Indian Point Nuclear Plant
While there are hazards at Indian Point, they differ from those at the Fukushima reactor in Japan. Reuters

Governor Andrew Cuomo has said that he favors shutting down the nuclear reactors at Indian Point, largely due to the possibility of an earthquake in the area that might damage the reactor.

The issue becomes more urgent in the wake of the disaster at the Fukushima Daiichi nuclear power plant in Japan, which was hit by a magnitude 9 earthquake and a tsunami that disabled the plants cooling systems, putting the reactor cores and spent nuclear fuel in danger of melting down and spreading radioactive contamination into the environment.

There are several differences between the facility at Indian Point and the Fukushima reactor, and those differences show that while Indian Point, like other nuclear power plants, has risks, they are different risks from those at Fukushima.

Different Designs
The Fukushima Daiichi plant consists of a set of boiling water reactors. There are six reactor units, and all work on the same principle. Water is pumped into the reactor vessel and heat from the nuclear reactions in the fuel boils it, creating steam which is then used to power a turbine. The water is then pumped into a condenser, where it is cooled down and re-used in the reactor.

Indian Point is a pressurized water reactor, or PWR, a much more common design in the U.S. In a PWR there are two coolant circuits. One pumped directly through the reactor core, and kept at high pressure, typically 150 atmospheres. Ordinarily water boils at 100 degrees C (212 F) but pressurizing it raises the boiling temperature and allows for more efficient cooling. The high-pressure circuit runs from the reactor into a steam generator, which is filled with water at more ordinary pressures. The water in the steam generator boils and runs the turbines. The water from the two circuits never mixes.

One of the advantages of a PWR is that the cores are more stable. This is because water also slows down the neutrons produced by the uranium fuel in the reactor, allowing the nuclear reaction to sustain itself and generate heat. If the water boils away, there are fewer hydrogen and oxygen atoms for the neutrons to collide with, which means they have a tougher time sustaining the chain reaction in the core.

In the case of a problem with the coolant water at Indian Point, the nuclear reactions can actually slow down and generate less heat, reducing the chances for meltdowns. The two separate cooling circuits also means that the water in the second loop is not contaminated by radioactivity, whereas in a boiling water reactor it is.

Another design difference is the control rods. In Fukushima and other reactors of the same design, the control rods are inserted into the core from the bottom. That means that if power is lost there isn't any way to get the control rods in. The Indian Point reactors are designed with the control rods held up by electromagnets. If power is lost (as it was in Fukushima) the rods simply fall into place. The control rods absorb neutrons and slow the reactions in the core down.

This doesn't mean that Indian Point will be free from problems. The high pressure in the first coolant circuit means that the pipes and vessels have to be much stronger. The steel, after exposure to radiation, becomes brittle, and has to be replaced periodically if the plant isn't to be rebuilt completely or shut down.

Indian Point also uses water from the Hudson as part of its cooling system. The river water is taken up to cool the water used in the condenser for the secondary coolant circuit. Thus far Indian Point has been locked in a battle with local environmental officials over permits to use the water, which is discharged at a higher temperature that can stress local wildlife.

Spent Fuel
One of the biggest problems at Fukushima has not been the actual reactor cores, but the spent fuel. In four of the reactors at Fukushima the pools, which are housed near the top of the reactor vessel, had to be supplied with water to cool them down. When the power went out the pumps that sent the water there were out of commission, raising the possibility that the spent fuel at reactor number 4 would release radionuclides into the air.

The pools that house the spent fuel at Indian Point also have to be kept full of pumped water. A failure of the coolant system there, or a leaking fuel pool, could cause result in spent fuel overheating and releasing radionuclides into the environment. One advantage Indian Point has is that the fuel rods, generally speaking, are older than at Fukushima, meaning they are less radioactive.

The biggest issue around Indian point is leakage of the fuel pools into groundwater. In 2006 the New York Times reported finding traces of radioactive contamination in the groundwater. Among the elements found were tritium and nickel-63. At the time the Nuclear Regulatory Commission noted that the groundwater was not used in any drinking water sources. (The Hudson River is not used for drinking).

Seismic Hazard
The Fukushima reactors were hit by a 9.0 magnitude earthquake, and in fact the reactors themselves suffered only minor damage. It was the tsunami that knocked out the generators that supplied the water. Tsunamis are not an issue for Indian Point as the plant is located far from the coast.

Entergy, the operator of Indian Point, says the facility is designed to handle anything up to a magnitude 6.1 temblor. The most intense earthquake recorded in New York was a magnitude 5.8. Indian Point would be able to handle a quake 2.8 times as powerful. The earthquake in Japan, at magnitude 9.0, beat out the most powerful in New York by a factor of 63,000.

While Indian point sits near a fault line - which was only discovered after the plant was built -- the USGS says it is not likely that any quake as powerful as the one that hit Japan will hit the area. That said, a 2008 study found that a magnitude 7 temblor happens once every two to three thousand years. In addition, earthquakes that are smaller than their west coast counterparts can cause damage over a wider area in the northeast, largely because the rock is colder and denser and transmits energy more efficiently. The NRC is studying the issue of seismic hazards, though it has thus far said there is no immediate need to retrofit many nuclear plants.