Nuclear Fuel Cycle and Waste Management
Core concepts
Understand the front end (mining, conversion, enrichment, fuel fabrication) and back end (reprocessing or direct disposal). Know enrichment concepts: U-235 assay, tails assay, separative work units (SWU), and the mass balance relationships. Be familiar with the once-through cycle vs closed cycle, MOX fuel, and the distinction between low-level, intermediate-level, and high-level waste. Understand decay heat, vitrification, dry cask storage, and the concept of geological disposal and institutional control periods.
Common traps
Questions often confuse enrichment with conversion, or tails assay with feed assay. Watch for the assumption that all spent fuel is high-level waste regardless of reprocessing, or that reprocessing eliminates waste (it changes its form and volume). Another trap: forgetting that decay heat drives spent fuel cooling requirements and cask design. Be careful with SWU intuition - more SWU means more energy required to reach a given enrichment at a given tails assay.
Worked example / rule of thumb
Rule of thumb: higher tails assay lowers SWU requirement but wastes U-235. If a question asks how to reduce enrichment cost, lowering tails assay increases SWU per unit product - the opposite of intuition for many candidates. Always check which variable is being optimized.
Study tip
Draw the full fuel cycle as a loop with mass flows. Most exam items can be answered by tracing where U-235, U-238, and fission products go at each step.