Ah, most of my misspent working life was in the land of "Ballooning Costs". I remember when we were building Darlington, we had a "Scheduling Department", who's only job was to rewrite the schedule, after the fact. They were never right!
I always figured we did well, if it was only twice as expensive, and twice as long. What causes this sort of thing in the nuclear industry? The official, isolated 'estimators' never talk to anybody who knows anything. For example, the ridiculously low price for Pickering A. They piled on all sorts of requirements to clean up the paperwork, etc. At the time, the people 'in the know' just rolled their eyes at the cost estimate!
Now, Bruce is in the same boat with AECL. Quel surprise! Up to 3.05 billion, the ratepayers share half the overrun, then it gets worse for the owners. Who wants to bet the cost is exactly 3.05 billion? Actually, I think they are lucky they can hold it to that.
The new plant at Darlington will also be grossly under-estimated. They are adding things that are almost impossible to do. Whenever you get into 'new engineering', you know you are doomed! Cost estimates only work when you are doing something 'tried and true', and already done a zillion times.