Shutting down nuclear power plants will have significant economic and environmental consequences, according to a new study by researchers atCarnegie Mellon Universityand DAI Management Consultants, Inc. Shifting from nuclear to other types of power plants could affect the reliability of the electricity supply, electricity costs, air pollution, carbon emissions, and the reliance on fossil fuels like coal and natural gas, the researchers said.

The recent earthquake and tsunami that destroyed the nuclear power plants in Fukushima,Japanhas led to an international reevaluation of policies related to nuclear power.Germanyhas decided to shutdown all nine of its nuclear power plants by 2022, andSwitzerlandwill shutdown all five of its plants by 2032. Nuclear power currently supplies 25 percent ofGermany's power, 39 percent ofSwitzerland's power, and 20 percent of the electricity consumed in the U.S.

"Turning off a single large nuclear power plant could require dozens of coal and gas-fired plants to ramp up production to make up the difference," saidPaul Fischbeck, a professor ofsocial and decision sciencesandengineering and public policyatCarnegie Mellon. "These plants use fossil fuels, cost more to operate, and emit pollution that can lead to acid rain and ozone, and CO2, a greenhouse gas."

Fischbeck, a risk expert, added that some of the differences are large. "Replacing the Brown's Ferry plant inAlabamawith a mix of coal and gas power plants would cause CO2 emissions to increase by approximately 24 million tons each year. That's the same as the annual emissions of over 4 million cars," he said.

To measure the impact of what the selective shutdown of any combination ofthe United States' 104 reactors located at 65 nuclear power plants would have on regional economic and environmental measures, the research team, using a national database of more than 15,000 power generators, determined what existing non-nuclear plants could be used to make up the shortfall in electricity generation. As a conservative first step, the researchers turned on the least expensive power plants that had excess capacity.

The researchers also looked at shutting down reactors based on various risk characteristics, such as being in an earthquake, tornado, or hurricane zone. "If plants that are in 'tornado alley' were shutdown, national coal consumption for power generation would go up over 160 million tons or 16 percent, and we would be spending$9 billionmore for electricity every year," saidDavid Rode, managing director ofDAI.

Given time and enough investment, some of the generation lost by shutting down nuclear plants could be made up by developing renewable resources and improving energy efficiency, but the size of the potential shortfall is daunting.

"To replace the nuclear plants located in counties with populations over half a million with wind power would require the construction of 25,000 large wind turbines on land greater than one and half times the size ofRhode Island," Fischbeck said.

He added, "Nuclear power is a major component of the nation's electricity generating capability, and policies that lead to its curtailment must be carefully planned recognizing the long-term negative impacts that are very real."