So did South Africa, So did Yugoslavia. Both gave it up voluntarily.

So could any country with nuclear power plants. There are a few with reactors but no weapons.

Did you know Sweden had one? From scratch with no outside help?

In the bay of Kotor, what is today Montenegro, the bottom of the sea contains very thick black mud that has traces of Uranium. It is being dragged up, cleaned and used in hydrotherapy in the nearby institute for physical rehabilitation. The Yugoslav military examined the mud to see if there is enough Uranium to be worthwhile creating a bomb. It wasn't but they tried. There was, I think still is a nuclear power plant in Slovenia that was then Yugoslavia and there were some trials there too. It wasn't just the issue of can they make a bomb but what to do with it? You need a delivery missile with range long enough not to kill your own forces.

The difference was South Africa actually had the weapons, others just stopped programs that had yet to produce weapons.

Sweden's program was wild though. They were basically going to skip from basic designs to a fairly small two point ignition design. They are the only program I know of that was planning to start with a more advanced design. Just very ambitious.

I did not know this, but they have historically been a leader in science and technology, so I am not shocked.

They also built one of the coolest looking airplanes, ever; behind only the SR-71 Blackbird

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"What's your claim?" - Ben Gravy
"Your best work is the work you're excited about" - Rick Rubin

It isn't rocket science. The Chinese did it in 64 and the North Koreans backwards as they are have done it.

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They constantly try to escape from the darkness outside and within
Dreaming of systems so perfect that no one will need to be good T.S. Eliot

I could be wrong but isn't the science on how to do this pretty well known to everyone at this point?

So, whilst I didn't know about Sweden, I am not shocked to learn this.

If you live beside Russia, it behooves you to explore this.

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How does Danny Hart sit down with balls that big?

Yes. The high bar for entry is uranium enrichment. A one stage fission gun-type device is trivially simple to make if U235 is available. Implosion devices and plutonium, are trickier. Multi stage fusion devices are very tricky but no need if one's goal is nuclear terror.

The detailed science and practical solutions was generally less known even in the science community in the 50's and 60's when this program was active. Today is different.

The program "only" aimed at developing tactical weapons, not strategic. This mainly due to lack if weapon carriers. I.e. these nukes would be comparatively small and used against invading ships coming across the Baltic Sea, sea ports on the eastern side of the same sea, etc. Not to threaten to take out Leningrad/Moscow, but instead used as "very big bombs", having an effect against large military targets. Naturally, it would still have been bad for any civilians living close to the sea ports of Gdansk, Riga, Kaliningrad, ...