Both Alzarez and Jaczko have voiced concerns about pool 4, but it is true only Alvarez is quoted as saying the zirconium caught fire.

Anderson Cooper 360: Blog Archive - Official: Spent fuel rods exposed, heightening concerns « - CNN.com Blogs

"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."

So, in what may be my last act of "advising", I'll advise you to cut the jargon. -- My old PhD advisor, to me, 26/2/11