Nuclear Fission initiated fusion

[legoclone09]

Nuclear fusion needs lots of power to start it up, so why not use a smaller fission reaction to initiate a controlled fusion reaction? Would it be possible? Or would it explode like a fission-initiated nuclear bomb, or would it need the thingy that is in between the fission and the fusion part of a nuclear bomb that the government hasn't told us what it is?

EDIT: I mean using a nuclear fission reaction to jumpstart a nuclear fusion reaction, like for civilian or industrial power for home/business electricity.

Edited February 16, 2016 by legoclone09

[KSK]

I'm not sure it would work. If I remember correctly, the Ulam-Teller mechanism relies on focusing the radiation from a fission explosion into the fusion fuel, triggering the fusion reaction. I'm not sure that a controlled fission reaction (whch I presume you have in mind) would create enough radiation pressure to cause a fusion reaction.

You could of course go for a Super Orion type design using small (for certain values of small) hydrogen bombs rather than fission bombs but I'm not sure I'd really describe those as controlled.

 

Edited February 10, 2016 by KSK

[sevenperforce]

What if you filled a cylinder with uranium, lithium, and deuterium, then spun it up centrifuge-style? The uranium would migrate outward and the lighter elements would migrate inward. Eventually, the uranium would reach a high enough density to go critical, producing radiation pressure on the lighter elements in the center, ultimately causing them to fuse.

I think.

[fredinno]

58 minutes ago, legoclone09 said:

Nuclear fusion needs lots of power to start it up, so why not use a smaller fission reaction to initiate a controlled fusion reaction? Would it be possible? Or would it explode like a fission-initiated nuclear bomb, or would it need the thingy that is in between the fission and the fusion part of a nuclear bomb that the government hasn't told us what it is?

No, the main problem isn't getting the temperature and pressure for fusion-that's easy. The problem have to do with energy production, tritrium, and neutron irradiation.

[legoclone09]

Yeah, the fission reaction would use less electrical energy than the reaction outputs, and it would only need to be used when you first start the reactor.

[MatterBeam]

While the magnets of a fusion reactor would be able to contain the hydrogen plasma, they would collapse under the strain of hot uranium ions, many dozens of times heavier. A fission detonation would destroy the reactor before any contained fusion could take place.

[wumpus]

2 minutes ago, MatterBeam said:

While the magnets of a fusion reactor would be able to contain the hydrogen plasma, they would collapse under the strain of hot uranium ions, many dozens of times heavier. A fission detonation would destroy the reactor before any contained fusion could take place.

I was assuming that the uranium would shield the plasma from the magnets, causing the plasma to escape and destroy the reactor.  I'm not sure there is really a difference between the two explanations (there is an academic difference if the uranium atoms don't move, if they do they are the same).

My guess is that you would have to make the magnetic generators out of uranium* and actually have them react while conducting all the electricity and generating the necessary fields.  Very non-linear design, very difficult, but assuming all the likely showstoppers (starting with getting the uranium to conduct electricity) don't stop the show, it might be something (although there are likely millions of more likely ways to make a fusion reactor.  Learn the issues first...)

3 hours ago, fredinno said:

No, the main problem isn't getting the temperature and pressure for fusion-that's easy. The problem have to do with energy production, tritrium, and neutron irradiation.

Er, as far as I know, while you can get the temperature and pressure for fusion, the problems with energy production mostly come from getting it to sustain itself (tritium and neutron issues are for later).  This is certainly a means of producing said temperatures economically, while getting the pressures is going to be another story (thus all the issues I mentioned about magnetics.  I seem to recall my chemistry professor mentioning that heat wasn't a big issue in chemical engineering, but pressure was the huge cost.  Now think in terms of pressures higher than any chemical reaction needs...).

If you really like this idea (I like it, I just can't see any way to maintain the pressure), find out when it was proposed in the 1940s and 50s (or possibly in the 60s) and all the arguments against it (there really isn't anything new under Kerbol, there is just stuff that there wasn't infrastructure and failed and stuff that there was infrastructure for that worked).  Try to figure out how modern technology can get around those arguments in ways that were inconceivable in that era.  Then propose it again.

* I'm assuming some sort of alloy.  Pretty much all U, and expect to need more U235 to replace both the U235 and U238 that the alloy stuff for conduction is replacing.  Also conduction goes down with heat, so don't even think this will ever work.

[magnemoe]

41 minutes ago, MatterBeam said:

While the magnets of a fusion reactor would be able to contain the hydrogen plasma, they would collapse under the strain of hot uranium ions, many dozens of times heavier. A fission detonation would destroy the reactor before any contained fusion could take place.

This gives me an idea.
We have the nuclear salt water engine http://www.projectrho.com/public_html/rocket/enginelist.php#nswr
Basically an continuous nuclear explosion. It gives great trust and and a less bumpy ride than an orion, 
However the isp is only 8000s who is pretty low. How about injecting some tritium, this should increase both trust and ISP. 

[MatterBeam]

1 minute ago, magnemoe said:

This gives me an idea.
We have the nuclear salt water engine http://www.projectrho.com/public_html/rocket/enginelist.php#nswr
Basically an continuous nuclear explosion. It gives great trust and and a less bumpy ride than an orion, 
However the isp is only 8000s who is pretty low. How about injecting some tritium, this should increase both trust and ISP. 

The NSWR might be pushed to sufficient temperatures in its most extreme versions, but it will never reach the pressures required to contain the tritium long enough to force it to interact and fuse.

[DerekL1963]

3 hours ago, magnemoe said:

We have the nuclear salt water engine http://www.projectrho.com/public_html/rocket/enginelist.php#nswr

No, we don't.   We have a proposal that's not actually on a bar napkin because Robert Zubrin translated his handwaving into the formal language of a scientific paper.   And that's pretty much where the matter rests,  there's been no analysis or simulation done at any significant level.   Nobody knows if the thing will actually work or not.

And to answer the OP's original question, no, it's not possible.

[magnemoe]

10 hours ago, DerekL1963 said:

No, we don't.   We have a proposal that's not actually on a bar napkin because Robert Zubrin translated his handwaving into the formal language of a scientific paper.   And that's pretty much where the matter rests,  there's been no analysis or simulation done at any significant level.   Nobody knows if the thing will actually work or not.

And to answer the OP's original question, no, it's not possible.

You are right, its an very theoretical concept with lots of unknown factors. 
Also the idea is pretty insane as it is, wherefore boosting it with fusion is more insane ans make sense.

Now its plenty of concept for pretty realistic fusion engines a few have even been tested. They don't use fission. 
An fusion engine does not have to be break even, it just have to let the fusion energy improve ISP and trust so much over an ion or vasmir engine its look like an good idea. Vasmir design itself reminds me of a fusion engine even if it don't produce any fusion. 

[fredinno]

On February 11, 2016 at 4:45 PM, wumpus said:

I was assuming that the uranium would shield the plasma from the magnets, causing the plasma to escape and destroy the reactor.  I'm not sure there is really a difference between the two explanations (there is an academic difference if the uranium atoms don't move, if they do they are the same).

My guess is that you would have to make the magnetic generators out of uranium* and actually have them react while conducting all the electricity and generating the necessary fields.  Very non-linear design, very difficult, but assuming all the likely showstoppers (starting with getting the uranium to conduct electricity) don't stop the show, it might be something (although there are likely millions of more likely ways to make a fusion reactor.  Learn the issues first...)

Er, as far as I know, while you can get the temperature and pressure for fusion, the problems with energy production mostly come from getting it to sustain itself (tritium and neutron issues are for later).  This is certainly a means of producing said temperatures economically, while getting the pressures is going to be another story (thus all the issues I mentioned about magnetics.  I seem to recall my chemistry professor mentioning that heat wasn't a big issue in chemical engineering, but pressure was the huge cost.  Now think in terms of pressures higher than any chemical reaction needs...).

If you really like this idea (I like it, I just can't see any way to maintain the pressure), find out when it was proposed in the 1940s and 50s (or possibly in the 60s) and all the arguments against it (there really isn't anything new under Kerbol, there is just stuff that there wasn't infrastructure and failed and stuff that there was infrastructure for that worked).  Try to figure out how modern technology can get around those arguments in ways that were inconceivable in that era.  Then propose it again.

* I'm assuming some sort of alloy.  Pretty much all U, and expect to need more U235 to replace both the U235 and U238 that the alloy stuff for conduction is replacing.  Also conduction goes down with heat, so don't even think this will ever work.

Also, it produces long-lasting nuclear waste, something that fusion aims to prevent.

[wumpus]

10 hours ago, fredinno said:

Also, it produces long-lasting nuclear waste, something that fusion aims to prevent.

Unless you can make multi-tesla magnets with only helium*, you are going to scatter neutrons into matter that is going to get radioactive.  At some point we will have to get over the idea that diffusing pollution is always better than concentrating pollution (is it better to litter than throw you trash in a landfill?).  While I'm not against chasing fusion, we really need to do more with fission and less with coal.

* for Tokomak-style reactors.  The national ignition facility laser confinement might be able to pull this off.

[MatterBeam]

The problem with fusion, in my opinion, is not feasability or technical issues. Those can be solved eventually. It's the fact that there's a long way to go with current energy sources, and applying today's technology to breeder reactors and seawater uranium filtering will power civilization for millions of years.

 

DT fusion is the easiest, and produces neutron radiation, but it is less radioactive than fission, and I'm confident we're handling current levels quite well.

[legoclone09]

On 2/12/2016 at 9:55 AM, MatterBeam said:

The problem with fusion, in my opinion, is not feasability or technical issues. Those can be solved eventually. It's the fact that there's a long way to go with current energy sources, and applying today's technology to breeder reactors and seawater uranium filtering will power civilization for millions of years.

 

DT fusion is the easiest, and produces neutron radiation, but it is less radioactive than fission, and I'm confident we're handling current levels quite well.

Our current handling of nuclear waste isn't the best because environmental groups want to 'save' the environment by not letting us make Yucca mountain for storing waste.

[MatterBeam]

33 minutes ago, legoclone09 said:

Our current handling of nuclear waste isn't the best because environmental groups want to 'save' the environment by not letting us make Yucca mountain for storing waste.

As far as I know, the storage of nuclear waste 'problem' is entirely a political issue. The US asks countries to store their waste on its soil, at prices that make it cheaper than developing waste recycling or storage infrastructure of their own.

[legoclone09]

8 hours ago, MatterBeam said:

As far as I know, the storage of nuclear waste 'problem' is entirely a political issue. The US asks countries to store their waste on its soil, at prices that make it cheaper than developing waste recycling or storage infrastructure of their own.

Ah, I heard in another thread it was environmentalists as well. It probably is both, to be honest. 

[MatterBeam]

16 minutes ago, legoclone09 said:

Ah, I heard in another thread it was environmentalists as well. It probably is both, to be honest. 

To be fair, environmentalists have very little influence in the grand scheme of things. What really matters in which way the money is flowing in politician's pockets. The vast majority of 'green money' in politics actually originates from oil companies and the biggest polluters.

[legoclone09]

1 hour ago, MatterBeam said:

To be fair, environmentalists have very little influence in the grand scheme of things. What really matters in which way the money is flowing in politician's pockets. The vast majority of 'green money' in politics actually originates from oil companies and the biggest polluters.

Ah, didn't know that. Let's not derail and talk about the possibility of this idea.

[MatterBeam]

45 minutes ago, legoclone09 said:

Ah, didn't know that. Let's not derail and talk about the possibility of this idea.

True.

A more pertinent fusion enabler is antimatter!

[Guest]

Meanwhile in @legoclone09's house...

"Come on, dinner time!"

"Hold on!  I need to finish taking apart this smoke detector!"

On February 12, 2016 at 1:18 AM, fredinno said:

Also, it produces long-lasting nuclear waste, something that fusion aims to prevent.

True

[legoclone09]

23 minutes ago, CliftonM said:

Meanwhile in @legoclone09's house...

"Come on, dinner time!"

"Hold on!  I need to finish taking apart this smoke detector!"

True

Rather ironically, I was eating dinner when you posted that.

 

32 minutes ago, MatterBeam said:

True.

A more pertinent fusion enabler is antimatter!

Well, antimatter is insanely hard to get. And it's terrible if it spills. Once we can get it 'easily' (relative to getting it now) antimatter fusion would be useful.

Edited February 16, 2016 by legoclone09

[magnemoe]

1 hour ago, legoclone09 said:

Ah, didn't know that. Let's not derail and talk about the possibility of this idea.

An large scale orion nuclear pulse engine would use this. Yes its nuclear bombs exploding but used controlled. You must have something like an asteroid or starship to push but can then use multi megaton bombs as charges, this will give far better ISP than the fision version. 

[legoclone09]

36 minutes ago, magnemoe said:

An large scale orion nuclear pulse engine would use this. Yes its nuclear bombs exploding but used controlled. You must have something like an asteroid or starship to push but can then use multi megaton bombs as charges, this will give far better ISP than the fision version. 

Yeah I know Orion would be more efficient, but what I meant in the OP was using a controlled-ish fission reaction to jumpstart a controlled nuclear fusion reaction in a reactor. Let me edit the OP to clarify what I meant.

[MatterBeam]

This might re-invigorate the topic:

NSWR revisited

Neutron flux from fissioning sources initates fusion within fusion fuels.