An Iranian nuclear facility is so deep underground that US airstrikes likely couldn’t reach it

DUBAI, United Arab Emirates — Near a peak in the Zagros Mountains in central Iran, workers are building a nuclear facility so deep into the ground that it is likely beyond the range of the last US weapon designed to destroy such places, experts and satellite images they analyzed say. The Associated Press.

Planet Labs PBC photos and videos show Iran digging tunnels in a mountain near the Natanz nuclear site, which has been hit by repeated sabotage attacks over Tehran’s nuclear program against the West.

With Iran now producing near-weapons-grade uranium following the collapse of its nuclear deal with world powers, the facility will complicate Western efforts to prevent Tehran from developing a nuclear bomb as diplomacy over its nuclear program remains stalled.

Completing such a facility would be “a nightmare scenario that could trigger a new spiral of escalation,” warned Kelsey Davenport, director of nonproliferation policy at the Washington-based Arms Control Alliance. “Given how close Iran is to a bomb, it has very little room to ramp up its program without disrupting the US-Israeli border. So any further escalation at this point increases the risk of conflict.”

Construction at Natanz took place five years after then-President Donald Trump unilaterally withdrew America from the nuclear agreement. Trump argued that the deal would not affect Tehran’s ballistic missile program or its support for militias in the wider Middle East.

But it has done so by strictly limiting Iran’s uranium enrichment to 3.67% purity, high enough to power civilian power plants, and keeping its stockpiles at just 300 kilograms (660 pounds).

Since the end of the nuclear deal, Iran has said it is enriching uranium to 60%, although inspectors recently discovered that the country was producing uranium particles with a purity of 83.7%. This is just a short step away from reaching the 90% threshold for weapons-grade uranium.

The head of the International Atomic Energy Agency said in February that international inspectors estimated Iran’s stockpile was more than 10 times larger than under the Obama-era deal and that it had enough enriched uranium for Tehran to build “several” nuclear bombs.

President Joe Biden and Israel’s prime minister have said they will not allow Iran to build nuclear weapons. “We believe that diplomacy is the best way to achieve this goal, but the president also made it clear that we have not taken any option off the table,” the White House said in a statement to the AP.

The Islamic Republic denies it is seeking nuclear weapons, although officials in Tehran now openly debate whether they can pursue one.

In response to AP questions about the construction, Iran’s UN mission said “Iran’s peaceful nuclear activities are transparent and under International Atomic Energy Agency safeguards.” However, Iran has restricted access to international inspectors for years.

Iran says the new facility will replace the Natanz above-ground centrifuge production center, which suffered an explosion and fire in July 2020. Tehran blamed the incident on Israel, which has long been suspected of waging sabotage campaigns against its program.

Tehran has not acknowledged other plans for the facility, although the site would have to be notified to the IAEA if they plan to inject uranium into it. The Vienna-based IAEA did not respond to questions about the new underground facility.

The new project will be built near Natanz, about 225 kilometers (140 miles) south of Tehran. Natanz has been a cause of international concern since he became known two decades ago.

Protected by anti-aircraft batteries, fences and Iran’s paramilitary Revolutionary Guard, the facility covers 2.7 square kilometers (1 square mile) of the country’s arid central plateau.

Satellite photos taken by Planet Labs PBC in April and analyzed by the AP show Iran digging into Kūh-e Kolang Gaz Lā, or “Pickle Mountain,” just beyond Natanz’s southern fence.

Another sequence of images analyzed by the James Martin Center for Nonproliferation Studies shows that four entrances were dug into the mountainside, two to the east and two to the west. Each is 6 meters (20 ft) wide and 8 meters (26 ft) high.

The scale of the work can be measured in large mounds of earth, two in the west and one in the east. Based on the size of the spoil piles and other satellite data, experts at the center told the AP that Iran is likely to build a facility between 80 meters (260 feet) and 100 meters (328 feet) deep. The center’s analysis, made available exclusively to the AP, is the first to estimate the depth of the tunnel system based on satellite images.

The Institute for Science and International Security, a Washington-based nonprofit that has long focused on Iran’s nuclear program, recommended last year that the tunnels go even deeper.

Experts say the size of the construction project indicates that Iran would likely be able to use the underground facility for uranium enrichment — not just centrifuges. The tubular centrifuges, arranged in large cascades of dozens of machines, rapidly spin the uranium gas to enrich it. The rotation of additional cascades would allow Iran to rapidly enrich uranium under the protection of the mountain.

“So the depth of the facility is a concern because it would be much more difficult for us. It would be much more difficult to destroy with conventional weapons, such as a typical bunker buster bomb,” said Steven De La Fuente, a research associate at the center who led the tunneling analysis.

The new Natanz facility is likely to be located even deeper underground than Iran’s Fordo facility, another enrichment facility uncovered in 2009 by the United States and other world leaders. That facility has sparked fears in the West that Iran is hardening its program for airstrikes.

According to the US military, these underground facilities led the US to create the GBU-57 bomb, which can plow through at least 60 meters (200 ft) of earth before detonating. U.S. officials reportedly discussed using two such bombs back-to-back to ensure the site was destroyed. It is not clear that such a one-two punch would damage a facility as deep as Natanz.

With such bombs potentially off the table, the US and its allies are left with fewer options to target the site. If diplomacy fails, sabotage attacks may continue.

Natanz is already the target of the Stuxnet virus, believed to be an Israeli and American creation, which destroyed Iranian centrifuges. Israel is also believed to have killed scientists involved in the program, struck facilities with bomb-carrying drones and launched other attacks. Israel’s government declined to comment.

Experts say such disruptive actions could push Tehran even closer to the bomb — and push its program even deeper into the mountain, where airstrikes, further sabotage and spies might not be able to reach it.

“Sabotage may set back Iran’s nuclear program in the short term, but it is not a viable long-term strategy to defend against a nuclear-armed Iran,” said Davenport, the nuclear deterrence expert. “Putting Iran’s nuclear program further underground increases the risk of proliferation.”

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