Earlier quoted context omitted.
1. There was an explosion (edit: two explosions) that began the incident which destroyed the reactor and ejected matter a significant distance. 2. Chernobyl, IIRC, isn't really so dangerous to visit but you should avoid eating or drinking anything in the exclusion zone. Cesium-137 and Strontium-90 will poison you from the inside out. The latter ends up bio-accumulating in bone.
IIRC the uptake rate of Cs-137 is about 10%. Meaning you only store about 10% of what you ingest. Also, we are SUPER safe when it comes to radiation. No chances. No ifs ands or buts. When it comes to dosage, rad workers already have several safety factors from what we can detect an increase risk of cancer, as it should be.
The sensitivity of our tools for detecting radiation never ceases to amaze me. In some ways it's a problem because most people don't understand just how good we are at detecting radiation. Like, not only can we find it in old bits of wood, we can find it so well that we can tell you whether that old bit of wood stopped gathering radioactive carbon from the atmosphere in 10,000 BCE or 10,300 BCE. We can measure how much radiation you get from the sun precisely enough to tell whether you're living on the first story or the second story of your apartment building. But we still get people freaking out about any headline with the word radiation in it. It's crazy.