Preserving Quad Cities and Clinton nuclear plants will save businesses and consumers in Illinois more than $3 billion in power costs in the next 10 years, a study conducted by global consulting firm The Brattle Group showed on Monday. Exelon Corp, which owns the plants and plans to close them, has been trying to get the Illinois Legislature to adopt legislation, known as the Next Generation Energy Plan, that would provide a subsidy for nuclear reactors for their production and environmental and economic benefits.In June, Exelon said it would close the Clinton plant on June 1, 2017, and Quad Cities, on June 1, 2018. The reactors have lost a combined $800 million in the past seven years, according to the company.