Climate change creates new flooding risks for U.S. nuclear reactors safety

Extreme weather disasters, especially floods, are on the rise (see Two seminal Nature papers join growing body of evidence that human emissions fuel extreme weather, flooding). Last year, we had Tennessee’s 1000-year deluge aka Nashville’s ‘Katrina’. And Coastal North Carolina’s suffered its second 500-year rainfall in 11 years.

Craig Fugate, who heads the U.S. Federal Emergency Management Agency, said in December, “The term ‘100-year event’ really lost its meaning this year” (see Munich Re: “The only plausible explanation for the rise in weather-related catastrophes is climate change”).

A couple weeks ago, I asked how many U.S. nuclear plants are vulnerable to a tsunami and/or a 500-year 100-year flood? Here a very initial treatment of the flood vulnerability issue.

The following article by Sean Pool, Elaine Sedenberg and Matt Woelfel is cross-posted at Science Progress.

As the situation at Japan’s damaged Fukushima Daiichi nuclear facility continues to worsen, policymakers in the United States are taking the opportunity to review the safety policies for our aging nuclear reactors.


Japan’s recent 9.0 magnitude earthquake and the tsunami it caused together killed 9,737 people and left an additional 16,501 missing. The destruction left millions homeless and caused almost $200 billion in damage.

These natural disasters caused severe damaged to 4 of the 6 reactors at the Fukushima Daiichi nuclear plant, leaving them without functioning primary, secondary, or tertiary cooling systems. The resulting partial meltdown of the core at one reactor and of a waste fuel rod storage tank in another has resulted in the release of radioactive material into the atmosphere, soil, and water, forcing the evacuation of what was at first a 12-mile radius and now a 19-mile radius surrounding the facility.

Though reactors in the United States are built to strict safety standards, they are nevertheless vulnerable to any number of natural and manmade disasters, from earthquakes and tsunamis to flash floods, droughts, and hurricanes. U.S. reactor safety standards have been effective in preventing catastrophe, though a recent report highlights 14 “near misses” where improperly implemented safety protocols nearly caused major problems. More troublingly, many of these standards were based on an understanding of our climate system that is now 40 years out of date. Today we know that climate change is making floods, droughts, and hurricanes stronger and more frequent, which means we must ask whether our safety standards, even when followed perfectly, are enough to prevent disaster.

As the Nuclear Regulatory Commission conducts its review of U.S. nuclear safety in the wake of the Fukushima meltdown, they need to be sure they are doing a thorough review of all possible risks, and should not ignore recent science about how climate change could increase those risks.

Current state of US nuclear plant safety

The United States currently has 104 functioning power reactors at 65 sites around the country, roughly a quarter of which use the same “Mark 1” containment vessel design used in the failing Japanese reactors. They supply roughly 20 percent of the country’s total electricity needs. Nuclear plants demand large sources of water in order to cool and control the core temperatures of the reactors that power them. To meet this inevitable requirement, nuclear plants are situated in low-lying areas near rivers and lakes, and many others are built on the coasts. This proximity leaves these plants vulnerable to floods and other water-related disasters. (See our map below.)

(click for a high res version.)

Many regulations are already in place to ensure that nuclear energy remains safe from floods, surges, tsunamis, and droughts. The Nuclear Regulatory Commission, or NRC, oversees licensing applications, reactor specifications, and radioactive waste disposal. The Advisory Committee on Reactor Safeguards, or ACRS, also reviews the adequacy of proposed safety standards and creates individualized specifications to withstand the projected worst-case disasters for each plant location. Nuclear facilities are initially granted a 40-year license that must be renewed after 20 years. They then have the opportunity to extend their license for additional 20-year increments.


The problem is that our nuclear reactors are all old. Thirty years old on average in fact, since political will for new nuclear reactors has weakened since the 1979 Three Mile Island incident. Seven operating reactors have eclipsed their original 40 year lifespans and been permitted to operate for another 20 years. This makes them vulnerable to problems, like stronger floods caused by climate change, about which we had considerably less knowledge three to four decades ago when the plants were built.

Climate change will increase certain risks

Climate change will compound existing weather-related risks. In the years since most of our nuclear reactors were built, we’ve learned that climate change is increasing the risk profile of many kinds of extreme weather. Two scientific studies published this year in Nature have supported this. Large and destructive floods once thought likely to happen only once in 100 years on average are now expected to happen every 20 years: a five-fold increase. Similar trends hold for droughts, hurricanes, and wildfires. Droughts and heat waves can impact nuclear reactors because they use large amounts of water in the power generation process. If water levels drop too low, or the temperature of adjacent water bodies rises too high, the ability of the reactors to operate can be impaired. Sea-level rise is also of particular concern, since many of our nuclear facilities are located on the coast.

In response to this growing awareness of disasters that can result from climate change, the International Atomic Energy Agency, or IAEA, released a safety guide in 2003 detailing flood-related hazards to nuclear power plants on coastal and river sites. The safety guide suggests that newly constructed plants should account for several consequences of climate change over the lifespan of the plant:

  • Rise in mean sea level: 35–85 cm
  • Rise in air temperature: 1.5–5 °C
  • Rise in sea or river temperature: 3 °C
  • Increase in wind strength: 5–10 percent
  • Increase in precipitation: 5–10 percent

Higher sea levels, in combination with the warmer air, water, and sea temperatures will produce larger, stronger waves, increase the flow rate of rivers, and alter the dominant wind patterns, according to the report. The IAEA recommendations offer a good framework for assessing siting of new nuclear facilities, but current safety standards at the 104 operating nuclear reactors in the United States remain in question. Are they sufficient to deal with the increased risks caused by climate change?

This is a question we must answer, and soon. As we have written at Science Progress before, climate change creates considerable uncertainty for businesses and governments who must make difficult decisions that will affect the way we do business over the next 10, 20, or 40 years. In making long-term decisions about policy and business, decision makers need to have all the data they can get. The problem is that extremely rare events by definition provide us with little opportunity for study, even though their impacts can be catastrophic.


The seawalls at the Fukushima Daiichi reactor complex, for example, were designed to withstand an 18-foot wave, though the tsunami that caused the eventual nuclear meltdown was estimated to have been more than 40 feet high. Japanese engineers simply didn’t have enough data to accurately predict just how big a tsunami could be. Could this happen in the United States? For reference, the San Onofre reactor in California is built right on Pacific coast, with a sea wall of only 23 feet.

The bottom line is that sometimes, what we think to be a “worst case” scenario is not really the worst case. Just because there is uncertainty about how climate and weather will affect our nuclear reactors does not mean we should ignore the issue. Quite the opposite; it would be negligent to ignore this uncertainty as we continue to assess our nation’s nuclear safety standards.

The Nuclear Regulatory Commission has taken some steps to incorporate current climate science into its standards, but it has not gone far enough. In 2009, the NRC released an information notice that suggested plants re-evaluate flood protection measures, but they did not require action. To make matters worse, the guidelines in use were established in 1977, with the latest updates occurring in 1984. As the Nuclear Regulatory Commission conducts its review of U.S. nuclear safety in the wake of the Fukushima meltdown, they need to be sure they are doing a thorough assessment of all possible risks, and should not ignore recent science about how climate change could increase those risks.

Countries around the world have already begun to take increased risks from climate change into account in their nuclear safety protocols. It’s high time the United States follows suit. The United Kingdom has insisted that new nuclear plants demonstrate countermeasures taken to prevent damage from more extreme floods, France has begun reviewing all 58 of its reactors to check how much flooding they can handle, and Austria has even called for nuclear “stress tests” similar to those banks undergo. Germany has even ordered all reactors built prior to 1980 (all American reactors would qualify) to be shut down for three months.

The disaster in Japan has afforded the United States the opportunity to re-examine the safety of its own fleet of nuclear reactors. Given how often we underestimate the “worst-case” scenario, this is an opportunity we cannot afford to miss.

— Sean Pool is Assistant Editor for Science Progress, Elaine Sedenberg is an Intern with Science Progress, and Matt Woelfel is an Intern with CAP’s Energy Opportunity team. The authors would like to thank Kate Gordon, Richard Caperton, and Valeri Vasquez, and Evan Hansleigh for their invaluable contributions to the article.

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