[en] The Almirante Alvaro Alberto Nuclear Center (CNAAA), located at the city of Rio de Janeiro and the liquid effluents are released into the Ilha Grande Bay (BIG). The objective of this work was to simulate mathematically the dispersion of ³H and ¹³⁷Cs present in the liquid effluents that are routinely released into the environment, and in this way contribute to the improvement of the radiological impact assessment associated to these releases. The hydrodynamic circulation pattern of the bay and the transport of radionuclides were simulated by means of numerical modeling techniques by the computational system SisBAHIA (Sistema Base Hidrodinâmica e Ambiental). The results indicate that the local circulation pattern is mainly driven by the propagation of the tidal wave, and is characterized by low current velocities of about 0.1 m.s^-1. The wind stress (normal or extreme ones ) over the free surface does not alter the local circulation pattern significantly. The effluents are released in a rate of about 120 m³.s.^-1 . As a result, the local hydrodynamics is markedly altered by means of the formation of a huge vortices close to the release area. According to the annual amount of the released radionuclides predicted in the Nuclear Licensing Document, and considering a continuous release it could be predicted that the radionuclide plume would present a low mobility, with most of the activity concentration amount being restricted close to the source. The activity concentration distribution reach the transportation steady state by the end of the 51 st day of simulation. A conservative behavior of both radionuclides in the water column was assumed in the performed simulation. (author)