Plutonium in the air in Kurchatov, Kazakhstan

Weekly air samples of 25000 m3 volume were taken with two air samplers over a period of one year in 2000–2001 in the town of Kurchatov in Kazakhstan. For another three-month period in 2001, the samplers were run in the city of Astana, about 500 km west of Kurchatov. 137Cs, Pu and U concentrations were determined from the filters. Pu activities in Kurchatov varied in a 100-fold range; median 239,240Pu activities were 100 nBq/m3 and 238Pu activities 34 nBq/m3. The corresponding values for Astana were considerably lower: 29 and 9 nBq/m3, respectively, and in half of the filters the 238Pu activity was below the detection limit. Plutonium concentration correlated with the amount of dust retained on the filters only at the highest dust loads. Also no correlation between wind speed and the plutonium activity in the filters was observed. Thus, resuspension does not seem to be the mechanism responsible for the airborne plutonium. No clear seasonal variation of Pu air concentration was observed, though levels were somewhat elevated in February to April. There was no correlation between the plutonium and 137Cs concentrations. In most of the filters the cesium concentration was below the detection limit, but in those filters where it could be detected the cesium concentration was practically constant at 3.9F1.6 ABq/m3. Dose estimation for the inhalation of the airborne plutonium gave a low value of 0.018 ASv/a for the inhabitants in Kurchatov, which is about a thousand times lower than the dose caused by the naturally occurring 210Po. Air parcel trajectory analysis indicated that the observed Pu activities in the air could not unambiguously be attributed to the most contaminated areas at the Semipalatinsk Test Site.