Can the second fluid be a fine powder

Processing the liquid fuel/blanket of a fluoride reactor.
cloa513
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Can the second fluid be a fine powder

Post by cloa513 » Aug 30, 2011 8:14 am

Can the second fluid be instead finely ground Thorium or a thorium compound powder (micro or nano) in a carrier fluid to separate particles and enable flow, then you can achieve high cross-section to neutrons so small tubing is needed, the powder could be clean then vapourised continuously in a laser high vaccuum tube so its a continuous process. Powders are abrasive but not corrosive. Has this been considered?

Owen T
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Re: Can the second fluid be a fine powder

Post by Owen T » Aug 30, 2011 9:10 am

The aqueous homogenous reactor was a predecessor of the molten salt reactor. In that design a slurry was considered for the blanket because no suitable water-soluble thorium compound existed.

A slurry is difficult to manage without settling and clogging. It was only considered out of necessity. Since thorium salts soluble in the carrier salt exist there is no good reason to go back to slurries.

cloa513
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Re: Can the second fluid be a fine powder

Post by cloa513 » Aug 30, 2011 8:07 pm

No reason the fluid can't be a gas and continuously flowing.

Cyril R
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Re: Can the second fluid be a fine powder

Post by Cyril R » Aug 31, 2011 11:49 am

cloa513 wrote:No reason the fluid can't be a gas and continuously flowing.
There is a reason - not enough density. The blanket needs to grab neutrons in fertile material. Neutrons won't be much bothered by a gas.

Besides, there are no radiation resistant thorium gasses.

jagdish
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Re: Can the second fluid be a fine powder

Post by jagdish » Sep 01, 2011 12:19 am

Rolls of metallic wire gauze is the alternative I keep thinking of. They could be dipped in the core fuel and raised or lowered to act as fertile fuel and a control system. They will have a large surface area, somewhere between solid fuel and the suspended fuel for nuclear/chemical systems.
Strips at the periphery could act as a reflector-blanket.
Solid fuel dipped in moderator/coolant is what we are used to. With liquid fuel, variable fertile fuel will control neutron flux effectively. Irradiation of fertile fuel and reactivity could be balanced. It could be something like regenerative braking of vehicles.

Lars
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Re: Can the second fluid be a fine powder

Post by Lars » Sep 01, 2011 9:55 am

What is this gauze made of?
It needs to tolerate hot fluoride salts, intense neutron flux, and a pretty strong fluid flow (something like 0.5 meters/sec even in the slowest region of flow and several times this at the entrance and exit points).

Cyril R
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Re: Can the second fluid be a fine powder

Post by Cyril R » Sep 01, 2011 3:15 pm

Lars wrote:What is this gauze made of?
It needs to tolerate hot fluoride salts, intense neutron flux, and a pretty strong fluid flow (something like 0.5 meters/sec even in the slowest region of flow and several times this at the entrance and exit points).
Jagdish is talking about a thorium metal wire. Dip it in the molten fluoride fuel salt to put more thorium and U233 in.

It is interesting. I don't know if it will work.

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Lindsay
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Re: Can the second fluid be a fine powder

Post by Lindsay » Sep 01, 2011 5:56 pm

I have looked at metallic thorium as neutron shield and it does a remarkably poor job, one needs at least 50 mm or more to keep the leakage to an acceptably low number and unfortunately one also needs proper simulation codes to evaluate the real neutron stopping power of a specific structural element and I don't have access to that unfortunately.

For thin structural metals, neutrons generally seem to zip straight through with few interactions. So I'm not confident that a thorium gauze will do much of anything, aside from providing some fine regulation if you were looking for it.

Lars
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Re: Can the second fluid be a fine powder

Post by Lars » Sep 01, 2011 8:51 pm

Cyril R wrote:
Lars wrote:What is this gauze made of?
It needs to tolerate hot fluoride salts, intense neutron flux, and a pretty strong fluid flow (something like 0.5 meters/sec even in the slowest region of flow and several times this at the entrance and exit points).
Jagdish is talking about a thorium metal wire. Dip it in the molten fluoride fuel salt to put more thorium and U233 in.

It is interesting. I don't know if it will work.
You are going to put a fine gauze made of material that dissolves in the salt under the flow of 0.5 meters/sec - won't it simply dissolve almost instantly?
I thought Jagdish was talking about something to provide a control rod like function?
This seems like another way to add thorium to the fuel salt and little else.

Am I missing something?

jagdish
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Re: Can the second fluid be a fine powder

Post by jagdish » Sep 02, 2011 12:28 am

There is a limit to solubility of thorium in any medium, usually quite small. Most of thorium will hang around as metal. If U233 created dissolves somewhat more, it is all to the good.
In the light water breeder, raising or lowering of fuel rods was used to control the reactivity. It could be used in other reactors. The absorption cross-section of thorium is more than that of uranium. I am suggesting using rolled metallic thorium wire gauze it in place of suspended thorium powder but in the manner of fuel rods and control rods. Handling rolls of wire gauze should be as easy as fuel or control rods in a conventional reactor.
Use of thorium as shielding is a different issue which I have suggested in another thread.

Cyril R
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Re: Can the second fluid be a fine powder

Post by Cyril R » Sep 02, 2011 3:42 am

Lars wrote:
Cyril R wrote:
Lars wrote:What is this gauze made of?
It needs to tolerate hot fluoride salts, intense neutron flux, and a pretty strong fluid flow (something like 0.5 meters/sec even in the slowest region of flow and several times this at the entrance and exit points).
Jagdish is talking about a thorium metal wire. Dip it in the molten fluoride fuel salt to put more thorium and U233 in.

It is interesting. I don't know if it will work.
You are going to put a fine gauze made of material that dissolves in the salt under the flow of 0.5 meters/sec - won't it simply dissolve almost instantly?
I thought Jagdish was talking about something to provide a control rod like function?
This seems like another way to add thorium to the fuel salt and little else.

Am I missing something?

I think that, in this idea, you’d have a 1.5 fluid with a metal blanket (dry, solid) that is pulled mechanically around the core barrier. Then the bred U233 would be added by submersing the irradiated metal in the fuel salt loop. Like you said the latter is just a way to put thorium and U233 in, but not a very good one probably, for two reasons. First you can’t control the amount of thorium versus U233 that goes in the fuel salt. You’ll have too much thorium in it most likely. Second this method of adding Th and U233 is going to push the redox on the far side of reducing, which then plays havoc with your internal fuel chemistry and structural materials (formation of uranium-233 carbides on graphite for example).

The problem of the blanket isn’t that you can’t have fluoride on the blanket side. The problems are with the neutron flux damaging the barrier. If you already have fluoride on the fuel side, it is not a big deal to also have fluoride on the blanket side. In fact that would reduce oxide corrosion and also eliminate the hydrostatic stresses. So I guess I’m not convinced of the thorium metal concept.

cloa513
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Re: Can the second fluid be a fine powder

Post by cloa513 » Sep 03, 2011 6:31 pm

Cyril R wrote:
cloa513 wrote:No reason the fluid can't be a gas and continuously flowing.
There is a reason - not enough density. The blanket needs to grab neutrons in fertile material. Neutrons won't be much bothered by a gas.

Besides, there are no radiation resistant thorium gasses.
The gas is a carrier fluid. The Thorium or Thorium compound is still a powder so it would have extremely high cross-section.

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