their stockpile of enriched uranium is ~400kg, they had plenty of time to move it (400kg of uranium is 28 cubic cm or a half of an airline carry-on luggage bag)

upd: corrected the weight from 100 to 400kg

Difficulty: if you put 400 kg of 60% U-235 in an airline flight bag, the rest of your day is going to go downhill in a hurry.

I'd imagine you'd need at least a few trucks to move that stuff from point A to point B.

It's 400 kg.