POWER
Power
Heavy elements such as Uranium (U235) or Thorium (Th232) are subjected to nuclear fission reaction in a nuclear reactor. Due to fission, a large amount of heat energy is produced which is transferred to the reactor coolant. The coolant may be water, gas or a liquid metal. The heated coolant is made to flow through a heat exchanger where water is converted into high-temperature steam. The generated steam is then allowed to drive a steam turbine. The steam, after doing its work, is converted back into the water and recycled to the heat exchanger. The steam turbine is coupled to an alternator which generates electricity. The generated electrical voltage is then stepped up using a transformer for the purpose of long-distance transmission.
NUCLEAR REACTOR
A nuclear reactor is a special apparatus used to perform nuclear fission. Since the nuclear fission is radioactive, the reactor is covered by a protective shield. Splitting up of nuclei of heavy atoms is called as nuclear fission, during which a huge amount of energy is released. Nuclear fission is done by bombarding slow-moving neutrons on the nuclei of heavy elements. As the nuclei break up, it releases energy as well as more neutrons which further cause fission of neighboring atoms. Hence, it is a chain reaction and it must be controlled, otherwise, it may result in an explosion. Two types of nuclear reactors that are widely used.
Pressurise Water Reactor (PWR) –This type of reactor uses regular water as a coolant. The coolant (water) is kept at very high pressure so that it does not boil. The heated water is transferred through a heat exchanger where water from the secondary coolant loop is converted into steam. Thus, the secondary loop is completely free from radioactive stuff. In a PWR, the coolant water itself acts as a moderator. Due to these advantages, pressurised water reactors are most commonly used.
Boiling Water Reactor (BWR) – In this type of reactor, only one coolant loop is present. The water is allowed to boil in the reactor. The steam is generated as it heads out of the reactor and then flows through the steam turbine. One major disadvantage of a BWR is that the coolant water comes in direct contact with fuel rods as well as the turbine. So, there is a possibility that radioactive material could be placed on the turbine.
HEAT EXCHANGER
In the heat exchanger, the primary coolant transfers heat to the secondary coolant (water). Thus, water from the secondary loop is converted into steam. The primary system and secondary system are a closed loop, and they are never allowed to mix up with each other. Thus, heat exchanger helps in keeping the secondary system free from radioactive stuff. The heat exchanger is absent in boiling water reactors
STEAM TURBINE
Generated steam is passed through a steam turbine, which runs due to the pressure of the steam. As the steam is passed through the turbine blades, the pressure of steam gradually decreases, and it expands in volume. The steam turbine is coupled to an alternator through a rotating shaft.
ALTERNATOR
The steam turbine rotates the shaft of an alternator thus generating electrical energy. The electrical output of the alternator is the delivered to a step up transformer to transfer it over distances.
CONDENSER
The steam coming out of the turbine, after it has done its work, is then converted back into water in a condenser. The steam is cooled by passing it through a third cold water loop.