Why Iran’s new claims of not pursuing nuclear weapons programme lack credibility | Explained News

Khamenei said Iran was the only nuclear-capable country not to have developed a bomb, “and we won’t have one”, but maintained that it would not give up on its enrichment capabilities — something that the United States and Israel have been demanding.

This satellite photo from Planet Labs PBC shows reconstruction efforts at Iran’s Shahroud solid propellant plant outside of Shahroud, Iran, Sept. 5, 2025. (Planet Labs PBC via AP)
Enriching uranium

Nuclear weapons are powered by fissile materials, like uranium, whose nucleus can be split into nuclei of lighter elements in a sustained chain reaction. A huge amount of energy is released in this process.

Under controlled conditions, this same process is used to produce electricity in nuclear power stations. In nuclear weapons, the splitting of nuclei is allowed to happen uncontrollably which results in the release of immense amount of energy in a very short duration of time, causing largescale devastation.

Uranium is the most common fissile material used in these processes, either to make electricity in civilian reactors, or in the weapons. But naturally occurring uranium is not fissile, meaning its nucleus is relatively stable and does not readily break up into nuclei of smaller elements. Naturally occurring uranium is primarily U-238, a slightly heavier isotope of the element. It is the slightly lighter uranium, called U-235, which is fissile. More than 99 per cent of naturally occurring uranium is U-238.

Enrichment is the process of increasing the concentration of U-235 in a uranium sample.

An enrichment of 3-5 per cent is sufficient for use in nuclear power plants for the production of electricity. This process is carried out in a very controlled manner, so that the number of U-235 atoms undergoing fission in a chain reaction, and the consequent energy that is released, is strictly regulated.

Nuclear weapons, on the other hand, are designed to produce enormous amounts of energy to cause maximum devastation. For this many more atoms of uranium are needed to split. Therefore, the uranium used as fuel in nuclear weapons is enriched to very high levels, typically 90 per cent or above. This means that a fuel sample used in a weapon contains over 90 per cent concentration of U-235.

Highly-enriched uranium

These are the two most common use cases of enriched uranium — a 3-5 per cent enrichment for civilian power reactors, and over 90 per cent enrichment for building nuclear weapons.

There is little use for uranium enriched to intermediate levels in between these extremes.

A uranium sample enriched beyond 20 per cent is called highly enriched uranium, or HEU, and its production and use is carefully monitored globally. Production or storage of HEUs are definitive pointers to a nuclear weapons programme, because there is no civilian use for anything enriched beyond 20 per cent.

That is why Iran’s claim that it was not pursuing a nuclear weapons programme because it had capped enrichment at 60 per cent does not sound very credible. There is no other use of a 60 per cent enriched uranium, and achieving 90 per cent enrichment from a fissile material already enriched to 60 per cent is a pretty quick affair.

Technically, a 60 per cent enriched uranium is good enough to make a nuclear weapon, though its power and efficiency might be reduced. Countries usually go for more highly enriched uranium (90 per cent or more) because it enables the development of smaller and lighter weapons and delivery systems, and packs in much more devastating power. A weapon using 60 per cent enriched uranium might be more bulky, and the designs of the delivery system might also get a little more complicated. But 60 per cent enriched uranium is definitely bomb-material.

Occasionally, HEUs may be required in research reactors but this research is also directed towards military uses, and the development of nuclear weapons and not civilian purposes.