The main principle work of nuclear power reactor is to produce electricity. It is done by the use of released energy as heat to make steam for generating electricity. The main parts of nuclear power plant are described as below.
Some factors should be taken care in the working of nuclear power plant are
- Fuel- The isotope of Uranium U-235 is used as the basic nuclear fuel. It is used in form of pallets. The uranium oxide (UO2) pallets are arranged in tubes known as fuel rods. These pellets are backed at high temperature up to 1400°C. The pellets are inserted into zirconium alloy thin tubes or stainless steel tubes to get the fuel rods. Thus the fuel rods are arranged to form the fuel assemblies in reactor core.
- Moderator and coolant- Water or graphite is used as a moderator. This is material of core which uses to slow down the speed of released neutrons that can be undergo other fission. Water is also used as coolant. It circulates from the core to transfer the heat.
- Control rods- As in the nuclear fission reaction, the nuclear explosion also can takes place if the reaction is not controlled. So the control rods control the rate of nuclear reaction to avoid the nuclear explosion. The neutron-absorbing material like cadmium, hafnium or boron etc is used to make the control rods. The rate of nuclear reaction can be increased or decreased by inserting or withdrawn the control rods from the core according to the requirement of process.
- Pressure vessel- The pressure vessel is a robust steel vessel that contains the reactor core and moderator or coolant. It can be also in the form of pressure tubes. If the tubes are used then these are series of tubes that holds the fuel.
- Steam generator- The cooling system contains the steam generator. The heat from the reactor comes in the steam generator from the primary coolant and then it is used to make steam for the turbine.
- Containment- It works as protector. It protects the reactor form outside intrusion and the effects of harmful radiation. This is a meter thick concrete and steel structure around the reactor core.
- Control the fission reaction to avoid explosion
- Safety in fission reaction
- Addition of nuclear fuel (refueling process)
- Production of waste,
- Efficiency of nuclear power plant for generating heat
The first nuclear power plant in world comes in operation in 1954 at Obninsk situated outside of Moscow. It was established on June 27, 1954 and remained active up to April 29, 2002. The Obninsk is technical university where research process is done on various subjects like nuclear-power engineering, technology of radiations and non-metallic materials, radiology, and environmental protection etc. This power station has single reactor with electrical capacity of 6MW and 5MW net capacity. It was also used graphite as a moderator and water as coolant. The total output was approx 30MW.
In India, the first nuclear power plant is Tarapur Atomic Power Station. It is first operated in 1969. It is one of the biggest pressurized heavy water reactors based power station of India.
The two pressurized heavy water reactors with the capacity of 540MW were operated in Tarapur. The atomic station is under control of Nuclear Power Corporation of India Limited.
The diagram of nuclear power plant is given below.
- In the nuclear power plant, the released heat of a nuclear fission reaction is used to turns a steam turbine and it produce electric power.
- The nuclear fission of uranium-235 occurs by bombardment of neutrons on nuclear fuel uranium and thus the decaying process takes place.
- The absorption of neutrons by the atom of nuclear fuel uranium causes the splitting of uranium into smaller atoms.
- The uranium pellets are arranged as long rods. These rods are collected together to form bundles.
- The bundles are dropped in water of a pressure vessel.
- The control rods prevent the overheating by absorbing neutrons to control the rate of nuclear reaction. If more energy is required then the rods are lifted out from the bundle to absorb few electrons.
- The control rods can be lowered into the uranium bundle for reducing the level of heat. The heat from the fission of uranium bundle turns the water in to steam.
- This steam turns a turbine and thus generator starts spin and produces the electric energy.
- As the high energy neutrons are emitted so these are directly absorbed by the other uranium atom in fast reactors.
- This tendency is greater in isotope Uranium-238 than Uranium-235. This is the main reason to use much larger fraction of U-235 is used as fuel in fast reactors.
- While in slow reactors or thermal reactors, the speed of produced neutrons is in control so that neutrons are absorbed by the correct isotope of uranium-235.
The simulator of a nuclear power plant consists in a set of programs. The simulator tools are used in the first stage of nuclear power plant. They are used for training of operation staff about control methodologies and physics phenomena of nuclear power plant. They are also used for knowing about the accidental situation of power plant and learn to cope with those critical conditions.
The single models of the plant are used to design the simulators. It is possible for interacting only two people on simulator. The one is instructor and other is an operator. An instructor works to evaluate the response of second person while the operator works on control actions and previously fixed objectives of operation. There is a set menu which display in front of the instructor. By the use of menu the instructor is enabled to make the instructions like start, stop, finish or continue a simulation, global memory configure, the initial conditions of a specific simulation etc.
There are two visors for indicating last performed instruction to the instructor like configured, unconfigurated, running or stopped etc. There are also some operations only for instructor to change the simulator state. The simulator computer is attached with another computer and thus simulator sends the variables to the operators and waits for control action of operator. The graphical presentation is used to represent all the functions. The data and presentation system is called displayer.
Simulator ModelThe main components of thermo-hydraulic model of simulator are given as below.
- Primary circuit- It consists in only one loop with a reactor, a pressurizer, a steam generator, and a main pump. The variables are measured by mass and energy balance equations rather than the momentum balance equations.
- Nucleus- The temperature of fuel element is determined by considering the heat transfer form fuel to coolant. . The nuclear power value is measured form control results or from the temporal table. The special tables are used to calculate the nuclear power in case of setback, step-back or trip of reactor.
- Pressurizer- The ideal gas model (PV = nRT) is used to measure the pressure for steam compression condition while thermodynamic volume equilibrium with steam is used for expansion case. Some other models like control, heaters, and discharge and relief valves are also used.
- Auxiliary circuit- It involves the models like bleed, purification circuits, hydraulic resistances, the heavy water storage tank, feed pumps, filters and the degasser-condenser tank etc.
- Secondary circuit- The turbine power is evaluated from table or instantaneous and ideal control systems. The turbine power is worked in different operation modes of plant like normal or alternative. The various models of secondary circuit are feed-water, steam generator etc. The special evaluation table is also used to measure the turbine power in case of turbine trip.
- Control- The model has various controllers for specific operations like primary circuit and steam generator pressure, pressurizer and steam generator level, primary circuit inventory, and turbine and reactor power etc.
Limitations of model
The power range is 10% to 100% of full power plant. The power of operation can be changed in a range of 30% to 100% full power plant. The full power plant operates in two modes. The one is normal and the other is alternative
. There is some failure in the model like shutdown of pumps, valve failure, lost of coolant and regulation in system etc.
The model is not suitable when the primary circuit transient depends on the momentum equations and steam generator level shows negative value. The asymmetric primary circuit is not possible to simulate. It can measure the small lose of coolant but not the large one.