The head of the UN warned on a landmark visit to Chernobyl on Wednesday that the Ukrainian tragedy and the recent accident in Japan prompted "painful questions" about the future of atomic power.
United Nations chief Ban Ki-moon visited the site of the Chernobyl disaster a day after world donors pledged 550 million euros ($800 million) towards a permanent shelter to secure the ruined reactor, which exploded on April 26, 1986.
Speaking in Kiev afterwards, he warned that the recent quake damage to Japan's Fukushima nuclear plant showed that accidents like Chernobyl were likely to occur again in the future.
"The unfortunate truth is we are likely to see more such disasters. The world has witnessed an unnerving history of nuclear accidents," he said at a conference, calling for a global debate on the safety of nuclear energy.
"To many, nuclear energy looks to be a relatively clean and logical choice in an era of increasing resources' scarcity. Yet the record requires us to ask painful questions: have we correctly calculated its risks and costs?" he said.
Ban spoke after flying to Chernobyl by helicopter, standing outside the power plant for around 20 minutes with Ukrainian President Viktor Yanukovych on a visit that he described as an "extremely moving experience."
He warned the effects of climate change were likely to lead to more disasters like that at the Fukushima plant, which was damaged by a quake and tsunami in a disaster that Japan has labelled at an equal level of severity as Chernobyl.
"We have seen in Japan the effects of natural disasters particularly in areas vulnerable to seismic activities," the UN secretary general said.
"Climate change means more incidents of freak and increasingly severe weather (and) with the number of nuclear energy facilities scheduled to increase substantially in the coming decades our vulnerability will only grow."
The UN chief's visit came after dozens of international donors gathered in Kiev Tuesday to come up with the funds needed to replace the temporary casing now protecting Chernobyl with a more permanent outer shell.
But the high-profile gathering, which included the head of the European Commission and the prime minister of France, fell short of the 740 million euros sought by Ukraine.
The pledged money will go to a project administered by the European Bank of Reconstruction and Development (EBRD), with part also funding a safe storage facility for spent nuclear fuel from inside the reactor.
Both the new outer shell and the storage centre are due to be operational in 2015 and Yanukovych stressed Wednesday that the money pledged was enough to complete the construction of the shelter on time.
"Yesterday we raised the main part of the sum. The rest, I am sure, will be gathered shortly. De facto, we have the possibility to build the new shelter to finish the construction here by 2015," he said.
The EBRD said in a statement Tuesday that it would work with major donors "to close the remaining financial gap."
The UN chief said he was impressed by the construction work he saw at Chernobyl.
"I saw the Chernobyl command centre and the encouraging progress in building a new shelter for a damaged reactor," he said.
"It was a very impressive, creative and ambitious project to shelter the damaged reactor for the coming 100 years."