Analysis of the disposal of spent nuclear fuel in Brazil

• Autor(a) principal: Raoni Adão Salviano Jonusan
• Data de Publicação: 2021
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Repositório Institucional da UFMG
• Texto Completo: http://hdl.handle.net/1843/41268; https://orcid.org/0000-0002-4533-2362
• topic: Spent fuel; Deep geological repository; Cost estimation; Thermal analysis; Site selection; Engenharia nuclear; Análise térmica; Combustíveis nucleares; Resíduos radioativos

The disposal of radioactive waste has been the subject of scientific research since the beginning of the nuclear industry. For high-level waste or spent fuel, the final disposal in deep geological repositories is the global scientific consensus. In this doctoral thesis, aspects related to the process of disposal of spent nuclear fuel (SNF) in Brazil were studied, from a purely academic point of view. The radioactive decay process releases thermal energy that is absorbed by the geological environment. However, some of the safety barrier components have a maximum operating temperature limit. Furthermore, the heat released can help the migration of fluids in the geosphere. As the heat transfer process is passive, the repository must be dimensioned so that the thermal limits are not exceeded during its operation. The simulation of heat transfer allows the determination of the smallest acceptable geometric dimensions of the repository for each type of SNF. Given the Brazilian Government's apparent interest in reprocessed nuclear fuels, the thermal behavior of two reprocessed fuels for the Angra 2 nuclear power plant, a Mixed Oxide (MOX) and a thorium-enriched reprocessed fuel was simulated. The MOX fuel can be disposed of in a repository after 50 years of its removal from the reactor. The spent fuel containing thorium, however, cannot be disposed of in a repository under the same conditions, since the maximum safe temperature would be exceeded. The dimensioning of the repository for the SNF is an important piece of information for the process of selecting areas with the potential to house a geological repository. With the application of a method based on geographic information systems and multi-criteria analysis for the selection of an area for the construction of a repository for the SNF, sites of interest were selected for further. Candidate sites have areas greater than the minimum areas estimated as necessary by the heat transfer simulation. As both the nuclear fuel cycle and the total number of nuclear power plants to be built in this century remain undefined, there is no estimate of back-end costs in Brazil. To estimate the costs associated with this phase of the nuclear fuel life cycle, strategic scenarios were created. These scenarios, together with the possible fuel cycles, were modeled in the energy planning tool MESSAGE to estimate the amount of SNF generated. Using stochastic methods, the most likely total cost was calculated. Values range from $12.84 billion to $83.71 billion depending on the scenario. With this range, it was estimated that the energy sale value should be between 40% and 60% higher than the current value charged to finance the SNF disposal activities.