USSR As The Only Nuclear Power Or Substantially Ahead Of Every Other one!

Did the Soviets take nuclear weapons research seriously during WW2, what if they got the bomb first or were the only nuclear power or developed nuclear weapons which were substantially in advance of its enemies?
 
This would require them having years of peace, no purges of any type, and becoming a de-facto technocracy, as the last would allow them to overcome limitations scientifically to things like that.
 
About the only scenario where this *might* be possible is something like my A Sound of Thunder where the Soviets use their secretive M-I Complex, hijack German nuclear physicists *and* their spies in Tube Alloys to make their Bomb in a few years as much for Stalin's ego as for anything else. Even then the Soviets have until the USA gets the Bomb to enjoy their
monopoly, and they have no means to sustain a lead in nuclear technology for any length of time.
 
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