G. A. Sulaberidze

CASCADES FOR SEPARATION OF MULTICOMPONENT ISOTOPE MIXTURES

This article reviews and analyzes the state-of-the art on separation of multicomponent isotope mixtures in cascades. Different methods, which are applied to calculate the cascade configurations and designs as well as those used to describe some transient processes in cascades when separating multicomponent isotope mixtures are discussed and analyzed in detail. The main directions for the further development of isotopes fractionation using cascades are formulated.

The separation power and thermodynamic work of separation for a three-flow unit during the equilibrium separation of a binary gas mixture

Equations for calculating the separation power and thermodynamic work of a three-flow separation element and cascade for the separation of a binary gas mixture are discussed.

On a Criterion Efficiency for Multi-Isotope Mixtures Separation

The criterion for efficiency for separation of binary isotopic mixtures is the well-known value function. However, in the case of multi-isotope separation, this value function does not exist. In this paper we develop a criterion to define the efficiency for separation of multi-isotope mixtures. It is based on the concept of the match-abundance ratio cascade (MARC) originally introduced by De La Garza for a ternary isotope mixture. The criterion has the property that, when applied to binary mixtures, it is the same as the value function. This approach has demonstrated that for obtaining the optimal parameters of a single stage in the cascade it is necessary to minimize the linear combination of the inverse values of “partial separative powers” for all mixture components. A numerical example using this efficiency criterion is presented using the separation of chromium isotopes by a single gas centrifuge.

Comparative Study of the Model and Optimum Cascades for Multicomponent Isotope Separation

The possibility of estimating the minimum total flow in a cascade with concentrations of a target component given in the product and waste flows by means of a model match abundance ratio cascade (MARC) is studied. The parameters required to describe MARC characteristics are the total number of separation stages, the feed flow location, and the M* parameter, which is equal to a half-sum of mass numbers of the target and the supporting components. Specific research carried out independently in two scientific labs in China and Russia has demonstrated that the integral parameters of the MARC, optimized by the M* parameter, are very close to that of the optimum by the minimum total flow cascade found by means of numerical optimization. The calculation is performed for separation of krypton isotopes when the end component 78Kr and the intermediate component 83Kr are considered to be the targets. It paves the way to use the optimized MARC parameters for two purposes: first, for fast and easy evaluation of the real cascade parameters and second, as an initial guess in its further direct numerical optimization, thereby allowing significant savings in computation time.

Quasi-ideal cascades with an additional flow for separation of multicomponent isotope mixtures

The theory of the R-cascade is generalized to a cascade with an additional external flow, which can be either one more feed flow to the cascade or an additional product flow from the separator at arbitrary degrees of enrichment in the stages of the cascade. Calculations are performed for the enrichment of recycled fuel in the R-cascade to a necessary concentration, provided that the effect of the isotope 236U is compensated and the concentration of the isotope 232U is decreased. It is demonstrated that the theory of the R-cascade with an additional product flow from an intermediate section of the cascade with the maximal component concentration and an intermediate mass number can be used to calculate the optimal conditions in simultaneous separation of several enriched isotopes in the cascade.

The Q-Cascade Explanation

The physical meaning of a continuous profile cascade, which is frequently used in the study of multicomponent isotope separation and named as the Q-cascade is explained. It is found that the parameter Q for a component at a stage is nothing but the relative increase of the concentration of the component, and is constant at all cascade stages. The Q-cascade is classified as the quasi-ideal cascade playing an importantrole for fast evaluation of the separation cascade parameters for multi-isotope mixture separation.

Designing a Rectangular Sectioned Cascade by Approximating the Separation Factor

A powerful method is suggested for the calculation of the steady-state mass transfer for a multicomponent isotope mixture separated in a rectangular sectioned cascade. Based on the progressive approximation of the outlet concentration ratios, the method provides appreciable savings in computational time.

Features of Mass Transfer of Intermediate Components in Square Gas Centrifuge Cascade for Separating Multicomponent Mixtures

Based on an analysis of the results of a series of numerical experiments, the principles of isotope-selective mass transfer have been analyzed in ordinary square cascade from gas centrifuges to separate multi-component mixtures depending on the relationship between external flows. It has been shown that the ratio of product and feed flows considerably affects the mass transfer of the components of separated mixture along the square cascade primarily on the components with intermediate mass number (in a series of mass numbers of all components of separated mixture). With change in the given ratio, the transfer of intermediate components may undergo qualitative changes and shift the direction of enrichment, e.g., from the light end of the cascade to the heavy end. The determined principles rationalize the opportunities to control mass transfer of intermediate components due to the change in the ratios between external flows of cascade.

Q-cascades for obtaining highly concentrated intermediate components of separated mixtures

A comparative analysis of a Q-cascade with a monotonic flow profile and a Q-cascade with flow expansion in the enrichment part is performed under the condition of equal total flows in both cascades. The given cascade schemes are proposed in order to obtain highly concentrated intermediate (with respect to their mass number) components in the separation of multicomponent isotope mixtures. It is shown that the cascade with expansion provides a higher concentration of the target component in the additional product than the usual cascade with monotonic flow profile. However, the amount of isotope accumulated product per unit feed mixture mass in the Q-cascade with expansion is much lower than in the usual Q-cascade.

Isotopically Selective Mass Transfer in the Q-Cascade with Losses of Working Substance

The theory of the model Q-cascade is generalized for the case of presence of losses of working substance. Analytical solutions are obtained to determine the cascade parameters for specified rates of losses. Calculations to reveal the effect of the losses on the total and feed flows for given concentrations of a target component in the product and waste flows are carried out. The dependence of the total and feed flows on the losses for multi- and binary isotope mixtures is defined.