Three-dimensional model of the process of thermal decomposition of ammonium polyuranate


Аuthors

Kim V. V.1, Brendakov V. N.2*

1. Tomsk State University, 36 Lenin Ave., Tomsk, Tomsk region, 634050, Russia
2. 2Seversky Technological Institute - branch of National Research Nuclear University “MEPhI”, Seversk, Russian Federation

*e-mail: vnbrendakov@mephi.ru

Abstract

Carrying out natural scientific experiments on modern high-tech operating equipment is a labor-intensive and often difficult task. Description of complex technological processes using created simplified models is a promising direction in the development of modern science. Construction of physical models of equipment and processes is associated with material and time costs. An attempt to take into account a large number of influencing factors can significantly complicate the created model. Mathematical modeling as an opportunity to formalize a real operating process is the simplest and most accessible scientific method.
This article describes the results of work on creating a theoretical model of the process of thermal decomposition of ammonium polyuranate to uranium oxides in a rotary drum kiln. An important factor influencing the speed and efficiency of the process of thermal decomposition of ammonium polyuranate in a rotary drum kiln is the thermal environment formed in the working area of the apparatus. The rate of the decomposition reaction significantly depends on the thermodynamic environment developing in the process zone. In turn, the temperature field in the layer of reacting powder is affected by the thermal environment inside the rotary drum furnace. In the created mathematical model describing the process of ammonium polyuranate denitration, an attempt was made to combine three different mathematical problems to display one process: the flow of a continuous viscous heated medium inside the apparatus, thermodynamic heating of a moving layer of chemically active powder and the chemical kinetics of the thermal decomposition reaction.
The recorded mathematical model of the process of thermal decomposition of ammonium polyuranate to uranium oxides in a rotary drum furnace is a closed system of second-order differential equations in partial derivatives and algebraic dependencies. The resulting system was solved numerically by successive iterations based on the finite difference method. To test the operability of the created model, gas flow calculations in a rotating tube were performed in comparison with the existing experiment. A sufficiently good match between the calculation and the experiment indicates the reliability of the results obtained using the mathematical model. The calculations performed using the created model allowed us to obtain the velocity and temperature field in the working volume of the rotary drum furnace. Based on these data, we calculated the temperature, the rate of thermal decomposition reaction, and the concentration of ammonium polyuranate in the layer of moving chemically active powder. Having estimated the average value of ammonium polyuranate concentration across the powder layer, we were able to compare the degree of thermal decomposition of ammonium polyuranate along the length of the calcining furnace with the available experimental data. Good agreement between the obtained numerical results and the available experimental data indicates the adequacy of the created mathematical model.
Numerical studies performed using the constructed mathematical model can be used to increase the efficiency of operating equipment. The created mathematical model of the process of thermal decomposition of ammonium polyuranate to uranium oxides in a rotary drum furnace can be used to optimize the operation of existing devices, as well as to create new promising designs of calcining furnaces in various areas of modern industry.

Keywords:

rotary drum furnace, ammonium polyuranate, degree of thermal decomposition, uranium oxide, mathematical model, iterative process, numerical method, degree of thermal decomposition

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