Fernando Carvalho da Silva

A new approach to the use of genetic algorithms to solve the pressurized water reactor's fuel management optimization problem

Abstract A Genetic Algorithm (GA) based system, coupling the computer codes GENESIS 5.0 and ANC through the interface ALGER has been developed aiming at pressurized water reactors (PWR) fuel management optimization. An innovative codification, the List Model (LM), has been incorporated into the system. LM avoids the use of heuristic crossover operators and only generates valid nonrepetitive loading patterns in the reactor core. The LM has been used to solve the Traveling Salesman Problem (TSP). The results got for a benchmark problem were very satisfactory, in terms of precision and computational costs. The GENESIS/ALGER/ANC system has been successfully tested in optimization studies for Angra 1 power plant reloads.

Synthesis of α‐ and β‐Pyran Naphthoquinones as a New Class of Antitubercular Agents

A series of α‐ and β‐pyran naphthoquinones (lapachones) have been synthesized and evaluated for their in‐vitro antibacterial activity against Mycobacterium tuberculosis strain H37Rv (ATCC 27294) using the Alamar‐Blue susceptibility test; the activity was expressed as the minimum inhibitory concentration (MIC) in μg/mL. The synthetic methodology consisted of the formation of methylene and aryl o‐quinone methides (o‐QMs) generated by Knoevenagel condensation of 2‐hydroxy‐1,4‐naphthoquinone with formaldehyde and arylaldehydes. These o‐QMs then undergo facile hetero Diels–Alder reactions with dienophiles in aqueous ethanol media. Some naphthoquinones exhibited inhibition with MIC values of 1.25 μg/mL, similar to that of pharmaceutical concentrations currently used in tuberculosis treatment. These results justify further research into the value of these quinones as part of an original treatment for tuberculosis.

Potencialidades e oportunidades na química da sacarose e outros açúcares

Non-renewable biomass, such as coal, oil and natural gas are not only energy sources but also important starting materials for the production of a variety of chemicals ranging from gasoline, diesel oil and fine chemicals. In this regard, carbohydrates, the most abundant class of enantiopure organic compounds, are very suitable for generation of chemicals of great practical value. Their bulk-scale availability associated with low cost make them unique starting materials for organic preparative purpose. They are a most attractive alternative for construction of enantiopure target molecules by asymmetric synthesis. This review addresses, in addition to the use of low molecular weight carbohydrates, issues related to renewable biomass from photosynthesis and alternatives for the production of bulk and fine chemicals.

Recent advances in spectral nodal methods for X,Y - geometry discrete ordinates deep penetration and eigenvalue problems

Abstract We describe the recent advances in a class of nodal methods applied to multidimensional discrete ordinates (SN) transport problems in Cartesian geometry. This class of coarse-mesh methods is referred to as spectral nodal methods. The basic numerical schemes that we present are the spectral Greens function (SGF) nodal method and the spectral diamond (SD) nodal method. First we describe a spectral nodal method applied to monoenergetic X,Y-geometry deep penetration SN problems with flat approximations for the transverse leakage terms of the transverse integrated SN nodal equations. This method is referred to as the SGF constant nodal (SGF-CN) method. Furthermore, we describe the SGF exponential nodal (SGF-ExpN) method, wherein the transverse leakage terms are approximated by exponential functions. Next, we describe a hybrid spectral nodal method applied to monoenergetic X,Y-geometry SN eigenvalue problems with flat approximations for the transverse leakage terms of the transverse integrated SN nodal equations. For the multiplying regions of the nuclear reactor core, e.g. the fuel regions, we use the SD constant nodal (SD-CN) method, and for the non-multiplying regions, e.g. the reflector regions, we use the SGF-CN method. Numerical results are given to illustrate the accuracy of each method presented.

Formulation for the Calculation of Reactivity Without Nuclear Power History

This paper presents a new method for the solution of the inverse point kinetics equation. This method is based on the integration by parts of the integral of the inverse point kinetics equation, which results in a power series in terms of the nuclear power in time dependence. With the imposition of conditions to the nuclear power, the reactivity is represented as first and second derivatives of this nuclear power. This new calculation method for reactivity has very special characteristics, amongst which the possibility of using longer sampling period, and the possibility of restarting the calculation, after its interruption, allowing the calculation of reactivity in a non-continuous way. Beside that, the reactivity can be obtained independent of the nuclear power memory.

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 derivation of the doppler broadening function using frobenius method

An analytical approximation of the Doppler broadening function ψ(ξ,x) is proposed. This approximation is based on the solution of the differential equation for ψ(ξ,x) using the methods of Frobenius and parameters variation. The analytical form derived for ψ(ξ,x) in terms of elementary functions is very simple and precise. It can be useful for applications related to the treatment of nuclear resonances, mainly for calculations of multigroup parameters and resonances self-protection factors, the latter being used to correct microscopic cross section measurements by the activation technique.

Transverse net leakage into the second-order Nodal expansion method

Abstract A new formulation of the second-order version of the Nodal Expansion Method (NEM) is presented, based on the inclusion of a high-order transverse leakage source term into the Galerkin-weighted one-dimensional equations. This is done in a way that enhances the coupling between average group fluxes and incoming partial currents in the nodal balance equation. The equations for outgoing partial currents then take into account the transverse leakage contributions from the node of interest and the neighboring ones, in a manner similar to the standard fourth-order nodal expansion method. This formulation establishes a more physically coherent neutron balance inside an arbitrary node and preserves the iterative structure of the various versions of the NEM family, i.e., equations for outgoing currents and average fluxes in the inner iterations and fission source in the outer iterations. To illustrate the efficiency and accuracy of this second-order approach, numerical results for a typical 2-D, two-group benchmark model problem are presented.

Depletion Calculation for a Nodal Reactor Physics Code

This paper deals with an alternative numerical method for calculating depletion and production chains of the main isotopes found in a pressurized water reactor. It is based on the use of the exponentiation procedure coupled to orthogonal polynomial expansion to compute the transition matrix associated with the solution of the differential equations describing isotope concentrations in the nuclear reactor. Actually, the method was implemented in an automated nuclear reactor core design system that uses a quick and accurate 3D nodal method, the Nodal Expansion Method (NEM), aiming at solving the diffusion equation describing the spatial neutron distribution in the reactor. This computational system, besides solving the diffusion equation, also solves the depletion equations governing the gradual changes in material compositions of the core due to fuel depletion. The depletion calculation is the most time-consuming aspect of the nuclear reactor design code, and has to be done in a very precise way in order to obtain a correct evaluation of the economic performance of the nuclear reactor. In this sense, the proposed method was applied to estimate the critical boron concentration at the end of the cycle. Results were compared to measured values and confirm the effectiveness of the method for practical purposes.Copyright

Sensitivity analysis on the accident rate of a plant equipped with a single protective channel by generalized perturbation methods

Abstract In this paper we discuss the application of the GPT methodology to a reliability engineering problem which is of great practical interest: that of the analysis on the influence of the demand rate of the accident rate of a process plant equipped with a single protective channel. This problem has been solved in the literature by traditional methods; that is, for each demand rate value the system of differential equations which governs the system behavior (derived from a Markovian reliability model) is solved, and the resulting points are employed to generate the desired curve. This sensitivity analysis has been performed in this paper by means of a GPT approach in order to show how it could simplify the calculations. Sensitivity studies were performed on the repair efficiency and the demand rate, then on the repair rate and repair efficiency and, finally, on the demand rate and repair rate. GPT results of third order approximations were well in agreement with direct calculations. The relevance of the GPT approach is discussed in the context of redundant protective channels.