Title : MODELAGEM COMPUTACIONAL DE UM ADS PARA TRANSMUTAÇÃO DE REJEITOS E PRODUÇÃO DE HIDROGENIO
language : Portuguese
Abstract
Nuclear fission devices coupled to particle accelerators ADS (Accelerator Driven System-ADS) are being widely studied. These devices have many applications, including nuclear waste transmutation and production of hydrogen, both with significant social and environmental impact. The main objective of this dissertation was to use probabilistic methods of computational modeling to simulate ADS geometry with TRISO fuel. Specifically, we were concern with the characterization of the spallation region of ADS geometry for three different target materials: lead, uranium and tungsten. New studies on the deep burns strategy of the TRISO fuel in the pebble bed ADS were also carried out as a part
of this project. Several aspects were evaluated for characterizing the spallation target, including the neutron source intensity, neutrons, photons, and electrons spectra and the neutron production per energy unit of incident proton as function of beam energy, target material and geometric dimensions. In addition, the variations of the neutron flux, the thermal power, the effective multiplication factor (keff), and the isotopic composition of the TRISO fuel, during the stationary cycle for minor actinides and plutonium isotopes, were studied as a function of the simulated target materials. The recharge cycles during one year of reactor operation for each simulated target were determined by the decreasing of thermal power to a set minimum value. Modeling was performed using Monte Carlo code MCNPX 2.6E. It can be concluded, from the optimization study of the solid target dimension in cylindrical geometry, that the neutron production per incident proton for the three considered target
materials increases with the increasing of the spallation target dimensions of (thickness and radius) until it achieves the highest production of neutrons per incident proton or the saturation region. The solid target of tungsten material is the target that offers better features. From the analysis of the ADS geometry modeling with TRISO fuel we concluded that the extension of burning time without recharging in the reactor core is the key factor to reduce the masses of the plutonium isotopes and minor actinides in the core. It is then necessary to modify the geometrical configuration proposed for the subcritical core, in order to increase the power and neutron flux in the core. The power increment in the core is the main future goal of this dissertation.
COMPUTER MODELING OF A WASTE OF TRANSMUTATION ADM FOR HYDROGEN PRODUCTION