The concrete sarcophagus encasing the wrecked reactor at Chernobyl is deteriorating, threatening another release of radioactivity.
Ukraine, which is seeking billions in Western aid to clean up the reactor that exploded in 1986, warns that water dripping into the ruins could set off another uncontrolled reaction and spread radiation over a wide area of Europe.But the U.N. atomic agency plays down that threat, saying the danger is limited to radioactive dust getting out and contaminating the local area around the power plant.
Ukrainian and Western scientists have worried for years about a growing number of cracks and holes in the sarcophagus put up around the damaged No. 4 reactor. They say radioactive dust could escape through the cracks.
But the crusted, lavalike fuel is also developing cracks, and Ukrainian scientists say that increases the danger. They say rain and melting snow that drip through the sarcophagus to the warm fuel mass could cause fission of uranium atoms, causing a vapor explosion that could burst the sarcophagus.
"Water getting inside the fuel mass . . . might lead to a spontaneous and uncontrollable nuclear chain reaction," Boris Gorbachev, one of those responsible for monitoring the sarcophagus' safety, wrote in the newspaper Vse-Ukrainskiye Vedomosti.
Vladimir Tokarevsky, director of Ukrytia, the government agency that monitors the sarcophagus, also warns of the threat of an explosion because of water getting into the nuclear fuel.
"Initially we saw lava with a glasslike unbroken surface, but now there are numerous splits and dust emerging," he said of the fuel, which is monitored by remote cameras and other equipment.
David Kyd, a spokesman for the International Atomic Energy Agency in Vienna, Austria, said the U.N. agency considered an explosion unlikely but is concerned about radioactive dust filtering out of the sarcophagus.
The structure was "designed to last for 30 years, (but) it's very doubtful it will even last 20 years," Kyd said. "It is not air and water tight . . . What they try to do is keep the radioactive dust inside with a sprinkler system."