Treatment of the Equations of Metal Oxidation Rates at Nuclear Power Plants and Thermal Power Plants in Terms of Thermodynamics

Abstract

The results of the thermodynamic analysis of experimental data and the kinetics equations of hightemperature steam oxidation of iron-based alloys (in the process of a thermal power plant operation) and of zirconium and iron alloys applied in manufacturing of fuel element cladding (at loss-of-coolant accident (LOCA)) are presented. The method of sorting data on the Arrhenius equation parameters and criteria of their reliability are proposed. The dependence of the Arrhenius equation parameter variance depends on the alloy composition and concentration of oxidants (oxygen, steam). The results of isothermal tests in one medium allow relating the activation energy of alloy oxidation to their chemical composition in order to study the process of their oxidation. The algorithm for calculation of oxidation rates and the thermodynamic model of alloy steam oxidation dependence on their composition are developed. The simulation engages the exponential dependence of the molecule collision frequency factor on the entropy of reaction activation in the Arrhenius equation for reactions proceeding on the surfaces of different alloys according to a uniform mechanism and the notion of pseudobinarity of alloys when all dopes in the alloy behave as a single second alloy component, each with its own stoichiometrical coefficient. The verification of the model is accomplished using the plausible experimental data, and the kinetics of steam oxidation is determined (the temperature interval is 1073–1473 K) for zirconium alloys E110opt, E635 on the sponge base, and comparison with the kinetics of M5 alloy oxidation is carried out. For iron–chrome alloys with different contents of the latter, the results of calculations by the proposed model are compared to the data of the experiment on oxidation of alternative cladding alloys. The established laws can be used as a basis to develop the calculation code module for changing the physical state of iron–zirconium alloy fuel element cladding during the failure. The changes can be caused by such phenomena as oxidation, creep strain, and rupture of cladding.