USSR might have a problem with procuring uranium. In the 1930s known reserves were in Belgian Congo (company mining it was owned 30% by Brits), Canada, US and a mine in Czechoslovakia.
USSR had no real idea on how to enrich uranium or that plutonium can be used as fissionable materiel until they cheated and copied off Manhattan Project
This is a real problem for the USSR that shouldn't be underestimated.