ASN Report 2017

50 ASN report on the state of nuclear safety and radiation protection in France in 2017 Chapter 01  - Nuclear activities: ionising radiation and health and environmental risks 2. The different sources of ionising radiation 2.1 Natural radiation In France, exposure to the different types of natural radioactivity (cosmic or terrestrial) represents on average about 65% of the total annual exposure. 2.1.1 Natural terrestrial radiation (excluding radon) Natural radionuclides of terrestrial origin are present at various levels in all the compartments of our environment, including inside the human body. They lead to external exposure of the population owing to gamma rays emitted by the uranium-238 and thorium-232 daughter products and by the potassium-40 present in the soil, but also to internal exposure by inhalation of particles in suspension and by ingestion of foodstuffs or drinking water. The levels of natural radionuclides in the ground are extremely variable. The external exposure dose rate values in the open air in France, depending on the region, range from a few nanosieverts per hour (nSv/h) to 100 nSv/h. The dose rate values inside residential premises are generally higher owing to the contribution of construction materials (about 20% higher on average). Based on assumptions covering the time individuals spend inside and outside residential premises (90% and 10% respectively), the average effective dose due to external exposure to gamma radiation of terrestrial origin in France is estimated at about 0.5 mSv per person per year. The doses due to internal exposure of natural origin vary according to the quantities of radionuclides of the uranium and thorium families incorporated through the food chain, which depend on each individual’s eating habits. According to IRSN (the Institute of Radiation Protection and Nuclear Safety) (2015), the average dose per individual would be about 0.32 mSv per year. The average concentration of potassium-40 in the organism is about 55 Bq per kilogram, resulting in an average effective dose of about 0.18 mSv per year. Waters intended for human consumption, in particular groundwater and mineral waters, become charged in natural radionuclides owing to the nature of the geological strata in which they spend time. The concentration of uranium and thorium daughters and of potassium-40 varies according to the resource exploited, given the geological nature of the ground. RADON EXHALATION POTENTIAL in metropolitan France (source: IRSN) Areas of the potential for radon exhalation Bounds of 31 priority départements for radon monitoring