CNN Wire Staff
Tokyo (CNN) - Spent fuel rods in Unit 4 of Japan's stricken Fukushima Daiichi nuclear plant have been exposed, resulting in the emission of "extremely high" levels of radiation, the head of the U.S. Nuclear Regulatory Commission said Wednesday.
"What we believe at this time is that there has been a hydrogen explosion in this unit due to an uncovering of the fuel in the fuel pool," Gregory Jaczko told a House energy and commerce subcommittee hearing. "We believe that secondary containment has been destroyed and there is no water in the spent fuel pool, and we believe that radiation levels are extremely high, which could possibly impact the ability to take corrective measures."
The water served to both cool the uranium fuel and shield it. But once the uranium fuel was no longer covered by water, its zirconium cladding that encases the fuel rods heated, generating hydrogen, said Robert Alvarez, senior scholar at the Institute for Policy Studies and a former official with the Department of Energy.
That caught fire, resulting in a situation that is "very, very serious," he told CNN. He said the next solution may involve nuclear plant workers having to take heroic acts. Asked to be more specific, he said, "This is a situation where people may be called in to sacrifice their lives. ... It's very difficult for me to contemplate that but it's, it may have reached that point."
Photographs of the building released Wednesday by the power company showed a hole in a wall and deterioration of the roof.
A Japanese Self-Defense Force helicopter aborted its mission to drop water over the reactor because of the high radiation levels in the area, Japanese public broadcaster NHK reported.
Officials have been working to resolve cooling problems at four of Fukushima Daiichi's six reactors in the wake of the 9.0-magnitude earthquake and tsunami that devastated northeast Japan Friday.
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