GB is a linking code developed at the Departamento de Engenharia Nuclear/UFMG to couple MCNP with the depletion and burnup capability of ORIGEN2.1. In the first version of GB, code described the behavior during the burn up of only 25 isotopes. The amount of isotopes to be considered in the simulation was increased in the GB version used in this paper (named GB5). It was simulated 75 time steps at 800kw of a Heat Pipe Power System model. Results showed that GB5 is able to generate very similar results compared to MCNPX2.6.0. The small difference encountered with the neutron flux parameter between GB5 and MCNPX2.6.0 is explained by the form that recoverable energy per fission is calculated in GB5. Radiotoxicity and radioactivity results are also presented.