According to Wikipedia, there was less than 200k people evacuated for Chernobyl. Also, if you take a 30km radius, multiplied by the population density of California, you get only 274k people. (And I'm pretty sure that the powerplant are build in area which are less populated than the average).

As we leaned since, 30km radius is probably over-doing it.

That's considering the life of someone being evacuated to be "ruined"