(AP) -- A quarter-century after the Chernobyl nuclear reactor explosion, a week of meetings on the world's worst nuclear accident pressed home the message that the Chernobyl cleanup will remain expensive and anxiety-provoking for decades to come.
Still, differences over the true consequences of the calamity meant that no formal conclusions were issued as the meetings ended Friday.
The Ukrainian government organized four days of conferences in the capital Kiev to mark the 25th anniversary of the April 26, 1986, blast that sent radioactive fallout over much of Europe.
An international donors' conference raised pledges of euro550 million ($802 million) to build a shelter to cover the exploded reactor building for the next century. But that was short of the euro740 million ($1.1 billion) sought for the shelter and a facility for storing spent reactor fuel.
Once the enormous shelter is completed and slid over the reactor building on rails, expected in 2015, workers can begin disassembling the reactor and disposing the hundreds of tons of radioactive material inside. It is still not clear how that will be done or how much it will cost.
"Right now, we don't have the processes, but we are working on developing them," Igor Gramotkin, director of the now-decommissioned power plant, told delegates.
The human and ecological tolls of the explosion are equally difficult to nail down.
More than 6,000 cases of thyroid cancer have been detected in people who were children or adolescents when exposed to high levels of fallout in the period immediately after the blast, and at least 28 people have died of acute radiation sickness from close exposure to the shattered reactor.
But Mikhail Balanov of the U.N. Scientific Committee of the Effects of Atomic Radiation told Friday's conference that other medical effects were difficult to project because the margins of error in various studies are too high to allow reliable assessment.
Balanov did say that radioactive contamination of mushrooms and berries - both popular delicacies in Ukraine - remain high "and we will face elevated levels for decades to come."
Concern is high in Ukraine that contaminated mushrooms and berries are sold in unregulated local markets.
Around 115,000 people were evacuated from the plant's vicinity after the blast. A 30-kilometer (19-mile) area directly around the plant remains largely off-limits and the town of Pripyat, where plant workers once lived, today is a ghostly ruin of deteriorating apartment towers.
In the face of continuing uncertainty about the disaster's effects and debate about future measures, the conference delayed its intention of producing a final document.
"It is clear it is not possible to come up with crystal-clear conclusions," said moderator Volodymyr Holosha, director of the guarded "exclusion zone" around the plant.
Throughout the week, officials drew attention to the ongoing crisis at Japan's Fukushima Dai-ichi nuclear power plant, with many declaring that it and Chernobyl show that "radiation does not respect borders."
U.N. Secretary-General Ban Ki-moon used the conference to call for "top-to-bottom" review of nuclear safety standards and for strengthening the role of the International Atomic Energy Agency.
Later Friday, seven employees of the British and French Embassies in Kiev launched a non-stop, 24-hour 110-kilometer (68-mile) charity walk to Chernobyl to raise money for children affected by the disaster.
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