Nuclear reactor which produce delayed neutrons have half lives for their decay by neutron emission that range from milliseconds to as long as several minutes, and so considerable time is required to determine exactly when a reactor reaches the critical point. Keeping the reactor in the zone of chain-reactivity where delayed neutrons are "necessary" to achieve a critical mass state allows mechanical devices or human operators to control a chain reaction in "real time"; otherwise the time between achievement of criticality and nuclear meltdown as a result of an exponential power surge from the normal nuclear chain reaction, would be too short
Integral reactor often deliberately small, allowing passive cooling in emergencies. Integral reactor In the nuclear power field, an integral reactor is a nuclear reactor design principle where the reactor core, primary cooling loop, steam generators and any required emergency cooling are contained within a single reactor vessel. The concept can be applied to any sort of underlying reactor design, there are examples of integral pressurized water reactors, sodium-cooled fast reactors, and others. The main goals are mass production of the reactor, as the entire working design can be delivered as a single unit and then connected to the non-nuclear generation sections of