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 Post subject: Dual Fluid Reactor
PostPosted: Mar 11, 2013 6:04 pm 
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The Institute für Festkörper Kernphysik has design has an MSR design called the Dual fluid Reactor

http://festkoerper-kernphysik.de/dfr

the video and the pdf are in english

http://festkoerper-kernphysik.de/dfr.pdf

i found it via the climate skeptics of EIKE

http://www.eike-klima-energie.eu/news-c ... aerz-2013/


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PostPosted: Mar 13, 2013 8:00 am 
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Marcus, thanks for posting it.
This deserves to be commented.

They are looking for investors. And their idea seems to compete with Transatomic Power WAMSR. I guess the main challenge is in piping materials. On the other hand R+D on chlorides chemistry seems to be lagged behind fluorides chemistry.


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PostPosted: Mar 13, 2013 8:44 am 
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A lead-cooled fast neutron MSR carries some risks that don't appear to be addressed in the DFR documents, including the pdf.
If there is a leak from the fuel tubes, the salt will be buoyant relative to the lead, and may collect somewhere, potentially creating a supercritical mass.
This is made more likely by the fact that the effective dilution of the fuel by lead coolant in the normal configuration requires a fissile concentration that is substantially higher than the undiluted fuel salt that may collect somewhere following a leak.

From the FAQ section of the DFR pdf:
" A small system with 1 GWth working with U-Pu cycle has a concentration of 35% plutonium and 65% (depleted) uranium."


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PostPosted: Mar 15, 2013 1:31 pm 
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From the pdf:
Quote:
The material which separates the two fluids must have sufficient heat conduction and resist to cor-
rosion by the salt and the liquid metal. In comparison to the conditions in thermal neutron reactors
the choice of nuclides for the structural wall material opens widely because of the low neutron
capture cross sections for fast neutrons. Appropriate materials have been developed decades ago;
however they contain rarer and more expensive chemical elements.


Is it really that easy? A barrier material that operates without fault at over 1000 degrees under a very high (fast) neutron spectrum.


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PostPosted: Mar 16, 2013 10:44 am 
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It is true that the cross-section is smaller to fast neutrons. However, at least for Hastalloy, the damage done by fast neutrons matches that done by the thermal ones. There are two mechanisms for generating helium internal to the metal one that requires slow neutrons and one that requires fast ones.


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PostPosted: Mar 16, 2013 12:05 pm 
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There is also physical damage caused by fast neutrons. This is the limiting factor for graphite, which has no helium generation but gets damaged by more energetic neutrons. Fast neutron damage will also be the limiting factor for non-nickel alloys and most other materials as well. Specifically, fast neutrons cause embrittlement of most materials.


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PostPosted: Mar 16, 2013 6:06 pm 
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One advantage of nickel alloys, like Hastalloy N, is that it does not typically have a shelf, that you go over and suddenly have a massive brittle fracture like lower alloy steels. Therefore, fast neutron displacement damage does not push you over a cliff to failure and it can be easier to design than staying away from a cliff and failure should be more gradual.

Also, since the LFTR is at very low pressure there should be much less pressure stress than the reactor vessel for a PWR. Of course the downside of a LFTR is that the helium created that collects at the grain boundaries will be at higher temperature, than if a PWR were to use a nickel allow vessel, which they don't.
The higher temperature increases the helium pressure, and thus the local stresses for high helium concentrations. And, if there were a upward temperature excursion of the LFTR vessel, these helium pressures and stresses would increase, so they would have to be allowed for/tested for in the design.


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PostPosted: Mar 18, 2013 11:43 am 
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The design is a fast spectrum MSR.
If set up in the neighborhood of Germany in Czech Republic or France, which have not forsaken nuclear energy, it could make up the local power deficiencies in the Europe. It could also help burn the SNF (and depleted uranium) stocks held by them.
The fresh uranium could be spared for Asians (and Africans), who have not used much of mined uranium in the days of cheap uranium.


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PostPosted: Mar 18, 2013 2:05 pm 
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Ed P wrote:
One advantage of nickel alloys, like Hastalloy N, is that it does not typically have a shelf, that you go over and suddenly have a massive brittle fracture like lower alloy steels. Therefore, fast neutron displacement damage does not push you over a cliff to failure and it can be easier to design than staying away from a cliff and failure should be more gradual.

Also, since the LFTR is at very low pressure there should be much less pressure stress than the reactor vessel for a PWR. Of course the downside of a LFTR is that the helium created that collects at the grain boundaries will be at higher temperature, than if a PWR were to use a nickel allow vessel, which they don't.
The higher temperature increases the helium pressure, and thus the local stresses for high helium concentrations. And, if there were a upward temperature excursion of the LFTR vessel, these helium pressures and stresses would increase, so they would have to be allowed for/tested for in the design.

I don't think the helium pressure is the issue. It is that the helium migrates in the metal. In the initial metal the helium would concentrate in the grain boundaries creating a weak spot and failure much earlier than forecast based on a uniformly distributed helium content. Later formulations of Hastalloy included some carbide atoms which provided distributed locations for the helium to migrate to and IIRC this reduced the helium problem sufficiently that it wasn't a concern anymore for single fluid designs.


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PostPosted: Apr 18, 2013 4:13 am 
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I recall late last year, TerraPower hired a molten salt specialist.
That made me wonder if they weren't considering an upgrade of their TWR (Travelling Wave Reactor) similar to this new German DFR idea.

The existing TWR concept involves a lot of fuel rod shuffling around the reactor core, to maintain criticality with extremely high fuel burnup (including high fission product loading, of course).

With fluid fuel, like in the DFR, there is no need for fancy robotics and associated automation to manipulate fuel rods in the opaque metal coolant inside the core: A much simpler and likely more reliable system (no moving mechanical parts).
Plus you get the option of simplified fuel processing as a bonus (the TerraPower solid fuel processing concept is similar to IFR, which they call "recladding", but which is in fact more complicated than the moniker implies...)

One thing that is a little puzzling in the DFR description is the type of fuel salt they intend to use:
" undiluted molten- salt fuel can be used and the amount of fissile materials in the fuel can be increased significantly."
" Nominally, The fuel consists of undiluted actinide salt."
" the employment of chlorine salts (preferable Cl37)..."
" Higher halogens are more practical with respect to both properties. For the metals in the used fuel mixture chlorine salts have sufficiently low boiling points yet still higher than 1000 °C as required in the DFR core."

......which points to UCl4 and PuCl3 as the "undiluted actinide salts".

UCl4:
Melting point: 590°C
Boiling point: 791°C

PuCl3:
Melting point: 767 °C
Boiling point: 1767 °C

The 200-degree difference between mp and bp for UCl4 looks problematic.
Normally MSRs are designed to run with a minimum operating temperature about 100 degrees above mp: That leaves only a 100 degree margin to boiling.

The DFR situation is different however, since the fuel salt is not circulated through an HX, but rather remains quasi-static. It could presumably even be left to solidify in the fuel piping - assuming the phase change doesn't cause damage to the piping (no word about that in the DFR description).

An obvious intermediate step between the current TWR concept and the DFR would be a lattice of un-connected fuel salt tubing to make up a liquid metal cooled reactor.
This would already have a huge advantage over a solid-fuel TWR, because the ability to vent volatile fission products would avoid the danger of damaging fuel tubes by over-pressurization, during the extremely long service (high burnup).
With appropriate fuel tube material, this could possibly even be done using liquid U/Pu metal, thus avoiding the issue of isotopically pure Cl37 (another issue of concern with the DFR idea).

-------

Edit:

It is also possible DFR may use UCl3 instead of UCl4:

" The molten form of uranium(III) chloride is a typical compound in pyrochemical processes as it is important in the reprocessing of spent nuclear fuels.
UCl3 is usually the form that uranium takes as spent fuel in electrorefining processes."

Melting point: 837 °C
Boiling point: 1657 °C

....a potential issue then is the very high mp.

http://en.wikipedia.org/wiki/Uranium_trichloride


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PostPosted: Apr 18, 2013 8:49 am 
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jaro wrote:
" The molten form of uranium(III) chloride is a typical compound in pyrochemical processes as it is important in the reprocessing of spent nuclear fuels.
UCl3 is usually the form that uranium takes as spent fuel in electrorefining processes."

Melting point: 837 °C
Boiling point: 1657 °C

....a potential issue then is the very high mp.

http://en.wikipedia.org/wiki/Uranium_trichloride


http://www.ornl.gov/info/reports/1957/3445603227087.pdf tells of a 54RbCl-46UCl3 composition that melts at 515°C.

_________________
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Oxygen expands around B fire, car goes


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PostPosted: Apr 18, 2013 9:35 am 
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There are also many attractive eutectics with ThCl4, suggesting that a hybrid ThCl4-UCl3-UCl4-NaCl would be very attractive.


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PostPosted: Apr 25, 2013 2:29 am 
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With Germans scared even of their working reactors, only the Chinese are likely to benefit from past studies. Recent events make it quite clear.
As for ThCl4-UCl3-UCl4-NaCl, you could probably add some MgCl2 for better fluidity. NaCl-MgCl2 is a low melting eutectic.


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PostPosted: Apr 28, 2013 5:44 pm 
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jagdish wrote:
With Germans scared even of their working reactors, only the Chinese are likely to benefit from past studies. Recent events make it quite clear.
As for ThCl4-UCl3-UCl4-NaCl, you could probably add some MgCl2 for better fluidity. NaCl-MgCl2 is a low melting eutectic.


Germans never know what is good for their country. Germans are too quick to follow the leader. And in this case, the leader is the anti-nuclear groups that promote fear, uncertainty, and doubt.


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PostPosted: May 14, 2013 11:59 am 
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A recent reply from the DFR folks, on their facebook page....


Quote:
The pictures/videos shown here describe only the schematics of a reference plant, no construction drawings, nothing is really fixed here.
From the core picture you might get the impression that the core is not accessible, but in a final draft, means will be provided to access the complete core and replace it.
In maintenance mode, not only the fuel but also the lead will be drained (the lead store is indicated by the grey block behind the reactor core in the main picture), and all parts can be removed by cranes from the top (not shown in the pictures).
The lead flow must be parallel to the fuel tubes, otherwise the tensile stress and other loads on the tubes become too large.
The direction for the lead flow as well as for the fluel flow is also pretty much fixed from bottom to top by the temperature gradient, providing always a minimum flow by gravity without pumps.
On the other hand, maintaining a monolithic array of ten-thousands of rods might be challenging but not that unusual.
Turbo chargers (of course on a smaller scale) have ten-thousands of tubes to deposit the heat from the compressed air, and they also work under extreme conditions (high temperature, high pressure, dust and smoke particles).
The DFR core works at atmospheric pressure and at "only" 1000 C, but otherwise with pretty clean conditions.
Of course, we have to deal with corrosion from lead on the one side and salt from the other side but durable materials exist, e.g. alloys from refractory metals like MHC (Molybdenum-Hafnium(1%)-Carbon(<1%)) or TZM (Molybdenum-Titanium(<1%)-Zirconium(0.5%)-Carbon(0.1%))).
Reg. the seismic liability, again we point to the schematic character of the drawings shown here.
A more realistic draft provides a much more compact donut-like shape of the lead loop which can be made very shock and vibration safe.
Seismic activities (affecting the construciton as a whole) are less problematic anyway than internal vibrations and resonances.
In the lead flow, inert gas buffers (e.g. Argon pockets) are provided to balance possible vibrations, e.g. from the lead propeller pump.
https://www.facebook.com/photo.php?fbid=523769177669375&set=a.523767561002870.1073741831.522620164450943&type=1&comment_id=1708041&reply_comment_id=1711781&offset=0&total_comments=3


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