Types of Nuclear Reactors
en.anglumea.com - First and foremost, it is essential to understand that the nuclear reactor is the most crucial component of a nuclear power plant. The nuclear chain reaction occurs here, generating energy through nuclear fission. The heat produced can be utilized to generate electricity,that what we call the nuclear energy utilization. The primary purpose of a nuclear reactor is to contain and control the released energy. Uranium is used as fuel in these reactors. The heat generated from the nuclear reaction is used to convert water into steam, which is then transformed into carbon-free electricity via turbines.
Table of Contents
Various types of nuclear reactors exist based on the moderator, coolant, and technology employed. Nuclear power reactors operate based on nuclear fission reactions. While the thorium fuel cycle is also feasible, most reactors use uranium and its derivative, plutonium, as nuclear fuel.
Nuclear fission reactors can be categorized into two types based on the energy of neutrons sustaining the fission reaction: thermal reactors and fast neutron reactors.
1. Thermal Reactors
Thermal reactors, the most common type of nuclear reactor, use slow or thermal neutrons to sustain fuel fission. Most modern reactors fall into this category. These reactors contain neutron moderators to slow down neutrons. The moderator is often also the coolant, typically high-pressure ordinary water. These reactors have a high fission probability due to slow neutrons. Enrichment of 2–5% fissile material is sufficient to maintain the chain reaction. However, they generally produce more radioactive waste.
Boiling water reactors (BWRs), pressurized water reactors (PWRs), and heavy water reactors (HWRs) operate using thermal neutrons and utilize moderators.
I. Light Water Reactor (LWR)
Light water reactors (LWRs) and heavy water reactors (HWRs) are categorized
based on their coolant and moderator. LWRs use ordinary water instead of heavy
water as the coolant and neutron moderator.
Thermal neutron reactors are
the most common nuclear reactors, and LWRs are the most widely used type among
them. There are three types of LWRs: pressurized water reactors (PWRs),
boiling water reactors (BWRs), and (in most designs) supercritical water
reactors (SCWRs).
II. Pressurized Water Reactor (PWR)
PWRs use ordinary water as the coolant. The primary coolant is maintained at extremely high pressure to prevent boiling. PWRs constitute the majority of nuclear power plants in the Western world.
In a PWR, the primary coolant (water) is pumped at high pressure into the reactor core, where it is heated by the energy released from nuclear fission reactions. The heated water then flows to a steam generator, transferring thermal energy to a secondary system where steam is produced and directed to a turbine to drive an electric generator.
Unlike boiling water reactors, the pressure in the primary cooling loop prevents the internal reactor water from boiling. PWRs were initially developed as propulsion systems for nuclear-powered submarines.
III. Boiling Water Reactor (BWR)
BWRs are the second most common type of nuclear power reactors after PWRs.The primary difference between BWRs and PWRs is that in a BWR, the reactor core heats water directly, converting it into steam that drives the turbine. In contrast, PWRs heat water that does not boil, transferring the heat to a secondary low-pressure water system, which then turns into steam to power the turbine.
IIII. Supercritical Water Reactor (SCWR)
SCWRs utilize supercritical water as the working fluid. Supercritical water oxidation (SCWO) is a process that occurs in water at temperatures and pressures above its thermodynamic critical point.
Under these conditions, water becomes a fluid with unique properties that can be exploited for the destruction of hazardous waste. SCWRs are similar to LWRs but operate at higher pressures and temperatures than PWRs and follow a once-through cycle similar to BWRs. SCWRs are promising advanced nuclear power systems due to their high thermal efficiency and simpler design. However, they are still in the developmental phase.
V. Pressurized Heavy Water Reactor (PHWR)
This reactor uses heavy water (deuterium oxide, D2O) as both the coolant and neutron moderator. Since heavy water coolant is maintained under pressure, it can be heated to high temperatures without boiling, similar to a PWR.
Heavy water is significantly more expensive than ordinary light water, but it greatly improves neutron economy. This allows reactors to operate without fuel enrichment facilities (offsetting the additional cost of heavy water), utilize alternative fuel cycles, and enhance reactor capabilities.
2. Fast Breeder Reactors
Fast breeder reactors (FBRs) or fast neutron reactors use fast neutrons to induce nuclear fission in fuel. These reactors are rare due to their complexity and high costs. They are more challenging to construct and expensive to operate. Unlike thermal reactors, they lack neutron moderators and use minimal coolant, which has a lesser neutron-slowing effect.
To sustain the chain reaction, the fuel must be highly enriched in fissile material (approximately 20% or more) due to the relatively low fission probability of fast neutrons. Fast reactors can generate less radioactive waste since all fissile material undergoes fission with fast neutrons, using highly enriched fuel containing fissile material.
Fast breeder reactors operate using fast neutrons and do not require neutron moderators.
Conclusion
Nuclear reactors play a pivotal role in energy production, with thermal reactors being the most commonly used due to their efficiency and established technology. Fast breeder reactors, though complex and costly, hold promise for minimizing nuclear waste and maximizing fuel efficiency. With ongoing advancements in reactor designs, nuclear energy continues to be a critical component of sustainable and low-carbon power generation.
