This document discusses mathematics models related to fusion reactors and energy gain factor. It provides equations to calculate energy gain factor (Q), which is the ratio of fusion power density to externally supplied power. It also discusses characteristics of Gen-4 nuclear reactors including reactivity control mechanisms using heavy particle scattering and gadolinium oxide. Additionally, it covers reactor kinetics models, prompt neutron lifetime, confinement times, and industrial applications of accelerators in nuclear reactors.