I recommend reading a blow-by-blow account of the causes of the Chernobyl disaster, and compare the long list of failures and coverups with that of the other disasters you mentioned.
But it is preposterous to draw conclusions about state vs private enterprises from this N=1 example. There have been many successful government-run megaprojects (Panama Canal, Dutch North Sea dams, China's high-speed-rail). There have been many unsuccessful private ones.
Adjudicating this question would require careful enumeration and analysis across many instances, not just throwing out one example.
McKinsey, for example, states that megaprojects can fail "when big projects cross state or national borders and involve a mix of private and government spending."
https://www.mckinsey.com/capabilities/operations/our-insight...
Private US health care is way more expensive than basically anywhere else in the world, while delivering worse outcomes than most places.
Want to trade anecdotes all day? We can do that. Or you can address the question at hand seriously, as I suggested before.