EVALUATION OF RADIONUCLIDE TRANSFER-FUNCTIONS FROM DRAINAGE BASINS OFFRESH-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 ev aluated using contamination data collected by some European Laboratori es in the rivers Po, Prypiat, Dnieper, Teterev, Uzh and Rhine followin g the Chernobyl accident. The transfer function Phi(Gamma)(t) (t = tim e) may be generally expressed as the sum of some time-dependent expone ntial 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 detect ion of two main exponential decay components. The order of magnitude o f 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 t he 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-li nearity of Sr-90 transfer functions with respect to the water flow thr ough the drainage basin was detected.