Eliminating nuclear energy could increase air pollution

Policymakers are debating whether to decommission the ageing reactors or reinforce their structures in order to continue producing nuclear energy, which is viewed by many as a low-carbon alternative to climate-warming coal, oil, and natural gas.

Now, according to MIT researchers, air quality is another factor to consider when evaluating the future of nuclear power. In addition to being a source with low carbon emissions, nuclear power produces relatively little air pollution. How would the pattern of air pollution change without nuclear power, and who would be affected?

In a new study published in Nature Energy, the MIT team tackled these questions. They present a scenario in which every nuclear power plant in the country has been shut down and consider how other energy sources, such as coal, natural gas, and renewable energy, would meet the country's annual energy demands.

Eliminating nuclear energy could increase air pollution. (Illustrative image).

Their analysis demonstrates that air pollution would indeed increase as coal, gas, and oil sources ramp up to compensate for the absence of nuclear power. This may not be surprising in and of itself, but the team has quantified the prediction by estimating that the increase in air pollution would result in an additional 5,200 pollution-related deaths each year.

However, if, as expected by 2030, more renewable energy sources become available to supply the energy grid, air pollution would be reduced, albeit not entirely. Even under this more robust renewable scenario, the team discovered a slight increase in air pollution in certain regions of the country, leading to a total of 260 pollution-related deaths per year.

Black or African American communities, of which a disproportionate number live in close proximity to fossil-fuel plants, were the most exposed to the increased pollution, according to a study of the populations directly affected by the pollution increase.

Lead author Lyssa Freese, a graduate student in the Department of Earth, Atmospheric, and Planetary Sciences (EAPS) at MIT, explains, "This adds another dimension to the environmental health and social impacts equation when considering nuclear shutdowns, where the conversation often focuses on local risks due to accidents and mining, or long-term climate impacts."

Noelle Selin, a professor at MIT's Institute for Data, Systems, and Society (IDSS) and EAPS and the author of the study, notes that air quality has not been a focus of the debate over keeping nuclear power plants operational. "What we discovered was that air pollution from fossil fuel plants is so harmful that anything that increases it, such as a nuclear shutdown, will have significant consequences, and for some people more than others."

Principal Research Scientist Sebastian Eastham and Guillaume Chossière SM '17, PhD '20 are among the MIT-affiliated co-authors of the study, along with Alan Jenn of the University of California, Davis.

Future phase-outs

In the past, when nuclear power plants were shut down, fossil fuel consumption increased. The closure of reactors in Tennessee Valley in 1985 led to an increase in coal consumption, while the closure of a plant in California in 2012 led to an increase in natural gas consumption. In Germany, where nuclear power has been nearly eliminated, coal-fired power initially increased to fill the void.

Noting these trends, the MIT group pondered how the U.S. energy grid would react if nuclear power were to be completely phased out.

"We wanted to consider anticipated future changes in the energy grid," says Freese. "We were aware that coal use was declining, and a great deal of research had already been conducted on the effects of this on air quality. We also noticed a decline in air quality and nuclear power, which no one had considered.

In the new study, the team utilised Jenn's energy grid dispatch model to assess how the U.S. energy system would respond to a nuclear power shutdown. The model simulates the output of every power plant in the nation and runs continuously to estimate the hourly energy demands in 64 regions across the nation.

Similar to how the actual energy market operates, the model decides whether to increase or decrease a plant's output based on cost: Priority is given to the plants that produce the cheapest energy at any given time over those that produce more expensive energy.

Throughout an entire year, the team fed the model data on each plant's fluctuating emissions and energy costs. They then ran the model under various scenarios, such as an energy grid with no nuclear power, a baseline grid similar to the one in place today that includes nuclear power, and an energy grid with no nuclear power that also includes the additional renewable sources that are expected to be added by 2030.

They combined each simulation with a model of atmospheric chemistry to simulate the movement of each plant's various emissions across the country and overlaid these tracks on population density maps. They calculated the risk of premature death for populations in the path of pollution based on their level of exposure.

System response

Their analysis revealed a clear pattern: Without nuclear power, air pollution worsened globally, primarily affecting East Coast regions where nuclear power plants are most prevalent. Without these plants, the team observed an increase in coal and gas plant production, which resulted in an additional 5,200 pollution-related deaths across the country compared to the baseline scenario.

In addition, they calculated that more people will likely die prematurely due to climate impacts caused by the increase in carbon dioxide emissions as the grid compensates for the absence of nuclear power. The climate-related effects of this additional carbon dioxide inflow could result in an additional 160 thousand 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 says. "Because the grid system will respond, shutting down something that doesn't have direct emissions can still lead to an increase in emissions."

"This may necessitate the deployment of even more renewables to fill the void left by nuclear, which is essentially a zero-emissions energy source," Selin explains. Otherwise, we will experience a decline in air quality that was not anticipated. This study was partially funded by the United States Environmental Protection Agency.