[en] In this work, the steps adopted in the operation planned for the deactivation and decommissioning of the previous plant (building 24), to manufacture the tablets of dioxide of Uranium of the Nuclear and Energy Research Institute, IPEN - CNEN/SP are shown, with decommissioning aims. This operation involved the planning, training the operators of the installation, radiometric analysis of the workstations and surveys for monitoring external radiation, contaminated surfaces and air contamination. The training involved the procedures for the manipulation of radioactive materials, decontamination of surfaces, segregation of materials and practical procedures for monitoring the individual surface body contamination, footwear and clothes. Procedures for the transport of radioactive materials had also been established, relative to the internal rules of the installation; provisory confinement of wastes; effluent, riddance of materials and finding areas free of contamination. (author)