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PostPosted: Mar 20, 2016 10:14 pm 
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I am curious to see what opinions everyone has in regards to high entropy alloys. Thank you

New alloys could lead to next generation of nuke plant metals


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PostPosted: Mar 21, 2016 4:20 pm 
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Rebecca: From the article you linked:
Quote:
The scientists ran simulations to figure out which combinations might be most resistant to radiation, and settled on alloys of nickel-iron and nickel-cobalt-chromium. They then made micrometre-thin discs of the new metals and fired a beam of gold and nickel nuclei at them to simulate what might happen in a real nuclear reactor.
and from:

http://moltensalt.org/references/static/downloads/pdf/ORNL-TM-4189.pdf

there were ten conclusions you can see in the attached image from the above pdf, where #10 is:
Quote:
"Hastelloy N is suitable for long-term use as a container material for a molten salt of the type used in this test and has acceptable air oxidation resistance at the temperatures used."
Is Hastelloy N high-entropy? From Table 2.2 of ORNL-TM-4189, Hastelloy N (INOR-8) is:

Ni 66-71%

Mo 15-18

Cr 6-8

Fe, max 5

and traces of C, Ti + Al, S, Mn, Si, Cu, B, W, P, and Co. And Nb was used in the weld study.


Attachments:
ORNL-TM-0728 Table 2.2 INOR-8.jpg
ORNL-TM-0728 Table 2.2 INOR-8.jpg [ 69.51 KiB | Viewed 3510 times ]
ORNL-TM-0728 Conclusions.jpg
ORNL-TM-0728 Conclusions.jpg [ 167.14 KiB | Viewed 3510 times ]

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PostPosted: Mar 22, 2016 11:44 am 
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Hi Rebecca, welcome to the forum.

I think the idea of a high-entropy alloy is an interesting one. In some ways it mirrors the idea of the ionically-bonded salts, in that they exist at a state of maximum entropy, and this means that all that banging around from neutrons and gammas does not change their bulk properties. Could something like that be done with metallic alloy? Perhaps, but one would still have to contend with the neutron absorption problems that are going to exist in any nickel-based alloy. There are going to be helium-forming reactions in nickel from the neutron flux:

58Ni + n --> 59Ni

59Ni + n --> 4He + 56Fe

It has always seemed to me most prudent, and actually achievable, to keep metallic alloys out of the neutron flux as much as possible. With the two-fluid molten-salt reactor design this appears to be possible, since the reactor vessel can be protected from the neutron flux of the core by the neutronically-absorptive blanket fluid. Through proper design, the only materials that have to be in the really intense part of the neutron flux are the fuel and blanket salts (which are impervious to radiation damage) and the graphite (which unfortunately isn't, but we need it anyway). The reactor vessel, which will be metallic, can be kept "shielded" by the blanket in a good two-fluid design.

Of course, the ORNL MSRP departed from the two-fluid design in about 1968 and was on a one-fluid design for the remainder of time that the project ran, until about 1976, so contending with more significant neutron damage to the metallic alloy was something that they were thinking about.

In this 1978 report, Herb McCoy goes over the materials challenges for MSRs and the current state of the art. Since this document was finished about two years after the program was really finally cancelled, it is probably about as good a resource as anywhere to commit to understanding before attempting an effort in materials development.

ORNL-TM-5920: Status of Materials Development for Molten-Salt-Reactors

Quote:
Iron- and nickel-base alloys can be embrittled in a thermal neutron flux by the transmutation of tramp 10B to helium and lithium. This process generally results in the transmutation of most of the 10B by fluxes of thermal neutrons on the order of 10^20 n/cm^2, and usually yields from 1 to 10 atomic ppm of He. With Ni there is a further thermal two-step transmutation involving these reactions:

58Ni + n --> 59Ni

59Ni + n --> 4He + 56Fe

This sequence of reactions does not saturate, and although the cross sections are still in question, it would produce a maximum of 40 atomic ppm of He in the vessel over a 30-year MSBR lifetime. Helium from both sources collects in the grain boundaries and causes degradation of the mechanical properties at elevated temperatures. The effect manifests itself in reduced rupture life and reduced fracture strain.


I don't know if you've already reviewed this document, let me know. I think it's a very good place to start.


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PostPosted: Mar 22, 2016 4:44 pm 
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Is there a difference between high chemical entropy and high nuclear entropy?

Most salts will have high chemical entropy, but could still absorb neutrons (e.g. Li6). Does Iron at atomic mass 56 have highnuclear entropy - and should therefore be fairly resistant to radiation damage. It is though rubbish chemically, so needs protecting with oxides of chromium.

I did raise the question on another thread of using silicon dioxide - glass - either on its own, or as an enamel. For example, in the tube walls of the moltex reactor. What is its radiation resistance?

Of course, Thorcon and Terrestrial think they've got round this issue by swapping out components after 4 to 7 years.


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PostPosted: Mar 23, 2016 9:25 am 
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It's fairly easy to keep the metals in relatively low flux,
what we need is max entrophy graphite.


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PostPosted: May 04, 2016 10:35 am 
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Max entropy graphite because no other material makes for a better LFTR (Flibe Energy design) moderator material? There isn't a better way to achieve the necessary moderation?

And solving the moderator problem is required to gain the benefits and superior performance of burning thorium (initiated with external U-233) in the thermal spectrum particularly to succeed in the effort to move away from U-235 and the U/Pu fuel cycle? The LFTR moderator seems to be from my limited viewpoint an Achilles heel to the LFTR business case. I imagine concerned, science-educated citizens as myself, who are pro advanced nuclear reactor policy, and are on the outside looking in and not qualified to work for the developers, "we" may not become privy to the present state of this LFTR technology development.

Another relevant material crucial for the LFTR salt cleaner is bismuth. Continuous liquid metal (bismuth)-molten salt reductive extraction (LBRE) with the relatively nontoxic and fairly available bismuth sounds ideal. Is this system technologically ready? For my ability and access I have not yet found papers that show a performing system so one as I can understand the development. According to the October 2015 EPRI LFTR Assessment, the proposed LBRE is still under development.

And the goal of the Flibe Energy LFTR LBRE design to do protactinium blanket salt processing alarms the fissile inventory folks--not a trivial concern--that also appears to be another hurdle for licensing; elevated reactor security requirements.

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PostPosted: Oct 14, 2017 7:24 pm 
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Researchers Explore Coating for Tanks Holding Molten Salts

Quote:
Bare stainless steel alloys tested in a molten chloride corrode as quickly as 4,500 micrometers per year, so NREL researchers are looking at different types of nickel-based coatings, which are commonly used for reducing oxidation and corrosion. One such coating, NiCoCrAlYTa, has shown the best performance so far. It limited the corrosion rate to 190 micrometers per year—not yet at the goal but a large improvement, reducing corrosion by more than 96% compared to uncoated steel. That particular coating was pre-oxidized over a 24-hour period before coming in contact with the salts, during which a uniform and dense layer of aluminum oxide was formed and served to further protect the stainless steel from corrosion.


This is for chloride salts...


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PostPosted: Oct 15, 2017 7:21 pm 
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It seems prudent to provide an additional liner for chemical deterioration in addition to the basic design based on strength at expected temperature and neutron flux. It will be generally a different material. It is more important in high erosion molten salt reactor.


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PostPosted: Oct 18, 2017 6:39 am 
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Do you have any comment, Kirk, on the Moltex design of uranium chloride salts in solid fuel-style steel tubes ? They claim that some sacrificial zirconium in the mix will protect the insides of their fuel tubes (though not the outsides, which are in a fluoride secondary salt.)


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PostPosted: Oct 18, 2017 1:04 pm 
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Recently had a discussion with someone on my NTEC course who actually works for Moltex.

Apparently they aren't even planning on the salt to contain nuclear grade (as opposed to commercial grade) Zirconium - and just take the neutron efficiency penalty.
At least in the first generation reactors.


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PostPosted: Oct 19, 2017 2:00 am 
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Moltex claim the fast neutrons doing the fission will ignore the ~2% hafnium, while the thermalised ones will be absorbed before they get to the edge of the reactor vessel. They're talking about a thermal spectrum variant now though. Do they have many people working for them ?


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PostPosted: Oct 20, 2017 7:33 pm 
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Fast MSRs are required to burn all the used fuel from LWRs. They will also present challenges of chemical action, high temperature and neutron flux. It is time to work out composite construction to meet the needs.


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