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Why is enrichment necessary when uranium is used as a reactor fuel?
The most common isotope of uranium, 238U, has a poor cross-section (the ability to assimilate neutrons) for slow neutrons. In order to enhance the reaction, we enrich the uranium to 235U, from a natural level of about 0.7% to about 4%. This enhances the ability of the uranium to participate in a fissile reaction, i.e. one that sustains neutrons that fission atoms which creates neutrons, etc.
What chemical reactions are involved in a nuclear reactor?
Chemical reactions are undesirable and are not a feature of the intended reactor behaviour. The water quality in the primary circuit in a PWR or BWR must be well controlled both to avoid chemical reactions with the reactor materials (steel and zircaloy) and to avoid picking up radioactivity as far as possible. What is wanted is a reactor assembly that undergoes as little chemical reaction as possible, in order to prolong the reactor life up to 60 years. In gas cooled (that is carbon dioxide cooled) reactors as built in the UK, corrosion of steel components was a problem in the magnox type and resulted in maximum gas temperature being limited with loss of output. In the AGR all the hot end of the reactor had to be made of stainless steel to avoid corrosion.
What is needed to make an nuclear bomb?
You need a supply of plutonium or uranium 235. You then need the ability to use machinery to shape these incredibly toxic and dangerous materials. You need different types of high explosives shaped in the correct way to initiate the bomb. You need precision electrical timing devices to fire the explosives in exactly the right order. You will also need several million dollars to pay for all of this, and a rather large truck- the first atomic bomb weighed roughly 6 tons.
Is uranium a unique structure?
Uranium is a metal, and, at atomic number 92, it's the heaviest of the elements produced by stars in fusion. Note that it's not made in "regular" stellar nucleosynthesis, but is created in the spectacular supernovae events of certain stars when they reach the end of their lives. In that light, that makes uranium like all the other elements heavier than iron. Uranium is also very dense, and it is nearly 20 times heavier than the same volume of water. There's more. Uranium is radioactive. All the isotopes of uranium have unstable nuclear configurations. These nuclei will decay over time, all of them, and they all transform by spontaneous fission or by alpha decay. The three isotopes that make up natural uranium, 234U, 235U and 238U, have long half-lives. The 234U has a half million year half-life, and the half-lives of the other two are on the order of a billion years. There's one other thing, and that's that 235U is fissile. It turns out that 235U is capable of creating a nuclear chain reaction when critical mass is reached because it fissions when undergoing neutron capture. All uranium is going to be decaying over time, but when the critical mass of 235U is reached, a chain reaction will begin where neutrons spontaneously released from some 235U atoms will cause other atoms to fission and release neutrons. The chain will begin, and only the physics and geometry associated with the critial mass will determine how far the chain will build and how long it will progress. The translation of that is that if use conventional explosives to drive subcritical masses of 235U together, we can, if things are optimized, create a nuclear explosion. We can also design "surrounds" that will cause a chain reaction to begin and will also promote the chain to be continuous, as in a nuclear reactor. Note that a trace of plutonium can be found in naturally occurring uranium ores, but uranium is generally thought of as being the heaviest naturally occurring nucleus. Let's not split hairs here. Oh, and if you need more information on uranium, use the link below. It will take you to the Wikipedia post, and it's a good read. You will be measureably smarter having gone through their article. But be warned that it may very well provide one or more questions for each answer it supplies - just like most good science.
How is nuclear chemistry used in nuclear bombs?
Well first start of nuclear bombs has more common in physics that chemistry. Sense Chemistry is really assosiated with elemnts while the atom and it spliting is more assosiated with physics. The answer is easy in order to produce an atomic bomb you need uranium or plutonium which is part of chemestry. The fission process is more physic related
Describe the difference between weapons grade and reactor grade nuclear fuel?
Uranium in nature is only about 0.7% 235U. In order to have a chain reaction, the percentage of 235U must be increased by enrichment. The percentages of 235U in nuclear reactors are generally low, about 3% to 5%. For bombs, the percentage is generally 85% or more.
How much of Uranium is used in nuclear fuel?
A typical PWR has fuel assemblies of 200-300 rods each, and a large reactor would have about 150-250 such assemblies with 80-100 tonnes of uranium in all. It produces electric power in the order of 900 to 1500 MW.
A radioactive element in nuclear power stations?
The metal most commonly used is enriched uranium, meaning that it has a higher percentage of uranium-235 than occurs in nature. Plutonium is also used in some reactors, in combination with uranium. And thorium can also be used, though research on its use has only just begun. Usually it is not the metal that is used in any case, but a compound of the metal. There is a link below.
What material is needed in nuclear power stations?
Most nuclear power stations run on enriched uranium in one form or another, either as uranium compounds, or as uranium metal. Some use other fuels, but all plants based on nuclear fission use fuels based either thorium or uranium, which are the only fertile element found in any abundance in nature. Fusion plants are envisioned, but none has been designed so far; these would use isotopes of hydrogen for fuel. To get enriched uranium, ore has to be mined, and the uranium in it extracted and refined. The resulting uranium is usually about 99.28% made up of 238U, and 0.71% of 235U. In order to be used in most conventional nuclear plants the 235U has to be increased to 3% to 5% of the total. There are various ways of doing this, but the commonest seems to be to react the uranium, making UFl6, uranium hexafluoride, which is a gas, and concentrate the lighter portions in a centrifuge at very high speeds. The enriched UFl6 is then reacted to form the form of uranium needed for the particular design of the power plant. In most plants, the uranium is packaged in rods, enclosed in sheathing of some special material such as zirconium. These are assembled in bundles that can be put into and taken out of the reactor relatively easily. There are other ways of fueling nuclear reactors. But this is the most common.
What part of a nuclear reactor is designed to absorb neutrons?
The control rods are used as a variable absorber, otherwise the reactor is designed not to absorb more neutrons than can be helped, in order to reduce the amount of enriched fuel needed. Around the outside of the reactor will be a concrete shield to protect operating staff.
What must metal fuel rods inside a nuclear reactor be bombarded with in order to start a chain reaction?
The metal fuel rods inside a nuclear reactor must be bombarded with neutrons in order to start a chain reaction. This process triggers the fission of uranium atoms in the fuel rods, releasing energy in the form of heat.
Why do uranium ore have be enriched?
Because only the isotope 235U is fissionable with thermal neutrons and also is good for nuclear weapons. This is because normal uranium in the Earth is 0.7 % 235U and 99.3 % 238U. The 235U needs to be enriched to 4 % or greater in order to be effective as a fissile material (fission with neutrons producing fission and more neutrons that can continue the reaction) reaction. Power plants run around 4 % to 5 %; but CANDU type reactors work with natural uranium. Weapons run +99 %. Small high capacity reactors, such as on a submarine, run around 20 %.
Why can ordinary uranium not be used to fuel a reactor cooled by ordinary water?
Because "ordinary" uranium is mostly 238U, which won't fission and create a chain like its lighter cousin 235U will. When critical mass is achieved with the 235U isotope of uranium, fission will occur spontaneously. Or with a significantly enriched uranium fuel (one where the natural concentration of 235U has been increased a bunch so the fuel has a much higher percentage of this isotope), fission and a chain reaction is also possible. But with just natural uranium, a big pile of it will just sit there. It won't fission and create a chain reaction. Note that 238U is radioactive and decays over time because it is unstable, but it has a long half-life. Also, the fact that it's unstable (radioactive) doesn't mean it's fissile. It isn't.
Does uranium need to be changed in order to be used?
Yes, the nuclear fuel from a nuclear reactor must be replaced at some intervals, because the fuel can be poisoned with neutron absorbers and the clad can become fragile and unsure; the "burned" fuel is recycled.
What does uranium bond?
Uranium is a metal, and it will bond with a number of different other elements to create compounds just like many (most) other metals. It has oxidation states of +3, +4, +5 and +6. Just one example of a uranium compound is uranium fluoride (UF6), which is the compound of uranium which is made in preparation for centrifuging in order to effect some isotopic separation to enrich the uranium. Then the enriched product can be used as nuclear fuel, or in making a nuclear weapon, perhaps. Wikipedia has more information, and a link to their post can be found below.
Why is enrichment necessary when uranium is used as a reactor fuel?
The most common isotope of uranium, 238U, has a poor cross-section (the ability to assimilate neutrons) for slow neutrons. In order to enhance the reaction, we enrich the uranium to 235U, from a natural level of about 0.7% to about 4%. This enhances the ability of the uranium to participate in a fissile reaction, i.e. one that sustains neutrons that fission atoms which creates neutrons, etc.
How much kg of uranium is required to become critical mass?
There is no single quantity, it depends on many factors some are:enrichment levelpresence/absence of moderatortype of moderatorpresence/absence of reflectorthickness of reflectortype of reflectorpresence/absence of absorbertype of absorberhas the uranium been compressed beyond standard densityetc.For some general order of magnitude values:in a typical water moderated reactor, the critical mass of the 3% enriched uranium is usually several tonsin a typical atomic bomb with a depleted uranium tamper/reflector, the critical mass of the 93.5% enriched uranium is 15 to 20 kg depending mostly on the thickness of the tamper/reflector
