the load was not even that bad, but when you have 40% of the grid coming to a grinding halt.....your load max is much lower.
Put that on top of normal maintenece cycle which puts a lot of generation off line in the winter when they "thought" they could afford for them to be off line.
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tidal waves and meltdowns are unusual too, but they plan for them and we've seen what happens when they cheap out on the "planning"