| Abstrakt: |
A model is presented for the explosive cloud of particulates that produced the western trace of high radioactive ground contamination in the Chernobyl accident on 26 April 1986. The model was developed to reproduce measured dose rates and nuclide contamination and to relate estimated doses to observed changes in: (1) infrared emission from the foliage and (2) morphological and histological structures of individual pines. Dominant factors involved in ground contamination were initial cloud shape, particle size distribution, and rate of particle fallout. At time of formation, the cloud was assumed to be parabolicaland to contain a homogeneous distribution of spherically shaped fuelparticulates having a log-normal size distribution. The particulateswere dispersed by steady winds and diffusion that produced a straight line deposition path. The analysis indicates that two clouds, denoted by Cloud I and Cloud II, were involved. Fallout from the former dominated the far field region and fallout from latter the region near the reactor. At formation they had a full width at half maximum of 1800 m and 500 m, respectively. For wind velocities of 5--10 m s-1 the particulates' radial distribution at formation had a standard deviation and mode of 1.8 mu m and 0.5 mu m, respectively. This distribution corresponds to a release of 390 GJ in the runaway explosion. The clouds' height and mass are not uniquely determined but are coupled together. For an initial height of 3,600 m, Cloud I contained about 400 kg fuel. For Cloud II the values were, respectively, 1,500 m and 850 kg. Loss of activities from the clouds is found to be small. Values are obtained for the rate of radionuclide migration from thedeposit Various types of biological damage to pines, as reported in the literature, are shown to be mainly due to ionizing radiation fromthe deposit by Cloud II. A formula is presented for the particulate size distribution in the trace area. [ABSTRACT FROM AUTHOR] |
