Material losses and gains are generally unavoidable in isotope separation cascades because of air leakage into the cascade and chemical reactions of the materials in contact with the process gas. Both losses and gains are incorporated into the well-known Q-cascade theory and can be considered differently for each component. The theory is applied, as an example, to investigating the separation of natural uranium to produce low-enriched uranium of 5% 235U, in which UF6 incurs material losses, generating the light impurity hydrogen fluoride (HF).

Two approaches are discussed, one using a carrier gas and another purging the light impurity to prevent the light impurity from exceeding the upper limit in the cascade product end for safe cascade operation. The results show that using carrier gas increases the relative total flow of the cascade, whereas purging the light impurity requires the development of a purging technology. The investigation presents a complicated but real practical scenario, where the components of different physical and chemical properties (some with and without material losses, and some with gains) all appear in the process gas, and demonstrates the applicability of the theory in the study of separation cascades.