China has asked Japan to take back its decision to release more than 1 million tonnes of treated water from the Fukushima nuclear plant into the ocean.

Important points:

  • The Fukushima Daiichi Nuclear Power Plant is a disabled nuclear power plant located on a 3.5-square-kilometre site in the towns of Ōkuma and Futaba in Fukushima Prefecture, Japan.
  • The plant suffered major damage from the magnitude 9.0 earthquake and tsunami that hit Japan on March 11, 2011.
  • The chain of events caused radiation leaks and permanently damaged several reactors, making them impossible to restart. By political decision, the remaining reactors were not restarted.
  • In April 2021, the Japanese government approved the dumping of radioactive water of this power plant into the Pacific Ocean over the course of 30 years.

What is a Nuclear Reactor?

  • A nuclear reactor is the most important part of a nuclear power plant. It is where the nuclear chain reactions occur that produce energy by fission. The heat thus produced can be used to produce electricity.
  • The main purpose of a reactor is to contain and control the energy released. Uranium is used as the nuclear fuel in the reactors.
  • The heat produced by nuclear reactions is used to convert the water into steam, which is further converted into carbon-free electricity with the help of turbines.


Types of Nuclear Reactors
Light Water Reactors (LWR) LWR is a type of Thermal Neutron Reactor.

Uses Normal Water instead of Heavy Water as its coolant and Neutron Moderator.

BWR & PWR are Light Water Reactors.

The BWR drives the steam turbine when the reactor core heats the water converting it into steam. Example: Fukushima Daiichi, Japan.

The PWR drives the steam turbine in two stages.

Pressurized water has a higher boiling point. The reactor core heats the water without producing any steam in the core.

This pressurized hot water then exchanges heat with a secondary low-pressure water unit which turns into steam.

This steam drives the steam turbine.

Heavy Water Reactors HWR is also a type of Thermal Neutron Reactor.

Uses Heavy Water (deuterium oxide D2O) as its coolant and Neutron Moderator.

The HWR follows the working principle of the Pressurized Water Reactor.

Even though Heavy Water is very expensive, it allows the nuclear reactor to operate without any fuel enrichment due to the enhanced neutron economy.

This also allows the Nuclear reactor to use alternate fuel cycles.

Gas-Cooled Reactors BWR, LWR, HWR & PWR can’t operate at very high temperatures and thus don’t provide great thermal efficiency.

In Gas-Cooled reactors, gas is replaced as a coolant and that drives the turbine.

These reactors are called High-Temperature Gas-Cooled Reactors (HTGRs).

Gases like Helium & Carbon-Dioxide are used as coolants.

HTGRs provide high thermal efficiency (Upto 50%) as they can operate at high temperatures.

HTGRs can have multiple applications other than power production which involve heat processes like hydrogen fuel cells, water desalination, oil refineries, etc.

Gas being, not the most efficient coolant, HTGRs need a highly- efficient back-up coolant.

Fast Reactors The reactors discussed above use moderators that slow the high-energy (fast) neutrons down to low-energy (slow).

Fast reactors don’t use moderators and use Fast Neutrons.

To sustain the fission reaction by fast neutrons, the fission material needs to be highly enriched.

Uranium enrichment is very expensive thus making the use of Fast reactors uneconomical.

Main Components of a Nuclear Reactor

The main components of a nuclear reactor are listed below.

  • The Core: It contains all the fuel and generates the heat required for energy production.
  • The Coolant: It passes through the core, absorbing the heat and transferring into turbines.
  • The Turbine: Transfers energy into the mechanical form.
  • The Cooling Tower: It eliminates the excess heat that is not converted or transferred.
  • Neutron Moderator: Moderators are used for reducing the speed of fast neutrons released from the fission reaction and making them capable of sustaining a nuclear chain reaction.
  • Usually, water, solid graphite, and heavy water are used as a moderator in nuclear reactors.
  • Commonly-used moderators include regular (light) water (in 74.8% of the world’s reactors), solid graphite (20% of reactors), heavy water (5% of reactors).
  • The Containment: The enveloping structure that separates the nuclear reactor from the surrounding environment.
  • Neutron Poison: A neutron poison (also called a neutron absorber or a nuclear poison) is a substance with a large neutron absorption cross-section.

Types of Nuclear Reactor

Based on various components and working principles of Nuclear Reactors, one can distinguish them into the following types discussed below. Even though all the commercial nuclear power reactors use Nuclear Fission, they can be classified into two categories based on the energy of neutrons that sustain the fission chain reaction.

Nuclear Reactors in India

The list of the locations of the installed nuclear reactors in India is given below.

  1. Rajasthan (Rawatbhata)
  2. Tamil Nadu (Kudankulam; Kalpakkam)
  3. Gujarat (Kakrapar)
  4. Uttar Pradesh (Narora)
  5. Karnataka (Kaiga)
  6. Maharashtra (Tarapur)


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