Iran’s underground nuclear sites not immune to U.S. bunker-busters, experts say

The U.S.-Israeli rift over the urgency of stopping Iran’s nuclear progress stems in part from the belief among some Israeli officials that their window for successfully attacking Iran’s nuclear installations is rapidly closing as Tehran moves key assets into bunkers. Barak, in a speech this month, spoke of Iran’s progress in creating a “zone of immunity” for its nuclear program.

To U.S. military planners, a “zone of immunity,” if it exists at all, is years away. The Obama administration, while not ruling out a strike, regards military action as a last resort, preferring to allow more time for changing Iran’s behavior through economic and political pressure.

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Hardened targets

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 A string of volatile incidents has raised tensions between the two countries.

U.S. officials also remain unconvinced that Iran has decided to build a nuclear bomb, though they think it is pursuing the capacity to do so. Iran says its nuclear program is for peaceful energy production.

Under a mountain

Fordow is in the barren hills of northwestern Iran just outside Qom, an ancient city that is the spiritual home of the 1979 revolutionary movement. U.S. intelligence officials think tunneling began nearly a decade ago for what was intended to be a secret uranium-enrichment site that would operate parallel to the country’s much larger, declared enrichment plant at Natanz.

The CIA began monitoring the site at least four years ago, and in 2009, President Obama, flanked by other world leaders, publicly exposed the partially built facility and demanded that Tehran come clean about its intentions.

Iran acknowledged that it was building a second uranium-enrichment plant and soon allowed the International Atomic Energy Agency in for a visit. The U.N. inspectors saw a series of chambers built into the side of a mountain and connected by tunnels with thick walls and blast-proof doors. Some of the bunkers were protected by as much 200 to 300 feet of mountain.

The underground plant — not yet fully operational — is relatively small, with space for about 3,000 centrifuges, compared with the tens of thousands planned for Natanz. But analysts say it’s big enough to process the enriched uranium necessary for at least one nuclear weapon a year, should Iran decide to build them.

Iran started enriching uranium in the Fordow plant in January. A report by U.N. inspectors last week confirmed that the plant is making a purer form of enriched uranium that can be relatively easily converted to weapons-grade fuel.

Iran has publicly defended Fordow’s unusually robust fortification, citing repeated threats by Israel to destroy the country’s nuclear program.

Western analysts think Fordow has not only the protection afforded by natural rock but also additional hardening that draws on North Korean bunker-building expertise. A report last week by the Center for Strategic and International Studies, a Washington think tank, said the facility was thought to include multiple “blast-proof doors, extensive divider walls, hardened ceilings, 20-centimeter-thick concrete walls, and double concrete ceilings with earth filled between layers.”