Radon-222 signatures of natural ventilation regimes in an underground quarry.
Radon-222 activity concentration has been monitored since 1999 in an underground limestone quarry located in Vincennes, near Paris, France. It is homogeneous in summer, with an average value of 1700 Bq m(-3), and varies from 730 to 1450 Bq m(-3) in winter, indicating natural ventilation with a rate ranging from 0.5 to 2.4 x 10(-6) s(-1) (0.04-0.22 day(-1)). This hypothesis is supported by measurements in the vertical access pit where, in winter, a turbulent air current produces a stable radon profile, smoothly decreasing from 700 Bq m(-3) at 20 m depth to 300 Bq m(-3) at surface. In summer, a thermal stratification is maintained in the pit, but the radon-222 concentration jumps repeatedly between 100 and 2000 Bq m(-3). These jumps are due to atmospheric pressure pumping, which induces ventilation in the quarry at a rate of about 0.1 x 10(-6) s(-1) (0.009 day(-1)). Radon-222 monitoring thus provides a dynamical characterisation of ventilation regimes, which is important for the assessment of the long-term evolution of underground systems.
Perrier
Frédéric
F
Service Radioanalyses, Chimie, Environnement, Département Analyse Surveillance Environnement, Commissariat à l'énergie atomique, B.P. 12, 91680 Bruyères-le-Châtel, France. perrier@dase.bruyeres.cea.fr
Richon
Patrick
P
Crouzeix
Catherine
C
Morat
Pierre
P
Le Mouël
Jean Louis
JL
D004784:Environmental Monitoring; D005602:France; D008906:Mining; D011886:Radon / Q000032:analysis*; D012621:Seasons; D012990:Soil Pollutants, Radioactive / Q000032:analysis*; D013696:Temperature; D014691:Ventilation
D012990:Soil Pollutants, Radioactive; D011886:Radon