A magnitude-9 earthquake and tsunami struck Japan in March 2011, causing a meltdown at the country's Fukushima Daiichi nuclear power station.
Yukiya Amano, director general of the International Atomic Energy Agency, said in his annual address to the U.N. General Assembly that the nuclear power sector was well into what he described as the post-accident phase.
"Already, it is fair to say that nuclear power is safer than it was before the Fukushima Daiichi accident," he said.
Growth in the nuclear power sector, he added, was slower than expected, though momentum should develop in the next 20 years. Most of the new developments in nuclear power reactors are in Asian economies, where countries like China, India and South Korea are planning "significant expansions" in the energy sector, he said.
"Nuclear energy offers many benefits," he said. "It can help to improve energy security, reduce the impact of volatile fossil fuel prices, mitigate the effects of climate change and make economies more competitive."