Potasium iodide will protect you from radioactive iodine, I-131. Nothing else. The thyroid absorb iodine, radioactive or not. If you flood the thyroid with non-radioactive iodine, the thyroid wont absorb radioactive iodine.
But I-131 has a half life of 8 days. Fukushima no longer has any radioactive iodine. All of the iodine from Fukushima has since decayed. Your advice is more harmful than helpful
Well I’m glad you were here to correct me. Appreciate it.