EVALUATION OF RADIONUCLIDE TRANSFER-FUNCTIONS FROM DRAINAGE BASINS OF FRESH-WATER SYSTEMS

Radionuclide transfer functions, defined as the amount of radionuclide flowing per unit time from an upstream drainage basin to a water body following a single pulse deposition of radioactive substance, were evaluated using contamination data collected by some European Laboratories in the rivers Po, Prypiat, Dnieper, Teterev, Uzh and Rhine following the Chernobyl accident. The transfer function Phi(Gamma)(t) (t = time) may be generally expressed as the sum of some time-dependent exponential components Phi(Gamma)(t) = Sigma(i)k(i)e(-(lambda i+lambda r)t) where lambda(r) + lambda(i) are the effective decay constants, lambda r is the radionuclide decay constant k(i) are parameters depending on the deposition and the water flow. The data analysed here allow detection of two main exponential decay components. The order of magnitude of the short term effective decay constant calculated here is 10(-7) s(-1) (radionuclides Cs-137, Sr-90 and Ru-103). The geometric means of the effective decay constants of the long term component are 1.5 X 10(-8) s(-1) (Cs-137) and 4.9 x 10(-9) s(-1) (Sr-90). A significant non-linearity of Sr-90 transfer functions with respect to the water flow through the drainage basin was detected.