Abstract <p>Despite careful optimization, the separative power of gas centrifuges (GCs) has always been less than the upper limit determined by Dirac’s formula [1]. It has recently been shown that this limit is greatly overestimated [2]. Nevertheless, the separative power of modern GCs remains several times lower than the upper limit that we refined. The aim of this work is to determine the causes of the separative power deficit and to develop measures that would increase this capacity. Our analysis shows that suppression of separation occurs in rarefied regions of the gas, where the radial diffusion velocity exceeds the axial convection velocity. This leads to a solid-state distribution of concentration and suppression of separation. We assumed that an increase in the mass flux density in the rarefied region should lead to an increase in the separative power of GCs. In a concurrent GC model, the separative power of the optimal GC was calculated to be only three times lower than Dirac’s upper limit due to an increase in the mass flux density in the rarefied region.</p>