Development of a methodology for predicting areas with high Radon exhalation potential.
Géraldine IELSCH, doctorate thesis of the University of Bretagne Occidentale, Speciality: geosciences, Defended on the 16th October 2000.
Report CEA - Order n°: 5968
Radon 222 is a radioactive natural gas originating from the decay of radium 226 which itself originates from the decay of uranium 238 naturally present in rocks and soil. Inhalation of radon gas and its decay products is a potential health risk for man. Radon can accumulate in confined environments such as buildings, and is responsible for one third of the total radiological exposure of the general public to radiation. The problem of how to manage this risk then arises. The main difficulty encountered is due to the large variability of exposure to radon across the country. A prediction needs to be made of areas with the highest density of buildings with high radon levels. Exposure to radon varies depending on the degree of confinement of the habitat, the lifestyle of the occupants and particularly emission of radon from the surface of the soil on which the building is built. The purpose of this thesis is to elaborate a methodology for determining areas presenting a high potential for radon exhalation at the surface of the soil. The methodology adopted is based on quantification of radon exhalation at the surface, starting from a precise characterization of the main local geological and pedological parameters that control the radon source and its transport to the ground/atmosphere interface. The methodology proposed is innovative in that it combines a cartographic analysis, parameters integrated into a Geographic information System, and a simplified model for vertical transport of radon by diffusion through pores in soil. This methodology has been valildated on two typical areas, in different geological contexts, and gives forecasts that generally agree with field observations. This makes it possible to identify areas a high exhalation potential within a range of a few square kilometers.