I remember reading a list of industrial disasters, and Dam breaks always had absurdly high death tolls. I remember reading one from China that had several hundred thousand IIRC.
I couldn't find the exact Wikipedia article, but this one is still a pretty interesting read.
Attributing casualties from a dam break as energy-related is a stretch. The vast majority of dams are built for flood control. Energy production just helps pay the bills. It's not the 'purpose' of the dam.