Enrichment is the process of increasing the concentration of Uranium-235 (U235) in a sample of natural uranium which is primarily — more than 99 per cent — Uranium-238 (U238). It is only U-235 that is fissile, meaning its nucleus is susceptible to being broken (fissionable) through a process that produces energy, and is capable of sustaining a chain reaction. An enrichment of 3-5 per cent is adequate for producing electricity in nuclear power stations, but for making nuclear weapons, HEU, which has concentrations of 90 per cent or more of U235, is required.

The attacks have led to fears of a major nuclear disaster, in the form of nuclear explosion, or at least largescale nuclear radiation leaks. However, an explosion is not expected under these circumstances, and thankfully, no major radiation leak has been detected so far.

The International Atomic Energy Agency (IAEA), the global nuclear watchdog, said it had not seen any increase in ‘off-site radiation levels’ following Sunday’s attacks. Iran has also said that there was no risk to public health because of the attacks.

How nuclear weapons are different from other bombs

A nuclear bomb is very different from the traditional explosives and chemicals used in warfare. Traditional bombs use a variety of chemicals that are generally designed to explode on impact, like when they are dropped. These chemical explosives can go off in other circumstances as well, like when they are exposed to heat or friction. These are explosive in themselves, and can get triggered and cause damage even when they are not used in the way they are designed to. Specifically, stored chemical explosives can lead to blasts when these are struck by other weapons.

Nuclear weapons, or nuclear material, do not behave like that. A nuclear bomb causes damage not by exploding the way traditional bombs do, but by releasing very high amounts of energy in a very short span of time. This large amount of energy sets off a series of processes that cause widespread damage.

Nuclear weapons are designed to detonate mid-air, not on impact like traditional explosives. They release a massive amount of energy in a few milliseconds, which heats up the surrounding air to millions of degrees Celsius, leading to the formation of what are known as blast waves, an expanding bubble of extremely hot air. Most of the damage is caused by these blast waves.

A nuclear explosion also releases electromagnetic radiations of different kinds, and these also cause a lot of destruction.

The release of energy from a nuclear device is the result of completion of the chain reaction in the fissile material. The initiation of the chain reaction requires a very precise set of processes to be followed and very precise conditions. These precise conditions cannot be met accidentally, or when the fissile material is under some kind of stress, like when it is struck by a missile or a bomb.

That is why the Israeli, or the American, strikes on Iran’s nuclear facilities do not result in a risk of a nuclear explosion. The sites, and the infrastructure it contained, could have been damaged, but there is no likelihood of a nuclear explosion.

But what about radiation leak

This is a more realistic threat. There are risks of both chemical and radiological leaks. Nuclear facilities, by their very nature, store a lot of radioactive substances, particularly uranium in different forms, including in gaseous state like uranium hexafluoride (UF6), and dust. Radioactive substances are unstable and release radiation over time. Some of these radiations, like gamma rays, are extremely harmful. They can penetrate the skin, damage cells and DNA, and can cause cancer.

These radioactive substances are stored, and handled, in carefully designed containers in any nuclear facility. These facilities are constructed in ways to minimise the risk of any leak of radioactive substances in outer environment or in sources of water or food.

An attack on these facilities, like the one carried out by Israel or the US, can damage or disrupt the mechanisms that ensure safe storage and handling of these substances. Two of the biggest instances of radiological leaks are the accidents that happened in Chernobyl in 1986 and Fukushima in 2011. In both these cases, largescale radioactive substances escaped into the atmosphere as a result of accidents, posing a major threat to human beings and others.

A more recent threat was seen at the Zaporizhzhia nuclear power plant in Ukraine that has been caught in the fight between Russian and Ukrainian forces. The Zaporizhzhia plant is the largest in Europe, and has come under direct attack several times during the conflict. Thankfully, it continues to operate safely.

The IAEA, which monitors nuclear activities worldwide, including radiation incidents, has said there has been no increase in radiation levels in areas surrounding the targeted sites in Iran. “…the IAEA can confirm that no increase in off-site radiation levels has been reported as of this time. IAEA will provide further assessments on situation in Iran as more information becomes available,” it said on Sunday morning, within hours of the US attack.