In traditional chemical reactions, a catalyst is a substance that increases the rate of a reaction without being consumed. In the context of nuclear fission, the concept of a catalyst is somewhat abstract but can be understood through materials that facilitate or control the fission process. For instance, moderators like graphite or heavy water slow down neutrons, making them more likely to cause further fission events in fissile material. These moderators are not consumed in the reaction, drawing a parallel to how traditional catalysts operate.
