Drawing No. EH–NR–010 // Nuclear Engineering & Radiation
Reviewed August 2026
Calculate the separative work, natural uranium feed, and tailings for enriching uranium to a target fuel assay — the standard feed/product/tails balance used across the enrichment industry.
Natural uranium contains only about 0.711% of the fissile isotope U-235; most power reactor fuel needs 3–5%. Enrichment plants raise that concentration by splitting a stream of natural uranium (the feed) into an enriched stream (the product) and a depleted stream (the tailings, or depleted uranium). This calculator applies the standard feed/product/tails mass balance and the separative work model used across the enrichment industry to size how much natural uranium and enrichment capacity a given batch of fuel actually requires.
The separative work unit (SWU) is the industry's measure of enrichment effort. It is not a unit of energy — it depends on the feed, product, and tails assays, not on which technology performs the separation. A more thoroughly depleted tails stream extracts more U-235 from the same feed (using less natural uranium) but costs more separative work; a "richer" tails stream leaves more U-235 behind (using more natural uranium) but costs less separative work. That trade-off, visible in the tails assay field above, is the central economic decision every enrichment plant operator makes.
Enrichment Effort Curve
This figure shows the separative work required as product U-235 enrichment increases. It uses the calculator’s current feed and tails assays. The shaded bands identify commonly discussed fuel-enrichment ranges, and the orange marker shows the current calculation.
The horizontal axis is product U-235 enrichment and the vertical axis is enrichment effort. The detailed view covers reactor-fuel and HALEU applications; the full-range view shows the mathematical trend toward very high enrichment. Values are calculated live using the ideal binary U-235/U-238 mass-balance and separative-work model. The shaded ranges are contextual guides, not regulatory limits.
Independent Numerical Validation
The implementation was checked against published industry examples. Differences below the displayed precision are due only to rounding.
Verification date: 3 August 2026. World Nuclear Association source page updated 6 June 2025. Market-price inputs are editable assumptions and are not part of the engineering validation.
Worked Example
Produce 1 kg of uranium enriched to 5% U-235, from natural uranium feed (0.711% U-235), at an enrichment plant operating with a 0.25% tails assay.
EngineerHub.orgF = P·(xp − xw) / (xf − xw) = 1·(5 − 0.25) / (0.711 − 0.25) ≈ 10.30 kgW = F − P ≈ 9.30 kgV(x) = (2x−1)·ln(x/(1−x))SWU = P·V(xp) + W·V(xw) − F·V(xf) ≈ 7.9 SWUWhy tails assay matters
Re-running the same example at a 0.20% tails assay instead needs only 9.4 kg of natural uranium — but 8.9 SWU of work, not 7.9. Operating a plant with a leaner tails stream trades natural uranium consumption for separative work, which is why enrichers adjust tails assay in response to the relative market price of uranium and SWU.
Try it yourself: set product to 5, feed to 0.711, and tails to 0.20 in the calculator above.
Include the inputs and assumptions used.