Analysis of the Range of Applicability of Thermodynamic Calculations in the Engineering of Nitride Fuel Elements
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ysis of the Range of Applicability of Thermodynamic Calculations in the Engineering of Nitride Fuel Elements A. S. Ivanova,*, A. A. Rusinkevicha,**, G. V. Belova, and Yu. A. Ivanovb a
b
National Research Centre Kurchatov Institute, pl. Akademika Kurchatova 1, Moscow, 123182 Russia Bochvar High-Technology Scientific Research Institute for Inorganic Materials, ul. Rogova 5a, Moscow, 123098 Russia *e-mail: [email protected] **e-mail: [email protected] Received October 30, 2014
Abstract—The domains of applicability of thermodynamic calculations in the engineering of nitride fuel are analyzed. Characteristic values of the following parameters, which affect directly the concentration equilibration time, are estimated: nuclide production rate; characteristic times to local equilibrium in the considered temperature range; characteristic time needed for a stationary temperature profile to be established; characteristic time needed for a quasi-stationary concentration field to be established on a scale comparable to the size of a fuel pellet. It is demonstrated that equilibrium thermodynamic calculations are suitable for estimating the chemical and phase composition of fuel. However, a two-layer kinetic model should be developed in order to characterize the transport processes in condensed and gaseous phases. The process of diffusive transport needs to be taken into account in order to determine the composition in the hot region at the center of a fuel element. Keywords: nitride fuel, thermodynamics, fission products DOI: 10.1134/S1063778817080075
INTRODUCTION Traditional methods and means are often inapplicable to the problems existing in modern science in technology. One is commonly forced to use several models simultaneously to examine a certain process or phenomenon. This approach to the analysis of complex systems, which involves simulation of interrelated processes of different nature (e.g., heat and mass transfer processes accompanied by nuclear and chemical transformations), is called multiphysics in the scientific literature [1–3]. In the context of thermodynamic modeling, nuclear fuel and structural materials used to construct nuclear reactors are regarded as complex objects. Therefore, in spite of the efforts of researchers and experts in nuclear power engineering, reliable methods for predicting the state of nuclear fuel based on model approximations have not been developed yet. New chemical elements are produced in nuclear reactions over the course of reactor operation. These elements interact with nuclear fuel and structural materials. In the context of thermodynamics, the studied system is a multicomponent heterogeneous object with hundreds of chemical compounds that may form solutions. The elementary composition of
fuel changes continuously in the process of its burnup, thus disturbing the equilibrium, while chemical reactions in the system work toward bringing it to equilibrium. Condensed solutions forming in the system are technically not ideal, and the list of substances present in a particular
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