Wikipedia points to a source that says it is used for parts of a multi-stage fusion bomb:

> Uranium with enrichments ranging from 40% to 80% U-235 has been used in large amounts in U.S. thermonuclear weapons as a yield-boosting jacketing material for the secondary fusion stage

Source: http://nuclearweaponarchive.org/Nwfaq/Nfaq6.html#nfaq6.2

Ah yes, alongside the weapons grade steel and weapons grade copper.

There’s no minimum qualification for steel to be useful in a bomb, there is for uranium which this meets.

Just to be clear, this isn't "useful [to make] a bomb" - it's useful in a thermonuclear warhead that already has a primary fission stage using the originally-mentioned highly enriched weapons grade uranium, plus a second fusion stage that (as far as I'm aware) Iran is not working to develop.

edit: phrasing. it feels like we're going around in circles nitpicking based on a poor framing and the tendency for innuendo on this topic

You might want to rephrase that as a thermonuclear warhead is obviously a bomb making it “useful in a bomb.”

Also, you can use 60% enriched uranium in the primary stage at the cost of a much larger, less efficient, and dirty device.

> plus a second fusion stage that (as far as I'm aware) Iran is not working to develop.

All modern nukes are two stage designs, Iran would be insane not to have a fusion stage. It would basically be a Hiroshima style dirty bomb with just 1.5% fissible mass actually fissioned.

I'm well aware of the difference in yield, but I thought a second fusion stage required modeling and testing well beyond basic development? Like I take a quick look at Wikipedia for what devices (for example) India has, and it seems to say whether they contain a significant fusion stage is an open question.

Hiroshima was pretty terrible as it was. And I thought the capability that everyone focuses on because it gets nations a seat at the nuclear table was just basic fission weapons. But please correct me if I am wrong.

> I thought a second fusion stage required modeling and testing well beyond basic development

The bottleneck is UF₆ centrifuges, not the modeling. They're definitely aiming for a fission-fusion design: "The sources note that Iran has attempted to produce deuterium-tritium gas on its own inside Iran - with the help of Russian scientists - but has so far been unable to do so, and due to pressures by the Iranian leadership to accelerate the weapons production program, decided to try to purchase this substance abroad." [0]

India and Pakistan did their first tests ~30 years ago, a lot has changed since then and if you're building a nuke in '25 might as well spend some cash on a simulation cluster and buy some multiphysics simulation software from Russia..

[0] The sources note that Iran has attempted to produce deuterium-tritium gas on its own inside Iran - with the help of Russian scientists - but has so far been unable to do so, and due to pressures by the Iranian leadership to accelerate the weapons production program, decided to try to purchase this substance abroad.

Aren't there some R&D difficulties there? Like that whole fogbank thing the US forgot how to make? I hear trying to obtain deuterium and I figure it's for development and small-scale experiments, rather than an ingredient for a straightforward bomb recipe.

Maybe I'm just putting too much weight on the trials and tribulations of developing the first fusion bombs, and the details of solving or working around those problems is widely known in the right circles these days? Plus advancements in simulation accuracy?

When the only purpose of stepping into that gap is to get to weapons grade, it doesn't really work as a gray area.

Yes, it does actually. It's called "not weapons grade."

Do words mean nothing to you?

Fuel grade is like 3%. It's exponentially harder to go from 3%-60% (months-years) than 60%-90%(days-weeks). So no, the only reason to enrich that high is to keep your breakout time threateningly short.

Which still, astonishingly, does not make it weapons grade.

True, but can you name a reason to create a stockpile of 60% enriched uranium that doesn't involve weapons?

Yep! Negotiation.

Yes brother you are technically correct about that substring of that comment. “Weapons-grade” was indeed not 100% accurate and therefore, technically , inaccurate. That is true, you are right.

That same comment also said, even led with “flies in the face of”. That was the most important part of the comment: ‘saying that Iran is enriching weapons-grade uranium “flies in the face of” intelligence reports which reported no weapons-grade uranium.’ But that part was not correct: the difference between Iran’s uranium (60% enriched) and weapons-grade uranium, while >0, is not large enough to characterize that assessment “flying in the face of”.

So yes if you focus on that substring of the comment you are right. But why would you? It’s not the point of the comment.

Which makes it nit picking. Which is why you’re getting so much pushback.

The parent comment says it flies in the face of the US IC's holistic assessment of Iran's efforts. Which it does.

The only reason to make 60% is to make a weapon, and it’s actually useful in a weapon.

Saying it’s not weapons grade only means you haven’t finished or intend to use something else for the initial stage.

> only means you haven’t finished or intend to use something else for the initial stage

So in other words it’s not weapons grade?

No, 60% is a weapons grade enrichment level, but does not qualify in specific weapons grade categories.

Reduced fat milk is often specifically referring to 2% milk, but 1% milk is also reduced fat milk.

I don’t think you even believe the words you’re writing.

Everything I just said was factually accurate.

There’s a lot of misunderstanding around this stuff. Technically all you need for a bomb is the ability to go prompt critical on demand which you can do at surprisingly low enrichment levels. What’s a useful weapons grade enrichment to you has a lot to do with your delivery systems not some universal constant. If you’re looking to fit something in a WWII bomber or early generation ICBM that imposes specific limitations.

Being able to produce weapons grade uranium != producing weapons grade uranium. It's not that complicated.

And yes, in an alternative universe where delivery systems also just appear out of nowhere, you could sprinkle a million tons of 1% uranium over a city.

It’s not about delivery systems just appearing, the logistics of tossing around nuclear weapons in the Middle East using modern technology allows for a vastly larger bombs without significant issues.

You can buy a used A380 for a few 10’s of millions. Convert that to a drone is fairly cheap, and you end up with a deleverage system vastly cheaper than the cost of producing a nuclear bomb.

Obviously a subsonic aircraft isn’t ideal, but historic ICBM’s ended up being designed for multiple bombs that’s a lot of leeway if you use the same system to deliver a single bomb. What the US considered weapons grade in the 40’s through the Cold War is based on assumptions that simply don’t apply here.