If I ingest a grain of sand size piece of the Chernobyl Reactor No.4 core

In the image below is a piece of reactor fuel I found at the Chernobyl plant in 2010 roughly the size of a grain of sand. Chip of nuclear fuel from Chernobyl, on my pinkie finger for scale

You would have some other problems to be sure. You would probably be escorted somewhere under supervision until you excreted the bulk of the activity, and then taken to one of these:

Me, riding the whole body counter in SP1430, Chernobyl Nuclear Power Plant, after being inside the Unit 4 “Sarcophagus”

It’s a chair with built-in calibrated sodium iodide scintillators that calculates your body burden of Cs-137 and your dose.

Source: www.quora.com