José M. Aragonés

A Linear Discontinuous Finite Difference Formulation for Synthetic Coarse-Mesh Few-Group Diffusion Calculations

A linear discontinuous finite difference formulation to solve the diffusion equations in coarse mesh and few groups is developed. The correction factors for heterogeneities, coarse mesh, and spectral effects are general interface flux discontinuity factors that can be explicitly calculated (synthetized) from detailed diffusion or transport solutions in fine mesh (heterogeneous) and multigroups, preserving the integrated fluxes and interface net currents. The stability is explicitly established for general synthetizations and for specific fine to coarse mesh and group reductions. Computing methods have been implemented for one-group (grey) synthetic diffusion acceleration, two-dimensional nodal/local solutions, and three-dimensional nodal simulation of pressurized water reactor cores. Results demonstrate the simplicity and stability of the formulation, a regular behaviour of the correction factors, an outstanding acceleration performance, and high potential for parallel and vector computing.

The Analytic Coarse-Mesh Finite Difference Method for Multigroup and Multidimensional Diffusion Calculations

Abstract In this work we develop and demonstrate the analytic coarse-mesh finite difference (ACMFD) method for multigroup—with any number of groups—and multidimensional diffusion calculations of eigenvalue and external source problems. The first step in this method is to reduce the coupled system of the G multigroup diffusion equations, inside any homogenized region (or node) of any size, to the G independent modal equations in the real or complex eigenspace of the G × G multigroup matrix. The mathematical and numerical analysis of this step is discussed for several reactor media and number of groups. As a second step, we discuss the analytical solutions in the general (complex) modal eigenspace for one-dimensional plane geometry, deriving the generalized Chao’s relation among the surface fluxes and the net currents, at a given interface, and the node-average fluxes, essential in the ACMFD method. We also introduce here the treatment of heterogeneous nodes, through modal interface flux discontinuity factors, and show the analytical and numerical application to core-reflector problems, for a single infinite reflector and for reflectors with two layers of different materials. Then, we address the general multidimensional case, with rectangular X-Y-Z geometry considered, showing the equivalency of the methods of transverse integration and incomplete expansion of the multidimensional fluxes, in the real or complex modal eigenspace of the multigroup matrix. A nonlinear iteration scheme is implemented to solve the multigroup multidimensional nodal problem, which has shown a fast and robust convergence in proof-of-principle numerical applications to realistic pressurized water reactor cores, with heterogeneous fuel assemblies and reflectors.

An analysis of the Physical Causes of the Chernobyl Accident

AbstractThe initiating events and propagating mechanisms of the Chernobyl accident are the subject of this analysis. The neutronics and thermohydraulics of RBMK reactors under different regimes are studied. It is found that the reactor response to a loss of pumping power was a reactivity trip that could not be fully overcome by the Doppler effect because of the neutronic importance of hydrogen captures under the conditions before the accident. This very high importance was induced by an incorrect hydraulic regime being established before the accident in order to conduct an electromechanical experiment. This experiment was responsible for the loss of pumping power that triggered the accident.

Analytic Coarse-Mesh Finite-Difference Method Generalized for Heterogeneous Multidimensional Two-Group Diffusion Calculations

Abstract In order to take into account in a more effective and accurate way the intranodal heterogeneities in coarse-mesh finite-difference (CMFD) methods, a new equivalent parameter generation methodology has been developed and tested. This methodology accounts for the dependence of the nodal homogeneized two-group cross sections and nodal coupling factors, with interface flux discontinuity (IFD) factors that account for heterogeneities on the flux-spectrum and burnup intranodal distributions as well as on neighbor effects. The methodology has been implemented in an analytic CMFD method, rigorously obtained for homogeneous nodes with transverse leakage and generalized now for heterogeneous nodes by including IFD heterogeneity factors. When intranodal mesh node heterogeneity vanishes, the heterogeneous solution tends to the analytic homogeneous nodal solution. On the other hand, when intranodal heterogeneity increases, a high accuracy is maintained since the linear and nonlinear feedbacks on equivalent parameters have been shown to be as a very effective way of accounting for heterogeneity effects in two-group multidimensional coarse-mesh diffusion calculations.

Methods and Results for the MSLB NEA Benchmark Using SIMTRAN and RELAP-5

Abstract The purpose of this paper is first to discuss the methods developed in our three-dimensional pressurized water reactor core dynamics code SIMTRAN and its coupling to the system code RELAP-5 for general transient and safety analysis. Then, we summarize its demonstration application to the Nuclear Energy Agency (NEA)/Organization for Economic Cooperation and Development (OECD) Benchmark on Main Steam Line Break (MSLB), co-sponsored by the U.S. Nuclear Regulatory Commission (NRC) and other regulatory institutions. In particular, our work has been supported by the Spanish “Consejo de Seguridad Nuclear” (CSN) under a CSN research project. Our results for the steady states and the guided-core transients, proposed as exercise 2 of the MSLB benchmark, show small deviations from the mean results of all participants, especially in core average parameters. For the full-coupled core-plant transients, exercise 3, a detailed comparison with the University of Purdue–NRC results using PARCS/RELAP-5, shows quite good agreement in both integral and local parameters, especially for the more extreme return-to-power scenario.

Detailed Calculations in Energy and Space of Effective Neutron Resonance Cross Sections

A method is developed for calculating effective neutron cross sections in the resolved resonance groups of homogeneous mixtures of cylindrical cells in regular reactor lattices. A rigorous treatment of the nucleonic and neutronic problems provides accurate numerical solutions with detailed dependence in energy and space for both Doppler-broadened cross sections and self-shielded neutron fluxes. The common simplifying approximations are not introduced, so that the method is used as a reference to analyze some of the detailed self-shielding effects that are commonly ignored or approximated in applications ranging from homogeneous mixtures of different resonant nuclides to cylindrical cells with nonuniform temperatures and concentrations within the fuel.

Recent results in the analysis of heavy-ion-beam-driven ICF targets☆

Abstract As a continuation of previous work on the analysis and optimization of ICF beam and target configurations, the influence of the energy deposition profi

Fuel Management and Core Design Code Systems for Pressurized Water Reactor Neutronic Calculations

A package of connected code systems for the neutronic calculations relevant in fuel management and core design of pressurized water reactors (PWRs) has been developed and applied for validation to the startup tests and first operating cycle of a 900MW(electric) PWR. The package includes the MARIA code system for the modeling of the different types of PWR fuel assemblies, the CARMEN code system for detailed few group diffusion calculations for PWR cores at operating and burnup conditions, and the LOLA code system for core simulation using onegroup nodal theory parameters explicitly calculated from the detailed solutions.

Core-State Models for Fuel Management of Equilibrium and Transition Cycles in Pressurized Water Reactors

Fuel management requires that mass, energy, and reactivity balance be satisfied in each reload cycle. Procedures for selection of alternatives, core-state models, and fuel cost calculations have been developed for both equilibrium and transition cycles. Effective cycle lengths and fuel cycle variables--namely, reload batch size, schedule of incore residence for the fuel, feed enrichments, energy sharing cycle by cycle, and discharge burnup and isotopics--are the variables being considered for fuel management planning with a given energy generation plan, fuel design, recycling strategy, and financial assumptions.

High-Gain Direct-Drive Target Design for ICF

The study of the efficiency of high-gain direct-drive targets for ICF has been increased during last years because of the significant progress achieved in laser experiments. Two major key issues have been observed. First, main advances on the uniform illumination to implode targets, due to the techniques developed at NRL1, Rochester2 and Osaka3. Second, lower growth rates for the hydrodynamic instabilitites up to a 30% of the clasical value by using short wavelength lasers.