Expansion of nuclear power capacity has slowed dramatically over the past 25 years, according to a report by the nonprofit organization Worldwatch Institute. Although 75 gigawatts of nuclear power plant capacity was added during the past quarter-century, nearly four-times that much was added during the previous quarter-century, the report says. Over the past 10 years, the share of the world’s energy supplied by nuclear power fell from 6.4% to 4.5%. However, nuclear power generation capacity showed a small increase of 1.1% to 373 GW in 2012. The number of operational reactors also increased by two units, raising the global total to 437 reactors. The U.S., with 104 operating reactors, is the world’s leader, followed by France, with 58 reactors. In 2012, construction began worldwide on seven new reactors with a combined capacity of 6.9 GW, the report says. Globally, some 67 reactors are under construction, but seven of those have been under construction for more than 20 years, the report notes, suggesting their completion is doubtful. The report attributes the decline to costs, safety concerns, and waste disposal problems.