he is not sure if they were deployed. One reason may be that the first pumps affected by rising water would be those used to cool the condenser, cooling steam generated by an operating plant, but the plant was not operating. By 6:12 a.m., the waters had receded to 6.5 feet and levels were still dropping.

Even though the reactor generates power, it also uses power from the grid for operations. When the storm knocked out the reactor's power, the diesel operated backup generator kicked in, Sheehan said. But because the plant was in shutdown mode, not as much power was required, he said.

The warning sirens are a relatively low priority, Sheehan said, particularly since the plant is in shutdown mode. They are being repaired as crews handle various storm-related issues. When warning sirens are not working, the backup plan is for first responders to drive through the area to alert people to any dangers.