It's not necessarily a faulty design. It simply requires maintenance that's not happening just like you car engine needs oil and you need to keep swapping that oil out after a while.

ex: A spent fuel pool is actually really simple and 'safe' just add water and keep cool. That does not mean you can walk away and not touch one for a year and expect everything to be ok. https://en.wikipedia.org/wiki/Spent_fuel_pool