The nearly 15,000 centrifuges operating at Iran's largest uranium enrichment plant at Natanz have likely been badly damaged or destroyed by a power outage caused by an Israeli attack, the head of the UN nuclear watchdog told the BBC on Monday.
The International Atomic Energy Agency (IAEA) and its director general, Rafael Grossi, had previously said that centrifuges at the underground Natanz enrichment plant may have been damaged by an airstrike targeting its power supply, but that the plant's warehouse did not appear to have been hit.
“Our assessment is that with this sudden loss of external power, it is very likely that the centrifuges have been severely damaged, if not completely destroyed,” Grossi said in an interview with the BBC.
“I think there has been damage inside,” he said, going further than in an update for a rare meeting of his agency’s 35-country Board of Governors hours earlier.
Power outages pose a threat to fragile, finely balanced machines that spin at extremely high speeds.
Israeli airstrikes have put at least two of Iran's three uranium enrichment plants out of service. The Natanz aboveground pilot enrichment plant was destroyed, Grossi repeated in his update to the board.
Grossi told the board there was no damage to the Fordow enrichment plant, dug deep into a mountain, but later told the BBC: “The damage recorded is very limited.”
Although the IAEA has been unable to carry out inspections since the attacks, it uses satellite imagery.
Grossi detailed the damage to four buildings at the Isfahan nuclear complex, including a facility for converting uranium “yellowcake” into uranium hexafluoride, the raw material for centrifuges, in order to enrich it with greater fissile purity.
How uranium is enriched
A uranium enrichment plant is a highly technical facility that transforms natural uranium, as mined, into a material useful for generating nuclear energy or, in more sensitive cases, for making weapons. Natural uranium mostly contains an isotope called U-238, which is unusable for nuclear fission, and a small proportion—less than 1%—of U-235, which is fissile and therefore useful for reactors. But for it to work in a power plant, that proportion of U-235 must be increased, and that is precisely what the enrichment process achieves.
It all starts with “yellowcake,” a concentrated form of uranium obtained after refining mined ore. This yellow powder is then converted into a gas through a chemical reaction that transforms it into uranium hexafluoride (UF₆). Once gaseous, it can be physically manipulated to separate the isotopes. The separation relies on a tiny mass difference between the U-235 and U-238 atoms. Although it may seem insignificant, this difference allows very precise technologies to separate one from the other.
The most widely used method currently is centrifugation. In this system, uranium gas is introduced into metal cylinders that rotate at extremely high speeds. Due to centrifugal force, the heavier atoms (U-238) concentrate at the edges, while the lighter ones (U-235) tend to remain closer to the center. Through a chain of thousands of connected centrifuges—known as a"cascade"—a gas increasingly enriched in U-235 is progressively obtained. This system replaced a much more inefficient and expensive system decades ago: gaseous diffusion.
Although other technologies exist, such as laser enrichment, these are still in the experimental stages or are used in very specific cases. The output from the process can have different levels of enrichment. For a power reactor, 3% to 5% U-235 is usually sufficient. But if that percentage exceeds 90%, the uranium becomes suitable for nuclear weapons, something that raises international concern. Therefore, these plants are strictly monitored by organizations like the IAEA.
The end result is two materials: one enriched, which serves as nuclear fuel, and another depleted, which contains primarily U-238 and is considered waste. Although the process is not technically complex to understand, it requires sophisticated infrastructure, advanced knowledge of physics and chemistry, and rigorous controls to prevent diversion for military purposes.
