As Hurricane Sandy bore down on the East Coast, the U.S. Nuclear Regulatory Commission shut down three nuclear power plants and issued an alert for the Oyster Creek plant in New Jersey.

This is an important reminder that the United States has several low-lying nuclear plants on the Eastern seaboard, with minimal protection against inundation. Particularly with climate change increasing the likelihood of extreme weather, this hidden threat to public safety should be remedied.

The disaster at Fukushima Dai-ichi in Japan on March 11, 2011, revealed how much damage a tsunami can inflict on a nuclear power plant.

To assess the vulnerability of nuclear power plants around the world, we collected information on plant height, sea wall height and the location of emergency power generators for 89 nuclear power plants that lie next to water. We compared this to historical information on high waves triggered by various sources such as earthquakes, landslides and hurricanes.

Our findings were striking.

Several nuclear plants in Japan had inadequate protection — the average height of a historical tsunami exceeded the height of the sea wall, the plant itself and on-site emergency power generators. Fukushima Dai-ichi was not even the most vulnerable plant in Japan. We found that plants operated by the largest power companies — Tokyo Electric, Kansai Electric and Chubu Electric — were particularly unsafe.

Equally striking, our data also suggest that several U.S. nuclear power plants are unprepared for high waves. In our database, the United States came in second, behind Japan, as the country with the largest number of inadequately protected nuclear power plants.

The 1938 New England hurricane triggered a storm surge as high as 25 to 30 feet, considerably higher than waves generated this week by Sandy. A wave that tall would easily overtake many nuclear power plants on the East Coast, which on average lie about 20 feet above sea level, with minimal sea wall protection.

According to our data, the U.S. nuclear power plants most vulnerable to inundation are the Salem and Hope Creek plants on the New Jersey/ Delaware border; the Millstone plant in Connecticut; and the Seabrook plant in New Hampshire.

All of these are close to large cities: The Salem and Hope Creek plants are about 90 miles from Washington and about 35 miles from Philadelphia. The Millstone plant is about 40 miles from Hartford, Conn., and 100 miles from New York City. The Seabrook plant is about 35 miles from Boston.

As points of reference, consider that the U.S. government recommended a 50-mile evacuation radius during the Fukushima disaster, and Tokyo is about 140 miles away from the Fukushima Dai-ichi site.

The threat posed by extreme weather is not hypothetical. In 1999, waves caused by high tide and a storm surge breached the sea wall at the Blayais nuclear power plant in France, cutting off external power and knocking out several pieces of equipment.

That incident did not result in a major accident, but the outcome could have been much worse. Blayais is situated on a river adjacent to the ocean, and it was protected by a 17-foot sea wall at the time of the accident.

The Salem and Hope Creek nuclear plants similarly lie slightly inland on the Delaware River, but the plants would be threatened with inundation if wave heights exceed 11 feet.

To the credit of U.S. regulators, nuclear safety was enhanced dramatically after the Sept. 11, 2001, attacks. Backup energy sources in the United States have generally been made watertight, while those in Japan were left vulnerable — and the loss of on-site backup power was the final straw that led to the Fukushima catastrophe. In addition, surges caused by hurricanes and storms usually offer more time for preparation than tsunamis triggered by earthquakes.

There are, however, other reasons to question the safety of U.S. nuclear power plants. Our research found that the risk to plants in this country is probably understated.

Historical data regarding tsunamis are available going back about 2,000 years for East Asia and only about 350 years for the United States. Most information about historical waves comes from written records, and records are scarce for the Americas before European settlement.

The 2011 tsunami in Japan is often compared to the 869 Jogan earthquake and tsunami. Japanese regulators were widely criticized for failing to prepare for a “one-thousand-year” wave. In the United States, we don’t even know what a once-in-a-thousand-years wave looks like.

This uncertainty means we should do much more to protect U.S. nuclear power plants against potential threats. Many nuclear plants on the East Coast are perilously close to major population centers.

More sea walls should be constructed, and existing walls should be raised to minimize the danger of inundation. All backup power generators should be located well above sea level and within watertight structures. We should not wait for a major disaster to take reasonable precautions.

Phillip Lipscy is an assistant professor of political science and a fellow at the Shorenstein Asia-Pacific Research Center at Stanford University. Kenji Kushida is a research associate in Japanese studies at the Shorenstein Center, where Trevor Incerti is a researcher. This column was distributed by The Washington Post, where it first appeared.

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