More nuclear distortions - part II

The US and Israel continue their campaign of nuclear disinformation vis-à-vis Iran. From Ha'aretz:

The IAEA report showed a significant increase in Iran's reported stockpile of low-enriched uranium (LEU) since November to 1,010 kg - enough, some physicists say, for possible conversion into high-enriched uranium for one bomb.

What's disingenuous about this is that it's probably the truth but certainly not the whole truth.

Low enriched uranium (LEU) contains about 3 - 5 w% of U 235, the fissionable isotope needed for civilian or military nuclear purposes (the balance is mainly U 238). Assuming the figure of 1,010 kg to be accurate and assuming the U 235 content to be in the upper side of the range, i.e. 5 w%, then, in theory, Iran would possess 1,010 kg x 0.05 ≈ 50 kg, which is indeed enough for 1 Little Boy (Hiroshima) type A-bomb.

But. There is a big But. Weapons grade uranium has a U 235 content of at least 85 w% and this can only be achieved by further enrichment (by means of gas centrifuges). Just consider this: natural uranium only contains about 0.72 w% of U 235, so to obtain LEU at 5 w% of U 235, the enrichment process has to increase the U 235 content by a factor of about 5 / 0.72 ≈ 7. To further enrich the LEU even to a lower specification highly enriched uranium (HEU) of, say, 85 w% of U 235, the enrichment process has to increase the U 235 content by a factor of about 85 / 5 ≈ 17. So clearly the obtaining of LEU from natural uranium is by far the smallest leg of the journey.

This is even more so if we assume LEU = 3 w% of U 235 and HEU = 90 w% of U 235 because the respective enrichment factors then become approx. 4 and 30!

The above quoted statement thus shows that even if it's 100 % correct, the uranium would remain in a physical form that is wholly unsuited for nuclear bombs and that to obtain the required weapons grade HEU from LEU requires a hat trick many times more complicated than obtaining LEU from natural uranium.

Lastly it's likely that the quoted inventory includes civilian nuclear fuel bought legitimately from Russia, and that would be LEU that cannot be tampered with.

And why, if it wants nuclear weapons, Iran didn't choose the plutonium route is also far from clear. Plutonium is much easier to produce, separate and refine. Its critical mass is lower than U 235 and that makes it easier to weaponise (miniaturise).