FirstEnergy’s plans to shut down nuclear power plants has focused the attention of clean energy boosters on environmental impacts. FirstEnergy's three nuclear plants under threat generate more zero-carbon power than all of the mid-Atlantic region’s wind and solar power put together. On Monday, research firm Brattle Group released its own analysis in the wake of FirstEnergy’s planned nuclear closures, underscoring a worrisome combination of environmental and economic costs. Brattle Group’s study was conducted for industry advocacy group Nuclear Matters.