Hermes Alves Filho

The application of spectral nodal methods to discrete ordinates and diffusion problems in Cartesian geometry for neutron multiplying systems

We describe in this paper the recent advances in spectral nodal methods applied to discrete ordinates (SN) and diffusion problems in Cartesian geometry for neutron multiplying systems. We divide this paper into three major parts. Part I and II deal with SN and diffusion eingenvalue problems. In Part III we describe the progress of spectral nodal methods applied to time-dependent diffusion model for reactor kinetics calculations. Numerical results to various typical model problems are given, and we close with general concluding remarks and suggestions for future work.

The Luus-Jaakola algorithm applied to a nuclear reactor core design optimisation

The Luus-Jaakola (LJ) algorithm is a random search optimisation method that has been successfully employed mainly in chemical engineering problems. In this paper, we apply this algorithm to an optimisation problem solved previously with genetic algorithms, particle swarm optimisation and Metropolis algorithms. This problem consists of adjusting several reactor cell parameters, such as dimensions, enrichment and materials, in order to minimise the average peak factor in a three-enrichment-zone reactor, considering restrictions on the average thermal flux, criticality and submoderation. LJ is compared with the aforementioned optimisation algorithms and is shown to perform well, thus demonstrating its potential for other applications.

Simulação Computacional da Estabilização de Sistemas Subcríticos segundo o Modelo Unidimensional de Difusão de Nêutrons Monoenergético

Com o objetivo de descrever o perfil do fluxo escalar de neutrons monoenergeticos em geometria unidimensional usando o modelo de difusao, desenvolvemos um metodo numerico espectronodal de difusao (END) em duas versoes. A primeira versao considera problemas de autovalor, cujas solucoes numericas geradas pelo metodo END, sendo livres de erros de truncamento espacial, coincidem com a solucao analitica dominante, afora erros da aritmetica finita computacional. A segunda versao considera problemas de fonte fixa, onde a fonte e obtida analiticamente a partir da reconstrucao espacial do fluxo escalar gerado pelo metodo END para problemas de autovalor. Neste caso tambem sao obtidas solucoes livres de erros de truncamento espacial. Um codigo computacional que implementa o metodo END foi desenvolvido em linguagem de programacao C# (C Sharp), a fim de gerar as solucoes numericas. A titulo de ilustracao, sao apresentadas solucoes numericas, geradas atraves deste codigo.

Computer Deterministic Modelling of Nuclear Problems using Nodal Methods

In this paper we propose a numerical nodal methodology for the development of a method of spectral nodal class [1, 2] which is tested as an initial study of the solutions (spectral analysis) of neutron transport equations in the formulation of discrete ordinates (SN ), in one-dimensional geometry, two energy groups, isotropic scattering and considering heterogeneous domains. These results are compared with the traditional fine mesh method DD and the spectral nodal method SGF [1].The solution algorithms problems will be implemented in a computer simulator made in MatLab language, the same that was used to generate the results of the reference work.

Coarse-mesh diffusion synthetic acceleration of the scattering source iteration scheme for one-speed slab-geometry discrete ordinates problems

The scattering source iterative (SI) scheme is traditionally applied to converge fine-mesh numerical solutions to fixed-source discrete ordinates (SN) neutron transport problems. The SI scheme is very simple to implement under a computational viewpoint. However, the SI scheme may show very slow convergence rate, mainly for diffusive media (low absorption) with several mean free paths in extent (low leakage). In this work we describe an acceleration technique based on an improved initial guess for the scattering source distribution within the slab. In other words, we use as initial guess for the fine-mesh scattering source, the coarse-mesh solution of the neutron diffusion equation with special boundary conditions to account for the classical SN prescribed boundary conditions, including vacuum boundary conditions. Therefore, we first implement a spectral nodal method that generates coarse-mesh diffusion solution that is completely free from spatial truncation errors, then we reconstruct this coarse-mesh so...