Simulation of the atmospheric dispersion of radioactivity from the Chernobyl accident

Measurements of airborne radioactivity over Europe, Japan, and the United States indicated that the release from the Chernobyl reactor accident in the Soviet Union on April 26, 1986, contained a wide spectrum of fission products up to heights of 7 km or more within a few days after the initial explosion. This high-altitude presence of radioactivity would in part be attributable to atmospheric dynamics factors other than the thermal energy released in the initial explosion. Indications were that two types of releases had taken place - an initial powerful explosion followed by days of a less energetic reactor fire. The Atmospheric Release Advisory Capability (ARAC) at the Lawrence Livermore National Laboratory utilized three-dimensional atmospheric dispersion models to determine the characteristics of the source term (release) and the evolution of the spatial distributions of the airborne radioactivity as it was transported over Europe and subsequently over the northern hemisphere. This paper describes the ARAC involvement and the results of the hemispheric model calculations, which graphically depict the extensive dispersal of radioactivity