On April 11, Iran reported an “incident” at the Natanz nuclear facility that completely shut down its power supply. Initially, no explanation was given. However, on the very next day, several Iranian officials spoke of “sabotage” by a “terrorist attack.” Iranian leaders initially tried to create the impression that the damage was minimal and claimed that the plant’s full capacity would soon be restored. One reason for playing down the “incident” was to not grant Israel, which was soon named as the cause of the attack, any triumph.

But it was all to no avail. By the third day, when more reliable reports on the damage started to appear, the flow of information could no longer be contained. The attempted trivialization of the “incident” came to an end when the former head of the Iranian Atomic Energy Authority, Behrouz Kamalvandi, reported on Iranian television from his hospital bed that while inspecting the plant he had suddenly fallen into a seven-meter-deep hole and had injured himself considerably. Another televised statement by Alireza Zakani, the head of the Iranian Parliament's research center, according to which the explosion had destroyed “thousands” of centrifuges, underscored that what happened at Natanz was much more than a mere “incident.”

Meanwhile, the facts have become clearer. It appears that the Israeli intelligence service Mossad—possibly with the help of Iranian anti-government groups—had been able to smuggle an explosive device into the Natanz uranium enrichment facility and detonated it remotely.

The Natanz uranium enrichment plant is a complex of six buildings covering an area of 220,000 square meters. The actual production facility consists of two halls dug eight meters deep into the earth. In 2004, the ceiling of the underground hall was hardened by several meters of reinforced concrete and about 25 meters of soil. This information about Natanz is reliable, as the project had been monitored by satellites as well as by Israeli “tourists” from its very beginning. Initial uncertainties about the true purpose of the plant resulted from the fact that Iran would usually hide its nuclear facilities underground. By contrast, Natanz sported a large facility above ground, which the Iranians obviously wanted to protect by an extremely robust ceiling.

And now this! The Mossad had apparently infiltrated the Natanz facility and introduced an unknown quantity of high explosives (probably C4) into the underground halls. Based on current information, the explosion must have been devastating. The halls where the uranium was enriched may have been largely destroyed. Possibly not a single one of the approximately 5,000 centrifuges survived. The reason for this level of destruction lies in the delicacy of centrifuges. In their book Deception, Adrian Levy and Catherine Scott Clark described how a series of powerful earthquakes between 1989 and 2005 destroyed many Pakistani P-1 centrifuges. These centrifuges, which produced uranium-235 at 1,500 revolutions per second, could not be subjected to the slightest vibration without eventually self-destructing due to imbalances. When a centrifuge finally burst, it had the effect of several hand grenades. The earthquakes also revealed that a centrifuge that has been thus “shocked” cannot be repaired and is rendered permanently unusable.

Despite these facts, parts of the media still cling to the idea that after an air attack on Natanz, for example, the Iranians could promptly repair the damaged centrifuges. However, such views miss the mark. Gholam Reza Aghazadeh, the longtime head of Iran's Atomic Energy Agency, once described just how delicate ultra-centrifuges are. In 2006, he revealed on Iranian television the country’s problems in dealing with the challenge of centrifuge technology.

In the early stages of our work we realized that our centrifuges had many malfunctions. We could not determine the reason, because there were no references or books we could consult to solve this. After considerable effort, we noticed that when our experts assembled the centrifuges, they did not wear cloth gloves. We realized that if you assemble the centrifuges with bare hands, a little bit of sweat from between the fingers may transfer to the rotor, and increase the mass. When the rotor spins, it becomes a problem, which completely unbalances the centrifuge, causing it to explode. When I say that it explodes, it doesn't merely explode, but turns to powder.

In light of these facts, it is clear that a powerful explosive device, detonating at the lowest point of the underground halls, has eliminated Natanz as the sole site for Iran’s national uranium enrichment. This view was echoed by some nonproliferation experts, who argued that Tehran would now have to activate the underground enrichment plant at Fordow and the above-ground pilot plant at Natanz. There was a ring of desperation to this response because these experts knew very well that the nuclear agreement regulated the functions of both facilities—and that any significant enrichment of uranium in these facilities is prohibited.

If any further proof had been needed regarding the fate of the underground uranium enrichment facility at Natanz, it came in an announcement by the International Atomic Energy Agency (IAEA) on April 13. According to the IAEA, Iran, which had announced with great fanfare that it would now start enriching uranium up to 60 percent, would not do so at the underground Natanz facility on the basis of P-1 centrifuges, as originally intended, but at the above-ground unprotected pilot fuel enrichment facility. On April 19, the IAEA published its analysis of this enrichment process, and the Iranian government proudly announced the result. Tehran omitted any reference to the relocation of the procedure because this would inevitably have resulted in the implicit admission that the originally planned use of the underground facility and the mandatory use of the P-1 centrifuges were no longer possible. However, the IAEA reported that “UF-6 enriched to five percent U-235 was fed simultaneously into four cascades of IR-4 centrifuges and IR-6 centrifuges at the pilot fuel enrichment plant at Natanz.”

Soon thereafter it became clear that Iran had used the centrifuges at the above-ground pilot fuel enrichment plant not just for a short period of time but was operating them continuously since early April. The IAEA estimates that about 2.4 kilograms of UF-6 enriched to 60 percent have been produced so far—in a plant in which the enrichment of uranium to high levels is prohibited by the Joint Comprehensive Plan of Action (JCPOA). This is another serious violation of that agreement and also of the Nuclear Non-Proliferation Treaty.

Even though 25 kilograms of U-235 enriched to 90 percent are required to build a complete nuclear device, this activity by Iran, conducted in parallel with the ongoing negotiations, is an unprecedented challenge to the negotiators in Vienna and should be met with the immediate termination of the negotiations. Anyone producing uranium enriched to 60 percent is definitely working on nuclear weapons—there is no other conclusion.

Moreover, the future of Natanz is completely unclear. It is true that Iran still has enough centrifuges to equip a corresponding facility. However, it is more than questionable whether the underground halls would be ready for operation again in about nine months, as Tehran is saying. The damage is too severe. According to a confidential IAEA report in late May, before the April 11 “incident” Iran’s quarterly production of low enriched uranium had been consistently 525 kilograms. During the quarter from March to May 2021, however, production had decreased to 273 kilograms. The difference between 525 kg and 273 kg is a strong indication that the facility had been producing at its normal rate, until the April 11 “incident” brought the production to a standstill.

But these are secondary questions for now. What makes the current situation unique is that Israel has succeeded in crippling Iran’s Natanz uranium enrichment facility for the unforeseeable future—with a single explosive device and without significant collateral damage. This is particularly important because the 2015 nuclear agreement stipulates that Natanz is Iran’s sole facility for enriching uranium—Natanz “exclusively,” as the text of the JCPOA puts it. Moreover, since Iran’s part in the agreement consisted essentially of reductions in its enrichment capacity at Natanz, the extensive destruction of that facility would thus have made it objectively impossible for Iran to fulfill its obligations under the agreement. Thus, the JCPOA is obsolete and should be terminated; in any case, current developments at Natanz should lead to an indefinite suspension of negotiations.

Of course, Iran and some European states will try to continue the negotiations. However, it is more than questionable whether the United States will be willing to conduct such fake negotiations without the Iranians being able to bring something to the table. Such negotiations would then revolve just around lifting the sanctions imposed on Iran, without Tehran reciprocating and—according to Iran's demands in the run-up to the new round of negotiations—the United States paying damages in the triple-digit billions.

Hence, there is no other way to put it: with the attack on Natanz, Israel has pulled off a brilliant coup. The reactions of the real and self-proclaimed experts reveal as much: shock and deafening silence. One now has to deal with Iran’s nuclear program without being able to focus on the Natanz enrichment facility—a most unwelcome prospect. Over the past ten years the Natanz facility, which was initially part of Iran’s civilian nuclear program and intended only to supply the light-water reactor at Bushehr, had been redefined as Iran’s sole military enrichment facility. At the same time, the real nuclear threat from Iran, namely the secret nuclear program that the paramilitary Islamic Revolutionary Guards have been running since the mid-1990s, disappeared from the debate.