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