Every ten years the Swiss government distributes potassium iodide tablets to people living near nuclear plants, but how effective are they? (SRF/swissinfo.ch)

In Switzerland there are four nuclear power plants currently generating electricity. They are in the cantons of Aargau, (Beznau and Leibstadt), Solothurn (Gösgen), and Bern (Mühleberg).

Potassium iodide tablets (also known as iodine) are sent out by the Swiss National Emergency Operations Centre, as a precautionary measure in the event of a nuclear accident.

Potassium iodide is similar to table salt. It is routinely added to the salt to make it "iodised."

If taken in time and at the appropriate dosage, it blocks the thyroid gland's uptake of radioactive iodine.

So it can reduce the risk of thyroid cancers and other diseases that might otherwise result from exposure to radioactive iodine.

Formerly residents within 20 km of a plant received them, but this year the radius has been extended to 50km.

While potassium iodide tablets offer protection from radioactive iodine, they do not protect against other radioactive substances.

Three of these so called radionuclides pose a major health risk.

Cesium 137 spreads through the body and particularly affects the muscles.

Strontium 90 is held in the body by calcium, and mainly attacks the bones, triggering bone tumours and leukaemia.

So as well as taking the tablets, the authorities also advise people to stay indoors or hide in a cellar or shelter, in the event of a nuclear accident.