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Nuclear fuels

Nuclear fuel consists of a fissionable isotope, such as uranium-235, which must be present in sufficient quantity to provide a self-sustaining chain reaction. In the United States, uranium ores contain from 0.05–0.3% of the uranium oxide U 3 O 8 ; the uranium in the ore is about 99.3% nonfissionable U-238 with only 0.7% fissionable U-235. Nuclear reactors require a fuel with a higher concentration of U-235 than is found in nature; it is normally enriched to have about 5% of uranium mass as U-235. At this concentration, it is not possible to achieve the supercritical mass necessary for a nuclear explosion. Uranium can be enriched by gaseous diffusion (the only method currently used in the US), using a gas centrifuge, or by laser separation.

In the gaseous diffusion enrichment plant where U-235 fuel is prepared, UF 6 (uranium hexafluoride) gas at low pressure moves through barriers that have holes just barely large enough for UF 6 to pass through. The slightly lighter 235 UF 6 molecules diffuse through the barrier slightly faster than the heavier 238 UF 6 molecules. This process is repeated through hundreds of barriers, gradually increasing the concentration of 235 UF 6 to the level needed by the nuclear reactor. The basis for this process, Graham’s law, is described in the chapter on gases. The enriched UF 6 gas is collected, cooled until it solidifies, and then taken to a fabrication facility where it is made into fuel assemblies. Each fuel assembly consists of fuel rods that contain many thimble-sized, ceramic-encased, enriched uranium (usually UO 2 ) fuel pellets. Modern nuclear reactors may contain as many as 10 million fuel pellets. The amount of energy in each of these pellets is equal to that in almost a ton of coal or 150 gallons of oil.

Nuclear moderators

Neutrons produced by nuclear reactions move too fast to cause fission (refer back to [link] ). They must first be slowed to be absorbed by the fuel and produce additional nuclear reactions. A nuclear moderator    is a substance that slows the neutrons to a speed that is low enough to cause fission. Early reactors used high-purity graphite as a moderator. Modern reactors in the US exclusively use heavy water ( 1 2 H 2 O ) or light water (ordinary H 2 O), whereas some reactors in other countries use other materials, such as carbon dioxide, beryllium, or graphite.

Reactor coolants

A nuclear reactor coolant    is used to carry the heat produced by the fission reaction to an external boiler and turbine, where it is transformed into electricity. Two overlapping coolant loops are often used; this counteracts the transfer of radioactivity from the reactor to the primary coolant loop. All nuclear power plants in the US use water as a coolant. Other coolants include molten sodium, lead, a lead-bismuth mixture, or molten salts.

Control rods

Nuclear reactors use control rods ( [link] ) to control the fission rate of the nuclear fuel by adjusting the number of slow neutrons present to keep the rate of the chain reaction at a safe level. Control rods are made of boron, cadmium, hafnium, or other elements that are able to absorb neutrons. Boron-10, for example, absorbs neutrons by a reaction that produces lithium-7 and alpha particles:

Questions & Answers

Whats d IUPAC Numenclature of bromine
Emmanuel Reply
The common name is therefore propyl bromide . For the IUPAC name , the prefix for bromine (bromo) is combined with the name for a three-carbon chain (propane), preceded by a number identifying the carbon atom to which the Br atom is attached, so the IUPAC name is 1-bromopropane.
crystal
What is Quantum number
Derick Reply
what are the chemical properties of group IIA Element and their atomic structure?
NATHAN Reply
What is mixture
Azeez Reply
A mixture is a mix of substances that can be separated
Lillie
what is quantum number
Baba Reply
Hmm
kedis
I suck at chemistry I need a tutor
kedis
h20 hydrates, nitrogen/dry ice lowers pressure similar to space environment when heated at what location/temp.? +or-, expect location (xyz)
Brian
hey kedis,never say that u suck,u don't,all u need is to calm down,get the book and get the points,no need to read it word by word or a-z. ur good bro,u r veeeery intelligent
UDUJI
awwwww
Cereal
what's neuron?
Kelvin Reply
neuron or neutron?
John
cell of the nerve
Kamaluddeen
prepare a solution of 1m iodine in 250mls of water
Dj Reply
Really
Wisdom
Hiiii am new here
Wisdom
Really
Wisdom
WHAT IS CHEMISTRY?
RJ
Chemistry is the study of matter
Wisdom
chemistry is the study of matter and changes it undergoes
Mercy
what is equilibrium
Fatai Reply
what is biology
Fatai
biology is said to be the science of studying life and living organism including theirs physical structure,chemical processes, molecular interaction development and evolution
David
atomic number of sodium
bose
that'll be 11
Kamaluddeen
ok
bose
anymore questions 😁
Franklin
re u writing jamb
bose
please, how man Bond are present when a methane under goes a complete combustion
moses Reply
Combustion of Methane The reactants are on the left side of the equation and the products are on the right. In the reaction, the bonds in the methane and oxygen come apart, the atoms rearrange and then re-bond to form water and carbon dioxide.
saidi
how is ethanol produced using ethene
Glory
Ethanol is manufactured by reacting ethene with steam. The reaction is reversible, and the formation of the ethanol is exothermic. Only 5% of the ethene is converted intoethanol at each pass through the reactor
saidi
Ethanol can be made by reacting ethene (from cracking crude oil fractions) with steam. A catalyst of phosphoric acid is used to ensure a fast reaction. Notice that ethanol is the only product. The process is continuous – as long as ethene and steam are fed into one end of the reaction vessel, ethano
saidi
the mole concerpt and its tricks
Mary Reply
what are atoms
ola Reply
the individual elements of matter.
Reginald
tiny particles that make up a all matter.
Reginald
smallest particles of an element
Osuji
What is the meaning of hybridization
JOSEPH Reply
Differentiate between latent heat and specific latent heat of fusion and vaporization
Amos Reply
Ans: The amount of heat energy released or absorbed when a solid changing to liquid at atmospheric pressure at its melting point is known as the latent heat of fusion. while Vaporization of an element or compound is a phase transition from the liquid phase to vapor.
Acquah
a student was required to prepare 500cm of 1.0M solution of glucose(C6H12O6). (C=12, H=1, O=16).determine a.molar mass of glucose b.amount of glucose in mole c.mass of glucose contained in the solution
Mac Reply
what is radio isotope
Mac
what are ionic compound
elepo Reply

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Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
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