For those concerned about Iran becoming a nuclear-armed state, it is important to understand not only how U.S. and Israeli attacks have affected Iran's uranium enrichment capabilities, but also the status of Iran's existing nuclear fuel stockpile. Before the air strikes, Iran had accumulated a certain amount of highly enriched uranium, which if further processed, would be enough to provide fuel for 10 nuclear bombs. The international inspectors who have been tracking this batch of stockpiles currently have no idea where they are going.
What is highly enriched uranium?
Natural uranium is mainly composed of two isotopes: uranium-238 and uranium-235. The latter is directly involved in the nuclear fission reaction crucial for nuclear energy and nuclear weapons, but is present in very low amounts in natural uranium ores. Therefore, the abundance of uranium-235 must be increased through enrichment.
An abundance threshold of 3.7% needs to be reached to fuel most nuclear power plants. For nuclear weapons, it must reach 90%. But as long as the abundance exceeds 20%, it can be defined as "highly enriched uranium" because at this time the material requires special processing, and the process of further enriching it to weapons grade is relatively fast.
How does the international community track Iran’s highly enriched uranium?
Before the attack on Iran, 274 inspectors from the International Atomic Energy Agency (IAEA), the global nuclear watchdog, were rotating through Iran to track its declared uranium stockpile. They visit no less than one location every day to ensure that materials are documented and are not being diverted to weapons manufacturing.
The IAEA reported in May that Iran had accumulated 409 kilograms (902 pounds) of uranium with a 60% abundance, an increase of almost 50% from the amount recorded three months earlier.
Iran insists that its nuclear program is not military in nature. But on June 12, the IAEA condemned Iran, saying it had failed to fulfill its obligation to cooperate with inspectors and that the agency could not determine whether Iran's nuclear program was "entirely for peaceful purposes."
Where is Iran's highly enriched uranium currently located?
This is an open question.
According to IAEA Director General Rafael Mariano Grossi, the last time inspectors saw Iran's highly enriched uranium was on June 13, days before the Israeli air strikes began. The airstrikes halted inspections. At the time, the enriched uranium stockpile was located at the Isfahan Nuclear Technology and Research Center, a chemical processing hub that converts uranium ore into feedstock ready for enrichment. The Isfahan facility, located in central Iran, was attacked by Israel and subsequently by the United States.
Satellite images show damaged buildings at the Isfahan Nuclear Technology Center after an airstrike.
In a note circulated by the IAEA, Iran said it would take "special measures" to move the highly enriched uranium to a reinforced site if such an attack occurred. The note was dated three weeks before the first Israeli attack.
Highly enriched uranium storage tank
After the bombing began, Grossi said he received a letter from Iranian Foreign Minister Abbas Araghchi saying the measures had been implemented. Grossi asked Iran to inform inspectors of the new location of enriched uranium, but the Iranian authorities did not respond.
The risk is that uranium that is close to weapons grade could be hidden indefinitely. The last known uranium stockpile reported by the IAEA could be stored in 16 tanks each 36 inches (91.4 centimeters) high, according to estimates released by U.S. regulators. This is approximately the size of a large scuba tank. Each tank weighs about 25 kilograms, enough to be carried on a person's back.
Grossi said he was optimistic that a lasting ceasefire could pave the way for the resumption of negotiations on the Iranian nuclear issue and the resumption of institutional inspections.
If the conflict with Israel resumes and Iran surrenders unconditionally — as Trump demanded in a June 17 social media post — the surrender would allow Israel and the United States to implement an inspection regime similar to the one implemented in Iraq after the 1991 Gulf War. Iran's Supreme Leader Ayatollah Ali Khamenei has rejected this possibility.