Exelon Corp declared an "alert" at its New Jersey Oyster Creek nuclear power plant due to a record storm surge, the Nuclear Regulatory Commission said on Monday.

It warned that a further rise in water levels could force operators to use emergency water supplies from a fire hose to cool spent uranium fuel rods.

The alert -- the second lowest of four NRC action levels -- came after water levels at the plant rose by more than 6.5 feet (2 metres), potentially affecting the pumps that circulate water through the plant, an NRC spokesman said.

Those pumps are not essential since the plant is shut for planned refuelling at the moment. However a further rise to 7 feet could submerge the service water pump motor that is used to cool the water in the spent fuel pool.

The spokesman said the company could use water from a fire hose to cool the pool if necessary. The used uranium rods in the pool could cause the water to boil within 25 hours without additional coolant; in an extreme scenario the rods could overheat, risking the eventual release of radiation.

The NRC said in a statement that it expected water levels would begin to abate within the next several hours.

Sandy made landfall earlier in the evening as the most powerful Atlantic storm to hit the United States, bringing an over 13-foot storm surge.

There have been about a dozen instances of alert-level nuclear incidents in the past four years, according to NRC press releases. An alert-level incident means there is a "potential substantial degradation in the level of safety" at a reactor.

The concerns over the status of the spent fuel pool at Oyster Creek were reminiscent of the fears that followed the Fukushima disaster in Japan last year, when helicopters and fire hoses were enlisted to ensure the pools remained filled with fresh, cool water.

The nuclear industry has said that the spent fuel rods at Fukushima were never exposed to the air. – Reuters