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NUMERICAL MODELLING OF RADON-222 ENTRY INTO HOUSES: AN OUTLINE OF TECHNIQUES AND RESULTS

Claus E. Andersen
Risø National Laboratory, Building NUK-125, DK-4000 Roskilde, Denmark, +45-4677 4912
(direct); Fax: +45-46774959; e-mail: claus.andersen@risoe.dk

Numerical modelling is a powerful tool for studies of soil gas and radon-222 entry into houses. It is
the purpose of this paper to review some main techniques and results. In the past, modelling has
focused on Darcy flow of soil gas (driven by indoor-outdoor pressure differences) and combined
diffusive and advective transport of radon. Models of different complexity have been used. The
simpler ones are finite-difference models with one or two spatial dimensions. The more complex
models allow for full 3D and time dependency. Advanced features include: soil heterogeneity,
anisotropy, fractures, moisture, non-uniform soil temperature, non-Darcy flow of gas, and flow caused
by changes in the atmospheric pressure. Numerical models can be used to estimate the importance of
specific factors for radon entry. Models are also helpful when results obtained in special laboratory or
test structure experiments need to be extrapolated to more general situations (e.g. to real houses or
even to other soil-gas pollutants). Finally, models provide a cost-effective test bench for improved
designs of radon prevention systems. The paper includes a summary of transport equations and
boundary conditions. As an illustrative example, radon entry is calculated for a standard slab-on-grade
house.
Keywords: Advection; Diffusion; Houses; Modelling; Radon-222; Soils; Transport.