Reactivity accidents have multiple safety features in the form of com­ponent-failure and flux-increase trips that initiate a shut-down of the reactor system before much has happened (beyond minor overheating of the fuel in the worst cases). This section therefore deals with those hypothetical accidents in which the reactivity addition is uncontrolled and in which eventual shut-down of the system is only achieved by a dispersion of the core.

Section 5.4 treats a discussion of design basis accidents; here we are simply concerned with the behavior of the system in the event of a complete loss of control and with the energy release from a superprompt critical system.