[en] Sodium-24 radionuclide is the major contributions of concentration of total gamma activity in primary system of HFETR. In this paper, the mechanism of sodium-24 nuclide production in primary system is analyzed, and the process of sodium-24 radionuclide with excitation in the core material, release to primary system and primary migration are researched, which is to establish calculation model of sodium-24 radioactive term in primary system of HFETR. The concentration of sodium-24 radionuclide in primary system of HFETR in a power operation is calculated through Monte Carlo N-Particle extended code (MCNPX), and comparing with the actual monitoring results. It turns out that the calculation model of sodium-24 radioactive term is reasonable, and some sensitivity analysis is carried out, which can provide reference for activated term calculation in primary system of the same type of research reactor. (authors)