PARIS (Reuters) – France will offer free iodine tablets to around 2.2 million people living close to nuclear plants to help protect them from radiation in case of an accident.

Nuclear regulator ASN said on Tuesday people living within 10-20 km of one of utility EDF’s 19 nuclear plants, as well as some 200,000 institutions such as schools, will receive a letter in coming days informing them that they can pick up free iodine tablets from pharmacies.

Five years after the nuclear disaster in Fukushima, Japan in 2011, France distributed free iodine to people living within 10 km of a nuclear plant, but is now widening that radius.

French daily Les Echos quoted a nuclear information official as saying that in 2016 only about half of the people targeted bothered to pick up their iodine.

Nuclear accidents typically release radioactive iodine in the atmosphere. When inhaled or swallowed, it is absorbed by the thyroid gland, where it can lead to cancer in later years. By saturating the thyroid gland with stable iodine, it will no longer absorb radioactive iodine.

The ASN said that in case of a nuclear accident, people living nearby need to seek shelter in buildings, monitor the situation via the media and not go and pick up their children at school. They also should limit telephone communication, take iodine and prepare for a possible evacuation.

The American Thyroid Association says on its website that when thyroid cells take in too much radioactive iodine, this can cause thyroid cancer to develop several years after the exposure. Babies and young children are at highest risk, while the risk is much lower for people over 40.

France is the world’s most nuclear-reliant nation, with three quarters of its electricity produced in state-owned EDF’s 58 nuclear reactors in 19 plants spread all over the country.

Most French people live within a few hundred kilometers of a nuclear plant. EDF’s Nogent-sur-Seine plant is about 100 km east of Paris, while the nuclear plants of Penly and Paluel are about 180 km northwest of Paris, on the Atlantic coast.

The river Rhone in the Provence region of southern France also has several nuclear plants along its banks.

(Reporting by Geert De Clercq; Editing by Mark Heinrich)