(CNN) -- Japanese efforts to prevent a nuclear meltdown by flooding reactors with seawater are a last-ditch attempt, but do not mean that a nuclear tragedy is imminent, experts said Sunday.
Nuclear experts who have followed the developments at the damaged Fukushima Daiichi nuclear plant in northeastern Japan say that despite several setbacks, the possibility of massive radiation exposure remain low -- at least for now.
Japanese officials are keeping an eye on two nuclear plants that have released radiation beyond normal levels. At the Daiichi plant in Fukushima, two of the three reactors -- Nos. 1 and 3 -- are at risk for meltdown because of the powerful earthquake and tsunami that struck on Friday. At a second plant, in Onogawa, excessive radiation levels also were recorded, though officials have told the United Nations' atomic watchdog agency that the situation is "under control."
An explosion caused by hydrogen buildup Saturday blew the roof off a concrete building housing the plant's No. 1 reactor, but the reactor and its containment system were not damaged in the explosion. Officials say the No. 3 reactor would also likely withstand a similar blast, noting that workers had already released gas from the building to try to prevent an explosion.
"I don't think we're really close to a meltdown," said Dale Klein, vice chancellor for special engineering projects at the University of Texas, referring to the Daiichi plant.
There does appear to be some fuel damage to one of the reactors, but the seawater method to keep them cool seems to be working.

Credit: CNN World News