The major cause of the excellent propagation during the 50s was Solar Cycle 19 - the largest on record. Meanwhile we seem to be in one of the weaker cycles right now, and some of the forecasts for Cycle 25 don't seem very promising at all.
Compared to the Sun, ionization due to fallout from Fukeshima simply isn't a factor. Plus the fallout is mostly in the lower atmosphere, and gets washed out by rain fairly quickly (which is one reason we're not seeing much of it here in the USA).
High altitude nuclear tests produced very short term effects on the ionosphere, but through an entirely different mechanism.