But there is an even bigger risk, than "just" meltdowns:
Did you ever ask yourself what they do with the spent fuel?
--> They just have to store it forever. And the "cosmetic" explosion of the roofs of several buildings lead to a quite dangerous situation.
Read this article:
A 1997 study by the Brookhaven National Laboratory on Long Island described a worst-case disaster from uncovered spent fuel in a reactor cooling pool. It estimated 100 quick deaths would occur within a range of 500 miles and 138,000 eventual deaths.