RADIOACTIVITY & NUCLEAR REACTIONS
NUCLEAR POWER PLANT
The nuclear power plant is a device in which controlled fission reaction of U-235 is done to produce electricity. Nuclear reactor consists of nuclear fuel, coolant, moderator and controlling roads.
Construction of Nuclear Power Plant
A nuclear reactor consists of following parts:
1. Nuclear Fuel
Nuclear fuel may be defined as the fissionable material which is used in nuclear reactor to produce energy. Generally, in nuclear reactor rods of U-235 are used as fuel. But the percentage of U-235 present in natural uranium is very low (0.7 %). Thus, it becomes necessary to increase the percentage of U-235 in natural uranium so that we can use it as fuel in nuclear reactor. The percentage of u-235 in natural uranium is increased by processing natural uranium. The process of increasing the percentage of U-235 in natural uranium is called enrichment.
2. Control Rods
To control the chain reaction of nuclear fission, rods of cadmium or boron are used in the nuclear reactor. These rods are good absorber of neutrons. So, when these rods are inserted in the nuclear reactor up to a desirable length, they absorb desired number of neutrons and keep the fission reaction under control.
For the fission of U-235 it is necessary that the speed of neutrons hitting the nuclei of U-235 must of slow. This objective is achieved by using moderator in nuclear reactor. A moderator is the substance which is used in the nuclear reactor to slow down the speed of neutrons. Generally, graphite or heavy water is used as moderator in nuclear reactor.
Coolant may be defined as the substance which is used in the nuclear reactor to take out the heat produced during fission of U-235 nuclei. The heat energy produced during fission of U-235 in the reactor is absorbed by the coolant and passed on to the water in heat exchanger to produce steam. Usually, heavy water or liquid sodium is used as coolant in nuclear reactors.
5. Protection Shield
The whole nuclear reactor is protected by enclosing it with a 2 to 2.5 meters thick wall of concrete. This is done to avoid the harmful effects of radiations emitted during fission reaction on the person working on the reactor.
Working of Nuclear Power Plant
The working of a nuclear reactor is based on the principle of controlled fission reaction of nuclear fuel. To start the fission reaction, the control rods of cadmium or boron are pulled outward after putting the fuel rods of U-235 in the nuclear reactor. The control rods are pulled outward up to a certain length so that they absorb desired number of neutrons and keep the fission reaction under control. In this way, a manageable amount of energy is produced in the form of heat at a steady rate.
The heat energy produced in the nuclear reactor is taken out by circulating liquid sodium through the pipes embedded in the reactor. The hot liquid sodium coming out is then passed through heat exchanger to give the heat absorbed by it to water and to produce steam. This steam is passed into turbine chamber with high pressure to rotate the turbines which are connected to generators. In this way, electricity is produced. The used steam from steam chamber is converted into water by passing it through a condenser. This water is then used again to form steam by sending it back into the heat exchanger.
Test Your Understanding and Answer These Questions:
- What is nuclear power plant?
- What is nuclear fuel?
- What is enrichment of uranium?
- Name control rods of a nuclear reactor.
- Give name of moderator in nuclear reactor.
- Give name of a coolant in a nuclear reactor.