Fukushima? Three Mile Island (partial only, though)? That's a (partial) melt-down every 24 years, if we start counting the nuclear age with 1945 and count till today.
If we use the numbers for civilian power plants, we need to start with the commision date of U.S.S.R. power plant "Obninsk", wich was connected to the public grid in 1954. If ending the count today, that would be 21 years. Or, if we take the last melt-down as the reset value for our clock, we will find it at 19 years, for every (partial) meltdown. With more than 500 new nuclear power plants either planned or in production, well....
Let's see, whether Molten Salt Reactors are going to show as an overall positive development...They would make things, as far as I am informed, at least a little bit safer, till we have real fusion power.