The jet pumps of a BWR-5 nuclear reactor are part of the core cooling water system. This system has 20 jet pumps in the annular zone between the core casing and the reactor vessel. Its function is to regulate the flow of water through the core and control the power of the nuclear reactor. This paper reports the cross-flow-induced vibrations generated by the suction flow of the reactor’s annular section. A computational fluid dynamics analysis was performed using the Fluent module of ANSYS, employing a Reynolds Averaged Navier–Stokes (RANS) approach with the K-omega turbulence model. The results obtained in the time domain were transformed to the frequency domain using the fast Fourier transform to estimate the vortex generation frequencies. Then, this data was compared with the natural frequencies of the structure, which were obtained through fluid–structure interaction analysis. The first four natural frequencies were 27.4, 38.9, 39.9 and 41.5 Hz. The frequencies induced by the crossflow do not produce a structural resonance. Consequently, the structural integrity of the system can be guaranteed under ordinary operating conditions.