Nuclear engineering is the branch of engineering concerned with the application of the nuclear fission as well as the nuclear fusion and the application of other sub-atomic physics, based on the principles of nuclear physics. In general, nuclear engineering deals with the application of nuclear energy in a variety of 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 engineering of nuclear reactors, and to deal with topics like fluid dynamics, power plant thermodynamics, reactor heat generation and removal (single-phase as well as two-phase coolant flow and heat transfer), materials in nuclear engineering and structural mechanics.
Thermal Hydraulic Considerations
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 which produces electricity. But in nuclear power plants reactors produce enormous amount of heat (energy) in a small volume. The density of the energy generation is very large and this puts demands on its heat transfer system (reactor coolant system). Therefore we have to start by 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 is one of the most important considerations in the design of a nuclear reactor.
The temperature in an operating reactor varies from point to point within the system. As a consequence, there is always one fuel rod and one local volume, that are hotter than all the rest. In order to limit these hot places the peak power limits must be introduced. The peak power limits are associated with a boiling crisis and with the conditions which could cause fuel pellet melt. However, metallurgical considerations place an 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 a nuclear reactors is to provide for the removal of 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. In order to avoid the undesirable power changes nuclear reactors must be equipped by proper safety systems.