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Author Topic: Combining fusion and fission energy  (Read 5690 times)

Offline YordanGeorgiev

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Combining fusion and fission energy
« on: 28/11/2007 08:13:12 »
Fusion energy is pointed to be the probable energy problem solver for the humanity.

Yet in order to produce it economically different hurdles have to be overcome.
One of them is the extremely large amount of energy, which is used to get the temperature of the plasma higher and the second is to keep the plasma confined ...

My question is:

Why do they not use a small but sufficient amount of radioactive material as an additive to the fusion fuel to help boost the reaction?


 

lyner

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Combining fusion and fission energy
« Reply #1 on: 28/11/2007 12:51:12 »
The conditions for fission in a  normal reactor are not the same as those needed for fusion.
Agreed, a fusion (H) bomb has been made to work using extreme conditions generated by a fission explosion (A) but the extra problems of containing the products of a fission reaction and actually controlling the reactions, would surely make it impracticable to use that system in a working reactor.
Without fission, the fusion process is, essentially, fairly clean, remember. Fission generates a lot of products which decayed from the Earth's surface  hundreds of millions of years ago, in some cases.
 

Offline syhprum

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Combining fusion and fission energy
« Reply #2 on: 28/11/2007 21:02:41 »
I should think the energies realised by fission are trivial compared to the 10^8 K temperatures needed for fusion and would probably impare the process
 

lyner

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Combining fusion and fission energy
« Reply #3 on: 28/11/2007 21:51:21 »
Were not the early fusion bombs initiated with fission?
I understood that the first British 'Fusion' Bomb never got beyond the Fission stage.
It served its  political purpose, though, apparently. It made a big hole in an atoll.
 

Offline Mr Andrew

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Combining fusion and fission energy
« Reply #4 on: 28/11/2007 23:07:37 »
As far as the confinement bit, I read somewhere that researchers have managed to confine super hot plasma in a magnetic coil system.  I think it was on the website, PhysOrg.com, which is a science news website.
 

another_someone

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Combining fusion and fission energy
« Reply #5 on: 29/11/2007 01:36:22 »
As far as the confinement bit, I read somewhere that researchers have managed to confine super hot plasma in a magnetic coil system.  I think it was on the website, PhysOrg.com, which is a science news website.

That is what the tokamak is all about, but last time I heard, they'd only got it to work for a very short period of time before it became unstable, and not long enough to generate useful amounts of energy (if this problem has been overcome, then we are well on the way to a viable continuous fusion reactor that can eb used to commercial energy generation).
 

another_someone

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Combining fusion and fission energy
« Reply #6 on: 29/11/2007 01:37:41 »
Were not the early fusion bombs initiated with fission?
I understood that the first British 'Fusion' Bomb never got beyond the Fission stage.
It served its  political purpose, though, apparently. It made a big hole in an atoll.

The first British 'fusion' bomb was a hoax used to con the Americans into co-operating with the British scientists to hand over all their secrets, and allow the British to create a real fusion bomb.
 

another_someone

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Combining fusion and fission energy
« Reply #7 on: 29/11/2007 01:42:19 »
The conditions for fission in a  normal reactor are not the same as those needed for fusion.
Agreed, a fusion (H) bomb has been made to work using extreme conditions generated by a fission explosion (A) but the extra problems of containing the products of a fission reaction and actually controlling the reactions, would surely make it impracticable to use that system in a working reactor.
Without fission, the fusion process is, essentially, fairly clean, remember. Fission generates a lot of products which decayed from the Earth's surface  hundreds of millions of years ago, in some cases.

My understanding is that it rather depends on the type of fusion you are using.  Some of the lithium3He reactions can be fairly clean (which is why all the fuss was made about the moon having slightly higher ratio of 3He than the Earth), but conventional hydrogen fusion, I believe, still gives off quite a lot of neutrons, which could cause problems when it irradiates the container in which the reaction is happening (maybe not as bad as fission, but still not totally clean).
« Last Edit: 29/11/2007 22:55:12 by another_someone »
 

lyner

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Combining fusion and fission energy
« Reply #8 on: 29/11/2007 18:21:21 »
So help me, please. How is the fusion initiated in a fusion bomb, if it's not with a fission explosion?
I heard the same sort of story about the 'fusion bomb' but that it was a failure rather than a hoax.
« Last Edit: 29/11/2007 18:24:09 by sophiecentaur »
 

Offline lightarrow

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Combining fusion and fission energy
« Reply #9 on: 29/11/2007 19:44:22 »
Fusion energy is pointed to be the probable energy problem solver for the humanity.

Yet in order to produce it economically different hurdles have to be overcome.
One of them is the extremely large amount of energy, which is used to get the temperature of the plasma higher and the second is to keep the plasma confined ...

My question is:

Why do they not use a small but sufficient amount of radioactive material as an additive to the fusion fuel to help boost the reaction?
Because a small amount wouldn't be enough; differently from fusion, fission requires a minimum amount of matter (the "critical mass": http://en.wikipedia.org/wiki/Critical_mass).
You can control a fission reaction in a nuclear fission reactor, but if you want fusion you couldn't controll it and you would have...an H bomb.
« Last Edit: 29/11/2007 19:48:54 by lightarrow »
 

Offline Soul Surfer

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Combining fusion and fission energy
« Reply #10 on: 29/11/2007 19:48:42 »
To initiate fusion in a suitable material you need to do two things; firstly to heat it up to a high enough temeperature and secondly to hold it confined while it has time to fuse and create the energy. The energy form a fission explosion is about the only way this can be done on a large scale to create a fusion explosion.  An intense blast of penetrating radiation from the fission bomb is focussed to heat up the fusion material almost instantly thoroughout its bulk.  Similarly the design allows the shock wave from the fission explosion to be reflected hold the fusion material together.  All this has to be precisely designed to work first time because there is no way of creating a series of experiments that lead up to the design of the device.

It is not appropriate to go into much more detail on these pages
 

Offline Soul Surfer

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Combining fusion and fission energy
« Reply #11 on: 29/11/2007 19:52:49 »
Fusion power generators do the same thing but use much smaller quantities of material confined using electromagnetic fields.  The fusion comes from the nucleii colliding at high temeperature and extra radiation from a radioactive source would do little to help this.
 

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Combining fusion and fission energy
« Reply #11 on: 29/11/2007 19:52:49 »

 

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