I grew up 90km from Chernobyl (in Kiev) and was born 3 years after the explosion.
My grandmother and parents told me that when it happened they weren't told about it for a couple weeks, not until the BBC reported and people picked up the story from the radio. Apparently Sweden picked up radiation approaching them and didn't know where it was coming from. Finally, the Soviet Union came out and acknowledged that Chernobyl power plant did blow up. They told people living in the immediate area to stay at home and not go outside

Anyway, that's what I heard from family.
As a consequence, I get blood work done every year on my hormone levels (primarily thyroid). So far so good, no abnormalities or mutations *fingers crossed*.
Interestingly enough, in Canada (where I currently reside), even though we have public healthcare, when I go to a doc (I don't have a family doc, so I go to a clinic) and get blood work done, they always tell me how hormone levels are too expensive to test and because I "look healthy" I most likely don't need the tests done. When they finish giving me their shpeel I tell them I grew up near Chernobyl and they immediate check everything on the sheet off!