Carlos Rafael García Hernández | Universidad de la Habana (original) (raw)

Papers by Carlos Rafael García Hernández

DOAJ (DOAJ: Directory of Open Access Journals), May 1, 2016

Análisis de los parámetros de funcionamiento de una celda de combustible de óxido sólido regenera... more Análisis de los parámetros de funcionamiento de una celda de combustible de óxido sólido regenerativa Operating parameters analysis of a solid oxide regenerative fuel cell using modeling techniques

International Journal of Hydrogen Energy, 2019

Hydrogen, rather than oil, must be produced in volumes not provided by the currently employed met... more Hydrogen, rather than oil, must be produced in volumes not provided by the currently employed methods. In this work, two high-temperature hydrogen production methods coupled with an advanced nuclear system are presented. A new design of a pebble-bed accelerator nuclear-driven system called TADSEA (Transmutation Advanced Device for Sustainable Energy Applications) was chosen because of the advantages in transmutation and safety. A detailed flowsheet of the high-temperature electrolysis process coupled to TADSEA through a Brayton gas cycle was developed using chemical process simulation software: Aspen HYSYS ®. It is obtained 0.1627 kg/s of hydrogen with the model with optimized operating conditions, resulting in an overall process efficiency of 34.51%, a value in the range of results reported by other authors. A conceptual design of a plant using the iodine-sulfur thermochemical water splitting cycle was carried out producing 5.66e-2 kg/s and electric energy in cogeneration. The overall efficiency was calculated performing an energy balance resulting in 22.56%. A brief hydrogen production cost estimation was performed for both methods obtaining 5.

International Journal of Exergy, 2019

In this work, a computational model to develop the conceptual design for hydrogen production and ... more In this work, a computational model to develop the conceptual design for hydrogen production and seawater desalination based on a modular nuclear reactor as an energy source is presented. The four-step copper-chlorine (Cu-Cl) process is used to produce hydrogen coupled to the gas turbine modular helium reactor (GT-MHR) nuclear system through a Brayton cycle for the electrical energy generation. A fraction of the thermal energy from the GT-MHR system is used to reach and maintain the temperature requirements in the Cu-Cl process. The rejected heat from the oxy-decomposition reaction is used to desalinate seawater through a multi-stage flash (MSF) process. It is employed a chemical process simulator in order to develop a computational model of the proposed system. The global energy and exergy efficiencies of the proposal are 32.47% and 52.20% respectively, producing 0.2190 kg/s of hydrogen and desalinating 4.9492 kg/s of seawater. It is made an estimate of the cost of hydrogen produced using HEEP ® , resulting in 2.77 $/kgH 2 .

Energy, Mar 1, 2018

Sulfur-Iodine thermochemical water splitting cycle coupled is one of the most promising methods f... more Sulfur-Iodine thermochemical water splitting cycle coupled is one of the most promising methods for hydrogen production using a nuclear reactor as the primary energy source. However, there are not references in the scientific publications of a test facility that allow to evaluate the efficiency of the overall process. A computational model for the evaluation and optimization of the sulfur-iodine cycle coupled to a very high temperature reactor for nuclear hydrogen production was developed using a chemical process simulator Aspen HYSYS ®. Some operational and design parameters of the cycle sections can be optimized in order to obtain the maximum hydrogen production and higher efficiency. The optimized sections of the flowsheet are coupled to a very high temperature nuclear system (TADSEA) through a Brayton gas cycle for power cogeneration. It is proposed a closed flowsheet for the sulfur-iodine thermochemical water splitting cycle coupled to an accelerator driven system, considering a Brayton cycle for the energy production. It is obtained an acceptable value of global efficiency for the initial operating condition. Several parametric studies are conducted using the flowsheet proposed to evaluate important operating parameters in the overall process efficiency.

International Journal of Hydrogen Energy

Brazilian Journal of Radiation Sciences

The use of advanced generation III+ and IV nuclear reactors, and their applications, has become i... more The use of advanced generation III+ and IV nuclear reactors, and their applications, has become important, seen as a means capable of contributing to the global transition to more sustainable, affordable and reliable energy systems. This technology, which could be integrated into future carbon-free electric power generation systems with high proportions of different renewable energy sources, includes Small Modular Reactors (SMR). There are about 100 different proposed projects of Generation III+ and IV, of which about 50 are SMR concepts, in various stages of development and of different types of technologies. Other important issues for achieving the long-term sustainability of nuclear energy are the proper use of its fuel sources and the improvement of nuclear waste management. Therefore, fuels based on a mixture of oxides have been used successfully in several countries. In addition, the incorporation of thorium-based fuel is a current challenge for the new designs of advanced rea...

Progress in Nuclear Energy, 2021

Abstract The integral pressurized water reactor (iPWR) will play an important role in nuclear ene... more Abstract The integral pressurized water reactor (iPWR) will play an important role in nuclear energy development considering its outstanding safety features. To achieve high proliferation resistance, extended fuel cycles have been proposed. Other important issues to achieve nuclear energy long-term sustainability are the proper use of its fuel sources and the improvement of nuclear waste management. Therefore, fuels based on oxides mixture have been successfully used in several countries. Also, Thorium-based fuel incorporation is a current challenge for the new advanced reactor designs. This paper compared different fuel compositions using recycled Plutonium and Uranium in a conceptual reactor of the type iPWR. The use of Thorium as fertile material is presented as well. The presented study considers a standard fuel cycle with slightly enriched Uranium (below 5%) as reference. One-third of the conceptual iPWR’s core is loaded with MOX fuel assemblies and the other two-thirds with conventional UO2. These proposed fuel cycles are compared with the standard full-UO2 cycle, regarding the behavior of main safety parameters, fuel depletion, and waste production. The studied fuel compositions reached a fuel cycle length of 4 years, approximately. The results for the core parameters show that using MOX and Thorium-based fuels in iPWR fulfills the safety constraints.

Revista Cereus, 2020

In the last 15 years, there has been a growing interest in the small modular nuclear reactors (SM... more In the last 15 years, there has been a growing interest in the small modular nuclear reactors (SMR) and their applications. SMRs offer numerous benefits, including inherent safety features. SMRs are under development for all main reactor lines, but an important role for its outstanding safety features will be played by the so-called integral pressurized water nuclear reactors (iPWR). To achieve high proliferation resistance, extended fuel cycles for iPWR have been proposed. Obtaining such a large cycle length, using low fuel enrichment, without shuffle, and with a relatively small core size is a challenge for the neutronic design of the reactor core. In this work, a full-core neutronic computational model based in Serpent code was developed, it permitted to simulate the performance of the proposed reactor core configurations. Different variants of use of integral burnable absorbents in 48-months fuel cycle were studied, and the reactivity worth of the control rod groups was estimated. A fuel cycle extended of more than 1400 EFPDs is reached, and a minimal reactivity penalty was obtained.

Annals of Nuclear Energy, 2021

Abstract Accurate solution of neutron transport problems in the discrete ordinates (SN) formulati... more Abstract Accurate solution of neutron transport problems in the discrete ordinates (SN) formulations is relevant in many areas of engineering and nuclear science. Several researches have led to a variety of numerical differencing schemes in order to generate even more accurate numerical solutions. However, most differencing schemes seem to become unstable for sufficiently large spatial cell width and negative solutions may arise, which are non-physical results. In this work, we present a spectral analysis of the Extended Linear Discontinuous (ELD) and the classical Linear Discontinuous (LD) difference schemes for one-dimensional monoenergetic SN problems with isotropic scattering in non-multiplying media. This analysis can predict analytic threshold values for the discretization cell width, beyond which SN numerical solutions become unstable. Analytical threshold values were calculated by means of the spectrum of spatially discretized SN equations and tested by solving two model problems to compare the practical results with the theoretical predictions offered in this paper.

International Journal of Nuclear Energy Science and Technology, 2019

At present, neutron density calculation in non-multiplying media is relevant in many areas of eng... more At present, neutron density calculation in non-multiplying media is relevant in many areas of engineering and science. In this paper, we propose the Extended Linear Discontinuous (ELD) method in multi-group discrete ordinates formulation, originally formulated for one-energy group fixed-source problems with isotropic scattering source in slab geometry. The proposed auxiliary equations are uncoupled on angular directions and combine the linear discontinuous approximation of the finite element method and the quasianalytical general solution of the spectral nodal method. Thus, we can implement an efficient and simple algorithm using the conventional source iteration scheme for the sweeping equations. Numerical results for benchmark 71 problems are presented to illustrate the accuracy and computational performance of the ELD method. The work shows that the main advantages of the proposed method are that the numerical scheme is stable for coarse-meshes, and its numerical results are more accurate than those generated by the Diamond Difference (DD) and Linear Discontinuous (LD) methods.

International Journal of Exergy, 2021

The work describes two proposals for hydrogen production using the HTR-PM reactor as an energy so... more The work describes two proposals for hydrogen production using the HTR-PM reactor as an energy source. Both proposals take advantage of the high output temperatures of the 2 × 250 MWth HTR-PM project to increase the efficiency of hydrogen production processes. Two proposals are analysed, the hydrogen production through the Cu-Cl cycle and the high temperature electrolysis process. To evaluate the efficiency of the proposed conceptual designs, two computational models were developed in a chemical process simulator. A determination of the efficiency of the hydrogen production process coupled to the HTR-PM was carried out using the computational model developed. The high temperature electrolysis (HTE) process can produce 0.7821 kg/s of hydrogen with 27.37% of efficiency. The Cu-Cl process, although producing less hydrogen, 0.5637 kg/s, has higher overall efficiency (32.12%) than the HTE, mainly due to less global exergy destruction and higher exergetic efficiency.

$Research paper thumbnail of Effects of some calculation parameters on the computational modelling of temperature, velocity and gas volume fraction during steady-state operation of an aqueous homogeneous reactor$

International Journal of Nuclear Energy Science and Technology, 2017

This paper is part of the ongoing efforts to contribute to the thermalhydraulic analysis of one o... more This paper is part of the ongoing efforts to contribute to the thermalhydraulic analysis of one of the most promising alternatives to produce medical isotopes and meeting current and future demand for 99 Mo: the use of D.M. Pérez et al. Aqueous Homogeneous Reactors (AHRs). In this paper, the effects of some calculation parameters like mesh refinement, time step size, turbulence models, transient schemes and numerical advection scheme on the computational modelling of key parameters of an AHR steady-state operation have been investigated. For this purpose, a 75 kWth AHR conceptual design based on the ARGUS reactor, six meshes, five time step sizes, three different models for solving flow problems, three numerical advection schemes and the available transient schemes were used in the simulations. The numerical simulations were carried out using the Computational Fluid Dynamic (CFD) code ANSYS CFX 14. The results of the CFD simulations allow developing a detailed and improved CFD model of the AHR core on which the effects of the investigated calculation parameters are quantifiable.

fisica.uh.cu

Page 1. KEVISTTA CUBANA DE FISICA Voi. 16, No. 2,1999 MÉTODOS NUMÉRICOS DE DIFERENCIAS FINITAS AV... more Page 1. KEVISTTA CUBANA DE FISICA Voi. 16, No. 2,1999 MÉTODOS NUMÉRICOS DE DIFERENCIAS FINITAS AVANZADOS PARA RESOLVER LA ECUACIÓN DE DIFUSIÓN DE LOS NEUTRONES Daniel Millian Lorenzo1 ...

Proceeding Series of the Brazilian Society of Computational and Applied Mathematics, 2017

In this paper we propose a numerical nodal methodology for the development of a method of spectra... more 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 (S N), 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.

XXI Encontro Nacional de Modelagem Computacional e IX Encontro de Ciência e Tecnologia de Materiais, Dec 22, 2018

A viabilidade tecnologica de sistemas nucleares depende de um sistema de seguranca eficiente na o... more A viabilidade tecnologica de sistemas nucleares depende de um sistema de seguranca eficiente na operacao de suas plantas. Para os promissores reatores de temperatura muito elevada refrigerados a gas, esforcos estao sendo empreendidos com alguns reatores experimentais,a exemplo do modelo HTR (High Temperature Reactors)-10. Neste trabalho, sao realizadas simulacoes termohidraulicas do nucleo do reator de tipo leito de bolas HTR-10, usado como estudo de caso, para investigar, dentre outros fatores, o efeito da reducao da taxa de escoamento do fluido refrigerante no perfil de temperatura do nucleo. Adotou-se tecnicas de dinâmica de fluidos computacional (CFD) com uma abordagem realistica para modelar e simular uma geometria que representa uma coluna da secao central do nucleo do reator. Para simplificar a disposicao dos elementos combustiveis no interior do nucleo, e usado o arranjo cubico centrado no corpo (BCC). Os dados de entrada usados foram extraidos do relatorio tecnico de problemas de benchmark divulgado pela IAEA (TECDOC-1694). Os resultados mostram os perfis de temperatura no interior das bolas de combustivel considerando regimes de perda de refrigerante. As temperaturas maximas alcancadas nao excedem o limite de seguranca projetado para o tipo de combustivel nuclear do reator.

TEMA (São Carlos), 2019

Nowadays, the obtainment of an accurate numerical solution of fixed source discrete ordinates pro... more Nowadays, the obtainment of an accurate numerical solution of fixed source discrete ordinates problems is relevant in many areas of engineering and science. In this work, we extend the hybrid Finite Element Spectral Green's Function method (FEM-SGF), originally developed to solve eigenvalue diffusion problems, for fixed source problems using as a mathematical model, the discrete ordinates formulation in one energy group with isotropic scattering in slab geometry. This new method, Extended Linear Discontinuous Discrete Ordinates (ELD-SN), is based on the use of neutron balance equations and the construction of a hybrid auxiliary equation. This auxiliary equation combines a linear discontinuous approximation and spectral parameters to approximate the neutron angular flux inside the cell. Numerical results for benchmark problems are presented to illustrate the accuracy and computational performance of our methodology. ELD-SN method is free from spatial truncation errors in S2 quadr...

Nuclear fission devices coupled to particle accelerators driven system (ADS) are being widely stu... more Nuclear fission devices coupled to particle accelerators 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 work was to use probabilistic methods of computational modeling to simulate ADS geometry with TRISO fuel. Specifically, we were concern with a comparative study of three different spallation target materials: lead, uranium and tungsten in the pebble bed ADS with TRISO fuel. The variations of the neutron flux, the thermal power, the effective multiplication factor, 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 refueling 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. 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 obtained with the uranium spallation target is the key factor to reduce the mass of the plutonium isotopes and minor actinides in the core. The main future goal of this work is increase the core power for the three spallation target materials simulated.

International Journal of Nuclear Energy Science and Technology, 2010

... Dany S. Dominguez* Laboratório de Computação Científica Universidade Estadual de Santa Cruz R... more ... Dany S. Dominguez* Laboratório de Computação Científica Universidade Estadual de Santa Cruz Rod. Ilhéus/Itabuna km 16 45650000, Ilhéus, BA, Brazil E-mail:dany@labbi.uesc.br *Corresponding author Carlos RG Hernandez ...

Journal of Thermodynamics, 2015

Tc99m is a very useful radioisotope, which is used in nearly 80% of all nuclear medicine procedur... more Tc99m is a very useful radioisotope, which is used in nearly 80% of all nuclear medicine procedures. Tc99m is produced from 99Mo decay. A potentially advantageous alternative to meeting current and future demand for 99Mo is the use of Aqueous Homogeneous Reactors (AHR). In this paper, a thermal-hydraulics study of the core of a 75 kWth AHR conceptual design based on the ARGUS reactor for 99Mo production is presented. As the ARGUS heat removal systems were designed for working at 20 kWth, the main objective of the thermal-hydraulics study was evaluating the heat removal systems in order to show that sufficient cooling capacity exists to prevent fuel solution overheating. The numerical simulations of an AHR model were carried out using the Computational Fluid Dynamic (CFD) code ANSYS CFX 14. Evaluation shows that the ARGUS heat removal systems working at 75 kWth are not able to provide sufficient cooling capacity to prevent fuel solution overheating. To solve this problem, the number ...