English Abstract In the framework of the Dutch ministerial research
programme Stratego (Radiation in buildings) there was a need for information
on the consequences of possible measures to be taken to reduce the average
radon (Rn-222) concentration in dwellings in the Netherlands. This study
was devoted to that question starting of from the trends in building methods
and use of building materials and using these trends as a reference
development. The trend defined as the development without taking measures
directed at reducing the radon concentration, predicts a slow increase of
about 15% until approximately the year 2025. The scenario that is directed
at using concrete with low Ra-226 concentrations in new houses almost stops
this trend. A reduction of the average radon concentration in dwellings
with 25% by the year 2025, compared to 1990, might be possible if measures,
directed at decreasing the infiltration from the crawlspace to the house, in
existing as well as in new buildings are applied. The effective
dose-equivalent due to inhalation of radon-daughters and external exposure
to them from building materials would then be reduced from the present 1,9
mSv.a-1 to 1,4 mSv.a-1. These reduction percentages have to be handled
with some care however, because the effect of the obviously occurring
uncertainties in several parameters used, are not yet quite
clear.