The Japanese are competent engineers who are used to earthquakes and tsumais. They would have taken steps to protect their citizens against even the most severe 'quakes.
The fact that, despite this, 20,000 people died shows that the 'quake involved was far more severe than anything which they or anyone else expected or had planned for.
And despite this quake being so unexpectedly massive, and despite the fact that 20,000 peole drowned in the consequent flooding, not a single person was killed by a nuclear power station.
The only people who (like the BBC) persist in describing this massive earthquake and flooding disaster (which it was) as a "nuclear disater" (which it was not) are either ignorant and incompetent journalists, or are willfully and deliberately misrepresenting the facts because of their irrational paranoia about "nasty wicked nuclear energy".