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PostPosted: Mar 30, 2014 7:25 am 
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Hi Cyril,

I do not know what is your profession...................

Graphite is a well established material for gaskets in high temperature applications in nuclear and chemistry. Phlogopit mica is another material such gaskets are made of. A few month ago I visited Gysi in Switzerland that are producing such gaskets.

Slide bearings are using today PTFE (low temp.), lead alloys for higher temperatures and graphite for high temperature applications.

" Tungsten carbide and silicon carbide are excellent candidates" That are very brittle materials. An engineer would not say this.

Another candidate for sealings could be a gold/pt alloy.

Gaskets and slide bearings require a soft material and the bearings require as a first priority an excellent lubrication to work for years.

I do not have doubts that suitable centrifugal pumps can be made for MSR reactors. High temperatures, corrosion might require of course some R&D efforts and may face as well the one or other failed attempt.

Holger


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PostPosted: Mar 30, 2014 8:35 am 
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HolgerNarrog wrote:
Graphite is a well established material for gaskets in high temperature applications in nuclear and chemistry. Phlogopit mica is another material such gaskets are made of. A few month ago I visited Gysi in Switzerland that are producing such gaskets.


Alas, high temperature fuel salt is not one of those well established applications. There are some unique requirements relating to radioactivity and the chemistry of fluoride that are unseen in any industrial application today. What little experience there was is long gone.

Quote:
" Tungsten carbide and silicon carbide are excellent candidates" That are very brittle materials. An engineer would not say this.


I don't know what to say. If you've never heard of composite materials, then maybe its time to crawl out under the rock. But perhaps you're one of those old-school engineers who are still in a state or denial on heterogeneous materials for high temperature applications. Or maybe I should have been more explicit.

Quote:
Another candidate for sealings could be a gold/pt alloy.


Too diffusive. It'll weld itself onto Hastelloy N at temperature.

Quote:
Gaskets require a soft material


Not necessarily. High temperature cavity seals often use alloys such as Inconel 718. Which is about as soft as a dai-katana.

Quote:
I do not have doubts that suitable centrifugal pumps can be made for MSR reactors. High temperatures, corrosion might require of course some R&D efforts and may face as well the one or other failed attempt.


The hydraulic part itself isn't that difficult. Its the electric motor that is the trouble spot. It doesn't like neutrons, high temperature, and all that. When you try to isolate the motor (or even just the rotor) from the hydraulic part, that's when the fun starts.


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PostPosted: Mar 30, 2014 1:02 pm 
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Joined: Sep 22, 2013 2:27 pm
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Some weeks ago I visited Gysi in Switzerland. Gysi is a manufacturer of valves and gaskets for chemistry, pharmacy and nuclear.

They did show me gaskets made of expanded graphite with a tanged metal insert. The inserts are made of SS 1.4571, or Hastelloy alloys. Such sealings are used till 600°C and 250 bar pressure. The limitation is given by oxygen contact to the outside (I would recommend to have a modified atmosphere in the reactor building) and the mechanical properties of the metal insert at higher temperatures.

I saw as well sealings made of phlogopit (mica) with tanged metal inserts. They are as well used for high temperatures. I would estimate the corrosion properties in contact with chloride salts inferior to graphite.

In my concept such sealings are used for the flanges and pumps. Challenges in MCFR reactor are the purity of the graphite and the potential carburization of the Mo-TZC structure material.


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PostPosted: Mar 30, 2014 1:12 pm 
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Joined: Apr 28, 2011 10:44 am
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On big tankers, it is common practice to have vertical centrifugal pumps
with a 3 to 5 m shaft between the motor(or turnbine) and the pump.
This is necessary since we want to get the prime mover
out of the pump room which is a gas dangerous space.

Our experience was that on the well engineered ships
these shafts and their flexible couplings were not a problem.
On the poorly built ships, they were a constant headache.


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PostPosted: Mar 30, 2014 1:23 pm 
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But again, that is for a low temperature, no radiation, no gas injection limits, no fluoride salt environment application.

Rotor and stator windings, insulation, and sensors aren't bothered by toxic or flammable gasses. But they can't stand high radiation and high temperature. We have both.


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PostPosted: Mar 30, 2014 1:27 pm 
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Joined: Jun 12, 2011 2:24 pm
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Location: Taunusstein, Germany
There are companies with experience in the field, examples:
http://www.flowserve.com/files/Files/Li ... d-16-e.pdf
http://www.friatecna.net/pdfs/solar-power-pumps.pdf
http://www.ceramtec.com/ceramic-materia ... n-carbide/


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PostPosted: Mar 30, 2014 2:16 pm 
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Burghard wrote:


None of these can supply a nuclear pump.


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PostPosted: Mar 30, 2014 4:11 pm 
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Joined: Sep 22, 2013 2:27 pm
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The main pump suppliers for nuclear applications in the German speaking countries are KSB and Sulzer.

If you have a look in my previous comments you will find a drawing of a KSB feed pump for a PWR. It has a long shaft.. no bearing in the fluid... 3 shafts, the impeller shaft...an intermediate shaft...and the motor shaft seperated by couplings. It is quite similar to the pump I roughly designed for the MCFR.

3-4m should be sufficient to protect the motor from neutrons/gammas and as well the heat of the fluid.


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PostPosted: Mar 31, 2014 6:36 am 
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Joined: May 05, 2010 1:14 am
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MAX phase materials like Ti3SiC2 and Ti3AlC2
http://en.wikipedia.org/wiki/MAX_phases
combine metallic and ceramic properties: this paper was looking at them as bearings for a lead-cooled reactor -
http://proceedings.asmedigitalcollectio ... id=1628092

Ti3SiC2 has been proposed as a coating for LWR fuel cladding, to stop the zirconium oxidising at high temperatures.


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PostPosted: Mar 31, 2014 2:27 pm 
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Hi Jon...

the corrosion properties of some nickel alloys in contact with fluoride and chloride salts are somehow researched. The same applies for graphite. Tests for ex. chloride salts with some ceramics as SIC show corrosion at high temperatures.

Is there any report about the corrosion behavior of Ti3SiC2 and Ti3AlC2 in a molten fluoride/chloride salt?


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PostPosted: Apr 01, 2014 3:57 am 
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Couldn't find anything detailed about the MAX phase stuff in molten salts that wasn't behind a paywall, though there's a few references to them in relation to solar thermal salts. There's an article in the Journal of the Australian Ceramic Society about heating five of them till they dissociate at about 1300-1500 C.
file:///C:/Documents%20and%20Settings/User/My%20Documents/Downloads/ACS-Paper-Vol-47-2.pdf
pages 16-22.
There are seven zirconium based ternary compounds listed in the wikipedia article on them, some of which might be better than the titanium based ones for neutron absorption. I think the Aussies are saying that the vapour pressure of the middle A group element determines what temperature the compound starts dissociating at.


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