As the article below points out, stopping the nuclear fission by inserting the control rods is just one initial step. You have to keep cooling the reactor core.
If external power supply fails, New Jersey's four nuclear reactors will continue to be cooled by pumps powered by backup generators which are supposed to last for seven days.
To assure people further, newsroomjersey.com article says:
Such containment structures are tough enough to withstand the impact of a 747 airliner crashing into it.
From newsroomjersey.com (10/28/2012):
Hurricane Sandy and N.J. nuclear power plants: Keeping it cool in high winds
On Sunday, New Jersey’s four nuclear power stations, along with another dozen or so along the Eastern Seaboard,were prepped to deal with Hurricane Sandy as that massive storm crawls up the East Coast toward the Garden State.
Federal regulators require nuclear reactors to be in a safe shutdown condition at least two hours before hurricane force winds strike, according to Alec Marion, VP of nuclear operations at the Nuclear Energy Institute, an energy industry association.
Typically, plant operators begin shutting down reactors about 12 hours before winds exceeding 74 miles per hour arrive.
One of the most significant challenges in the shutting down process is keeping the reactor core cool. Stopping the fission, or atom-splitting, process can be accomplished simply by lowering control rods into the core. However, the heat-producing decay of nuclear materials continues long after fission is terminated – at high intensity for days and at progressively lower intensity for very long periods.
Because potentially dangerous heat levels persist, it is essential that cooling pumps continue to operate long after the reactor has been shut down.
When the reactor is operating, it produces abundant electricity, enough to power tens of thousands of homes and businesses and power its own cooling pumps. When it is shut down, the reactor requires electricity produced at other, distant generating plants to power its cooling pumps. If hurricane force winds, or some other phenomenon, damage the power lines connecting a shut-down nuclear station to the power grid, there are emergency generators located at each nuclear station that can supply power to the cooling pumps.
At the Fukushima nuclear disaster in Japan last year, the plants were cut off from the national power grid and the emergency generators were also knocked out of service by a powerful Tsunami, a gigantic wave of sea water created by a nearby earthquake.
Nuclear operators such as Exelon and PSE&G in New Jersey seek to locate and protect emergency generators and other key equipment so that they are unlikely to be affected by strong winds or unusually high tides. Federal regulations require that companies keep a minimum seven days of fuel on site to keep generators operating.
There are four nuclear generating stations in Jersey: Salem I, Salem II, and Hope Creek all situated next to one another in Salem County on Delaware Bay; and Oyster Creek located in Lacey Township near the Jersey Shore. Each of these reactors is enclosed in a containment building, a protective shell of four-foot-thick concrete designed to keep radioactive materials from escaping in case of emergency. Such containment structures are tough enough to withstand the impact of a 747 airliner crashing into it.