, Volume 49, Issue 1-2, pp 139-158

Urban storm water transport and wash-off of Cæfesium-137 after the chernobyl accident

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Abstract

Radiation protection planning in urban areas after a radioactive fallout requires knowledge of decontamination caused by storm water transport. This report elucidates the transport of 137Cs from a roof and three storm sewers in Uppsala during the first rainfall after those, on 29–30 April 1986, causing the Chernobyl contamination. Runoff and concentration Of 137Cs in storm water were determined with an accuracy of 10 to 15%. The origin of storm water was determined from its content of 18O. Surface contamination was measured on 3 July 1986. Total fallout was 25 kBq m−2. During the rainfall on 11 May, 4 kBq m−2 were transported from the roof and approximately 1 kBq m−2 from the sewered areas. From 30 April to 4 July there was a decontamination of 13 to 20 kBq m−2. Measurements from another project showed that the fallout rain events washed off 10 to 16 kBq m−2. The wash-off by the small rainfall on 11 May constituted one third of the remaining decontamination occurring up until 4 July. The transport of 137Cs during the 11 May event increased when the runoff increased, but was less efficient as the event proceeded. The relations between 137Cs concentrations and runoff implied that the wash-off of 137Cs in Uppsala was totally dominated by that bound to particles.