LONDON/MADRID Japan is still far from solving its nuclear crisis despite some signs of progress on Friday and restoring power to the Fukushima plant is its best hope, European experts said.
Getting mains power back in to the plant might enable pumping of water to cool crippled reactors and spent fuel stores, they reasoned, saying it was too early to consider burying the complex in concrete or sand.
"We are possibly at a turning point for improving the situation," said Luis Echavarri, Director-General of the OECD's Nuclear Energy Agency, on the prospect of bringing new cooling systems on-line.
Laurence Williams, Professor of Nuclear Safety, John Tyndall Institute, University of Central Lancashire, said that restoring power was the key.
"If they can get those electric pumps on and they can start pushing that water successfully up the core, quite slowly so you don't cause any brittle failure, they should be able to get it under control in the next couple of days," he said.
He said that reactors were probably generating new heat now equivalent to less than 0.1 percent of their full output, cooling with time.
The worst-case case outlook remained a serious but probably local release near the plant of radioactive caesium, if a fire broke out at over-heated ponds containing spent fuel.
Such a fire was unlikely, said Tony Roulstone, nuclear energy expert at Cambridge University, and a former industry adviser, pointing to the fact that the uranium fuel was removed from the reactor about 100 days ago, making it cooler.
The U.S. designer of the plant, General Electric, could detail the risk, said consultant John Price, formerly from the National Nuclear Corporation UK.
"Basically GE Energy has been almost silent. I think we deserve to hear more from GE," he said.
Health consequences from the crisis remained limited said Malcolm Sperrin, director of medical physics and clinical engineering, Royal Berkshire Hospital.
"My feeling is that they are starting to get things under control. If things are not properly managed then we're back to square one and the risk rises again."
TEPCO said on Friday that it had raised the limit for the emergency work to 100 millisieverts an hour, subject to an overall maximum of 250 millisieverts a year.
"That's a sensible limit bearing in mind what is going on, and that is vastly, vastly smaller than anything that was experienced from Chernobyl," said Sperrin.
In Tokyo, Japanese engineers said on Friday that burying crippled nuclear reactors in sand and concrete may be a last resort to prevent further radiation release, the method used to seal huge leakages from Chernobyl in 1986.
Experts said it was too early to be sure of the disposal outcome, but doubted a "Chernobyl sarcophagus" was necessary as less radioactive material had been released, with core reactor vessels intact at Fukushima but blown part at Chernobyl.
"At Chernobyl there's a steel case around it. You haven't got that amount of material open to the atmosphere (at Fukushima)," said the John Tyndall Institute's Williams, also former chief inspector of UK nuclear installations.
The clean-up challenge was more comparable to U.S. Three Mile Island, where workers took the reactor apart, removed the fuel and sealed the site over a period of about 10 years, said Cambridge University's Roulstone.
(With additional reporting by Kate Kelland in London and Alister Doyle in Oslo; editing by Janet McBride)