Retiring America’s nuclear plants could result in killing 5,000 people a year.

As our society continues to grow, there is a growing need for energy, and with it comes the responsibility to find ways of generating it that are safe and sustainable. In the United States, nuclear energy accounts for nearly 20% of electricity generated. With 92 reactors dotting the country, the US is the world’s largest producer of nuclear energy.

However, many of these plants are aging and are approaching the end of their lifespan, which poses a dilemma: maintain them or replace them.

The debate now centers on whether to retire these plants or reinforce their structures to continue producing nuclear energy, considered a low-carbon alternative to climate-warming coal, oil, and natural gas. But, according to a new study by Massachusetts Institute of Technology (MIT) researchers, policymakers should also consider air quality when making this decision.

“This adds one more layer to the environmental health and social impacts equation when you’re thinking about nuclear shutdowns, where the conversation often focuses on local risks due to accidents and mining or long-term climate impacts,” says lead author Lyssa Freese, a graduate student in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS).

The study in Nature Energy examined the effects of shutting down every nuclear power plant in the U.S. and replacing them with other sources such as coal, natural gas and renewable energy. The researchers found that the resulting increase in air pollution would have serious health effects, resulting in an additional 5,200 pollution-related deaths over a year.

Researchers also found that Black or African American communities would experience the greatest exposure to the increased pollution, as a disproportionate number live near fossil-fuel plants. The authors concluded that policymakers need to consider this when deciding to shut down nuclear power plants.

“In the debate over keeping nuclear power plants open, air quality has not been a focus of that discussion,” said study author Noelle Selin, a professor in MIT’s Institute for Data, Systems and Society (IDSS) and EAPS. “What we found was that air pollution from fossil fuel plants is so damaging, that anything that increases it, such as a nuclear shutdown, is going to have substantial impacts, and for some people more than others.”

The MIT team used an energy grid dispatch model to assess how the U.S. energy system would respond to a shutdown of nuclear power. The model simulates the production of every power plant in the country and estimates, hour by hour, the energy demands in 64 regions across the country.

Much like the actual energy market, the model chooses to turn a plant’s production up or down based on cost. Plants producing the cheapest energy at any given time are given priority to supply the grid over more costly energy sources.

The team fed the model available data on each plant’s changing emissions and energy costs throughout an entire year. They then ran the model under different scenarios, including an energy grid with no nuclear power, a baseline grid similar to today’s that includes nuclear power, and a grid with no nuclear power that also incorporates additional renewable sources that are expected to be added by 2030.

The model showed that air pollution worsened in general without nuclear power, mainly affecting regions on the East Coast, where nuclear power plants are mostly concentrated. Without those plants, the team observed an uptick in production from coal and gas plants. They also calculated that more people are also likely to die prematurely due to climate impacts from the increase in carbon dioxide emissions, as the grid compensates for nuclear power’s absence. The climate-related effects from this additional influx of carbon dioxide could lead to 160,000 additional deaths over the next century.

However, the study found that even under a heartier renewable scenario, where more renewable energy sources become available to supply the energy grid, there is still a slight increase in air pollution in some parts of the country, resulting in a total of 260 pollution-related deaths over one year.

“We need to be thoughtful about how we’re retiring nuclear power plants if we are trying to think about them as part of an energy system,” Freese says. “Shutting down something that doesn’t have direct emissions itself can still lead to increases in emissions, because the grid system will respond.”