Toy model for enrichment mass balance + SWU. Explore how tails assay trades feed vs SWU, and find the cost-minimizing tails.
Example: xp=0.04 means 4.0% U-235
Natural uranium ≈ 0.00711
Feed is the amount of natural/low-enriched uranium you must supply to make a given amount of enriched product. Tails is what remains after enrichment, with a residual U-235 fraction xt.
Lowering xt extracts more U-235 from the feed (less feed needed) but requires more separation effort (more SWU). The economically optimal xt depends mainly on uranium price vs SWU price.
This is a simplified teaching tool (no cascade details, losses, constraints, contracts, etc.).