Fuel Recycling in the Central Cell

Most helium-3 is not burned in a single pass; recovering and recycling the unburned fraction is essential to using a scarce fuel efficiently.

Burn fraction is not one

A fuel atom injected into the plasma has a probability of reacting before it leaves; the fraction that actually burns per pass is well below one. For a scarce fuel like helium-3, letting the unburned remainder escape unrecovered would waste a bred resource. So the fuel cycle is built to recover unburned helium-3 (and deuterium) from the exhaust, clean it, and return it to the fuel stream.

Recovery, cleaning, return

Exhaust from the burn is a mix of helium-4 ash, unburned helium-3 and deuterium, and trace species. Processing removes the helium-4 ash (by isotope separation) and any impurities, and returns clean helium-3 and deuterium to the store. Effective recycling multiplies the useful output of every gram the breeder makes: a fuel that is used many times over stretches a fixed supply much further than one burned once and lost.

• Burn fraction per pass is well below one
• Unburned helium-3 and deuterium are recovered from exhaust
• Helium-4 ash and impurities are separated out
• Recycling stretches a fixed, bred helium-3 supply

Recycling ties directly to fuel accountancy: the recovered fraction is one of the terms that must balance in the helium-3 mass ledger, and improving recovery is one of the levers for feeding more burners per breeder.