Abstract: In view of the dilution and diffusion of liquid effluents from NPPs in the receiving water, the two-dimensional numerical simulation method is often used for analysis. And the calculated flow field is often verified by hydrological test data. However, for radionuclides with longer half-life, the reduced fraction resulted from decay is smaller, and the size of calculation range has a greater impact on the calculation results. Combined with engineering examples, two computational domains with different sizes are selected, numerical simulations are carried out respectively, and the calculated flow regime, concentration, flux and total conservation are compared and analyzed. It turned out that within the scope of computing power, a larger computational domain should be selected; under the condition of satisfying the calculation accuracy and efficiency, the range between the discharge outlet and the calculation boundary should be more than 80 km. The results can be used as a reference for calculating the computational range of NPP liquid effluents.

Key words: NPP, Liquid effluent, Numerical simulation, Computational domain