Unsteady State Performance and Stabilization Time in Square Cascades for Stable Krypton Isotope Separation

Document Type : Research Article

Authors

1 Nuclear Fuel Cycle Research School, Nuclear Science and Technology Research Institute, Tehran, Iran.

2 Reactor and Nuclear Safety Research School, Nuclear Science and Technology Research Institute, Isfahan, Iran.

Abstract

The inherently low single stage separation factor of stable krypton isotopes makes their enrichment through multistage cascades a challenging task, requiring precise optimization of cascade parameters and a thorough understanding of transient behavior. In this work, we numerically investigate the unsteady state performance of a square cascade for krypton isotope separation, using a multicomponent mass balance model discretized by the Crank–Nicolson scheme and solved iteratively via a q method. The study focuses on how two key design variables—the cascade cut (θ) and the unit separation factor (α)—affect the stabilization time of individual isotopes and of the entire system. Simulations are conducted for θ = 0.142 (targeting light isotopes in the product) and θ = 0.827 (targeting heavy isotopes in the waste), at α = 1.2 and 1.4. Results reveal that the isotope governing the overall transient response is not fixed: at low cut, intermediate isotope Kr 82 controls the stabilization (≈184 min), whereas at high cut, the heaviest isotope Kr 86 becomes the rate limiting component (≈150–884 min depending on α). Increasing α from 1.2 to 1.4 substantially prolongs the global steady state attainment—from ~190 to ~481 min at θ = 0.142, and from ~156 to ~941 min at θ = 0.827—due to sharper concentration gradients and stronger interstage coupling. These findings demonstrate that steady state analysis alone is insufficient for cascade design; transient simulation is essential to correctly identify the bottleneck isotope and to optimize start up strategies.

Keywords

References

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Chemical Process Design
Volume 5, Issue 2
December 2026
Pages 149-159

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