There is the fission stage and the fusion stage. The fission stage in this image is not well represented. It is generally known how to make a fission stage similar to the “Fat Man” device but the “Fat Man” device is larger than the whole warhead with both a fission and fusion stage that fits on a Minuteman 3.
The fission stage in that warhead has numerous refinements that help miniaturize it, for instance the implosion is probably not spherical so it can fit in the pointy end of the warhead. A really refined modern weapon is packed with details like that.
The secondary isn't well represented either: that radiation case isn't focusing any X-Rays and the stairstep in the tamper would tear it in two when ablation started. Plus, as you note, the primary is impossibly screwed up as well, with what looks like a single point of initiation and zero details on the boosting. It doesn't just look simplified, it looks like every part has been corrupted with a feature that makes it impossible to mistake for real while being slightly less crude than the "Mastercard" or British designs.
Besides, real engineering doesn't just need a schematics, it needs details, and some of the missing ones are notorious (FOGBANK) and inherently difficult to figure out with any confidence in the absence of weapons tests (or even more expensive giant buildings crammed to the gills with lasers).
So yeah, not very useful to an aspiring designer. I understand the author's surprise but I suspect they really did just become a few notches less crazy about the redundant protection on information that has been public for 30 years.
Also the mental models of proliferation are warped by secrecy. For instance, Iraqis got caught building Calutrons when the official line was to watch out for plutonium reprocessing and centrifuges... Despite the fact that the enriched uranium used for the first nuclear weapon used in war was produced with a Calutron!
Anyone responsible who thinks about this stuff, even if they don't have a security clearance, will look into the question of what the ethics are and what the legal consequences of secrecy laws are if you talk about certain things you think about. I had dinner with a nuclear scientist at a conference, for instance, who told me that he hadn't told anyone else about his concern that Np237 was the material that terrorists would most want to steal from a commercial reprocessing facility (if they knew what we knew) and I told him it was no problem because people from Los Alamos had published a paper with specifics on that a few years earlier.
They would be in possession of an image. It is hard to understand what the author is hand-wringing about. It is not that nobody knows how these weapons are supposed to work. The real barrier is that to obtain the materials necessary you need a big-ish industrial base and if you do that that leaves signatures the relevant agencies can detect.
It is not even clear if when he speaks about "safe" is he talking about being safe from nuclear proliferation, or safe from clueless bureaucrats causing you legal trouble.
The author is a historian who has published a book that is specifically about the history of nuclear secrecy in the United States. Not about the history of nuclear tech or nuclear weapons, about the history of restricted data, the special classification grade for the information. How the classification works and what is considered safe to release and what isn't is in itself one of his main research interests.
My impression from his book is that his position on nuclear secrecy is that a lot of it is pointless or outright contra-productive, but that isn't really the point of the blog post. The point of the blog post is that if something has changed about what information is considered safe to release, that is interesting to him. He is more interested in the humans and institutions than in the technology, I'd say.
> It is hard to understand what the author is hand-wringing about.
The issue seems to be “Organisations party to classified information have to keep it secret regardless of whether it’s in the public domain”.
As an academic historian the author is intrigued by the diagram - was it a mistake or was it authorised as a declassified representation? Either way, the consequences would be of interest.
> It is not that nobody knows how these weapons are supposed to work.
Optimally small, lightweight, robust, safe, reliable - all sorts of engineering short-cuts or novel techniques … you don’t want to give way accidental insights about the “hows” an enemy hasn’t thought of.
The "large industrial base" is required primarily to highly enrich uranium (or plutonium).
A modern fusion bomb requires much less of that than the initial fission bombs.
So I don't know how much a state actor could infer from an image like that, if we assume it's a schematic of an actual bomb.
But it's just not true that someone in possession of detailed plans for how to construct a bomb isn't put into a much better position. They'll need a much smaller amount of fissionable material than they otherwise would with a cruder design.
The fission stage in that warhead has numerous refinements that help miniaturize it, for instance the implosion is probably not spherical so it can fit in the pointy end of the warhead. A really refined modern weapon is packed with details like that.