You are in luck, this is exactly the sort of questions that accelerator designers like to answer. You can find the answers on the first 70 pages in volume 1 of the FCC feasibility report: https://cds.cern.ch/record/2928193 just the first

You think North Korea stole its nukes?

They got paid mainly in nuclear fuel, there was some disagreement at the rate by which they got fuel in exchange for the weapons and maybe they didn't get quite all the fuel they should have, but for sure they did get paid at least partially.

The US and Russia would have done a joint invasion under UN flag if Ukraine tried to steal the nukes dude, it's downright embarrassing to pretend that's the sort of thing you can do unpunished.

And doing that for some design info is really not worth the risk: just recruit some soviet weapons designers, for sure there are Ukrainians in that project already.

Right stealing nukes you cannot immediately operate as a 0-year old nation, to me it doesn't seems like an incredibly bright idea in a world where the existing nuclear states doesn't want anyone else to get nukes too.

And in any case it's was not simply removing the safety devices on the weapons, you need to be able to target the ICBMs at Russia, which Ukraine could not do:

> In fact, the presence of strategic nuclear missiles on its territory posed several dilemmas to a Ukraine hypothetically bent on keeping them to deter Russia. The SS-24s do not have the ability to strike targets at relatively short distances (that is, below about 2000 km); the variable-range SS- 19s are able, but Ukraine cannot properly maintain them. [...] the SS-19s were built in Russia and use a highly toxic and volatile liquid fuel. To complicate matters further, targeting programs and blocking devices for the SS-24 are Russian made. The retargeting of ICBM is probably impossible without geodetic data from satellites which are not available to Kiev.

> Cruise missiles for strategic bombers stored in Ukraine have long been 'disabled in place'.[...] As with ICBMs, however, retargeting them would be impossible for Ukraine, which does not have access to data from geodetic satellites; the same goes for computer maintenance.

From SIPRI research report 10; The Soviet Nuclear Weapon Legacy

So Ukraine did not have usable weapons at hand. But it did, and does, certainly have the capacity to build entirely new weapons, if given time.