> The primary fissile material remains a threat
That's difficult to ascertain. Russia (then the Soviet Union) stopped testing nuclear weapons in 1990. The US in 1992, the UK in 91 and France in 96[1]. Since then, their nuclear arsenals had to be maintained "by model". Is this difficult? Is it reliable? I don't know, and I suppose that 99.9% of the people who know are not allowed to talk.
But what we do know is that it's expensive. The latest US budget (2022) allocated $20 billion for "Nuclear Security" [2], $15 of which are for "weapons activities". I'm not an expert, but I think it roughly means the money needed to keep the nuclear weapons functional.
But maybe the US if very spendthrift. You know, the military-industrial complex, and all that. Well, it turns out France and the UK are not doing it on the cheap either. France spends a about $5.9 BN per year [3], and the UK about $6.2 BN/year on nuclear deterrence, and they have a much smaller arsenal compared to the US.
Well, Russia has a larger arsenal. And their total defense spending is less than $50 BN/year. I don't know if they spend $10 BN / year on their nuclear forces, but if they did, it would not surprise me if a lot were siphoned out. How would anyone know, if there is no actual nuclear test going on?
As a cute little tidbit of information. All current nuclear bombs are "boosted" [4]. Boosting requires Tritium (an unstable Hydrogen isotope). Tritium happens to be the most expensive substance on the planet, with a price of about $30k per gram. It has a half-life of 12 years, so there have been about 2 half-lives since the Soviet Union collapse. A nuclear bomb needs to have its Tritium replaced periodically if it is to remain effective. What is the probability that someone in Russia dipped a bit in the Tritium fund to buy a yacht or something?
[1] https://en.wikipedia.org/wiki/Nuclear_weapons_testing#/media...
[2] https://www.energy.gov/sites/default/files/2021-05/doe-fy202...
[3] https://sldinfo.com/2020/10/an-update-on-the-french-nuclear-...
[4] https://en.wikipedia.org/wiki/Boosted_fission_weapon