Like the ProtoMechs from the Clans, Chimeras may use both military grade and civilian fusion reactors as a power source, provided the reactors don't weigh more than 2 tons.
Civilian reactors have a slightly worse power to weight ratio, but are much cheaper and require far less maintenance than a reactor used by the military, as only specially trained personnel may perform this dangerous task. Otherwise, unskilled techs might accidently damage vital parts that keep the hot plasma contained, which would then smash through the torus and ignite the reactor's hydrogen fuel tank. The resulting explosion is strong enough to destroy anything within 50-60 meters. However, any concerns about a possible uncontrolled fusion reaction like in a hydrogen bomb is nothing more than an urban legend.