Why did Iran move nuclear fuel to above-ground facility?

Laura Rosen, here

"Policymakers and analysts from the U.S., Israel and Arab countries are puzzling over why Iran moved its entire stockpile of low enriched uranium to an above ground facility earlier this month where it is conducting higher enrichment. On the one hand, the 2,000 kilos of LEU is far more than Iran needs to higher enrich for the country's domestic medical needs. On the other, it has only one cascade at the pilot facility to carry out the higher enrichment, and the stockpile is now in a vulnerable, above-ground facility. By design -- or screw up, the New York Times asks:

The strangest of the speculations — but the one that is being talked about most — is that the Iranian Revolutionary Guard Corps is inviting an attack to unify the country after eight months of street demonstrations that have pitted millions of Iranians against their government. As one senior European diplomat noted Thursday, an Israeli military strike might be the “best thing” for Iran’s leadership because it would bring Iranians together against a national enemy.

It would offer an excuse some Iranians might sorely want to throw out the nuclear inspectors and renounce the Nuclear Non-Proliferation Treaty. That would leave Iran in the position North Korea is in today: free to manufacture fuel or bombs without inspectors to blow the whistle.

Other, including some officials in the White House, say they do not buy that theory. Iran has worked too hard to let its supply be destroyed, they argue. [...]

...Another explanation: brinkmanship. The Iranians have made clear that they do not like the terms their own negotiators came home with for swapping their nuclear fuel for specialized fuel for the medical reactor. By moving their fuel supply to the enrichment plant, they are essentially threatening to turn it all to near-bomb-grade fuel — and perhaps force the United States to reopen negotiations.

But the simplest explanation, that the Iranians had no choice, has its proponents. The fuel is stored in one big, specialized cask. When someone ordered that the fuel begin being fed into the giant centrifuges for further enrichment, engineers moved it to the only spot available — the exposed plant. Or, as one American intelligence official said, “you can’t dismiss the possibility that this is a screw-up.”