The linked tweet doesn't provide a citation or context for the "helped prevent ~2M deaths" claim. But there is work in this area which suggests that "~2M lives saved" in the last 50 years underestimates the benefits of nuclear power by a lot.
One commenter here writes
> What is the actual claim here? Nuclear power didn't prevent any deaths, after all everyone will eventually die for one reason or another. So it must be something like two million people would have died earlier without nuclear power, but by how much?
That's a better way to think about the problem: not "lives saved," but life-years saved. Calculations of life-years saved are necessarily sketchy, but there is at least one promising preliminary effort [1]. See especially page 22.
One commenter here writes
> What is the actual claim here? Nuclear power didn't prevent any deaths, after all everyone will eventually die for one reason or another. So it must be something like two million people would have died earlier without nuclear power, but by how much?
That's a better way to think about the problem: not "lives saved," but life-years saved. Calculations of life-years saved are necessarily sketchy, but there is at least one promising preliminary effort [1]. See especially page 22.
[1] https://storage.googleapis.com/production-sitebuilder-v1-0-1...