The migration behavior of radionuclides in soil and groundwater has a great impact on safety of nuclear waste disposal. Usually

there are two kinds of models to study the migration behavior of radionuclides in soil and groundwater system at present: hydraulic model and geochemical model

As an important part of the geochemical model

the reaction path simulation method can be used to not only the material concentration of the system in equilibrium

but also the change process of the system from disequilibrium to equilibrium. In this paper

principle of the reaction path simulation and characteristic of program EQ3/6 are summarized. Then

with an example of CIRP’s field test site

the reaction path of Np and Pu in loess-groundwater system is simulated using program EQ3/6

and the chemical component variation of Np and Pu in the course of irreversible water-rock reaction reaching local equilibrium with the reaction process is investigated. A comparison is also presented between simulated and measured results.