Burner Neutron Fraction: Honest

The burner is low-neutron, not aneutronic: 5.44% of its energy arrives as neutrons, which is honestly stated and shapes shielding and cooling.

The burner's deuterium–helium-3 reaction is often described loosely as “aneutronic.” That is not accurate, and Kronos does not use it that way. The burner is low-neutron, not neutron-free: about 5.44% of its fusion energy is carried by neutrons, arising from unavoidable side reactions. This distinction matters for shielding, activation, and cooling, and stating it honestly is part of the program's candor.

Low-neutron versus aneutronic

A truly aneutronic reaction would release no neutrons; the deuterium–helium-3 cycle does, because deuterium–deuterium side reactions occur alongside the main reaction and produce neutrons. At 5.44%, the neutron fraction is far lower than the breeder's deuterium–tritium reaction, where the great majority of energy is neutronic, but it is not zero. That residual flux still activates nearby structure and deposits heat that must be managed.

Why the honesty matters

Overstating the burner as aneutronic would understate its shielding and activation requirements and mislead on its environmental profile. The accurate framing — low-neutron, 5.44% — supports genuinely reduced shielding and activation compared with deuterium–tritium, and enables direct energy conversion of the dominant charged-particle output, while acknowledging the residual neutron handling the machine still requires.

• The burner is low-neutron, not aneutronic.
• About 5.44% of its energy is carried by neutrons, from D-D side reactions.
• Far below the breeder's D-T neutron fraction, but not zero.
• The residual flux still requires shielding, activation control, and cooling.

Design-and-simulation framing. The Kronos machines are today design and simulation studies: the breeder (Hyperion) and the burner (Aegis / MetroVolt). No hardware net-gain has been demonstrated. Breeder construction is planned to begin Q2 2027, with first-of-a-kind (FOAK) first tritium targeted around 2030. Comparisons on this page are qualitative and use only public, defensible figures; nothing here is a performance guarantee.

Precise language here is a matter of integrity: low-neutron is a real advantage; aneutronic would be an overclaim, and Kronos does not make it.