Nuclear reactors are very important for the power generation of a country. In today’s world, Nuclear energy is playing a very crucial role in the development of a country and this now becomes the symbol of the advancement of a country. In this article, we are going to discuss the important types of nuclear reactors and their functioning mechanism.
Nuclear Reactor :
- A nuclear reactor is the most important organ of a nuclear power plant. A nuclear chain reaction takes place here and energy is produced by nuclear fission. The produced heat can be used to generate electricity.
- The primary purpose of nuclear reactors is to contain and control the released energy.
- Uranium is used as fuel in these reactors. The heat produced by nuclear reactions is used to turn water into steam, which is further converted into carbon-free electricity using turbines.
Types of Nuclear Reactors:
- There are different types of reactors based on the moderators, coolants, and technology used.
- Nuclear power reactors are based on nuclear fission.
- Thorium fuel cycles are also possible, but they generally use uranium and its product plutonium as nuclear fuel.
- Nuclear fission reactors can be broadly divided into two classes based on the energy of the neutrons that maintain the fission reaction: thermal reactors and fast neutron reactors.
1. Thermal Reactors :
- Thermal reactors (the most common type of nuclear reactor) use slowed, or thermal, neutrons to sustain the fission of their fuel.
- Almost all modern reactors are of this type.
- These contain neutron moderators that slow down neutrons. The moderator is often also a coolant, i.e. ordinary water under high pressure. There is a high possibility of fission by slow neutrons. A 2 – 5% enrichment of fissile material is sufficient to sustain the chain reaction.
- They often produce more radioactive waste.
- Boiling water reactors (BWR), pressurized water reactors (PWR), and heavy water reactors (HWR) operate with thermal neutrons [using moderators]
Types of Thermal Reactors
A. Light water reactor (LWR)
- Light water reactors [LWR] and hard water reactors [HWR] are reactors based on coolants and moderators.
- A light water reactor (LWR) is a type of thermal neutron reactor that uses ordinary water, rather than heavy water, as both a coolant and a neutron moderator.
- Thermal neutron reactor is the most common type of nuclear reactor and light water reactor is the most common type of thermal neutron reactor.
- There are three types of light water reactors: pressurized water reactors (PWR), boiling water reactors (BWR), and (in most designs) supercritical water reactors (SCWR).
B. Pressurized water reactor (PWR)
- PWRs use normal water as a coolant. The primary cooling water is kept at very high pressure so that it does not boil.
- Pressurized water reactors (PWRs) make up the majority of all nuclear power plants in the West.
- In a PWR, the primary coolant (water) is pumped at high pressure into the core where it is heated by the energy produced by the nuclear fission of atoms.
- The heated water then flows to a steam generator, where it transfers its thermal energy to a secondary system where steam is produced and flows to a turbine, which drives a generator.
- Unlike boiling water reactors, the pressure in the primary coolant loop prevents the water inside the reactor from boiling. PWRs were originally developed to serve as propulsion for nuclear-powered ships in nuclear submarines.
C. Boiling Water Reactor (BWR)
- It is the second most common power generation reactor after the pressurized water reactor (PWR).
- The main difference between BWRs and PWRs is that in BWRs the core of a nuclear reactor heats water, which turns into steam and drives a steam turbine. In a PWR, the reactor core heats non-boiling water.
- This hot water exchanges heat with the low-pressure water system and turns into steam, which drives a turbine.
D. Supercritical Water Reactor (SCWR)
- A supercritical water reactor (SCWR) uses supercritical water as the working fluid. Supercritical water hydration (SCWO) is a process that occurs in water at temperatures and pressures above the thermodynamic critical point of the mixture.
- Under these conditions, water becomes a liquid with unique properties that can be used to advantage in the destruction of hazardous waste.
- SCWRs are similar to light water reactors (LWRs), but operate at higher pressures and temperatures than pressurized water reactors (PWRs) and operate on a once-through cycle like boiling water reactors (BWRs).
- SCWR is a promising advanced nuclear power system due to its high thermal efficiency and simpler design.
- Still in the development stage.
E. Pressurized Heavy Water Reactor (PHWR)
- It uses heavy water (deuterium oxide D2O) as a coolant and neutron moderator because the heavy water coolant is kept under pressure, it can be heated to high temperatures without boiling, similar to a pressurized water reactor.
- Heavy water is much more expensive than ordinary light water, but it greatly improves neutron economy, allows reactors to operate without fuel enrichment facilities (which offsets the additional cost of heavy water), utilizes alternative fuel cycles, and increases the reactor’s ability.
2. Fast Breeder Reactors:
- A fast Breeder/neutron reactor uses fast neutrons to cause nuclear fission of the fuel.
- These are very rare due to their complexity and cost. They are harder to build and more expensive to run.
- They have no neutron moderator and use less moderating coolant.
- To sustain the chain reaction, the fuel would need to be highly enriched in fissile material (about 20% or more) due to the relatively low fission potential. Fast reactors may produce less radioactive waste because all fissile material undergoes fission with fast neutrons [the fuel is highly enriched with fissile material].
- Breeder reactors run on fast neutrons [no moderator needed]
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