How the world's nuclear watchdog monitors facilities around the world - and what it means that Iran kicked it out

Once a country signs the treaty, the world’s nuclear watchdog, the International Atomic Energy Agency, provides continuous and technical proof that the country’s nuclear program is peaceful.

The IAEA ensures that countries operate their programs within the limits of nonproliferation agreements: low enrichment and no reactor misuse. Part of the agreement allows the IAEA to inspect nuclear-related sites, including unannounced surprise visits.

These are not just log reviews. Inspectors know what should and should not be there. When the IAEA is not on site, cameras, tamper-revealing seals on equipment and real-time radiation monitors are working full-time to gather or verify inside information about the program’s activities.

Safeguards toolkit

The IAEA safeguards toolkit is designed to detect proliferation activities early. Much of the work is fairly technical. The safeguards toolkit combines physical surveillance, material tracking, data analytics and scientific sampling. Inspectors are chemists, physicists and nuclear engineers. They count spent fuel rods in a cooling pond. They check tamper seals on centrifuges. Often, the inspectors walk miles through hallways and corridors carrying heavy equipment.

That’s how the world learned in April 2021 about Iran pushing uranium enrichment from reactor-fuel-grade to near-weapons-grade levels. IAEA inspectors were able to verify that Iran was feeding uranium into a series of centrifuges designed to enrich the uranium from 5%, used for energy programs, to 60%, which is a step toward the 90% level used in nuclear weapons.

Around the facilities, whether for uranium enrichment or plutonium processing, closed-circuit surveillance cameras monitor for undeclared materials or post-work activities. Seals around the facilities provide evidence that uranium gas cylinders have not been tampered with or that centrifuges operate at the declared levels. Beyond seals, online enrichment monitors allow inspectors to look inside of centrifuges for any changes in the declared enrichment process.

When the inspectors are on-site, they collect environmental swipes: samples of nuclear materials on surfaces, in dust or in the air. These can reveal if uranium has been enriched to levels beyond those allowed by the agreement. Or if plutonium, which is not used in nuclear power plants, is being produced in a reactor. Swipes are precise. They can identify enrichment levels from a particle smaller than a speck of dust. But they take time, days or weeks. Inspectors analyze the samples at the IAEA’s laboratories using sophisticated equipment called mass spectrometers.

In addition to physical samples, IAEA inspectors look at the logs of material inventories. They look for diversion of uranium or plutonium from normal process lines, just like accountants trace the flow of finances, except that their verification is supported by the ever-watching online monitors and radiation sensors. They also count items of interest and weigh them for additional verification of the logs.

Beyond accounting for materials, IAEA inspectors verify that the facility matches the declared design. For example, if a country is expanding centrifuge halls to increase its enrichment capabilities, that’s a red flag. Changes to the layout of material processing laboratories near nuclear reactors could be a sign that the program is preparing to produce unauthorized plutonium.

Losing access

Iran announced on June 28, 2025, that it has ended its cooperation with the IAEA. It removed the monitoring devices, including surveillance cameras, from centrifuge halls. This move followed the news by the IAEA that Iran’s enrichment activities are well outside of allowed levels. Iran now operates sophisticated uranium centrifuges, like models IR-6 and IR-9.

Removing IAEA access means that the international community loses insight into how quickly Iran’s program can accumulate weapon-grade uranium, or how much it has produced. Also lost is information about whether the facility is undergoing changes for proliferation purposes. These processes are difficult to detect with external surveillance, like satellites, alone.

An alternative to the uranium enrichment path for producing nuclear weapons material is plutonium. Plutonium can’t be mined, it has to be produced in a nuclear reactor. Iran built a reactor capable of producing plutonium, the IR-40 Heavy Water Research Reactor at the Arak Nuclear Complex.

Iran modified the Arak reactor under the now-defunct Joint Comprehensive Plan of Action to make plutonium production less likely. During the June 2025 missile attacks, Israel targeted Arak’s facilities with the aim of eliminating the possibility of plutonium production.

With IAEA access suspended, it won’t be possible to see what happens inside the facility. Can the reactor be used for plutonium production? Although a lengthier process than the uranium enrichment path, plutonium provides a parallel path to uranium enrichment for developing nuclear weapons.

Continuity of knowledge

North Korea expelled IAEA inspectors in 2009. Within a few years, they restarted activities related to uranium enrichment and plutonium production in the Yongbyon reactor. The international community’s information about North Korea’s weapons program now relies solely on external methods: satellite images, radioactive particles like xenon – airborne fingerprints of nuclear activities – and seismic data.

What is lost is the continuity of the knowledge, a chain of verification over time. Once the seals are broken or cameras are removed, that chain is lost, and so is confidence about what is happening at the facilities.

When it comes to IAEA inspections, there is no single tool that paints the whole picture. Surveillance plus sampling plus accounting provide validation and confidence. Losing even one weakens the system in the long term.

The existing safeguards regime is meant to detect violations. The countries that sign the nonproliferation treaty know that they are always watched, and that plays a deterrence role. The inspectors can’t just resume the verification activities after some time if access is lost. Future access won’t necessarily enable inspectors to clarify what happened during the gap.