This starship technology was based on agrinium plated Hull Armor, especially Ablative Hull Armor, as an energy source. When the armor plating absorbed energy, either solar or from weapons-fire, it would re-route the energy to the Reactor, thus creating a constant renewable energy source. However, for times when there was not enough of either, it saved excess leftover energy from previous flights.
Its name was very accurate, each Reactor was actually four micro-nuclear-Fusion reactors that generated power through a Proton-proton chain reaction. It could, on its own, generate enough power to keep a small garrison operating for a few years. Or a Starfighter for Several weeks at full combat readiness. Most ships had just one, though some featured two, and Larger ships Larger versions capable of lasting for months or years, the City of Aeturna was powered by multiple large scale Reactors.