Abstract The effective contribution of nuclear energy will depend on various factors related to economics, safety, public acceptance and sustainability. To assure, however, the nuclear energy development, reactor accident impacts, as Fukushima, must be evaluated in a predictive way. Environmental assessment models are used for evaluating the radiological impact of potential releases of radionuclides from nuclear reactors to the environment. It is important to evaluate, to the extent possible, the reliability of the predictions of such models, by comparing with measured values in the environment or by comparing with the predictions of other models. Tritium has a complex environmental behavior once released into the environment. It is essential to establish reference scenarios to allow the simulation of tritium aquatic pathway subsequent to accidental releases. For this purpose, two scenarios for seawater circulation were analyzed by hydrodynamic modeling. An inverse modeling procedure was successfully applied to estimate tide elevations on the borders, which are based on applying the harmonic constants and using the same overestimation percentage produced by model results to correct the border values. Simulations of validated model for postulated accidental releases of tritium inventory from heavy water reactors, whose doses could be relevant, were presented here. It was observed differences between the two scenarios for the transport modeling that were caused by the removal of large volume of polluted waters from the accident site and its dilution in the discharge area, which has minor tritium concentrations. Moreover, the processes involved in the dynamic transfer of tritium in the environment were analyzed in dependence on the environmental conditions of tropical coastal ecosystem.