The Chernobyl Accident - A Meteorological Analysis of how Radionuclids Reached and Were Deposited in Sweden

The atmospheric transport to Sweden and the deposition of radioactive material following the Chernobyl accident have been described on the basis of radiological and meteorological data and theoretical calculations of dispersion. The radioactive cloud created by the explosion at 01.23 local time on April 26, 1986, was transported north west and north over the Baltic Sea, with the first radionuclides probably reaching southeast Sweden early on April 27. High concentrations of radionuclides began to appear on the evening of the same day. Sweden was affected by dry deposition, including fairly large hot particles and also by wet deposition. Wet deposition occurred via precipitation over eastern Sweden on April 28 and over parts of northern Sweden until April 30. The deposition of radionuclides over the country was mapped in detail, by extensive measurements of gamma radiation using aircraft and by in situ spectroscopy on the ground. Deposition of cesium mainly occurred through wet deposition. In the case of other nuclides, for example, Zr 95 Np 239, a considerable part occurred as dry deposition. An integration of the total cesium deposition shows that as much as about 10 percent of the total quantity of cesium released from Chernobyl may have been deposited over Sweden. (authors)