Simulation of the Steady-State Transport of Radon from Oil intoHouses with Basements under Constant Negative Pressure

Abstract

1987Lawrence B e r k e l e y L a b o r a t o r y U n i v e r s i t y o f C a l i f o r n i a B e r k e l e y , CA 9 4 7 2 0The U n i t e d S t a t e s Department of Energy h a s t h e r i g h t t o u s e t h i s t h e s i s for any p u r p o s e w h a t s o e v e r i n c l u d i n g t h e r i g h t t o r e p r o d u c e a l l o rany p a r t t h e r e o f . Normal conditions in a house can produce negative pressures as high as 20 P a relative to the outside. This underpressure, which is a maximum at the base of the house (the basement, for instance), can induce a flow of soil gas into the house, through cracks or any other openings in the understructure of the building. Radon (Rn-222), which is produced in the soil and mixed in the soil gas, can then be transported into the house through a complex combination of molecular diffusion and forced convection. In many of the cases where high levels of indoor radon concentrations have been observed in houses, the soil gas has been concluded to be the main source.A theoretical model was developed to simulate this phenomenon, under some specific assumptions. The model simulates: 1) the generation and decay of radon within the soil; 2) its transport throughout the soil due to diffusion and convection induced by the pressure disturbance applied at a crack in the basement; 3) its entrance into the house through the crack; and 4) the resultant indoor radon concentration. The most important assumptions adopted in the model were: 1) a steady-state condition; 2) a house with a basement; 3) a geometrically well-defined crack at the wall-floor joint in the basement; and 4) a constant negative pressure applied at the crack in relation to the outside atmospheric pressure.Two three-dimensional finite-difference computer programs were written to solve the mathematical equations of the model. The first program, cdled PRESSU, was used to calculate: 1) the pressure distribution within the soil as a result of the applied disturbance pressure at the crack; and 2) the resultant velocity distribution of the soil gas throughout the soil matrix. The second program, ca!led MASTRA, was used t& 1) solve the radon mass-transport equation, and to calculate the concentration distribution of radon in the soil gas within the whole soil; and 2) to calculate the entry rate of radon through the crack into the basement, and the final indoor radon concentration.A parametric sensitivity analysis performed on the model, revealed several features of the mechanisms involved in the transport of radon into the house. Then, based on the theoretica.1 simulations, the influences of all important parameters on these radon transport mechanisms were described in detail. Results of the tests showed that the model performs consistently with physical expectations. Among all the parameters analyzed, it was concluded that the most important are: 1) k -the soil permeability; 2) the pressure differential from inside to outside; and 3) the radium (Ra-226) concentration in the soil particles. My graduate studies at The Univers...