Nuclear energy

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Why do we not use a nuclear fuel instead of uranium that decays into stable elements? Why do we use uranium?
 

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  • #2
Tom Mattson
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Which nuclear fuel decays into stable elements?
 
  • #3
chroot
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All radioactive materials eventually decay into stable products, Tom.

We use uranium for a couple of reasons:

1) because it is capable of producing a chain reaction.
2) because it is relatively abundant on earth.

- Warren
 
  • #4
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As far as i remember uranium eventually decays into Pb, which is quite stable.
 
  • #5
russ_watters
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As far as i remember uranium eventually decays into Pb, which is quite stable.
Doesn't virtually EVERY radioactive material eventually decay into lead since it is one of the heaviest stable elements?
 
  • #6
Janus
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Originally posted by russ_watters
Doesn't virtually EVERY radioactive material eventually decay into lead since it is one of the heaviest stable elements?
It depends upon whether it belongs to the Uranium, Thorium, Actinium or Neptunium series.

The members of the first three decay to Lead 206, 208 and 207 respectively.

The Neptunium series decays to bismuth 209 (after passing through Lead 209)

All three pass through radioactive isotopes of lead on their way to stability. (the uranium series passes through both lead 214 and lead 210).

This doesn't count the nonseries radionucleides. (such as carbon 14)
 
  • #7
Integral
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Iron is the element which has no energy to release, through either fission or fusion so will be the ultimate end point of nuclear reactions which release energy. When you consider the nature of the fission process it seems very unlikly that stable isotopes can be the immediate result. It is an environment rich in energetic free neutrons, in order to have stable isotopes each atom would have to complete the process with the unique number of neutrons required to form that element. This is very unlikely, sort of like walking in a rain storm and not getting wet.
 
  • #8
RuroumiKenshin
Originally posted by chroot
All radioactive materials eventually decay into stable products, Tom.

We use uranium for a couple of reasons:

1) because it is capable of producing a chain reaction.
2) because it is relatively abundant on earth.

- Warren
Hm.., I was under the impression uranium is not a natural material. As it was "created" when scientists split the nucleus of plutonium, and the alpha particles (or beta, i haven't studied np in a while) where the uranium?
 
  • #9
chroot
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Originally posted by MajinVegeta
Hm.., I was under the impression uranium is not a natural material.
Your impression is wrong.
where the uranium?
Generally, in the ground.

- Warren
 
  • #10
Janus
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Originally posted by MajinVegeta
Hm.., I was under the impression uranium is not a natural material. As it was "created" when scientists split the nucleus of plutonium, and the alpha particles (or beta, i haven't studied np in a while) where the uranium?
Uranium is found in mine-able concentration in the minerals:
Pitchblende, uraninite, carnotite, torbernite, tyuyamunite, autunite, uranophane, and brannerite,

It is also found in varying trace amounts throughout most of the rocks of the crust.
 
  • #11
dav2008
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Yea, the hard part is refining the abundant U-238 into the U-235 which is used in nuclear bombs.
 
  • #12
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Originally posted by chroot
Your impression is wrong.
<Where is the Uranium >
Generally, in the ground.
However, if you are clever enough you may find some in an underground bunker in Iraq, labeled "For peaceful purposes only"
 
  • #13
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I was thinking about eliminating nuclear watse so is there nothing we can use that will do this?
 
  • #14
dock
Originally posted by Jack
I was thinking about eliminating nuclear watse so is there nothing we can use that will do this?
we could substitute fission with fussion i.e. instead of using uranium we can use H2 and H3 to get energy and He4 + n0.
according to the quantity burned/gained energy ratio the fussion reactions are more effective.
 
  • #15
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Originally posted by dock
we could substitute fission with fussion i.e. instead of using uranium we can use H2 and H3 to get energy and He4 + n0.
according to the quantity burned/gained energy ratio the fussion reactions are more effective.
So why do we not do this because the main problem with using nuclear energy at the moment is the waste that it produces.
 
  • #16
chroot
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Fusion is not as easy as fission -- you have to generate huge temperature and confine the reacting gas in a magnetic containment system.

Fusion is reaching the point where it will be economically feasible. A reactor called DEMO is currently being built that has the express purpose of breaking even economically.

Fusion does not eliminate the waste problem, however -- the neutrons ejected by the reaction are unaffected by the magnetic containment fields. As a result, they strike the walls and cause the walls to become radioactive. There are still hurdles to overcome in that department.

- Warren
 
  • #17
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Originally posted by MajinVegeta
Hm.., I was under the impression uranium is not a natural material. As it was "created" when scientists split the nucleus of plutonium, and the alpha particles (or beta, i haven't studied np in a while) where the uranium?
The truth is actually the other way round....
http://www.fas.org/nuke/intro/nuke/plutonium.htm
 
  • #18
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Thanks for real facts

Originally posted by Janus
It depends upon whether it belongs to the Uranium, Thorium, Actinium or Neptunium series.

The members of the first three decay to Lead 206, 208 and 207 respectively.

The Neptunium series decays to bismuth 209 (after passing through Lead 209)

All three pass through radioactive isotopes of lead on their way to stability. (the uranium series passes through both lead 214 and lead 210).

This doesn't count the nonseries radionucleides. (such as carbon 14)
Thank You Janus for your statement of really true facts of a much-misunderstood area of real matter. Allow me to share with this string my career long labor of sorting all this stuff out.
1. By scanning the isotopes of the transuranic elements back to Fermium for a contiguous clump of 4 alpha (long-lived) emitters and then skipping Einsteinium to Fermium’s alpha decay daughters, Californium, etc, there is revealed the reality that this 4 isotope contiguousness of the four series you mentioned above is repeated until the Radium contiguum where the Neptunium series isotope was more unstable to beta emission which resulted in that series ending in Bismuth-209.
2. The interesting thing about the Bismuth series was that there were no “alpha-dams” nor “alpha-super-dams” in that series and therefore all the Bismuth precursor isotopes in nature’s aboriginal 4 element clump had decayed completely to the Bi-209 ultimate daughter in 112 million years after creation. Note that U-238 is a super-dam outside the U-clump that decays by alpha-beta-beta string to U-234 that along with the long ago disappeared U-233 and the “dam”, U-235 and U-236 comprise the contiguous Uranium clump. Thorium-232, which is the daughter of U-236, is a super-dam that is also a member of the Th-clump. Plutonium-242 is a dam in the Pu-clump but Pu-244 is a super-dam.
3. The series of super-dams includes Curium-250, Pu-244, U-238, Th-232, and Radium-226 and the pattern of 6-nucleon-spacing of these is notable.
4. If you ever wondered where the Pb-204 isotope came from, remember this: Thallium-203 + a neutron has no other place to go. Cheers, Jim
 
  • #19
pmb
Jack asked
Why do we not use a nuclear fuel instead of uranium that decays into stable elements? Why do we use uranium?
I find that a very confusing question. What exactly do you mean by "nuclear fuel"? Isn't uraniam "nuclear fuel"??

Pete
 
  • #20
russ_watters
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I find that a very confusing question. What exactly do you mean by "nuclear fuel"? Isn't uraniam "nuclear fuel"??
Typo, pmb. What he meant to say (i think) is "Why don't we use a different nuclear fuel instead of uranium that decays into stable elements? Why do we use uranium?"
 
  • #21
pmb
Thanks Jack

The question is
Why don't we use a different nuclear fuel instead of uranium that decays into stable elements? Why do we use uranium?
The answer is that elements which are heavier than than iron yield a net release of energy (in the form of kinetic energy of the constituent parts as well as in the form of photons which can be thought to be all kinetic energy) when the atoms are split. As a general rule - The higher the atomic weight the higher the energy release. There may be other reasons like U(235) releases neutrons when it splits and those neutrons can then split other atoms yielding a chain reaction. And those neutrons have to have a certain range of energy in order for that to happen.

Pete
 
  • #22
pmb
I stated above the the reason uranium is used rather lighter elements was that the heavier elements release more energy than the lighter ones. That's true as a rule of thum of elements whose atomic number is higher than iron. For elements whose atomic number is less than iron the opposite is true - fusing the atoms together produces a net energy release.

The reason for all of this is the binding energy per nucleon. If you look at a curve of the binding energy per nucleon it starts out small and rises steeply as a general rules (there are flucuations which are exceptions to this rule) and peaks around A = 60 where A = Z (number protons) + N (number neutrons) then slows less steeply towards higher A.

See the binding energy curve here

http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/nucbin.html#c2



The reason for the shape of the curve has to do with potential energy. This is rather complicated to describe here but you can search the internet for this - Search for the "Liquid Drop Model".

A rough search gave this

http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/liqdrop.html

Basically you have effects like when A is greater there is a decrease in the surface to volumne ratio and therefore the surface tension plays less of a role etc. Forces on the nucleons at the surface are exposed to less nucleons than those nucleons in the middle which are surrounded by nucleons and the strong force, the force which binds these nucleons together, are short range and don't extend too far past the nearest nucleon. See details above.


Pete
 
  • #23
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Originally posted by Jack
I was thinking about eliminating nuclear watse so is there nothing we can use that will do this?
Possibly .... there is an ongoing line of research into transmutation techniques where neutrons are used to artificially decay the waste products. There are also a number of different types of non-proliferation fuels in development which use plutonium instead of uranium. A lot of work is being conducted but these sort of things still take time to get right.

Incidentally uranium is not used on it's own as the fuel normally the Oxide form (UO2) is used with numerous added elements (e.g. erbium, gadolinium) which help create cetain desired fuel properties.
 
  • #24
selfAdjoint
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Originally posted by Jack
I was thinking about eliminating nuclear watse so is there nothing we can use that will do this?
There is a safe reactor design called the Integral Fast Reactor (IFR) that eats waste from ordinary reactors and produces only low level waste on its own. Development of it was killed by the Clinton administration to satisfy their anti-nuke political supporters. The current administration makes noises about restarting it but doesn't actually do anything.

IMHO it would be a geat aid both in the energy problem and in reducing greeanhouse emissions, without the usual nuclear waste problem.
 
  • #25
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Radiation is a terrible thing to waste. Go IFR, selfAdjoint, and transmutation, sir-pinski! I never imagined harmful nuclear byproducts to have a solution.

At least most deuterium and even tritium ingested is eventually flushed from the body in the form of heavy water. The interior of a fusion reactor might be filled with pressurized hydrogen so that at least some of the containment byproducts bred there could be reused.
 

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