Nuclear fuels are the materials that undergo nuclear fission in nuclear power stations. This article covers a wide variety of nuclear fuels examples in detail.
Some of the nuclear fuels examples are:
- Uranium dioxide
- Mixed oxide fuel
- TRIGA fuel
- Actinide fuel
- Molten plutonium
- Uranium nitride
- Uranium carbide
- Molten salt fuel
- Aqueous solutions of uranyl salts
- Liquid metals
- Pressurized water reactor fuel
- Boiling water reactor fuel
- CANDU fuel
- Magnox fuel
- TRISO fuel
- QUADRISO fuel
- Accident tolerant fuels
- Spent nuclear fuel
- Sodium-bonded fuel
Let’s discuss each of the above in detail.
Nuclear Fuels Examples: Detailed Explanations
Uranium-233 has been used as a nuclear fuel in several reactor types and the fission of one Uranium-233 atom releases 197.9 MeV (mega electron volt) of energy. It is also a fissile isotope of Uranium that is produced from Thorium by neutron irradiation.
Uranium-235 is the most widely used nuclear fuel in almost all nuclear reactors. A uranium-235 atom comprises 92 protons and 143 neutrons. When a moving neutron is captured by U-235 nucleus, fission takes place resulting in the release of more neutrons as well as generation of energy. The released neutron collides with more U-235 nucleus and hence chain reaction takes place releasing huge amount of energy.
Plutonium-239, an isotope of Plutonium, is also extensively used in nuclear armaments apart from Uranium. Nuclear fission of an atom of Plutonium-239 generates around 207.1 MeV of energy. The probability of fission of Plutonium-239 is higher than that of Uranium-235.
Uranium dioxide is an oxide nuclear made from uranyl nitrate. Several light water reactors, gas-cooled reactors and other reactors widely use uranium dioxide as the fuel. Uranium dioxide is significantly advantageous over other fuels like uranium metal alloys due to its relatively high melting point and chemical stability in water.
Mixed oxide fuel
Mixed oxide fuel or commonly known as MOX fuel is a mix of plutonium and natural or depleted uranium. This fuel is used as an alternative to uranium fuel (low enriched) in the light water reactors in power generation. This fuel provides a means to produce electricity from military sources by burning weapons-grade plutonium.
TRIGA fuel is a metal fuel which is advantageous over oxide fuels due its higher heat conductivity. TRIGA is used in Training, Research, Isotopes, General Atomics reactors. The fuel component is uranium zirconium hydride which has a negative fuel temperature coefficient of reactivity. This implies that the reactivity decrease when temperature of the core rises.
Actinide fuels are used in fast neutron reactors. The neutron capture of uranium and plutonium in a fast neutron reactor produces actinides which can be used as a nuclear fuel. Actinides are extensively used in nuclear reactors.
Molten plutonium has a large negative temperature coefficient of reactivity. Fast breeder reactors uses molten plutonium.
Uranium nitride has a better thermal conductivity than uranium oxide and in addition, it has a high melting point. Uranium nitride is used as a fuel mainly in the reactors designed by NASA. Also, uranium nitride seems to be a promising accident tolerant fuel.
Uranium carbide is characterized by high thermal conductivity and high melting point. Both these properties make it an attractive fuel. The absence of oxygen in the fuel enables it as an ideal fuel for gas-cooled fast reactors. It occurs mainly in the form of pellets or tablets. In the latest design of nuclear thermal rockets, uranium carbide fuel was been used.
Molten salt fuel
Molten salt fuel is a kind of liquid fuel where the nuclear fuel is dissolved in a molten salt coolant. The fuel is used in the form of a very hot fluoride or chloride salt rather than the common occurrence in the form of solids. This provides an advantage in two forms, it can act as a fuel as well as a coolant.
Aqueous solutions of uranyl salts
Small research reactors like aqueous homogeneous reactors (AHRs) makes use of a solution of uranyl salt in water i.e., the fuel here is an aqueous solution. The most common use of solution reactors is for the production of medical isotopes, and the technique is potentially advantageous. The main reasons behind the usage of solution reactors are their low cost, small critical mass, inherent passive safety, and simplified fuel handling, processing and purification characteristics.
Liquid metal fuels may occur like Uranium-Chromium alloy or Uranium-Iron alloy.
Pressurized water reactor fuel
The fuel deployed in pressurized water reactors is enriched uranium. The reactor consists of bundles of cylindrical rods. The bundles comprise the fuel. These reactors were initially developed for nuclear submarine propulsion reactors during and after the Second World War. The enrichment level of uranium in PWR is slightly greater than that used in a boiling water reactor.
Boiling water reactor fuel
Boiling water reactors use enriched uranium similar to a pressurized water reactor but the enrichment level is less when compared to PWR. The reactor contains around 370-800 fuel assemblies or bundles. Boiling water reactors are considered to be the second most commonly used nuclear reactor for power generation next to pressurized water reactor.
Natural uranium is the nuclear fuel in CANDU reactors. Natural uranium basically comprises 0.7% uranium-235 and the remaining 99.3% is uranium 238. CANDU specifically implies Canada Deuterium Uranium and consists of fuel bundles.
Magnox or magnesium non-oxidizing reactors has the fuel natural uranium in metallic form and is canned with an alloy of magnesium. Graphite is used as a moderator in this reactor thereby enabling itself to make use of natural uranium as the fuel.
TRISO fuel is tri-structural isotropic particle fuel, and is a kind of micro-particle fuel. TRISO particles are encapsulated into small graphite pellets. Each TRISO particle contains a kernel of uranium, carbon and oxygen fuel. TRISO fuels are more resistant to oxidation, corrosion, neutron irradiation, high temperatures compared to other fuels and hence they are safe.
Quadruple isotropic coated fuel or QUADRISO fuel is wherein a TRISO particle is surrounded by a burnable poison like a carbide layer. This arrangement manages excess reactivity.
Accident tolerant fuels
Accident tolerant fuels are an innovation to improve fuel performance in reactors under accident conditions. These can widen the safety measure for nuclear plants, can endure the loss of active cooling in a reactor core, improve the performance of the nuclear power plant.
Spent nuclear fuel
Spent nuclear fuel is a mixture of uranium, plutonium, fission products, and transplutonium metals. The radiation hazard from the spent nuclear fuel gets reduced when its radioactive components decay.
Sodium-bonded fuel contains sodium in between the cladding and the pellet. The sodium bonding has the advantage of reducing the temperature of the fuel. This fuel is most commonly used in sodium-cooled liquid metal fast reactors.