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
Nuclear reactor heat removal total heat produced in the nuclear reactor is: formula_5 where formula_6 is the mean neutronic flux and V is the fuel volume (normally measured in formula_7). Recovery of this amount of heat is achieved by using cooling fluids whose temperature at the entrance to the reactor channel formula_8 will increase with the distance traveled in the channel. The thermal balance of the channel is expressed by the relationship: formula_9 where formula_10 is the flow rate of the cooling agent, formula_11 is the specific heat at constant pressure, formula_12 is the increase in the temperature of the fluid after passing a