China's leaders think nuclear power offers a partial remedy for ills ranging from the pall of smog hanging over its cities to a growing addiction to foreign oil.

But analysts and environmentalists warn a range of challenges, from waste disposal to the daunting price tag on new generators, could give the energy cure a bitter taste.

Beijing began commercial nuclear generation late, after devoting resources and scientists to weapons development during Mao Zedong's rule. The country's first atomic bomb exploded in 1964 but civilian reactors only came online in the 1990s.

It is now racing to catch up and to meet booming energy demand with plans to more than quadruple capacity by 2020 and work on a new technology that scientists tout as accident-proof.

At present, nine reactors contribute barely 2 percent of the nation's power -- just one eighth of the global average. The target is to raise this to 40 gigawatts, or 4 percent over the next 15 years by building 30 new reactors.

"China started late, but to build two major reactors a year is a very ambitious programme and I don't think anyone has ever attempted that," said Clarence Hardy, vice-president of the Pacific Nuclear Council.

REACTOR MIX

China has what is probably the largest variety of nuclear technologies within a single nation's borders. It has used Canadian, French and Russian designs and is considering signing up for a US one, as well as supporting home-grown technology.

"It was a deliberate, not accidental, mix and it probably was a good strategy as it keeps them up to speed on what is going on worldwide," said Beijing-based energy analyst James Brock.

Besides cherry-picking the best international technology, Chinese scientists believe they may have found a way to lay to rest the ghost of the 1986 Chernobyl explosion, which still haunts the industry.

The pebble bed reactor being developed at Tsinghua University is meltdown-proof, said scientist Wu Zongxin, who has worked on the project for over two decades.

It uses fuel "pebbles" -- roughly the size of tennis balls and wrapped in graphite with a higher melting point than the uranium inside -- to prevent runaway reactions, he explained.

"It is impossible that the nuclear fuel could melt ... the passive safety mechanism does not rely on humans to control the temperature," Wu told Reuters.

A 10-megawatt test reactor is on-line near Beijing and work starts on a demonstration plant in Shandong in 2008, he said.

Chinese power developers are also pursuing designs that use less uranium. As nations trying to cut pollution take another look at nuclear power, world uranium prices have risen, more than tripling since 2004.

Despite the new research, China's government may struggle to persuade listed utilities to help fund the nuclear expansion.

Although nuclear plants are cheap to run, with low exposure to fuel costs particularly valuable as oil and gas prices rise, they are very expensive to build.

"I do not think Chinese power producers are going to rush into nuclear power because it's the 'in' thing," said Joseph Jacobelli, utilities analyst at Merrill Lynch in Hong Kong.

"For a 2-gigawatt power plant, you have costs of around US$3 billion and all of that is front-loaded. They will want a high level of guarantees," he added.

WASTE, MONITORING CONCERNS

Rigorous safety procedures copied from the designers have given China a solid record so far despite the variety of reactors it uses. A single operating company, China National Nuclear Corporation, helps unify safety plans.

But if something does go wrong and officials are tempted to cover up, there may be no one to call them to account in a society that brooks limited dissent from central control.

"Civil society safeguards -- press freedom, whistleblower protection, human rights laws -- form a more amorphous layer of protections which are largely absent in China," said Jim Green, nuclear campaigner from Friends of the Earth in Australia.

Disposing of the over 1,000 tonnes a year of radioactive waste that the expansion could produce, according to the World Nuclear Association, is another minefield.

There are plans to expand a small facility in western Gansu province to deal with much of the spent fuel, but Green says details are opaque and, with concern over environmental issues growing in wealthier east coast areas, poorer areas may be forced to host their nuclear waste.