Earlier quoted context omitted.
Fukushima was a boiling water reactor, which is not a good design. A good design would be passively safe, which more or less means that you can turn off the plant and walk away without a disaster occurring.
"Good" design is ill defined. The fact that a design is riskier than an alternative does not immediately make it worse. Especially when safety can be engineered to arbitrary standards with enough money.
There is not 'enough money'. If a reactor shows cracks in the steel in critical places, preventing this upfront might not be technologically possible and afterwards repairing might also be so expensive, that it economically makes no sense.
The big problem: if there is a technical problem, it is politically a very tough decision to close it, because of the costs involved (loss of profits from selling electricity, costs of decommissioning, costs of replacement, ...). Thus a more or less clear need to shutdown the reactor because of technical unfitness will conflict with financial interests and the scale of the money involved makes it worse.