G3: The Fuel Loop Gate

The third gate proves neutrons breed tritium in the blanket and the fuel cycle recovers, measures, and accounts for it.

What G3 proves

G3 is the fuel loop gate and coincides with first tritium. It demonstrates the full breeding chain: fusion neutrons enter the blanket, breed tritium in lithium-bearing material, and the tritium plant recovers, measures, and accounts for the product. G3 is the proof that Hyperion functions as a foundry.

The breeding ratio lever

Tritium breeding ratio (TBR) is treated as a design lever, studied across values of 1.1, 1.5, and 1.8. TBR above 1.0 means the blanket breeds more tritium than the plasma consumes, the condition for a self-sustaining and product-yielding fuel cycle. G3 measures the achieved TBR against the registered prediction for the installed blanket.

• Measured quantity: neutron yield, achieved TBR, and recovered tritium mass
• Pass criterion: closed, accounted fuel loop with TBR consistent with the design lever
• Registered prediction: neutron yield and TBR with uncertainty, filed before the test

Accountability

A breeder must account for every gram of tritium for both product and regulatory reasons. G3 therefore includes demonstrating the measurement and accountancy system, not just producing tritium. Recovery efficiency and inventory tracking are part of the pass criterion.

Honest reconciliation

There is an open reconciliation between a design-level TBR of 1.8 and the net breeding available in a real three-dimensional blanket with penetrations and structure. G3 is precisely where that reconciliation is settled by measurement. Until then, product figures near 4 kg/yr tritium class remain design values.