Spent fuel pool analysis for a pwr using different nuclear fuels

• Autor(a) principal: Jéssica Achilles Pimentel
• Data de Publicação: 2019
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Institucional da UFMG
• Texto Completo: http://hdl.handle.net/1843/34293
• topic: Reprocessed fuel; Spent fuel pool; Criticality calculation; Multiplication factor; Decay heat; Radioactivity; Inhalation radiotoxicity; Ingestion radiotoxicity; Supercell; Delayed neutron fraction; Nuclear reactor safety parameters; Engenharia nuclear; Combustíveis nucleares; Criticalidade (Engenharia nuclear); Radioatividade; Reatores de água pressurizada; Tório

A spent fuel pool (SFP) of a typical Pressurized Water Reactor (PWR) was evaluated considering six types of fuels: standard PWR fuel, MOX, (Th-U)O2-16%, (Th-U)O2-19.5%, (TRU-Th)O2 and (TRU-U)O2 fuels. The following benchmarks: MOX and UO2 Phase IV-B Burn-up Credit Criticality Benchmark as well as Thorium Pin Cell Burnup Benchmark were validated using SCALE 6.0 code with KENO-VI transport code in the CSAS6 sequence. Then, the dimensions of the modeled fuel assembly from the benchmark were used to evaluate burnup and depletion studies. The six fuel assemblies were submitted to a burnup of 16 GWd/teHM with three operating cycles consisting of 420 days full power over 3.61 years. Considering the core refueling configuration, a supercell model was adopted to validate the MOX and UO2 fuels benchmark. The assemblies and supercells were irradiated in a PWR core and after irradiation, the fuel assemblies and supercells were inserted in the pool. Three different geometric arrangements considering the core refueling configuration for assemblies were designed into the pool. It was required to find the minimum pitch distance that would optimize the assemblies’ disposition in the SFP keeping the system under the upper criticality limit. Based on the criticality analyses, radioactivity, decay heat as well as inhalation and ingestion radiotoxicity were also studied over 50 years in the pool. After that, the delayed neutron fraction for each assembly and supercell were compared using the NEWT code. The kinf evolution and the delayed neutron fraction (DNF) for all fuels’ assemblies and supercells were evaluated during the burnup and compared with the standard UO2. It was shown that in no case the pool needed to be resized. The results also show that the DNF of the assemblies using reprocessed fuel is smaller than the standard fuel, which is due to the 239Pu presence and the 233U production, which contribute to the low values obtained for delayed fission neutron fraction. These lower values of DNF suggest that reactors fueled with (TRU-Th)O2 or (TRU-U)O2 assemblies are harder to control. In contrast, the use of UO2-supercells in combination with other types of fuels can provide the burnup extension especially when transuranic fuels are used.