Balderdash—where’s your spirit of adventure? 
The advantages of a gun type device are significant if you are not a serious industrial power, or wish to do your work in secret. The gun device is really simple to design and build (in comparison to an implosion type.) The little boy device had never been tested, but there was almost unanimous agreement that there was no need, and that it would work. That level of simplicity and reliability are what you want if you are a minor player looking to develop nukes in quiet.
An implosion device is vastly harder to make, and really you are going to want to test it. The Trinity test’s Gadget did work first time, but there was doubt, and the amount of effort that went into it was of course a measurable fraction of the national GDP. And you still need to keep the [sup]240[/sup]Pu concentration very low unless you have the technology to make an initiator that is a reasonably potent nuclear device in its own right.
The two competing issues are what keep nukes out of the hands of every two-bit belligerent that is having a bad hair day. Neither a gun type weapon - with its requirement for highly enriched [sup]235[/sup]U levels, or the serious technical challenges of designing and fabricating an implosion device, plus its still significant difficulties in creating weapons grade Pu are at all easy.
Owning a few reactors helps in that it does give you a plausible mechanism to actually obtain the raw ingredients. Either by diverting Uranium fuel for concentration, or by production of Plutonium. Which is why people worry about them. But actually starting on the path of creating a weapon undetected is not going to be trivial. Geopolitics, and the fraught question about what to do about a nation building nukes is a different question. No doubt, bombing runs to take out infrastructure may be the simplest answer. Does however raise a few more questions for the future.
A gun type uses a lot of Uranium, something like 3-4 times what an implosion does, more if its completely untested.
So, if you want to use a gun-type; you still need the technological and industrial bases need to actually enrich the damn U-235.
As it is, one of the biggest limitation is financial. Its often said to make nuclear weapons you need to make the machines which make the machines which make your components., and all these are restricted for sale in the global market, so you are going to have to make everything from the ground up yourself and thats going to cost money.
The reason these have a restricted sales complicates it for many of these precursor components and parts, their is no non-weapon related use so you have no one with experience in country to design it and that takes time and money to rectify.
Not insurmountable challenges; but ones that have taken nuclear weapons into the realm of the unfeasible for many otherwise advanced nations and will still pose a challenge for SKOR.
Exactly. Little Boy (a gun-type uranium weapon) used 64 kg of U235 to produce a 15 kiloton explosion. This means that roughly a kilogram (0.91) of uranium was actually fissioned, with the rest not contributing to the bomb’s yield, but was necessary to produce the supercritical mass.
Trinity/Fat Man(a plutonium implosion design) by comparison, had a pit containing 6.19 kilograms of plutonium, and fissioned slightly more (1 kilogram), giving a yield of 21 kilotons.
So implosion is much, much more efficient, but drastically more complicated to get right.
I’d guess that a country like South Korea would first go for the low-hanging fruit (gun-type nuke) to have a nuclear deterrent ASAP, then advance to implosion-weapons later.
By the way, what would be a ranking of the world’s 10 most could-build-nukes-quickly countries be?
Maybe
- Japan
- South Korea
- Germany
- Iran
- Australia
- Canada
- Sweden
- Saudi Arabia
- Poland
- Taiwan?
Note: HEU is not required for a uranium fission bomb. They apparently can be made from as low as 18% enriched U-235, however this has a cost in efficiency and overall mass. This is discussed in the Harvard Kennedy School lecture “Nuclear 101: How Nuclear Bombs Work”, by Matthew Bunn:
Part 1: https://www.youtube.com/watch?v=zVhQOhxb1Mc
Part 2: https://www.youtube.com/watch?v=MnW7DxsJth0
The relevant chart about required enrichment level is at 45:05 in part 1.
China Guy and I disagree on this. He believes it’s likely that Taiwan actually had nukes or the capacity to assemble them in a few months. According to someone I know who formally worked in the Taiwan Defense Ministry, their nuke program was shut down. Impossible to say, but I still believe they are higher up than No. 10. Certainly in the Top 5.
I do think Japan is up there.
I would put Australia a lot lower than Canada. We have one tiny research reactor. Canada has a significant level of expertise in reactors and quite a number of reactors. They also have ready access to uranium. Australia has lots of uranium as well, but all we do is export yellowcake.
The list seems to be a mix of countries with lots of industrial/scientific ‘muscle’, ones which may have worked on nukes already, and just generally ‘advanced’ countries. I also doubt the capability of Australia or Canada to rapidly nuclearize. They are as advanced or more by most measures as ROK (or even Japan) by general measures, but don’t have the degree or ROK/Japanese concentration on fully independent self contained heavy/defense industries.
Saudi Arabia is presumably on the list based on suspicion of a real program in cooperation with Pakistan, or some access to that program. Iran obviously as well is believed to have spent a lot of time and effort already. As was discussed, Taiwan might be a candidate based on either suspicion of a head start or perhaps ability from standing start. South Africa might be a different kind of example, ex-nuclear with own scientists closely involved in development, so perhaps some expertise might remain, probably not as much a factor for ex-nuke FSU’s which just handed back Soviet weapons.
But for standing start, no outside help, to say a pretty elegant bomb in a missile or manageable tactical a/c load (B-61 style), I would think the top three of ROK, Japan and Germany (not necessarily that order) would be pretty far from others. Maybe Taiwan could be argued. But for other ‘western’ countries it would IMO be a longer process of building industries/capabilities they are inherently capable of building but don’t, in the natural process of industrial specialization (and with no particular reason to have nukes), have.
South Africa actually had nuclear weapons before (they got rid of them after apartheid ended), and IIRC Brazil and Argentina were toying with the idea at one point. Brazil is one of the world’s largest ten economies (total, not per capita), so I’m surprised that those three aren’t on your list.
move Iran from #4 to #1