Nuclear energy provides about 10% of the world's electricity from about 440 power reactors.
Nearly 20 percent of the electricity in the United States today comes from nuclear power. The US has the largest nuclear fleet in the world, with 92 reactors across the country. Many of these power plants have been operating for more than half a century and are nearing the end of their expected useful lives.
Policymakers are debating whether to retire old reactors or strengthen their structures to continue producing nuclear power, which many see as a low-carbon alternative to climate-warming coal, oil and natural gas.
Now, MIT researchers say there's another factor to consider when weighing the future of nuclear power : air quality. In addition to being a low carbon source, nuclear power is relatively clean in terms of the air pollution it generates. Without nuclear power, how would the pattern of air pollution change and who would feel the effects?
The MIT team answered these questions in a new study that appeared in the journal Nature Energy. They lay out a scenario in which every nuclear power plant in the country shuts down and consider how other sources such as coal, natural gas and renewable energy would meet the resulting year-round energy needs.
Their analysis finds that air pollution would indeed increase as sources of coal, gas and oil increase to compensate for the absence of nuclear power. This in itself may not be surprising, but the team put the numbers into a prediction, estimating that an increase in air pollution would have serious health consequences, resulting in an additional 5,200 pollution-related deaths over the course of a year.
If, however, more renewable energy sources become available to supply the energy grid, as is expected by 2030, air pollution would be reduced, but not completely. The team found that even under this stronger renewable energy scenario, there was still a slight increase in air pollution in some parts of the country, resulting in a total of 260 pollution-related deaths in one year.
When they looked at populations directly affected by increased pollution, they found that African-American communities—a disproportionate number of which live near fossil fuel plants—experienced the greatest exposure.
"This adds another layer to the environmental and social impact equation when thinking about nuclear shutdowns, where the conversation often focuses on local risks from accidents and mining or long-term climate impacts," said lead author Lisa Freese, a graduate student at MIT- to this Department of Earth, Atmospheric and Planetary Sciences (EAPS).
"In the debate about keeping nuclear power plants open, air quality has not been the focus of that debate," adds study author Noelle Selin, a professor at MIT's Institute for Data, Systems, and Society (IDSS) and EAPS. "What we found is that air pollution from fossil fuel plants is so harmful that anything that increases it, such as a nuclear shutdown, will have significant impacts."
The MIT study was co-authored by principal investigator Sebastian Eastham and Guillaume Chaussier and Alan Zhen of the University of California, Davis.
Future Withdrawals
When nuclear power plants were shut down in the past, the use of fossil fuels increased in response. In 1985, the shutdown of a reactor in the Tennessee Valley caused a surge in coal use, while the shutdown of a California plant in 2012 led to an increase in natural gas. In Germany, where nuclear power was almost completely phased out, coal-fired power was initially ramped up to fill the gap.
Noting these trends, the MIT team wondered how the US energy grid would react if nuclear power were phased out entirely.
"We wanted to think about what future changes are expected in the energy grid," says Friese. "We knew coal use was going down, and there was already a lot of work looking at the impact it would have on air quality. But no one looked at air quality and nuclear power, which we also noticed was declining.”
In the new study, the team used a power grid dispatch model developed by Jen to estimate how the US power system would respond to a nuclear shutdown. The model simulates the output of every power plant in the country and runs continuously to estimate, hour by hour, the energy needs of 64 regions across the country.
Similar to the way a real energy market works, the model chooses to increase or decrease plant output based on cost: Plants producing the cheapest energy at any given time are prioritized to supply the grid over more expensive energy sources.
The team provided the model with available data on each factory's variable emissions and energy costs throughout the year. They then ran the model under different scenarios, including: a power grid without nuclear, a basic grid like today that includes nuclear, and a grid without nuclear that includes additional renewables expected to be added by 2030.
They combined each simulation with an atmospheric chemistry model to simulate how each plant's various emissions travel across the country and overlay these tracks onto population density maps. For populations in the path of pollution, they calculated the risk of premature death based on the level of exposure.
System response
Their analysis showed a clear pattern: without nuclear power, air pollution generally worsened, mostly affecting regions on the East Coast, where nuclear power plants are mostly concentrated. Without those plants, the team observed an increase in production from coal and gas plants, resulting in 5,200 pollution-related deaths nationwide, compared to the baseline scenario.
They also calculated that more people are likely to die prematurely from climate impacts due to increased carbon dioxide emissions, as the grid compensates for the absence of nuclear power. The climate effects of this additional influx of carbon dioxide could lead to 160,000 additional deaths over the next century.
"We have to think about how we retire nuclear plants if we're trying to think of them as part of the energy system," Freese says. "Turning off something that itself has no direct emissions can still lead to an increase in emissions, because the grid system will react."
"This could mean that we have to deploy even more renewable energy sources, to fill the hole left by nuclear power, which is essentially a zero-emission energy source," adds Selin. "Otherwise, we will have a decrease in air quality that we did not necessarily count on."
This study was supported in part by the US Environmental Protection Agency.
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