Chain Reaction is a process in which the products themselves promote or spread the reaction. Nuclear Chain Reactions are a simple, yet powerful method which to produce both constructive and destructive forces. Only understood to a significant degree within the last century, nuclear chain reactions have many practical uses in the modern era. Chain reactions can be addressed into two categories: first, controlled (like a nuclear power plant) and uncontrolled (an atomic bomb). Both are motivated by fission reactions, which are elaborated in this section.