HR: 0800h
AN: H21E-1059    [Abstracts]
TI: Natural Radioactive Characterization by Gamma Ray Mapping in Relation with Radon-222, Radium-226 Contents in the Atmosphere, Dripping Groundwater and Mineral in a Dead-end Horizontal Tunnel
AU: * Richon, P
EM: Patrick.Richon@cea.fr
AF: CEA, Departement Analyse Surveillance Environnement, BP12, Bruyeres-le-Chatel, 91680 France
AU: Perrier, F
EM: Frederic.Perrier@cea.fr
AF: CEA, Departement Analyse Surveillance Environnement, BP12, Bruyeres-le-Chatel, 91680 France
AU: Perrier, F
EM: Frederic.Perrier@cea.fr
AF: Laboratoire de Geomagnetisme, Institut de physique du Globe de Paris, 4 Place Jussieu, Paris, 75015 France
AU: Pili, E
EM: Eric.Pili@cea.fr
AF: CEA, Departement Analyse Surveillance Environnement, BP12, Bruyeres-le-Chatel, 91680 France
AU: Bureau, S
EM: Sarah.Bureau@cea.fr
AF: CEA, Departement Analyse Surveillance Environnement, BP12, Bruyeres-le-Chatel, 91680 France
AU: Provost, A
EM: Ann-Sophie.Provost@cea.fr
AF: CEA, Departement Analyse Surveillance Environnement, BP12, Bruyeres-le-Chatel, 91680 France
AU: Sabroux, J
EM: Jean-Christophe.Sabroux@irsn.fr
AF: Institut de Radioprotection et de Surete Nucleaire, Centre de Saclay, Gif-sur-Yvette, 91192 France
AB: The concentration of radon-222 has been monitored since 1995 in the atmosphere of a 2 m transverse dimension, 128 m long, dead-end horizontal tunnel located in the French Alps, at an altitude of 1600 m. The total volume of the tunnel is about 496 m$^{3}$ with an estimated total wall surface area of 1041 m$^{2}$. Most of the time, the radon concentration is stable, with an average value ranging from 200 Bq m$^{-3}$ near the entrance to about 1000 Bq m$^{-3}$ in the most confined section, and with an equilibrium factor F between radon and its short-lived decay products varying from 0.61 to 0.78. However, radon bursts are repeatedly observed, with amplitudes reaching up to 36 x 10$^{3}$ Bq m$^{-3}$ and durations varying from one to several weeks, with similar spatial variations along the tunnel as the background concentration. These spatial variations are qualitatively interpreted in terms of natural ventilation. To understand the source term, we realised a comprehensive 3D map of total gamma emission of rock on all surfaces of the tunnel, i.e., floor, wall and roof, representing 700 measurements points with a section of eight points by two-meter steps along the tunnel. Dose rate varies from 100 to 350 nSv h$^{-1}$ and reveals two major contrasted geological structures, correlated with the radon-222 profile in the air along the tunnel (230 Bq m$^{-3}$ at the entrance to 770 Bq m$^{-3}$ at the end, measured during a period of background radon level), and with other profiles measured in previous work. In addition, a correlation is evidenced with the radon-222 contents in dripping groundwater and with the radon precursors - i.e., the daughters of uranium-238 (radium-226, for example) - content in rocks. The radon and radium contents in water and rocks, and the study of flow rate of the dripping groundwater are in direct relation with the mechanism of radon gas transport by water in porous media. By interpreting all available measurements, it is now possible to model the time variation of radon-222 in the tunnel, and to constrain the origin of the radon peaks generated in the gallery. The bursts result from transient radon exhalation upsurges at the tunnel wall, that could be due to meteorological effects, or possibly to combined hydrological and mechanical forcing associated with the water level variations of the nearby Roselend reservoir lake.
DE: 4860 Radioactivity and radioisotopes
DE: 1829 Groundwater hydrology
DE: 0932 Radioactivity methods
DE: 0994 Instruments and techniques
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting