A consistent radionuclide vector after the Chernobyl accident.

Abstract

The radionuclide vector in the release plume from the destroyed unit 4 of the Chernobyl Nuclear Power Plant was assessed. Emphasis was laid on radionuclides relevant for the internal dose, including those with short half-lives, and on the radionuclide vector in the 30-km zone where practically no data in air or foodstuff are available. An evaluation of data was performed by comparing core analysis data and actual measurements of air filters and deposition data. The derived nuclide vector is consistent with most measurements and core analysis data. The ratios of the various radionuclides with regard to the guide isotope 137Cs vary both with direction of release and with increasing distance from the power plant. The variation and its causes are discussed, and a credible, consistent model for the vector at arbitrary distances from the nuclear power plant, in particular with regard to non-volatile radionuclides, is given. In that way the observed large discrepancies of the radionuclide vector determined by Russian and Ukrainian researchers, and those measured in Central and Northern European are explained by the fact that 90Sr, 95Zr, 140Ba, and 144Ce, which showed a much higher ratio to 137Cs close to the reactor than at 1,000 km distance, were attached to particle sizes of 8 microm and thus quicker deposited than the volatile radionuclides which were attached to 1 microm particulates on average. Also, the 131I to 137Cs ratio changes with distance by almost one order of magnitude which is explained by the higher deposition velocity of iodine.