Análise neutrônica do projeto de um reator rápido para transmutação em um sistema híbrido fusão-fissão

Abstract

This work proposes a project of a small subcritical fast reactor with an external neutron source for actinide transmutation. The reactor integrates features of ADS and fusion system based on Tokamak technology. Both external neutron sources were evaluated, one from the evaporation spectrum and the other from the fusion spectrum applied to the designed small fast subcritical reactor. The analysis involved the evaluating the neutron flux and actinide transmutation rates through a fuel burnup simulation at 1200 K. The primary objective was to evaluate the possibility of implementing this system through the analysis of neutronic parameters using the neutron spectrum of a fusion source from a study Tokamak as an external source in the proposed system, comparing it with the same system using the evaporation source of ADS. First of all, the analyzes took into account the same fuel composition for a working temperature of 1200 K for fresh fuel. Secondly, a fuel burnup simulation was performed to show the neutron flux behavior and mainly the actinide transmutation rates for each external source in the modeled system. The results indicated the importance of external neutron sources in subcritical systems. Furthermore, the results showed that the system with the external fusion neutron source exhibited high actinide transmutation after the fuel burnup evaluation. After this primary analysis of the system modeled in a semi-heterogeneous way, the same reactor was also designed in a heterogeneous way, with the aim of comparing the two proposed models, considering the external source of fusion-fission neutrons in the system. In this analysis, the GANEX fuel was also evaluated, both diluted in thorium and depleted uranium, in order to analyze the burnup parameters in systems with these two fuels. Furthermore, an analysis of the ‘cold zero power’ and ‘hot full power’ systems was also carried out, showing the neutronic behavior in the modeled systems. Finally, an actinide transmutation analyzes were carried out in the proposed SSFR using the fusion external neutron source with an insertion of a reflective layer surrounding the reactor core, comparing with the system without this reflective layer. The analysis also compared different reflective materials for this respective layer. The purpose was to mitigate the neutron leakage from the system core, which would increase the neutron flow in the reactor core and, consequently, could improve the transmutation parameters in the system. All analyzes were performed using the MONTEBURNS code, which executes the MCNP5 and ORIGEN2.1 codes in a connected way. The neutronic data were obtained by the MCNP code and the burnup and fuel composition variation data were obtained by ORIGEN2.1. The cross section libraries were provided by JEFF-3.3 generated by NJOY-2012.