RADON TRANSPORT IN FRACTURED POROUS-MEDIA - EXPERIMENTAL-STUDY IN CAVES

The spatial and temporal variation of Rn-222 concentration in three ho rizontal caves and in one vertical cave was measured to study the infl uence of different morphological and meteorological parameters on the forming of airborne radon concentrations inside. In horizontal caves, the daily mean radon concentration as a function of the daily average surface temperature showed a step-function type dependence with low wi nter and high summer values reflecting the main direction of undergrou nd airflows, Restriction of airflows increased winter but decreased su mmer radon levels. The transition pattern between the low winter and h igh summer values gradually linearized as the number of vertical fract ures communicating with the surface increased. Contrary to horizontal caves, in the vertical cave barometric pressure variations played the most important role in controlling subsurface radon concentrations. De creasing pressure increased radon levels, and increased pressure decre ased radon levels, In the pressure-radon correlation curve, there was a small hysteresis which indicated the nonlinearity of the process. Co pyright (C) 1996 Elsevier Science Ltd.