Nuclear fuel explained — enrichment, fuel cycles, spent fuel, and waste — broken down by a reactor engineer using primary data.
HALEU and LEU aren’t two different fuels — HALEU is a high-assay slice of LEU, enriched above 5% and below 20% U-235. A working reactor engineer explains what the “vs” framing gets wrong, what physically changes above the 5% line, and why that distinction is holding up the entire advanced-reactor fuel supply.
Everyone blames the centrifuges. But HALEU is made in five steps and the U.S. chain is thinnest at conversion and deconversion, the two links on either side of enrichment. A reactor engineer walks the fuel cycle from ore to fuel.
Enriching uranium to 19.75% HALEU takes almost six times the separative work of ordinary 4.5% reactor fuel — but that ratio is only half the story. Here’s why most of the enrichment work happens below 10%, where the real cost cliff actually sits, and why supply, not physics, is the binding constraint.
Most advanced reactors need HALEU to run — and the West can barely make any. What this fuel is, why it matters, and the supply gap holding nuclear back.