Nuclear power is the use of sustained nuclear fission to generate heat and electricity. Nuclear power plants provided about 5.7% of the world’s energy and 13% of the world’s electricity, in 2012. In 2013, the IAEA report that there are 437 operational nuclear power reactors (although not all are producing electricity), in 31 countries. More than 150 naval vessels using nuclear propulsion have been constructed. There is an ongoing debate about the use of nuclear energy.