Nuclear engineering is the branch of engineering concerned with applying nuclear fission and nuclear fusion and applying other sub-atomic physics based on nuclear physics principles. Nuclear engineering generally deals with applying nuclear energy in various branches, including nuclear power plants, naval propulsion systems, food production, or medical diagnostic equipment such as MRI machines.
Our goal here will be to introduce the engineering of nuclear reactors, and deal with topics like fluid dynamics, power plant thermodynamics, reactor heat generation and removal (single-phase and two-phase coolant flow and heat transfer), materials in nuclear engineering, and structural mechanics.
A nuclear power plant (nuclear power station) looks like a standard thermal power station with one exception. The heat source in the nuclear power plant is a nuclear reactor. As is typical in all conventional thermal power stations, the heat is used to generate steam which drives a steam turbine connected to a generator that produces electricity. But in nuclear power plants, reactors produce an enormous amount of heat (energy) in a small volume. The density of the energy generation is very large, which puts demands on its heat transfer system (reactor coolant system). Therefore we have to start with the reactor heat generation and removal from the reactor.
For a reactor to operate in a steady state, all of the heat released in the system must be removed as fast as it is produced. This is accomplished by passing a liquid or gaseous coolant through the core and through other regions where heat is generated. The heat transfer must be equal to or greater than the heat generation rate or overheating, and possible damage to the fuel may occur. The nature and operation of this coolant system are some of the most important considerations in designing a nuclear reactor.
The temperature in an operating reactor varies from point to point within the system. Consequently, there is always one fuel rod and one local volume hotter than all the rest. Peak power limits must be introduced to limit these hot places. The peak power limits are associated with a boiling crisis and conditions that could cause fuel pellet melt. However, metallurgical considerations place upper limits on the temperature of the fuel cladding and the fuel pellet. Above these temperatures, there is a danger that the fuel may be damaged. One of the major objectives in the design of nuclear reactors is to remove the heat produced at the desired power level while assuring that the maximum fuel temperature and the maximum cladding temperature are always below these predetermined values.
It must be noted that theoretically, there is no upper limit to the power level (from the criticality point of view), which can be attained by any critical reactor having sufficient excess of reactivity to overcome its negative temperature coefficient. Nuclear reactors must be equipped with proper safety systems to avoid undesirable power changes.