Equilibrium Time and Criticality Considerations in Uranium Enrichment by the Chemical-Exchange Process

The equilibrium time for production of enriched uranium and the effective neutron multiplication factor k_eff are calculated for ion-exchange uranium enrichment based on the U(IV)-U(VI) electron-exchange reaction process. Experimental data are shown to fit well with the calculated equilibrium time curve. It is concluded that under the assumed process operating conditions, as much as 10 yr would be required to attain 50% ²³⁵U enrichment of the product starting with natural uranium feed. The k_eff calculations indicate that the U(IV)-U(VI) exchange system reaches the critical state at a production enrichment grade of 61% ²³⁵ U in anion-exchange systems. From the safety viewpoint, however, it is suggested that the product enrichment grade of the process be limited to 11% or less.