When Hurricane Sandy hit the East Coast, it forced three nuclear reactors to shut down, including the Indian Point 3 plant along the banks of the Hudson, about twenty-five miles north of New York City. Three more reduced their output as a precaution. At the nation’s oldest nuclear plant, the Oyster Creek facility, about thirty-three miles north of Atlantic City, operators faced an unusual event: wind, a rising tide, and the storm surge sent more water than normal into the plant’s water-intake system. At the same time, the plant, which was already down for maintenance, lost its electrical power from the grid. Operators called an “alert” that escalated the plant a step up from the lowest emergency level, and they turned to backup generators to keep cooling the reactor.

Nobody was ever in danger, and, all in all, America’s hundred-and-four nuclear reactors handled the storm with far less trouble than other parts of the power grid. Nobody was quicker to applaud the nuclear industry than the nuclear industry. “Hurricane Sandy once again demonstrates the robust construction of nuclear energy facilities, which are built to withstand extreme flooding and hurricane-force winds that are beyond that historically reported for each area,” said Marvin Fertel, president of the industry lobbying group, the Nuclear Energy Institute.

The enthusiasm was not unanimous. Arnie Gundersen, an industry critic who is the chief engineer of the non-profit Fairewinds Energy Education Corp, told Bloomberg that if Oyster Creek had been operating, flood waters just six inches higher could have knocked out pumps and caused a disaster—a claim that a spokesman for the plant’s operator, Exelon, called “unequivocally false.” Who’s right? I asked David Lochbaum, a former nuclear-plant engineer who directs the nuclear-safety project at the Union of Concerned Scientists. He said, “I disagree with Exelon’s statement that Arnie was ‘unequivocally false.’ It’s precisely that kind of closed or narrow mindedness that allowed Fukushima to happen.”

Fukushima, of course, was the site of the triple meltdown in Japan, in March of 2011, which was triggered by an earthquake and tsunami beyond anything that Japanese nuclear officials had planned for. It became the world’s largest nuclear disaster since Chernobyl. And one of the clearest lessons from Fukushima was that the vagaries of the future have a way of confounding the comforts of the past. When the nuclear industry says that it can withstand conditions “beyond that historically reported,” we should want to know a lot more, according to three researchers at the Shorenstein Asia-Pacific Research Center at Stanford. Phillip Lipscy, Kenji Kushida, and Trevor Incerti measured the vulnerability of nuclear plants built near water, by comparing their defenses to historical data on earthquakes, landslides, and hurricanes. In the Washington Post this week, they assessed the effects of Sandy and said their data “suggested 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 plants on the East Coast, which on average lie about 20 feet above sea level, with minimal sea wall protection.

They found vulnerable plants on the New Jersey/Delaware border, in Connecticut, and in New Hampshire—each less than fifty miles from a big city. (During the Fukushima disaster, the United States urged its citizens to stay at least fifty miles from the plant.) Part of the problem is that the United States is simply too young to know much about its physical past. In Japan, seismologists had warned that the Fukushima Daiichi plant was acutely vulnerable to tsunamis based on records of a wave in the year 869 that historians, at the time, described as so large that it left “no time to get into boats or climb the mountains.” The plant ignored the advice, and the rest, as they say, is history. As for the United States, the Stanford team wrote, “the risk to plants in this country is probably understated” because American records go back only about three hundred and fifty years, so in “the United States, we don’t even know what a once-in-a-thousand-years wave looks like.” One of the curious things about disasters is how short our memory is for them. After years of warnings about New York’s growing vulnerability, a flood wreaked havoc on New York subways for a few hours in 2007, and transit officials spent thirty-four million dollars on flood protections. But that was the end of it. “No additional state money has been forthcoming for an overhaul,” the Times reported this week, quoting a former transit official who said: “We’ve just been lucky. We need hardening for the risk we’ve always faced. Until things happen, people aren’t willing to pay for it.”

In endorsing President Obama’s reëlection, in part on the basis of his dedication to fighting climate change, Michael Bloomberg lent his name to the recognition that history is moving faster than some would like to admit. Coastal waters in New York rose roughly an inch a decade for the last century; they are on track to climb as fast as six inches per decade in the years to come. The regulatory fallout from the Fukushima meltdowns is still very much being felt. Last March, the Nuclear Regulatory Commission imposed new rules on plants, including reassessing flood protections and keeping emergency equipment in place to survive an indefinite blackout.

Some advocates think they fell short. (The Stanford team calls for more and higher sea walls, and other measures.) For Lochbaum, the key now is not to pretend that the nuclear grid is a house of cards—it is not, and Sandy proved that—but to prevent a non-disaster from begetting a disaster. “Some plants have already found that existing protection levels were insufficient. More homework is ongoing,” he said. “But safety I.O.U.s protect no one. We need to continue this effort and reach its destination—all shortcomings identified and fixed. Then, the N.R.C. and the nuclear industry can honestly tell the public that all reasonable measures have been taken to protect them from severe acts of nature. Until then, luck is playing a larger role—not the entire role, but a larger role than necessary.”

Read Osnos’s dispatches from Japan during the Fukushima disaster in 2011.

Photograph by Stan Honda/AFP/Getty.