Numerical investigation of the separation of sulfur isotopes in a single gas centrifuge

Abstract

The centrifuge technology for enriching uranium isotopes, after being implemented in our country on a commercial level, was successfully used for obtaining highly enriched stable and radioactive isotopes of some other chemical elements [1]. Interest in the use of a gas centrifuge for producing stable isotopes is indicated by the recently published works [2][3][4]. It is obvious that the centrifuge apparatus, designed for enriching uranium isotopes, cannot separate equally efficiently isotopic mixtures with arbitrary molecular mass. For this, it is necessary to solve in each specific case the problems associated with optimizing the working parameters of a single gas centrifuge. In the present work, which was initiated by the Institute of Molecular Physics at the Russian Scientific Center "Kurchatovskii institut," we investigate theoretically the separation of isotopic mixtures of average molecular mass -100-200 on a single centrifuge apparatus for the example of a four-component mixture of sulfur isotopes in the form of sulphur hexafluoride (SF6).Physical-Mathematical and Numerical Model of Transport Processes in a Gas Centrifuge. To study the flow and separation of a multicomponent isotopic mixture, we solved a stationary system of equations describing the dynamics of a viscous compressible gas and diffusion equations by a finite-difference method. Because of the rapid rotation of the rotor the problem was solved in an axisymmetric approximation. Estimates show that in modern centrifuges with a tangential rotational velocity of the rotor reaching 600 m/sec the radial and axial change in the concentration, for most isotopic mixtures, is small enough so that the spatial variation of the coefficient of viscosity and thermal conductivity can be neglected. For this reason, the problem of calculating the separation characteristics of centrifuges can be solved in two stages even for nonuranium isotopes. At the first stage, the gas-dynamic problem is solved for an average-mass velocity, density, and temperature of the mixture as a whole. At the second stage, the values found for these parameters are employed for solving the diffusion equations, written for each component of the mixture. The matrix of generalized diffusion coefficients was written in a diagonal form found as a result of the investigations conducted.The boundary conditions were the standard conditions, used in the investigation of internal flows of gas mixtures: attachment on solid surfaces, prescribed temperature on the boundaries of the computational region, all parameters of external flows flowing into the centrifuge rotor are given explicitly, the density and radial and axial components of the velocity vector are given explicitly, and no azimuthal stagnation and temperature gradient in the outgoing flow of extraction of the light fraction. For the diffusion problem, it is assumed that there is no diffusion flow on all boundaries of the computational region. The centrifuge rotor with the computational region is shown schematically in Fig. 1. We note tha...

Overall Separation Factors for Stable Isotopes by Gas Centrifuge

“…The gas centrifuge process has made it possible to produce many nonuranium isotopes economically, especially when large quantities are needed. Many countries, such as the United States (1,2), Russia (3)(4)(5), and China (6), and organizations, such as URENCO (7), have reported their activities in the public literature in the field of multicomponent separation by gas centrifuge.…”