Plans by Baltimore-based Constellation Energy to mass-produce carbon-free hydrogen could be jeopardized under proposed federal guidelines that exclude existing nuclear plants from tax subsidies designed to boost a budding clean hydrogen industry. The newly released rules outline qualifications for clean hydrogen production credits offered through the Biden administration’s Inflation Reduction Act, which, in part, aims to cut greenhouse gas emissions 40% by 2030. Constellation, which produces electricity at power plants, including the nation’s largest fleet of nuclear power plants, had been counting on the credits to help make clean hydrogen production cost-effective.