Satellite Analysis Suggests Iran Moved Highly Enriched Uranium to Secure Tunnels Days Before Strikes
In a significant development with major implications for global nonproliferation efforts, new analysis of high-resolution satellite imagery indicates that Iran likely transferred nearly its entire stockpile of highly enriched uranium HEU up to 540 kilograms enriched to 60% U-235 into a deep underground tunnel complex at the Isfahan Nuclear Technology Center just four days before airstrikes began in June 2025.
A very high-resolution Airbus Pléiades Neo image captured on June 9, 2025 shows a large flatbed truck carrying 18 shielded blue containers resembling nuclear transport casks at the southern tunnel entrance of the underground facility. Accompanied by a crane truck and security vehicles, the convoy appeared positioned to offload cargo into fortified mountain tunnels designed to protect sensitive nuclear assets during conflict.
Nuclear experts, including François Diaz-Maurin of the Bulletin of the Atomic Scientists and analysts at the Institute for Science and International Security, assess that the containers’ size, shielding, and capacity align closely with transport systems capable of holding Iran’s full pre-strike inventory of roughly 441 kilograms of 60% enriched uranium as previously reported by the International Atomic Energy Agency. This suggests Iran may have preemptively emptied vulnerable enrichment sites such as Natanz and Fordow, relocating the material to deeper and more protected tunnels at Isfahan, a site that sustained comparatively less severe damage during subsequent Israeli and U.S. strikes.
The timing raises critical questions about the effectiveness of those strikes. Post-strike assessments indicate that while surface facilities and some access points were damaged, the underground tunnel complex likely shielded the HEU stockpile. The IAEA has since raised concerns regarding the exact location and security of Iran’s enriched uranium, citing restricted access and continued vehicular activity around the tunnels, while lacking full verification inside undamaged sections. Iran has reportedly reinforced tunnel entrances with soil and concrete.
Technical analysis indicates that uranium enriched to 60% can be further processed to weapons-grade levels of around 90% in as little as 10 days using advanced centrifuges, although Iran’s broader nuclear program is believed to have suffered setbacks from the strikes.
Alternative explanations such as decoy materials, medical isotopes, or construction equipment were considered but are assessed as less likely given the characteristics of the containers, their positioning at a nuclear facility, and the timing shortly before anticipated military action.
This assessment is based on detailed visual and technical analysis published by the Bulletin of the Atomic Scientists in March 2026, supported by reporting from Le Monde and corroborating analysis from the Institute for Science and International Security.
Source: Bulletin of the Atomic Scientists, with supporting reporting from Le Monde and the Institute for Science and International Security
This development highlights ongoing challenges in verifying Iran’s nuclear activities amid limited international access and underscores continued global concern over the status of near weapons-grade nuclear material.