(And I'd question that "50 kg" est. - for a gun-type weapon: that being the rationale for U vs Pu, which cannot be detonated in that way.) That's a number based upon the techno of 'Little Boy', and antedates what has been learned of 'tampers' and much other cleverness re more efficient mass murder.
But we see that most numbers bandied about by -especially this admin- will perpetually lack credibility, especially when used to justify some next fantasy-situation. I see no remedy for their utter unpredictability, unless/until they are thrown out. They are proven Liars.
ie never mind the number, size, configurations of somebody's centrifuges: they won't.