While it was an okay plant, they'd actually been warned about the emergency cooling system as early as 1967. Also, they ignored a 2008 study saying that their plant was vulnerable to tsunamis. The Fukushima Nuclear Accident Independent Investigation Commission found that all the causes of the accident were foreseeable prior to 2011.
> The best designs cannot account for everything.
The common factor in nuclear accidents so far has been operator error, and it's true the best designs cannot completely account for that.