A radiologically significant nuclides catalog is paramount to the classification of radioactive waste. In order to produce such a catalog, it is required to know the isotopic composition of the radioactive waste produced in the nuclear power plants, their isotopic inventories and both short and long term toxicity for each relevant nuclide in each exposure scenario. Estimating the waste produced in a power plant is an old problem that still poses a great challenge, even with current technology and methods. This paper describes an attempt at estimating the radionuclide concentration levels of the radioactive waste produced in the Angra dos Reis nuclear power plant. A review on the various methods used around the world to estimate these isotopic compositions was needed in order to achieve such a result. Alongside the review was used a computer simulation with the Origen 6.0 code and calculations to find out the future activities and toxicities for each analyzed radionuclide in each considered exposure scenario. The resulting data is used to build on a radiologically significant nuclides catalog that can be used as guiding tool for the development of radiological containment policies. This data will be helpful for the long term storage of the studied radionuclides.