There are hw many main types of nuclear reactor?
Two types of nuclear reactors :The radioactive decay one that emit radiation as it decays or transform and the second one is the billard ball type of reactions where the nucleus or a nuclear particle like proton is formed.
What is the purpose of nuclear reactor?
The two main types of nuclear reactor are:
• Burner reactors
• Fast breeder reactors
Most operational nuclear reactors make use of the reaction in the following equation. They are called burner reactors.
Fast breeder reactors use the conversion of uranium-238 into plutonium-239, as in the following equation:
The object of a burner reactor is to use up or ‘burn’ as much uranium-235 as possible. For some reactor designs the uranium-235 content of natural uranium is increased chemically to produce enriched uranium, which contains up to 3% uranium-235 (compared with the naturally occurring 0.7%). The chain reactions during nuclear fission produce neutrons with a wide range of energies.
Fast neutrons are slowed down using a moderator - graphite, ordinary water or heavy water - so that they can cause fission of uranium-235. The reaction rate is adjusted using control rods made of boron that absorb neutrons. These rods can be raised or lowered into the reactor core to increase or decrease the heat output.
The core coolant, either carbon dioxide gas or water depending on the reactor type, is heated by nuclear fission in the core. The heat from the core coolant is transferred to a closed steam-water circuit, which includes the turbine plant.
The steam in the turbine circuit is condensed to water on the low-pressure side of the turbine by a cooling water circuit that is open to the environment. The requirement for large volumes of cooling water means that nuclear reactors must be sited in coastal locations or near large rivers or lakes.
There are three types of burner reactors:
• Magnox reactors (Magnox)
• Advanced gas-cooled reactors (AGRs)
• Pressurised water reactors (PWRs)
Magnox reactors are fuelled by metallic uranium containing the natural proportion of uranium-235 (i.e. 0.7%) held in tubes of a magnesium alloy (Magnox). The moderator is graphite, the coolant is carbon dioxide and the operating temperature is about 400°C.
Advanced gas-cooled reactors (AGRs) are very similar to Magnox reactors (they have the same moderator and coolant), except that uranium oxide, enriched in uranium-235 (2.3% instead of 0.7%) and packed in stainless steel tubes, is used as a fuel.
The operating temperature, 800°C, is higher than that in a Magnox reactor, leading to greater conversion efficiency and output by increasing steam pressure. Although the capital cost of building AGRs is very high, they have many additional safety features over Magnox reactors and, because of their greater efficiency, produce cheaper electricity.
Pressurised water reactors (PWRs) are the most widely used globally. The fuel contained in zirconium alloy tubes is uranium oxide enriched in uranium-235, and pressurised water is both coolant and moderator. They operate at 300-400°C. The UK Sizewell ‘B’ plant is of this kind.
Fast breeder reactors
If fast neutrons produced in the chain reactions are not moderated or absorbed, the rate of conversion of uranium-238 into plutonium-239 can exceed the fission rate of plutonium-239. Reactors that use fast neutrons in this way are called fast breeder reactors.
The main fuel of fast breeder reactors is uranium-238, together with an initial charge of plutonium-239 which is needed to start the chain reaction that ‘breeds’ plutonium-239 from uranium-238. (This charge of plutonium-239 is obtained from the spent fuel rods of burner reactors.) The attraction of the fast-breeder concept is the excess plutonium-239 that they produce.
About 60% of the fuel used in fast breeder reactors is converted into useful energy, compared with the 0.5-2% in burner reactors. Not only are fast breeder reactors more efficient, they generate more plutonium than they consume and can use the uranium-238 in the waste from burner reactors.
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