- EVALUATION OF RADIATION RISKS FROM ALL RADIATION SOURCES AND OPTIMIZATION OF RADIOPROTECTION.
- THE RADIOLOGICAL BURDEN OF MAN FROM NATURAL RADIOACTIVITY.
Analysis of the dynamic aspects of radon entry indicated that our knowledge is still insufficient to fully comprehend the problem of radon ingress to a dwelling. The processes of radon transport are much more complicated than previously anticipated. In our opinion the greatest uncertainty is in soil transport.
Changing groundwater levels and precipitation vary radon source strength, medium porosity and radon permeability. For an actual dwelling inhomogeneities in the soil and uncontrollable variations in soil parameters make an assessment of radon transport difficult.
Work undertaken includes:
final tests of the continuous radon monitor;
correlation measurements of radon concentrations against pressure, temperature differences and rainfall as a function of time in 2 test dwellings;
evaluation of data using model calculations;
suggestions for countermeasures.
A continuous radon monitor suitable for measuring (low) radon concentrations in the average dwelling was designed, constructed and tested. The equipment was set up in a test dwelling in order to measure continuously radon concentrations and possible relevant parameters like pressure differences, temperatures, relative humidities, barometric pressure, precipitation rate and groundwater level. A multiroom model was constructed to describe radon concentrations based on static and dynamic sources and advective flow and a ventilation duct plus fan was installed to connect the crawl space with the outside air to introduce forced ventilation either by creating low pressure or high pressure. Measurements in a test dwelling yielded radon concentrations in crawl spaces and living rooms which were greater than those calculated from measured static source strengths. Time evolution of radon concentrations measured simultaneously with pressure differences indicated that pressure driven flow through the soilmay account for the missing contribution to the concentration in the crawl space as well as in the living room. This is the result of the preliminary analysis of 2 weeks in the summer with different weather characteristics.
From this analysis it is concluded that the effective strengths of diffusive and pressure driven terms are not constant in time. It is proposed as a hypothesis that changes in water content of the soil due to precipitation may temporarily increase the radon concentration below the wet layer and that the increased water content may reduce the pressure driven flow. Although the analysis of the data has just begun and hypothesis may be replaced it is tempting to state that understanding radon infiltration into dwellings is not so much a problem of transport in the dwelling rather it is a problem of radon transport in soil.
Measurements on the effect of countermeasures indicate that bringing the crawl space to a low pressure with a fan in a ventilation duc t from the crawl space to the outside air has a clear reducing effect on the radon concentration in the crawl space but has no significant influence on the radon concentration in the living room. This latter result is surprising since during fan on periods the direct current between living room and crawl space reverses when compared to fan off situations. Since the concentration remains higher than expected on the basis of concentration in the outside air and exhalation by surfaces it is suspected that an unaccounted entry route of radon is present. A more detailed analysis and further investigations are imperative to understand these phenomena.
INFLUENCE OF CRAWL SPACES ON THE RADON INGRESS IN DWELLINGS AND EVALUATION OF TRANSPORT MECHANISMS (DIFFUSION AND CONVECTION) IN ORDER TO INCREASE THE UNDERSTANDING OF SHORT TERM VARIATIONS OF THE INDOOR RADON CONCENTRATION.
Funding SchemeCSC - Cost-sharing contracts