What Happens When a Nuclear Site Is Hit?

Into the second month of the US-Iran war, the conflict in the Gulf continues to escalate—airstrikes widening, oil markets reacting, and pressure mounting around the Strait of Hormuz. But beyond the immediate security and economic concerns, another question is quietly taking shape: What actually happens if a nuclear site is hit?

In most cases, even if a nuclear facility is hit, a large-scale radiological disaster is unlikely. Modern sites are designed with multiple safety systems that can shut down reactors and contain damage.

The risk isn’t defined by the strike itself, but by what the strike damages inside the facility. The risk becomes significantly higher, however, if those systems fail—or if an operational nuclear power plant is directly affected.

Where the Risk Begins

On February 28, when the US and Israel launched a coordinated military campaign against Iran’s leadership and military infrastructure, Iran’s nuclear and ballistic missile sites were marked as potential targets. As the conflict deepened, Iranian officials reported strikes on the Natanz nuclear facility, a primary uranium enrichment complex, located around 140 miles from Tehran.

This was followed by strikes on the Ardakan facility as well as the Khondab heavy water reactor, which was left inoperable after the attack. Earlier this week, additional heavy bunker-buster bombs were also launched in Isfahan, in close proximity to the Isfahan Nuclear Technology Center.

So far, international watchdogs have reported no radiation leaks from the targeted facilities. The International Atomic Energy Agency (IAEA) has said there is no indication of off-site contamination, even after reported strikes on sites such as Natanz and near Isfahan.

But the concern isn’t limited to the impact site.

Across the Gulf, the risks are shaped by geography and infrastructure. Much of the region depends on desalinated seawater—systems that pull directly from the sea. If radioactive material were to enter marine environments, it wouldn’t just spread through ecosystems, but through the infrastructure that supplies drinking water to millions.

The Bushehr nuclear power plant, located along Iran’s Gulf coastline, sits within close proximity to neighboring states. While it has not been directly affected, experts have repeatedly warned that any escalation involving coastal nuclear infrastructure could have cross-border consequences.

What Happens Next

Not every strike on a nuclear site leads to a dramatic mushroom cloud explosion or an immediate radiation release. What matters is where the site is hit and how much damage is done to its safety systems.

Within minutes of impact, a reactor is designed to shut down automatically. This stops the nuclear reaction, acting as the first line of defense. But shutdown doesn’t eliminate the risk.

The reactor core continues to generate heat through radioactive decay, and that heat must be controlled. The extent of the damage—whether to buildings, control systems or backup infrastructure—determines how effectively those safety mechanisms can continue to function.

In past incidents, including the Fukushima Daiichi nuclear disaster in Japan, the shutdown worked as intended. The crisis began only after a tsunami disabled critical systems in the hours that followed.

Without cooling, heat begins to build inside the reactor core. If cooling systems are damaged, whether through loss of power, failed pumps, or destroyed backup generators, the temperature continues to rise. In water-cooled reactors, this can lead to the accumulation of hydrogen gas, increasing the risk of explosions that can further damage the facility.

As conditions worsen, fuel rods inside the reactor begin to degrade. This is the point at which radioactive materials can be released.

These materials include different types of radioactive isotopes, such as noble gases, volatile isotopes, long-lived isotopes and fuel particles. While some, like noble gases, disperse quickly and have limited short-term impact. Others, particularly long-lived isotopes—which can remain in the environment for years or even decades—and fuel particles, can cause serious contamination if not contained.

For example, Russia’s Chernobyl disaster caused a complete fuel meltdown, releasing dangerous long-lived isotopes into the atmosphere and contaminating large parts of Europe.

How the World Responds

In the event of a nuclear incident, the IAEA’s Incident and Emergency Centre (IEC) acts as the global focal point for preparedness and response.

Amgad Shokr, director of IEC, says the process begins by verifying information with national authorities and assessing the situation and its potential impact.

“When alerted, the IEC gathers and verifies information with national authorities to understand the situation and its possible implications,” he says. “Its objectives are to provide accurate, timely updates to the public and all member states,” he adds.

International communication begins shortly after information is confirmed, with the IAEA issuing updates, providing public information, and coordinating with relevant organizations under established response plans.

Impact on the Environment

The spread of radioactive material depends on distance as well as how it moves through air, water, and soil.

In the event of a containment breach, gases can travel long distances, but their concentrations decrease over time and distance. Radioactive gases from the Fukushima incident, for example, reached North America at harmless levels.

Heavier isotopes behave differently. When they enter water bodies, they dilute but can still affect marine life—and in the Gulf, potentially desalination systems. Long-lived isotopes such as cesium-137 and strontium-90 can settle into soil, contaminate farmland and crops, and persist for decades.

To manage these risks, the IAEA has developed safety standards aimed at maintaining critical systems even during high-risk scenarios such as the ongoing conflict.

Once a breach is identified, Shokr explains that experts assess whether essential safety functions—such as power supply, cooling systems, structural integrity and communication—are still intact. If any of these fail, the agency evaluates the likelihood of a radiological release and models how radiation could spread using weather data and international monitoring systems.

From a public-health perspective, the level of direct exposure is more significant than distance alone. If radiation dispersion is detected, standard protocols are activated, including evacuation measures, the distribution of iodine tablets to reduce thyroid absorption of radioactive iodine and coordinated emergency responses based on the severity of the incident.

Most Likely vs. Worst-Case Scenarios

Most strikes on nuclear facilities are unlikely to trigger a large-scale radiological disaster. Modern sites are designed with multiple safety systems, meaning that even in the event of damage, shutdown and backup cooling can prevent significant radiation release.

In these scenarios, any contamination would likely remain localized, with limited cross-border impact.

A worst-case scenario, however, would involve sustained damage to critical safety systems—particularly cooling infrastructure—leading to a reactor meltdown. In such cases, radioactive material could be released into the air and surrounding water, potentially spreading across borders depending on wind patterns and ocean currents.

In the Gulf, this risk is amplified by the region’s reliance on desalinated water and its relatively enclosed marine environment, where contamination could persist longer and affect both infrastructure and ecosystems.

At the time of writing, there have been no confirmed reports of radiation leaks or radioactive plumes crossing borders from Iran’s nuclear sites. For now, the risk remains contained—but it depends on whether the systems designed to prevent escalation continue to hold.