As the single-largest carbon-free source of electricity, nuclear power often plays a big part in plans to decarbonize energy. Many policymakers insist that nuclear must be part of any solution to avoid the worst consequences of climate change over the coming decades.
But as the debate over preserving existing nuclear plants and supporting advanced nuclear technologies continues, it is becoming clear that the relationship between nuclear power and climate change is a two-way street: While nuclear's role in the energy mix can decrease CO2 emissions and thus help governments meet climate goals, consequences of climate change are influencing nuclear power itself.
Academics expect rising air and water temperatures to cut into the operational efficiency of nuclear power plants, and an increase in severe weather patterns may necessitate more elaborate — and costly — disaster mitigation measures by plant operators. While low power prices and competition from cheap renewable energy and natural gas continue to be the most important economic headwinds against nuclear power, these climate effects could become another source of financial stress.
Financial, climate risks
An Aug. 18 report from Moody's Investors service found that credit risks for nuclear plant operators will grow over the next two decades due to climate hazards. That timeline is too long for climate change to be financially material for nuclear plant owners today, Glenrock Associates equity analyst Paul Patterson said. "I don't think it's at the front burner of people's minds," he said.
At the same time, some nuclear plants are operating on thin margins, so a single catastrophic disruption can lead to early retirement. "If it comes to the point where they will have to make substantial capital investments ... maybe it is the straw that breaks the camel's back," Patterson said.
For example, in 2018, Exelon closed the Oyster Creek nuclear plant in New Jersey, one of the longest-running plants in the U.S., rather than spend $800 million developing a new water cooling system in order to reduce the amount of heated water the plant discharged into the local bay, which environmental groups argued was harming the aquatic ecosystem.
That plant's cooling issue cannot be linked specifically to climate change, but scientists expect that over time rising water temperatures will degrade the efficiency of thermal power plants' water cooling systems. As a result, those plants may need to draw greater and greater volumes of water in order to make up for the efficiency losses, or consider switching to more expensive air cooling systems.
Other potential effects of climate change on nuclear plants include higher flood levels that surpass what plants were originally designed to handle. These and other impacts will require nuclear regulators and plant operators around the world to cooperate to properly assess risk and determine solutions, according to an article in the journal Global Environmental Politics, "The Climate Vulnerabilities of Global Nuclear Power," published last year.
"We have no standard by which these risks are being mitigated across the world," said Sarah Jordaan, assistant professor at the Johns Hopkins School of Advanced International Studies and a co-author of the article.
These are long-term problems, with the most serious impacts not projected to occur until the second half of the century. But the decisions about which nuclear reactors will be around if those impacts come to pass are being made right now. The Nuclear Regulatory Commission has already approved license extensions for two plants that will allow them to operate for a total life of 80 years, and other plants are seeking or are expected to seek similar extensions. Those licenses will not expire until into the 2050s.
The Natural Resources Defense Council has filed a legal challenge against the NRC for its decision to extend the license at Florida Power & Light's Turkey Point plant. There is currently no regulatory standard for reviewing how a nuclear plant like Turkey Point can withstand climate change impacts as it approaches 80 years of operation, according to Caroline Reiser, Nuclear Energy Legal Fellow in NRDC's Climate and Clean Energy Program.
"We are looking at a future where we know the climate will be worse, but nobody is talking about the risks for nuclear power," she said.
High water temperatures have already forced many nuclear plants in the U.S. and elsewhere to pull back from operating on occasion. Each one degree (Celsius) increase in temperature is expected to reduce a thermal power plant's output by 0.4% to 0.7% due to "reduced thermal efficiencies," leading to a global cut in thermal plant capacity by 7% to 12% by around 2050, according to a 2018 study from researchers at the University College London.
Coal-fired and natural gas-fired power plants are susceptible to the same cooling problems as temperatures rise. But nuclear plants need particularly large amounts of cooling water, using more water per unit of electricity generated compared to these other plants.
In 2019, there were 17 instances where a U.S. nuclear plant had to reduce power and stay running at a diminished level until hot weather subsided, according to an NRC spokesperson. In 2020, there were 25 such instances.
But, demonstrating that climate change is hardly linear, the NRC reported 30 of these incidents in 2018 and 60 in 2012.
About 48 GW of U.S. nuclear capacity—or about half of the current total nameplate capacity in the country—have "elevated exposure to combined rising heat and water stress," according to the Moody's report. The specific plants that Moody's identified as particularly exposed are Entergy's Arkansas Nuclear One plant, Exelon's LaSalle County Generation Station and Braidwood Generating Station in Illinois, Vistra Energy Corp.'s Comanche Peak plant in Texas, and Exelon and PSEG Power's Peach Bottom plant in Pennsylvania.
The Palo Verde plant, operated and partially owned by Pinnacle West Capital Corp. subsidiary Arizona Public Service, is also exposed due to its location in the desert west of Phoenix, but is addressing the risk around access to cooling water by sourcing water through contracts that last through 2050, the report said.
The nuclear industry is aware of the issues around water temperature and so far has not seen any impact on the capacity factors fof the U.S. nuclear fleet, which was over 93% in 2019, according to Jennifer Uhle, vice president of generation and suppliers for the Nuclear Energy Institute, the political organization for the industry.
Each nuclear plant has an "ultimate heat sink" such as a lake or river — the system that dissipates heat generated by the reactor after it shuts down and must stay below a certain temperature — as set in the plant's license from the NRC. If the temperature rose to a level where the plant cannot operate, the plant can reduce its power level or receive a license change from regulators after submitting a detailed analysis to show how the plant can safely run at the higher temperature, Uhle said.
While a warmer climate has not yet had a large impact on existing nuclear reactors, the next generation of nuclear technology is planning for a world where cooling a reactor with water is much more difficult.
The Utah Associated Municipal Power Systems (UAMPS), pursuing what could be the first small modular nuclear reactor project in the U.S., has decided to use a "dry cooling" system in which large fans dissipate heat, reducing the amount of water used by over 90%, but at the cost of cutting electric output by 5% to 7%. The project would use a reactor design by NuScale Power, that recently became the first small modular reactor developer to receive a safety approval from the NRC.
NuScale asserts that its design, in which several small reactors are installed at a single site to share infrastructure, is appealing to locations with scarce water resources because some of the modules at a site can be designated to produce electricity and steam for desalination. Climate change-driven droughts could drive many nuclear power customers to seek out dry cooling, the Nuclear Energy Institute wrote in a blog post about the technology.
Researchers are projecting that nuclear plants need to be concerned not just with water temperature, but also water levels, especially when severe weather events linked to climate change like hurricanes can cause the water level a plant was designed to handle to rise rapidly.
About 37 GW of nuclear power capacity face "higher exposure to flood risk," according to the Moody's report. These include plants along the Atlantic and Gulf coasts, as well as inland plants located on rivers, like the Nebraska Public Power District's Cooper plant on the Missouri River near the Omaha Public Power District's now-retired Fort Calhoun plant, which was inundated with flood waters in 2011, forcing the plant to shut down for almost three years.
Over the long term, severe weather and rising sea levels could make the need to solve the puzzle of where to store spent fuel from reactors more urgent.
Due to the failure to develop a central waste repository like the long-stalled Yucca Mountain facility, much of the spent fuel is stored on-site in pools within the reactor that shield the potentially dangerous radiation from the discarded fuel assemblies, or, in the case of older spent fuel, stored in dry casks. Spent fuel pools must be actively cooled to avoid a scenario like the Fukushima disaster in 2011.
A 2020 academic journal article by Jordaan and other Johns Hopkins researchers looked at what would happen to spent fuel pool sites at U.S. nuclear plants if sea levels rose by six feet — as the National Oceanic and Atmospheric Administration has projected could happen over the next 80 years.
Seven plants would be at essentially the same level as coastal water, "meaning that the water will be encroaching on the plant with regularity," the article said. One active plant — Turkey Point — and two decommissioned plant sites — Humboldt Bay in California and Crystal River in Florida — would "be partially or completely submerged by water" in this scenario. To avoid a Fukushima-like incident or the corrosion of dry casks, the article calls for "a long-term and comprehensive storage plan that is less vulnerable to climate change."
As part of the regulatory response to Fukushima, U.S. nuclear plants updated their evaluations of the potential hazards they face based on their geographic locations, including floods. In some cases, those flood reevaluations have led to changes at some plants, such as new watertight barriers, according to Uhle.
There has been controversy both within and outside the NRC regarding whether the agency has done enough to ensure plants' flooding protections are in line with the current estimated threats, which are in some cases far more severe than was thought when plants were initially licensed.
In early 2019, a divided NRC approved a rule incorporating "lessons learned" from Fukushima into regulatory requirements, but it did not contain provisions that would have required more extensive protections against the reevaluated hazards.
"Instead of requiring nuclear power plants to be prepared for the actual flooding and earthquake hazards that could occur at their sites, NRC will allow them to be prepared only for the old, outdated hazards typically calculated decades ago when the science of seismology and hydrology was far less advanced than it is today," NRC Commissioner Jeff Baran said when explaining his objection to the majority's decision.
The regulations the NRC stopped short of imposing would have forced plant operators to, in some cases, take flood mitigation steps beyond what the plant was originally designed to withstand, according to Ed Lyman, director of nuclear power safety for the Union of Concerned Scientists, who was a strong critic of the commission's move. For example, if a building containing critical safety equipment for a plant was built to stay above water in a flood, and new studies showed the potential water level was higher than previously thought, the NRC regulations would not require that building to be moved to a higher location, Lyman said.
"Even without additional concerns from climate change, the plants aren't protected today," he said.
The Nuclear Energy Institute, however, defended the NRC decision on the basis that enough safety margin has already been built into plants so that the additional requirements were not necessary.
"All existing US nuclear plants have recently assessed flooding hazards using modern methods and data which explicitly account for the potential future impacts of climate change," Uhle said. "No plants have had to move [significant safety] equipment, such as diesel generators, as a result of reevaluated flooding levels because of margins built into the original design."