The main interest of Hybrid Reactors is the possibility of incineration of transuranics (TRU) by a fast spallation neutron source in a sub critical reactor waste burner. It takes into account that the fission cross section is much higher than the capture cross section at these energies for most of TRU, and therefore transmuting long lived TRU in medium or short lived waste. Besides the incineration of TRU and FF (fission fragments), a coupled system consisting of spallation source and a sub critical array of fuel, may have a positive gain of energy (net energy/energy to operate the accelerator). For this purpose, a precise description and prediction of spallation reaction is necessary. To describe the nuclear reactions at intermediate and high energies, Monte Carlo calculations have being used.

Recently, research groups from IFUSP (Physics Institute of University of Sao Paulo) and CBPF (Brazilian Center of Physics Research) developed a Monte Carlo program to reproduce the intranuclear cascade process and the nuclear evaporation/fission competition process (CRISP code). The evaporation of neutrons, protons and alpha particles are taking into account. Some results of Hybrid Reactors interest are presented and discussed.