In 2011, a tsunami sent waves as high as 49 feet crashing over the seawalls surrounding the Fukushima Daiichi Nuclear Power Plant in Japan, causing meltdowns at three of the plant's reactors. After that incident, the United States Nuclear Regulatory Commission (NRC) ordered nuclear facilities in the U.S. to review and update their plans for addressing extreme seismic activity and potential flooding from other events, such as sea level rise and storm surges. Those plans aren't due until March 2015, which means that many plants have yet to even lay out their their potential vulnerabilities, let alone address them.
During the 1970s and 1980s, when many nuclear reactors were first built, most operators estimated that seas would rise at a slow, constant rate. That is, if the oceans rose a fraction of an inch one year, they could be expected to rise by the same amount the next year and every year in the future.
But the seas are now rising much faster than they did in the past, largely due to climate change, which accelerates thermal expansion and melts glaciers and ice caps. Sea levels rose an average of 8 inches between 1880 and 2009, or about 0.06 inches per year. But in the last 20 years, sea levels have risen an average of 0.13 inches per year -- about twice as fast.
And it's only getting worse. The National Oceanic and Atmospheric Administration (NOAA) has laid out four different projections for estimated sea level rise by 2100. Even the agency's best-case scenario assumes that sea levels will rise at least 8.4 inches by the end of this century. NOAA's worst-case scenario, meanwhile, predicts that the oceans will rise nearly 7 feet in the next 86 years.
But most nuclear power facilities were built well before scientists understood just how high sea levels might rise in the future. And for power plants, the most serious threat is likely to come from surges during storms. Higher sea levels mean that flooding will travel farther inland, creating potential hazards in areas that may have previously been considered safe. During Superstorm Sandy, for example, flooding threatened the water intake systems at the Oyster Creek and Salem nuclear power plants in New Jersey. As a safety precaution, both plants were powered down. But even when a plant is not operating, the spent fuel stored on-site, typically uranium, will continue to emit heat and must be cooled using equipment that relies on the plant's own power. Flooding can cause a loss of power, and in serious conditions it can damage backup generators. Without a cooling system, reactors can overheat and damage the facility to the point of releasing radioactive material.