Assessment of the long-term safety of radioactive waste disposal: 2. Isotopic study of water exchange in a multilayer system

Abstract

As a continuation of previous studies of 3H, δ2H, δ18O, Ar, 40Ar/36Ar, and 234U/238U isotope systems, data of uranium-helium dating of groundwater at the radioactive waste repository of Siberian Chemical Works are quantitatively interpreted. The interpretation is based on analytical models taking into account the inflow of deep-earth helium and the diffusion-advection exchange between layers. Estimated flow velocities in reservoir beds and buffer horizons are in agreement with previous hydrodynamic estimates. The obtained velocities of horizontal mass transfer were used to evaluate the age of groundwater in sampling points. Water age varies from 7 to 14 (with a mean of ∼9) in the lower (II and III) aquifers, into which the radioactive wastes are pumped, from 2 to 4 in buffer horizon IV, and from 1 to 2 thousand years in the upper V horizon.