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 Post subject: Re: Lifespan of a LFTR?
PostPosted: Feb 25, 2011 4:55 am 
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I think it'll be better to use an electrolytic copper coating than Ni-60. Unless you want to go up very high in temperature.

I had also worried a bit about zirconium and titanium as they form rather stable fluorides and would tend to leach out of the surface of the alloy, embrittling it. ORNL used some TZM and molybenum test stands for the vacuum still but this is without the high neutron loadings in the reactor.


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 Post subject: Re: Lifespan of a LFTR?
PostPosted: Feb 25, 2011 5:28 am 
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I am sure we could use more advanced vapour deposition technique for coatings of either copper, nickel or something else more radical.


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 Post subject: Re: Lifespan of a LFTR?
PostPosted: Feb 25, 2011 5:47 am 
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Well I'm no expert on coatings but it appears electrolytic coating for copper is simple and effective. For nickel the favored choice appears depositing a volatile nickel species by CVD. PVD might work but AFAIK it requires molten metal which is tricky with refractories such as molybdenum. Looking at the chemical inertness, copper, carbon and tungsten (for fast reactor) appear the best choices.

ORNL made some batches of fluoride salt in a copper coated/lined tank and they said the corrosion product contamination was near zero.


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 Post subject: Re: Lifespan of a LFTR?
PostPosted: Feb 25, 2011 6:14 am 
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From a corrosion perspective pure Ni is very good with fluoride salts, and coating by nickel vapour deposition should work or closely controlled electroplating.

Regarding high temperature operation we need to remember that the MP is 1455C


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 Post subject: Re: Lifespan of a LFTR?
PostPosted: Feb 25, 2011 6:21 am 
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Copper is even better than nickel the free energy of formation of copper fluoride per fluorine is about half that of nickel fluoride.

However copper is lower melting, under 1100 Celcius. I wonder if this is a problem. Probably not since the coating is non-structural and is in direct contact with with fuel salt which is ‘only’ 700 Celcius.


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 Post subject: Re: Lifespan of a LFTR?
PostPosted: Feb 25, 2011 11:07 am 
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Reading over ORNL's studies on TZM it looks like they thought it would do fine as far as corrosion goes. They were considering it for the still at 1100C. Yes the Zr and Ti leach out from the surface and one gets grain regrowth there. The net effect is that the strength reduces to that of pure moly (about 1/3 the strength of TZM). But the leaching effect is limited by the diffusion of Zr and Ti through the moly metal. If you apply the formula they have you find that after 60 years the leaching has penetrated 2 mm into the metal. So, if we use TZM it looks like we might need to budget 4mm thickness for leaching of Zr and Ti. From a strength perspective it TZM is better than Hastalloy-N.

TZM is talked about being used in high temperature fast reactors so perhaps it will do fine as far as surviving the neutron bombardment.

Manufacturability was very much a concern by ORNL but perhaps that is better now.

Chemical corrosion by fission products has not been tested.

Possible interactions between Hastalloy and TZM where you have a bi-metal connection would be another thing to check on.


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 Post subject: Re: Lifespan of a LFTR?
PostPosted: Feb 25, 2011 1:02 pm 
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High level nuclear heat is important for the Lftr as a product because it minimizes cost. First, increased reactor operational temperature increases the power density of the reactor. For any given arbitrary power level (say one gigawatt), the hotter the temperature that can be produced at the output of the reactor, the less material and reactor volume is required. The smaller the reactor, the faster it can be fabricated, built and installed.


The hotter the reactor can run, the more thermodynamically efficient it will be; and the more efficiently it can produce electric power.


On the process heat application which is where the high temperature molten salt reactor really shines, the higher the temperature at the reactor outlet, the more industries it can serve.


1100C serves hydrogen production, shall oil extraction and refining both In-situ and above ground, nitrogen extraction and fertilizer production, oil refining, synthetic oil production, natural gas to liquids, and biomass to oil production, the Hall–Héroult aluminum refining process.


1500C serves cement making, and glass making.


1600C metal smelting and steel making.


At the end of day, a higher heat reactor can do many more things, it is a more versatile industrial tool, and is therefore more valuable.

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Last edited by Axil on Feb 25, 2011 1:10 pm, edited 1 time in total.

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 Post subject: Re: Lifespan of a LFTR?
PostPosted: Feb 25, 2011 1:09 pm 
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Sure but high temperatures are challenging and process heat is usually worth less than electricity. What we've got for electricity now is steam Rankine which needs 600 C. There's not much point in going above 750 C for the moment. Higher temperatures can be used as gradual improvements in materials allow. If you can start with what's certified for nuclear use then you've got a big advantage.


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 Post subject: Re: Lifespan of a LFTR?
PostPosted: Feb 25, 2011 1:21 pm 
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I consider process heat more efficient than heat produced by electric resistance heating. The production of electricity imposes a thermodynamic penalty on the industrial heat production process. Direct heat production is close to 100% efficient.

This is why current industrial heat processes use the heat from natural gas and coal directly, in preference to the electrically resistive heat that these fossil fuels produce from electricity conversion.

Take the long view. What happens when coal and natural gas are no more, where will the high temperature process heat come from?

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 Post subject: Re: Lifespan of a LFTR?
PostPosted: Feb 25, 2011 1:34 pm 
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Sure there will be a need for high temperature heat but don't you agree this is a hard starting point?

You want to compete against 1 cent per kWh thermal coal for iron production with a really hard materials challenge for the reactor? Iron and steel is entrenched in coal and it will be the last bastion of fossil fuel, the final lock-in, that we can possibly break.

Better start with electricity. We need this, lots of it, and its growing rapidly. We'll need more for heat pumps and electric transport.

IF you can make a reactor that puts out 1600 C (means peak temps around 1700 C) then maybe you also have figured out how to make 75% efficient Brayton cycles and can make electricity almost as efficiently as the direct process heat.

But its better to start with stuff thats certified for use and we can start with short term. If you've got a 700 C MSR it will be relatively easy to go to 2x the temperature. Right now we have nothing and 1600 C MSRs are little more than a luxurious fantasy.


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 Post subject: Re: Lifespan of a LFTR?
PostPosted: Feb 25, 2011 1:41 pm 
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Quote:
Right now we have nothing and 1600 C MSRs are little more than a luxurious fantasy.


Quote:
We do big things.

From the earliest days of our founding, America has been the story of ordinary people who dare to dream. That’s how we win the future.

We are a nation that says, “I might not have a lot of money, but I have this great idea for a new company. I might not come from a family of college graduates, but I will be the first to get my degree. I might not know those people in trouble, but I think I can help them, and I need to try. I’m not sure how we’ll reach that better place beyond the horizon, but I know we’ll get there. I know we will.”

We do big things.



So Sorry…please excuse me, I just had a dream.

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 Post subject: Re: Lifespan of a LFTR?
PostPosted: Feb 25, 2011 1:55 pm 
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As a born and raised bay area kid, I believe what made the US big is the acceptance of getting started with the good rather than let the perfect be our enemy. In recent years there is a discomforting drive toward the opposite, and much less has been achieved because of it.


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 Post subject: Re: Lifespan of a LFTR?
PostPosted: Feb 25, 2011 4:00 pm 
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Cyril R wrote:
Right now we have nothing and 1600 C MSRs are little more than a luxurious fantasy.

No way are you going to produce 1700 C directly by using MSRs. Use your MSR to produce hydrogen, and then burn the hydrogen to produce your 1700 C heat.


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 Post subject: Re: Lifespan of a LFTR?
PostPosted: Feb 25, 2011 5:54 pm 
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Cyril R wrote:
Sure there will be a need for high temperature heat but don't you agree this is a hard starting point?

You want to compete against 1 cent per kWh thermal coal for iron production with a really hard materials challenge for the reactor? Iron and steel is entrenched in coal and it will be the last bastion of fossil fuel, the final lock-in, that we can possibly break.

Better start with electricity. We need this, lots of it, and its growing rapidly. We'll need more for heat pumps and electric transport.

IF you can make a reactor that puts out 1600 C (means peak temps around 1700 C) then maybe you also have figured out how to make 75% efficient Brayton cycles and can make electricity almost as efficiently as the direct process heat.

But its better to start with stuff thats certified for use and we can start with short term. If you've got a 700 C MSR it will be relatively easy to go to 2x the temperature. Right now we have nothing and 1600 C MSRs are little more than a luxurious fantasy.

Has someone been spiking your corn flakes with something unusual? There is no need to have systems operating at 1700C to efficiently produce cheap electrical power and heat for industrial processes. Steel melts at about 1400C, that's the hottest industrial process I can think of and they can do that just fine without MSR technology. One might chose to integrate MSR's into steel and aluminium manufacture as a means of preheating the material reducing the fossil fuel input, or use MSR electricity in arc furnaces to do the melting step and MSR produced hydrogen (as Charles mentioned) for additional heating and reducing iron oxide to metallic iron. They are all near term technologies within our grasp at an economic cost, we don't need to chase extreme temperatures to achieve truly great things for humanity.

If we are talking about utility electricity generation on a large scale, MSR/LFTR at peak temperatures between 700 and 950C are plenty good enough to provide conversion efficiencies of 46 - 54% efficiency. If you are dealing with an energy source that is effectively inexhaustible for humanity, a 50% conversion efficiency is plenty good enough. The cost and practicality of pushing on past this point is questionable.

Quote:
..you've got a 700 C MSR it will be relatively easy to go to 2x the temperature
I don't see any easy path to 1400C and beyond, at those temperatures you have moved out of the working range for metals and then most of the materials science developed for metal based systems has to be left behind. As understand there remain a lot of work to be done to prove carbon and silicon composites in an irradiated fluoride salt environment, but hopefully that too will come to pass in the fullness of time. Right now we can do a lot with metal based systems at 700 -950C, and that's where the big effort is required IMHO.


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 Post subject: Re: Lifespan of a LFTR?
PostPosted: Feb 25, 2011 8:39 pm 
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First off, obviously we are not going to have 1600 C temps as that is well past the boiling point of the salts!

Second, when your fuel is basically free, there is a whole lot less incentive to try to get thermal efficiency up. In fact, feel free to think I'm crazy but I think 550 C might actually be a better peak temperature than 700 C. 550 C is plenty for Supercritical CO2 to get around 40% and the lower temp would likely mean you can use stainless steel for everything instead of Hastelloy (about 1/7th the cost). At 550 C your heat exchangers might be 10 to 20% larger but way cheaper overall since you can make them out of steel. A little bit bigger core is also not a big issue if you can use cheap steel for the vessel and piping. 550 C peak temp means changing to lower melting point salts (like NaF-BeF2) but you enter some very interesting design space.

A couple years ago I was picking the brain of ORNL's best guy on materials in a neutron flux and in our conversation back and forth he was explaining the issues and problems with Hastelloy , Molybdenum etc at 700 C or even above. One day I asked him, what if the peak temperature was down to 550 or so? Oh sure, then anything will work was his response!

David LeBlanc


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