About 20% of the electricity generated in the United States today is produced through nuclear power, thanks to the country’s 92 reactors located throughout the nation, comprising the largest nuclear fleet globally.

However, many of these power plants have surpassed their anticipated lifespan, having been in operation for over half a century. As such, policymakers are currently weighing up whether to retire these aging reactors or reinforce their structures to prolong their use.

The debate revolves around nuclear energy’s status as a low-carbon alternative to fossil fuels such as coal, oil, and natural gas, which are believed to contribute to climate change.

The future of nuclear power in the United States may have another key consideration – air quality, according to new research by MIT. While nuclear power is a low-carbon alternative to fossil fuels, it also generates relatively little air pollution.

MIT researchers explored what would happen if all nuclear power plants in the country were shut down, and how other energy sources such as coal, natural gas, and renewables would fill the resulting energy needs throughout an entire year. The results of their study are published in Nature Energy.

They found that shutting down all nuclear power plants in the United States could have serious implications for air quality and human health. The researchers analyzed a scenario in which all nuclear power plants were retired and replaced with other energy sources such as coal, natural gas, and renewables. They estimated that the resulting increase in air pollution would lead to 5,200 additional pollution-related deaths in just one year.

However, if more renewable energy sources become available by 2030 to supply the energy grid, as expected, air pollution would be reduced, although not entirely eliminated. Even under this more optimistic scenario, the team found that some parts of the country would still experience a slight increase in air pollution, resulting in a total of 260 pollution-related deaths over one year.

After examining the demographics most affected by the escalated pollution, the researchers discovered that Black or African American communities, who are already disproportionately located near fossil-fuel plants, were most heavily impacted.

“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,” points out lead author Lyssa Freese.

“In the debate over keeping nuclear power plants open, air quality has not been a focus of that discussion,” points out study author Noelle Selin. “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 co-authors of the study, affiliated with MIT, include Principal Research Scientist Sebastian Eastham, Guillaume Chossière SM ’17, PhD ’20, as well as Alan Jenn from the University of California at Davis.

The closure of nuclear power plants in the past has resulted in increased use of fossil fuels. For instance, the closure of reactors in Tennessee Valley in 1985 led to a surge in coal consumption, while the shutdown of a plant in California in 2012 caused an uptick in natural gas usage. Similarly, the phasing out of nuclear power in Germany led to a surge in coal-fired power generation. The MIT team took note of these trends and wondered how the U.S. energy grid would respond if nuclear power were entirely phased out.

“We wanted to think about what future changes were expected in the energy grid,” Freese adds. “We knew that coal use was declining, and there was a lot of work already looking at the impact of what that would have on air quality. But no one had looked at air quality and nuclear power, which we also noticed was on the decline.”

The MIT team utilized an energy grid dispatch model created by Jenn in their new study, which aimed to evaluate how the U.S. energy system would react to the shutdown of nuclear power. The model mimics the production of all power plants in the nation and operates continuously to estimate energy requirements per hour in 64 regions throughout the country. Similar to the actual energy market, the model considers costs when determining whether to raise or lower a plant’s production, prioritizing plants that produce energy at the cheapest price over more expensive sources.

The team performed various simulations using the model, including a scenario with no nuclear power, a baseline grid that includes nuclear power, and a grid without nuclear power but with additional renewable sources that are expected to be integrated by 2030. They then coupled each simulation with an atmospheric chemistry model to study the movement of emissions and overlay them onto population density maps. The team also calculated the risk of premature death for populations exposed to pollution.

The MIT team’s analysis revealed a distinct trend: the absence of nuclear power resulted in an overall deterioration of air quality, predominantly affecting regions on the East Coast that host most nuclear power plants. The researchers observed a rise in production from coal and gas plants in the absence of nuclear plants, leading to 5,200 pollution-induced deaths across the United States, compared to the baseline scenario. The team also estimated that more people are likely to experience premature death due to the effects of climate change resulting from the increased carbon dioxide emissions as the grid compensates for the lack of nuclear power. This additional influx of carbon dioxide could cause 160,000 more deaths over the next century.

“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 adds. “Shutting down something that doesn’t have direct emissions itself can still lead to increases in emissions, because the grid system will respond.”

“This might mean that we need to deploy even more renewables, in order to fill the hole left by nuclear, which is essentially a zero-emissions energy source,” Selin says. “Otherwise we will have a reduction in air quality that we weren’t necessarily counting on.”

The U.S. Environmental Protection Agency partially supported this study.

Image Credit: Diablo Canyon nuclear power plant – David Middlemamp/San Luis Obispo Tribune/Tribune News Service via Getty Images