fuel recycling is the recovery and reuse of unburned fuel exhausted from a 📝fusion plasma — the on-site loop that captures, cleans, and reinjects the deuterium and tritium that pass through the machine without fusing.
The term invites confusion with fission's fuel reprocessing, and the distinction is worth drawing: reprocessing dissolves spent fissile fuel in chemical plants, handling long-lived actinides, while fusion's fuel recycling is an on-site gas loop with no fissile material anywhere in it, turning over its contents on timescales of hours rather than years. Recycling exists because a fusion plasma is a remarkably inefficient burner per pass: only a few percent of the fuel injected into the 📝plasma fuses before being exhausted, so the great majority of each hour's 📝tritium and 📝deuterium throughput is not consumed but circulated.
The loop runs continuously: vacuum pumps draw the exhaust from the plasma edge, the stream is stripped of helium ash — the spent product of the reaction — and of impurities, then 📝isotope separation sorts the hydrogen species so fresh fuel can return to the machine as pellets or gas. Because tritium is scarce and expensive, the speed and completeness of this loop directly set a plant's required 📝tritium inventory: fuel sitting in the recycling plant is fuel the plant must own but cannot burn.