Note that there wasn't a roof over these bags. Understandable 1 year after the catastrophy but not now, almost a decade later. The typhoon didn't even have to blow off the roof.

This isn't an engineering problem. The art to build roofs is wel researched. It's a human problem. That nuclear is only "cheap" if you aren't building roofs over little/medium radioactive waste storage sites, or don't design reactors to be as safe as possible. More safe == more expensive.

I wonder what happens the next time a tsunami similar to the one from 2011 hits the fukushima site. How much better prepared are they now?