Abstract: In order to obtain more real environmental impact assessment results for groundwater,a simulation study on vadose-saturation zone coupling was carried out by using quasi-three-dimensional method based on experiment and numerical simulation. To further explain the hysteresis effect of vadose medium on nuclides migration, simulation without considering the vadose medium was carried out and the results was compared with that of the coupling simulation. The results show that: (1) For strong adsorbed Se-79, Pd-107, Cs-135 and Sn-126, their concentration arriving at water table is far less than the leaked liquid due to the hysteresis effect. And their annual committed effective dose for public will be less than the dose limit of 0.1 mSv. For weakly adsorbed C-14, the annual committed effective dose for public will be more than 0.1 mSv and it requires coupling simulation. (2) C-14 migrates to downstream by convection, and pollution range increases through dispersion. At the same time the C-14 concentration decreases by dilution, decay and adsorption, therefore the annual committed effective dose for public will be less than 0.1 mSv. (3) The concentration of C-14 in groundwater decreases greatly and the migration distance decreases obviously because of the hysteresis effect of vadose medium on nuclides migration. The peak concentration of C-14 in groundwater is 2.15 Bq/L taking vadose zone into consideration; while leaving out the vadose zone, the peak concentration of C-14 will be 9.4×10⁴ Bq/L.The migration distance of C-14 is 1.5 m, 4 m and 4.2 m respectively in 1, 5 and 10 years after the accident, taking vadose zone into consideration; while leaving out the vadose zone, the migration distance of C-14 will be 3 m, 12 m and 17 m respectively.

Key words: quasi-three-dimensional, radionuclide, vadose zone, groundwater, coupling simulation