With an all-powerful company running things, you get Bhopal.

This isn't a fair or useful comparison. The USSR was a command and control political and economic system which creates a kind of capture in decision making that is meaningfully different from what we encounter in the U.S. To put it simply, they got Chernobyl and the U.S. got three mile island which is a very different kind of nuclear (and governmental) failure.

Seems to me that the power of government or lack thereof is far less a factor than the nature of that government (eg corruption or other self serving tendencies) when it comes to man made disasters.

There are enough examples of man made disasters in countries with weak governments, and powerful governments without a history of these kinds of disasters.