Fission-Fusion Reactor

[Iago]

The holy grail of nuclear engineers everywhere is the power of fusion, but it has yet to be properly utilized. Fusion has been promised "within the decade" since the 70 (or whatever).

The only application fusion has been used for is in H-bombs, and bombs are quite different to reactors. How do you replace the fuels after you've spent them? How do you keep the fissiles equal on all sides of the fusion?

The only way I can think of is some kind of gas-core reactor, which uses vaporized/powder fissiles. Also, any nuclear reactor should use Thorium from now on. Much better.

Any thoughts?

[StrandedonEarth]

Yes, from everything I've read about thorium, I keep wondering why it isn't more widely used. I know that it wasn't popular originally because it can't be used to breed weapon-grade material, but we just want power now...

Edited March 16, 2016 by StrandedonEarth
stupid typo has been quoted a few times now, I can't believe I missed it. It makes me sound so unedjumacated.

[Iago]

The reason Uranium and Plutonium has been used is because of weapons development, yes. But also because Thorium needs a specific reactor. You can't just toss Thorium in a conventional uranium reactor.

[SingABrightSong]

10 minutes ago, Iago said:

The reason Uranium and Plutonium has been used is because of weapons development, yes. But also because Thorium needs a specific reactor. You can't just toss Thorium in a conventional uranium reactor.

Except for CANDU, as I recall.

[Bill Phil]

The holy grail isn't the fusion itself, it's keeping it going.

[sgt_flyer]

4 hours ago, Iago said:

The holy grail of nuclear engineers everywhere is the power of fusion, but it has yet to be properly utilized. Fusion has been promised "within the decade" since the 70 (or whatever).

The only application fusion has been used for is in H-bombs, and bombs are quite different to reactors. How do you replace the fuels after you've spent them? How do you keep the fissiles equal on all sides of the fusion?

The only way I can think of is some kind of gas-core reactor, which uses vaporized/powder fissiles. Also, any nuclear reactor should use Thorium from now on. Much better.

Any thoughts?

they don't use fissile material to provide the necessary energy to kickstart the fusion reaction in fusion reactors , and current fusion reactors only use magnetically confined plasmas  (so basically 'gas core')

in H-Bombs, they use a fission core to give the fusion precursor (lithium 6) enough pressure & temperature + an intense neutron shower. those neutrons will fuse with the li-6, breaking it into Helium + Tritium. the newly formed Tritium will fuse too, (tritium + tritium) forming Helium + 2 neutrons, some of which would end up colliding on any remaining LI-6, furthering the fusion.

concerning fusion, current test reactors all use only gaseous fusion fuels (deuterium  and tritium,those a re easier to fuse), though they would ultimately want other more energetic fusions.

there's two 'main' fusion processes currently experimented, one used in Tokamaks and Stellarators, the other in polywells.

in Tokamaks / Stellarators, they heat up the fuel gases (one technique used is microwave heating) to a hot enough plasma state. under these conditions, the fuel atoms are ionised simply by entering plasma state, allowing to trap them in a magnetic field, preventing the plasma from expanding. (so you have enough density to get a chain reaction).

the resulting heavier fusion products end up being too heavy to be maintained in the field for long.

 

in Polywells, they generate a 'potential well' in the middle of the device, and the send the ionised atoms towards this well where they'll end up compressing each other, increasing the temperature through compression until fusion is achieved.

 

Current main problems for fusion are : maintaining the reaction for long durations, generating net power (as you need to power your electromagnetic coils), keeping the magnetic field stable, and managing the high energy neutron damage (as the free neutrons can't be magnetically confined, if they don't impact another atom before leaving the magnetic field, it'll collide with the fusion equipment hard enough to do some damage and make it become radioactive.

for testing reaction duration, generating net power, and managing Neutron damage, the tokamak ITER being built in France (through international funding).

ITER won't be generating electricity to sustain itself, they'll just send up the resulting heat into radiators. (still, they'll know if they'll have enough thermal energy output)

for neutron damage management, one possibility they'll study will be to use Lithium blankets to catch the escaping neutrons. those neutrons would end up fusing with the lithium, breeding some tritium, which could be used as fusion fuel later.

 

concerning magnetic field stability, the Stellarator Wendelstein 7-X is undergoing preliminary test now they finished to build it in germany. (in stellarators, the magnetic coils are 'torsaded' to generate a more uniform magnetic field).

Polywells by themselves are being tested to see how this alternative fusion system handle itself.

 

 

Edited March 16, 2016 by sgt_flyer

[lajoswinkler]

8 hours ago, StrandedonEarth said:

Yes, from everything I've red about thorium, I keep wondering why it isn't more widely used. I know that it wasn't popular originally because it can't be used to breed weapon-grade material, but we just want power now...

For thorium to work, you need uranium. Thorium by itself won't do anything. The reason it's not used is way more complex than just weapons uranium/plutonium could offer.

[peadar1987]

5 hours ago, lajoswinkler said:

For thorium to work, you need uranium. Thorium by itself won't do anything. The reason it's not used is way more complex than just weapons uranium/plutonium could offer.

Exactly. Thorium reactors work by "breeding" Uranium 233 from the Thorium, and using that to fuel a reactor. Thorium is not "better", in fact it is significantly worse as a fission fuel. Its main advantage is that it is far more abundant (which as advantages go isn't a bad one, but it hardly makes it a perfect fuel)

[fredinno]

21 hours ago, StrandedonEarth said:

Yes, from everything I've red about thorium, I keep wondering why it isn't more widely used. I know that it wasn't popular originally because it can't be used to breed weapon-grade material, but we just want power now...

Nuclear Fission research in general has slowed to a crawl because of how much people dislike nuclear power.

6 hours ago, peadar1987 said:

Exactly. Thorium reactors work by "breeding" Uranium 233 from the Thorium, and using that to fuel a reactor. Thorium is not "better", in fact it is significantly worse as a fission fuel. Its main advantage is that it is far more abundant (which as advantages go isn't a bad one, but it hardly makes it a perfect fuel)

And, it produces less nuclear waste.

And it is very difficult to be turned into bomb material.

https://en.wikipedia.org/wiki/Thorium-based_nuclear_power#Possible_benefits

[Bill Phil]

7 hours ago, peadar1987 said:

Exactly. Thorium reactors work by "breeding" Uranium 233 from the Thorium, and using that to fuel a reactor. Thorium is not "better", in fact it is significantly worse as a fission fuel. Its main advantage is that it is far more abundant (which as advantages go isn't a bad one, but it hardly makes it a perfect fuel)

The funny thing is that fission relies on relatively rare elements and isotopes, while fusion relies on relarively abundant elements and isotopes.

[sgt_flyer]

2 hours ago, fredinno said:

Nuclear Fission research in general has slowed to a crawl because of how much people dislike nuclear power.

And, it produces less nuclear waste.

And it is very difficult to be turned into bomb material.

https://en.wikipedia.org/wiki/Thorium-based_nuclear_power#Possible_benefits

@StrandedonEarth

beware, incoming wall'o'text

the key advantage in reducing waste in thorium reactors comes not from Thorium itself, but from using molten salts. there has been some proposed uranium salts too.

the main problem for solid fuel rod based fission reactors is that the atoms in the rod don't move. as soon as too much of the fissile material has been transmuted during the fission reaction, the fission reaction can't be sustained anymore (too much neutrons would impact the already transmuted atoms, not contributing to the chain reaction))

which means you end up having a lot of spent material that could still be usable, if it was not so radioactive  (reprocessing spent fuel rods into Mox fuel rods is a way to 'increase' the amount of fissile material used in solid fuel rods.)

Molten salt reactors overcome this problem by continuously reprocessing the fuel, because of it's liquid nature, it can be pumped in and out of the reactor (and passed through heat exchangers at the same time).

this means you need to keep the salts in liquid state all the time during reactor operation.

you'll also have an easier time for separating the used fuel from the fuel still fissile while in liquid state,  allowing to use almost all your nuclear fuel (as you add fresh fuel to replace those that were extracted)

some problems / advantages :

most molten salts notably use fluoride in the composition of the salts  so extra care is needed before making the salts, and be sure that the materials (from your pumps, reactor core and pipes) can handle all the high temperature molten salts, though thankfully molten salts don't require high pressure in the primary loop in addition to the rest . the reactor would also need a way to manage the damage that could caused by escaping neutrons. (one possibility, also valid for fusion reactors, is to have 'blankets' of precursor material, so you can breed those materials instead of damaging the reactor walls) 

one big inconvenient of thorium molten salt reactors, is the need to 'kickstart' the initial reaction (so enough thorium becomes transmuted to sustain further reactions). to kickstart it, you basically need weapon grade fissile material (uranium or plutonium) - and in larger amounts than the current production used for making nuclear weapons. 

so while you are having waste that is not usable to make weapons, you need to make weapon grade fuel before, which poses several problems, as a country that would build the enrichment facilities needed to make that fuel could also use it to make weapons too - politically limiting it only to the countries already using nuclear weapons. if another country wanted thorium reactors, it would likely need to have to rely on those countries to get this fuel. imagine the unbelievable amount of security that would surround such a transfer  - which would lilely make the 'buying' country entirely dependant on his supplier. (hopefully, once you have enough thorium MSR running,if you use thorium panels to protect the reactor you potentially could use the breeded atoms on those to kickstart other reactors)

 

Edited March 16, 2016 by sgt_flyer

[StrandedonEarth]

34 minutes ago, sgt_flyer said:

to kickstart it, you basically need weapon grade fissile material (uranium or plutonium) - and in larger amounts than the current production used for making nuclear weapons.

That was one part I hadn't heard.  I thought it could be kickstarted by bombarding it with neutrons, from some sort of particle accelerator.

[sgt_flyer]

12 hours ago, StrandedonEarth said:

That was one part I hadn't heard.  I thought it could be kickstarted by bombarding it with neutrons, from some sort of particle accelerator.

well, that's just breeding fertile thorium-232 into uranium-233 . you'll have better results doing it before turning the stuff into salts  your neutron generators would only affect the 'surface' of the fuel, and would have to resist the high temperatures of the liquid fuel (as the neutron source would need to be quite close). adding salts of fissile fuels in the reactor would allow for a much broader and homogen transmutation

keep in mind - you can't magnetically accelerate 'lone' neutrons by themselves - they have no charge  neutron generators basically accelerate ions of hydrogen isotopes against a 'thin' target (fusion level of power), to get some lone neutrons upon impact . 

you'd likely need to have neutrons energetic enough to breed it. - the kind of power required to breed enough of your thorium with neutron generators would likely be extremely innefficient compared to the powers needed to enrich fissile fuels (which is basically 'concentrating'  only the fissile atoms that you are interested in.)

edit :

@StrandedonEarth

found a theoritical thorium reactor that uses a particle accelerator.

https://en.wikipedia.org/wiki/Accelerator-driven_sub-critical_reactor

built to remain subcritical, the reaction would stop if the particle accelerator stops.

though, couldn't find how much power such an accelerator would need

Edited March 17, 2016 by sgt_flyer

[peadar1987]

13 hours ago, fredinno said:

Nuclear Fission research in general has slowed to a crawl because of how much people dislike nuclear power.

And, it produces less nuclear waste.

And it is very difficult to be turned into bomb material.

https://en.wikipedia.org/wiki/Thorium-based_nuclear_power#Possible_benefits

Pretty much what Sgt_flyer said. Although I'd forgotten about the weapons proliferation thing, so thanks for reminding me.

[Angeltxilon]

On 14/3/2016 at 11:13 PM, Iago said:

The only application fusion has been used for is in H-bombs, and bombs are quite different to reactors. How do you replace the fuels after?you've spent them? How do you keep the fissiles equal on all sides of the fusion?

Have you heard about PACER project?

https://en.wikipedia.org/wiki/Project_PACER

Edited April 14, 2016 by Angeltxilon

[Iago]

No, but I had considered it. I came to the conclusion that it would be the only fusion power we can extract with current technology. Doesn't seem very efficient.