Strikes on any nuclear facilities could, in theory, release clouds of deadly radiation that endanger human lives and health. But in the case of Israel’s attacks on Iran overnight on Friday, that appears so far to not have been the case.
The earliest attacks and targets seem for the moment to rule out the most dangerous outcomes, limiting possible radiation threats to the realm of the relatively minor.
The most dangerous kind of threat would arise from successful attacks on nuclear reactors. Over time, the splitting of atoms in reactor fuel results in buildups of highly radioactive spinoffs. Among the worst are Cesium 137, Strontium 90 and Iodine 131.
If Iodine 131 is inhaled or ingested, it ends up in a person’s thyroid gland. There, its intense radioactivity raises dramatically the risk of thyroid cancer, particularly in children. The other isotopes can also result in cancers.
But so far, no reports or evidence suggest that Iran’s nuclear reactors were hit in the Israeli attacks. Apparently spared were a power plant on the Persian Gulf, a research reactor in Tehran and a heavily guarded site ringed by antiaircraft weapons and miles of barbed wire.
Known as Arak, that isolated complex was long suspected of being built to produce plutonium, one of the two main fuels for atom bombs. But the Obama administration’s 2015 deal with Iran turned the complex into a nuclear relic unusable for that purpose. The Arak reactor never came to life.
A lesser threat to human health revolves around uranium, the other fuel of atom bombs. In recent years, Iran has focused on it with great intensity, building an increasingly wide array of industrial plants and complexes to refine the fissile element.
Uranium ore that miners dig up is relatively harmless. But it contains tiny amounts of a rare radioactive isotope, Uranium 235, that can be used to power nuclear reactors at low levels of enrichment, and to fuel atom bombs at higher levels. The percentage of U-235 in mined uranium is less than 1 percent.
The goal of uranium enrichment is to raise the percentage, which is often done through the use of centrifuges — machines that spin at extremely high speeds. Iran started with low percentages and, over decades, has increasingly raised its enrichment levels. The highest now stand at 60 percent, which is just short of bomb grade.
For human health, the higher the level of U-235 enrichment, the greater the danger. The isotope and its decay products emit three types of radiation: alpha particles, beta particles and gamma rays. The first two are relatively weak. Alphas cannot penetrate skin. Betas can be stopped by a layer of clothing.
But gamma rays are highly energetic and can penetrate the human body, damaging DNA and sowing the seeds of cancer. It takes thick concrete or lead to stop the penetrating rays.
Satellite images and expert analyses show that a main target of the Israeli strikes was the Natanz complex, the largest of Iran’s enrichment sites. Fully destroyed was the Pilot Fuel Enrichment Plant, where Iran was producing uranium enriched to near 60 percent. The images show a dark craterlike scar. And videos from a distance show clouds of dark smoke.
It’s possible that some of that smoke contained U-235 particles, which may pose a regional health hazard. But the International Atomic Energy Agency, which monitors the Iranian site, said it had so far detected no such danger.
“The level of radioactivity outside the Natanz site has remained unchanged and at normal levels indicating no external radiological impact to the population or the environment from this event,” Rafael Mariano Grossi, the agency’s director general, said Friday before the U.N. Security Council.
He mentioned concerns about alpha particles inside the Natanz facility, but called them “manageable” with appropriate radiation protection measures.
Acknowledging reports of attacks at Fordo and Isfahan, two other nuclear fuel sites in Iran, he said “we do not have enough information.”
Aside from the radiation danger, a complicating factor in the health calculus is that uranium in all its forms is a toxic heavy metal, similar to lead. If ingested it can produce a cascade of adverse health effects, with the kidneys a main target. Acute exposure can lead to renal failure. The main routes of exposure are ingestion of contaminated food and water, inhalation of airborne dust, and, to a lesser extent, contact with the skin.
The inhalation of uranium dust — a common hazard in mining and milling — is also a hazard. Inhaled particles can lodge in the lungs, leading to respiratory irritation, inflammation, and, over time, such lung diseases such as fibrosis.
A number of diplomats expressed their worries before the Council about the radiation threats from Israel’s strikes.
“We are particularly concerned by the potential radiological consequences,” said Vasily Nebenzya, Russia’s permanent representative to the U.N. They can lead, he added, “to the most dire consequences not just for the Middle East region, but for the world as a whole.”
Mr. Nebenzya said Russia was following closely the status of the inspectors in Iran of the I.A.E.A.
“The life and health of its personnel has been threatened,” he said. “And we expect that the director general of the agency is going to provide us with objective assessment and analysis of the developing situation, including from the viewpoint of radiological consequences.”
William J. Broad has reported on science at The Times since 1983. He is based in New York.
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