Nuclear Fuel Cycle and Waste Management
Front end
Uranium is mined, milled to yellowcake (U₃O₈), converted to UF₆, enriched (gas centrifuge dominates), and fabricated into UO₂ pellets in Zircaloy cladding. Reactor-grade LEU is below 20% U-235, typically 3–5%; HEU is ≥20%. Enrichment accounting uses feed, product, and tails assays and is measured in separative work units (SWU).
Back end
After discharge, fuel cools in the spent fuel pool, then may go to dry cask storage, reprocessing (PUREX), or direct disposal. Burnup is expressed in GWd/MTU; modern PWR fuel runs roughly 45–60 GWd/MTU. Spent fuel is intensely radioactive and thermally hot; heat and shielding, not criticality alone, drive pool and cask design.
Waste classification
Low-level waste classes A, B, C, and GTCC come from 10 CFR 61, with concentration limits and stability requirements. High-level waste (including reprocessing raffinate) is vitrified into borosilicate glass for geologic disposal; transuranic waste goes to WIPP. Deep geologic disposal is regulated under 10 CFR 63 for a potential repository.
Traps
- Confusing enrichment assay with tails assay, or forgetting that tails carry most of the mass.
- Assuming all spent fuel is classified as HLW regardless of reprocessing.
- Mixing up waste classes and their disposal site requirements.
Worked example
Feed 0.711% U-235, product 4.5%, tails 0.30%. Feed per kg product = (0.045 − 0.003)/(0.00711 − 0.003) = 0.042/0.00411 ≈ 10.2 kg. Roughly 10 kg of natural uranium per kg of 4.5% product - a useful sanity check on any enrichment mass-balance question.