The first nuclear power plant was built in the 1950s. The global installed nuclear capacity grew to 100 GW in the late 1970s, and then expanded during the 1980s, reaching 300 GW by 1990. The 1979 Three Mile Island accident in the United States and the 1986 Chernobyl disaster in the Soviet Union resulted in increased regulation and public opposition to nuclear power plants. These factors, along with high cost of construction, resulted in the global installed capacity only increasing to 390 GW by 2022. These plants supplied 2,586 terawatt hours (TWh) of electricity in 2019, equivalent to about 10% of global electricity generation, and were the second-largest low-carbon power source after hydroelectricity. As of August 2023, there are 410 civilian fission reactors in the world, with overall capacity of 369 GW,[1] 57 under construction and 102 planned, with a combined capacity of 59 GW and 96 GW, respectively. The United States has the largest fleet of nuclear reactors, generating almost 800 TWh of low-carbon electricity per year with an average capacity factor of 92%. The average global capacity factor is 89%.[1] Most new reactors under construction are generation III reactors in Asia.