Among the nature great intensity manifestations that have happened in some brazilian regions, one that needs more directed attention in civil enginnering structures design is the tornado. For being a phenomenon that cannot be prevented, the occurrence of such disaster can cause innumerable ambient and partner-economic impacts. With the intention to evaluate the action of a tornado on certain nuclear power plant civil engineering structures, mechanical forces, barometric effects and the action of flying missiles,under a tornado action on three selected structures: the Reactor Building, the Emergency Feed Building and the Vent Stack. For this, it is being adopted the Wen’s wind field model, based on the theoretical Kuo’s solution. Furthermore, for better model understanding, variations on the used parameters are made to indicate how these changes may influence the calculated velocities. Also a comparative analysis is done between inertia and drag effects, beyond the global effects on the evaluated structures, as material point and extensive body, for instance, and a short description on the generation of a tornado hazard curve for Angra dos Reis region, according to Almeida. And, finally, by a numerical simulation, a dynamic response is studied for the Vent Stack reached by an artificial tornado.