Environmental group Greenpeace calls it a "dying and dangerous" industry and Europe's biggest engineering conglomerate, Siemens, is exiting the sector altogether.

Japan's Fukushima nuclear accident six months ago sparked doubts about the future of nuclear power across the globe and especially in Europe, highlighted by Germany's decision to quit the energy source and Italy's referendum to ban it for decades.

But in a sign that the worst such disaster in a quarter of a century may slow rather than stop nuclear energy growth, other big economic and political powers used a U.N. meeting this week to reaffirm their commitment to atomic energy.

U.S. Energy Secretary Steven Chu, whose country has the most nuclear reactors in the world, spoke of its role becoming more "valuable" as the world confronts climate change, growing energy demand and a struggling global economy.

The head of fast-growing India's atomic energy commission, Srikumar Banerjee, told the same annual member state gathering of the U.N. International Atomic Energy Agency (IAEA) of plans in his country for a "major expansion" of nuclear capacity.

Managing Director George Felgate of the World Association of Nuclear Operators, an industry body set up to help strengthen safety after the 1986 Chernobyl accident, said 66 reactors were under construction worldwide, many in China.

"We haven't seen any of those 66 cancelled or pulled back," he said on the sidelines of the week-long IAEA conference.

"Germany is an extreme reaction in my opinion. I think the whole world is watching Germany to see if in fact solar and windmills can replace nuclear. My personal opinion is no."

The IAEA itself says it still sees "significant" growth ahead -- forecasting at least 90 new reactors by 2030 to add to the world's existing 432 -- even though Fukushima has prompted it to cut its forecast somewhat.

After a huge earthquake and a massive tsunami struck on March 11, reactor fuel rods at the Japanese plant began melting down when power and cooling functions failed, causing radiation leakage and forcing the evacuation of some 80,000 people.

"Following the Fukushima Daiichi accident there was speculation that the expansion in interest in nuclear power seen in recent years could come to an end," IAEA Director General Yukiya Amano told delegates at the meeting in Vienna.

"However, it is clear that there will, in fact, be continuous and significant growth in the use of nuclear power in the next two decades, although at a slower rate than in our previous projections."

Before the Fukushima crisis, the IAEA had expected up to 25 countries to bring their first nuclear power plants on line by 2030. Today, 29 countries have nuclear energy.

Interest remains strong in nations which are considering introducing nuclear for energy purposes, although a few have cancelled or revised their plans after Fukushima, Amano said.

Even though it sees continued growth in nuclear capacity, the IAEA's projections made clear that the energy form could struggle to hold on to its market share of about 13 percent as total electricity output may increase even faster.

PROJECTIONS "MEANINGLESS"

In its low-growth scenario, nuclear's share of total electricity generation by 2050 is projected to fall to 6.2 percent. At most, it would remain steady compared with now.

The projections did not specify how other energy sources -- such as oil- and gas-fired power plants, hydropower or renewables -- are expected to develop.

Greenpeace, which opposes nuclear power on safety grounds, dismissed the IAEA's latest forecast as a sign of "unrealistic optimism," saying the U.N. agency was a promoter of the industry, not an independent judge.

"The fact that agency is never late in coming up with upbeat messages to please the dying but dangerous nuclear industry confirms that it puts politics ahead of science and often even protection of public health," said Jan Beranek, head of Greenpeace's nuclear campaign.

The IAEA rejects such criticism, saying an action plan it drafted after Fukushima will significantly help boost safety.

In a sign of how Fukushima has already had an impact on industry, at least in Germany after its U-turn on nuclear energy, Siemens this month said it was pulling out of nuclear work, leading it to scrap a venture with Russia's Rosatom.

"The (nuclear) chapter is closed for us," Chief Executive Peter Loescher told German weekly magazine Der Spiegel in an interview published on Sunday.

Siemens' decision came after more than two years of turmoil around the engineering giant's nuclear business.

Japan itself, the world's third-biggest economy, has signalled it wants to reduce its reliance on nuclear power.

"Fukushima certainly has an impact on nuclear growth, but this must be kept in perspective," said deputy director general Stephen Kidd of the World Nuclear Association, an industry body.

"Several countries have reaffirmed their strong support for nuclear post-Fukushima, to counterbalance Germany, Italy etc."

Malcolm Grimston, a nuclear expert at London's Chatham House, suggested projections on where the industry will be in four decades may turn out to be "pretty much meaningless" because of the many uncertainties that could change the outlook.

"Fukushima will have a short-term effect and maybe a medium-term effect," Grimston said.

"But how any estimate of nuclear power in 2050 can be made without making vast unwarranted assumptions for example about climate change, geopolitics, the effectiveness of renewables, the organisation of power markets etc etc etc escapes me."