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Ensheng Zhao - One of the best experts on this subject based on the ideXlab platform.

Baigui Bian - One of the best experts on this subject based on the ideXlab platform.

Giuseppe Filardo - One of the best experts on this subject based on the ideXlab platform.

  • A new simple Static Method for the determination of solubilities of condensed compounds in supercritical fluids
    The Journal of Supercritical Fluids, 2002
    Co-Authors: Alessandro Galia, A. Argentino, Onofrio Scialdone, Giuseppe Filardo
    Abstract:

    Abstract A simple Static Method based on gravimetric measurements has been adopted to measure the solubility of benzenecarboxylic acid, 2-hydroxy-benzenecarboxylic acid, 4-hydroxy-benzenecarboxylic acid and 1,8-dihydroxyanthraquinone along several isotherms in the temperature range 318–357 K and the pressure interval 7–23 MPa. Solubility data have been correlated with the Zieger–Eckert approach, using the Fedor atomic and group contribution Method to estimate the solubility parameter and the molar volume of the solutes. A good agreement was obtained between data reported in the literature and those determined using the proposed Method which allows one to measure solubility mole fraction as low as 10 −5 . Provided that a suitable analytical technique is adopted the Method can be extended also to multicomponent systems.

Can Erkey - One of the best experts on this subject based on the ideXlab platform.

Piero Ravetto - One of the best experts on this subject based on the ideXlab platform.

  • Adaptive time step selection in the quasi-Static Methods of nuclear reactor dynamics
    Annals of Nuclear Energy, 2017
    Co-Authors: Dominic Caron, Sandra Dulla, Piero Ravetto
    Abstract:

    Of the Methods available by which to integrate the neutron and delayed neutron precursor balance equations in time, at present the quasi-Static Methods are among the most practical and favourable. However, the correct application of the quasi-Static Method requires the use of appropriately determined time steps, for both the reasons of accuracy and efficiency. This work presents a Methodology for the adaptive selection of the time steps employed by the quasi-Static Method, thereby allowing the quasi-Static approach to be applied in an efficient manner while maintaining a prescribed level of accuracy. The Method is applied to and studied using some numeric test problems.

  • New aspects in the implementation of the quasi-Static Method for the solution of neutron diffusion problems in the framework of a nodal Method
    Annals of Nuclear Energy, 2016
    Co-Authors: Dominic Caron, Sandra Dulla, Piero Ravetto
    Abstract:

    Abstract The ability to accurately model the dynamic behaviour of the neutron distribution in a nuclear system is a fundamental aspect of reactor design and safety assessment. Due to the heavy computational burden associated to the direct time inversion of the full model, the quasi-Static Method has become a standard approach to the numerical solution of the nuclear reactor dynamic equations on the full phase space. The present paper is opened by an introductory critical review of the basics of the quasi-Static scheme for the general neutron kinetic problem. Afterwards, the implementation of the quasi-Static Method in the context of a three-dimensional nodal diffusion theory model in hexagonal- z geometry is described, including some peculiar aspects of the adjoint nodal equations and the explicit formulation of the quasi-Static nodal equations. The presentation includes the discussion of different formulations of the quasi-Static technique. The results presented illustrate the features of the various formulations, highlighting the corresponding advantages and drawbacks. An adaptive procedure for the selection of the time interval between shape recalculations is also presented, showing its usefulness in practical applications.

  • The quasi-Static Method revisited
    Progress in Nuclear Energy, 2008
    Co-Authors: Sandra Dulla, Ernest Mund, Piero Ravetto
    Abstract:

    The quasi-Static Method is a standard tool for the space-time solution of neutron transport problems in multiplying media. Its basic principle lies in a factorization of the angular flux into the product of two functions, 'amplitude' and 'shape', where the amplitude depends only on time (and contains the major part of the time-dependence) while the shape function depends on all variables, time included. The shape equation is solved on a long time-scale, while the amplitude is determined on a short time-scale. The factorization is made unique by proper normalization conditions for the shape function. Most implementations replace the basic equation (transport or diffusion) by the set of coupled amplitude and shape equations derived from the factorization, the so-called 'Improved Quasi-Static Method' (IQM). In this paper we describe an alternate approach already known for some time we have called 'Predictor-Corrector Quasi-Static Method' (PCQM). We discuss its efficiency for both solid- and liquid-fuel systems dynamics. © 2008 Elsevier Ltd. All rights reserved.

  • Accuracy of a predictor-corrector quasi-Static Method for space-time reactor dynamics
    2006
    Co-Authors: Sandra Dulla, Ernest Mund, Piero Ravetto
    Abstract:

    The quasi-Static Method is a standard tool for the space-time solution of neutron transport problems in multiplying media. Its basic principle lies in a factorization of the angular flux into the product of two functions, 'amplitude' and 'shape', where the amplitude depends only on time (and contains the major part of the time-dependence) while the shape function depends on all variables, time included. The shape equation is solved on a long time scale, while the amplitude is determined on a short time scale. The factorization is made unique by proper normalization conditions for the shape function. Most implementations replace the basic equation (transport or diffusion) by the set of coupled amplitude and shape equations derived from the factorization, the so-called 'Improved Quasi-Static Method' (IQM). In this paper we describe an alternate approach already known for some time, called here 'Predictor-Corrector Quasi-Static Method' (PCQM), and we discuss its efficiency for both solid- and liquid fuel systems. (authors)

  • Neutron kinetics of fluid–fuel systems by the quasi-Static Method
    Annals of Nuclear Energy, 2004
    Co-Authors: Sandra Dulla, Piero Ravetto, M. M. Rostagno
    Abstract:

    The quasi-Static Method for the neutron kinetics of nuclear reactors is generalized for application to neutron multiplying systems fueled by a fluid multiplying material, typically a mixture of fissile molten salts. The Method is derived by the application of factorization formulae for both the neutron density and the delayed precursor concentrations and the projection of the balance equations upon a weighting function. A physically meaningful weight can be assumed as the solution of the adjoint model, which is constructed for the situation considered, including delayed neutrons. The quasi-Static scheme is then applied to calculations of some transients for a typical configuration of a molten-salt reactor, in a multigroup diffusion model with a one-dimensional slug-flow velocity field. The physical features associated to the motion of the fissile material are highlighted.