The radius for free iodine tablets was previously ten kilometres.
France will give out 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.
The country's nuclear regulator agency ASN said on Tuesday people living within 10-20 kilometres from one of EDF's 19 nuclear plants, as well as some 200,000 institutions including schools, will receive a letter in the incoming days informing them they can pick up the tablets from the nearest pharmacy.
Previously, France distributed iodine tablets to people living within a 10 kilometre radius from a nuclear plant but has now decided to widen the radius.
During nuclear accidents, radioactive iodine is released into the atmosphere that when inhaled or swallowed by the thyroid gland can cause cancer in later years.
When the thyroid gland is saturated with stable iodine, it no longer absorbs the radioactive iodine.
The ASN said that in case of a nuclear accident, people should seek shelter in buildings and not go pick up their children from school.
France is the world's most nuclear-reliant nation, with three-quarters of its electricity produced by state-owned EDF's 58 nuclear reactors in 19 plants spread all over the country.