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Nuclear Power Generation

Updated on December 17, 2014

Power generation using fossil fuels damages the environment. Also, fast depletion on natural resources and rapidly increasing need for electric energy are two major factors that paved the way for nuclear power generation. When we think of providing clean and inexpensive alternative for the conventional methods of power generation, then there is no other way than trusting the nuclear power generation. Nuclear power plants are capable of generating a huge amount of power with a very small amount of fuel. Also nuclear fuel is inexpensive, abundant and easy to transport.

Where does the energy required for power generation in a nuclear reactor come from?

The energy required for power generation in a nuclear power is obtained by bombarding the nucleus of a heavier element such as Uranium with neutrons (Nuclear fission) inside a closed chamber called nuclear reactor. The fission process is accompanied by the release of enormous amount of heat energy, neutrons and beta and alpha particles and gamma.

The neutrons released during the fission reaction may strike other nuclei and start chain reaction.

Layout of a Nuclear Power Plant

Source

Components of a Nuclear Power plant

A nuclear power plant consists of the following components.

Nuclear reactor

Nuclear fission reaction is carried out in a nuclear reactor. The nuclear reactor is a closed chamber inside which controlled fission reaction is carried out. The nuclear reactor is continuously monitored by the workers in the control room.

Main components of Nuclear reactor

Fuel rods

A fuel rod is a zircaloy tube – filled with pellets of uranium fuel. Enriched uranium fuel is made in the form of solid ceramic pellets of approximately 1 inch long and is arranged in a zircaloy tube to form fuel rods. These rods are bundled and inserted into the reactor.

Moderator

Neutrons are released during the process of nuclear fission. Moderators are used to slow down those neutrons. The normally used moderators are Graphite, heavy water, beryllium and ordinary water.

Control rods

Control rods are used to control the chain reaction. Control rods are made up of nuclear absorbing materials such as boron carbide, carbide or hafnium. The rate of chain reaction can be controlled by either inserting or removing the control rods from the bottom of the core to absorb the neutron, which controls the rate of fission. An additional main control rod is inserted from the top down and provides automatic and emergency control.

Coolant

Coolants are used to transfer the heat produced inside the core during the nuclear fission to the heat exchanger for power generation. Coolants may be gaseous or pressurized liquid. Gaseous fuels used are carbon-di-oxide, air, hydrogen and helium and liquid coolants used are ordinary water, heavy water, liquid metals such as sodium and potassium and some other organic liquids.

Heat exchanger

Nuclear power plants have two cooling systems, one inside the reactor and the other outside it. The coolant inside the reactor is used to absorb the heat from the core. As the coolant is circulated over the core, it may be radioactive. So it is separated from the coolant in the external cooling system. Heat exchange between the both happens inside the heat exchange. The coolant used in the external cooling system is the normal water. At the heat exchanger, it is converted into steam which runs the turbine.

Shielding

Shielding is used to prevent the harmful radiations from reaching the external environment. The core is enclosed in a large steel pressure vessel of about 20 cm thickness and is enclosed inside a robust concrete structure with walls having a thickness of a meter or more. All these are placed inside an outer concrete structure that can withstand earthquakes and other hazards.

Turbine and Generator

Turbine and generator are placed outside the concrete structure. Turbine is coupled with the generator and runs it when driven by the steam.

Operating principle of a nuclear power plant

The operating principle of a nuclear power plant is same as that of a thermal/ steam power plant. The only difference is that in nuclear power plant the energy required for the production of steam is obtained from nuclear fission. The process of power generation in a nuclear power plant is explained step by step below.

  • Heat energy is produced in the nuclear reactor by bombarding the process of nuclear fission.
  • The coolant circulated around the core absorbs the heat produced and reaches the heat exchanger.
  • At the heat exchanger coolant transfers its heat to the water and converts it into steam. The coolant is again circulated back to the core and the process continues.
  • The steam thus generated is used to run the turbine.
  • The turbine is connected to the shaft of an alternator, which converts the mechanical energy of the turbine into electrical energy.

Layout of a Nuclear Power Plant

Classification of Nuclear reactors

Basis of classification
Types
Type of core
Homogeneous reactors
 
Heterogeneous reactors
Moderator used
Graphite reactors
 
Beryllium reactors
 
Ordinary water reactors
 
Heavy water reactors
Coolant used
Ordinary water reactors
 
Heavy water reactors
 
Gas cooled reactors
 
Liquid metal cooled reactors
 
Organic liquid cooled reactors
Neutron energy
Thermal reactors
 
Fast reactors
Fuel used
Enriched uranium fuelled reactors
 
Natural uranium fuelled reactors
 
Plutonium fuelled reactors
 
Thorium fuelled reactors
Fuel:
Enriched Uranium
Moderator:
Pressurized water
Coolant:
Pressurized water
Layout of a Pressurized Heavy Water reactor
Layout of a Pressurized Heavy Water reactor
Pressurized Heavy Water reactor
Pressurized Heavy Water reactor

Pressurized Water Reactor (PWR)

Pressurized water reactors have been originated in USA. In this reactor, water at 155 bars acts as coolant as well as moderator. Pressurized water has a boiling point higher than that of an ordinary water. In order to pressurize the water, a pressurizer and a surge tank are included in the primary water circuit. As the water in the primary cooling circuit circulates around the reactor core, it would be radioactive. So the pressurizer, heat exchanger and the surge tank are properly shielded.

Advantages of Pressurized Water Reactor

  • As water is used as moderator and coolant it is very cheap.
  • It is smaller in size than other types of nuclear reactors.
  • This can be easily converted into breeder reactor by surrounding the fuel rods with U-238.

Disadvantages of Pressurized Water Reactor

  • Low thermal efficiency.
  • Additional heat loss occurs at the heat exchanger.
  • More safety precautions should be taken.

Fuel:
Enriched Uranium
Moderator:
Ordinary water
Coolant:
Ordinary water
Layout of a Boiling Water Reactor
Layout of a Boiling Water Reactor
Boiling Water Reactor
Boiling Water Reactor

Boiling water reactor (BWR)

The difference between other reactors and the boiling water reactors can be clearly identified from the layout itself. Boiling water reactors have only one cooling circuit. Steam is produced in the reactor core itself and is used to run the turbine and generate electricity. Thus water performs three operations as the coolant, the moderator and the working fluid.

Advantages of Boiling water reactors

  • Less costly than the PWR reactors.
  • Due to the absence of heat exchanger, it is more efficient than the Pressurized water reactors.
  • More stable than PWR.

Disadvantages of Boiling water reactors

  • Since same water performs the functions of moderator, coolant and working fluid, it will be highly radioactive and all the equipments including the turbine and condenser need to be properly shielded.
  • It is not suitable to meet the sudden increase in load.

CANDU reactors

Fuel:
Enriched Uranium
Moderator:
Heavy water (Deuterium monoxide)
Coolant:
Heavy water (Deuterium monoxide)

Canadian Deuterium Uranium reactors (CANDU).

Heavy water (Deuterium monoxide) Reactors
Heavy water (Deuterium monoxide) Reactors

Heavy water cooled and moderated reactors

Here I have explained CANDU reactors. These reactors were designed and developed in Canada and are popularly known as Canadian Deuterium Uranium reactors (CANDU). In this type of reactors, heavy water (D2O) is used as moderator and coolant and are fueled by enriched uranium.

Advantages of (CANDU)

CANDU reactors do not require control rods and has low fuel consumption. It requires lesser time for construction compared to other nuclear power plants.

Disadvantages of (CANDU)

Disadvantages of CANDU reactors is its high initial cost and high running cost due to the high cost of heavy water.

Fuel:
Natural Uranium
Moderator:
Graphite
Coolant:
Carbon dioxide or helium

Gas cooled Reactor

Gas cooled Reactor

As the name implies, in gas cooled reactors carbon dioxide or helium gas is used as coolant. Of these two, helium is more preferred as it is chemically inert and has more heat transfer capacity than carbon dioxide.

Advantages of Gas cooled reactors

  • Gas cooled reactors are safer than water cooled reactors.
  • These reactors have less corrosion problem than the water cooled reactors.
  • Natural uranium can be used as fuel in these reactors.

Fuel:
Mixture of Pu-239 and U-238
Coolant:
Liquid Sodium

Fast breeder reactors (FBR)

Fast breeder reactors (FBR)

Fast breeder reactors convert more fertile material into fissile material. Fuel rods are filled a mixture of U-238 and Pu-239. These fuel rods are surrounded by fertile U-238. The neutrons emitted during the fission reaction are captured by the surrounding U-238 and turns into Pu-239. In fast breeder reactors three cooling circuits are used due to the induced radioactivity of liquid sodium. The working fluid is water and the coolant used in the intermediate circuit is either NaK or Na.

Pros of Nuclear Power Plants

  • Nuclear is less costly, more abundant and easy to transport.
  • The volume of waste produced in a nuclear power plant is a billion times smaller than that of a coal fired power plant.
  • Nuclear power plants require very little fuel and refilling is required only once in three years.
  • Nuclear do not emit any green house gases and are non pollution and clean source of energy.

Cons of Nuclear Power Plants

  • Even though the cost of nuclear fuel is low, the overall cost of power production is higher than the others.
  • High installation cost.
  • Radioactive wastes that are buried remain radioactive for millions of years.
  • If meltdown occurs, it not only causes immediate danger but also contaminate the area for years after the disaster. It would cause severe health problems and would increase the risk of cancer.
  • Crops grown in contaminated region may contain high levels of radioactive elements.
  • Even a properly operating reactor can emit harmful radiations to the environment.

Safety in Nuclear Power Generation

What do you think about the safety in Nuclear Power Generation?

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Safety in nuclear reactors

As far as nuclear power plants are concerned safety is the primary factor. Exposure to radiation can severe damage to human skin and internal organs. Radiations can also cause bone, lung cancers and leukemia. However a dose of 100mrems per year is considered as safe.

Any process inside the reactor is done by remote handling. In addition to providing adequate shielding, the environment and the workers are continuously monitored for radiation exposure. It is ensured that the radiation level is lower than those of any other industries. However nuclear energy applied to electricity generation is extremely safe.

Disposal of radioactive wastes

Once the fuel pellets in the fuel rods have completely undergone nuclear fission, the remaining rods are said to be spent. No wonder, at that instant it would be the most radioactive material in the earth. They emit harmful gamma rays and should not be exposed to the biosphere. So they are shielded with boxes having thick lead walls. They are treated to remove the radiation and buried in repositories. Less radioactive wastes are buried in dirt trenches or pumped out to sea.

What is meant by meltdown?

Melting of fuel in the nuclear reactor is called as meltdown. The fuel starts melting as soon as the temperature inside the reactor core reaches 2800 degree centigrade. On the occurrence of meltdown, the reactor runs out of coolant water. The fuel rods would be corroded; the fuel would be exposed and then would melt its way out of the containment. But all will happen only if the overpressure in the containment and the steam explosion occurs. Also the containment cooling system and emergency control system have to fail. Therefore the workers have sufficient time to restore the coolant to the core.

Nuclear Meltdowns

show route and directions
A markerThree Mile Island -
Three Mile Island, Londonderry, PA, USA
get directions

An accident happened here in 1979 in which the reactor was severely damaged.

B markerChernobyl -
Chornobyl, Kyivs'ka oblast, Ukraine
get directions

Destruction of reactor here in 1986 killed 30 people and had significant health and environmental consequences.

C markerFukushima daiichi -
Daiichi Hobaramachi Nakaze, Date, Fukushima Prefecture, Japan
get directions

15-metre tsunami damaged the cooling system of three reactors here in11 March 2011. All the three core were almost melted in this accident.

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    • DDE profile image

      Devika Primić 2 years ago from Dubrovnik, Croatia

      Informative and a greatly researched hub on such a topic.

    • alluammu profile image

      Susmitha 2 years ago from Kerala

      Its really good article osbert

    • goodnews11 profile image
      Author

      OSBERT JOEL C 2 years ago from CHENNAI

      Thank you

    • goodnews11 profile image
      Author

      OSBERT JOEL C 2 years ago from CHENNAI

      @CurbNumberscom

      That's really a very good suggestion Mr. David. I agree with you.

    • Writer Fox profile image

      Writer Fox 2 years ago from the wadi near the little river

      For many reasons, I wish nuclear power had never been invented. But, that is a genie that can't be put back in the bottle. Good article.

    • goodnews11 profile image
      Author

      OSBERT JOEL C 2 years ago from CHENNAI

      Thank you Writer Fox.. Nuclear power generation technologies have to be enhanced so as to make it more safe and reliable.

    • dilipchandra12 profile image

      Dilip Chandra 2 years ago from India

      So well explained, good and informative hub this is. Thanks for sharing :)

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