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PostPosted: Jan 31, 2014 10:06 pm 
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Couldn't one use zirconium deuterium for a moderator?


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PostPosted: Feb 01, 2014 3:31 am 
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Lars wrote:
Couldn't one use zirconium deuterium for a moderator?


Yes. This is also part of the Transatomic patent. But they won't go this route because deuterium has a low slowing down power, meaning a lot more atoms D are needed. That then means more atoms Zr to hold the D which cancels the neutronic advantage.


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PostPosted: Feb 01, 2014 8:49 am 
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Why can't the cladding for the ZrH moderator just be Zr? Too leaky? Dissolves in Flibe by exchanging Zr for Be or Li?


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PostPosted: Feb 01, 2014 9:59 am 
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robert.hargraves wrote:
Why can't the cladding for the ZrH moderator just be Zr? Too leaky? Dissolves in Flibe by exchanging Zr for Be or Li?


Any fluoride salt would eat up metallic zirconium immediately, converting it to zirconium tetrafluoride (ZrF4). The tendency of fluoride salt to convert metals to fluorides rules out most candidates for cladding materials. What makes Hastelloy-N special is its ability to resist corrosion by fluoride salts, but it wouldn't hold up in the fast and thermal neutron flux required for a cladding material.


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PostPosted: Feb 01, 2014 10:03 am 
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robert.hargraves wrote:
Why can't the cladding for the ZrH moderator just be Zr? Too leaky? Dissolves in Flibe by exchanging Zr for Be or Li?


Zr corrodes easily in fuel salt, not by Li or Be but from U.

4UF4 + Zr = 4UF3 + ZrF4

The latter is more stable so is favored. In fact, Zr is a good alternative redox control material (if Be rods are unacceptable).

Other than that, Zr is very weak at 700C and will take up hydrogen from the hydride like crazy at 700C, embrittling it badly.


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PostPosted: Feb 01, 2014 2:57 pm 
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Thermal-radiation processes in the MeIV–H system. Synthesis of hydrides of metals says zirconium binds hydrogen a little more strongly than hafnium does. So experience with hafnium hydride is applicable.

Some of this was reviewed in http://energyfromthorium.com/forum/viewtopic.php?f=66&t=4025.

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PostPosted: Feb 01, 2014 4:11 pm 
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GRLCowan wrote:
Thermal-radiation processes in the MeIV–H system. Synthesis of hydrides of metals says zirconium binds hydrogen a little more strongly than hafnium does. So experience with hafnium hydride is applicable.

Some of this was reviewed in http://energyfromthorium.com/forum/viewtopic.php?f=66&t=4025.


Again though, what experience is there with long term high temperature power reactor core neutron levels for hydrides? There are many short term out of pile (thermal only) tests, and some medium term out of pile tests, but no long term, inpile tests resembling the Transatomic proposal conditions.

Even if the hydride turns out to be stable, it is still corrosive (actually embrittling) to cladding.

It is also clear that beyond design basis accident temperatures with fuel salt close to boiling, will rapidly dissociate the hydrogen, exacerbating the accident. This could be obstruction of either passive aircooling flow (severe structural failures) or just local fuel salt blockage from reactor internal debris/warped moderator rods. Graphite would perform much better in such accidents (at least it won't make things worse).


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PostPosted: Feb 01, 2014 5:08 pm 
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It is also clear that beyond design basis accident temperatures with fuel salt close to boiling, will rapidly dissociate the hydrogen, exacerbating the accident.


In the document, they only speak about the good aspects : the loss of the moderator ensures subcriticality.


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PostPosted: Feb 02, 2014 5:17 am 
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fab wrote:
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It is also clear that beyond design basis accident temperatures with fuel salt close to boiling, will rapidly dissociate the hydrogen, exacerbating the accident.


In the document, they only speak about the good aspects : the loss of the moderator ensures subcriticality.


Same advantage for LWRs. The real issue is decay heat removal. Not even the stored thermal energy that they talk about. Fukushima shut down fine, no criticality accident. And it cooled down fine, when the power was lost the fuel had already been cooled down. BDBA hydrogen was a problem. Transatomics reactor appears to have similar potential for BDBA hydrogen (higher threshold for hydrogen reaction, but then again a higher normal operating temperature).

Transatomic don't specify their decay heat removal system other than that it is some kind of natural draft air cooled system. I can imagine quite a few ways for that to fail. A particular problem with natural draft systems, especially for molten salt reactors, is that leaks can push radionuclides out. It is quite a challenge to ensure this does not happen even with multiple structural failures (from an earthquake or the like).

It looks like they are at a very early design point. So it isn't really a very technical white paper, more a sales paper for them to get more money so they can work on more details.


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PostPosted: Feb 02, 2014 10:54 am 
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Does anyone know whether Transatomic has any technical facilities or workshops ? Or do they just have an office where they write technical papers ?

BTW:

Cyril, congratulations, you posted your 5000th message on this forum, a really impressive effort !


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PostPosted: Feb 02, 2014 12:07 pm 
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Transatomics reactor appears to have similar potential for BDBA hydrogen


Yes, they say that the hydrogen release would be too small to cause an explosion threat, I guess we need more details on their design to judge that.

Back to the moderator cladding, using some carbide (silicon carbide, zirconium carbide, ...) or other carbon based material is not possible ? They won't retain hydrogen ? They will react with it to form hydrocarbons ?


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PostPosted: Feb 02, 2014 12:45 pm 
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fab wrote:
Quote:
Transatomics reactor appears to have similar potential for BDBA hydrogen


Yes, they say that the hydrogen release would be too small to cause an explosion threat, I guess we need more details on their design to judge that.

Back to the moderator cladding, using some carbide (silicon carbide, zirconium carbide, ...) or other carbon based material is not possible ? They won't retain hydrogen ? They will react with it to form hydrocarbons ?


The hydrogen release depends on the temperature. Its quite small at 1100C but very big at 1400C.

SiC is corroded by hydrogen at high temperatures (>1000C).

http://ntrs.nasa.gov/archive/nasa/casi. ... ion_detail

However, there appears no embrittlement like you get with most metals. Just a corrosion rate that reduces thickness/density that translates into lower strength, but it is acceptable (about a third loss).

Carbon of any type should react with hydrogen at elevated temperatures to produce hydrocarbon, one expects methane primarily. This may be a problem because SiC is often coated with pyrolytic carbon to improve resistance to fluoride salt corrosion. But perhaps it is likely not so bad at 700C.

If a SiC cladding works then the hydride looks a lot better. Quite a few questions remain as to how it will be sealed up but work is under way in PWR triplex SiC cladding to do that.


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PostPosted: Feb 02, 2014 1:12 pm 
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Well, thanks.


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PostPosted: Feb 02, 2014 7:34 pm 
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There is mention of several MSR concepts using ZrH for moderator in this paper :

http://moltensalt.org/references/static/downloads/pdf/ANL-7092.pdf

They use molybdenum alloys and Ni-Mo alloys for cladding.


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PostPosted: Feb 04, 2014 9:21 am 
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Would love to hear some opinions from the experts on this paper, now that some details are published.

http://transatomicpower.com/white_paper ... _Paper.pdf


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