LONDON - Nuclear power's credentials as a carbon-free energy source have helped to calm fears about its safety, but scientists have yet to solve the problem of the hundreds of thousands of years of toxic waste it generates.

Most countries' nuclear waste is stored in steel and concrete containers kept in indoor cold water ponds over ground or ventilated shafts.

Ideally, scientists say, it should be placed in deep, underground repositories.

That technology is not yet proven. But the government, which earlier this month backed a new generation of nuclear power plants, said it believed deep geological waste reserves would be viable and some scientists agree.

"I think there's sufficient evidence that internationally all the technology is there and the safety analysis has been done many times over," said Neil Chapman of the School of Underground Waste Management, based in Switzerland.

"The problem is that those people who have been opposed to nuclear have persistently said there isn't a solution to waste disposal because there are no purpose-built underground facilities in the world to deal with this," he added.

So far, some 270,000 tonnes of spent fuel are in storage in cold water facilities around the world and 10,000 to 12,000 tonnes are added each year, according to the International Energy Agency, energy adviser to industrialised nations.

France, which produces almost 80 percent of its electricity from nuclear power, in June 2006 decided to pursue deep geological disposal and aims to have its first deep underground repository open by 2025 at a cost of 15 billion euros (11.1 billion pounds), according to the World Nuclear Association.

DEEP PROBLEMS

While deep underground facilities are best suited to keeping nuclear waste away from the population, it is not problem-free.

To try to overcome the obvious difficulty of local opposition, the government has asked communities to volunteer to host a deep underground repository.

The bulk of nuclear waste is stored at Sellafield and some analysts regard it as the only potential volunteer because it is already home to so much waste.

The public consultation on waste and decommissioning will take place between February and March 2008 and will be followed by an application for volunteers.

"The volunteerism angle is pretty much unprecedented... it's an unusual way of going about things," said Julian Boswall, planning partner at the nuclear energy group at law firm Eversheds.

"The real battle is going to be around...exactly where the site is going to be depending on how many communities are prepared to come forward."

In theory, there are many suitable sites.

"There's lots of places you could go. This exercise has been done several times before, the general findings done over the last 20 years showed a quarter to a third of the UK was geologically suitable," Chapman said.

But even when the problem of location is solved, another issue is funding.

The government has repeatedly said it will not fund nuclear power, but analysts have said the private sector would not be able to afford the huge costs of waste disposal on top of the at least 2 billion pounds required to build a nuclear plant.

"In terms of the costs of building a repository for future waste, there's no way the private sector is going to be able to fund that," said Robert Pitcher head of nuclear energy at Eversheds law firm.

For many, practicalities are a much lower consideration than the ethical dilemma of leaving a legacy for generations to come.

"That stuff doesn't go away and will last for thousands if not millions of years and that is imposing a burden on future generations," said Andrew Blowers, a former member of the Committee for Radioactive Waste Management (CoRWM), which advised the government.

"We don't need to have nuclear because there are other alternatives... fundamentally it seems to me the moral issue is if you don't need it, then don't have it," Blowers said.

Even the carbon-free credentials of nuclear are for some doubtful.

While nuclear proponents say atomic power generation does not produce any of the emissions blamed for global-warming, that is disputed by environmentalists who point to the carbon-intensive uranium extraction and refining process.

They also say the amount of carbon emissions nuclear generation would prevent is insignificant.

"In this context it's difficult to see how nuclear would deal with our global warming problems," Paul Dorfman, senior research fellow at Warwick University and former scientific adviser to the government said.