If Ukraine had held on to those nukes, disconnected, an engineer today could re-work them to function under Kiev’s command. (American PALs from the era have de-classified weaknesses that merited upgrades. Post-USSR nuclear safekeeping was roundly criticised for decades [1].)
Even barring that, possessing fissile material is no small feat. It would give Kiev the credible capability to e.g. threaten large sections of Russian agricultural production. That’s the sort of thing that deters tanks.
I don't know where they got it, the book author cited in Wiki. The man cited read too much Tom Clancy I guess.
USSR nuclear weapons had no permissive action links as such
Kazakhstan's, and Ukrainian's nukes were fully operational, sans confused nuclear weapons officer command chain.
The launch codes were employed, but they were used solely for checking the authenticity of launch, and targetting commands.
“Until then, Ukraine had the world's third-largest nuclear weapons stockpile, of which Ukraine had physical, but not operational, control. Russia alone controlled the codes needed to operate. Their use was dependent on Russian-controlled electronic Permissive Action Links and the Russian command and control system” https://en.wikipedia.org/wiki/Budapest_Memorandum_on_Securit...