Actually the Russkis ought to be celebrating Klaus Fuchs and Julius Rosenberg who did more to give the Soviets the bomb than any Russian scientist.
The Soviets were independently reaching the same end, using Kurchatov’s work. The Rosenbergs and such only confirmed that Kurchatov was heading in the right direction. Sakharov’s research however was original, including some of his fusion work on the Tokamak.
The research done by the scientists in the Soviet Union (disregarding obvious frauds like Lysenko) is sometimes amazing considering the political crap they had to put up with. The KGB handlers during the Soviet fission bomb project were a real bunch of dunces. Kurchatov was running his equivalent of Chicago Pile 1 while Lavrenty Beria was in attendance. Beria was starting to think that the whole thing was a sham, since there was no noise, no vibration when the fission reaction was taking place. He almost walked into the room where the graphite pile was. If he did, he would have been fried by the neutron flux.