CALLAWAY COUNTY, Mo. -- The 31-year-old Callaway Energy Center is doing some heavy lifting. Missouri's lone nuclear power plant produces 11.7 percent of the state's electricity from one reactor, making it the third-largest electricity producer in the state. But Callaway really flexes its muscles when it comes to zero-carbon-emissions energy in a coal-heavy portfolio. Missouri gets 82 percent of its electricity from coal.