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PERFORMANCE TEST OF AN ACTIVE SUB-SLAB DEPRESSURIZATION SYSTEM
DEVELOPED FOR A RADON TEST-HOUSE

M.C. Akis¹ ², H. Stadtmann ¹ , P. Kindl ² , F. Steger ¹
¹Austrian Research Centre Seibersdorf
Dep. Radiation Protection, A-2444 Seibersdorf, Austria
²Graz University of Technology, Institute of Technical Physics
Petersgasse 16, A-8010 Graz, Austria

A radon Test-House was realised and equipped with an Active Sub-Slab Depressurization (ASD)
system to test and quantify its performance as a radon remediation measure. As active element, a
centrifugal fan of power 136 W was used. The characteristic point of operation of the fan was
determined as 370 m³/h air flow rate, with –120 Pa pressure drop in each suction branch with
respect to the atmospheric pressure. The radon activity concentration in the sub-slab region (in
gravel) was artificially increased by means of a flow-through radon-gas source of 3.7 MBq
activity. When the performance of the system was tested under an indoor concentration of ~17x10³
Bq/m³, a 75% reduction of the initial concentration was observed within 60 min , although the
radon enrichment process in the sub-slab region was going on, and then the concentration kept on
decreasing. A considerable radon-concentration increase inside the test-house was never observed
while the ASD system was in operation. A pressure drop of about 40 Pa was established under the
concrete slab of the test-house while the fan was in operation. For the sake of comparison, a
statistical analysis of single radon measurements (each 10 min) was realised to monitor the
variation of radon-concentration in time, both when the ASD was on and off. The mean radon-concentration
was found as 133 Bq/m³ while the ASD was off, although the same quantity was
determined as 15 Bq/m³ when the ASD was on. The occurrence probabilities of EPA action level
(148 Bq/m³) was determined as 60% and <1% when ASD was off and on respectively. Similarly,
the repetition frequencies of EPA action level was determined as 100 when ASD was off, although
this level was not reached at all when the ASD was on.