Civilian nuclear power supplied 2,586 terawatt hours (TWh) of electricity in 2019, equivalent to about 10% of global electricity generation, and was the second largest low-carbon power source after hydroelectricity. there are 442 civilian fission reactors in the world, with a combined electrical capacity of 392 gigawatt (GW). There are also 53 nuclear power reactors under construction and 98 reactors planned, with a combined capacity of 60 GW and 103 GW, respectively. The United States has the largest fleet of nuclear reactors, generating over 800 TWh zero-emissions electricity per year with an average capacity factor of 92%. Most reactors under construction are generation III reactors in Asia.