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Topic: Compare: energy 1 tonne burned coal to E of fission of U,Th,Pu,fusion H  (Read 6073 times)

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Offline yesufreeko

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i need to use coal as the measuring stick for comparing energy efficiency, production, and such

specifically,

using TCE or energy produced with 1 metric ton of coal burned:
(numbers for this value seem to vary a bit, but here is the one I'm going with (willing to use another number if you have a better source):
29.3076E9J per TCE

find:

# kg for fission of U-235 to produce same amount of energy as TCE, and nuclear chem and calculations explaining said fission

# of kg for fission of Pu-239, with energy equaling 1 TCE, and nuclear chem and calculations explaining said fission

# g for fusion of H (most commonly used isotope(s)) to produce same amount of energy as TCE, and nuclear chem and calculations explaining said fusion

# g for fission of Th-232 to produce same amount of energy as TCE, and nuclear chem and calculations explaining said fusion

I'm not sure where to start. equations for fission of U235 that I'm seeing online seem to vary greatly as well.
« Last Edit: April 16, 2016, 11:09:58 PM by yesufreeko »

Offline ATMyller

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What are the products of 235U fission and what are their masses? Hint: it's less than the mass of 235U.
Chemists do it periodically on table.

Offline Enthalpy

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You could seek reliable sources for the fission energy of 235U. It's around 200MeV, but doesn't result from a simple calculation, because it depends on how much Pu is side-produced and consumed: this increases easily by 1/4. As well, the fission products give some heat by radioactivity, which  isn't negligible.

Same uncertainty for hydrogen fusion. The only reaction accessible to Tokamaks is D+T, but as we have very little T, the plans want to regenerate T from Li and the fast neutron emitted by D+T, and this second reaction changes the balance from roughly 17MeV to 24MeV, which depends on the neutron multiplicator.

232Th is NOT a fissile material, sorry. Some people have considered it as a fertile material to produce the fissile 233U in a breeder, but even with a reactor kernel of plutonium, regeneration seems impossible to achieve. Though, some limited proportion of 232Th can be and is consumed in normal pressured-water reactors (VVER) as a complement to 235U, so you could base on the heat produced by the fission of 233U, and optionally its production from 232Th.

Offline Enthalpy

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equations for fission of U235 that I'm seeing online seem to vary

That's a good thing, because the fission of 235U is very varied. Check "fission products": there are hundreds of nuclides, some of them very short-lived. The fission makes often two big mid-sized nuclides but sometimes three, and the number of emitted neutrons varies too. Even spontaneous fission makes a vast spectrum of products.

Offline gippgig

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If you just want a rough figure divide the energy produced from the coal by the average energy produced by fission/fusion of the particular nuclide(s) (being careful to convert the units properly). To get a fairly precise answer you need to specify exactly what is meant by "fission of U-235 to produce same amount of energy" etc. Is it the number of fissioning atoms that would immediately produce the same amount of energy? The number of fissioning atoms that would eventually produce the same amount of energy (since decay of fission products produces roughly 7% of the final energy)? The number of atoms that would produce the same amount of energy if used to fuel a nuclear reactor (since some of the atoms don't fission when hit by a neutron, and the fraction varies depending on the type of reactor (thermal reactor vs. fast reactor))? Do you include energy produced when neutrons from 235U fission split other nuclides if any fissionable ones are present? Energy from neutrons splitting other atoms bred from fertile nuclides if any are present? And on and on and on...

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